me. mamamou AND Psomms. or SOME 41 muwmw AND TUNGSTEN COMPOUNDS Thesis ‘or ”to chm of pk. D. MICHIGAN STATE UNIVERSITY 'D. Paul Riflema 1969 anus» LIBRARY Michigan State University This is to certify that the thesis entitled THE PREPARATION AND PROPERTIES OF SOME d1 MOLYBDENUM AND TUNGSTEN COMPOUNDS presented by DONALD PAUL R I LLEMA has been accepted towards fulfillment of the requirements for CM, Major professor Date JULY 28. 19-69 0-169 ABSTRACT THE PREPARATION AND PROPERTIES OF SOME d1 MOLYBDENUM AND TUNGSTEN COMPOUNDS BY D. Paul Rillema Solutions of WCl5 in alcohols were investigated. The solutions were acidic with HCl, neutral, or basic with alkoxide ion. A number of tetrachlorodialkoxo and penta— chloroalkoxotungstates(V) were prepared and characterized. A yellow compound, [(C2H3)4N]2[W(OC2H5)C16], was isolated from ethanol solutions which had been saturated with HCl. The pentachloroalkoxotungstate(V) decomposed by the elimina- tion of alkyl chloride to give a mixture of solid materials which probably contain tetrachloroxotungstate(V). Neutral solutions which were evaporated to dryness produced dimeric compounds, [W(OCH3)3C12]2. Molybdenum pentachloride underwent similar reactions with alcohols. A direct preparation of tetrachlorodieth- oxomolybdate(v) was found. The compound, believed to be the pentachloroethoxomolybdate(V) salt of a tetraalkylam- monium cation, was isolated at —78°. The compound rapidly evolved ethyl chloride and formed the salt of the tetra- chloroxomolybdate(v). D. Paul Rillema Electronic properties of the compounds were extensively investigated. Some of the three possible d—d transitions from 32 -¢ E, Bz -$ B1, and 82 —> A1 were found. These transitions and state assignments were made on the basis of C4y symmetry for MoOCl4- and W(OR)C15- ions and D4h sym- metry for dialkoxide complexes. ‘According to esr measure- ments, only Egggg alkoxides were present. The gi value changed as ligands were displaced on the C4v axis of symmetry, for W(OCH3)C15- 91.: 1.50 and for W(OCH3)2C14- 9-1. = 1.73. 'For [(C2H5)4N][MO(OCH3)2C14] in nitromethane glass, g|l = 1.970, gi = 1.923, A = +70 x 10-4 cm-l, B = +30 x 10-4 cm-l, and the isotopic con- tact term, K, is -39.6 x 10—4 cm-l. In addition, an esr signal was detected for [(C2H5)4N](WC13) in the powder. Magnetic moments of tungsten complexes showed varia— tions as the spacings between the B2 and E statesgchanged. The effective magnetic moment3was approximately 1.36 for monoalkoxo complexes and about 1.53 for dialkbxo compounds. In addition to the typical C-O stretch at ~4080 cm“1 and. cation, absorptions in the infrared region, for infra- red vibrations were recorded in the range 650 - 80 cm—l. The M-OR stretch has been assigned and several trends which depend on the nature of the alkoxide, halide, and metal were found. THE PREPARATION AND PROPERTIES OF SOME d1 MOLYBDENUM AND TUNGSTEN COMPOUNDS . BY o A t D. Paul Rillema A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Chemistry 1969 To my wife, Necia ACKNOWLEDGMENT The author wishes to acknowledge the leadership and guidance of Professor Carl H. Brubaker, Jr., who also added inspiration during this investigation. Financial support by the National Science Foundation was deeply appreciated. Gratitude is also extended to Michigan State University for a National Defense Loan. iii II. III. TABLE OF CONTENTS INTRODUCTION . . . . . . . . . . EXPERIMENTAL . . . . . . . . . . Materials . . . . . . . . . . . Analytical Methods . . . . . Apparatus and General Methods of Procedure Preparation of Tungsten(V) Compounds from.W015 froszCle . . . . . . . . . . Preparation of Tungsten(V) Compounds from WBr5 Preparation of Molybdenum(V) Compounds from MoC15 . . . . . . . . . . . . Spectroscopic Measurements . . Magnetic Moments . . . . . . Electron Spin Resonance . . . . RESULTS AND DISCUSSION . . . . . REFERENCES . . . . . . . . . . . iv Attempted Preparation of Tungsten(V) Compounds Page 25 27 28 31 35 107 Table 10. LIST OF TABLES Page Magnetic tensor elements for some molybdate and tungstate complexes . . . . . . . . . . . 3 Infrared absorption frequencies of moxg' with possible assignment . . . . . . . . . . 5 ~Infrared absorption frequencies (cm-1) of M(OR)3C14- ions (with possible assignement) . 59 Infrared absorption frequencies (cm-1) of M(OR)3C14 ions (with possible assignment) . 60 Infrared absorption frequencies (cm-1) of MoCl4 ions and dimeric tungsten species (with possible assignment) . . . . . . . . . 61 Electronic absorptions of compounds . . . . . 81 Maymmic properties of compounds . . . . . . . 84 Magnetic tensor values for tungsten(V) complexes . . . . . . . . . . . . ... . . . . 91 Magnetic tensor values for molybdenum(v) complexes . . . . . . . . . . . . . ,., . . . 99 Isotopic contact term, K, and x, 63, and P for molybdenum (V) in glasses at 780K . . . . 105 Figure 1. 2. 3. LIST OF FIGURES Page Reactions of WC15 in alcohols . . . . . . . . 36 Reactions of MoCl5 in alcohols . . . . . . . 38 Infrared s ectra of: A: "[(C4H9)4N][MO(OC2H5)c15]" B: [ C4H9 4N](MOOC14); c: [ c3H5 4N][w(0c3H5)c15]; D: [ 03H5 4N](WOC14) . . . . . . . . . . . . 39 Infrared spectra of: A: CH3C1 from [(C3H534N](WEOCH3)C15]; B: c3H3c1 from [ c3H5 4N][w 0c3H3)c13] . . . . . . . . . . 43 Infrared spectra: _1A: [(C3H7)4N][W(OgiH5)C15]. (1) 5000 - 650 cm , 2 650 - 80 cm ; B: [(C4H9)4N][W(QC2H5 C15), (1; 5000 -650 cm 2 650 - 80 cm -i c: [(c3H5 4N][w(ocn3) c131. D1 5000 - 650 cm (2)650 - 80 cm 1; [(C2H5)4N][W(n-OC3H7)C15], (1) 5000 - 650 cm 1, 2) 650 - 80 cm . . . . . . . . . . . 46 -1 Infrared spectra: A: [(C3H3)4N][Mo(gcn3)3c14]. (1) 5000 - 650 cm 1 (2 650 - 80 cm 1; B:_[(C H )4N][MO(OC2H5)2C14], (1) 5000 - 650 cm 1, 2 650 - 80 cm‘1; c: [(CH3)4N]{W(OC2H5)2C14] (1) 5000 — 650 cm 1, (2)1650 - 80 cm D: [(CH3)4N][W(QCH3)2C1] (1)5000 - 650 cm 1, (2g65 50 - 80 cm 1; E: [(c3H3)4N][w(oc3H3)3c14], 1 5000 - 650 cm 1 (2 650 - 80 cm 1° F:)[(C3H3)4N][W(OCH3) 2Br4]. (1) 5000 - 650 cm 1 (2 650 - 30 cm . . . . . . . . . . . . . . . 51 Proton nmr spectrum of [W(OCH3)3C13]2 . . . . . 65 Structure proposed for [W(OC2H5)3C13]2 . . . . 65 Electronic spectra of: A: Solution-nitromethane; B: Reflectance-solid; C: Reflectance-mull . . 68 vi LIST OF FIGURES (Continued) Figure 10. 11. 12. 13. 14. 15. 16. Page Electronic spectra of: A: Solution-nitro- methane; B: Reflectance-solid: C: Reflectance-mull . . . . . . . . . . . 72 Electronic spectra of: A: Solution-nitro- methane; B: Reflectance-solid; C: Reflectance-mull . . . . . . . . . . . 77 'Electron 3 in resonance spectra of: A: [(C2H5§4N][W(1-0C3H7)C15] in froxen nitromethane; B: [(C2H5)4N][W(OC2H5)C15] in the powder . . . . . . . . .1. . . . 87 Electron 3 in resonance spectra of: A: [ C2H5§4N][W(OC3H533C14] in the powder; B: [ C2H5 4N][W OC3H5 2Cl4] in frozen nitromethane . . . . . . . . . . . . . Electron spin resonance spectra of [(C2H5)4N][Mo(OC2H5)2Cl41 in: A:The powder: B: Nitromethane solution: C: Frozen nitro- methane solution . - . . . . . . . . . . . 93 Electron spin resonance spectra of [(C3H7)4N](MOOC14) in: A: The powder; B: :Nitromethane solution: C: Frozen nitromethane solution . . . . . . . . . . . 96 Electron 8 in resonance spectra of : A: [ C3H7§4N](M00C14) in CH30H: B: [ c3H5 4N][Mo(OC2H5]2Cl4] in c3H50H . . 102 vii INTRODUCTION The chemistry of molybdenum(v) and tungsten(V) is es- sentially described by their ability to form a metal-oxygen double bond. ~At room temperature the pentahalo salts of of both transition metals react violently with solvents con- taining the OH group and form oxo products. Similar species are obtained by abstraction of oxygen from acetone1I2, di- methylsulfoxidel, dioxane2'3, sulfur dioxide‘, and tetrahydro— furan.2'3 In an extreme case, Kepert and MandyczewSki5 formulated a compound as (Ph3AsCl)+(MoOC14)- rather than the previously reported adduct, MoC15-Ph3AsO. Consequently, the more numerous molybdenum(V) and tungsten(V) complexes contain a metal-oxygen double bond. These complexes generally are of the anionic form, beg- where x = Br, Cl, F, and SCN.4:6 The anionic species is prepared by dissolving the pentahalo compound or reducing some M(VI) product"!8 in strongly acidic HX solutions. These solutions stabilize monomeric Moxg- ions and allow their precipitation with-NH4+, Na+, K+, Rb+, and Cs+ cations. Since these compounds contain one unpaired d electron, properties due to the electron comprise the greatest part of studies which have been made. 2 Gray and Hareg'10 devised a molecular orbital scheme to account for the electronic spectrum of MoOCl§-. The ligand field transitions, B2 -P E and B2 +9 B1, were assigned to bands at 14,050 and 22,500 cm.1 respectively. The three ultraviolet absorptions were considered to be transitions from a w bonding orbital which is largely aesociated with the oxygen atom to either nonbonding or antibonding orbitals essentially d in character. The assignments were: 1. 133 —> 133(1) at 32,260 cm-l, and 33 —> E(II) at 28,010 cm- B3-> E(III) at 40,000 cm-l. These transitions are re- spectively: the e” electron to the nonbonding b2 orbit- al(d ), the er electron to an antibonding e; orbital- XY (dxz or dyz)' and the e” electron to an antibonding orbital, b:(d ). Inherent in the calculation of the x2_y2 energy scheme is the assumption that w bonding occurs be- tween the metal and oxygen but none between the metal and chloride. Neglect of the latters v bonding capability is the reason for the claim of Allen gt_§l.4 that the molecular orbital diagram does not qualitatively explain the electronic spectra of MoOBr:-, WOCl§-, and WOBr§-. Electron spin resonance spectra (esr) of these species were recorded by a number of workers.7‘2° Representative magnetic tensors are given in Table 1. In addition to the hyperfine structure, ligand hyperfine structure is reported for bromidell, chloridezl, fluoridezz, and the nitrogen atom of the thiocyanate ligand.23 .mwsHm> UmumHSUHmo Os "Av wl HI80 m0 muficbm AH ses.H men.“ -«Aenozv 6H“ «66.6“ «66.6“ «66.6“ He use Awne.av eow.H mse.fi TNAAHoon on“ «66.6“ «66.6“ «66.6“ HH am Anee.ev oem.fi one.” Tuxnnmozv m.oA H.oA no.6“ «66.6“ «coo.oe mooe.oA ea o.mm H.ne mm.ee emm.H meem.fi seem.“ -H3HONAemuovosH AA «66.6“ 6H e.ee ovm.a Tannfimozvoosl n.ve n.en e.m« neo.oe noo.oe no.6“ me n.em m.we o.ne eem.fi mum.“ new.” Tammxzonvooza NH «H.6e mm.mm «.me flee.” eem.H new.“ -«Annoozv e.mA 6.6“ p.63 666.6“ eoo.oA «06.6“ e e.om e.ee H.se mem.H mem.fl one.“ -«A3H6002V n.oe. n.ee «66.6“ «66.6“ «60.6“ HH Aomv o.ee s.fie Anem.fiv omo.m mmm.H -«Anumoozv .mom. mm m4 mAmv .fim __m Amv xmamfioo .mOxmamaoo mkummssu use muNOQSHOE 050m How muamfiwdw Homcmugoflumnmmz .H magma 4 Magnetic moments for the molybdenum compounds are very close to spin only values. However, for tungsten complexes considerable spin orbit coupling is indicated by moments which range from 1.35 - 1.55 B.M. Both molybdenum and tungsten compounds obey the Curie-Weiss law with small values of 6.4 In addition to electronic properties, metal-ligand vibrations have also been measured. A. Sabatini and I. Bertinis'34-work is summarized in Table 2. In a complex such as MOX§-, which has C4v symmetry, there should be four A1 and four degenerate E modes which are infrared active. The A1 vibrations include two M-X vibrations, one M-O stretch and one O-M-X, X-M-X deformation. The modes that 'arebasesfor :theE representation are pairs of M-X stretching modes, two pairs of X—M-X bending modes, and a pair of O-M-X bending vibrations. If one adds pyridine or quinoline to an aqueous acid solution of WOClg- or WOBr§-, one precipitates (pyH)(WOX4) or (qH)(WOX4) respectively,25:26 where py = pyridine and q - quinoline. The molybdenum analogues are prepared in liquid sulfur dioxide which contains the appropriate cationic halide. Molybdenum pentachloride is presumably first solvolyzed to give MoOCl3 which then picks up halide ion4 to give MoOC1;. Magnetic and electronic properties are similar to the moxi' species. Electron spin resonance properties remain uninvestigated. .pmoun .Q numpasosm .nm «>HO> .> nxmo3 .3SnEdfipoE .E nmconum .mm r68 0.: m mom Moon on: mE 0mm .mop Hulzrao E vw .Hum H012 Q.m won Hmlzuum E mHH .uum Hmlz m CNN .wop Honzrau 3E va .uum Hon: 3 man HmIZTHm 3 mes .Hum 0T2 m> com .wop HUTSTHU mE eta .Hum 0:2 m> 5mm Aeumozv «no 13005 «no Moon 012 E mma xoou 012 E van .moo Hmnzlnm 3 mam xoou on: 3E mom .Hum Hon: am can .mmp Hmnzrum 3 man .Hum Hmnz n.m> ova .mmp HOIZTHO E mm. .Hum HUI: m mam .moo umlztum 3 mmfi .uum 0:: m> wvm .mop Hunzrao E wbu .uum 0:: m> «mm Annmoozvumo Anauoozvano m.uE0EEmHmmm wanflmmom zufl3 Imxoz mo mowuamsvmum coflumuomnm oOHmHMEH .N manna 6 Even more stringent conditions are required in systems where formation of oxo complexes is to be avoided. Strictly anhydrous conditions are employed. Hexahalo compounds are prepared by various procedures. The tetraethylammonium salt of hexachloromolybdate(v) is prepared by the reaction of MoC15 and [(C2H5)4N]Cl in methylene chloride.27 A similar procedure produced [(C2H5)4N](WBr3) fromWBr5 and [(C2H5)4N]Br in chloroform.28 The compound formed by reduction of-WC13 in thionyl chloride was WC13—. It was precipitated with tetraethylammonium ion.29o30 Brisdon §£_§l.27 assigned values of 10 Dq for 1, WCl; at 23,300 cm—l, and.WBr; at noel; at 21,700 cm‘ 18,900 cm-l. In addition Dowsing and Gibson17 report that [(C2H5)4N](M0C13) gives a room temperature electron spin resonance spectrum with gli = 1.977 and gi = 1.935. It was argued that considerable distortion of the lattice took place because Jahn-Teller distortion is too small to account for a signal under those temperature conditions. The compound, [(C3H5)4N](WC13), exhibits antiferro- magnetism and has a room temperature magnetic moment of approximately 0.8 B.M.29 The magnetic moment of [(C3H5)4N](WBr3) is reported as 1.28 B.M.28 A final property of concern is a tungsten-chloride stretch assigned at 305 cm-1.3° A different non oxo system investigated by several authors involved reactions of MX5 compounds with amines. Reduction of molybdenum pentachloride in primary and secondary 7 amines_yielded complexes of the type Mx4-L2 whereas ad- ducts, st-L, formed with tertiary amines.31 In contrast to molybdenum, both tungsten pentachloride and pentabromide reacted with primary amines to give WX2(NHR)3 products. However, reduction products were produced with secondary and tertiary amines.32 Pyridine and acetonitrile cause reduction of both (molybdenum and tungsten pentachloridesfimi'35 Brown and Ruble36 synthesized compounds by the reaction of MoCl5, WCl5, and WBr5 with 2,4,6-trimethylpyridine and benzo— nitrile in methylene chloride. Based on conductance data the compounds were formulated as (MX4L2)X. A similar form- ulation was given by Boorman §E_§l.37 for compounds WClspyz, WClabipy and WClsdiphos which were prepared by reaction of WC13 with the appropriate ligand in benzene or carbon tetrachloride. The abbreviations: py = pyridine: bipy = 2,2'-bipyridy1; and diphos = 1,2-bis(diphenylphospino)- *ethane. 7 Magnetic moments are lower for amine substituted com- pounds than spin only values; yet moments are similar to values reported for other Mo(V) and W(V) compounds.38 Only for WX2(NHR)3 compounds were magnetic moments so low (“eff = 0.3 B.M.) that bridging between chloride ligands was proposed. In this case, bridging was further.substanti- ated by molecular weight data. The absorption coefficients (~200.M:1cm_1) for (MX4L2)X compounds were higher than normal for d—d 8 transitions. The bands, however, did occur in the visible region which is normally associated with these types of transitions. It is unfortunate that electron spin resonance parameters have not been determined because the data would aid the understanding of the bonding and the stereochemistry of the complexes. The final molybdenum(v) and tungsten(V) complexes re- ceiving attention were complexes which contain alkoxide as ligand. Klejnot39 examined the reduction of WC16 in methanol and ethanol. He isolated two products, a blue compound, W(OR)3C13, and a red product, W3(OR)3C14, R = CH3 and C3H5. Nuclear magnetic resonance evidence and dipole data led to the prediction of chloride bridging in the di- meric compounds. Funk and coworkers“°"‘*2 found that molybdenum penta— chloride and tungsten pentachloride behaved similarly in methanol solutions. At low temperature and with continual cooling, the adduct, MCl3(OCH3)3-3CH3OH, was isolated. Ad- dition of pyridinium chloride to a methanol solution of the adduct or pyridine to a reaction solution of .MCl5 in methanol precipitated (pyH)[M(OCH3)2Cl4]. Solutions which were made basic with pyridine yielded dimeric products [M(OCH3)3C13]2 and [M(OCH3)4Cl]3. -Although concentrated solutions of the tetrachloroalkoxotungstate(V) anion were stable at room temperature, similar solutions of molybdenum rapidly formed oxo compounds. Some compounds isolated were ‘MoO(OCH3)3°%CH3OH, Mooc13-ZCH3OH, and (pyH)(MoOCl4'CH30H). 9 The pyridinium salt of pentachloroxotungstate(v) could be isolated by boiling a reaction solution of WCl5 in methanol until a clear green solution was obtained. Addition of pyridinium chloride and cooling caused (pyH)2(WOC15) to separate. Funk and Schauer43 described the alcoholysis of WBr5 and its reactions with phenols to give W(OR)3Br3 and W(OR)3Br3-ROH and with aldehydes to give WBr2(OH)3-aldehyde. They reported that WBr5 gives permanent deep red methanol solutions at low temperature. However, at room temperature, the red solution becomes yellow, then green, and finally blue. No compound was isolated from these solutions. The only characterizations of the tungsten complexes were given for (pyH)[W(OCH3)3Cl4] and (pyH)3(WOC15). Magnetic moments were reported as 1.48 and 1.52 B.M. re- spectively. A C-O stretch for the former was reported 1 at 1060 cm_ and pyridinium infrared structure was noted for each compound, .Due to the incompleteness of the work, McClung gt_al.44 synthesized four compounds, (pyH)[Mo(OCH3)2Cl4], i (qH) [Mo(ocn3 )3c14] , [(CH3 )4N] [Mo(OCH3 )3c14] , and (pyH)[Mo(OC3H5)3Cl4]. The general procedure for the prep- aration of the methoxide compounds involved slow addition of methanol to the solid molybdenum pentachloride which was contained in a closed flask at -78°. The desired cation was dissolved in methanol and the solution added slowly to precipitate the tetrachloromethoxomolybdate(V) anion. The ethoxide analogue was prepared by alkoxide exchange of (PYH)[MO(OCH3)2C14] in ethanol. 10 Properties of the complexes were more thoroughly in— vestigated. Magnetic moments were near spin only values. Electron spin resonance spectra indicated axial symmetry. A typical example of 9" and 91' values along with measured hyperfine values is given in Table 1. The authors concluded trans stereochemistry predominated. Consequently, the complex belongs to the point group, D4h. On this basis electronic transitions were assigned. These were a B2 —+ E at 14,000 cm.1 and Ba -9 B1 at 23,000 cm—l. The Ba -# A1 transition was masked by the charge transfer band. -Mc- Clung's45 conclusion was that the alkoxides had properties very similar to pentachloroxomolybdate(V) compounds. Several problems remained unresolved. McClung45 re- ported that a more complicated process existed with the solvent, ethanol. If ethanol were substituted for methanol under similar preparative conditions of Mo(OCH3)2Cl;, he obtained a mixture of products which he was unable to re- solve. The preference of trans_stereoisomerization rather than.gg§_was still not obvious. Bradley46 had found that the‘gig isomer was formed for transition metal alkoxides in their maximum oxidation state. The measurement of metal—ligand vibrations would offer a clue to the formation of the favored species with a metal- oxygen double bond. The effective charge on the metal atom is related to the electron density which is in turn related to the energy of a vibration. Thus, it may be that the lower the effective charge on the metal ion, the more stable the species. 11 There is other information which can be gained from a metal-ligand vibration study. Chloride bridging was proposed for [Nb(0R)c13]2 by Wentworth47 and [w(0R)3c13]2 by Klejnot.39 Bridging vibrations occur «60cm.1 below termi- nal vibrations. Thus, a vibration study should distinguish between bridging chloride or alkoxide. In complexes as M(OR)nC16_n, it would seem possible to vary n from zero to six. One might synthesize complexes with n < 2 in acidic solutions. Basic solutions produced dimers but no studies were reported where complexes with n > 2 had been isolated. Complexes where n varied from zero to six would not only be synthetically desirable, but also theoretically informative. The properties would un- fold trends in electronic transitions, magnetic moments, and magnetic tensor parameters for various ligand field symmetries. These would then produce a basis for predicting properties of other uncharacterized systems. An additional high light would be the production of a molecular orbital diagram which would have some general application for transition metal complexes. The initial transition metal ion chosen for study was tungsten(V). Tungsten pentachloride is more basic than molybdenum pentachloride, is stable to oxygen abstraction in methanol, and is a congener of molybdenum. Thus, its chemistry would also offer insight into the molybdenum sys- tem. Furthermore, additional characterization of known tungsten alkoxide complexes still remained necessary. EXPERIMENTAL Materials Tungsten Pentachloride: — Tungsten pentachloride was pre- pared by the method of G. E. Novikov, N. V. Andeeva, and O. G. Polyachenok.48 Climaerolybdenum's tungsten hexa- chloride was purified by sublimation before it was treated with red phosphorus.. The tungsten pentachloride that formed was sublimed to insure its purity. ‘gungsten Pentabromide: - Tungsten pentabromide was obtained from Alfa Inorganics. Inc. The compound was used without further purification. Molybdenum Pentachloride: - Commerical molybdenum penta— chloride was fractionally sublimed to remove impurities.49 Two sublimations were usually required. Solvents: - Methanol was dried by distillation in the presence of magnesium. The magnesium was activated with iodine according to the prescription of Lund and Bjerrium.5° Absolute ethanol was dried by distillation in the presence of sodium ethoxide and diethylphthalate; Efpropanol was dried by distillation in the presence of sodium propoxide. 12 13 .Nitromethane was dried by distillation in the presence of Drierite. The distillate was then passed over a Dowex 50W-X8 resin to remove basic impurities.51 Thionyl chloride was reagent grade. Ethyl ether was stored over sodium. chloroform and methylene chloride were dried by distillation in the presence of phosphorus pentoxide. Tetraalkylammonium Salts: - All substituted ammonium salts were Eastman Organic Chemicals' White Label grade. Water was removed by recrystallization of the salt from an acetone- methanol mixture and/or dried in an oven at 100°. Nitrogen, Hydrogen Bromide, and Hydrogen Chloride: — Liquid Carbonic's oil pumped, prepurified nitrogen was passed over copper turnings at 6000 and BTS catalyst to remove oxygen impurities. The nitrogen was then passed through drying towers of calcium chloride and Drierite for removal of water. Anhydrous HCl and HBr were used directly from the cylinder. Analytical Methods Preparation of Compounds for Analyses: - A weighed portion of a compound was dissolved in an ammonium hydroxide-hydro- gen peroxide solution. Excess hydrogen peroxide was destroyed by boiling. The solution was cooled and diluted in a volumetric flask. .1: Tungsten52 or Molybdenum53 Analysis: - An aliquot of the solution of molybdate or tungstate was diluted and about a ten fold excess of a solution of 49 of 8-hydroxyquinoline in 100 ml of absolute ethanol was added. The solution was heated to boiling and then acidified with glacial acetic acid. A yellow precipitate formed, was filtered, washed with a little hot water, and dried in the oven at 110°. The precipitate was weighed as M02(C9H60H)2. Bromide or Chloride Analysis: - An aliquot of the solution for halide analysis was diluted and acidified with sulfuric acid. The halide content was determined by potentiometric titration with a 0.1 M_silver nitrate solution. The Beck- man-Model G pH meter served as the potentiometer, silver- silver chloride as the electrodes, and a 0.1 M NaCl solution as the primary standard. Alkoxide Analysis: — A weighed quantity of compound was added to a dichromate solution which was acidified with sulfuric acid. Simultaneous precipitation of tungstic acid occurred with oxidation of M(V) to M(VI) and oxidation of the alcohol. Excess dichromate was treated with KI and the iodine liberated was determined with thiosulfate.54 Diffi— culties arose in the treatment of all tetraalkylammonium salts except those with the tetramethylammonium ion. The other cations precipitated some dichromate and some pre— cipitated iodide. 15 CarbonLygydrogen and Nitrogen Analyses: - Spang Microana- lytical Laboratory, Ann Arbor, Michigan,performed these analyses. Apparatus and General Methods of Procedure Reaction vessels, storage tubes, and fritted discs for filtering were all glass with stopcocks and ground glass joints. The former allowed control of the ;inert atmosphere, nitrogen, and the latter insured a closed system. Glass— ware was cleaned in an alkali bath, washed, dried in an oven at 110°, evacuated while it was cooling, and filled with nitrogen. When vessels were opened, nitrogen was rapidly forced through the stopcock to keep atmospheric air from entering. This general procedure allows more manipulating freedom than can be obtained in a dry box. The dry box was used primarily for pulverizing, storing and weighing start- ing materials. -Most solvents were continually allowed to reflux under nitrogen and were distilled in approximately 150 ml quantities. A Soxhlet extractor was converted to a collection vessel by sealing a 120°, three way stopcock in place of the siphon tube. A 24/40 ground glass joint was sealed to the third end of the stopcock. Thus, dry solvent was readily avail— able, easily collected, and delivered without contact With air. An aliquot of dry solvent was then removed from the collection flask with a dry pipet of the"desired quantity. Nitrogen was rapidly forced through the flask as the sample was withdrawn. 16 Filtrations were effected by suction. E23129; B, B is a tetraalkylammonium cation, for example + [(CH:)4N] . R, R is an alkyl group, for example CH3. Preparation of Tungsten(V) Compounds from‘WCl5 I. The Tetraalkylammonium hexachlorotungstates(v), B(WC16): Twenty ml of ROH was presaturated with HCl at 0°. This solution and 5.49 (0.015 mole) of tungsten pentachloride were cooled to -78° before mixing. AA green-black suspension formed which turned yellow-brown upon warming to 0°. Addi- tion of a solution of 0.015 mole BCl in 20 ml of ROH pre- cipitated a green compound. The compound was washed with a 5:1 ethyl ether-ethanol solution, then ethyl ether and was dried under vacuum. a. B = (C2H5)4N+: R = c3H3. The chloride analysis was approximately 1% low and the infrared spectrum showed a small C—O stretch, suggesting the presence of alkoxide. The compound was purified by re- crystallization and possible alkoxide replacement by chlor- ide ion in thionyl chloride. Analysis: Calculated for [(C2H5)4N)](WC16): W}.34.9033CI, 40.38; C, 18.247VH,.3.83; N, 2.66. Found: W, 34.78; C1, 39.94; C, 18.49; H, 4.02; N. 2.72. 17 The preceding process applies with the following: For B = (C3H7)4N+ and (C4H3)4N+ a green pre- cipitate was obtained but not characterized. If methanol or 1—propanol was used as the solvent, a similar green precipitate formed. ’11. The Tetraalkylammonium pentachloroalkoxotungstates(V). B[W(OR)C15]: a. Procedure I was followed through the precipitation of the tetraalkylammonium hexachlorotungstate(v) complex. Considerable heat was evolved when HCl was bubbled through the suspension and it was con- verted into a yellow compound. The compound was washed with a 5:1 ethyl ether-alcohol solution and then ethyl ether and was dried under vacuum. Procedure I was followed through the warming of the solution to 0°. If the solution is further warmed to room temperature and stirred approximately for 45 minutes, the color changes to a very light green. Addition of the cation dissolved in the appropriate solvent caused precipitation of the yellow compound, B[W(OR)C15]. Washing and drying instructions are given in part a. 1. B = (C2H5)4N+; R = CH3. Analysis: Calculated for [(C2H5)4N][W(OCH3)C15]: W, 35.19; Cl, 33.93. ‘Found: W, 35.35: Cl, 33.49. The compound decomposed too.rapidly to “18 obtain commerical C, H, and N analyses. 2. B = (C2H5)4N+; R = C3H5. Analysis: Calculated for [(C2H5)4N](W(OC2H5)C15]: W, 34.27: Cl, 33.06: OC3H5, 8.40; C, 22.39: H, 4.70: N, 2.61. Found: W, 33.99: Cl, 32.93: OC2H5, 8.04; C, 22.15; H, 4.84; N, 2.67. 3. B = (C3H5)4N+: R = C3H7. This compound was obtained only by method IIb. Analysis: Calculated for [(C3H5)4N][W(n-OC3H7)C15]: W, 33.45: Cl, 32.18. Found: W, 33.21, Cl, 32.11. 4. B = (C3H7)4N+; R = C3H3. Analysis: Calculated for [(C3H7)4N][W(OC3H5)C15]: W, 31.03: Cl, 29.92; C, 28.38: H, 5.61;.N, 2.36. Found: W, 30.72; Cl, 29.92; C, 28.15; H, 5.71; N, 2.36. 5. B = (C4H9)4N+; R = C3H5. Analysis: Calculated for [(C4H9)4N][W(OC2H5)C15]: W, 28.34; Cl, 27.33; C, 33.33; H, 6.37; N, 2.16. Found: W, 28.17; Cl, 27.76; C, 33.30: H, 6.45; N, 2.13. III. The Tetraalkylammonium tetrachloroxotungstates(V), B(WOC14): The tetraalkylammonium salt of pentachloroalkoxotung- state(V)Found: W, 22.71; Br, 59.78. II. Tetraethylammonium tetrabromodimethoxotungstate(V), [(c3H5 )4N] [W(OCH3 )2Br4] : Ten grams of [(C3H5)4N](WBr6) was added to 25 ml of methanol. The suspension was gradually heated until the precipitate changed color from black to yellow—green. The precipitate was washed with a 5:1 ether to methanol solution and then with ethyl ether, and was dried under vacuum. Analysis: Calculated for [(C2H5)4N][W(OCH3)3Br4]: W, 26.42; C1, 4594; C, 17.26; H, 3.77; N, 2.01. Found: W, 25.91; Cl, 46.21; C, 17.17; H, 3.61; N, 2.06. 25 Preparation of Molybdenum(V) Compounds from MoC15 I. Tetraethylammonium tetrachlorodimethoxomolybdate(V), [(C2H5)4N][Mo(OCH3)2Cl4]: A 4.49 (0.015 mole) portion of MoC15 was added to a 20 ml methanol solution (-78°) which had been presaturated with HCl at 0°. A 2.59 sample of [(C2H5)4N]Cl which was dissolved in 20 ml of methanol was added to the above solu- tion. As the solution warmed, the brown-orange suspension changed color to yellow. The precipitate was immediately filtered and was washed with a 5:1 ether to ethanol solu— tion and then dried under vacuum. The compound was photo- sensitive and became brown after several days exposure to light. Infrared evidence points to methanol as one of the degradation products. Analysis: Calculated for [(C2H5)4N](Mo(OCH3)2Cl4]: Mo, 22.30: c1, 32.97: Found: Mo, 22.04; Cl, 33.34. II. Tetraethylammonium.tetrachlorodiethoxomolybdate(V), [(C2H5)4N][Mo(OC3H5)2Cl4]: ‘ A 4.49 (0.015 mole) sample of MoC15 was added to a solution (-78°) of 20 ml of ethanol which was presaturated with HCl at 25°. The solution was allowed to warm to 0°. A solution of 2.59 tetraethylammonium chloride in 20 ml of ethanol was added to it. A yellow-green precipitate was obtained, washed with a 5:1 ether to ethanol solution and then with ether, and was dried under vacuum. -The compound was photosensitive and became brown after several days ;26 exposure to light. -Infrared evidence points to ethanol as one of the degradation products. Analysis: Calculated for [(C2H5)4N][Mo(OC2H5)2Cl4]: Mo, 20.94; Cl, 30.95. Found: Mo, 21.12; Cl, 31.32. III. The Tetraalkylammonium tetrachloroxomolybdates(V), B(MoOCl4): ' A 4.49 (0.015 mole) sample of MoC15 was added to a solution (-78°) of 20 ml of ethanol which was presaturated with HCl at 0°. A solution of 0.015 mole tetraalkylammonium Chloride in 20 ml ethanol was slowly added. -A brown—orange precipitate formed. It wasfiltered, washed with ethyl ether and dried under vacuum. All manipulations were car— ried out at -78°. The compound was maintained under a vacuum and was then allowed to warm to room temperature. The initial compound Changed color from brown-orange to light green. a. B = (C3H7)4N+ Analysis: Calculated for [(C3H7)4N](MoOCl4): Mo, 21.80; C., 32.22; C, 32.75; H, 6.56; N, 3.18. Found: Mo, 21.48: Cl, 32.38; C, 32.38: H, 6.70; N, 3.08. b. B = (C4H9)4N+ Analysis: Calculated for [(C4H9)4N](M00C14): Mo, 19.33: c1, 28.58: c, 38.73;.H, 7.31; N, 2.82. Found: .Mo, 19.47: Cl, 28.83; C, 38.45;.H, 7.26; N, 2.72. 27 Spectroscopic Measurements Optical Spectra: — Molecular vibrations were recorded in the infrared and far infrared regions. The former were ob— tained by means of a Unicam SP-200 instrument and the latter with a Perkin—Elmer 301 spectrophotometer. All spectra were determined in Nujol mulls. Sodium chloride plates were used from 5000 cm.1 to 650 cm-1, CsBr plates from 650 cm-1 to 320 cm-1, and polyethylene disks from 320 cm.1 to 80 cm’l. The low solubility and instability preclude a far infrared study in solution. -Electronic absorption spectra of solutions were deter— mined with a Cary Model 14 and Unicam SP-800 spectrophotom- eter. :Solution spectra were obtained by use of nitromethane, methylene chloride, and acidic alcohol solutions as solvents. Band positions in solutions were compared to those obtained from the solids whose spectra were recorded on the Cary Model 14 instrument and on a Bausch and Lomb Spectronic 600 with a reflectance attachment. The former instrument re- quired the use of Nujol mulls which were squashed between glass plates. In order to obtain spectra on the latter machine, an air tight tube with a special flat-windowed adapter was constructed. Nuclear Magnetic Resonance Spectra: - Nuclear magnetic resonance (nmr) spectra were recorded with a Varian A-60 spectrophotometer. 28 Electron Spin-Resonancegpectra: — X-Band esr spectra were recorded at 298° and 78°K with a Varian V-4502-04 spectro- photometer. First derivative absorptions were recorded on an X—Y recorder with the X—axis proportional to the magnetic field strength. A Hall probe was used as field sensor. Markings, which were placed on recorded spectra by means of a Hewlett—Packard 524C frequency counter, allowed calibra- tion of the magnetic field. These‘data enable calculation of hyperfine splittings. ‘The 9 values were calculated from the measured magnetic field and the Klystron frequency. .Magnetic Moment Measurements: - The Sony method was used to measure magnetic wsusceptibilities. Apparatus and techniques similar to those of Vander Vennen55 were used for low tem- perature work. MagnetiC,Moments Calculations were made by a comparative method. The equation used to determine the susceptibility was: 106x=a+7p . W The volume constant, a, was zero because the tube was filled with nitrogen rather than air. Thus, the equation reduced to: W In this equation, y equals the tube calibration constant, w is the weight of the sample, and F' is the force on the 29 sample, iyg, F' = (F - 6) where F is the measured force on the specimen and O is the measured force on the tube. The tube constant, y, was found by use of a known substance, CuSO4°5H20, which has a susceptibility of 5.92 x 10.6 c.g.s units at 25°. The molar magnetic susceptibility, Xm' was then found by multiplying by the molecular weight of the Specimen. Xm must be corrected for the diamagnetism of the ligands and cation. These were obtained from Pascal's constants,55 which are additive entities. The new value, X; , is the susceptibility of the metal ion. A plot of 1/Xg versus T gives a straight line whose intercept on the 'T axis is, 9 , the Weiss constant. Xm = T + e C is the slope and T is the absolute temperature in the equation. The value of X; is proportional to the square of the effective magnetic moment. '1/2 N~ l 1 (3k )- H (Xm T) /2 B.MJ 2.84 (Xn'n T)1/2 B.M. ueff N is Avogadro's number, B is the Bohr magneton, and k is Boltzman's constant. The moment can also be derived quantum-mechanically. neff = g [J(J + 1)]1/2 30. The Lande splitting factor, 9 , is a function of the amount of orbital and spin angular momentum which a state possesses. _ [SS+1)-LL+1)+JJ+1)] 9 ‘ 1 + ( 2JIJ + I7 i The sum of the spin quantum numbers is denoted by S: the quantum number, L, is obtained by adding the m1 values of all electrons in incomplete subshells: J is found by: IL + SI, IL + S - 1I, ----- , IL - SI. The quantum number, J, describes the total angular momentum of the system. The condition of L equal to zero gives rise to mo- ments with "spin only" values. The equation becomes: ”eff = 2[s(s + 1)]1/2. Two basic conditions give rise to quenching of orbital angular momentum (L = 0). It may be quenched by the ligand field or by an electron with the same spin as the electron in the other degenerate orbital. However, the degeneracy of the d orbitals may not be completely removed by the ligand field. ~For example, in an octahedral field, two de- denerate sets remain, the eg and tZg' The eg set can not give rise to orbital angular momentum since no rotation can turn the dz? into the dx2_y2 orbital. However, for the t set, rotation about the Z-axis turns dxz into 39 dyz or rotation about the X— or Y—axis turns the dxy orbital into the dxz and dyz: respectively. Thus, there is spin orbit coupling associated with the t29 set. ,31 Figgis57 has reported methods by which it is possible to compare results of measured magnetic susceptibilities over a wide temperature range with theory. His method ap— plies to complexes in which the t29 term has been removed by a ligand field component of axial symmetry or spin orbit coupling. Figgis defines (A as the separation of the t29 set into an orbital singlet and doublet by an axial ligand component. A is positive if the orbital singlet lies lowest. Another term, v , is defined as A/A where A is the spin orbit coupling constant. -Plots of ”eff ‘ys, kT/A are presented for assumed values of v and k. :The quantity, k , is the spin delocalization factor. Thus, a proper fit of an experimental curve over a wide temperature range to a theoretical curve leads to values of A, A, v, and k. The method works best for the intermediate dependence of ”eff on the temperature. Too little or too great a dependence creates ambiguity and allows only qualitative predictions. 6§1ectron SpinResonance The degeneracy of an electron spin state in the simplest case, (m8 = 1 1/2) can be removed by the appli- cation of a magnetic field. (A transition occurs from m8 = -1/2 to m5 = + 1/2 upon absorption of microwave radiation. The energy of the transition is given by: where h is Plank's constant, v the radiation frequency, 5 32 the Bohr magenton, g the spectroscopic splitting factor, and EH0 the field strength. The interaction between the electron spin and nuclear spin of a metal atom results in the splitting of the single absorption into 21 + 1 components, where ~I is the nu— clear spin of the central metal atom. There are as many hyperfine splittings as there are allowed orientations of the magnetic moments of the nucleus, mI = (-I, —I + 1, ----- , I — 1, I). The energy due to interaction of the nuclear magnetic moment with the electron magnetic moment for the hydrogen atom is given by: E(mSmI) = gfiHo + amsmI. The hyperfine coupling constant is a. The preceding phenomena become modified in transition metal complexes. The free ion now is surrounded by a ligand environment which exerts a strong electrical field on the unpaired electron. »An understanding of paramagnetic reso- nance spectra of complex ions is made possible through the ligand field concept and group theoretical properties. The ligand field gives rise to various possible symmetries which may be either isotropic or anisotropic. The degree of elec- 'tron interaction with the external magnetic field will vary with the orientation of the complex. This effect gives rise to more than one 9 value. The spin Hamiltonian which ac- counts for an electron spin resonance spectrum of a compound with axial symmetry in a liquid glass is:58 33. H = gllsnzsz +-gls(nxsX + HySy) + ASZIz + 13(stx + Sny) Where 5 = 1/2, 1(95Mo, 15.8%: 97M0, 9.6%) = 5/2, 1(133w, 14.2%) = 1/2. -At room temperature the anisotropies add to zero and the Hamiltonian becomes: H <9> = 1/3 (A +, 213) <9) BH-S + I'S 1/3 (gII + QJ) The eigenvalues which lead to correction of hv = gBHo are:59 for isotropic g _ a 2 , _ 2 HO — Hm + (a) mI + ZHm [1(1 + 1) mI ] for gII -2 _ 2 Ho=H +Am +B [1(I+1) “‘11 m I '2H ‘44___ m for 9i (A2 +'B2) 2 =- + + . + — H0 Hm BmI ‘ 4 H [1(1 1) m1 ] where Hm is the magnetic field position of the esr line due to the component m of the nuclear spin I,'v is the I klystron frequency, and TA and B are the nuclear hyper- fine splitting constants. These corrections were reitera- tive and were performed with a program designed for this purpose and were carried out on the M.S.U. Control Data 34 3600 computer. Five iterations were carried through. The program also contained a plot routine. The simulated spectrum was changed by altering magnetic tensor values until a match was obtained between the computed and experi- mental spectra. The program was written by T..Krigas and P. T. »Manoharan. RESULTS AND DISCUSSION The reactions of WCl5 in the alcohols which were stud- ied are summarized in Figure 1. Tungsten pentachloride reacted with alkoxide ion in neutral alcohol solutions and produced a mixture of W(OR)Cl; and W(OR)2C1;. By evaporation of the solution to dryness, dimeric Com— pounds, [W(OR)3013]3, were isolated, whereas both anions were precipitated upon the addition of a tetraalkylammonium cation, B+. The mixture could be converted into a single component, B[W(OR)3C14], by stirring a suspension of the precipitate in ROH for a long time. Solutions were made basic with 1R0- by reaction of metallic lithium or sodium with the appropriate alcohol. At ratios of 2:1 R0- to WC15, W(OR)2C1; complexes were precipitated. .Dimers°° formed at ratios greater than 2:1. > If an equilibrium process such as 2 W(OR)3Cl; <_____ [W(OR)3C13]2 + 2Cl- were involved in basic alkoxide solu- tion, one might expect to precipitate B[W(OR)3C13]. How- ever, addition of tetraalkylammonium chloride produced no precipitate. Tungsten pentachloride reacted with alkoxide and/or chloride ion in acidic HCl alcohol solutions. The compound, [(CH3)4N]2[W(OC2H5)C16], formed with the (CH3)4N+ cation. 35 HeHONAnmaooVSLHZeAREOVL HeHONAnmaooVRLHZeAAENOVL omN monmuo Hnaoflnmaoovz_flzeAamaova + HaHONAnmaooV3__z«AamaoVL m0nmao .HOHZvAnmaoVL x//// no ...t: . ,\ HaHoAnmaoovsLHZenamoVL + HeaoaflnmaoovsLHZvAnEUVL “shoonHzeAAEROVL Hum! Hasoflmovs__zeAnmaovuA .waonooam EH naoz mo mcoauomom «HaHoaAmoVSL .H mudmflm HeaoaAmoVSLLZVAamova g! mmmchuo on have 0» oumuomm>m MOHA Hum v . have con .Ho_z«AAEOVL Hum oo naoz on v n « Hofiz A m ova mqu Hum A HUHZeAamoVL e 1 AaaonHZVAAEROVL 13283322 emu: a_aaoaflamoovs_ aflaoefiamoov3L 37 Larger tetraalkylammonium catflzs precipitated WClg. Heat- ing the reaction suspension transformed B(WC13) into B[W(OR)(215]. This product lost alkyl halide and formed B(WOC14 ) . In contrast to B(WC13), heating a reaction suspension of B(WBr3) in alcohol resulted in the formation of B[W(OR)zBr4]. The B(WBr6) compound was prepared from the reaction of; WBr5. in acidic HBr solutions. The loss of alkyl halide from [(C2H5)4N][W(OC2H5)C15] prompted further investigations in molybdenum pentachloride Chemistry. .Figure 2 summarizes the results. A modified preparation of Mo(OCH3)2Cl: was used and a direct prepara- tion of Mo(OC2H5)3Cl; was found. rFurthermore, an attempt was made to prepare the analogous molybdenum monoalkoxide complex. Two compounds, which were prepared and isolated at -78°, changed color from brown-orange to green and evolved ethyl chloride at room temperature. The green end products were [(C4H9)4N](MoOCl4) and [(C3H7)4N](MoOCl4). Thus, the elimination of alkyl halide also occurred with Mo(OC2H5)Cl;, but in contrast to the tungsten monoalkoxide complexes, the molybdenum complexes evolved the alkyl halide rapidly. The alkyl halide evolution was demonstrated by infrared spectroscopy. Figure 3A illustrates that the molybdenum monoalkoxide species had a C-O absorption at 1020 cm-1 and Figure 3B shows that the green product had a molybdenum- oxygen double bond stretch at 990 cm-1. Similarly, "[(C4H9)4N](Mo(OC2H5)Cl5]" J I MoCl5 J I HCl at 0° -780 HCl at 0° -780 HCl at 25° 00 [(C2H5)4N][Mo(OC2H5)3Cl4) Figure 2. 38/ ‘C2H5C1 > > [(C4H9)4N](MOOC14) [(C2H5)4N][MO(OCH3)2C14] Reactions of MoC15 in alcohols 39 Figure 3: Infrared spectra A: “[(C4H9)4N][Mo(OC2H5)C15]" B: [(C4H9)4N](MOOC14) c: [(C2H5)4N][W(OC2H5)C15] D: [(C2H5)4N](WOC14) 4O I I I I I I 1800 1600 1400 1200 1000 800 wavenumber I I I' I I I 1800 1600' 1400 1200 1000 800 wavenumber Figure 3. 41 C I IU I ! I I I I l 4000 3000 2000 1800 1600 1400 1200 1000 800 wavenumber D I III I l I I I J I 4000 3000 2000 1800 1600 1400 1200 1000 800 wavenumber Figure 3. 42 Figures 3C and 3D demonstrate that the original C-O stretch at 1029 cm.1 was lost and a tungsten-oxygen double bond stretch appeared at 990 cm.1 after alkyl halide evolu- tion from B[w(oc3H3)c15] . In the decomposition of [(C3H5)4N][W(OCH3)C15], the vapors released were collected in a vacuum trap. The identity of methyl chloride obtained in the gases was veri- fied by vapor pressure measurements on the trapped liquids. The infrared spectra of methyl chloride and ethyl chloride, which were obtained by the elimination reaction, are given in Figure 4A and 4B respectively. These compare well with known spectra except additional absorptions are located at 1150 cm"1 and 2380 cm-1. The one at 2380 cm-1 is a C13 absorption: the other's identity is unknown. Presence of HCl is also probable since a solution of the trapped materials in water was acidic and formed a white precipitate upon the addition of AgNO3. The relative heterogeneous rates of alkyl Chloride evolution were determined qualitatively by use of a constant volume Warburg apparatus. With tetraethylammonium as the cation, the appearance rate of alkyl chloride was CH3C1 > C3H5Cl > C3H7Cl. The rate of ethyl chloride evolution was found to decrease as the cation increased in size, thus, tetraethyl > tetrapropyl > tetrabutyl. Under constant volume conditions, the reaction yields about one mole RC1 per mole of reactant. However, the solid which was under continuous vacuum lost more weight 43 Figure 4: Infrared spectra 'A: CH3Cl from [(C2H5)4N][W(OCH3)C15] B: C3H5Cl from [(C2H5)4N][W(OC2H5)C15] 44 .v— A W I I I I I l I I I 4000 3000 '2000 1800 1600 1400 1200 1000 800 wavenumber -_L III I L J J I I I‘I I I 4000 3000 2000. 1800 1600 1400 1200 1000 800 wavenumber Figure 4. 45 than necessary to produce one mole of RC1. Quantitative rate features of weight loss experiments were similar to constant volume results except the rate of decomposition of the alkoxocomplexes appeared to be tetraethyl > tetrabutyl > tetrapropyl. The complications of excess weight loss were due to evolution of other gases. Thus, the solid product which remained was not pure, and the impurities could not be removed. The results of infrared studies permit speculation into the nature of the processes which take place in alkyl halide elimination and will be considered after some remarks about spectra are made. In a complex, such as W(OCH3)C1; which has C4v sym- metry, there should be 4A1 and 4E modes as described in the introduction. In addition, ligand and cation vibra- tions were investigated. The C-O stretch (~1030 cm-l) occurred in a region characteristic of bound alkoxide groups.°1 The C-H vibrations were masked by Nujol. There were no O-H bands at 3600 cm-1. Thus, alcoholates or hydrolysis products were discounted. The spectra illus- trate these facts in Figure 5. The infrared spectra of dialkoxide complexes are shown in Figure 6. There were vibrations of the cation and the typical C-O stretch of the alkoxide ligand at ~4060 cm-1 and ~4100 cm—l. However, the framework vibrations were dif- ferent than for monoalkoxide complexes because the symmetry of the complex changed. The dialkoxide complexes have axial 46 Figure 5: Infrared Spectra A: [(C3H7)4N][W(OC2H5)C15] (1) 5000 - 650 cm‘1 (2) 650 - 80 cm'1 [(C4H9)4N][W(OC2H5)C15] 1 CO (1) 5000 - 650 cm- (2) 650 - 80 cm’1 C: [ (C2115 )4N] [W(OCH3 )C15] (1) 5OOO - 650 cm“1 (2) 650 - 80 cm“1 0 [(C2H5)4N][W(n-OC3H7)C15] (1) 5000 - 650 cm"1 (2) 650 - 80 cm‘1 47 I 11(1) I I I I I I I I I 4000 3000 2000 1800 1600 1400 1200 1000 800 wavenumber 3(1) I BI I I L I I I I 4000 3000 2000 1800 1600 1400 1200 1000 800 wavenumber Figure 5. 48 A(2) I I I I I I 600 500 400 300 200 100 wavenumber J L I I 600 500 400 300 200 100 wavenumber Figure 5. 491 I C“) I I I I I I I I I 4000 3000 2000 1800 .1600 1400 1200 1000 800 wavenumber m I 40(1) I I I I I I I I I 4000 3000 2000 1800 1600 1400 1200 1000 800 wavenumber Figure 5- 50 C(Z) I I I I I I 600 500 400 300 200 100 wavenumber D(2) - I I I I I L 600 500 400 300 200 100 wavenumber Figure 5. 51 Figure 6: Infrared spectra: A: [(C2H5)4N][MO(OCH3)2C14] (1) 5000 - 650 cm"1 (2) 650 - 80 cm'1 B: I(C2H5)4N][Mo(OCzH5)2Cl4] (1) 5000 - 650 cm‘1 (2) 650 - 80 on"1 c: ‘[(CH3)4N][W(0C2H5)2C14] (1) 5000 - 650 cm”1 (2) 650 - 80 cm'1 D: 1 [(CH3 )4N] [W(OCH3 )2C14] (1) 5000 - 650 cm”1 (2) 650 - 80 cm“1 E: [(C2H5)4N][W(OC2H5)2C14] (1) 5000 - 650 cm"1 (2) 650 - 80 cm"1 F: ([(C2H5I4NIIWIOCHBI2BI4I (1) 5000 — 650 cm'1 (2) 650 - 80 cm”1 52 m UI "V Ami .L I ! ! I I I 4000 3000 2000 1800 1600 1400 1200 1000 800- wavenumber I m I 3(1) I i I I I I I I J 4000 3000 2000 1800 1600 1400 1200 1000 800 wavenumber Figure 6. 53 A(2) 1 I J I I I 600 500 400 300 200 100 wavenumber I I I I r I 4 I 600 500 400 300 200 100 wavenumber Figure 6. 54 m I 0(1) I [U I I I I I_ I I 4000 3000 2000 1800 1600 1400 1200 1000 800 wavenumber I ”(13 I I I I I I I J I 4000 3000 2000 1800 1600 1400 1200 1000 800 wavenumber Figure 6. 55 0(2) I I ' J I I 4,.___, 600 500 400 300 200 100 wavenumber I I i I J I 600 500 400 300 200 100- wavenumber Figure 6. 56 E“) I LI I I l I I I I 4000 3000 2000,. 1800 1600 1400 1200 1000 800 wavenumber wx/‘W I ,.. I I FC1>I I I I I I I I1 4000 3000 2000 1800 1600 1400 1200 1000 800 - wavenumber Figure 6. 57 E(2) I I I I I I 600 500‘ 400 300 200 100 vmymmmmer F(2) ' - I I I J I I 600 500 400 300 200 100 wavenumber Figure 6. 58 symmetry, according to esr measurements, and so should pos- sess D4h symmetry. of the eleven normal modes, only five, the A2u and Eu are infrared active. The Azu species are an M-O stretching vibration and an O-M-x bending mode. The Eu representations are M~X,.XcM-X. and X-M-O bending modes. Tables 3 and 4 contain infrared absorptions for the monoalkoxo and dialkoxo complexes respectively. In polymeric Chromium alkoxides,62 M-O was considered to appear at 500 cm—1. The bridging frequency of Co-Cl in the polymer lies about 70 cm.1 lower than the terminal frequency of Co-Cl.63 Therefore, it seems reasonable that the absorption in the 600 cm-1 region be assigned as a M—O stretching vibration. The metal-halogen stretching frequencies are approxi- mately the same in monoalkoxo complexes as the hexachloro compound.3° Two of three metal-halogen stretching fre- 1 and 275 cm_1 for mono- quencie s were found near 300 cm- alkoxide complexes. The third probably lies under the other two. In the dialkoxide species, the stretching frequency is almost 20 cm.1 lower. TheMoOCl: ion gave the highest absorption, ~360 cm.1 (Table 5). Comparison of the M-X stretch, of the complexes studied, with the results of Sabatini and Bertini,24 leads one to conclude that the following is the order of metal-halogen bond strength; WOCl: > WOCl: > wc1; «AW(OR)C1;)> W(OR)2¢1: and MoOCl; > MoOCl: «vMoCl; ~'Mo(OR)Cl; > Mo(OR)3Cl; (R = CH3, C3H3, or c333). 59 umcouum mum> I Hum> “maouum I m “ESHUOE I E “Xm03 I #3 .HOCHSOQQ fl gm umUGMQ COHUMU HHM afiflmm a moon .a nooH a once .a once Aonov> e mnH a one Axuzrxv> s on“ a son Isuzuxvs rm can rm «Hm Axuzrovs sun> ”no sum> new Axusv> sun> non usm> con xxrzes rm enn so vnn Axuzrovs x3 Has a one Acuouov> 33 mum #3 mom a «on s non Aotzes .naoanmaooszH231ameoCL _naoxnmaoo.z__z.lsmaue_ reassessed a one“ a ouoa a once Aonovs s nnH e nnH e an” Axtznxv> a cue s nsH a one Axuzrxv> rm onu rm and an oHa Axuzrovs Hum> mum Hum> mmN Hun> mom Axrzv> Hum> mom Hum> eon Hum> mom ANIzv> no «no rm can so one xxuzuov> #3 was :3 «He #3 one AoIoro> a man a con e Hnn noises .naofismaoovsa_z¢finmaov_ Haaofinmaoovznmzeflnmaovg .naofiamoovs._z«finmaovH usmscoanme unnaamod rsazv acoA mHoAmovz no A HI . AucmEEmfimmm Eov mmflocmsvmum coaumuomnm COHMHMEH .m manna 0 6 “ozonum >H0> u th> "vacuum I m “Esflomfi n E .Hooasonm u Sm nxm03 n #3 “hogan soauco Ham msamm s3 nHHH .m nooH m nsoa x3 «can .m coca rotovs rm sea a «ca 8 nun Axnzrxv> 2 men sum> new 5 «on xxtzrovs una> no“ nuns con unm> oon xxtzes s wnn .e flan a men .e ”mm 2 Hon .nm snn xxuzrovs a men a sec m «on nonzes r3 can s3 nun 182359 E E. A assoc _ 162.369 oi :2. A assoc _ 26a 1 Amos 2: E. A assoc _ unassaamma x3 noon .m coo“ x3 mace .m anoa x3 oofia .m omoH Aouov> 33 Ana x3 on” x3 on” Axustxys e on“ a one, a one xxrzrxv> rm and an man an new Axuzroes usm> new usm> own num> can xxrzvs an snn rm Hnm Extraovs x3 one x3 «He Aououoes n eon a men a son Loans; 18: names 5 :2. A anus _ 3o“ A 3race 5 E. A are _ 132359 E E. A are H newscast: . . AusmEEmwmnm manflmmom £DH3V ncofl ”HUnAmovz mo AHIEUV mmflocmsvoum coaumnomnm COHMHmEH .v wanna 61 Table 5. :Infrared absorption frequencies (cm-1) of MOCl; ions and digeric tungsten species (with possible assignment) Assignment [W (0CH3 ) 2C13] 2 [W (0CH3 ) 3C12] 2 [W (0C2H5 ) 3C12] 2 V(M-O) " 567 s 566 s 623 s v(M—O) 542 s 520 m 519, 501 m vIO-M-O) 455 m 397 m v(O—M-X) 357 s 339 wk v(M—X) 328 s 318 s 305 s vIMeX) 291 s 305 s 288 s VIO-MeX) 279 s 247 sh v(O-M—X), (M-X) 255 s 252 m 218 m va-M-x) ' 177 s va-M-x) 91 m ,vIc-o) 99o sh, 990 s, 995 s, 1080 s, 1110 sh 1080 s, 1110 m 1050 s, 1105 wk fir ‘L_. Assignment [ (C3H7 ) 4N] .(MOOC14) I (C4H9 ) 4N] (M00C14) v(M-O) 990 wk 980 Wk v(M—X) 358 s 354 s v(X-M-x) 162 m .161 m v(X—er) 154 m 155 m '— aPlus all cation bands; wk = weak: m = medium; 9 - strong: vstr - very strong; sh = shoulder. 62 The metal-oxygen stretch is also interesting., As the alkoxide increaSed in size, the metal-oxygen stretch in— creased in frequenCy, OC3H7 > OC2H5 > OCH3. The metal- oxygen stretching frequencies are higher for monoalkoxide than the analogous dialkoxide complex, [(C2H5)4N][W(OC3H5)C15] > [(C2H5)4N][W(OC2H5)3C14]. The stretch occurs at 613 cm-1 for [(C2H5)4N][Mo(OC2H5)3Cl4] compared to 584 cm-1 for the tungsten case. The absorption was lowered slightly on Changing from chloride to bromide. *The XéM—X modes for monoalkoxo complexes were considered to be at rv170 cm.1 and ~150 cm—1 by comparison with WClfi' 'and MoClg- spectra.°4 A broad band began near 90 cm-1 but had no maximum above 80 cm-l. :Sabatini and Bertini assign a band in this region to an.X‘M-X vibration.24 _For dialkoxo and tetrachloroxo complexes, the.X+M-X vibrations should be those at ~160 and rv1.30 cm-l. The degeneracy of the Eu modes is apparently removed in the solid state. The OrM-X vibrations were assigned by comparison with [(C3H5)4N][W(OCH3)3Br4]. Three vibrations are observed in the 300 cm.1 region and are probably OAW-Br vibrations. Since x—M-X vibrations are slightly lower (~40 cm-l) for X =‘Br than Cl,24 one would expect a similar behavior for O-er modes. ~AnM-O rocking vibration rather than any of the O-Mex modes is observed24 in oxyhalide compounds and can be rationalized if one considers relative masses and bond strengths of the degenerate modes. However, none was: observed for MoOClz. 63 .In addition, a C-C-O bending mode at 370 cm—1 was ob- served for chromium ethoxide complexesfi2 A band found near 400 cm.1 is believed to be this vibration in the molybdenum and tungsten complexes. The release of an alkyl group by monoalkoxide complexes indicates the greater stability of a complete 7 bond for oxygen in M-OR. The far infrared data (Table 3) further probably indicate that the bond Egaps to the metal-oxygen is weakened. The low frequency m—x band is thought to be the M-X stretch Egagg to the alkoxide group. The greater instability of the molybdenum compound compared to the tung- sten complex ought to be due to better overlap of the oxy- gen p orbitals with the tag orbitals of the molybdenum in forming a molybdenum—oxygen multiple bond. Thus, a weaker metal—halide bond Egag§_to the alkoxide group is the result.. Although the frequency of the metal—oxygen bond £3935 to the halide increases as the size of the alkyl group increases, the rate of alkyl halide evolution de- creases.°° It is conceivable that the rearrangement in the solid state is hampered by the larger alkyl group. The elimination is viewed as a concerted process that involves an axial chloride from one ion with the alkyl group from a neighbor. Evidence points to an intermolecular process since the rate of alkyl halide evolution decreased as the size of the cation increased. The driving force is the formation of the more stable metal oxygen double bond. 64 The most stable arrangement for dialkoxo complexes would be trans alkoxides where there is competition for the same t2g orbitals. -Further evidence for this structure is found in a shift of 16-20 cm-1 to lower energy for M-Cl stretches in dialkoxo compared to the similar hexachloro compound and also it is supported by the number of observed vibrations. :Five normal modes are required in D4h sym- metry whereas thirteen are possible in C2v symmetry. The number of absorptions found for the tetrachloroxo anion indicate Dsh symmetry as was postulated previously.65 Only E;aps_dialkoxides have been prepared (as confirmed by esr studies discussed below). i The infrared absorptions of dimeric compounds are given in Table 5. The structure of the dimeric compounds is thought to be two edge—to-edge octahedra.39 The proton nmr absorption spectrum of [W(OCH3)2C13]3 in chloroform, Figure 7, gave a line absorption at T.= 5.6 i .1. This indicates the equivalence of the methyl groups and, thus, only chlor- ide bridges are possible. Two similar alkoxide groups could either lie in the equatorial plane or Egag§_to one another in axial positions, if one assumes an octahedral structure around each metal atom. The latter of the two is preferred because the vibrations are similar to the dialkoxide mono- meric species but shifted to slightly higher wavelength. The above observation is noted for absorptions of [W(OCH3)2C13]3 and [W(OCH3)3C12]2. The nmr studies of [W(OC2H5)3C12]2 indicate the non equivalence of the alkoxide 65 W £th -v 4 3 2 me(5) I L I I 1 1 Figure 7. Proton nmr spectrum of [W(OCH3)2C13]2. my “'T "I Figure 8. Strueture proposed for [W(OC3H5)3C12]2. 66 groups. Klejnot found a ratio of 2:1 for the proton nmr absorption spectrum of the dimer and he also found the molecule had a dipole moment. ‘Figure 8 shows the struc- ture he proposed.39 Since there are no observed X-er vibrations and the molecule has a dipole moment, one must assume the proposed 1 structure is correct. The band at 218 cm— for [W(OCH3)3C13]2 is attributed to the M—X bridging vibration. This band is probably that at 255 cm"1 for [W(OCH3)3C13]2 and 252 cm“-1 for [W(OCH3)3C12]2. For the latter two species the band probably contains some o—M-X character. The dimeric species also exhibit vibrations at ~520 cm-1 which are probably M-O stretches of terminal alkoxide groups in the equatorial plane. The O-M-O vibrations are probably found in the 400 cm-1 region by analogy with the other results.62 The other assignments were made in comparison with the other compounds studied. The number of possible vibrations was determined by a knowledge of the molecular symmetry. The interpretation of the electronic Spectra is also based upon the structure of the complex ion. Compounds of Oh symmetry, WBr; and WClg, gave elec- tronic spectra similar to ones previously reported.27'3° Values for 10 Dq wereWBr; = 18,900 cm.1 and WC1; = 21,700 cm—l. The paramagnetic alkoxide complexes demonstrated 94h or C4V symmetry. Both point groups give the same splitting 67 pattern of d energy levels. The splittings from lowest to highest energy are a singlet B3(dxy) state, a doublet E(dxz and dyz) state, and a singlet A1(d22) state. Three d-d transitions are Laporte forbidden but spin allowed. These transitions have absorption coefficients from 10-20 M cm 1. Illustrative spectra of dialkoxide complexes both in solid and solution are given in Figures 9 and 10. Transi- tions for molybdenum compounds are believed to be B2 —3 E and ~42,000 cm-1 and B2 -> B1 at ~21,500 cm-l. For tung- sten it seems that the degeneracy of the ~E state is re- moved. Thus two transitions are observed at ~41,000 and ~14,000 cm_1. The 32 —> B1 transition is thought to occur at «25,000 cm-l. -For both molybdenum and tungsten, the 32 -> A1 transition is masked by the charge transfer band. Dilute solutions of W(OR)2C1; in ROH were stable during measurement of the electronic spectrum, but slowly changed thereafter. The M(OR)3C1; anions were most stable in an- hydrous nitromethane which contained no HCl. It was pos- sible to measure electronic transitions of Mo(OR)3Cl; in acidic alcohol solutions at 0°. If the alcohol solution is not saturated with HCl or warmed to 25°, spectra change with time and suggest that reactions occur and the species is no longer Mo(OR)2Cl;. The spectra reported previously‘“:45 were more like the tetrachloroxomolybdate(v) species in alcohol than the absorptions found here. Furthermore, the 68 AeHooo=VAZeAameov AeaooonAZ A mnov_ _eHONAamoovosLAZ AnEaOVL AvaoaAnmaoovozLAZvAnENUVL .HHsEroogmuuoammm oflaomlmocmuumamom ocmnumEouquIEOHDSHom "mom «0 u< "mo muuommm UHEoHuumam .m onsmflm 69 “d ”‘1'.--- ---~¢-—-0----0 - g... —---“ b aouquosqV .2 .IL 800 900 1000 1100 700 millimicrona 500 600 Figure 9. 400 70 millimicrons Figure 9. '71 l l \ \ I " '— ‘5 - \ a ’ ~ ~ \ , ’ x I \ \ S‘ ’ a ’ \ U a u- a \ \ \ \ \ \ C I l I I I I I 500 600 700 800 900 1000 1100 millicrons Figure 9. 72 I . I . I . I _vHUNAmmauov3QHz«AnmuovH IIIIII 18: £08,: E: ammo: _vHU«AmmUOV3HHZvAmmUVH "mmx .HHUEImUcmuomammm U wHHOmeocmuumHmwm um wcmzumfiouuHaIGOHuSHom "4 mo muuummm aficonuomam .oH musmflm 73 coca com com .oH mnsmflm maonuwafifia oom aoueqzosqv I 74 I'\ I I l"’ I I I I I I I I I I I I I I I I I I I I I I, I r~~ ” I, l. \<;/ ‘4'” "x. I, I. \ I I \\ \.\ I/ I \ . \, l/ ,/ W-Iuo /\. J \u an- B l l I I 700 600 500 400 millicrons Figure 10. 75 coca _ coma .ofi «Human acouuaeflaflwfi OONH OOHH coca com com 005 com _ _ _ _ _I \ ‘ until—0-. #._O_~.~. “0 ~g~O—.-. #. A ——— 76 spectrum of the tetrachloroxomolybdate(v) anion changes slightly with time. The W(OR)Cl; anion in nitromethane shows two absorp- tions. A broad absorption at 5,800 cm.1 is probably an infrared overtone or multiple vibration. The transition at ~B,500 cm-1 is thought to be the B2 -¢ E transition. Nitromethane absorbs in the ultraviolet, but the solid re- flectance spectrum shows the Ba -¢ B1 transition at ~22,500 cm-l. The Ba -> A1 absorption is again masked by the charge transfer band. Several solid and solution spectra are given in Figure 11. Special precautions were taken to match qualitatively the electronic spectrum of the solid to that in solution. This adds insurance that the species in solution and the solid are the same and, hence, facilitates the interpreta- tion of electron spin resonance spectra. Table 6 gives both solution and solid data for the electronic absorptions of the compounds studied. The measured magnetic susceptibilities at 77°, 195°, and 298°K are given in Table 7. The weak temperature de- pendence of the magnetic susceptibilities is reflected in the small values of the Weiss constant (9 = -2°K) and near constant values of the magnetic moments. Thus, the conclu- sion which can be drawn from the Figgis calculations is qualitative. For tungsten dialkoxide complexes, v is greater than 10, A probably ranges from 8,000 to 11,000 cm-l, and x is approximately 500 cm.1 This value agrees with that found for A in tungsten(V) oxyhalide compounds.27 77 I . I HnHoAnmnoovza_z¢Aam¢ovH I I I _naofinmuoovza_z«Apmmov_ _naoAnmuoov3HHz«AnmuovH Hams. .Haofilmocmuuwamom "U Uwaomlmocmuomamwm um wcmnuofioHHACIaowuoaom "fl mo muuommm vacouuomam .HH musmflm 78 .HH musmwm msouuwaaaa OQ¢A coma coca com . coo — . o.H aoueqlosqv 79 700. 600 millimicrons Figure 11. 500 400 II 80 .HH musmwm acouuaaawa coma coma seen I coma coon .oom coo — q — d — a a .Illl| .IIIIo/ . \. / .\ /. . / / / 81 Table 6. Electronic absorption spectra of compounds3 . Absorptionr Compound Medium cm-1 x 10-3 (5 max in parenthesis) [(C2H5)4N][Mo(OCH3)2Cl4] Solid 11.9, 21.8, 27.4 Nitromethane 11.7(16), 21.8(27) CH3OH-HC1 11.7(16), 21.8(27) [(C2H5)4N][Mo(OC2H5)2Cl4] Solid 12.7, 21.3, 26.0 Nitromethane 12.1(19), 21.5(29) C2H5OH-HC1 12.1(19), 21.5(29) [(CgHs)‘N][W(OCH3)2Br4] Solid 11.9, 14.6, 23.5 Nitromethane 11.9(17), 14.7(19) Methylene 11.9 17), 17.7(19), Chloride 23.6 630), 26.0 5.0 x 103 35.0 3.0 x 103 31.7 3.8 x 103 29.0 5.9 x 103 [(C4H9)4N](MOOC14) Solid 14.8, 22.7(sh), 26 3(sh) Nitromethane 13.6(18), 22.5(17) Methylene 14.6 23}, 22.7(19), Chloride 26.4 240), 31.3 5.1 x 103) [(C3H7)4N](MoOC14) Solid 14.8, 22.7(sh), 26.7(sh) Nitromethane 13.6(14), 22.5(23) Methylene 14.6 23), 22.6(30), Chloride 26.4 280), 31.3 5.1 x 103) Methanol 14.1 25), 23.2 200), (initially) 30.8 2.0 x 103 , 37.7 sh) (after 2 hrs) 32.5 1.7 x 103 37.7 sh) I 14.1gzs), 23.0E241), Table 6. (Continued) 82 Absorption Compound Medium cm x 10 3 (s max in parenthesis) [(CH3)4N][W(OCH3)2C14] Solid 10.9, 13.5, 21.7(sh), 25.3 Nitromethane 10.6 10.9 , 13.7;12.6), 25.0 26.1 x, I Methanol 10.6 10.9), 13.7(12.6), 21.1 ~13.5)(sh), 25.0 ~26) sh), 30.8 ~775 (sh), 34.6 ~4,670)(sh) [(083)4N][w(oc235)2c14] Solid 11.1, 14.1, 24.7(sh) Nitromethane 10.8 12.5 , 14.0(13.6), 24.7 25.1 Ethanol 10.8 12.5), 14.0(13.6), 24.7 «20) sh), 30.8 ~750 ssh), 35.5 «5188 (sh) [(CH3)4N]2[W(OC2H5)C16] Solid 5.8, 7.5, 8.2, 15.4, 24.7(sh) [(C2H5)4N][W(OC2H5)2C14] Solid 11.6, 14.1, 24.5(sh) Nitromethane 10.9 12.7 , 13.9(13.4), 24.3 22.7 Ethanol 10.9 12.7), 13.9(13.4), 24.3 «20) sh), 30.8 ~750 sh), 35.5 «6188 (sh) [(C2H5)4N][W(OC2H5)C15] Solid 5.8, 8.6, 13.7, 23.3(sh) Nitromethane 5.7(4.6), 8.7(7.2), 23.3(7.2) [(C2H594N][W(OCH3)C15] Solid 5.8, 8.4, 15.1, 22.6(sh) Nitromethane 5.7(4.8), 8.4(6.8), 22.5(7.6) [(C2H5)4N][W(n-OC3H7)C15] Solid 5.8, 8.5 Nitromethane 5.8(5.2), 8.7(8.2) Table 6.(Continued) 83 Absorption3 Compound Medium cm 1 x 10 (8 max in parenthesis) [(C3H1)4N][W(OC2H5)C15] Solid 5.8, 8.5, 22.9 Nitromethane 5.8(4.7), 8.6(7.3) [(C4H9)4N][W(OC2H5)C15] Solid 5.8, 8.4, 23.3 Nitromethane 5.8(5.1), 8.6(7.1) [(C2H5)4N](WOC14) Solid 5.8, 9.6, 12.3, 17.5, 25.0 Nitromethane 11.2 11.6 , 14.2 18.4 . 26.0 14.4 sh = shoulder. Table 7. Magnetic properties of compounds 84 x' x 103 Compound Temp. C38 units uB.M 90K [(CH3)4N][W(OCH3)2C14] 297 973 1.53 -2 195 1465 1.52 77 3679 1.51 [(CH3)4N][w(oczns)2c14] 297 1002 1.55 —2 195 1503 1.54 77 3769 1.53 [(C2H5)4N][W(OC2H5)2C14] 297 977 1.53 —2 195 1486 1.53 77 3743 1.52 [(C2H5)4N][W(OCH3)C15] 297 745 1.34 -3 195 1195 1.33 77 1117 1.33 [(C2H5)4N][W(OC2H5)C15] 297 777 1.36 -2 195 1175 1.36 77 2966 1.36 [(C3H7)4N][W(OC2H5)C15] 297 831 1.41 -4 195 1246 1.40 77 3127 1.39 [(C4H9)4N][W(OC2H5)C15] 297 803 1.39 -2 195 1223 1.39 77 3012 1.39 [(C2H5)4N][W(OC3H7)C15] 297 797 1.38 -2 195 1219 1.38 77 3075 1.38 [(CH3)4N][W(OC2H5)C16] 297 873 1.45 -81 195 1143 1.34 77 1986 1.11 [(C3H5)4N](WOC14) 297 863 1.44 12 195 1226 1.39 77 3204 1.41 85 Table 7. (Continued) x$ x 10r Compound Temp. cgs units uB.M. [(C2H5)4N][Mo(OCH3)2Cl4] 297 1226 1.71 2 195 1885 1.72 77 4747 1.72 [(C2H5)4N][Mo(OC2H5)2Cl4] 297 1252 1.73 4 195 1915 1.74 77 4956 1.75 [(c285)4N][w(ocn3)28r4] 297 1067 1.60 —1 195 1605 1.59 77 4080 1.60 [(C3H7)4N](MoOCl4) 297 1216 1.71 2 195 1837 1.70 77 4628 1.70 [(C4H9)4N](M00Cl4) 297 1224 1.72 4 195 1912 1.73 77 4841 1.73 86 The magnetic moments of molybdenum(v) compounds were near the spin only values. The magnetic moments increase as the number of alk- oxide groups increases and suggest the formation of a strong tungsten oxygen multiple bond which increases the spacings between the e and b2 orbitals. As a result, the spin orbit contribution to the magnetic moment is lowered. Con— sequently, a large difference in g values was anticipated between [(CQHI5 )4N] [W(OC2H5 )c15] and [(C2H5)4N] [W(OC2H5)2Cl4] . Electron spin resonance spectra were obtained on pow— dered samples and on various solutions at 780 and 2970K. The 95Mo-97Mo hyperfine spectrum was observed. An absorption in an experimental spectrum of tungsten was thought to be the hyperfine component from 183W. Since no hyperfine structure could be duplicated by the computer, the absorption may have been due to a rhombic distortion or an impurity. The 183W hyperfine structure was probably masked by the broad absorption of the isotopes with I = 0 because the half width is approximately 100 gauss. Illustrative spectra of mono and dialkoxo complexes are given in Figures 12 and 13 respectively. In comparing the g values of mono and dialkoxo tungsten complexes as listed in Table 8, gl is found to change more than 9‘1. However, changing from C1. to Br- in [(C2H5)4N][W(OCH3)2X4] caused a greater alteration in the 9|] Value than gi. A similar observation is reported11 in complexes of the type WOX5=. Thus in compounds of C4v symmetry, it seems 87 Figure 12. Electron spin resonance spectra of A: [(C2H5)4N][W(1-OC3H7)C15] in frozen nitromethane B: [(C2H5)4N][W(OC2H5)C15] in the powder Key: Experimental Computed _________________ 88 3298.9 gauss 5446.6 Figure 12. m 3491.6 gauss 3957.1 89 Figure 13. .Electron spin resonance spectra of A: [(C2H5)4N][W(OC2H5)3C14] in the powder B: [(C3H5)4N][W(OC2H5)3C14] in frozen nitromethane' Key: Experimental Computed _________________ 90 1 | 3462.7 gauss 4403.4 Figure 13. 3535.4 gauss 4017.2 91 Table 8. Magnetic tensor values for tungsten(V) complexesa Temp Compound (9) g g °K . J. H [(C2H5)4N][W(OCH3)2Br4] CH3N03 297 1.80 78 1.94 1.79 Powder 297 1.85 1.75 [(C2H5)4N][W(OC235)2C14] CH3N02 297 1.74 78 1.79 1.72 CHZClz 297 1.73 Powder 297 1.76 [(CH3)4N][W(OC2H5)2C14] CH3N02 78 (1.75) 1.80 1.73 Powder 297 1.75 [(CH3).N1IW(OCH3)2CIII CH3N02 78 (1.75) 1.80 1.73 Powder 297 1.74 [(02H5)4N1Iw(ocna)c151 CH3N02 78 (1.56) 1.70 1.49 [(C2H5)4N][W(OC2H5)C15] CH3N02 78 (1.57) 1.71 1.50 [(C235)4N][W(1‘0C3H7)C15] CH3N02 78 (1.58) 1.71 1.51 [(C4H9)4N][W(OC2H5)C15] CH3N02 78 (1.57) 1.70 1.50 [(C3H7)4N]IW(OC2H5)C15] CH3N02 78 (1.57) 1.70 1.50 a( ) = Calculated values. 92 that axial ligands cause the greatest change in gl whereas equatorial ligands alter the 91' value to the greatest extent. Further evidence for this phenomenon was obtained from a comparison of molybdenum complexes. Powder, solu- tion, and frozen solution esr spectra for Mo(0C2H5)2Cl4- and MoOCl4- are shown in Figures 14 and 15. Table 9 con- tains measured magnetic tensor values. The value for gll is nearly the same for MoOCl4-, MoOC15=, and Mo(OCH3)2Cl4- and gl values are quite similar11 for MoOCl4- and MoOC15=. However, 91, values are lower for Mo(OCH3)2Cl4-. In an attempted ligand exchange experiment between Mo(OC2H5)2Cl4- and SCN-, the g .values essentially re— mained constant and probably indicate little exchange of either ethoxide or chloride todk place with SCN—. If MoOCl4— is dissolved in methanol, the spectrum changes with time. Two lines were obtained as illustrated in Figure 16A. Figure 16B shows the spectrum of Mo(OC2H5)2Cl4- in ethanol. Again two species are present. Since molybdenum(v) compounds are very susceptible to oxy- gen abstractionl‘5 and Funk g£_§l.4°'42 found that oxy- methoxy compounds could be isolated from methanol, the species present (in addition to parent compounds) are probably mixed alkoxooxo complexes. It is also interesting to note (9) values for MoOCl4- in methylene chloride and nitromethane. The (9) is 1.956 in CH2C12 and 1.949 in CH3N02. Electronic absorptions 93 Figure 14. Electron spin resonance spectra of [(C2H5)4N][Mo(OC2H5)2Cl4] in: A: The powder B: Nitromethane solution C: Frozen nitromethane solution. 94; [A I 3366.9 . gauss 3592.4 Figure 14. W l 4 ' l 3347.6 gauss 3647.5 95: C I | 3089.7 gauss 3563.6 Figure 14. 96 Figure 15. Electron spin resonance spectra of [(C3H7)4N](MoOCl4) A: The powder B: Nitromethane solution C: Frozen nitromethane solution. 97* 3280.6 gauss . * 3785.8 Figure 15. 3290.0 gauss 3712.8 98 3218.4 gauss 3671.0 Figure 15. 99 zomomz m.mm S.Ho mum.fl oom.H we .nmm + eczema wwm.e 6mm nmozom o.em m.on mum.H mom.e we omo.e new HomImOomso o.mm S.HS mam.” oom.H mu «.me omo.e now Nozomo Heaosfiomnoovoz__Zofiomsova onm.fi onm.fi 6mm Hmoaom «.mm m.on mum.“ Hem.” we m.ms mmm.~ new HomImOnmo o.Hm w.oo mum.H oom.H as «.me mmm.a 6mm nozomo _oaonflomoovozvflzvomnova m 4 Amv AW __m Amv dune vasomfioo m m m .mmxmameoo A>VEdGmUQmHOE How modam> HOmcmu owumcmmz .m manna «Ioa x HIEom 100 moo.fi sou HooSom H.ns ono.e one «Hoemo one. H moo. H on H.ov ovo.e now «ozone Asaooozv_z«Aomeova eno.e new Henson smo.e ooo.H we H.53 ovo.e sou «ozone AvaooosVHZoAsmoovg nAmv .am __m Adv Me @509 vasomfioo Aomscflusoov .m manna 101 attributed to the B2 -> E are at 14,600 cm_1 and 13,600 cm-l. Thus, the larger difference between the ground and excited state, the less spin orbit coupling occurs, and the greater is the g-value. Most powder samples gave a one line esr absorption spectrum except [(C2H5)4N](Mo(OCH3)2Cl4].and [(C2H5)4N][W(OCH3)2Br4], in whose spectra gll and gi could be resolved. Electron spin resonance spectra of pentachloroalkoxotungstate(V) could not be obtained at room temperature. A spectrum which is believed to be that of WOCl4-, the decomposition product of W(OC2H5)Cl5-, is observed at 78°K. The broad hump in the spectrum in Figure 12B probably arises from W(OC2H5)C15-. The g values of the presumed W0C14_ are gll and gi. equal to 1.80 and 1.77 respectively. These compare well11 to those 9 values of WOCl5=. The powdered complex, [(C2H5)4N](WC13), gave a one line absorption spectrum at room temperature with g = 1.79. One line was also observed for [(C2H5)2N](WC16) doped into [(C2H5)4N](TaC16), but the author66 only re- ported that the g value was less than 2. Dowsing and Gibson17 report that [(C2H5)4N](MoCla) gave a room tempera- ture spectrum with 9" = 1.977 and gi.= 1.935. Distor- tion of the lattice is believed to remove the degeneracy of the ground state and an esr signal is then observed in these hexachlorocomplexes.17 102 Figure 16. Electron spin resonance spectra of A: [(C3H7)4N](MOOC14) in CH3OH B: [(C2H5)4N][Mo(OC2H5)2Cl4] in canson. 103 g = 1.943 A g = 1.935 3331.6 gauss 3575.0 Figure 16. g = 1.945 . II J gr= 1.935 ' J 3397.9 gauss 3600.9 104 Certain values of theoretical interest can be calcu- lated for molybdenum(V) compounds. If it is assumed that the d1 electron is in the b2(dxy) orbital, the iso- topic contact term, K, and the fraction of time the electron spends in the dxy orbital, 32 , can be calcu- lated from the equations:67 A —K - 4/782p + (9H - 2.0023)p + 3/7(gi - 2.0023)p / I; B -x + 2/7829 + 11/14(gi - 2.0023)p. If p, which is defined at 2.00239nSeSn(r‘3) is taken av' 4 -1 3+ for the "free ion" (55.0 x 10' cm for Mo , i.e., the '1». average for the two isotopes and a net charge of +3 for the Mo(OCH3)23+- or Moo3+ unit57), then one may solve for BzP and thus determine 52. To determine gn, an average was employed for the two isotopes: = 1/2(-0.9099 - 0.9290) 9n 5/2 The quantity, x, which results from a polarization of the inner filled S orbital by the unpaired d elec- trons, is determined by the equation: [hcaosl X = -3/2 [2.0023ganBe] The values of K, x, 62, and P complex (= BZP) are listed in Table 10. 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