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ihkjk> ABSTRACT

CESIUMe133 NUCLEAR MAGNETIC RESONANCE STUDY OF CESIUM SALTS
AND COMPLEXES IN NON-AQUEOUS SOLVENTS
By

Lulu Liu Hsu

Non-proton NMR has been established as an important technique for the
the study of chemical systems in solution. In particular, alkali metal
NMR has been widely used in the investigation of solution interactions.
133Cs NMR has been little employed until recently. However, with the
advances in fourier transform NMR instrumentation, it is now readily
available.

13305 NMR has been used previously by DeWitte (see Ref. 27) to study
one-to-one electrolytes in different solvents. An attempt was made to
correlate the chemical shifts of the infinitely dilute cesium ion in each
solvent with the donor number established empirically by Gutmann. The
discussion includes all the 133Cs NMR data available from both studies.
The effects of solvent and anion on the ion pair phenomenon are examined
and association constants determined.

After Lehn first synthesized the macrobicycles, cryptands, consider-
able interest was generated as these ligands form unusually strong
complexes with alkali metal ions. Besides their biological applications,
these three-dimensional ligands have tremendous potential in chemical‘
reaction. The topology and selectivity of these compbunds can be used to
advantage in the control and study of alkali metal interactions in
solution. The C211, C221 and 0222 cryptands are used in this study and
the complexation interactions with the cesium ion are studied in various

solvents. Temperature effects on the complexation reaction are also given.

CESIUM-133 NUCLEAR MAGNETIC RESONANCE STUDY OF CESIUM SALTS

AND COMPLEXES IN NON-AQUEOUS SOLVENTS

By

Lulu Liu Hsu

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Chemistry

1976

ACKNOWLEDGEMENTS

The author wishes to thank Professor Alexander I. Popov for his
guidance, counseling and encouragement throughout this study.

Financial aid from the Department of Chemistry, Michigan State
University and the National Science Foundation is gratefully acknow-
ledged. Appreciation is extended to Frank Bennis and wayne Burkhardt
for their help with the NMR spectrometer.

I would like to thank all the members of Dr. A. I. Popov's
research group for the many enlightening discussions shared and the
general feeling of friendship and goodwill. And to Ada and Spiros
Hourdakis, special thanks for all the good times, both Greek and

Chinese, that we shared.

ii

TABLE OF CONTENTS

Chapter
I. HISTORICAL

NUCLEAR MAGNETIC RESONANCE STUDIES OF SOLVATION
AND IONIC ASSOCIATION . . . . . . . . . . . . .

COMPLEXATION STUDIES OF CRYPTANDS . . . . . . .

II. EXPERIMENTAL

SAI‘TS O O I O O 0 0 O l O O O O O O O O O I O O O O
m YPTANDS O O O O O O O O O O O O O O O O O O O O
S OLE NTS O O O ..... O O O O O O O O O O O O O

m SPECT'R OMB O O O O O O O O O O O O O O O O

CHEMICAL SHIFT MEASUREMENTS . . . . . . . . . . . .

MTA TREAMNT l O O O O O O O O O I O O O O O C

III. A CESIUM-133 NMR STUDY OF SOLUTIONS OF CESIUM SALTS

IN
VARIOUS SOLVENTS
INT'R OWCTION I O O I O O O O O ..... C C O O O

Page

. 1
o o 5
. 10
10

10

O O 11
. 12
. 12
. 15

RESLTI‘IIS AND DISCUSSION. 0 O O O O O O O O O O O C O O O 17

IV. A CESIUM-133 NMR STUDY OF CESIUM COMPLEXES WITH CRYPTANDS

C211, C221 AND 0222 IN NON-AQUEOUS SOLVENTS
INTRODUCTION. . . . . . . . . . . . . . . . . .
CESIUM-C21 1 CRYPTA'I‘ES o c o o o o o o o o o o o

CESIUM~C221 AND CESIUM-C222 CRYPTATES . .

iii

33

...46

TABLE OF CONTENTS (Continued)

Table

V. TEMPERATURE STUDY OF CESIUM COMPLEXES WITH CRYPTAND

C211, C221 AND C222 IN PYRIDINE

INTRODUCTION 0 O O O O O O O O O O O O O O O O O 0

RESULTS AND DISCUSSION. .
VI. APPENDICES
I. CESIUM-133 NMR CHEMICAL SHIFT DATA. . . . .

II. DETERMINATION OF COMPLEX FORMATION CONSTANT

WITH ION PAIR FORMATION BY THE NMR METHOD . . .

III. SUGGESTIONS FOR FUTURE WORK . . . . . . . .

VII 0 LITmmRE CITED. 0 O O O ..... O O O O O O O 0

iv

52
52

68

83
89

93

Table

10.

11.

12.

LIST OF TABLES

Page
Corrections Applied to Cesium-133 Chemical Shift . . . . 13
NMR Properties of the Cesium-133 Nucleus . . . . . . . . 16
Donor Numbers and Dielectric Constants of Solvents Used. . . 18
Cesiume133 Chemical Shifts at Infinite Dilution in
Different 801vents . . . . . . . . . . . . . . . . . . 19
Ion Pair Formation Constants of Cesium Salts in Various
SOlventS o '0 o o I o o o O o o o o c o o o o o o o c o o O 31
Formation Constants of Cs-C211 Cryptates . . . . . . . . 43
133Cs Chemical Shifts of Cesium Salt Solutions . . . . . . 68
Cesium-133 Chemical S ifts of Cesium-C211 Cryptates in
Various Solvents ([Cs =0. OI‘M). . . . . . . . . . . . . . 72
Cesium -133 Chemical Shifts of Cquu and C221 Cryptates
in Various Solvents. . . . . . . . . . . . . . . . . . . . . 77
133Ce. Chemical] Shifts of CsB¢l+ and C222 Cryptate in
PyIidine ([Cs =0. 01 M). O I O O O O O O O O O I O I C O 79
:33Cs Chemical Shifts of 05B and Cryptands in Pyridine

tdifferent Temperatures. 2flCs ] = O. 015‘M, MR = [cryptandJ
/[CS] 0 O C O O I O O O O O O O C O C O O O O O O O O O 0 8O
Cesium-133 Chemical Shifts of Cesium-C221 and Cesium-C222
fiyptates in Pyridine at Three Temperatures.

([CS 0. 01 -M_). o o o o o o o O I O o o o o o 82

Figure

10.
11.

12I

13.

1Q.

LIST OF FIGURES

Cryptands C222, C221 and C211 (with internal diameters).

Conformations of the C222 Cryptand . . . . . . . . . . . . .

Concentration Dependence of the 133cs Chemical Shifts of
Cesium Salts in Pyridine and Acetonitrile. fiindicates
data from mis Study I I I I I I I I I I I I I I I I I I

Concentration Dependence of the 133Cs Chemical Shifts of
Cesium Salts in PC and DMF. fiindicates data from this
Study. I I I I I I I I I I I I I I I I I I I I I I I I I

Concentration Dependence of the 133Cs Chemical Shifts of
Cesium Salts in Methanol and DMSO. iindicates data. '

from thi S S tudy I I I I I I I I I I I I I I I I I I I I I I I

Concentration Dependence of the 1330s Chemical Shifts of
Cesium Salts in H 0 and Formamide. fiindicates data

from this study. I . . . . . . . . . . . . . . . . . .

Concentration Dependence of the 133Cs Chemical Shifts of
Cesium Salts in MeNO and Acetone. flindicates data

from tms stlldyI I I 2 I I I I I I I I I I I I I I I I I I

Concentration Dependence of the 1330s Chemical Shifts of
CsB¢4 in Various Solvents. iindicates data from this
studyI I I I I I I I I I I I I I I I I I I I I I I I I I

Concentration Dependence of the 133Cs Chemical Shifts of
CsSCN in Various Solvents. (Taken from Ref. 93) . . . .

133Cs Chemical Shifts of CsB¢4rC211 Cryptate in Acetone. . .

133Cs Chemical Shifts of CsB¢l+-C211 Cryptate in Various

SOlvents I I I I I I I I I I I I I I I I I I I I I I I I I

133Cs Chemical Shifts of CsSCN-C211 Cryptate in Various

S Olvents I I I I I I I I I I I I I I I I I I I I I I I I I

133Cs Chemical Shifts of CsI-Czii Cryptates in Various
solvents I I I I I I I I I I I I I I I I I I I I I I I I

133Cs Chemical Shifts of Cesium-C211 Cryptates in
Various Solvents . . . . . . . . . . . . . . . . . . .

vi

Page

21

22

23

24

25

28

29
35

36

38

39

LIST OF FIGURES (Continued)

Figure

15.

16.

17.

18.

19.

20A.

20B.

21A.

21B.

22.

23.

24.

Computer fit of the 133Cs Chemical Shifts of CsClO -C211
Cryptate in MeNO means an experimental point, 0
means a calculatéd point, = means an experimental and
calculated point are the same within the resolution of

the P1 0 t I I I I I I I I I I I I I I I I I I I I I I I I I I

1330s Chemical Shifts of QSB¢4-C221 Cryptates in Six
Solvents. MR = [C221]/[Cs] . . . ..... . . . .

Computer fit of the 133Cs Chemical Shifts of CsB¢ -0221
Cryptate in DMF. X means an experimental point, 8
means a.calculated point, = means an experimental and
calculated point are the same within the resolution of

the Plot I I I I I I I I I I I I I I I I I I I I I I I I I

133Cs Chemical Shifts of CsB¢u-C222 Cryptate in
midine I I I I I I I I I I I I I I I I I I I I I I I I

Temperature Dependence of the 1330s Cgemical Shifts of
CsB¢ -C211+Cryptate in Pyridine. [Cs] = 0.015 M, MR=
[CZl¥]/[CS] I I I I I I I I I I I I I I I I I I I I I I

133Cs NMR Spectra of CsB¢ -0221 Cr tate in Pyridine at
different Temperatures. MR ==O. 64 . . . . . . . . . .

Temperature Dependence of the 1330s hemical Shifts of
CsB¢ -C221+Cryptate in Pyridine. [Cs =.o 015 g. MR=
[C22¥]/[ [CS] I I I I I I I I I I I I I I I I I I I I I I

133Cs NMR Spectra of CsB¢ -C222 Cr tate in Pyridine at
different Temperatures. = 0. 46 . . . . . . . . . .

Temperature Dependence of the 133Cs Chimical Shifts of
CsB¢%-C222+] +Cryptate in Pyridine. [Cs 0 015 M, MR =

[C22 ]/[Cs] . . . . . . . . . . . . . . . 1'. . . .

Concentration Dependence of the 133Cs Chemical Shifts of
CsB¢4-0221 Cryptate in Pyridine at Three Temperatures . .

Concentration Dependence of the 133Cs Chemical Shifts of
CsBTQ-CZZZ Cryptate in Pyridine at Three Temperatures . . .

Temperature Dependence of the Uncorrected 133Cs NMR Line
Widphs= of CsB¢fi70221 and -C222 Cryptates in Pyridine.

O. 015 I I I I I I I I I I I I I I I I I I I

vii

47

48

51

56

57

59

63

65

LIST OF FIGURES (Continued)

Figure Page
25 I sanlple Plot I I I I I I I I I I I I I I I I I I I I I I I I 90

26. Temperature Dependence of the Uncorrected 133Cs NMR
Line Width of CsB¢4-C211 Cryptates in Pyridine. MR =

[C211]/[Cs ] . . . . . . . . . . . . . . . . . . . . . . 92

viii

CHAPTERI

HISTORICAL

NUCLEAR MAGNETIC RESONANCE STUDIES OF SOLVATION AND IONIC ASSOCIATION

Alkali metal NMR has grown tremendously in the past few years as
an important analytical techniquein the study of interactions in
solutions. Such studies includes ion pair formation (1-5), complex-
ation (6-10) and competitive interactions (11) in aqueous and non-
aqueous solvents as well as mixed solvent work (12-14). In an NMR
experiment, the experimental parameters one can follow are the chemical
shift of the resonance, line width and relaxation time. These para-
meters can be monitored individually (5) or in concert (14).

In general, lithium-7 and sodium~23 NMR measurements have been
often used since these two nuclei have sensitivities of 1.94 and 1.32
respectively, relative to an equal number of protons at constant
frequency. Nuclear magnetic resonance studies of 39K, 4OK and.u1K
have been done by Sahm and Swenk (15) and other researchers (12,16) in
aqueous and a few non-aqueous solutions. The rubidium987 nucleus is
less conducive to NMR studies due to its extremely broad line widths
(17) though aqueous solutions have been investigated (16).

The nuclear magnetic resonance of the cesiume133 nucleus has not
been investigated in any detail until this time. As early as 1953,
Gutowsky and McGarvey (18) conducted a cesiume133 NMR experiment on
solid state cesium halides and showed that the chemical shifts varied
from one halide to another, which is indicative of some covalency in

the supposedly "ionic bond". A later work by Bloemberg and Sorokin

(19) determined the shielding constant, spin-lattice relaxation time

and isotrOpic exchange coupling for a single crystal of cesium bromide.
An average of 25% covalency was deduced. The cesium chloride crystal
structure was studied by monitoring the 133Cs chemical shift, line
width, lineshape and intensities in another study by Baron (20). This
was followed by more works on cesium salts in solution (21-24), the
most comprehensive of which are by Richards and co-workers (25,26) and
DeWitte, 23211.0 (27).

Other techniques commonly employed to study solvation and complex-
ation in electrolyte solutions are conductance, solvent extraction,
ultrasonic relaxation, ultra-violet, visible and infrared spectroscopy,
far infrared spectroscopy, potentiometry and electron spin resonance.

In a simple one-to-one electrolyte solution, there are different
kinds of interactions present. The type and magnitude of interaction
are dependent on a number of factors, solvation number of the ions,
solvating ability of the solvent, dielectric constant and structure
making or breaking ability of the solute. Gutmann's donor number* is
commonly used as a measure of the solvating ability of a given solvent
(30).

The association of ions can be described by three models (at low
concentrations): the contact ion pair, solvent shared ion pair and

solvent separated ion pair (31). The contact ion pair is the classical

 

‘*The Gutmann donor number (28) is the enthalpy of complex formation
'between the given solvent and antimony pentachloride in 1,2-dichloro-
ethane solution.

S+SbCl5 34—21% S-SbCl5
Tflhe term "donicity" refers to the donor ability of a solvent. Gutmann
Jmecently introduced the concept of acceptor number of a solvent (29).

Bjerrium ion pair with a finite lifetime. Bloor and Kidd (2) noted
varying degrees of concentration dependence of the 23Na chemical shifts
of the iodide salt and postulated contact interaction. Evans and Lo
(32) observed vibrational bands which are neither solvent or salt
vibrations and attributed them to the tetraalkylammonium cation and
halide anion vibration. Balasubrahmanyam and Janz (33) studied silver
nitrate solutions spectroscopically and observed two bands in the
nitrate stretching frequency region and showed that they correspended
to the free, solvated nitrate ion and the ion paired nitrate anion.
The concentration dependence of the 19F chemical shift observed by a
number of investigators (34,35) was explained by the contact ion pair
model.

The solvent shared and solvent separated ion pairs would be
expected to occur in solutions where the electron donating ability of
the solvent is much superior to that of the anion. Generally, if
solvent-solute interaction is stronger than solute-solute interaction,
ion pair formation would be limited. The extensive 23Na NMR study
conducted by Greenberg (36) with various solvents and salts showed that
the tetraphenylborate salt is only weakly associated in solvents of low
donicity and no ion pair formation was found in high donor solvents up
to a concentration of 0.5‘M. The iodide, thiocyanate and perchlorate
salt solutions show more concentration dependence of the chemical shift.
These results are supported by far infrared evidence of a solvent
dependent and anion independent vibration band of the sodium ion (37).

A conductance study of alkali halides in various solvents by Kay
(38) showed increasing ion pair association with increasing cation size

(for lithium, sodium and potassium ions) in ethanol, 1-propanol and

liquid ammonia solutions. These results would seem to contradict the
classical concept of the ion pair interaction, the strength of which is
determined by the distance of closest approach of the two charge
centers, which, in turn, is determined by the "ionic radii". Further
work by Kay, 2i.§l- (39) showed that in anhydrous acetonitrile, except
for cesium salts, alkali metal perchlorates are associated while the
tetraphenylborate salts are completely dissociated. Minc and Werblem
(40) also reported the same trend in ionic associations of the alkali
metal perchlorates in acetonitrile. These results seem to indicate
that, in the case of the smaller cations, solvation interaction is
strong while the larger ion, cesium, appears to be much less solvated
and ion pair formation, probably of the contact kind, can occur.
Atlani and Justice (41) studied the conductimetric behavior of one-
to-one electrolytes in dimethylsulfoxide and hexamethylphosphoramide
and concluded that solvation effects on the tetraalkylammonium salts
increase ion mobility and short range interactions between cations and
anions. Potassium and sodium salts, if they associate at all, show
contact ion pair formation. Further evidence for the importance of
ion size in ion pair formation is given by Berman and Stengle (42) who
used 35C1 NMR line widths to show that contact ion pair formation is
favored by high charge-to-size ratio of cation, low dielectric constant
and low donor number for the perchlorate salts of sodium, lithium and
magnesium. The extent of ionic association can be related to the
dipole moment of the resulting ion pair. This effect was studied by
Story and Hebert (43) by electric deflection experiments and they

report an increase in electric dipole moment in the order KI< RbI < CsI.

Nuclear magnetic resonance studies have also been conducted
using the anion as a probe (44-47). However, this approach is consi-
derably more difficult. Anion solvation is less readily detected in
solution as most solvents do not possess localized positive charges.
Furthermore, the choice of anion is limited to those possessing nuclei
that have easily accessible frequencies. Deverell and Richards (48)

81Br and 1271 resonances of alkali metal halides in

studied 3501,
aqueous solutions. From the concentration dependence of the chemical
shifts, they concluded that the potassium, rubidium and cesium halides

undergo contact ion pair formation while lithium and sodium halide

ion pairs are solvent mediated at low concentrations.

COMPLEXATION STUDIES OF CRYPTANDS

As early as 1968, it has been shown that in the transport of ions
through membranes (49), macrocycle compounds increase ionic permeabi-
lity and selectivity for the potassium ion over the sodium ion. Since
then, macrocyclic and macrobicyclic polyethers have been synthesized
(50) to serve as models in the simulation of ion transport in biological
systems. Cryptands are a class of bicyclic ligands first synthesized
by Iehn and co-workers (51,52). The remarkable complexing ability of
these diaza-polyoxamacrocycles with alkali metal ions aroused much
interest in biological and chemical areas of research. Cryptands 211,
221 and 222 are shown in Figure 1. The syntheses of these cryptands
are described by Lehn and co-workers (53) and Ceraso and Dye (54).

The complexed form, called the cryptate, has several conformations in
solution, as presented in Figure 2 for the 222 cryptate, while crystal

structure studies (55-58) indicate that the complexed ligand is in the

,/"\]

o’\,N

J

0222 (2.8A°)

g3
:3

E

0211 (1.oA°)

Figure 1. Cryptands C222, C221 and C211 (with internal diameters).

\vag/

__... o~0 /'0
.///C> 4f)\\}§ (;; 4-“\) ’//£) 1'

.103 "sf—«>3

()-—_()

exo-exo cndo-endo exo-endo

Figure 2. Conformations of

the C222 Cryptand.

endo-endo form. The metal ion within the ligand cavity is stabilized
by the ether oxygens and the electron pairs on the amine nitrogens.

The high selectivity and strong complexing ability of these
ligands are discussed fully in a recent paper by Lehn and Sauvage (59).
Cryptate stability is optimized primarily by the size relationship
between the diameter of the desolvated ion and that of the three-
dimensional cavity of the cryptand. Hence, the three cryptands in
Figure 1 show peak selectibity for the lithium, sodium and potassium
ions respectively, and the stabilities of complexes with other alkali
metal ions decrease sharply. Dietrich, 22.2l- (60) studied bivalent-
monovalent cation selectivity of several cryptands for the sodium,
potassium and barium ions in methanol and water solutions.

The techniques used in these complexation studies are ion-
selective electrodes, potentiometry and nuclear magnetic resonance.

The last method seems to be the most applicable to the study of these
cryptates as alkali metal NMR is quite sensitive and totally free from
chemical interferences. Lithiume7 NMR was used by Cahen (61) to study
lithium cryptates 0211, C221 and C222 in various solvents and he obtained
stability constants for the lithium-222 Cryptate in water and pyridine.
Ceraso and Dye (62) used the 222 cryptand to obtain the sodium anion,
which was studied by 23Na NMR and xeray crystallography (63). Dye,

213 ll, (64) extended this method to obtain other alkali anions and used
alkali metal NMR (65) to study these complexes in non-aqueous solvents.
Potassiume39 NMR is presently used by Shiih (66) to study the complex-
ation behavior of potassium cryptates and crown complexes in various
solvents. Cesium complexes of cryptands and crowns (67,68) are being

investigated by Mei (69) using 133Cs NMR.

The kinetics of the complexation have been the subject of much
research. Lehn, gt a1, (70) studied the temperature dependence of the
proton magnetic resonance spectra of the NaI-C222 and K+-0222 cryptates
in D20 and reported free energies of activation and exchange rates.
Shchori,‘gtnal. (71,72) showed that for the sodium dibenzo-18—crown-6
complex in dimethylformamide at ambient probe temperature, the sodium
exchanges rapidly between the solvated and complexed sites. The
correlation times for the sodium cryptates were determined by
Kintzinger and Lehn (73) using 13C and 23Na NMR measurements, together
with 23Na quadrupole coupling constants. Ceraso and Dye (74) reported
the exchange rates and activation energy of the sodium-C222 complex
in ethylenediamine. The kinetics of the lithiumeC211 and lithium-C221
complexes in various solvents were studied by Cahen, Eiuél- (75) and
the energies of activation were determined. It was found that the
energy of activation for the release of the lithium ion from the 211
cryptate increases with an increase in the donicity of the solvent. A
recent work by Loyola, gt al. (76) used spectrophotometric techniques
to study the kinetics of the formation of calcium cryptates in water
and methanol. Murexide was used as the color indicator. Shchori, 2;
.2l- (77) used the solubility technique to obtain stability constants
for a series of metal complexes of the dibenzo-18-crown-6 in water. An
interesting application of the complexation interaction was reported
by Villermaux and Delpuech (78) who used the sodium-221 cryptate to
study single ion free energies of transfer from water to methanol for
the chloride salts. Another paper (79) reports the use of cryptates
'in a conductance study in tetrahydrofuran to investigate the phenomena

of short and long range electrostatic interactions in solution.

Ligand design and structure is an actively expanding area of
research: many new ligands have been synthesized with varied topology
such as tricyclic polyethers (80-82). With the aid of these synthetic

macromolecules, a better understanding of interactions in solutions

may be achieved.

CHAPTER II

EXPERIMENTAL

SALTS

Cesium chloride, bromide, iodide and perchlorate were obtained
from Alfa (purity 3;99.9%) and were dried at 180°C for 48 hours.
Cesium thiocyanate (Rocky Mountain Research, Inc.) was recrystallized
from absolute ethanol and vacuum dried. Cesium tetraphenylborate was
prepared by a metathetical reaction between equimolar amounts of sodium
tetraphenylborate and cesium chloride in a tetrahydrofuran-water mix-
ture. The cesium tetraphenylborate precipitate was filtered and washed
with conductance water until flame photometry registered sodium content
on the order of conductance water. Drying was done under vacuum at
80°C for 48 hours. Cesium picrate was synthesized by an acid-base
neutralization reaction between picric acid (HPi) and cesium hydroxide.

CsOH + HPi = CsPi + H20

The insoluble cesium picrate was filtered, recrystallized from ethanol
and vacuum dried at 70°C for 5 hours. The yellow crystals decomposed

at 300°C, which compares favorably with the literature (83).

CRYPTANDS

The cryptands were purchased from EM Lab., Inc. under the trade

name "Kryptofix" and were used without further purification.

SOLNENTS

Reagent grade dimethylsulfoxide (J. T. Baker Co.) was dried over
freshly activated Linde Type 4A molecular sieves. Absolute methanol

(Baker) was refluxed over calcium hydride and fractionally distilled.

10

11

Reagent grade formamide (Matheson, Coleman and Bell, 98%) was purified
by six fractional freezings. Acetonitrile (Baker) was refluxed over
granulated barium oxide and fractionally distilled under dry nitrogen
atmosphere. 'N,Nrdimethylformamide (Fisher) was dried over phosphorus
pentoxide. Reagent grade propylene carbonate (Aldrich) was dried over
activated molecular sieves. Reagent grade acetone (Fisher) was reflux-
ed over calcium sulfate (Drierite) and fractionally distilled.
Pyridine (Fisher) was refluxed over granulated barium oxide and
fractionally distilled. Nitromethane (Aldrich Gold Label) was dried
over activated molecular sieves. The automatic Karl Fischer Titrator
(Aquatest) was used to check water content where possible. All

solvents were stored in an inert nitrogen atmosphere.

NMR SPECTROMETER

Cesium-133 NMR measurements were made on a pulsed spectrometer
equipped with a Varian DA-60 magnet operating at a field of 14.09 kG.
The wide band probe was based on the prototype described by Traficante,
33 al. (84). An external proton look at 60 MHz was used to maintain
field stability. A detailed description of the spectrometer is given
elsewhere (85). Data collection and treatment were done with a Nicolet
1083 computer (with the Nicolet 293 disk drive and disk system) using
the Nicolet FT-NMR (NIC-80/S-7202-D) software package. Wilmad 513-3PP
10 mm 0D precision sample tubes were used.

Temperature control was achieved with continuous nitrogen flow
using a Varian temperature controller. Calibration of probe tempera-
ture was done with two copper-constantin thermocouples, one of which

‘was built into the glass insert a short distance below the sample tube

12

and the other placed in neat.solvent in the sample tube. Temperature

stability was better than 1 1°.

CHEMICAL SHIFT MEASUREMENTS

All cesium-133 chemical shifts reported here have been corrected
for bulk susceptibility of the solvent according to the equation of
Live and Chan (86):

5 = oobsd + 211/3 (xref - xsa’mple) (1)
for the probe geometry where the magnetic flux is at right angles to
the sample tube. No correction was applied for the presence of the
salt as Templeman and Van Geet (87) have shown that the contribution of
the salt to the total susceptibility is neglible.

The 1330s chemical shifts at infinite dilution in water has been
reported by DeWitte (27) and for convenient comparison of data, all
chemical shifts are referred to the infinite dilution chemical shift of
the cesium ion in water. Table 1 lists the solvents used and the
respective susceptibily corrections. Positive chemical shifts
correspond to diamagnetic shifts (to high field), while negative shifts

indicate downfield or paramagnetic shifts, relative to the reference.

DATA TREATMENT

The fourier transform software package for the Nicolet computer
has data massaging facilities such as exponential multiplication to
enhance the signal-to-noise ratio. This results in some artificial
line broadening but as the chemical shift is essentially unaffected,
this function was routinely employed. However, for the temperature

study of the three cryptates of cesium (see Chapter V), the'line widths

13

Table 1. Corrections Applied to Cesium-133 Chemical Shift

Solvent
Ni trome thane (MeNO2 )
Acetonitrile (ACN)
Propylene Carbonate (PC)
Acetone
Formamide (ForNHZ)
Methanol (MeOH)
N,N-dimethylformamide (DMF)
Dimethylsulfoxide (DMSO)

Water

Pyridine (FY)

Volumetric
Susceptibility
(x 106)

-O.39l
-0-529
-O.64O
-0.460
-O.55l
-O.530
-O.5OO
-O.630
-O.720

-O.6lO

5 COI'I‘

-10.28
- 9.99
- 9.76
-10.13
- 9.94
- 9.99
-l0.05
- 9.78
- 9.59
- 9.82

PPm
(relative to do

14

are of great importance: consequently, the same exponential constant
was used for all free induction decay signals collected unless indica-
ted otherwise .

Data fitting was done on the CDC 6500 computer system with exten-

sive use of KINFIT, a non-linear curve fitting program developed by

Dye and Nicely (88).

CHAPTER III

A CESIUM4133 NUCLEAR MAGNETIC RESONANCE STUDY OF

SOLUTIONS OF CESIUM SALTS IN VARIOUS SOLVENTS

INTRODUCTION

The nuclear magnetic resonance properties of the cesium-133
nucleus are given in Table 2. The shielding constant for a nucleus is
a sum of several terms (89),

o = 0(1 + oP + 00 (2)
where Cd is the diamagnetic shielding factor arising from the induced

motion of a spherically symmetric electron cloud at a nucleus

approximated by Lamb's formula (90).

 

2
0d = 4fle2 {:rp(r) dr (3)

3mc

However, non-spherical symmetry would result in distortion of the

motion, the net effect of which is represented by the paramagnetic

 

term, 0 ,
P
-ezfiz r—32 (’4')
Up = 22 (3032 Wm)
m c AE vv' v v
2
where AE is the average excitation energy andf-5;-§;-'is the angular
v v'

momentum of the vthelectron. In the case of the cesium nucleus, AE is
small relative to the other alkali metals (91), and this fact, together
with the small quadrupole moment, permit ready mixing of the ground
state with excited states in the presence of an external field. As

a result, the paramagnetic term contributes predominantly to the total
shielding at the nucleus. The last term, 00, incorporates all other
inter- and intra-ionic effects such as bulk magnetic susceptibility of
the solvent, magnetic anisotropy of the environment and fluctuating

electric field gradients due to polar effects of the surrounding

15

16

um H v
Asfloam us mo.:H :Hv as: mosm.m

Ama mo Hopes:
Hmzwm op cosmmsoo .Uamflm pqdmeOOV nu.m
A0: =:\nm mo mpflnsv mien.m
ANEO smuoa x m mo mpaqzv 300.0-
A m} .8 323 NE.

ROOH

saga: mafia Hanspmz

hoqmswonm mocmcomom

spfl>npfimcom o>apmaom
Ofipmh oahhmopmzmwz

psmsos mHomzhudsw owhwomam
swam

mosdcnspm adnspmz

msmfiosz MMHIESHmmU msp mo mmwphmfiohm mzz .N canoe

17

medium (92). The relative magnitudes and signs of these effects are
difficult to determine: however, since these effects are small

relative to the paramagnetic shielding at the cesium nucleus, deviation
from spherical symmetry of the closed shell ion results in smaller
(downfield) chemical shifts as the electron density increases. The
negative sign of the 0p term yields a more negative overall shielding
constant with increasing electron density and results in a shift to

lower field at constant frequency.

 

H=(1-Ototal)Ho (5)
6
. (H -H )10
H = ref sample (6)
H
ref

Cesium—133 nucleus has a wide range of chemical shifts and is
therefore, sensitive to variations in the immediate environment. There
is a unique advantage of cesium-133 NMR over conductance and other
conventional techniques in monitoring solutions: because of the nature
of the nuclear magnetic resonance signal, localized interactions at the
resonating nucleus can be monitored to the exclusion of interactions
in the bulk of the solution. The major drawback is that the lower.
limit of concentration that can be practically and routinely used is

0.001 3.

RESULTS AND DISCUSSION

The chemical shifts of a number of cesium salts in different
solvents with respect to that of the infinitely dilute solution of
cesium ions in water are given in Table 7 in Appendix I. The choice

of salt and solvent were made in reference to a previous similar study

Table 3.

Solvent
MeNO2
ACN

PC
Acetone
ForNH2
MeOH
DMF
DMSO

H20

Pyridine

18

Donor Numbers and Dielectric Constants of Solvents Used

Donor

Number

2.7
14.1
15.1
17.0
24.7
25.7
26.6
29.8
33-0
33.1

Dielectric

Constant
35-9
38.8
69.0
20.7

109.5
32.7
36.7
45.0
78.6

12.0

Dipole

Moment

3.56
3.44

2.69
3-37
2.87
3.86
3.90
1.85
2-37

19

Table 4. Cesiumy133 Chemical Shifts at Infinite Dilution in Different

 

Solvents
Averaged
Solvent £2. 50 (from ref. 27)
MeN02(ClO,+-) 59.2 i 0.1 59.8 i 0.2
ACN(I") -33.3 i 0.6 ,
_ -32.0 i 0.4
ACN(B¢,+ )* -3L+.0
PC(B¢4')* 35-1 i 0.3 35-2 i 0-2
Acetone(B¢,+-) 26.3 3; 0.3 26.8 i 0.3
ForNH2(Pi-) 2.30 3; 0.6 2.2 i 0.2
DMF‘(B¢,+-) 0.40 i 0.03
_ 0.5 i 0.2
DMF‘(Pi ) 1.8 i 0.1
DMSO(B¢L;) -68.0 i 0.3
_ -68.0 i 0.2
DMSO(Pi ) -66.5 :5 0.5
H20(SCN') 0.11 3; 0.08 0.0 i 0.1
Pyridine(B¢4-) <<-13 _--

*E. Mei

20

(27) so as to further extend the characterization of cesium salts in
solution. Consequently, the data obtained from this study will be
discussed in conjunction with those reported by DeWitte (27) and Mei
(97). Table 3 lists the donor number, dielectric constant and dipole
moment of the ten solvents investigated. Figures 3 to 7 show the
concentration dependence of the 133Cs chemical shift in several
solvents. Asterisks mark the eleven solutions from this study. The
error in the measurement of the cesium chemical shift was less than
i 0.16 ppm and no appreciable broadening of the signal was observed
over the concentration range studied. Extrapolation to infinite
dilution was done by fitting a seventh order polynomial equation
using KINFIT, a program developed by Dye and Nicely (88). The pro-
cedural details have been discussed elsewhere (93). The chemical
shifts at infinite dilution are compared with those obtained by
DeWitte in Table 4 and they seem to agree well.

Of the alkali metal ions, the cesium ion is the most poorly
solvated because of the lower charge density of the large cesium cation.
Long range interactions are expected to be negligibly weak as a result
of the small charge-to-size ratio. Hence, the concentration dependence
of the cesium-133 chemical shift should reflect ionic interactions
within the primary solvation sphere. From Figures 3 to 7, it can be
seen that, in any one Solvent, increasing concentration of salt can
lead to upfield or downfield chemical shifts. Tetraphenylborate and
perchlorate salts belong to the former and the other five anions,
picrate, thiocyanate, chloride, bromide and iodide are in the latter
group. (There is one exception — cesium perchlorate in nitromethane

shifts downfield with increasing concentration. This case will be

21

4—

 

 

 

 

 

‘ cr
40~ -
l/P’ Ekfi4i*
:r
30L- [if Pyridine
d
20~ :5
:5
/
?’
IOF-IJ
' I
A. I
E o—
3; 99
60 I
no,
_ r_ _ _ __ __ __ _ __
Acetonitrile
~2o~ B07.
-30
13
a
40 SCN‘
I!
J I
o 0.0: H 0.02

Concentration (M)

Figure 3. Concentration Dependence of the 13305 Chemical Shifts of
Cesium Salts in Pyridine and Acetonitrile. * indicates

data from this study.

8 (ppm)

Figure 1+ .

22

 

 

 

 

 

 

 

 

 

2 ‘ Pi'fi if
9454
x - ' CIO‘
3 ' ”‘3 ' c 34:
A A
Q - 13
SCN-
_2 .-
I"
_4 __ DMF
l l l 1
0 0.005 0.0l 0.02

Concentration Dependence of the 133Cs Chemical Shifts of

Cesium Salts in PC and DMF. #indicates data from this

s tudy .

Concentration (M)

 

8 (ppm)

23

 

44

40»

38*-

34—

'—'A
1
a
0

Br'
I‘

“SCN'

METHANOL

l

 

-66~
-68
-70..

-72...

 

MMCIO‘E

Cl'

1

 

 

0.05

C0ncentrotion(M)

Figure 5. Concentration Dependence of the 133Cs Chemical Shifts of

Cesium Salts in Methanol and DMSO.

this study.

*indicates data. from

24

.883 m8» son.“ 8.8 m888§¥ .8828a

and cum 8 $18 588 .8 33cm H8888 8mmH 08. 8 88888 8888888 .8 8888

AS: ZO_.r<m._.2woZOU

 

    

 

v.0 No 0 No S o
.— a A . d 4):
.. N 1 NT
moi<2moa o I
L O_I
iH 1 mi
1 mi 8
.m w,
L.
- e. W
-6 . . .. m-
.28 7,; .
1: is
....O
L N
mOU. _d
m..

 

 

 

 

 

 

Nitromethane
48 r ---------- -

8 (ppm)

 

P"
24 i 13

 

20

  

I6- SCN‘
Acetone

 

 

 

 

l l
o 0.0: 0.02
Concentration (M)

Figure 7. Concentration Dependence of the 133Cs Chemical Shifts of

Cesium Salts in MeNO2 and Acetone. firindicates data from

this study .

26

duly discussed.) From the change in chemical shift, it can be seen
that the size, symmetry and type of anion play an important role in
ion association as a result of the small interaction energy of
salvation. At infinitely dilute concentrations, the cesium ion is
completely solvated by the solvent molecules, and the chemical shift
characteristic of the electron donating ability of the solvent is
observed. However, upon increasing the salt concentration, the solvent-
cation interaction is gradually replaced by cation-anion interaction
and the formation of solvent separated and/or contact ion pairs. In
the latter case, the electron density at the nucleus is either
decreased or increased relative to the free solvated state. For the
bulky, symmetric tetraphenylborate and perchlorate anions, it appears
that the electron density is indeed decreased, leading to an upfield
shift, whereas the thiocyanate, picrate, triiodide and halide anions
act as better electron donors than the solvent molecule(S)diSPlacedo
From equation 4 (page 15), it can be seen that the paramagnetic
shielding term is a function of the angular momentum of the electrons.
Solvent-cation interaction would reduce the symmetry of the closed
shell configuration of the cesium ion and induce some angular momentum
as the outer orbitals of the cesium ion are overlapped with the
appropriate molecular orbitals of the solvent. With the approach of
the anions giving downfield shifts, this effect is even more pro-
nounced due to the polarizability (in the case of the halides) and
localized negative charge (in the case of the picrate and thiocyanate
ions) of the anions, resulting in paramagnetic shifts.

The exception noted above in the case of cesium perchlorate in

nitromethane indicates that in this solvent of low donicity, the

27

perchlorate anion, even with its reduced charge density, is a better
donor of electrons than is the solvent molecule displaced and the net
effect observed on the NMR time scale is a shift to low field.

Solvent effect on the cesium-133 chemical shift is graphically
presented in Figure 8 for the tetraphenylborate salt and in Figure 9
for the thiocyanate salt. (Cesium thiocyanate is soluble in more
solvents than the other cesium salts used in this study.) There is a
noticeable trend in the range of chemical shifts of cesium thiocyanate
in each solvent. In oxygen donor solvents, nitromethane, methanol,
propylene carbonate and acetone, the 133Cs chemical shifts are upfield
relative to nitrogen solvents, dimethylformamide, formamide, aceto-
nitrile and pyridine. Dimethylsulfoxide, being a solvent of high
donicity and relatively high dielectric constant, apparently solvates
the cesium ion very efficiently, giving the most downfield shifts and
futhermore, little concentration dependence is observed. A similar
trend is found for the tetraphenylborate salt, except in the two
solvents acetone and pyridine. In these two solvents, increasing salt
concentration produces considerable change in electron density at the
cesium ion. These results seem to imply that the presence of the
anion is very much more significant for this salt over the concentra-
tion range studied than is found to be the case in the other solvents.

A glance at Table 3 will help explain the trends observed above.
Acetone and pyridine have the lowest dielectric constants and dipole
moments of all the solvents used. Consequently, the large, symmetrical
tetraphenylborate ion can readily approach the cesium ion even at low
concentrations as a result of the low dielectric of the medium, giving

rise to appreciable curvature in the plots.

28

 

 

 

 

 

 

 

 

 

 

Py“
50y
*.
Acetone
40- A ‘
I I I I I I}... I ‘ ‘
3O_ ‘ A, PC
20-
E l0L *
:5:- O I. DMF I
6!)
.. l0 ..
-2o __ 4n ACN
A O—i '
-30 -W
-40..
-50L
-60..
its
DMSO
-70 PM
I L
O -0! .02

CONCENTRATION (M)

Figure 8. Concentration Dependence of the 133Cs Chemical Shifts of

CsB¢l+ in Various Solvents. i» indicates data. from this
study.

60

50

40

-4o

-50

-60

-7O

0

29

 

 

 

 

 

 

 

 

 

 

 

 

~q.II"‘-—CL—_________‘F__ “JNBPQ()23
1__4’_q

MeOH
‘CF---—1.——~ V__‘}i, -j|_1
-o———O a PC 0—
H fl_ Acetone
#-

i3t>rPdt423
50:20 I :2

DMF

*VI: + ACN 1—
Py '

DMSO
-O———L a 4—
0,6: 0.02 0.025

CONCENTRATION (M)

Figure 9. Concentration Dependence of the 133Cs Chemical Shifts of

CsSCN in Various Solvents.

30

In cases where the solubility of the salt is equal to or greater
than 0.01 M, the ion pair formation constant was determined using the
program KINFIT. This method has been described elsewhere (93). The
values obtained are reported in Table 5 together with those from the
work done by DeWitte (93).

The association constants for CsSCN in different solvents are
listed in Table 5 in the order of increasing donor ability of the
solvent. It appears that as the donicity of the solvent decreases, ion
pair association increases with one exception - water. A possible
rationale is that water is a highly structured solvent with extensive
hydrogen bonding and the introduction of a solute into the bulk medium
apparently results in structure breaking effects leading to a greater
degree of association than is otherwise expected.

CsB¢4 in DMF and DMSO is negligibly associated. These two solvents
are good donor solvents and thus inhibit ionic association. The ion
pair formation for this salt in ACN and PC are larger than the
corresponding values for the CsSCN ion pair, which is rather surprising.
One can only speculate that the cesium ion could have remarkable
affinity to the tetraphenylborate anion as a result of unique struc-
tural orientation to the phenyl rings on the anion. Another point of
interest is the high degree of ionic association of the tetraphenyl-
borate salt in pyridine. Due to pronounced curvature of the plot (see
Figure 3), it is difficult to extrapolate to infinite dilution in
pyridine. However, it was established that the ion pair formation
constant is greater than 100. One can infer that the aromaticity of
the strong donor solvent, pyridine, stablilizes the ion pair. The

association constant for the tetraphenylborate salt in PC is 12.0 i 7.2

31

Table 5. Ion Pair Formation Constants of Cesium Salts

in Various Solvents

K.

Anion. Solvent _;2
SCN- Nitromethane 44.1 i 1.2
Acetonitrile 13.2 i 3.8
Propylene Carbonate 3.4 i 0.5
Methanol 3.9‘: 0.6
Dimethylformamide 1.1 i 0.2
Dimethylsulfoxide 1.6 i 0.5
* water 3.3 i 1.6
3%!" Acetonitrile 53.5 i 13.7 **
Propylene Carbonate 12.0 i 7.2 **
* Acetone 25.14”; 1.9 **
* Dimethylformamide m 0 **
* Dimethylsulfoxide m 0 **
* Pyridine >102 **
01‘ Methanol 9.1; 1.9
Br- Methanol 40.0: 7.1
I" Acetonitrile 34.0 .t 4.9
Methanol 15.3: 0.9

* From this work.

** Averaged values from two sets of experiments.

32

which is unexpectedly smaller than that in acetone. If the donor
ability of solvent is the dominant factor present, one would expect
ionic association to be stronger in a lower donor solvent such as PC.
However, PC has a high dielectric constant and this fact probably
accounts for the smaller ion pair formation constant.

The halides appear to be associated in varying degrees in methanol.
Instead of the expected trend of increasing ion pair formation with
increasing "softness" of the anion, the results follow the trend
Cl-<Br->I-. The iodide ion is isoelectronic with the cesium ion and,
therefore, ion pair formation should be strongest compared to the

three halides. However, the results indicate otherwise.

CHAPTER IV

CESIUM-133 NMR STUDY OF CESIUM COMPLEXES

WITH CRYPTANDS C211, C221 AND C222 IN NON-AQUEOUS SOLVENTS

INTRODUCTION

Since the advent of bicyclic diaza—polyoxamacrocyclic compounds
(cryptands) synthesized by Lehn and co-workers in 1969 (53), much
interest has been shown in the complexing behavior of these ligands
with alkali metal ions in various solvents. Cesium-133 NMR is used in
this study to monitor the complexation interaction of the cesium ion

with the cryptands 0211, C221 and C222 in various non—aqueous solvents.

CESIUM-C211 CRYPTATES

13305 chemical shifts were determined as a function of cryptand
to cesium ion mole ratio (MB). The results are shown in Figures 10
to 14 and Table 8 in Appendix I. Cesium ion concentration is main-
tained at 0.01 M. The estimated error in the measurements is i 0.01
ppm. The line widths observed show a slight increase from about 5 Hz
to 10 Hz (subject to the inhomogeneity of the field) with increasing
ligand concentration. Cesium tetraphenylborate-C211 complex in
acetone was studied up to a mole ratio of 20. The reaction appears to
be less than quantitative even with a large excess of ligand, which
is not unexpected considering the small ligand cavity (0.8 A radius,
endo-endo form) (94), and the size of the cesium ion (1.84 A radius).
The C211 ligand show peak selectivity for the lithium ion, with which
it forms a strong, inclusion complex, i.e. the metal ion is centro-
sytmnetric within the ligand cavity. This cryptand has been studied
by Cahen, gtwal. (75), who showed that the lithium-7 chemical shift

of the complex is essentially independent of solvent and counterion.

33

34

Cation exchange between the two sites (free and complexed) is slow on
the NMR time scale since two resonances of 7Li nucleus were observed
when the metal ion was present in excess.

From Figures 11 to 14, it can be seen that the downfield chemical
shifts are very much dependent on solvent and anion and that, in most
cases, the plots show very little curvature as a consequence of the
extremely weak cation-ligand interaction. In DMSO, a solvent of high
donicity and relatively high dielectric constant, no evidence of
complexation was observed for the cesium tetraphenylborate salt and
cryptand 0211. Apparently, the strongly interacting primary salvation
sphere excludes the 0211 cryptand effectively even at a 5:1 excess of
the ligand. On the other hand, complexation interaction is greatest
for the thiocyanate salt in nitromethane, a solvent of low donicity.
The poor donor ability of the solvent molecules, together with the
low charge-to-size ratio of the cesium ion enable the electrically
neutral ligand to approach and coordinate to the cesium ion. The
chemical shift varies over a wide range (almost 40 ppm) and a
greater degree of curvature is observed.

Figure 14 shows the complexation of cesium chloride, perchlorate
and picrate salts with 0211 in various solvents. The picrate salt
was sufficiently soluble in only three solvents, formamide, dimethyl-
formamide and dimethylsulfoxide, all of which are good donor solvents.
Consequently, little complexation was observed as indicated by the
almost linear, horizontal mole ratio plot for the complex in DMF
solution shown in Figure 14. Slight curvature is observed for the
MR plot of cesium chloride-0211 complex in methanol while the cesium

perchlorate-0211 cryptate in nitromethane exhibited pronounced

35

.8384 an oneness Smoke m8 .8 Berna H8280 momma .3 enema

Q +m8\ H _ _N: 020m 22>.

 

ON 0. O
1 q

dii

 

 

30

20

IO

36

  
 

Acetone
i.

Pyridine

 

 

 

 

 

 

I
: DMF
A—zo [-
E
a. 4
a.
‘9
‘0 - 30 r
Ac N
-4o~
-50 .
60 -
DMSO
:4 —% n n: a} A
-70- ' L J
1.0 2 0 3. 4.0 5-0

Mole Ratio ((C2H)/(Cs+))

1:‘igure 11. 1330s Chemical Shifts of CSB¢1+-C211 Cryptate in Various

Solvents.

37

Figure 12. 13305 Chemical Shifts of CsSCN-0211 Cryptate in

Various Solvents.

38

 

 

 

 

 

 

 

 

MeN02
50 i-
40 -
.. PC
30 ~ 0
' o
._ J
A 20 Acetone ‘
E
a
£3: 10 -
co
DMF
0&3‘“ + + ,_L__~
s 7“ 3‘ s3
-30
ACN
-40 .. N
—i
-50 ..
-50 -
(P DMSO
-70‘ l W l . 1 w?)
0 1.0 2.0 3.0 ‘ 4.0 5.0

 

Mole Ratio («zip/(03)

39

 

 

 

 

 

 

 

 

40
3O -
PC
20 -
10 —
’8.
3' 09.1 _ L n DMF
so ' —U _—._. fi— {3,_.. a
4 +
ACN
+
+ A—
-50 -
-60 _
4% DMSO
- 7O 0 1:0 2 0 3.0 4.0 50

Mole Rotio(tc2m/rcs+1)

Figure 13. 13305 Chemical Shifts of CsI—0211 Cryptates in Various ‘
Solvents.

40

    
 

 

 

 

 

 

 

 

i
. I CF/MeOH
+ 4
010;
AWeN02
20- \C’
ci— a1 ,. PI /DMF
o r ‘v M 4— —o
O I 2 3 4 5

Mole Ratio ([CZII] /[CS*J)

Figure 14. 1330s Chemical Shifts of Cesium-0211 Cryptates in Various

Solvents.

41

curvature. The complex in nitromethane is significantly stronger
than in other solvents as the cesium perchlorate ion pair is negligibly
associated (see Chapter III) in this poor donor solvent and complex—
ation is stabilized.

In solutions where complexation does occur, the following
equilibria are in effect:

+ — M+A'

3
+

>
II

M+ + L = (ML)+

The cesium ion and cryptand 0211 must form an exclusion complex since
the relative sizes of the metal ion and ligand cavity would prohibit
the entry of the ion into the central cavity. It is interesting to
note that the chemical shift values at high concentrations of ligand
do not appear to converge to a chemical shift value characteristic of
the cesium ion within the ligand cavity as they do for 7Li chemical
shifts in the Li+-0211 complex (97). The mole ratio plots exhibit
smooth curvature and no abrupt change in chemical shift was noted
which would indicate a change in stoichiometry of the complex as a
result of coordination to a second ligand.

Assuming that only cation-ligand interactions are important, the
observed 1330s chemical shift is a population average of the two
chemical environments of the cesium ion.

Gobsd = XM‘SM + "m‘sm. (7)

where 6M and 5 are the chemical shifts characteristic of the solvated

ML
and complexed metal ions respectively, and xM andjxML are the corre-
sponding mole fractions. Using this model, an.expression can be
derived for the observed chemical shift to which the experimental

data are fitted to obtain a value for the concentration formation constant

42

(61). This is accomplished with the help of the KINFIT program. The
results are given in the first column in Table 6 and a sample of the
computer fitting obtained for the cesium perchlorate-0211 complex in
nitromethane is presented in Figure 15.

However, comparison with ion pair formation constants reported in
Chapter II (also included in Table 6, column 2 for convenience) make
it quite apparent that this approach is too naive as the "formation
constants" of the cryptates are on the same order as the ion pair
constants. In other words, the anion should be taken into considera4
tion as both ligand and anion compete for the cesium ion in solution,
and the change in the observed chemical shift is partly due to
changes in the degree of anionic association with the cesium ion upon
complexation. The observed chemical shift therefore, is modified to
include a third factor, the chemical shift characteristic of the ion
pair: '

‘Sobsd = XMGM + XML‘SML + "MA‘SMA (8)
The derivation of the final expression for the observed chemical shift

can be obtained by applying the following equations,

Kip = [MAJ/[MIN] (9)
Kf = [ml/[NHL] (10)
CL = [ML] + [L] (11)
CM = [ML] + [M] + [MA] (12)
CM = [MA] + [A] (13)

where Kip is the ion pair association constant, Kf is the formation
constant of the complex, EMA], EM] and [A] are the concentrations of

the ion pair, free metal ion and free anion respectively, and CL and

Table 6.

Salt

CSB¢Z+

CsSCN

CsI

CsClOu

CsCl

Formation

Solvent

ACN

PC
Acetone
DMF

m
mw

MeNO
ACN

P0
Acetone
DMF

DMSO

ACN

MeNO

MeOH

Constants of Cs+¥CZ11 Cryptates.

782

39:25
55:18
2.8 : 0.3
1a9ia4
29:35
~0

m5:0J
nJ:25
9.0 : 5.4
05:08
~0

W O

43

K.

_l2

53.5 i 13.7

12.0 _-l_-_

25.7 i
< 1.0
>121.9 i

W O

44.1 :
13.2 :

3-9 i

90:

7.2
1.9

7.5

1.2
3.8
0.7

1.9

Ht

43.4 : 16.7
5.4: 2.1

42:05

MA: L2

85: 80

.poam asp mo soapsaommw one canvas 050m 0:» and pswom dogmasoaao was

HapCoEHHomxo as memos u .psflom dmpsfisoamo a memos o .psfiom Hapaosfihomxo so memos x

.mozos ca osnsaano Hamoieoauno to anthem ancasoso momma one no she nossaeoo .na enemas

 

.X
0.

 

 

525

45

CM are the analytical concentrations of the ligand and salt. With
these five equations and simple algebraic manipulations, the following
expression is readily derived.
foime + (KfKiPCL+KiP+Kf) [1432 + (KfCL+1-KfCM) [M] - CM = 0
(14)

A detailed derivation and the subroutine EQN used in KINFIT is
given in Appendix II. In order to use this model, the ion pair
formation constant has to be known. Using the values reported in
Chapter III, eight complexes were fitted to this equation and better
formation constants were obtained (Table 6, column 3).

The formation constants of the thiocyanate-0211 complex in the
six solvents studied show a trend analogous to that of ion pairing,
i.e. the stabilities increase with decreasing donor ability of the
solvent as the weak complex is stabilized by the low donor medium.
However, this is not observed for the cesium tetraphenylborate-0211
cryptates. It is interesting to note that the complexation is very
weak with the cesium halides. In fact, in methanol, negligible
complexation is found with cesium chloride while the cesium iodide-
0211 cryptate is somewhat more stable. These results support the
contention that the anion and cryptand are indeed competing for the
cesium ion and in the case of the halides, the anion coordinates better
to the cation than does the neutral ligand. The competitive formation
constant for the cesium tetraphenylborate-0211 complex in pyridine is
extremely small. Therefore, it is apparent that the curvature in the
mole ratio plot is the result of changes in the ion pair equilibrium as

the weak complex is formed.

46

CESIUM-C221 AND CESIUM-C222 CRYPTATES

From the above results, it seems quite evident that for the weak
cesium-0211 complex, the anion and the solvent can have strong influence
on the complexation interaction. The ligand effect is studied here
with the tetraphenylborate salt. The 0221 cryptand has a larger cavity
size (1.1 A radius, endo-endo form) (94) than the 0211 cryptand and one
would expect that it would form a stronger complex with the cesium
ion. The results show that the Cs+-0221 cryptate is indeed stronger
than the corresponding complex with the 0211 cryptand. The data are
presented in Table 9 in Appendix I and are plotted in Figure 16.

The most striking difference between these plots and those shown
in Figures 11 to 14 is that in propylene carbonate, acetone, aceto-
nitrile and pyridine, quantitative complexation is achieved around
a mole ratio (defined as the concentration of ligand over the concen-
tration of metal ion) of 1. Extrapolation of the linear portions of
the plots yield an intersection at equal concentrations of metal ion
and ligand (MR = 1) which indicates the formation of a 1:1 complex.

The line widths in the exchange region (O<MR<1) in acetone, P0 and
ACN show much broadening, from less than 10 Hz to over 100 Hz. In
pyridine, the exchange broadening is such that no signal was detected
in the region indicated by the broken line in Figure 16. However,

as the mole ratio approaches 1, most of the cesium ion is essentially
complexed and the line width decreases as the limiting line width of
the complexed cesium ion is reached. An attempt to obtain the
formation constant of the Cs+-0221 complex in ACN gave poor results

(Kf a: 107) as the complex is too strong.

8 (ppm)

47

 

 

 

 

 

 

40 p.
20
0e
- 20
Acetone“)
‘40 PC(A)
. DMF
Pyridine
- 60 ACN
Jh-~IL~‘I“‘l‘—-—4I—IF—-flI--I-—4l—4l———————lF--I[)hnsfia
1 1 l
O i 2 3

MOLE RATIO (tc2ziJ/LCs+1)

Figure 16. 133Cs Chemical Shifts of CsBoLf 0221 Cryptates in Six Solvents.

MR = [0221]/[0s+] .

48

.poam one mo compsaowoa one seeps: team may and pcflom Umpaasoaao
was HspCoEHHoQXo as memos u .ssfiom umpsHSOHao a memos o .psfiom amasostoQXm

so hence x .asn ca openness ammu-semno so namasm Hmoasoru momma one to has nossssoo .sa onsmam

 

.x
nu

 

 

49

In DMSO and DMF, two solvents of high donicity and medium
dielectric constant, complexation is very much weaker as shown by the
reduced curvature of the plots. The stability constants were readily
determined with the help of the KINFIT program. The Cs+-0221 complex
in D is given in Figure 17 as an example of the computer fit obtained.

The formation constants in DMF and DMSO are: log K = 3.33 f 0.04

DMF

and log K = 2.94 f 0.24 respectively.

DMSO
The chemical shifts characteristic of the complex are not inde-
pendent of solvent and one can conceive of a complexed state whereby
the cesium ion is partially occluded within the ligand cavity and
partially solvated. The 0221 ligand would be expected to be a good
electron donor due to the multiple donor sites - 5 oxygen and 2
nitrogen atoms. The shift to low field of 13303 resonance reflects an
increase in electron density at the nucleus upon complexation. Since
the complex is composed of the cesium ion, ligand and solvent
molecules, one would expect the chemical shift of the complex to
parallel somewhat the donor ability of the solvent. This is not the
case and, therefore, other factors must influence the shift, e.g.
solvent structure, dielectric constant, ring currents (in the case of
pyridine), etc. The range of chemical shifts between the free and
complexed cesium ions give a semi-quantitative idea of the energy
difference between the cesium environments. Assuming the same
activated state or energy barrier of the transition, a larger range
reflects a lower energy state of the complex. Greatest range of 133Cs
chemical shifts are observed in PC, acetone and pyridine and hence,

the strongest complexes.

50

The ligand effect is extended to the 0222 cryptand in pyridine.
The results are given in Table 10 in Appendix I and in Figure 18. Again,
the broken line indicates the region where the signal is broadened
significantly and is beyond the detectability limit of the spectrometer.
The larger 0222 cryptand (1.4 A radius, endo-endo form) (94) would
permit the cesium ion to enter the three dimensional cavity much more
readily and the complex formed would be the most stable. The 1:1
complex has a chemical shift of -224.15 ppm (compared to -57.90 ppm
for the 0221 cryptate) in pyridine, indicating the high electron
density at the cesium nucleus and the total range of chemical shifts
is a remarkable 250 ppm. Furthermore, all the cesium ions are
essentially complexed at a mole ratio of 1. The cesiumr0222 cryptate

in various solvents is studied in greater detail by Mei (96).

51

soL

(ppm)
/

-IOO"
\

8

-150. ‘\

-200r- \

 

-250
L l 1
0 L0 20

Male Ratio (1C2221/[c.+|)

Figure 18. 133Cs Chemical Shifts of CsBfiu-CZZZ Cryptate in Pyridine,

CHAPTERV

TEMPERATURE STUDY OF CESIUM COMPLEES

WITH CRYPTANDS 0211, C221 AND 0222 IN PYRIDINE

INTRODUCTION

Solvent and anion effects of the weak cesium—0211 complex were
discussed in Chapter IV together with the effect of the size of ligand
cavity of cryptands on the complexation reaction. The strength of
complexation is intimately related to the kinetics of the system,
which, in this case, involves the rate of exchange of the cesium ion
between the solvated and the complexed sites. The temperature
dependence of the 13303 chemical shifts of Cs+-0211, Cs+-0221 and
0s+-0222 cryptates were observed in pyridine solutions. The results
discussed here are the preliminary data obtained from the study of
temperature effects on the complexation of the cesium ion with these

cryptands.

RESULTS AND DISCUSSION

The complexation of cesium tetraphenylborate with 0211, 0221 and
0222 cryptands can be described by the following equilibrium, assuming
a 1:1 complex.

Cs+S + LS = CsL+S + (x+y-z)S
x y z

where S is the solvent molecule, L is the ligand and x, y and z are
the salvation numbers of the cation, ligand and the complex
respectively.

Depending on the strength of the complexation interaction, the
cesium ion undergoes exchange between the solvated state and the
complexed state which can be monitored by 133Cs NMR. At a given

temperature, if the mean lifetime at one site is less than 2/(wA-wB ,

52

53

where 9A and ”B are the resonance frequencies (in radians per second)
of the two different sites, only one signal is observed on the NMR
time scale. Furthermore, the signal is broadened by the exchange
mechanism especially around the coalescence temperature. The coales-
cence temperature (Tc) is the temperature at which the random
statistical exchange of the cesium nucleus between two (or more)
chemical sites is slowed down to the extent that only one averaged

signal is observed. If the exchange is slower than 107

per second, two
signals are observed, corresponding to the free, solvated cesium
nucleus and the complexed cesium nucleus.

Since the Cs+-0211 complex is weak (see Chapter IV), two mole
ratios of 2.49 and 6.63 were arbitrarily chosen for this study as the
amount of ligand required to reach a state of quantitative complex-
ation is impractical. For the other two ligands which form strong 1:1
complexes with the cesium ion, the samples are prepared such that the
exchange region can be observed, i.e. 0<MR<1. The temperature
dependence of the chemical shifts observed are presented in Table 11
in Appendix I and in Figures 19 to 21 together with that of the cesium
salt solution. For the cesiumr0221 and cesium-0222 cryptates, two
separate solutions with a large excess of ligand were also prepared
so as to monitor the changes in chemical shift of the complexed cesium
ion with changes in temperature. All chemical shifts reported in
this study have been corrected for bulk magnetic susceptibility of
the solvent and temperature effects on the reference and adjusted to
the final reference point of the infinitely dilute concentration of
cesium ions in water at 2500. The error of measurement is f 0.3 ppm

unless indicated otherwise. The line widths are included in Table 11

ARR = OJOO

5C)‘
A682: 2 49'

/ MR t‘ 6.63

 
 

14C)‘

3(Dr

   

1()P

8 (ppm)

-20—

 

..30 l l L .____J I

--25 o 25 * 50 75

Temperature ( oC )

Figure 19. Temperature Dependence of the 13305 Chemical Shifts of
CsB¢4-0211 Cryptate in Pyridine. [0s+] = 0.015 M,

MR = [02111/[Cs+].

55

Figure 20A. 133Cs NMR Spectra of CsB04-0221 Cryptate in Pyridine

at different Temperatures. (MR = 0.64)

56

 

71.7°c

58.0°c

43.4 °c_

 

 

W, '12'0 0C

 

 

 

{—717— . IOO ppm -————+H

‘ instrumental artifact.

57

 

 

‘ Ot0()AAR
,1 40-—
8
Ci ,spsv”’.””’.\\
. \
a O_ \
O
IE%D \\ OJ64.AAR
:9 \
g r- \\
00
/
-40 / 3.97m:
/ .
/
l 1 L I l
-25 O 25 5O 75

Temperature (°C)

Figure 20B. Temperature Dependence of the 133Cs Chemical Shifts of
05454-0221 Cryptate in Pyridine. [CsJ'] = 0.015 :4,
MR = [02211/[0s+].

58

Figure 21A. 133Cs NMR Spectra of CsB¢4-0222 Cryptate in Pyridine

at different Temperatures. (MR = 0.46)

59

 

M 843°C
* 71 .7°c
58.o°c

 

 

 

 

 

w 100 ppm H

‘ instrumental artifact .

60

50 h”)
\

I
(N
O

l

’,/’

\\\ CL463NRR

\VV/
-|00 )-

-|50" /

/ 3.67MR
-200r

8°°"(88‘-’°oi 25°c,ppm)

I

~250

 

L I l l 1

-25 o 25 50 75
Temp (°C)

Figure 21B. Temperature Dependence of the 133Cs Chemical Shifts of
CsBou- 0222 Cryptate in Pyridine. [Cs+] = 0.015 M,

MR = [02221/[Cs+].

61

These values include broadening due to field inhomogeneity, viscosity
and the exponential multiplication of the free induction decay signal
as discussed in Chapter II. Since only the relative line widths are
of interest in this study, no attempt was made to correct them to
obtain true line widths.

The 133Cs resonance of 0.015 M CsBm solution in pyridine move
to low field as the temperature is decreased (see Figures 19, ZOB and
21B). The two solutions of the Cs+-0211 cryptate show a linear
dependence of the chemical shift with temperature, with slight curva-
ture at low temperatures. The exchange between the complexed cesium
ion and the solvated cesium ion is still rapid, even at -25°0, which
is another indication of the weakness of the interaction between the
cesium ion and the cryptand 0211. At low temperatures, the rates
are reduced somewhat and the observed chemical shifts at lower field
imply an increase in the averaged electron density at the cesium
nucleus, i.e. the lifetime of the cesium complex is increased but is
but is still less than 10-7 seconds.

The stabilities of the Cs+-0221 and Cs+-0222 complexes in
pyridine are known to be very much greater than the corresponding
0211 complex. The effect of the cavity size of the ligand on the
exchange is shown in Figures 20A and 21A. For both of these complexes,
the temperature range studied includes the coalescence temperature.
In contrast to the much weaker Cs+-0211 cryptate where only one
signal is observed, these two complexes give two kinds of spectra:

a single resonance above room temperature and two signals at
temperatures below 0°C. The stronger complexation reaction with the

two ligands of larger cavity enable the exchange to be "frozen out",

62

i.e. the higher stabilities reduce the correlation times (the averaged
lifetimes of the environment) in the liquid medium.

In the region of rapid exchange (above Tc)' the single resonance
observed is a population averaged signal as a result of the fast two
site exchange. The chemical shift observed moves to low field as the
temperature decreases, which indicates an increase in the population
of the complexed site. The exothermic nature of the complex reaction
is further substantiated by mole ratio studies of the 0221 and 0222
cryptates at three temperatures. The data are presented in Table 12
in Appendix I and in Figures 22 and 23. The relative curvatures of
the plots are indicative of the strengths of interaction, and for both
complexes, the degree of curvature increases as the temperature
decreases. This trend implies that the complexation equilibrium is
shifted to the right with decreasing temperature,

M+ + L = Ml.+
with a subsequent increase in the concentration of the complexed
cesium and the equilibrium constant.

Extrapolation of the linear portions of the plot intersects at
a mole ratio of about 1 at all three temperatures.

The line widths observed for the uncomplexed cesium ion are
narrow (about 5 Hz) and are limited by the inhomogeneity of the magnetic
field. However, as shown in Figure 24, in the case of the 03+40221
and Cs+-0222 cryptates, line widths on the order of 500 Hz were
observed. This significant broadening is due to the exchange of the
cesium ion between the two radically different environments and is
especially pronounced as the temperature approaches To. The

asymptotic increase in line widths could be extrapolated to give an

63

 

 

 

 

 

 

*'50
d
6
+30—
; +10-
0.
a.
V i
.
GK) I
-10r
-30...
83° c
" 50L j‘j 71° c
- m e—l.‘ 47 55°C
I l l l J
0 1.0 2 O 3 O 4.0 5.0
. 4-
Male Ratio ([0221I/ (Cs 1)
Figure 2-2.

1
Concentration Dependence of the 3Cs Chemical Shifts of

05314-0221 CI‘YPtate in Pyridine at Three Temperatures.

 

 

 

 

 

5C)
\
0..
-5C)-
E
D.
D- I
y \
0
6CD
-100*
I
a
-150i-
I
' o
-200- 9 " . 483°C
I 571 C
o
I C) 5&5 C
J n 1!...
O 11) 21) 31)

Male Ratio ((C222]/le+l)

Figure 23. Concentration Dependence of the 133Cs Chemical Shifts of

CsBQQ-CZZZ Cryptate in Pyridine at Three Temperatures.

600 -

500 b

a.

O

O
l

300 -

Line Width( Hz )

200 '-

 

65

o 25
Temperature ( 0C )

[2221/[C +1:: 0.46

75

Figure 24. Temperature Dependence of the Uncorrected 133Cs NMR Line

Widths of CSB¢Z+- C221 and -0222 Cryptates in Pyridine.
[05+] = 0.015 p.

66

estimate of the coalescence temperature. In the case of the Cs+-0221
complex, coalescence appears to occur around room temperature while

the Cs+-0222 complex has a TC of about 40°C. This difference in
coalescence temperatures seems to indicate that the 0222 cryptate is

a stronger complex than is the 0221 cryptate since a higher temperature
is required for the signals to collapse in the rapid limit of exchange.

At the coalescence temperature, the lifetimes TM and TML are
on the same order as (wM - wML)-1’ where TM and TML are the lifetimes
of the free and complexed metal ions respectively, andwM and wML are
the corresponding frequencies in radians per second. Therefore, only
one broad signal is observed. At temperatures between 45°C and 2.500,
no signal was observed for either the 0221 or the 0222 cryptates. This
observation is not surprising if one considers the line broadening that
is observed even at 45°C. Extrapolation to lower temperatures would
result in very broad lines that are much below the detection limit
of the NMR spectrometer. Furthermore, the low cesium ion concentration
(0.015 M) would make even signal averaging unrealistically time
consuming. In Figures 20B and 213, this region around coalescence
is indicated by the broken lines.

Below Tc’ the exchange between the two sites is much slower than
107cycles per second, i.e.'tM,'rML > (an -‘”ML)-1 and two signals
emerge: one absorbs at the frequency characteristic of the uncomplexed
cesium ion in pyridine and the other at the frequency Characteristic
of the complexed cesium species, as indicated by the solid lines. The
"freezing out" of the exchange is explained by the relaxation model
deveIOped quantitatively by McConnell (95) for a nucleus possessing

a quadrupole moment: the assumption is made that the nucleus makes

67

sudden transitions from one site to another. The line widths of both
resonances grow progressively narrower as the extreme slow limit of
exchange is reached. At the lowest temperature studied, the line

widths are on the order of 20 Hz as the exchange is slowed down almost

to a standstill.

APPENDICES

APPENDIX I

CESIUM-133 CHEMICAL SHIFT DATA

Table 7. 133Cs Chemical Shifts of Cesium Salt Solutions

 

 

 

 

68

CsB¢u : DMF

Conc. M) Che(pp:)ift Conc. (M) Chettpiiift
0.0009 0.71 0.0704 2.01
0.0019 0.58 0.0803 2.10
0.0039 0.52 0.0897 2.32
0.0053 0.71 0.1002 2.50
0.0059 0.71 0.1254 2.97
0.0069 0.80 0.1499 3.50
0.0087 0.83 0.1755 3.87
0.0101 1.11 0.2004 4.27
0.0196 1.29 0.2256 4.93
0.0294 1.42 0.2493 5.48
0.0395 1.46 0.2752 5.83
0.0504 1.64 0.3001 6.57
0.0608 1.85 0.3368 7.41
0.3508 7.81

CsBQu : DMSO

0.0010 -68.40 0.0500 -67.97
0.0050 -68.40 0.0750 -67.84
0.0080 -68.03 0.1000 -67.54
0.0100 -68.34 0.2500 -66.05
0.0250 -68.16 0.5000 -62.57

69

 

 

 

 

 

Table 7. (continued)
CSBQQ : Acetone
Conc. (m) Che?pp:31ft Conc. (m) Chetgpiiift
0.0010 27.84 0.0124 37.08
0.0050 32.05 0.0150 38.57
0.0080 34.29 0.0177 39.68
0.0100 35.53 0.0205 40.68
05B?” : Pyridine
0.0010 - 0.98 0.0080 28.11
0.0020 7.11 0.0090 29.76
0.0030 12.67 0.0100 31.75
0.0040 16.89 0.0107 32.86
0.0050 20.24 0.0124 35.34
0.0060 23.25 0.0153 39.62
0.0070 25.70 0.0168 41.11
CsPi : Acetone
0.0010 25.98 0.0060 24.95
0.0020 25.42 0.0070 24.64
0.0030 25.38 0.0080 24.49
0.0040 25.27 0.0090 24.40
0.0050 24.98 0.0100 23.96

70

 

 

 

 

 

Table 7. (continued)
CsPi : ForNH2
Chem. Shift Chem. Shift
Cone. (M) (ppm) Cone. (M) (ppm)
0.0010 2.90 0.0070 2.68
0.0040 2.43 .0080 2.53
0.0050 2.63 .0090 2.63
0.0060 2.46 .0100 2.44
.0201 2.69
CsPi : DMF
0.0010 1.49 .0080 1.01
0.0030 1.25 .0090 1.08
0.0060 1.18 .0100 1.00
0.0070 1.13 .0151 1.03
.0363 0.96
CsPi : DMSO
0.0010 - 66.85 0.0050 - 67.94
0.0020 - 67.59 0.0060 - 68.56
0.0030 - 67.75 0.0070 - 68.15
0.0040 - 67.94 0.0080 — 68.16

0.0090 - 67.88

Table 7.

0

0

0

00000

Conc . (M)
.0010
.0020
.0030
.0040

.0050

.0010
.0020
.0030
.0040

.0050

.001
.005
.008
.010
.015

.020

(continued)

CsClOu

Chem. Shift

(ppm)
60.47
60.44
60.38
60.31

60.22

-34.81
-35-96
-36.66
-37.60
-38.36

-0.03
-0.16
-0.16
-0.22

-O.28

-0-35

CsI

CsSCN :

71

: MeNO

: ACN

H20

0

O

Conc . (fl)
.0060
.0070
.0080
.0090

.0100

.0060
.0070
.0080
.0090

.0100

.035
.040

.050
.065
.088

.100

Chem. Shift
(ppm)

59.97
60.25
59.94
59.82
59.82

'39.15
-39.92
-40.46
-4l.39
-4l.63

-0.53
-0.59
-0.65
-0.72
-1.09

-l.27

72

Table 8. Cesium-133 Chemical Shifts of Cesium-0211 Cryptates in
Various Solvents ([Cs+1 = 0.01 M)

CsB¢4 : Acetonitrile

 

 

1411* 112ml 18* 2.122111
0.00 -24.63 1.87 —28.48
0.45 -25.93 3.00 -30.65
1.00 -26.49 3.92 -32.26
1.50 -28.23 4.89 -33.32

6.14 -34.38
CsB¢4 : Acetone

0.00 35.56 3.00 27.78
0.24 34.78 3.22 28.58
0.50 33.76 3.54 26.84
0.75 33.39 4.00 26.41
0.99 32.70 5.00 24.73
1.26 31.99 6.00 22.03
1.50 31.50 7.00 20.61
1.74 29.98 8.00 19.96
2.01 29.82 9.00 18.47
2.25 29.54 10.00 17.54
2.46 28.92 15.00 11.64
2.75 27.90 20.18 6.00

Table 8.

In

1.56

0.00

1-53

1-53

(continued)

36.02
34.22
33-05
30.75

-67 o 74
-67.84
-68.22

0.81
0.56
0.31

0.13

32.92
29.76
26.59
25.29

73'

CsBQu : PC

 

CSBQQ : DMSO

 

CSB¢I+ 3 DMF

 

CsB¢g : Pyridine

 

“8

2.18
2.98

3.95
5.00

3.09
4.02

6.59

2.05
3-05
4.02

5-13

1.91
3-09

3.85
4.92

29.94
27.15
25.23
22.68

-68.40
-68.15
'67 o 78

0.06
-0.19

-0.56
—0.68

22.50
19.65
16.92
13.07

Table 8.

In

0.00
0.52
1.11
1.70
2.15

2.63

0.00
1.01

2.01

0.00
1.04

2.08

0.00
1.04

2.11

(continued)

54.83
48.10
42.76
37.61
34.17
30.79

17.26
15.68
13.63

-3’+ - 43
-36 o 39
'37-75

-O.3l
-0.50

—0.87

CsSCN :

74

MeNO

 

CsSCN

CsSCN

CsSCN :

: Acetone

: ACN

DMF

I8

3-09
3.47
4.09
4.68
5-03
5.62

3.02
4.06
6.03

3.12
3.88
5.06

3.19
4.09

5-13

28.12
25.14
22.32
19.68
17.68
15.78

11.99
9.94
6.81

-38.80

'39.76
-40.85

-1.18
-1.62

-l.80

75

Table 8. (continued)

 

 

 

CsSCN : PC
113 2.12211) 1133 1122111
0.00 34.45 3.26 26.07
1.14 31.00 4.47 21.91
2.36 25.94 5.31 19-77

CsSCN : DMSO
0.00 -68.09 3.22 -68.09
1.11 -68.06 3.81 -68.09
2.08 -68.09 5.06 -67.91

CsI : ACN
0.00 -41.88 2.95 -45.32
1.01 -43.05 4.06 -46.31
1.98 -44.45 4.96 47.49
CsI : DMF
0.00 -l.49 3.15 -l.86
1.00 -l.68 4.30 -2.83
1.80 -l.68 4.96 -2.86
051 : DMSO

0.00 -68.87 3.09 -68.95
1.01 -69.03 4.06 —68.87
2.01 -68.95 5.03 -69.03

 

 

Table 8.

0.00

0.00
0.97

2.11

2.95

(continued)

37.89
29.51
26.60

0.96
0.65

0.22

59.51
47.44
39.17
32.47

43.73
43.05
42.24
41.81

*MR = [02111/[Cs+1

76

PC

CsI :

CsPi

: DMF

 

CSC104 3

C801

MeNO

: Methanol

IE

2.98
3-95
5.55

2.95
3.92
5.06

3.95
5.41
8.05
10.26

12.10

3.92
4.99
5.79
6.45
7.39

24.30
22.04

18.72

0.06
-0.34
-0.93

27.22
20.03
11.24
5.14
1.88

40.85
40.33
39.64
39.80
38.56

77

Table 9. Cesium-133 Chemical Shifts of CsB¢4 and 0221 Cryptates

in Various Solvents

Acetonitrile ([Cs+] = 0.015 M)

 

 

188‘ 0ppm (Avl/2 in Hz) .83 oppm (1101/2 in Hz)
0.00 -21.16 ( 4) 1.04 -57.84 ( 8)
0.24 -24.34 : 2 (100)** 1.14 -59.85 ( 4)
0.50 -41.94.:_2 (104)** 1.34 -59.93 ( 4)
0.78 -51.40 ( 66)** 1.62 -59.93 ( 4)

2.09 -59.78 ( 5)

Acetone (£0s+1 = 0.015 M)

 

0.00 38.34 ( 5) 0.98 -40.22 ( 7)
0.28 13.91 :,3 (23o)** 1.12 —44.33 ( 2)
0.56 - 5.86 : 3 (200)** 1.22 -44.57 ( 3)
0.72 —17.88 ( 70) 1.64 -44.72 ( 4)

2.08 ~44u56 ( 4 )

DMF ([Cs+] = 0.015 M)

0.00 1.04 ( 3) 1.03 -43.86 ( 5)
0.32 -14.24 ( 12) 1.13 -46.41 ( 5)
0.61 -28.58 ( 10)** 1.34 -48.52 ( 4)
0.81 -37.74 ( 7)** 1.73 -5o.38 ( 3)
0.89 -40.37 ( 5) 2.03 -50.84 ( 4)

2.58 -51.31 ( 3)

78

Table 9. (continued)

P0 ([08+] = 0.012 M)

 

 

 

 

 

ME oppm (A0112 in Hz) ER- 6 ppm (110112 in Hz)
0.00 36.38 ( 3) 1.00 -40.77 (16)
0.25 26.75 : 5 (390)** 1.18 -44.03 ( 5)
0.73 -21.85 : 2.5 (237)** 1.35 -44.19 ( 6)
0.90 -40.24 ( 16) 2.11 -44.19 ( 5)

DMSO ([Cs+1 = 0-015.M)
0.00 -67.85 ( 4) 1.77 -71-57 ( 4)
0.30 -68.77 ( 4) 2.05 -71.69 ( 4)
0.70 -69.95 ( 6) 2.23 -71.67 ( 4)
1.10 -70.89 ( 6) 2.73 -71.81 ( 4)
1.24 -71.25 ( 4) 3.01 -71.94 ( 3)
1.51 -71.50 ( 3) 3.65 -71.81 ( 4)
Pyridine (19:1: 0.010 M)

0.00 31.74 ( 8) 1.23 -57.59 (11)**
0.54 --- --- 1.65 -57.90 ( 3)
0.84 -51.07 ( 61)** 2.68 -57.90 ( 2)

4.00 -57.90 ( 4)

*MR = [02211/[Cs+1

**Free induction decay signal was multiplied by large exponential
factor to optimize signal-to-noise ratio.

79

Table 10. 1330s Chemical Shifts of 0th4 and 0222 Cryptate in
Pyridine ([Cs+ = 0-01.1)

 

111* 21mm “112 (HZ)
0 0 30.81 3
0.25 --- -_
0 .50 --- --
0.75 --- --
l 00 -217.33 15
1 25 -223.85 14
l 50 -224.47 7
l . 75 —224.15 12
2.0 -224.15 9

*MR = [02221/[Cs+1

80

 

 

 

 

 

Table 11. 133Ce Chemical Shifts of CsB¢4 and Cryptands in Pyridine
at Different Temperatures ([Cs+] = 0-015.1.
m = [cryptand]/[Cs+])
CSB¢4-le Cryptate
MR = 0.00 MB = 2.49 MB = 6.63
18121. oppm (13y2 Hz) oppm (AulZZ Hz) oppm (001/2 Hz)
84.6 53.53 ( 3) 45.15 (24) 33.67 (27)
71.7 50.42 ( 4) 40.50 (17) 27.16 (24)
58.0 47.63 ( 2) 36.15 (15) 20.96 (22)
43.4 44.84 ( 2) 30.88 (15) 13.82 (20)
28.2 41.12 ( 2) 24.99 (15) 6.07 (17)
15.7 38.64 ( 2) 19.71 (17) 0.76 (17)
2.5 35.22 ( 2) 13.51 (17) - 8.20 (20)
-12.0 31.81 ( 2) 6.69 (17) -16.89 (27)
-25.8 28.71 ( 4) - 1.07 (24) -25.26 (29)
CsB¢u-221 Cryptate
MR = 0.64 MR = 3.92

84.6 -13.78 (32) -47.90 (12)
71.7 -l6.27 ( 54) -50.08 (12)
58.0 -19.06 :,2 (173)* -51.94 (12)
43.4 —31.47 : 2 (271)* -53.49 (10)
2.5 -59.69 (46)* 31.19 (81)* -58.76 (22)
—12.0 -61.86 (20) 26.85 (29) -60.31 ( 5)
-25.8 -63.41 (15) 22.82 (17) -61.55 (12)

81

Table 11. (continued)

CSB¢4-222 Cryptate

 

 

 

MR = 0.46 MB = 3.67
.1212; 6ppm (AVl/2 HZ) 6PPm-(Avl/2 Hz)
84.6 -70.24 ( 34) -200.20 (12)
71.7 -78.61 ( 59) -207.03 (15)
58.0 -82.65 : l (134) -212.61 (15)
43.4 -98.77 i 5 (515)* -217.57 (17)
2.5 -232.77 (400)* 31-50 (183)* -229.05 (15)
-12.0 -231.53 ( 63) 28.71 ( 46) -231.22 (17)
-25.8 -233.08 ( 29) 25.30 ( 22) -232.77 (20)

*Free induction decay signal was multiplied by large exponential
factor to optimize signal-to-noise ratio.

82

Table 12. Cesium-133 Chemical Shifts of Cesium-0221 and Cesium-0222
Cryptates in Pyridine at Three Temperatures
([Cs+1 = 0-01.M)

CsB¢4-C221 in Pyridine

 

 

0.00 47.52 43.52 39.16
0.54 2.23 - 3.01 _+_ 3 - 1.33 : 5
0.85 -35.30 -39.92 -43.65
1.23 -44.29 -48.30 -51.71
1.65 -48.33 -50.78 -52.95
2.68 -48.64 -50.78 -53.26
4.00 -48.95 -51.09 -53.26
4.36 ~48.95 -5l.09 -53.26
Csspu-szz in Pyridine

0.00 43.49 42.28 38.54
0.25 - 16.68 - 21.93 - 32.80 _+_ 3
0.45 - 70.10 - 76.83 : 2 - 85.22 : 2
0.72 -117.50 -128.01 -136.71
0.96 -166.82 -182.60 -197.19
1.27 -l83.57 -197.49 -208.98
1.46 -192.26 -203.39 -212.08
1.81 -196.29 -205.25 -213.01
1.97 -196.91 -205.87 -2l3.32
3.05 -199.70 -206.80 -213.01

*MR = [Ligand]/[Cs+]

APPENDIX II

DETERMINATION OF COMPLEX FORMATION CONSTANT WITH

ION PAIR FORMATION BY THE NMR METHOD

DETERMINATION OF COMPLEX FORMATION CONSTANT WITH ION PAIR FORMATION

BY THE NMR METHOD

Definition of symbols,
[M] = cation
[A] = anion
[L] = ligand
[MA] = ion pair

[ML] = metal complex

CM = analytical concentration of metal ion

CL = analytical concentration of ligand
KiP = ion pair equilibrium constant

Kf = formation constant of complex

Ion pair equilibrium,

00 +111 31131110
Kip 130%
Complexation equilibrigm,
[M] +1113?» [ma
Kf = M L
CL=IMJ +[L]
CM =tm1 +00 +08]
CM = [NM] +-[AJ
From (15),
[MA]

Ki}; MJE A]

From (16),

[ML] KiMHLJ

83

(15)

(16)
(17)
(18)
(19)

(20)

(21)

Substitute in (13),

cL = 16000.] + [L] = [1.10600 + 1)

CL

Kf[M] + 1

 

.'. [L] =

Substitute in (18),

0M = Kf[M1[L1 + [M] + KiPIMJIA]

Substitute in (19),

CM = [A] + KiP[M1[A1 = [A1(1 + KiP[M1)

C
. M
° W = 1 + Kipr]

 

Substitute (22) and (24) in (23),

f
C = K [MJCL + [M] + KiPEMJCM
M KfIM] + 1 1 + KiPEMJ

 

 

Multiply (25) across by (l + Kf[M])(l + KiP[M]),
0M(1 + Kf[M])(l + Kip[M]) = Kf0L[M](1 + KiP[M])

+ [M](1 + Kf[M1)(1 + KiP[M1) + KiPCMIM](1 + Kf[M1)

(22)

(23)

(24)

(25)

(26)

85

C + KiPCM[M] + KfCM[M] + KfKiPCM[M]2

M
= KfCL[M] + KfKiPCL[M]2 + [M] + KiP[M]2

+ Kf[M]2 + KfKip[M]3 + KiPCM[M] + KfKiPCMEMJZ

Collecting terms,

f 3 f 2
K KiP[M] + (KfKiPCL + Kip +fiK )[M]

 

 

 

+ (KfCL + 1 - KfCM)[M] - CM = 0
[M33 + (KfKiPCL + Kip + Kf) [M32
foip
+ (KfCL + l - KfCM) M] _ CM = 0
KfK. KfH.
1p 1p

Solution to cubic equation,

73 + Pyz + qy + r = 0

 

 

 

f
p = (K KiPCL + KiP + Kf)
f
K Kip
f
q = (K CL + 1 - KfCM)
KfK.
1p
I‘ = -CM
KfK.
1P

(27)

(28)

(29)

86

x3+ax+b=0

a = <3. - 12)/3

= (2:9 - 9pq + 27r)/27

 

 

3 2 3
b b a

A=I/-2+\Izr+§7
3

2 3

.. _b- b a_

B’\/'2 17+ 7

3

.84— >
+ 27 0 +1 real root

43°39

Case I

N
K...)

II £L-+§'-:7-=0+3 real roots

w

III < 0 +3 real roots

tIC’Eu

+
NIP!
\}

CaseI,x=A+B

Case II and III, use trigonometric form

 

3
0059 = - é—D fJ(-§_7
= 2"- .3. .1
x 3 Cos 3
‘l- P. .2 + 120°
2 3 Cos (3 )
2"- Cos (39 + 240°)

balm

87

Now, solve for [M] in (29).

Then substitute in following equations,

 

Kch[M]

[ML] = —f-———— (30)
K [M] + 1
K. CM[M]

[MA] = 11 (31)
KiP[M] + 1

6 =

obs XMGM + "141}st + XMAGMA (32)

._ D11 Dal m1
%m" 05M+c 5m+ c %A (B)
L M M
Use final form of oobs in EQN subroutine.
Coding symbols in EQN,

a = AA p = PP

b = BB q = QQ

A = AAA r = RR

B = BBB ¢ = FE

y = R Cos ¢ = CFE

CONST(1) = Kip

CONST(2) = CM

CONST(3) = ip

CONST(4) = 6M

U(1) = GML xx(1) = CL

U(Z) = K f xx(2) =

obs

88

SHHPOHT INl' EH”

COMMON KOUHT.IIAPE.ITAOE. IwT LAD.XINCR.NOPT.NOVAD.NOHNK. x.H.ITwA x.
IHI QTESTO['AVQQFQIHoIARorP‘H ITYPQXXoRXTYponXIIQF-Opo POOP-”9997] 0T0 E
PvaVALOXQTQTorITQI OMOJJJOYODYOVFCTQNCqTQCONST

DIMFNSIHN X(hol00)o H(?0)9 WTX(09100)0 XX(4). an(l00) F0(100)0 F
lHIIOO). PIPOoPIIo VFCT(?Oo?l)o ZL(lOO)o TO(?0)v FIGVAL( (PO). XST(IO
?0)9 Y(l0). DY(IU)o CONQT‘IA)

- no TO {791909991‘0 [TYP
I CONrINur

ITQPE=50

JIApE=61

HRIIF (ITADE 6

6 FORMAT(9 FORMATION CONQTAN] WITH ION PAIPINGOI/II/I

NOHNK=P

NOVAP=?

REIHRN

> CUNTINUF

OFFINIIIOMS OF IHE TFPMS
co “1 l) = ION ”Alp FORMATION COMfiTANT
CON‘T(2) = TOTAL CONC. OF MFTAI
CONQTFH = CHFM. c.HIFT 0F ION PAIR
CON9T(OI = CHFM QHIFT 0F MFTAL
“(1) = CHEM. qnfrr or cnupkaxen METAL
HI?) = FORMATION CONSIANT F COMPLEX
Xi”) = TUTAI CONC. 0F IIGAND
KIM?) = HHSERVH) CHFM. cIHIFT

CHH93‘o/1o

ITING THE COFFFICIENTS OF THF TERMs

”"=XX(|I°(l./U(?)Io(lo/CON9T( (I

00‘l|./(HI?I“C0MST(II))9(XX(l)-CON§T(?II/CON9T(I)

I?|’=-(‘0M‘3T(?)/(H(2)°CHN§T(I)l

AA‘(‘o”OU- 99““?I/3.

HH=¢2.”(Pv903)-°.°DD°OOo27. «ROI/27.
CHECKT DOINT rnu wHICH FORM OF IHE SOLUTION IS TO RE USFD

ZEST =én?:?2)ja.+§ AAooJI/27.
IH “I; HpIA 09M I9 uSEO MERE

A=I-HH/?. oSORIII
AAA=IAHSIIAII°ucqu
TH=(-RH/?.-§ORIITE§II)
nnR=IAH§(TO)I*°CHHR
(HECKING THE SIGN OF THE CHHEROOT TERMS
1§A(IA)I7 I7~In
IF (1H)19.I9.ZH
HHH: -Hnn
RH=AAAoHHn

60 IO 30
rue LntgnNOHFTRIC anM 0F IHE SOLUTION IS USED HEPF
F C: ‘
n n: 2. 9ACnsI—I.)
ANGLE=9AO/1.
CFE=I-nu/2. I/(SORIIAHS((- AAoo1)/27. III
CHECK FOR VAIIOITY OF COqINE IFQ
IFIIc.L1.-I.I OR.(CIE. fit .I. I) OO 10 20
FI- -RAD-ACO§(FFE)
Ia RR;?.'I§ODI(AH9(-AA/I. .III‘COGIFE/3.¢ANGLE0FLAGI
R- u-(Pp/1.I
CHECK FOR VALInITv 0F Tut CALCULATED METAL CONC
IF ("Il1013910
WRITE(ITAPF.??)
FORMAT(¢ COSINF OF FFE OUTSIDE OF 01 AND -IOI

SID
GO HACK AND FIND ANOIHER ROOT
FI An: FLAGoI.
IF§3.-FLAG)l§o}§ola

‘5 HR TE(IIADF 9 _
a; goanII 0 ALL THREE pants FLHNKLD*)
p
gunsTIIUIE CAI_CHLATED METAL CONC. IN ORIGINAL FOUATION
0551A=Ip¢rnnq1(ar3(”cpsonfixxtlrontlsIIII..U(2)¢pIo(cONST(I)690CONS
IT! IOCONSIIJII/(I.6CON§T(II¢DII/CONSII?)
RESIO=OELTA-XX(?I
1 CONTINuF
a CONTINHF
s CONTINUE
QETHPN

END

'fi'fi'fi
00:3
27.

0

000000002300
ZZZZZZZZZZZZ

’
_

—F'II‘—II‘—'~—'IIUWH
UUUNNNNNN‘UUN
OOOOO'D'JJLDDI'D 3
UNOOWN9m9U'V"

———

rand—-
UUU
VN‘
~00

UUU

33'V4‘

APPENDIX III

SUGGESTIONS FOR FUTURE WORK

SUGGESTIONS FOR FUTURE WORK

The results of this study have shown that 133Cs NMR can be used
advantageously as a powerful technique to study interactions in
solution. At the same time, this investigation emphasizes the comple-
xities of solvent-solute and solute-solute interactions. The following
suggestions highlights the key areas for further work.

The CsBQu ion pair appears to be highly associated in pyridine,
ACN, PC and acetone. The structural and chemical orientation of the
anion to the cesium cation remains unknown. One would expect that
perturbations at the phenyl rings would be reflected in the decoupled
13C chemical shifts. Functional group spectroscopy could also prove
to be illuminating.

Weak complexes in solution are difficult to monitor as shown by
the Cs+—C211 cryptates. Keeping in mind that anion, solvent and ligand
are all keen competitors for the cation, one can attempt to differen-
tiate mathematically the three interactions.

aobsd = XMGM + "mfsm. + XMAGMA.

The three terms in the above expression are in effect, the cation-
solvent, cation-ligand and cation-anion interactions. Assuming an
ideal situation whereby one can determine the chemical shift values of
the solvated, complexed and ion paired cesium ion, it is possible to
onceive of a plot such as in Figure 25. The cesium ion concentration
is kept constant and curves A and C are mole ratio plots where "anion"
and ligand respectively, are added to the solution. The former can be

approximated by using a large, inert counterion such as the tetra-

89

9O

alkylammonium cation. Curve B is the sum of curves A and C. Using

raw data from an experiment, one can breakdown the observed chemical
shift into into the components in Figure 25 and obtain some insight

into the phenomena occuring in solution. If the anion is involved in
the complex, the contribution from curve A, the cation-anion interaction,
would be fairly constant. However, should the complexed state consist
of only the solvated cesium ion and ligand, anions would be "released"
into the bulk medium. Finally, using data simulation, the process

can be reversed to obtain a better understanding of the relationship

between the various interactions.

\

Chem. Shift
on

 

 

Mole Ratio

Figure 25. Sample Plot.

91

The temperature study of the cesium ion with cryptand C211
produced some very interesting data. In Figure 26, the uncorrected
line widths are plotted against temperature for the two solutions of
the 0211 cryptate. There appears to be a minimum in both of these
curves. In the event of a 1:1 complex where only one mechanism is
predominant, the line width should decrease as the temperature
increases in the rapid limit of exchange. The unexpected and inexpli-
cable increase in line width beyond 25°C seems to indicate that more
than one relaxation mechanism is present. It also introduces the
possibility of a concentration dependent relaxation phenomenon and
second order kinetics. Furthermore, Lehn has suggested the possibility
of 2:1 complexes (53) of cesium cryptates. However, in this present
study, we have not observed evidence at ambient probe temperature, to
support the theory of a 2:1 complex. It would be interesting and
informative to obtain mole ratio plots of the Cs+-C211 complex at
various temperatures and extend the high temperature.limit to see if
the line widths do reach a limiting value.

The temperature study of the cryptates can be readily extended
to obtain kinetic information. Bloch's equations can be applied to
the exchange between the complexed and free cesium ion and the rate of
release of cesium ion from the complex can be determined together with

the activation energy.

92

30-

Line Width (Hz)
N
‘3

 

Io-

 

l I H I I J

-25 0 25 50 75
Temp (°C)

Figure 26. Temperature Dependence of the Uncorrected 133Cs NMR Line

Widths of 03B ‘94- C211 Cryptates in Pyridine.
MR = [0211] /[cS+].

LITERATURE CITED

10.

11.

12.

13.
14.

150
16.

17.

18.

19.
20.

LITERATURE CITED

Y. M. Cahen, P. R. Handy, E. T. Roach and A. I. Popov, J. Phy. Chem.,
22. 80 (1975).

E. G. Bloor and R. G. Kidd, Can. J. Chem., 4_6_, 3425 (1968).

M. S. Greenberg, R. L. Bodner andA. I. Popov, J. Phy. Chem. , 12,
2449 (1973)

G. E. Maciel, J. K. Hancock, L. F. Lafferty, P. A. Mueller and
w. K. Musker, Inorg. Chem., 5, 554 (1966).

 

R. H. Erlich and A. I. Popov, J. Am. Chem. Soc., 9;, 5620 (1971).

R. Bodner, M. S. Greenberg and A. I. Popov, Spectrosc, Lett.
5. 489 (1972)

Y. M. Cahen, J. L. Dye and A. I. Popov, J. Phy. Chem., 79,.
1289 (1975).

T. L. James and J. H. Noggle, J. Am. Chem. 800., g, 3424 (1969).

P. G. Gertenbach and A. I. Popov, J. Am. Chem. Soc. , 22. #738
(1975)

J. P. Kintzinger and J. M. Lehn, J. Am. Chem. Soc. , 2_6_, 3313
(1974)

J. L. Dechter and J. I. Zink, J. Am. Chem.Soc., @, 845 (1976).
E. G. Bloor and R. G. Kidd, Can. J. Chem., fl, 3926 (1972).
M. s. Greenberg and A. I. Popov, Spectrochim. Acta, 1A, 697 (1975).

A. I. Mishustin and Y. M. Kessler, J. Solution Chem., 1+, 779 (1975).

w. Sahm and A. Schwenke, z. Naturforsch., A29, 1754 (1974).
c. Deverell and R. E. Richards, Mol. Phys... 19, 551 (1966).

.2. 12. )Crawford and R. P. H. Gasser, Trans. Faraday Soc. , 63, 2758
19 7

H. s. Gutowsky and B. R. McCarvey, Phys. Review, 9_1_, 1423 (1953).

N. Bloembergen and P. P. Sorokin, Phys. Review, 110, 865 (1958).

R. Baron, J. Chem. Phys” 3§, 173 (1963).

93

21.

22.

23.

24.
25.

26.

27.

28.
290

30.
31 .
32.
33-

34.
35-
36.
37.
38.
39.

40.

41.

42.

43.

94

A. Carri ton, F. Dravnicks and M. C. R. Symons, Mol. Phys., 2,
174 (1968?.

0. Lutz, z. NaturforsCh., 9.22, 286 (1967).

J. Halliday, H. D. W. Hill and R. E. Richards, Chem. Commun.,
219 (1969).

A. Loewenstein and M. Shporer, Chem. Commun., 214 (1968).

J. D. Hallidat, R. E. Richards and R. R. Sharp, Proc. Roy. Soc.
London, A313, 45 (1969).

C. Hall, H. E. Richards and R. R. Sharp, Proc. Roy. Soc. London,
1332. 297 (1974).

H. J. DeWitte, R. C. Schoening and A. I. Popov, Inor& Nucl. Chem.
Lett., 1;, 251 (1976).

U. Mayer and V. Gutmann, Struct. Bonding (Berlin), 12, 113 (1972).

U. Mayer, V. Gutmann and W. Gerger, Monatshefte its: Chemie, 106,
1235 (1975).

v. Gutmann and E. Wychera, Inorg Nucl. Chem. Lett., 2, 257 (1966).
T. R. Griffiths and M. C. R. Symons, Mol. Phys., 3, 90 (1960).
J. G. Evans and G. 11.—s. Lo, J. Phy. Chem., _6_2, 3223 (1965).

1({. Balasubrahmanyam and G. J. Janz, J. Am. Chem. Soc., 22, 4189
1970 .

R. C. Connick and R. E. Poulson, J. Phy. Chem., 62, 1002 (1958).
A. Carrington and T. Hines, J. Chem. Phys” _2_8_, 727 (1958).

. S. Greenberg, Ph.D. Thesis, Michigan State University, 1974.
. H. Maxey and A. I. Popov, J. Am. Chem. Soc., fl, 20 (1969).

. L. Kay, J. Am. Chem. Soc., §_2_, 2099 (1960).

:10wa

. L. Kay, B. J. Hales and G. P. Cunningham, J. Phy. Chem., 11,
39 5 (1967).

5. Mine and L. Werblem, Electrochimica Acta, 1, 257 (1962).
c. Atlani and J-C. Justice, J. Solution Chem., _4, 955 (1975).

H. A. Berman and T. R. Stengle, J. Phy. Chem., 19, 1001 (1975).

T. L. Story, Jr. and A. J. Hebert, J. Chem. Phys, _6_4_, 855 (1976).

45.

47.

48.
49.
50.

51.

52.

53.

55-
56.
57.

59.
60.
61 .
62.

63.

65.

66.

95

A. Carri ton, F. Dravnicks and M. C. R. Symons, Mol. Phys., 3,
174 (19635.

R. E. Richards and B. A. Yorke, Mol. Phys., 6, 289 (1963).
C. H. Langford and T. R. Stengle, J. Am. Chem. Soc., 2_1_, 4014 (1969).

T. R. Stengle, Y-C. E. Pan and C. H. Langford, J. Am. Chem. Soc.,
.21. 9037 (1972).

C. Deverell and R. E. Richards, M01. Phys., 16, 421 (1969).
D. C. Tosteson, Fed. Proc., _2_Z, 1269 (1968).

R. M. Izatt, R. H. Rytting, D. P. Nelson, B. L. Haymore and J. J.
Christensen, Science, 164, 443 (1969).

B. Dietrich, J. M. Lehn and J. P. Sauvage, Tetrahedron Lett., 2885
and 2889 (1969).

B. Dietrich, J. M. Lehn, J. P. Sauvage and J. Blanzat, Tetrahedron,
22. 1629 (1973)-

J. M. Lehn, Struct. Bonding. fl, 1 (1973).

J. M. Ceraso and J. L. Dye, J. Org. Chem.,‘38, 1773 (1973).

D. Moras, B. Metz and R. Weiss, Acta Crystallogr., 329, 388 (1973).
.1211. 32 . 383 (1973).

D. Moras and R. Weiss, Acta Crystallogr., B29, 396 (1973).

112111.. 222. 400 (1973).

J. M. Lehn and J. P. Sauvage, J. Am. Chem. Soc., 97, 6700 (1975).
B. Dietrich, J. M. Lehn and J. P. Sauvage, Chem. Comniun., 15 (1973).
Y. M. Cahen, Ph.D. Thesis, Michigan State University, 1975.

J. M. Ceraso and J. L. Dye, J. PhL Chem., 61, 1585 (1974).

F. J. Tehan, B. L. Barnett and J. L. Dye, J. Am. Chem. Soc., 26,
7203 (1974).

J. L. Dye, C. W. Andrews and S. E. Mathews, J. Phy. Chem., 12,
3065 (1975).

J. L. Dye, C. W. Andrews and J. M. Ceraso, J. Phys. Chem., 29,
3076 (1975).

J. S. Shih, private communication.

96

67. C. J. Pedersen, J. Am. Chem. Soc., 89, 7017 (1967).
68. Ibid, 3, 5226 (1970).

69. E. Mei, J. L. Dye and A. I. Popov, J. Am. Chem. Soc., 28, 1619
(1976).

70. J. M. Lehn, J. P. Sauvage and B. Dietrich, J. Am. Chem. Soc., 2,
2916 (1970).

71. E. Shchori, J. Jagw-Grodzinski, Z. Luz and M. Shporer, J. Am.
Chem. Soc., 23, 7133 (1971).

72. E. Shchori, J. Jagur-Grodzinski and M. Shporer, J. Am. Chem. Soc.,
25. 3842 (1973).

73. J. P. Kintzinger and J. M. Lehn, J. Am. Chem. Soc., 96, 3313 (1974).
74. J. M. Ceraso and J. L. Dye, J. Am. Chem. Soc., 95, 4432 (1973).

75. Y. M. Cahen, J. L. Dye and A. I. Popov, J. Phy. Chem., 12, 1292
(1975).

76. V. M. Loyola, R. G. Wilkins and R. Pizer, J. Am. Chem. Soc., 22,
7382 (1975).

77. E. Shchori, N. Nae and J. Jagur-Grodzinski, J. C. S. Dalton, _2_2,
2381 (1975).

78. s. Villermaux and J—J. Delpuech, Chem. Commun., 478 (1975).

79. S. Boileau, P. Hemery and J-C. Justice, J. Solution Chem., 4,
873 (1975).

80. B. Dietrich, J. M. Lehn and J. Simon, Angew. Chem., _1_3, 406 (1974).
81. J. M. Lehn, J. Simon and J. Nagner,'§ngew. Chem.,l§5, 622 (1973).

82. J. Cheney, J. M. Lehn, J. P. Sauvage and M. E. Stubbs, Chem. Commun.,
1100 (1972).

83. S. M. Elinkova, Y. Y. Maksimov and E. Y. Orlova, Izv. Eyssh. Ucheb.
Zaved., Khim. Khim. Teckhnol., 14, 176 (1971).

84. D. D. Traficante, J. A. Simms and M. Mulvay, J. Mag. Res., 15,
484 (1974).

85. D. A. Wright and M. T. Rogers, Rev. Sci. Instr., fl, 1189 (1973).
86. D. H. Live and s. I. Chan, Anal. Chem., 4;, 791 (1970).

87. G. J. Templeman and A. L. Van Geet, J. Am. Chem. Soc., fl, 5578
(1972).

97

88. J. L. Dye and v. A. Nicely, J. Chem. Bd., 533, 443 (1971).
89. A. Saika and C. P. Slichter, J. Chem. Phys., 22, 26 (1954).

90. J. D. Memory. Quantum Theory of Magnetic Resonance Parameters,
New York: McGrawbHill Book Co., 1968, pp. 79-86.

91. R. F. Bacher, Atomic Energy States, New York: Greenwood Press,
1968.

92. A. D. Buckingham, T. Schaefer and W. G. Schneider, J. Chem. Phys.,
32, 1227 (1960).

93. W. J. DeWitte, Ph.D. Thesis, Michigan State University, 1975.
94. J. M. Lehn and J. P. Sauvage, Chem. Commun., 440 (1971).

95. H. M. McConnell, J. Chem. Phys., 2_8, 430 (1958).

96. E. Mei, private communication.

97. Y. M. Cahen, J. L. Dye and A. I. Popov, Inorg. Nucl. Chem. Lett.,
_1_9. 899 (1974).

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