SPECTROPHOTOMETREC AND
SPECTROFLUOROMETRIC STUDIES OF
CQWLEXING CF SQME LAN'E'HANEDE EONS
WITH 1, fO-PHENANTHROLINE. ETS
LMETHYL AND E-NITRO‘ DERWATIVES,
SULFQSALICYUC ACID, SALICYLIC ACED,

AND SALE-CYLALDEHYDE

Thesis {or ”)9 Degree of M. S.
MICHIGAN STATE UNEVERSITY

Bruce D. Powers

1963

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ABSTRACT

SPECTROPHOTOMETRIC AND SPECTROFLUOROMETRIC STUDIES
OF COMPLEXING OF SOME LANTHANIDE IONS WITH
1, lO-PHENANTHROLINE, ITS 5-METHYL AND 5-NITRO
DERIVATIVES, SULFOSALICYLIC ACID, SALICYLIC ACID,
AND SALICYLALDEHYDE

by Bruce D. Powers

Aqueous solutions varying in concentration from 1 x 10"6 M to
1 x 10'4 M of 1, lO-phenanthroline, 5-nitro-l, lO-phenanthroline,
5-methyl-l, lO-phenanthroline, sulfosalicylic acid, salicylic acid, or
salic ylaldehyde were tested individually as complexing reagents for the
following lanthanide ions: La (III), Gd (III), Ho (III), Er (III), Yb (III),
Lu (III), and Eu (III), Eu (III) being tested with l, lO-phenanthroline
only. The effect of pH on the absorbance and fluorescence of each
reagent solution was examined. The pH of each reagent-lanthanide solu-
tion was adjusted to a level where a pH change had the least effect on the
absorbance and fluorescence of the reagent solution, still being low
enough to keep lanthanide hydroxide formation negligible. Exciting wave-
lengths tested in fluorescence studies were 265, 297, and 313 mu. lines
from a mercury lamp. There was neither any significant increase nor
decrease in absorbance or fluorescence intensities nor any change in
the shape of either the absorbance or fluorescence spectra due to
lanthanide ion addition to the above reagent solutions. Thus these spectro-
scopic studies provide no evidence that complexation between the tested

lanthanide ions and the organic reagent occurs in aqueous solutions.

Bruc e D. Power 3

Factors which lead to this behavior are: comparatively large
size of the lanthanide ions and their unavailability of orbitals for
hybrid, bonding, the rigid phenanthroline ring system, high dielectric
constant of the solvent, and the high amount of stable hydrolysis

occurring in dilute aqueous lanthanide ion solutions.

SPECTROPHOTOMETRIC AND SPECTROFLUOROMETRIC STUDIES
OF COMPLEXING OF SOME LANTHANIDE IONS WITH
1, lO-PHENANTHROLINE, ITS 5-METHYL AND 5-NITRO
DERIVATIVES, SULFOSALICYLIC ACID, SALICYLIC ACID,
AND SALICYLALDEHYDE

By

Bruce D. Powers

A THESIS

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

MASTER OF SCIENCE

Department of Chemistry

1963

ACKNOWLEDGMENTS

The author would like to express his sincere appreciation to
Dr. A. Timnick for his guidance and encouragement throughout the
course of his graduate studies and during the course of the research
undertaken.

The author also wishes to express his appreciation to his wife
for her constant encouragement, and also to our parents for their
assistance.

>1: >:< >:: 3:: >:< >§< >:< 3:: >:< >:: ::<

ii

VITA

Name: Bruce Douglas Powers
Born: August ll, 1938, Melrose, Massachusetts
Academic Career: Forest Lake Academy

Maitland, Florida (1955)

Emmanuel Missionary College
Berrien Springs, Michigan (1955-1957)

University of Miami
Coral Gables, Florida (Summer, 1957)

Union College
Lincoln, Nebraska (1957-1960)

Michigan State University
East Lansing, Michigan (1960-1962)

Degree Held: B. A. Union College (1960)

iii

TABLE OF CONTENTS

INTRODUCTION ............ . . . . ......... l

HISTORICAL........................... 5

EXPERIMENTAL . . . ............. . ....... 8
Instrumentation ........... . . . . . . ..... 9
Reagents .......................... 11
Preparation of Solutions ........ . . . . . . . . . 13
Experimental Procedures .............. . . . 15

EXPERIMENTAL RESULTS AND DISCUSSION . . . ...... 18

CONCLUSIONS.......................... 54

LITERATURE CITED . . . . . ...... . ......... . 57

iv

TABLE

II.

III.

IV.

VI.

VII.

VIII.

IX.

XI.

LIST OF TA BLES

Absorbances of Solutions Containing Lanthanide Ions
and l,lO-Phenanthroline ...... . . . . . . . . .

Fluorescence Intensities of Solutions Containing

Lanthanide Ions and l, lO-Phenanthroline .......

Absorbances of Solutions Containing Lanthanide Ions

and 5-Nitro-l, lO-phenanthroline . . . . . ......

Absorbances of Solutions Containing Lanthanide Ions
and S-Methyl-l, lO-Phenanthroline. . . . . . . . . .

. Fluorescence Intensities of Solutions Containing
Lanthanide Ions and 5-Methyl-l, lO-Phenanthroline . .

Absorbances of Solutions Containing Lanthanide Ions
and Sulfosalicylic Acid ........ . . . . . . . .

Fluorescence Intensities of Solutions Containing

Lanthanide Ions and Sulfosalicylic Acid ....... . .

Absorbances of Solutions Containing Lanthanide Ions
and Salicylic ACid O O O O O O I O O O O O O O O ' O O 0

Fluorescence Intensities of Solutions Containing
Lanthanide Ions and Salicylic Acid. . . . . . . . . .

. Absorbances of Solutions Containing Lanthanide Ions

and saliCYIa-ldehyde O O O O O O O O O O O O O O O O O 0

Fluorescence Intensities of Solutions Containing
Lanthanide Ions and Salicylaldehyde ..... . . . .

.Page

21

24

28

31

33

37

40

44

47

51

53

FIGURE

10.

ll.

12.

LIST OF FIGURES

Page

. Block Diagram of the Spectrofluorometer . . . . . . . 10

Absorbance Spectra of 1, lO-Phenanthroline at pH 3.41
ande7.02 ..... . ..... 20

Fluorescence Spectra of 1, lO-Phenanthroline ..... 23

. Absorbance Spectra of 5-Nitro-l, lO-Phenanthroline

at pH 1.98 and pH 7.09 ........ . . . ...... 27

. Absorbance Spectra of 5-Methyl-l, lO-Phenanthroline

atpH1.90ande8.05 ..... ..... ..... 3o

. Fluorescence Spectra of S-Methyl-l, lO-Phenanthro-

line ..... ....... ..........32

. Absorbance Spectra of Sulfosalicylic Acid at pH 0. 95

and pH 4.94. . . ......... . . ......... 36
Fluorescence Spectra of Sulfosalicylic Acid ...... 39

Absorbance Spectra of Salicylic Acid at pH 0. 67 and ..
pH 4. 84 ..... . ................... 43

Fluorescence Spectra of Salicylic Acid ........ 46
Absorbance Spectrum of Salicylaldehyde at pH 3. 91. . 50

Fluorescence Spectra of Salicylaldehyde ....... 52

vi

INTRODUCTION

A relatively unentered field to date is the field of fluorometric
analysis. When a compound or a complex is excited with relatively
high energy radiation, usually ultraviolet radiation, photoluminescence
occurs. Photoluminescence is the phenomenon of reemission of
radiation after a finite amount of time has elapsed since excitation.

The greatest amount of fluorescence is produced by the exciting
monochromatic radiation which is most effectively absorbed by the
molecule or complex. After absorption, the energy can be given off by:

1) transfer of kinetic energy to other species,

2) reaction of the excited species with other species in the
system,

3) decomposition of the excited species,

4) reemission of energy as light quanta of the same or different
wavelength, immediately or after a finite time delay after
excitation. The latter is called fluorescence or phosphor-
excence.

The difference between phosphorescence and fluorescence is due

to the difference in the path that the energy takes in being reemitted.

The following is a diagramatic representation of these different paths.

Second
Excited

State

First

Excited

State

Ground

State

Singlet Levels Triplet Levels

 

 

 

 

 

Energy

 

 

 

 

 

. A molecule or a group in the molecule in the ground state first

absorbs radiant energy and is excited to any one of the excited
states; here the second excited state is illustrated. The period
of time required is on the order of 1 x 10'12 seconds.

. Energy may then be given up by any one of many nonradiative

transitions, through collisions with encountered species, leav-
ing the molecule or group at the lowest vibrational energy level
in the first excited singlet state. This is a singlet-—> singlet
transition.

. The change shown is a radiative transition to one of the vibra-

tional levels in the electronic ground state. The radiated energy
is fluorescence.

The transition shown is a radiationless "forbidden" transition of
a singlet —-> triplet type. The triplet state is a metastable state
due to the unpairing of electrons normally having paired spins.

The metastable triplet state will eventually undergo a triplet —->
ground state radiative transition. The lifetime of the metastable
state is governed by the triplet —> singlet transition probability.
The radiated energy is phosphorescence.

The exponential expression, If = Q 10 (1-10’abc), relates fluor-

escence intensity If to ID, the incident radiation intensity. In this
expression 9, is a proportionality constant whose value depends on the
method of measurement and the quantum efficiency, a the absorptivity,
b the path length, and g the concentration.

This expression can be transformed to the following exponential

series form:
If = Q 10 (2.30 abc - 1.15 aZb-ZcZ + 0.38 a3b3c3 - . . .)

At low concentrations where abc is less than 0.01, the second and

 

third terms become negligible, and the equation resolves to (15, 29, 69):
If : 2. 303 Q 10 abC

The tripositive lanthanide ions which fluoresce in solution are
samarium, europium, terbium, dysprosium, gadolinium, praseodymium,
neodymium, cerium, erbium, and lanthanum (42). Lanthanum, gadolinium,
and lutetium, with their empty, half full, and full 4f shells, respectively,
have a greater tendency to yield fluorescent complexes because the
possibility for loss of absorbed energy through intramolecular energy
transfer to electrons in these stable 4f configurations is eliminated.
When complexed with organic compounds, the lanthanide ions may influ-
ence the fluorescence characteristics of the organic reagent.

This project is a part of an investigation of reactions between
lanthanide ions and organic reagents, in particular those reagents which

form fluorescing complexes (16, 58).

HISTORICAL

Several books which review all phases of fluorescence are avail-
able. Most noteworthy is a book by Pringsheim entitled "Fluorescence
and Phosphorescence" (42). This book devotes a chapter to lanthanide
fluorescence. Another good book is entitled "Fluorescence of Solutions, "
by Bowen and Wokes (7), which discusses fluorescence theory and
fluorescence measurement. A book on the transformation of absorbed
radiation into fluorescence light was also written by Bowen and is en-
titled "The Chemical Aspects of Light” (6).

C. E. White, a worker in the field of fluorescence, reviews the
current research in that field every two years for Analytical Chemistry.
This series of reviews (60-68) offers a complete listing of references.

One, ten-phenanthroline and its derivatives are just beginning to
be used as reagents in aqueous fluorescent analysis. They were tested
by Veening and Brandt for the determination of ruthenium (56). The
preferred chelating agent, 5-methyl-1, lO-phenanthroline, showed no
pH dependence from pH 1 to 13. No fluorescence was noted for 5-nitro-l,
lO—phenanthroline. One, ten-phenanthroline was not selected for the
greatest amount of research, but was considered to give equally satis-
factory results. The investigators concluded that 5-methyl-l, lO-
phenanthroline formed a tris complex with ruthenium.

One, ten-phenanthroline and its derivatives have long been known
to be complexing agents, and have been used to complex many elements
(1, 2,12,13,14, 21, 22, 27, 31, 43, 48, 49, 52, 54, 59, 70). The review by
Brandt (8) on complexation with 1, lO-phenanthroline is quite thorough.
The complexation of any of the lanthanides by 1, lO-phenanthroline or any
of its derivatives was not even mentioned.

Salicylic acid and sulfosalicylic acid are complexing agents in
aqueous solution, and have been used to complex many elements (4, 9, 10,
11,18,19, 20, 23, 28, 33, 35, 37, 39,41, 45, 46, 51, 57, 71). Holleck described

salicylic acid as a relatively poor complexing agent of eurOpium (26),

but he used sulfosalicylic acid to complex neodymium (24). He also
described a colorimetric determination of lanthanides by making a lake

of the lanthanides with aurintricarboxylic acid, then adding sulfosalicylic
acid to break up the lake to form a colored solution for measurement (25).

Oliver and Fritz made an anionic complex of sulfosalicylic acid
with yttrium on an ion exchange column at pH 8-10 (38). Bhattacharya,
it a_l. claimed that a tris complex of Ce(III) was formed with salicylic
acid (5).

Very little information is available on the complexation of lanthanides
by salicylaldehyde. Kutzmetsova and Sevchenko described luminous com-
plexes formed between a combined reagent of ethylenediamine and salicyl-
aldehyde with europium, samarium or terbiurn (32). Salicylaldehyde is
quite well-known as a complexing agent for other elements (3, 17, 34, 36,

40, 44, 47, 54, 55).

EXPERIMENTAL

Instrumentation

 

The spectrofluorometer used for this investigation was a modifi-

cation by Fleck (16) of the instrument constructed by Thommes (53).

A block diagram of this instrument is shown in Figure 1. Its components

are as follows:

1.

The ultraviolet source is a Hanovia S-H high pressure mercury
arc lamp powered by a Hanovia 110/120 constant voltage trans-
former. The mercury lines which were used are the 265, 297,

and 303 mu. lines.

. The monochromator for the exciting ultraviolet light is a

Bausch and Lomb model 33-86-40 grating monochromator.
This is attached to the cell compartment by a light tight

"0 ring” rubber gasket.

. The cell compartment is as indicated in Figure 1. Light

passes into it from the Bausch and Lomb monochromator
through a quartz cylindrical lens. This lens produces a
parallel beam of ultraviolet light which illuminates the center

of the 20 mm. side of the sample cell.

. The cells used are a pair of matched clear window silica

cells which measure 10 x 20 x 50 mm. These cells were
purchased from the Farrand Optical Company. These silica
cells are transparent to all ultraviolet radiation used. The
cell compartment is made so that the cells are reproducibly

p0 sitioned within it .

. To measure the fluorescent light, a Beckman DU with photo-

multiplier attachment powered by an AC power supply was used.

This instrument was modified slightly as indicated in Figure 1,

10

 

 

 

 

 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

   

 

 

 

 

 

 

 

 

 

 

A
Beckman DU
monochromator
Bausch and Lomb
grating monochromator A w
Photomultiplier
/ JAE {IJI [— {Mtube housing
N 17 7 4
/.
I 7 Sample
cell
Mercury arc
housing »
._l_1 -
Transforme; AC powerTsupply and
' photomultiplier control
unit

Figure 1. Block Diagram of Spectrofluorometer.

11

so that the fluorescent light entered from the position the
photomultiplier usually occupies and was measured by a photo-
multiplier at the position usually occupied by the lamp housing.

The spectrophotometer used in absorbance work is a Beckman
model DK 2. The cells used with this instrument were matched
Beckman 0.988 cm silica cells.

A Beckman model G pH meter equipped with glass-saturated calomel
microelectrodes was used in all pH measurements. This instrument was
calibrated with a Beckman pH 4 or pH 7 buffer.

The constant temperature bath used was made up of the following
components: a Zero Current Relay and a Heater and Circulator for
Thermostatic Baths, both by E. H. Sargent and Company of Chicago;
controlled by a Princo Magna-Set mercury temperature control, catalogue
No. T-260 from Precision Thermometer and Instrument Company.

The light source used for the "Tyndall Effect" was the detached
visible light source for the Beckman DU. This was used in a dark room
with all other lights out and the solution to be measured silhouetted

against a dark background.
Reagents

Ammonium Hydroxide

Baker and Adamson Reagent grade, distilled and stored in a
sealed polyethylene bottle.

Ammonium Perchlorate

Baker's Analyzed Reagent.
Dichlorofluorescein

Eastman Kodak White Label.
Erbium Se squioxide

Michigan Chemical Corporation, St. Louis, Michigan, labelled
purity, 99.9%.

12

Europium Sesquioxide
Heavy Metals Company, Chattanooga, Tennessee, purity unknown.
Gadolinium Se squioxide

Michigan Chemical Corporation, St. Louis, Michigan, labelled
purity, 99.9%.

Holmium S e squi oxide

Michigan Chemical Corporation, St. Louis, Michigan, labelled
purity, 99.9%.

Lanthanum Se squioxide

Heavy Metals Company, Chattanooga, Tennessee, optical grade,

99. 9% pure.
Lutetium Sesquioxide

Michigan Chemical Corporation, St. Louis, Michigan, labelled
purity, 99.9%.

Five-methyl-one, ten-phenanthroline

G. F. Smith Chemical Company, Columbus, Ohio, reagent grade.
Five-nitro-one, ten-phenanthroline

G. F. Smith Chemical Company, Columbus, Ohio, reagent grade.
Perchloric Acid

Baker's Analyzed Reagent Grade (70-72%).
One, ten-phenanthroline monohydrate

G. F. Smith Chemical Company, Columbus, Ohio, reagent grade.
Salicylaldehyde

Eastment Kodak White Label. Redistilled under vacuum five
times, used immediately.

Salicylic Acid

Unknown source, recrystallized from absolute methyl alcohol.
Sulfosalicylic Acid

Merck and Company, Inc. , Rahway, New Jersey, reagent grade.
Water

Distilled water was passed through a ”Crystalab Demineralizer"
mixed ion exchange column until the meter indicated less than

13

0. 1 ppm. of NaCl, then redistilled from basic solution of
potassium permanganate. This treatment was used to make sure
all dissolved organic materials were absent.

Ytterbium Sesquioxide

Michigan Chemical Corporation, St. Louis, Michigan, labelled
purity, 99.9%.

Preparation of Solutions

 

Ammonium Hydroxide
Distilled ammonium hydroxide was diluted to approximately
1 N or 0.1 N for pH adjustment of the solutions.
Ammonium Perchlorate
This solution was made by weighing solid ammonium
perchlorate and dissolving and diluting to the mark in a volumetric
flask to give a 1 M solution.
Dichlorofluorescein
A 0. 4 y per ml. solution was used for standardization of
the spectrofluorometer and was made by dissolving the appropriate
amount of reagent in 95% ethyl alcohol and diluting to one liter
with water.
Lanthanum Perchlorate
Lanthanum sesquioxide was ignited in a platinum crucible
at 7500 :l: 150 to a constant weight. A calculated amount was then
weighed out and placed in a 500 m1. volumetric flask and dissolved
in 70-72% perchloric acid. This solution was diluted to 500 ml.
and all other solutions were made from this 0. 00100 M solution.
A solution of gadolinium was also made in the above manner.
Lutetium Perchlorate
Gadolinium Perchlorate

Europium Perchlorate

14

Ytterbium Perchlorate
Holmium Perchlorate
Erbium Perchlorate
The individual sesquioxides were heated at 7500 :l: 150 to
constant weight. The desired amount of an oxide was weighed
out into a volumetric flask and dissolved in the requisite amount
of 70- 72% perchloric acid. The resulting solution was diluted to
the mark. Individual solutions of all of these ions were made so
that the final concentrations were 1.0, 0.1, or 0. 01 milligrams
of the lanthanide sesquioxide per milliliter.
Perchloric Acid
The 70-72% solution of perchloric acid was weighed and
diluted to one liter in a volumetric flask to give approximately
5 N, 1 N, or 0.1 N solutions which were used in the adjustment of
pH of the various solutions.
One, ten-Phenanthroline and its derivatives
The l, lO-phenanthroline, 5-methyl-l, lO-phenanthroline and
5-nitro-l, 10-phenanthroline stock solutions were made by placing
a weighed amount of the solid reagent to yield a 0. 00100 M solu-
tion into a 500 ml. volumetric flask, almost filling the flask with
redistilled water, heating the flask and contents in a hot water
bath to aid dissolution, and diluting to the mark after dissolution
had taken place and the solution had been cooled to 250 d: 10.
A little dilute perchloric acid had to be added to the 5-nitro-
1, lO-phenanthroline before dissolution took place.
Salicylaldehyde
This solution was made by weighing out the appropriate
amount of reagent, after purification by aspirator distillation five
times, into a 500 ml. volumetric flask, adding redistilled water

almost to the mark, and then placing the volumetric flask and

15

contents in a hot water bath to speed up the dissolution. When
the reagent had been dissolved and the temperature attained
250 :1: 10, water was added to the mark on the volumetric flask.
The concentration, as determined by the weight added, was
0. 001275 molar.

Sulfosalicylic Acid

Salicylic Acid

Sulfosalicylic acid and salicylic acid solutions were made

by dissolving the appropriate amount of the solid acid in re-
distilled water in a 500 ml. volumetric flask and diluting to the

mark. The final concentration of each was 0. 00100 molar.

Experimental Proc edure s

 

All experimental work was carried out at room temperature, 260
:1: 10. If the room temperature deviated from this range the flasks
containing solutions were placed in the constant temperature bath main-
tained at 250 :1: . 020 for a minimum of one-half hour before making

measurements.

Method of sample preparation

 

Each sample was made by adding 5. 00 ml. of the organic reagent
solution by pipet, and 5. 00 ml. of the lanthanide solution by pipet to a
50.00 ml. glass stoppered volumetric flask. The sample was then
diluted to 41-47 ml. with redistilled water added from a separatory funnel
equipped with a ”Teflon" stopcock. To adjust the solution to the desired
pH, the sample was then placed in a 50 ml. beaker, a small "Teflon"
covered stirring bar was added. At this point the pH meter electrodes
were introduced, and the magnetic stirrer turned on. Minute amounts

of acid and/or base were added from medicine droppers with finely drawn

16

tips until the desired pH was approximated. The resulting solution was
returned to the volumetric flask and the sample was diluted to the mark.
Exact pH was measured after at least one hour had elapsed in order to

make sure that equilibrium had been established.

- Method of fluorescence measurement

 

All measurements of fluorescence in results described in this
thesis were made on the spectrofluorometer described on'Figure 1. The
Beckman DU, its AC Power Supply, and the mercury arc lamp were
turned on at least one hour, generally two hours before use to insure a
complete warm-up of the instrument. The selector knob on the DU was
set to 0. l, the photomultiplier sensitivity knob set on full position, and
the monochromator entrance and exit slits set to 2. 0 mm. slit width
unless otherwise designated.

Standardization was achieved, after allowing time for the instru-
ment to warm up, by placing the 0.47 /ml. dichlorofluorescein in the
silica reference cell in the sample compartment, setting the DU slit
width at 0. 5 mm. slit, the percent T knob at 50% T, the wavelength scale
at 540 mu. , and the exciting wavelength dial at 265 mu. The shutter was
opened, and the sensitivity knob on the DU was then turned until the
instrument was at the null position. After this standardization, the
instrument was considered "standardized" for a period of about one-half
hour. The instrument was then ready for use in fluorescence measure-

ment.

Method of absorbance measurement

 

All absorbance measurements were made on the Beckman DK 2.

Standard Operating procedure was used at all times.

17

Method of pH measurement

A Beckman model G pH meter equipped with glass-saturated
calomel micro electrodes was used in all pH measurements. This meter
was allowed to warm up for ten to fifteen minutes, then standardized by
the use of a Beckman pH 4 or pH 7 buffer solution. When exact measure-
ment of pH was desired, the solution was placed in the enclosed shielded

sample compartment. After two to four minutes the pH was read and

recorded to the nearest 0. 01 pH unit.

EXPERIMENTAL RESULTS AND DISCUSSION

l8

19

One, ten-Phenanthroline

 

Absorption spectra for 3 x 10"5 M 1, 10-phenanthroline in 0.1 M
NH4ClO4, with changing pH were recorded. Figure 2 shows spectra
for solutions of pH 3.41 and pH 7. 02. A slight shift in the absorbance
maximum from 271 mu. to 264 mu. is apparent. Absorption spectra
of this reagent solution containing lanthanide ions were also recorded.
Table I lists the absorbances of the lanthanide-1, lO-phenanthroline
solutions. In each case the blank contained everything the sample solu-
tions contained, with the exception of the lanthanide ion.

.Fluorescence spectra for 3 x 10'5 M 1, lO-phenanthroline in 0. 1 M
NH4ClO4 excited by 265 mu. radiation were recorded and are shown on
Figure 3. The fluorescence intensity, If, maximum is very close to
420 mg. for all solutions of pH 4 or less and changes to close to 365 mu.
for all solutions of pH 6 or greater. The fluorescence spectra of this
reagent solution containing lanthanide ions were also recorded.

Table 11 lists the fluorescence intensities of the lanthanide-1, 10-phen-
anthroline solutions.

There is a slight change in the absorbance of ytterbium giving an
indication of complexation but this change does not seem to be directly
dependent upon concentration. The 5.07 x 10'5 M stock solution shows
0. 01 absorbance at 270 mu. A difference was not noted when the
fluorescence spectra of the ytterbium-l, lO-phenanthroline solutions
were compared with those of blank solutions.

There was neither any significant increase nor decrease in absorb-
ances or fluorescence intensities nor any change in the shape of either
the absorbance or fluorescence spectra due to lanthanide ion additions to
l, 10-phenanthroline reagent solutions. The only exception is ytterbium

mentioned above.

Absorbance

20

 

 

 

 

1
° 00 1‘ 1, lO-Phenanthroline pH 3 41
-5 -
“ Conc. 3.00x 10 M ___-__. pH 7.02
l ["\\
o 90-7 ‘ \
\
1 / \
\ / \
a 1 ’ ‘
. l
0‘1 I l l
\ l 1
l I
| i |
.70— l I I
‘ l
| l
I 1 I
| I l
. 60— -| g |
i, . :
\ I |
l l
. 50... \ g l
\ ' l
\ I '
\ I
.40— \ l |
\ ' \
\ l
\ . \\
. 30— i I ‘
\
\ ’ \
\\/’l ‘\
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. 20— \
\
\
\
\
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.10— \
x
\
\
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. 00
I I ' l I I I
200 220 240 260 280 300 320 340
Wavelength in millimicrons
Figure 2.

Absorbance Spectra of 1, lO-Phenanthroline at pH 3.41 and

pH 7.02.

 

21

 

 

 

 

 

 

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23

 

 

110 1, lO-Phenanthroline 1 H 2 33
3.00 x10'5 M 2" EH 2'85
100— O o
3. pH 3.41.
4. pH 4.02
90— 5. pH 4.47
6. pH 5.03
7. pH 5.43
80 — 8. pH 6.01
9.. pH 6.60
m 11. pH 7.92
9
60-I 3
7
If
50— 6
\
40 A \
\
30 fi / I
20 d I,\
3
10 z
'I .1 u
0 r I I I I F" I I

 

 

350 370 390 410 430 450 470 490 510 530

Wavelength in millimic rons

Figure 3. Fluorescence Spectra of 1, lO-Phenanthroline.

Z4

 

 

 

 

 

 

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83380 - n 283.

26

Five -Nitro- one, ten- Phenanthroline

 

Absorption spectra for 1 x 10‘4 M 5-nitro-1, lO-phenanthroline
in 0. 1 M NH4C104 with changing pH were recorded. Figure 4 shows
spectra for solutions of pH 1.98 and pH 7.09. Absorption spectra of
this reagent solution containing lanthanide ions were also recorded.

- Table 111 lists the absorbances of the lanthanide-S-nitro-l,’lO-phen-
anthroline solutions. In each case the blank contained everything the
sample solution contained, with the exception of the lanthanide ion.

There was no fluorescence detected for 5-nitro-l, lO-phen-
anthroline solutions, either as the reagent solution or as the reagent
solution containing lanthanide ions. Four exciting wavelengths were
tested as follows: 265, 297, 313, and 365 mu. The entire region from
just above the exciting wavelength through the entire visible region
was scanned with the instrument "wide open. "

There was neither any significant increase nor decrease in
absorbances nor any change in the shape of the absorbance spectra due
to lanthanide ion additions to 5-nitro-l, lO-phenanthroline reagent

solutions .

Absorbance

Z7

 

2.00

 
  
 

.801

.60—1

.40-

.20...

5-Nitro-1, 10-phenanthroline Conc. 1.00 x 10" M

—_pH 1.98

----pH 7.09

 

 

 

'00 I I I I I I

200 220 240 260 280 300 320

Wavelength in millimic rons

Figure 4. Absorbance Spectra of 5-Nitro-1, 10-phenanthroline at pH
1. 98 and pH 7.09.

 

340

2.8

 

 

 

 

 

 

 

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Z9

Five-Meth yl- one , ten- Phenanthroline

 

Absorption spectra for l. 00 x 10"4 M 5—methyl-l, lO-phenanthro-
line in 0.1 M NH4C104 with changing pH were recorded. Figure 5 shows
spectra for solutions of pH 1. 90 and pH 8. 05. At the high concen-
tration used for fluorescence there was very little pH dependence noted,"
including the minimum at 245 mp. Absorption spectra of this reagent
solution containing lanthanide ions were also recorded. Table IV lists
the absorbances of the lanthanide-5-methy1-1, lO-phenanthroline solu-
tions at the 245 mu. minimum. In each case the blank contained every-
thing the sample solution contained with the exception of the lanthanide
ion.

AFluorescence spectra for 1.00 x 10-4 M 5-methy1-1, lO-phenan-
throline in 0. 1 M NH4C104 excited by 313 mu. radiation with changing
pH were recorded and are shown on Figure 6. The If maximum is at 349
mp. The fluorescence spectra of this reagent solution containing
lanthanide ions were also recorded. Table V lists the fluorescence
intensities of the lanthanide-S-methyl-l, lO—phenanthroline solutions.

There was neither any significant increase nor decrease in absorb-
ance or fluorescence intensities nor any change in the shape of either
the absorbance or fluorescence spectra due to lanthanide ion addition

to 5-methy1-1, lO-phenanthroline reagent solutions.

1.

.90"

.80...

.704

.60-4

. 50—

. 40—

. 30-1

. 20-

.00

30

 

00

 

 

 

 

5-Methy1-l, lO-phenanthroline Gone. 1. 00 x 10-4 M j

 

 

‘r I l r

l l . I
200 220 240 260 280 300 320 340

Wavelength in millimicrons

Figure 5. Absorbance Spectra of 5-Methyl-l, lO-phenanthroline
at pH 1. 90 and pH 8.05.

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110
5-Methy1- l, lO-Phenanthroline
Conc. 1.00 x10"4 M
100— 1. pH 0.96
2. pH 3.97
-- 3. pH 4.96
O
9 '7 4. pH 6.00
5. pH 6.96
80.. 6. pH 8.05
7. pH 9.10
70—4
60..
500
40-
30 "‘
1
20- 3"
10‘? A.
5
7
0 A .
1 l I I I I l l

350 370 390 410 430 450 470 490 510 530

Wavelength in millimicrons

Figure 6. Fluorescence Spectra of S-Methyl-l, lO-phenanthroline.

33

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34

Sulfo salicylic Acid

 

Absorption spectra for 1. 00 x 10'4 M sulfosalicylic acid with
changing pH were recorded. Figure 7 shows spectra for solutions of
pH 0. 95 and pH 4. 94. Absorption spectra of this reagent solution
containing lanthanide ions were also recorded. Table VI lists the
absorbances of the lanthanide-sulfosalicylic acid solutions at the 245 mu.
maximum. In each case the blank contained everything the sample solu-
tion contained with the exception of the lanthanide ion.

Fluorescence spectra for l. 00 x 10“ M sulfosalicylic acid excited
by 313 mp. radiation using a 1. 0 mm. exit slit were recorded and are
shown in Figure 8. If maximum is very close to 452 mg. for all solu-
tions of pH 1 or less and changes to close to 410 mu. for all solutions
of pH 5 or greater. The fluorescence spectra of this reagent solution
containing lanthanide ions were recorded. Table VII lists the fluorescence
intensities of the lanthanide-sulfosalicylic acid solutions.

Due to precipitate formation in aqueous solutions of sulfosalicylic
acid solutions containing the lanthanide ion, complexation was thought
to be present. All such solutions above pH 6. 5 formed a precipitate
which settled down or remained suspended. - It was assumed that the
settled precipitates would be similar to the precipitates which remained
dispersed and might be a solid complex of some type. A quantity of test
solution was centrifuged, and portions of the precipitate were tested
with strong acid and 95% ethyl alcohol. A lanthanide hydroxide is soluble
in strong acid, and insoluble in ethyl alcohol. Sulfosalicylic acid is
soluble in ethyl alcohol and if a complex was being precipitated, it is
presumed that it, too, would be soluble in ethyl alcohol. The portions of
the precipitate tested were soluble in strong acid and insoluble in ethyl
alcohol. This test may not be absolutely conclusive, but it is indicative

that the precipitate is the lanthanide hydroxide.

35

Some fluorescence quenching occurs in solutions in which the
concentration of the lanthanide ion is high and the pH is approximately
6 or higher. ~ This quenching was believed to be due to complexation.
Therefore, experiments were performed with Gd(III) in which the mole
ratios of reagent to lanthanide ion were varied from 1000/2 to 1/2.
The final concentration of sulfosalicylic acid in the test solutions was
1.00 x 10'4 M and that of Gd(III) started at 2.00 x 10'7 M and was in-
creased to 2.00 x 10"4 M. pH was maintained close to '7 since this
appeared to be close to the pH which yielded the highest quenching.
Precipitation was visually observed in the more concentrated solutions.
Solutions in which a solid precipitate had not been observed, were tested
for the‘"Tyndall Effect. " Light scattering was observed in all solutions
from 2.00 x 10-7 M to 2.00 x 10‘4 M in (30(111), starting with a slight
amount of light scattering and increasing with concentration. Later a
slight amount of light scattering was observed in a Gd(III) stock solution.
It is concluded that the quenching is due to light scattered by lanthanide
hydroxide formed at the high pH.

There was neither any significant increase nor decrease in
absorbance or fluorescence intensities nor any change in the shape of
either the absorbance or fluorescence spectra due to lanthanide ion

addition to sulfosalicylic acid reagent solutions.

Absorbance

36

 

1.00
Sulfosalicylic acid conc. is 1.00 x 10-4 M

pH 0.95
.90_ ‘ ----- pH 4.94

 

. 70—

.60—1

. 50—

. 40-

. 30—

 

 

.20—

.100

 

.00

 

 

 

I F T I
200 220 240 260 280 300 320 340

Wavelength in millimic rons

Figure 7. Absorbance Spectra of Sulfosalicylic Acid at pH 0. 95
and pH 4. 94.

37

 

 

 

 

 

 

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39

 

 

 

 

 

110
Sulfosalicylic Acid
Conc. is 1.00 x10'4M 1. pH 0.95
1004 2 pH 1.75
3. pH 2.95
90 _ 4. pH 3.84
5 pH 4.94
6 pH 5.98
80 —
70 ._
60 ._
If
50 4
40 —
30 A
20-—
10 —
2
/; -L fl
0 I I I I I I I I

 

 

350 370 390 410 430 450 470 490 510 530

Wavelength is millimicrons

Figure 8. Fluorescence Spectra of Sulfosalicylic Acid.

40

 

 

 

 

 

 

 

 

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00$ Offiw $0.$ 0.00 N>.$ 2 2 2
00$ 0.0m. 00.0 0.0K. 00.0 2 mIOH X 00.0 2
2 0.00. 00.0 0.HN. H0.0 2 2 2
00$ 0.Hw $0.$ 00.x. Hw.$ 2 2 2
00$ 0.0h 00.0 0.0b 00.0 «.IOH N 00.H oIOH X 00.0 n+Om
.15 .035 .038 HH 3% .038le $01 .2 .0000 2 .0000 00H
HH Mflmfim Cofidaow UfiU/W UfiTAUHHmmOHHSm wfifldmfiufimdn

 

 

$25.80 - 00> .33.

42

Salicylic Acid

 

Absorption spectra for 1. 00 x 10-4 M salicylic acid with changing
pH were recorded. Figure 9 shows spectra for solutions of pH 0.67
and pH 4.84. The absorbance maximum is very close to 302 mg. for
all solutions of pH 2 or less and changes to close to 295 mu. for all
solutions of pH 4 or greater. Absorption spectra of this reagent solution
containing lanthanide ions were also recorded. Table VIII lists the
absorbances of the lanthanide-salicylic acid solutions. In each case the
blank contained everything the sample solution contained with the ex-
ception of the lanthanide ion.

Fluorescence spectra for l. 00 x 10’4 M salicylic acid excited by
313 mu. radiation with changing pH were recorded and are shown on
Figure 10. If maximum is very close to 452 mp. for all solutions of pH
1 or less and changes to close to 410 mu. for all solutions of pH 5 or
greater. The fluorescence spectra of this reagent solution containing
lanthanide ions were recorded. Table IX lists the fluorescence
intensities of the lanthanide-salicylic acid solutions.

There was neither any significant increase nor decrease in
absorbance nor any change in the shape of either the absorbance or
fluorescence spectra due to lanthanide ion addition to salicylic acid
reagent solutions. There is a decrease in fluorescence intensities on
adding lanthanide ion to reagent solutions but the fluorescence intensity

does not vary with concentration of the lanthanide ion.

Absorbance

l

. 90—-

. 80—

. 70—

.600

.50—

.40-

.30—

43

 

.00

.20..

.10...

.00

Salicylic Acid Gone. is 1.00 x 10" M

 

 

 

 

 

200

 

‘ I I I l l

220 240 2.60 280 300 320 340

Wavelength in millimic rons

Figure 9. Absorbance Spectra of Salicylic Acid at pH 0.67 and

pH 4.84.

44

00.903000

 

 

 

 

 

 

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45

 

 

 

 

 

 

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000 000.0 05.0 000.0 00.5 2 2 2
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OUCNQHOWQafiV MGMHm COMHHHHOW UHU< UHHKnUHHmm wwwcmgwcmq

 

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46

 

 

 

 

 

 

 

110
Salicylic Acid
Conc. is 1.00 x10‘4 M 1. pH 0.67
100 -—+ 2. pH 2.11
3. pH 2.55
4. pH 3.98
90 — 5. pH 5.35
6. pH 6.73
80 __ 4
7o .2
so —a
50 —
40 ——I
30 ——- x
20 .—
10 —b
0 i ‘7 I F I T I l

 

 

350 370 390 410 430 450 470 490 510 ‘ 530

Wavelength in millimic rons

Figure 10. Fluorescence Spectra of Salicylic Acid.

47

0030300 0

 

 

 

 

 

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00$ 0 .5$ 50.0 0 .0$ 50.0 #100 an 00.H 0100 X 00.$ n+.m1_
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ounmg HH MCNHm GOHHHHHOW fivfiU< UHHNfiUMHNW DUNHHHNQHHHNJ

 

30¢. 0030.300 000 003 00000004 930000000 0003000m mo 003000000H 00000000000h .NH 00000

48

 

 

 

 

 

 

—- OoHo mMQm Oon mmVom : : .-
000V 0.00 mm.m m.0w 50.m 2 2 2
Oman mémv 0.0.0 m.N¢ v0.0 : .700 x 0N6 :
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omv m .50 no.0 m.m¢ 00.0 : 0700 x wN.m «+00
—- Oo®w MFoQ 0.0@ 05.0 : z :
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.0300 00 v00m0m0 000000om 0004 o00>o00mm 000090000010.

 

 

330qu - x0 28

49

Salicylaldehyde

 

Absorption spectra for 1. 275 x 10“ M salicylaldehyde with chang-
ing pH were recorded. Figure 11 shows a spectrum for a solution at
pH 3. 91. ~Absorption spectra of this reagent solution containing
lanthanide ions were also recorded. - Table X lists the absorbances of
the lanthanide-salicylaldehyde solutions at the 255 mu. maximum.

In each case the blank contained everything the sample solution contained
with the exception of the lanthanide ion.

Fluorescence spectra for l. 275 x 10"4 M salicylaldehyde excited
by 313 mu. radiation with changing pH were recorded and are shown
on Figure 12. The If maximum is at 510 mg. The fluorescence spectra
of this reagent solution containing lanthanide ions were recorded.

Table XI lists the fluorescence intensities of the lanthanide-salicylalde-
hyde solutions.

There was neither any significant increase nor decrease in
absorbance or fluorescence intensities nor any change in the shape of
either the absorbance or fluorescence spectra due to lanthanide ion

addition to salicylaldehyde reagent solutions.

Absorbance

.00

50

 

.80—

.60—4

.40—

.20....

.00..

.800

.600

.40

.20

.00

Salicylaldehyde cone. is 1.275 x 10-‘ M

 

-

 

—

 

 

 

l T l I l
200 220 240 260 280 300 32.0 340

Wavelength in millimic rons

Figure 11. Absorbance Spectrum of Salicylaldehyde at pH 3. 91.

51

 

 

 

 

 

 

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000.0 000” om.0 mw.m 2 0:00 h_vN.m «+000.
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OUGNQHOWQ< mm UUCMQHOWQ< mm 2 .00000 2 .UGOO QOH
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52

 

 

 

 

 

110
Salicylaldehyde conc. is 1.275 x 10" M
1000 1. pH 0.83
2. pH 1.95
3. pH 2.90 t
90- 4. pH 3.91
5. pH 4.98
80—.
70..
60—.
If
50-
40-
30-4
20-
10- 5iZzg;;;;;;:::::§§§§EEEEEEEEE
4
3
l 4
0 1 r* 1 1

F I l I
400 420 440 460 480 500 520 540 560 580

Wavelength in millimic rons

Figure 12. Fluorescence Spectra of Salicylaldehyde.

53

 

 

 

 

 

 

 

 

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0.m0 006 0.N0 mm.m : @100 0N6 «+00
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0:2 006 0.N0 21¢ : .0100 no.0.“ :
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060 00.m 0.1: $0.$ : 0100 m0.m 104
0.00.0 005 0.1: mm.¢ : m100 mm.m :
0.0: 006 m.N0 hmJV : .0100 mm.m .1000
0.M0 00.m m.N0 0.00.m 2 #100 00.0 2
060 005 0.M0 nmé 0.1000n mum; .0100 00.0V «+010
.0800 00 $0 .0000 00 T00 02 .0000 $0 .0000 000
x0m0m 000000om 00>0000m0>000mm 000000000010
00030300003

0000 0000 00000000004 w00003000 m0o0000om 00 0000000000 0000000000000

.HX 0000.0.

CONCLUSIONS

54

55

Aqueous solutions varying in concentration from 1 x 10"6 M to
1 x 10'4 M of 1, lO-phenanthroline, 5-nitro-l, lO-phenanthroline,
S-methyl-l, lO-phenanthroline, sulfosalicylic acid, salicylic acid, or
salicylaldehyde were tested individually as complexing reagents for
the following lanthanide ions: La (III). Gd (111),. H0 (111),“. Er (III),
Yb'(III),- Lu (III), and Eu (III). (Eu (III) being tested with 1, lO-phen-
anthroline only.) The effect of pH on the absorbance and fluorescence
of each reagent solutinn was examined. The pH of each reagent-
lanthanide solution was adjusted to that level where. a pH change had
the least effect on the absorbance and fluorescence of the reagent solu-
tion, and the pH was still low enough so that the lanthanide hydroxides
did not form to any discernable extent. The exciting wavelengths tested
in the fluorescence studies were the 265, 297 and 313 mu. lines from a
mercury lamp. There was neither any significant increase nor
decrease in absorbance or fluorescence intensities nor any change in
the shape of either the absorbance or fluorescence spectra due to
lanthanide ion addition to the above reagent solutions. Thus the spectro-
scopic studies provide no evidence that complexation between the tested
lanthanide ions and the organic reagents occurs in aqueous solutions.

It is generally recognized (30, 50) that lanthanide ions form ionic
complexes. Factors limiting the complexation of the lanthanide ions
are: (a) the spatial unavailability of 4f orbitals for hybridization in the
formation of strong covalent bonds, (b) the comparatively large size of
the ions which limits the space into which they can fit for close contact
with the complexing species.

The fused phenanthroline ring is quite a rigid structure in which
there is little or no possibility of change in the distance between the
l, 10 nitrOgens. An inorganic ion of compatible radius can be complexed.
If an ion is too large, no complexation can occur. A well-known example

of metal ion complexation with l, lO-phenanthroline is that of Fe (III).

56

Its ionic radius is 0.64 X. The radius of La (III) is 1.16 X (30). This
difference in size accounts for the difference in complexating behavior
with the phenanthrolines tested.

The l, lO-phenanthroline, 5-nitro-l, lO-phenanthroline, and
5-methyl-l, lO-phenanthroline reagents contain a small partially nega-
tive charge on the l, 10 nitrogens due to the unbonded electrons. In the
two derivatives, this effect is enhanced by the positive inductive effect
of the 5-methyl group and inhibited by the negative inductive effect of
the 5-nitro group. On the basis of this basicity, complexation with the
lanthanides might be expected. Since complexation apparently does not
occur, the size of the ion is a more significant factor. .Complexing of
the lanthanides with other organic nitrogen containing compounds by
bonding to the nitrogen are known, even though the tendency to do so is
slight. vSome of those mentioned are antipyrene with bonding believed
to be to the methyl substituted nitrogen, 8-quinolinol, and pyramidone
(30). It is interesting to note that none of these contained a fused ring
system as does 1, lO-phenanthroline.

.One other contributing factor is that of the dielectric constant of
the solvent. A high dielectric constant solvent favors the dissociation of
ionic species. Formation of ionic complexes in water would not be as
extensive as in a medium of lower dielectric constant.

The solvent molecules surround and tend to shield the attraction
for the lanthanide ions by the effect of the partially negative oxygen in
the water molecule. Obviously the competition between the solvent and
the complexing agent for the lanthanide ion is in favorof the water.

Complexing groups in the salicylic family are not as rigidly fixed
as in the phenanthrolines but apparently complexes still do not form.
Dimensions could still be a limiting factor as well as the solvent effects

and characteristics of the lanthanide ions.

- LITERATURE CITED

57

10.

ll.

12.

13.

14.

15.

16.

58

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61
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Ibid., _2_6_, 129 (1954).

 

Ibid., 28, 621 (1956).

 

Ibid., _3_9_, 729 (1958).

Ibid., 32, 47R (1960).

62

68.. Ibid. .34, 81R (1962).

69. Willard, H. H.,- Merritt, L. L., Dean, J. A., "Instrumental
Methods of Analysis, " Third Edition, D. Van Nostrand Company,
.Princeton, New Jersey, 1958.

70. Yasuda, M.,i Sone, K., Yamasaki, K., J. Phys. Chem. _6_0_, 1667-8
(1956).

71. Zolotov, Yu. A., Noikov, Yu.-P., Zhur. Neorg. Khim. _4_, 1693-7
(1956); C. A., _5_3_, 8387i (1959).

 

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