‘0.- . n. .1 I... , ...._.... . q . .. . . _ . _ .. . ... v. . . . . . . . . . . . . V . . . I , . v .. . ,. . _ . . . . . , . , . .f . 6.. _. . . , , . . . , . . v . . _ I... . a 3. _ T; .9643? _-_ .‘~._ >1“ - .v._.. -_. .A-.. -....-_. ""4. — . -..- on-.- -vm."‘ . . 3.. games". .5”....(¢v Thesis for the Degree of Ph. D. MICHIGAN STATE UNIVERSITY WILLIAM JOSEPH REAGAN 1970 THE PREPARATION'AND CHARACTERlZATION OF SOME TUNGSTEN (W) AND TUNGSTEN (V) COMPLEXES v w a 4 F... . . _ . . .. . .. . 2 . .. . . . . _ . . 5:55.15. he...” 1.. x ..!!1.. r ll III ' . 0 1| 1' I all: .luf Ill ' , .. I'v-J'Cin-«u-Mglhi- . I“: ‘3”) O ’. LIBRARY Michigan State f 9 University "III-'Ir‘ww" 3‘» This is to certify that the thesis entitled THE PREPARATION AND CHARACTERIZATION OF SOME TUNGSTEN 2 are unknown. A possible source Of these anions could be the dimers, [W(OR)XC15_X]2, which are formed in basic (with alkoxide ion) alcohol solutions. The study of the reactions and properties of these dimers has been negleCted. Since these compounds are diamagnetic, pmr spectroscopy can be used to study the orientation and reactivity of the alk— oxide ligands. A far infrared analysis may clarify the nature of the bridging groups in these dimers. ARecent ir studies8 have shown that in COC12(Y)2 polymers, the Co—Cl bridging frequency is about 50 cm"1 below the terminal Co-Cl vibration. HISTORICAL Tungsten has been studied since the characterization of tungstic acid by Woulffe (1779) and Scheele (1781). The early workers of the twentieth century extended the solution chemistry of tungsten by the preparation of anionic halide and cyanide complexes. Compounds of the lower oxidation states were unknown until the discovery of the hexacarbonyl (1928) and cyclopentadienyl (1954) complexes. Most of the modern (post 1930) tungsten chemistry was concerned almost entirely with the lower oxidation states. With the more extensive use of non-aqueous solvents some interest is now being shown in anhydrous complexes of the higher halides. This latter area will be reviewed in this section. One of the most important reactions of the tungsten halides is the abstraction of oxygen from solvents which contain oxygen or O-H groups. Oxo compounds, containing a metal oxygen double bond, are generally formed in this pro- cess. Oxygen abstraction occurred in the reaction of WCl5 with acetone, tetrahydrofuran and dioxane.9 Similar be- havior has been observed for McC15.1"'12 Tungsten(V) and molybdenum(v) oxo compounds, MOX5=. X = Cl_, Br-, 1‘, SCN_, have been well characterized.”-12 The metal halides are generally dissolved in concentrated 4 5 aqueous Hx solutions. The addition of cations such as, Na+. K+, Cs+ or NH4+ cause precipitation of solid M5MOX5 complexes.13-14 The electronic and magnetic properties of these compounds have been studied extensively. There are few examples of analogous quadrivalent com— plexes. A compound originally formulated15 as K2W(OH)C15 was prepared by the reduction of tungsten trioxide in con- centrated HCl. -More recently, this compound has been shown to be an oxygen bridged dimer, K4W20C110.16‘17 The magnetic properties of the MOX5=, M = M0, W. complexes11 are consistent with the presence of one d electron. ~Magnetic moments of the molybdenum complexes are close to the spin-only value. However, the tungsten com- pounds have lower moments (1.30-1.55 B.M.) which indicate some contribution from spin-orbit coupling. The magnetic moment and esr data for K4W20C11013 have been explained in terms of two unpaired electrons on each tungsten atom. -K6nigl7 has postulated that this compound is a W(III)4W(V) mixed valence compound. Electron spin resonance studies of these oxo compounds have been reported.13"29 The characteristic metal or li- gand hyperfine structure has been observed in several cases.25‘29 The electronic and charge transfer spectra of MoOCl5= was first studied by Gray and Hare.3° These workers based their assignments on the molecular orbital scheme of Ball- hausen and Gray,31 which successfully explained the long 2+ . wavelength transitions of [VO(H20)5] . The two ligand 6 field bands of MoOCl5= at ~14,000 cm'1 and ~22,000 cm"1 were assigned to the transitions, B2 ——> E and 32'_-> BI- >The charge transfer bands were assigned as follows: 28.0 x 1 1 103 cm- , 32 —> 3(1):); 32.3 x 103 cm- , 32 —+> 32(1); and 40.0 x 103 cm-l, Ba -—> E(III). These assignments were based on the assumption that charge transfer occurred pri- marily between the bonding metal-oxygen N-orbital and the metal nonbonding or antibonding orbitals. This work did not adequately explain certain experimental facts. For MOX5- complexes, a change from .C1 to Br ligands caused a large shift (6000-7000 cm-l) in the low energy charge transfer band. Other workers“:19 have pointed out that metal-halogen w-bonding must be considered to explain these data. Recent esr studies of the complexesz7?33”have con: firmed the presence of significant metal—halogen N—bonding. The far infrared spectra of a number of these oxo complexes have been measured. Sabatini and Bertini32 as— signed the vibrations of MOX5= species on the basis of C4v symmetry. 4A1 and 4E modes are infrared active. ‘The A1 modes are two M-X vibrations, one M-O stretch and O-M-X and .x—M-x deformations. ~The E modes include pairs of M—x stretching, x—M-X and O~M4X bending vi- brations. Under strictly anhydrous conditions, many hydrolytically unstable, nonoxo complexes of the tungsten halides have been prepared. 7 Solutions of WCle or MoC15 in acetone or similar sol- vents react with the thiocyanate ion to give substituted products, W(NCS)5 and Mo(NCS)5.33 These compounds were only isolated with at least two solvent molecules attached, as in W(NCS)6-2(CH3)2CO. Anionic complexes of niobium(V) and tantalum(V). M(NCS)6- have been isolated recently.34'37 Infrared spectra of these complexes indicate the presence of N-bonded thiocyanates. ~The corresponding molybdenum or tungsten derivatives are unknown. Certain solvents, such as pyridine and acetonitrile, cause reduction of W(V) or W(VI) chlorides and bromides. 'Either WCle or WC15 reacts with refluxing pyridine to form complexes of the type WC14(PY)2 (py = pyridine).6 The re- action proceeds with the formation of the 1—(4-pyridy1)— pyridinium ion. Prolonged contact of these reagents leads to theformation of WC13(py)2.38 The compounds,-WC14(RCN)2§9 R = CH3,~C2H5, C3H7, have been prepared by the reaction of the higher tungsten halides with anhydrous nitriles. The magnetic moments of the compounds, WCl4L2 are lower than predicted for W(IV) (d2) complexes: 'WCl4(py)2,5 1.60 B.M., WC14(CH3CN)2,39 1.78 B.M.. -A molecular weight measurement was obtained only for the propyl cyanide deriva- tive. It was monomeric in benzene. The observation39 of two C E N and two M-Cl stretching frequencies for MoC14(CH3CN)2 may be an indication of a gig octahedral configuration. 8 Under mild conditions, reduction of WC16 by nitrogen containing ligands proceeds only to the 45 state. Greenwood g£_31.4°:41 have isolated the complexes, WClst, L = pyridine, 2,2'-bipyridine and 1,2-bis(diphenylphosphinoethane) from the reaction of WC16 and the ligand in carbon tetrachloride. Brown andtRuble42 prepared similar products by the reaction of WClB, WC15 and WBr5 with 2,4,6-trimethy1pyridine and benzonitrile in methylene chloride. Conductivity data indicated that these compounds should be formulated as [WX4L2];f.x-. The magnetic moments of the WX5L2 complexes are in the range of other W(V) compounds. The absorption bands of these species in the visible region, usually assigned as d-d transitions, have abnormally high molar absorptivities (200 M-lcm-l). No esr data have been reported. The preparation of several complexes of W(III) and W(IV) by the reaction of WCl4 (CH3CN)2 and 1,2—bis(diphenyl- phosphinoethane)(diphos) has been reported.43i The compounds ‘were formulated as [WCl3(diphos)]2, [WCl3(diphos)2], and [WC12(diphos)2]+Cl-. Strong bands at 244 and 258 cm_1 in the far infrared spectrum of the dimer were assigned to bridging chlorine vibrations . A variety of complexes were prepared by the reaction of the tungsten halides with aliphatic amines. The reaction of secondary and tertiary amines with WC16 formed complexes of the type, (NH2R2)2WC16 and (NHR3)2WC13.44 The W(V) com- plexes WC12(NHR)3 were obtained when WCl5 was allowed to react with primary amines. 9 The hexahalo derivatives are known for both W(V) and W(IV). As indicated above, WCle= salts were formed by the reaction of WC16 with secondary and tertiary amines. The interaction of WClB with alkali-metal halides under dry conditions at 130° yielded the complex chlorides, M2WC16, M = K, Rb, Cs, Tl.46 Various procedures have been used to prepare the hexachlorotungstate(v) complexes. The reaction of WC15 with alkali metal chlorides in chlorobenzene formed MWC16.47 Thionyl chloride reduced WC16 to WC15_. *The addition of tetraalkylammonium chloride to this solution precipitated the complex, R4‘NWC15.48 The magnetic moments of these hexachloro complexes are lower than the predicted spin-only values. The compound (C3H5)4NWC13 has a room temperature magnetic moment of 0.66'B.M.“9 _Anti-ferromagnetism is indicated by a NeEl temperature of 1400K. The magnetic moment of KZWCls is reported46 as 1.43 B.M. A high 6 value (1900K) also suggests anti-ferromagnetic behavior. The metal-chloride stretching frequency of these com- pounds has been measured. In (CzH5)4NWC16, the W-Cl stretch is at 329 cm-1.48 CSZWCle has a similar absorption at 308 cmnlfl9 The M-Cl stretching frequency is lowered by about 25 cm-1 upon changing the metal oxidation state from +5 to +4. The same trend was observed for Nb) and Ta hexahalo complexes.5° rAn unusual W(IV) compound with 8-Hydroxyquinoline as a ligand has recently been prepared. Tetrakis(8-quinolino— lato)tungsten(IV)51 was isolated from the products of a 10 sealed-tube reaction between (NH4)3W3C19 and 8-quinolinol. This compound is believed to be the first completely chelated eight-coordinate complex of tungsten. The metal halide alcohol systems are also of interest. Under moderate conditions, metal alkoxides, M(OR)X, free of oxo impurities, can be isolated. Bradley52 and his co- workers have investigated the alkoxide chemistry of many transition metals. These complexes are generally polymers. Ti(OC2H5)4 is trimeric in the solid state.53 Heavy transi- tion metal alkoxides are usually dimers. An edge-shared bioctahedral structure has been proposed54 for [M(OR)5]2, M = Nb. Ta: R = CH3, C3H5. Yellow solutions of WC16 in alcohols have been known for many years. A green product, W2C14(OC2H5)655:53 was reportedly formed by the reduction of W(VI) ethanol solu- tions. Klejnot57 reexamined this system and found that re— duction took place. He isolated two blue, paramagnetic chloride alkoxides, W(OR)2C13, R = CH3, C2H5. A red, dia- magnetic dimer, [W(OC2H5)3C12]2 was isolated after prolonged treatment of W(OC2H5)3C13 with ethanol. A chloride-bridged, bioctahedral structure for the dimer was postulated on the basis of pmr spectra and dipole moment data. Compounds of the type WO(OR)458 have been prepared by the reaction of WOC14 with ammonia in alcohol. The reaction of WBr5 with phenol and methanol was studied.59 The com- pounds,‘W(OPh)zBr3 and W(OPh)3Br2'PhOH, Ph = C6H5, were pre- pared but no methoxide complexes were isolated. ‘W. Lu' 5‘ (_7 f) ('1 In 11 The reaction of MoC15 and WC15 with methanol has been investigated. Funk and co-workers“""62 isolated similar products in each case. At temperatures below -10°, a green solvate, M(OCH3)2Cl3°BCH30H, was isolated. -The addition of pyridine or pyridinium chloride to the reaCtion solution of the pentahalides in methanol precipitated the yellow-green (py)M(OCH3)3Cl4. The compound [M(OCH3)3C12]2 was obtained when a methanol solution of (py)M(OCH3)2Cl4 was made basic with pyridine. Another dimer, [M(OCH3)4C1]2 was isolated when pyridine was added to the reaction solution of MC15 and methanol. In excess pyridine, the W(V) chloride alk- oxides were reduced to a W(IV) compound, W(OCH3)2C12-2C5H5N. Under certain conditions, both MoC15 and WCl5 formed oxo compounds in methanol. The complex, (py)2WOCl5 was obtained by the addition of pyridinium chloride to a hot solution of WC15 in methanol. An attempt61 to prepare Mo(0CH3)5 resulted in the formation of an oxo-alkoxo complex,_ MoO(OCH3)3e%CH3OH. In alcohol solution, this decomposition proceeds with the formation of dimethylether: Mo(OCH3)5 > MOO (OCH3)3 + .(CH3)2O. In most cases, only the preparations and elemental analyses of these compounds were reported. The magnetic moments 0f (PY)W(OCH3)2C14 and (py)2WOC15 were reported62 as 1.48 and 1.52 B.M., respectively. ~McClung g£_gl.33 reexamined the MoCl5-alcohol system. The compounds, (py)Mo(OCH3)2Cl4..C9H3NMO(OCH3)3C14. 12 [(CH3)4N]MO(OCH3)2C14 and (py)Mo(OC2HshCl4, were prepared and characterized. The methoxide complexes were prepared by a variation of Funk's original procedure.61 Methanol was slowly added to MoCl5, which was cooled to -78°. ~A methanol solution of the appropriate cation was added and the yellow— green tetrachlorodialkoxomolybdate(V) salts were formed. The ethoxide derivative was prepared by alkoxide exchange of (py)Mo(OCH3)2Cl4 in ethanol. Several attempts to pre- pare a chloropentamethoxomolybdate(V) salt or other ethoxo complexes were unsuccessful. The magnetic properties and visible, uv, ir and esr spectra of these complexes were measured. The room tempera- ture magnetic moments were close to the spin—only value. The visible and uv spectra were measured and the transitions were qualitatively assigned by analogy to the results for the MoOC15= ion. The d-d transitions were the B; -—+ E 1 The third at 14,000 cm"1 and the 32 -—> B1 at 23,000 cm- ligand field band required by D4h or C4v symmetry, Bg -—> A1, was apparently masked by the intense charge trans- fer bands. The esr spectra of the solid compounds or of the frozen solutions of these complexes were resolved into 9" and gl values. On this basis, the t£§n§_isomer (axial symmetry) was required. Clark and Wentworth34 reported that yellow-green, dia- magnetic complexes, W2C14(OR)2(ROH)4, R = CH3, C2H5, 1-C3H7, were formed by the reaction of [(ng4H9)4N]3W2C19 with re- fluxing alcohol. The ir and pmr spectra of the ethoxoethanol 13 complex were similar to the data for Klejnot's dimer, -W§Cl4(OC3H5)6.57 No conclusion as to the nature of the bridging group in these W(III) dimers was made. EXPERIMENTAL A. Preparation and Standardization of Analytical Reagents Silver Nitratez- A 16.98 9 sample of reagent grade silver nitrate was dissolved in 1 liter of distilled water. The concentration (0.1N) of this solution was determined by titration with a standard sodium chloride solution. Potassium Dichromate:- To prepare a solution of about 1.0N potassium dichromate, 49.03 g of dried reagent grade potassium dichromate was dissolved in water and diluted to one liter. The concentration of this solution was determined by an indirect method. An aliquot of the dichromate solu— tion was added to an aqueous solution of excess potassium iodide. The iodine that was generated was then titrated with standard sodium thiosulfate solution. Starch solution served as the indicator. Sgdium Thiosulfate:- A 0.1N sodium thiosulfate solu- tion was prepared by diluting Fisher Scientific Co.'s analytical grade "concentrated" sodium thiosulfate solution. Cerium Sulfate:- A 0.1N cerium(IV) sulfate solution was prepared from Fisher Scientific Co.'s reagent grade cerium(IV) sulfate solution. The concentration of this 14 15 solution was checked by titration with standard ferrous am- monium sulfate solution. Ferroin was used as the indicator. Ferrous Ammonium Sulfate:- A 0.1N ferrous ammonium sulfate solution was prepared by diluting a Fisher Scien- tific Co.'s analytical grade "concentrated" ferrous ammonium sulfate solutiOn. B. Materials Tungsten Hexachloride:- A commercial grade (Climax Molybdenum Co.) of WCla was purified by repeated sublimation under vacuum. Analysis Calculated for WC16: W, 46.36; Cl, 53.64. Found: W, 46.47; C1, 53.74. Tungsten Pentachloride:- Tungsten pentachloride was prepared by the red phosphorus reduction of WC16.55 The product was purified by vacuum sublimation. Analysis Calculated for WCls: W, 50.91; Cl, 49.09. Found: W, 50.70. Tungsten Tetrachloride:— Tungsten tetrachloride was also prepared by the red phosphorus reduction of WC16.55 Slightly less than the stoichiometric amount of phosphorus was used to prevent the formation of lower tungsten halides. -WC14 was obtained as a grey-black solid. The compound was not volatile and could not be purified. Some preparations were contaminated with small amounts of unreacted phosphorus. 16 Analysis Calculated for WC14: W, 56.45; Cl, 43.54. Found: W, 55.70: Cl, 43.10. *Molybdenum Pentachloride:- Molybdenum pentachloride was obtained from Climax Molybdenum Co. It was purified by fractional sublimation. Molybdenum Tetrachloride:- Molybdenum tetrachloride was prepared according to the procedure of Larsen and Moore.66 Solvents:- Pyridine and triethylamine were dried by distillation in the presence of barium oxide. Ethyl ether was stored over sodium metal. Chloroform, methylene chlor- ide and carbon tetrachloride were dried by distillation in the presence of phosphorus pentoxide. -Methanol was dried by distillation in the presence of magnesium turnings.67 Ethanol was dried by distillation in the presence of sodium ethoxide and diethylphthalate.68 1-Propanol and 2-propanol were dried by distillation in the presence of sodium. ggtraethylammonium Chloride:- This material was Eastman Organic Chemicals white label grade. It was dried at 1100 for 8 hours. Nitrogen and Hydrogen Chloride:- Prepurified nitrogen (Liquid Carbonic Co.) was used after being passed through a system to remove residual oxygen and water. Copper turn- ings heated to 6000 and B»T.S. catalyst (Badische Anilin und 17 Soda-Fabrik AG)served to remove oxygen. -Drying towers con- taining Drierite and calcium chloride served for removal of water. Gaseous HCl was the Matheson Co.'s anhydrous material. C. Analytical Methods Ethoxide Determination:- Ethanol or ethoxide was deter- mined by the potassium dichromate oxidation method.69 A weighed sample of the compound was added to a known excess of acidic (~'15% H2804) dichromate solution. The mixture was allowed to boil until the tungsten was converted to yellow tungstic acid. Tungsten was oxidized from W(V) or W(IV) to W(VI) at the same time the alcohol was oxidized. An aliquot of the excess dichromate was then treated with an aqueous potassium iodide solution. The iodine that was formed was then titrated with standard sodium thiosulfate solution. A starch indicator was used. Oxidation State Determination:- Samples were hydro- lyzed in dilute ammonia and then acidified with sulfuric acid. vExcess Ce(IV) sulfate solution was added and the mixture was stirred for 12 hours. Cerium(III) tungstate was removed by filtration and the excess Ce(IV) was deter- mined with standard ferrous ammonium sulfate solution. Ferroin served as the indicator. Some oxidation of the alcohol ligands was observed. For compounds containing ethanol or ethoxide as ligands, the ethanol analysis served as an indirect oxidation state determination. Since the ethanol content was also known from elemental analysis, the 18 reducing equivalents of the tungsten present could be deter- mined by subtracting the equivalents of ethanol from the total number of equivalents found in the dichromate analysis. 'Tungsten and Chloride Analyses:- A weighed sample of the compound was hydrolyzed in dilute ammonia and then ox- idized with hydrogen peroxide. The solution was digested on a steam bath for one hour. The clear solution was then cooled and diluted in a volumetric flask. Separate portions were used for the tungsten and chloride analyses. An aliqUot of the tungstate solution was added to a 400 ml beaker. A large excess (10 ml) of a solution of 4 g of 8-hydroxyquinoline in 100 ml of absolute ethanol was added. The solution was allowed to boil and tungsten was precipi- tated by the addition of acetic acid. The yellow precipi- tate was collected on a pre-weighed extra-fine porcelain filter crucible, washed with hot water and dried at 110°. The amount of tungsten present was calculated from the weight of the oxinate complex,-W02(C9H50H)2.7° The chloride concentration of an acidified portion of the solution was determined by a potentiometric titration with standard silver nitrate solution. A Beckman model G pH meter and silver—silver chloride electrodes were used for the titration. Molybdenum Analysis:- Molybdenum was determined by the same procedure as tungsten. Carbon, Nitrogen, Hydrogen and Sulfur Analyses:- These analyses were performed by Spang Microanalytical Laboratory, Ann Arbor, Michigan and by Galbraith Laboratories,.Inc., Knoxville, Tennessee. 19 Molecular Weight Determinations:- The cryoscopic tech- nique was used to determine the molecular weights of com- pounds in benzene solutions. These analyses were performed by Galbraith Laboratories, Inc., Knoxville, Tennessee. D. -Apparatus and Experimental Techniques A dry-box was used for opening sealed reaction tubes and for weighing and storing starting materials and compounds. All the other operations were carried out under a dry nitrogen atmosphere or under vacuum. 'The "Schlenk tube" technique, recently outlined by Herzog,71 was used in this work. Reaction vessels were 100 and 250 ml round bottom Pyrex flasks. Glass tubes fitted with fritted glass discs were used for filtrations. Both types of apparatus were equip- ped with ground glass joints and sidearm stopcocks. Nitro- gen was forced through the sidearm when the flask was opened to provide an inert atmosphere. Clean glassware, which was dried at 110°, was cooled under vacuum and then filled with nitrogen. -Solvents were allowed to reflux under nitrogen until needed. The collection vessel was designed by D. P. Rillema.72 Liquids were transferred with a dry pipet under a strong nitrogen flow. 20 E. Preparation of Compounds Pyridinium Pentachlorooxotungstate(V):- A 5.0 9 sample of WC15 (0.0138 mol) was added to 15 ml of 2-propanol which was cooled to -15°. The solution became blue. ‘The suspen— sion was saturated with HCl at 0°. After one hour, an iso- propanol solution of pyridinium chloride (0.014 mol) was added to the mixture. VA light blue solid separated from the solution. The compound was filtered, washed with ether and a small amount of thionyl chloride and dried under vacuum. Analysis Calculated for (C5H6N)2WOC15: W, 34.23; C1, 33.00: C, 22.35; H, 2.25; N, 5.21. Found: W, 34.06; Cl, 33.00; C. 22.27; H, 2.18; N, 5.17. Triethylammonium Pentachloromethoxotungstate(V):- A 5.0 9 sample of WC15 was added to a solution of 10 m1 meth— anol which was saturated with HCl and cooled to —78°. The temperature of the solution was increased to 0°. The color changed from black to yellow brown. A solution of 3 ml triethylamine in 10 ml methanol which was saturated with HCl was added to the brown solution. The mixture was cooled to -78° and was saturated with HCl. After 10 minutes, a yellow precipitate formed. ~The compound dissolved when the temperature of the solution was raised above -20°. There- fore, the product was separated rapidly by filtration, washed with an ether-methanol mixture, then pure ether and it was then dried under vacuum. 21 Analysis Calculated for (C2H5)3NHW(OCH3)C15: W, 37.20; Cl. 35.87. Found: W, 37.29; Cl, 35.74. Triethylammonium Pentachloroethoxotungstate(V):- This compound was prepared by the same procedures as the previous complex except that ethanol was used in place of methanol. Analysis calculated for (C2H5)3NHW(OC2H5)C15: w, 36.18; Cl, 34.88. Found: W, 36.01; C1, 34.79. No commercial C, H analyses were obtained for these monoalkoxo compounds. Pyridinium Tetrachlorodimethoxotungstate(V):- A 13.5 9 sample of WC15 (0.037 mol) was added carefully to 23 ml methanol which was cooled to -40° in a Dry-ice-chloroform slush bath. The dark green solution was treated with either a methanol-pyridine mixture or pyridinium chloride (0.037 mol) and a green solid separated. The crystals were filtered. washed with ether and methanol, pure ether, and dried under vacuum. Analysis calculated for C5H6NW(OCH3)2C14: W, 39.31; Cl, 30.32: C, 17.96; H, 2.57; N. 2.99. Found: W, 39.32; Cl, 30.30; C, 17.94: H, 2.55: N. 2.90. Pyridinium Tetrachlorodiethoxotungstate(V):- A 10.0 9 sample of WC15 (0.027 mol) was added to 20 ml ethanol which was cooled to —78° in a Dry Ice-propanol bath. ‘The solution 22 was gradually warmed to 0° and stirred for one hour. Then pyridinium chloride or a pyridine-ethanol mixture (0.027 mol) was added. The light green product was separated by filtration, washed with ether and ethanol, then pure ether, and was dried under vacuum. ' Analysis calculated for C5H6NW(OC2H5)2C14: W, 37.09; Cl,.28.60; C, 21.79; H. 3.23; N, 2.82. Found: W, 36.90; Cl, 28.49; C, 21.86; H, 3.36; N, 2.86. Tetraethylammonium Pentachloroisothiocyanatotungstatejv):- A 6.13 9 sample of WC15 (0.0169 mol) was suspended in 20 ml CHC13. A CHC13 solution of tetraethylammonium thiocyanate (0.017 mol) was added to the mixture. After 1 hour of vigor- ous stirring, the solution changed from orange to dark brown. The reaction mixture was stirred for about 15 hours then the dark brown product was removed by filtration, washed with a mixture of CHC13 and ether, then pure ether and was dried under vacuum. The tetraethylammonium thiocyanate solu- tion was prepared by treating an ethanol solution of tetra— ethylammonium chloride (2.88 9, 0.0173 mol) with an ethanol solution of 1.33 g ammonium thiocyanate. The ammonium chloride that formed was filtered off and the filtrate con- taining the (C2H5)4NSCN was evaporated to dryness. A tech- nique of repeated ether washing and vacuum evaporation was used to remove residual alcohol from the product. Finally, 20 ml CHC13 was added and the solution was filtered to re- move a small residue of NH4C1. 23 Analysis calculated for (C2H5)4NW(NZS)CJ.5: W, 33.48; C1,.32.28; C. 19.67; H. 3.64: N. 5.10; S. 5.83. Found: W. 33.98; Cl, 32.03; C, 19.47; H, 3.47; N, 4.98; S. 5.76. Tetraethylammonium Tetrachloroethoxoisothiocyanato- tungstate(v):- A 7.45 9 portion of WCl5 (0.0206 mol) was added to 10 ml ethanol which was cooled to —78°. The temper— ature was increased to 0° and a solution of 3.14 g ammonium thiocyanate (0.041 mol) in 20 ml ethanol was added. Am— monium chloride separated from the dark green solution. The mixture was stored at -10° for three hours. The am- monium chloride was then removed by filtration and a solu— tion of tetraethylammonium thiocyanate (0.021 mol) in 15 ml ethanol was added. The yellow-green compound was separated by filtration, washed with a 1:1 mixture of ethanol and ether. followed by pure ether and was dried under vacuum. The tetraethylammonium thiocyanate solution was prepared by treating an ethanol solution of tetraethylammonium chloride (3.42 g, 0.021 mol) with 1.62 g (0.02 mol) am- monium thiocyanate in 25 ml ethanol. The volume of the solution was reduced by vacuum evaporation and the ammonium chloride was removed by filtration. Analysis calculated for (C2H5)4NW(OC2H5)(NCS)C14: W, 32.91; Cl, 25.38. Found: W, 32.37; Cl, 24.98. No Commercial C, H, N. S analyses were obtained. The compound decomposed with evolution of ethyl chloride. 23 Analysis calculated for (C2H5)4NW(1\CS)C15: w, 33.48; c1, 32.28; c, 19.67; H, 3.64; N, 5.10; s, 5.83. Found: W. 33.98; Cl, 32.03; C, 19.47; H, 3.47; N, 4.98; s, 5.76. Tetraethylammonium Tetrachloroethoxoisothiocyanato— tungstate(v):- A 7.45 9 portion of WCl5 (0.0206 mol) was added to 10 ml ethanol which was cooled to -78°. The temper- ature was increased to 0° and a solution of 3.14 g ammonium thiocyanate (0.041 mol) in 20 ml ethanol was added. Am— monium chloride separated from the dark green solution. The mixture was stored at -10° for three hours. rThe am- monium chloride was then removed by filtration and a solu- tion of tetraethylammonium thiocyanate (0.021 mol) in 15 ml ethanol was added. The yellow-green compound was separated by filtration, washed with a 1:1 mixture of ethanol and ether, followed by pure ether and was dried under vacuum. The tetraethylammonium thiocyanate solution was prepared by treating an ethanol solution of tetraethylammonium chloride (3.42 g, 0.021 mol) with 1.62 g (0.02 mol) am— monium thiocyanate in 25 ml ethanol. The volume of the solution was reduced by vacuum evaporation and the ammonium chloride was removed by filtration. Analysis calculated for (C2H5)4NW(OC2H5)(NCS)C14: W, 32.91; C1, 25.38. Found: W, 32.37; Cl, 24.98. No Commercial C, H, N, S analyses were obtained. The compound decomposed with evolution of ethyl chloride. sun SE SE m3 Tm .. I I 3. 24 Dimers of W(V): W2Cl4(OC2H5)6. W2Cl4(OC3H7)6:- W2Cl4(OC2H5)§: A 5.0 9 sample of WC15 (0.014 mol) was added to ethanol at -78°. The solution was gradually warmed to 0°. A sodium ethoxide solution (prepared by treating 0.64 g of Na (0.028 g-atom) with 20 ml ethanol)“was added to the green solution. The color became red-brown and sodium chloride separated from the solution. The sodium chloride was re— moved by centrifuging and decanting the mixture. The re- sulting solution was allowed to reflux for 2 hours and was then stored at -15° overnight. The dark red crystals were filtered, washed with a small amount of ethanol and dried in vacuo. Analysis calculated for W2Cl4(OC2H5)6: W, 47.15; Cl, 18.18; C. 18.48;. H, 3.88. Found: W, 47.21, Cl, 18.12; C, 18.41; H, 3.79. W2C11(OC3HZ)§: This dark red compound was prepared by the same procedure as W2Cl4(OC2H5)6 except that l-propanol was used in place of ethanol. Analysis calculated for W2Cl4(OC3H7)6: W, 42.58; Cl, 16.42; C. 25.01; H, 4.86. Found: W. 42.67; Cl, 16.49; C, 25.16; H. 4.88. The theoretical molecular weight of the dimer is 864. ‘The mass spectrum gave a series of peaks in the region of 862- 868 mass units. 25 Dimers of W(V): W3C12(OC2H5)3;.W2012(003H7)8:- W2C13(OCZH§)§: This compound was prepared by the same method as W2Cl4(OC2H5)6 except that a sodium ethoxide solution with an ethoxide to tungsten ratio of 4:1 was used. Analysis calculated for W2Clz(oc2H5)8:‘W, 46.04, Cl, 8.87; C, 24.04; H, 5.00; OC2H5, 45.08. Found: W, 46.35; Cl, 9.12; C, 23.45; H, 4.86; OC2H5, 44.34. W2C13(OC3H7)3: This compound was prepared by the same pro- cedure as W2Cl4(OC3H7)5 except that a sodium propoxide solu- tion with a propoxide to tungsten ratio of 4:1 was used. Analysis calculated for W2C12(OC3H7)3: W, 40.38; Cl, 7.78. Found: Cl, 8.63. W(OC:H§)§:- A 6.49 9 sample of WC15 (0.018-mol) was added to 10 ml ethanol cooled to -78°. The temperature of the solution was increased to 0°. A sodium ethoxide solu- tion [prepared by adding 2.11 9 Na (0.090 g-atom) to 60 ml ethanol] was added to the solution. The volume of the dark brown mixture was reduced by vacuum evaporation. ~The sodium chloride was then removed by centrifugation and filtration. The filtrate was then evaporated to dryness at 25° and 0.1 torr. The brown liquid residue was allowed to distill at 120° and 0.1 torr and a red-black liquid, which gelled upon cooling, was obtained in the distillate. Because this com— pound was extremely sensitive to moisture, no commercial C, H analyses were obtained. 26 Analysis calculated for W(OC2H5)5: W. 44.97; OC2H5. 55.03. Found: W, 44.40; OC2H5, 54.97. Sodium Hexaethoxotungstate(ylz- A 5.27 9 sample of WClg (0.015 mol) was added to 10 ml ethanol which had been cooled to —78°. The temperature of the solution was gradu- ally increased to 0°. A sodium ethoxide solution [prepared by adding 2.01 nga (0.087 g-atom) to 50 ml ethanol] was added to the green solution. Sodium chloride separated from the dark blue solution. The volume of the solution was reduced by vacuum evaporation. The sodium chloride was then removed by centrifuging and filtering. The dark blue fil— trate was evaporated to dryness and 20 ml benzene was added. The dark blue solution was cooled to -10° for 12 hours. The yellow solid was filtered, washed with a small amount of benzene and dried in vacuo. The W and OC§H5- anal- yses were low compared to those calculated for NaW(OC2H5)6 but the ethoxide to tungsten ratio was 6:1. Chloride was not an impurity. The compound was paramagnetic and decom- posed after standing in a sealed evacuated tube for several days. -Analysis calculated for NaW(OC3H5)6: w, 38.60; OC3H5, 56.60. Found: w, 36.05; OC2H5, 53.28. Potassium ethoxide was also used in the preparation above. A yellow solid, most likely KW(OC2H5)6, was isolated. 27 This compound was less stable than the sodium salt. Ethanol was identified as a decomposition product. 1A sodium eth- oxide solution with an ethoxide to tungsten ratio of 7:1 also gave a dark blue solution. However, the yellow com- pound isolated in the above manner had a Significant amount of sodium ethoxide impurity. Found: w, 25.32; OC2H5, 61.12. OC2H5/W ratio = 9.8/1. Dimers of W(IV): W2C14(OR)4(ROH)zJ R = CH3. C236: 1-C3H7. 2- :H1" W2Cl4(OCH3)A(CHfiOH)2: A 5.9 9 sample of WCl4 was added to 20 ml methanol that had been cooled to 0°. The temperature of the solution was increased to 25°. The grey-black solid gradually became yellow-green and the solu- tion became green. After the mixture had been stirred for three hours, the yellow-green compound was removed by fil- tration, washed with methanol and dried under vacuum. The product was then added to 20 ml methanol and stirred at 25° for 12 hours. Further reaction did not occur. The compound was sEparated by filtration, washed with methanol and dried under vacuum. Analysis calculated for W2Cl4(OCH3)4(CH3OH)2: W. 52.72, CL.20.33; C, 10.32; H. 2.87. Found: W, 52.14; Cl, 20.23; C, 10.17; H, 2.71. The oxidation state determination required 2.02 equivalents of cerium per g-atom W. WZCl‘(OC3H§)g(C3H§OH)3: This compound was prepared by the same procedure as chl4(OCH3)4(CH30H)2 except that ethanol K. 28 was used in place of methanol. The dark green compound was recrystallized from a CHC13 and ethanol mixture. Yield 45%. Analysis calculated for W3Cl4(OC2H5)4(C2H50H)2: w, 47.05; Cl, 18.14; C. 18.42; H. 4.09; OC3H5, 34.80. Found: w, 47.40; Cl, 17.95; c, 18.28; H, 4.02; oczns, 34.65. The theoretical molecular weight of the dimer is 782. The mass spectrum gave a series of peaks in the region of 778-784 mass units. The oxidation state determination required 2.23 equivalents of Ce(IV) per g-atom W. .EEC14(1'OC1§7)4(CQFTOH'IXE‘ This dark green compound was prepared by the same procedure as the previous complex ex- cept that 1-propanol was used. Analysis calculated for W3014(1-0C3H7)4(C3H70H-1)2: W, 42.48; Cl, 16.38; C, 24.95; H, 5.08. Found: W, 42.57; Cl, 16.35; C, 25.10; H, 5.04. E£Cl4(2-OC§H7)4(C1H7OH-2)2: An orange-brown solid was pre- pared by the same procedure as the previous complex. The compound was also recrystallized from a mixture of diethyl ether and 2-propanol. Analysis calculated for W2Cl4(2-OC3H7)4(C3H7OH-2)2: W, 42.48; Cl, 16.38; C. 24.95; H. 5.08. Found: W, 42.50; C1, 16.28; C, 24.67; H, 4.92. W2C14 (OC2H5)4(C5H5N)2:- A 2.26 9 sample Of W3C14 (0(3sz )4- (C2H5OH)2 was dissolved in 20 ml CHC13. A solution of 1 ml pyridine in 10 ml CHCl3 was added to the dark yellow-green solution. The volume of the dark-red solution, which 29 resulted, was reduced by evaporation. An orange precipitate formed when the mixture was cooled to -78°. The compound was separated by rapid filtration, was washed with a small amount of CHC13 and dried under vacuum. Analysis calculated for W3Cl4(OC3H5);(C5H5N)2: W, 43.38; C1, 16.73; C. 25.48; H. 3.54; N, 3.30. -Found: W, 43.40; Cl, 16.50; C, 25.24; H, 3.43; N, 3.26. The theoretical molecular weight of the dimer is 848. The mass spectrum gave a series of peaks in the region of 846- 852 mass units. W2C12(QC2H5)3(C§H5OH)2:- A 4.38 g (0.011 mol) portion of W3Cl4(OC2H5)4(C2H5OH)2 was suspended in 20 ml ethanol. A potassium ethoxide solution [prepared by adding 0.438 9 K (0.011 g-atom) to 15 ml ethanol] was added to the green mixture. The color became dark green and KCl separated from the sclution. The mixture was stirred for two hOurs and the KCl was removed by filtration. The resulting solution was stored at —10° for 12 hours. The black crystalline pro- duct was filtered, washed with a small amount of ethanol and dried under vacuum. Analysis calculated for W2C12(OC2H5)5(C2H5OH)2: W, 45.93; Cl, 8.85; OC2H5, 45.02. Fgggd; W, 46.00; Cl, 9.15; OC2H5, 41.10. The oxida- tion state determination required 1.96 equivalents of cerium per g-atom W. This compound decomposed with evolu- tion of ethanol vapor. Commercial C. H analyses were not obtained. 30 Attempts to Prepare W(OC3H5)1:- A 4.46 9 sample (0.012 mol) of W2Cl4(OC2H5)4(C3H50H)2 was suspended in 10 ml ethanol. A potassium ethoxide solution [prepared by treating 0.892 g R (0.023 g-atom) with 30 ml ethanol] was added to the mix- ture. The solution became black and KCl separated. The mixture was stirred for one hour then the ROI was removed by filtration. The blue-black filtrate was then evaporated to dryness. A black liquid residue was obtained. This residue was allowed to sublime at 110° and 0.1 torr. A very dark red liquid resulted from this treatment. ~Elemental analysis, ir and pmr spectra indicated that this compound was W(OC2H5)5 with a small amount of an unidentified impurity. Analysis calculated for W(OC2H5)5: W, 44.97; OC2H5. 55.03. Found: W, 45.17; 0C2H5, 51.22. Reaction of WCli_with Alcohols:- At 0°, WC14 formed a black suspension in alcohols. After the temperature was increased to 25°, green W(IV) complexes and dark green solu— tions were obtained. The addition of alcohol solutions of (C2H5)4NC1 resulted in the precipitation of light green solids. ~Elementa1 analyses and magnetic susceptibility measurements confirmed the identity of these compounds as tetraethylammonium salts of the tetrachlorodialkoxotung- state(V) anion. Analysis calculated for (C2H5)4NW(OC2H5)2C14: W, 33.69; Cl, 25.97. Found: w, 34.00; c1, 25.98. u(297°K) = 1.47 B.M. Analysis calculated for (C2H5)4NW(OCH3)3C14: W, 35.51; Cl, 27.39. Found: W, 35.66; Cl, 27.39. 0(297°K) = 1.51 B.M. 31 In acidic (with HCl) ethanol or propanol some evidence for oxygen abstraction was found. Impure complexes were isolated from these solutions, and spectra showed the presence of both W=O and W-O-C groups. Physical Properties of Tungsten Compounds:- The W(IV) methoxide complex was insoluble in methanol and other common organic solvents. The corresponding ethoxide and propoxide compounds were slightly soluble in the parent alcohol and very soluble in chloroform and benzene. All of these W(IV) compounds were insoluble in water and dilute acids but were readily decomposed by aqueous base. The W(V) dimers, W2Cl4(OC2H5)5 and W2Cl4(OC3H7)6 were slightly soluble in the parent alcohol and soluble in other organic solvents. These compounds were inert to water or dilute acids but were attacked by base. The compounds, W2C12(002H5)8 and W2C12(OC3H7)8, were very soluble in the parent alcohol and in other organic solvents. These complexes were readily decomposed by aqueous acid or base. In general, the W(V) monomeric compounds were much more sensitive to air and moisture. The dialkoxo species, C5H3NW(OR)2C14 were soluble in alcohol and other organic solvents. The thiocyanate complex, (C2H5)4NW(NCS)C15 was insoluble in common organic solvents. The mixed cohpound, (C2H5)4NW(OC2H5)(NCSX314, was similar. to the dialkoxo species. Reactions of W(OC2H5)5:- About 1.2 g of W(OC2H5)5 was added to a solution of 3 ml pyridine in 10 ml ethanol 32 saturated with HCl. The solution changed from a dark red to orange. No precipitate was observed after the solution was allowed to cool to —10°. No precipitate or color change was observed when a small sample of W(OC2H5)5 was added to a solution of tetraethylammonium chloride in ethanol. F. Spectroscopic Measurements I.R. Spectra:- Near infrared spectra were recorded by means of a Unicam SP-200 prism instrument. ‘Far infrared measurements were made by use of Perkin~Elmer model 301 and 457 spectrophotometers. Solid compoUnds were measured as Nujol mulls. In some cases, the spectra of samples, dis- solved in an appropriate solvent, were also determined. Sodium chloride or cesium iodide plates were used between 4000 cm.1 and 650 cm-1, cesium iodide plates from 650— -1 _ 300 cm and polyethylene discs from 650-100 cm 5. Optical Spectra:- Solution Spectra in the region of 8.0 x 103 cm-1 to 50.0 x 103 cm"1 were determined by means of Unicam SP-800 and Cary Model 14 spectrophotometers. -Samples were dissolved in the appropriate solvent and trans; ferred under nitrogen to dry cuvettes. Two methods were used to obtain solid reflectance spectra. A thick paste of the compound and Nujol was pressed between glass plates. ~Spectra were then recorded on the Cary Model 14 as if they were ordinary absorption spectra. Samples were also loaded into a flat—windowed adaptor for measurement on a Bausch and Lomb Spectronic 600 spectrophotometer equipped with a reflectance attachment. 33 Mass Spectra:- The mass spectra of some dimeric com— pounds were obtained by Dr. L. Shadoff, Dow Chemical Co., Midland, Michigan. Samples were sealed in melting point capillaries which were broken in the direct probe pumping chamber of a CECZl-llOB mass spectrometer. Magnetic SusceptibilityyMeasurements:- The magnetic susceptibilities of solid compounds were determined by the Gouy method. The experimental apparatus for variable tem— perature measurements was similar to that of Vander Vennen."3 The procedure was modified so that a stream of helium was passed over the sample tube.“ This action prevented the con- densation of water and contamination of the sample. The diamagnetism of some samples, including W(OC2H5)5 and W3Cl4(1-OC3H7)4(C3H7OH—1)2, was confirmed by the sharp pmr spectra and the absence of an epr signal. Proton Magnetic Resonance Spectra:— PMR Spectra were recorded by use of a Varian A56/60 spectrometer, equipped with a variable temperature controller. Tetramethylsilane (TMS) was used as an internal standard. 'Electron Spin Resonance Spectra:- ESR spectra were obtained with a Varian V—4502-04 Spectrometer with 100 kHz modulation. The magnetic field was calibrated by use of a Hewlett-Packard 524C Frequency Counter. ~The g values were obtained from the measured magnetic field and the Klystron frequency. 34 G. Proton Magnetic Resonance The theory and experimental applications of proton mag- netic resonance have been treated in many recent review' articles and textbooks.““75 No detailed discussion of these topics will be given here. The usefulness of the method is related to its two main features, the chemical shift and proton or nuclear spin-spin coupling. For diamagnetic alk- oxide compflexes, the spin-spin coupling constant is invar- iant (J = 7 cps). The chemical shift, which is sensitive H-H to the environment about the nuclei or protons, is of primary concern. This quantity is related to the orientation and reactivity of the various alkoxide ligands. The chemical shift, 0 , is defined by the equation:75 where VS and VR are the applied fields fin.units of fre- quency, cps) necessary to cause the sample and reference protons to undergo resonance and Va is the fixed frequency of the probe (for protons, v0 = 60 mc sec-1). H. Electron Spin Resonance The basic theory and application of esr spectroscopy to transition metal complexes have been the subject of many excellent reviews and texts. The review by McGarvey76 and the chapter by Kuska and Rogers in "Radical Ions"77 are recommended. 35 An unpaired electron in a transition metal complex may interact with an external magnetic field (Zeeman interaction), with the nuclear spin (metal hyperfine) and with the ligand nuclear spin (ligand hyperfine or superhyperfine). ESR spectroscopy is used to study these phenomena. These ef— fects are generally described by the spin Hamiltonian. For an electron in a complex with axial symmetry (X =*Y =.i' z = II), the spin Hamiltonian can be written: H = s[g| lSsz + gl($xHx+ SyHy)] + [Al ISZIZ + A_L(sx1x +SI , yy)] where 9" and gl are the spectroscopic splitting fac- tors, B is the Bohr Magneton, Hx’ H . Hz are the compo— Y nents of the magnetic field in the x, y, z directions; Sx' Sy’ Sz are the components of the electron spin operator along the respective axes and Ix’ I . I are the components y z of the metal nuclear spin along the respective axes. ~The measurable parameters in ordinary esr spectra are the g values (position of absorptions) and A values (distance between metal hyperfine absorptions). For tung— sten complexes, the low isotopic abundance [133W I = 1/2 = 14.2%) generally prevents the resolution of metal hyper~ fine structure. 36 I. -Magnetic Susceptibility The calculation of the magnetic susceptibility was made by use of the equation:78 1 .t 106x = fl wS where X is the gram susceptibility (cgs units) of the sample, B is the tube constant, ws is the weight of the sample in grams and F' is the force (in mgrams) exerted on the sample alone, that is, F' = F - 5, where 6 is the force on the tube. The tube constant, B , must be determined by use of a substance of known susceptibility. In this work, CuSO4'5H30 was used. Its susceptibility is 5.92 x 106 cgs units at 25°. The molar susceptibility, Xm , was found by multi- plying the gram susceptibility by the molecular weight of the sample. The diamagnetism of the organic ligands and cations present forms an appreciable portion of the sus- ceptibility of the complex. The susceptibility of the metal ion, x$ , is obtained by adding to Xm the Pascal's constants,78 which are a measure of the diamagnetism of the ligands. The value of the magnetic moment is related to the square root of” XQ : , 1 ”eff = 2.84 (Xm T) /2 B.M. 37 The CurieAWeiss Law: | C Xm — T + 6 is used to describe the variation with temperature of the magnetic susceptibility of normal paramagnetic substances. A plot of l/Xg against T gives a straight line whose intercept 6 , is the Weiss constant. The magnetic moment is often discussed in terms of spin and orbital contributions: “eff = g[J(J + 1)]1/2 _1+[S(S+1)-L(L+1)+J(J+1)] where g — 2J(3»+ 1) ' and J, the total angular momentum, = [L + S], [L + 5-1]..: |L - SI. -When a system has no angular momentum (L = 0) then J = S and g = 2.00, ”eff = 2[5(5 + 1)]1/2 This is the so—called "spin only" formula. The degeneracy of the d orbitals may not be com- pletely removed by a ligand field. For this reason, orbital angular momentum remains to some extent with the tag or— bitals. Figgis"9 has developed a method for estimating the orbital contribution to the magnetic moment of transition metal complexes. The degeneracy of the t29 orbital may be removed by spin-orbit coupling or by a ligand field of 38 symmetry lower than cubic. -Figgis defines k as a measure of the delocalization of the electron on the ligands. A is the separation between the orbital singlet and doublet of the t29 term created by tetragonal distortion of the li- gand field and v is A/A, where A is the spin—orbit coupling constant. Figgis has calculated ”eff as a func- tion of kT/A for different values of k and v. If the experimental curve can be matched over a wide temperature range, values of k, A, v and A can be obtained. This method must be used cautiously, computer fits are desirable and too little or too great a dependence of “eff on temperature prevents quantitative correlations. RESULTS AND DISCUSSION This section is divided into two parts: A. W(V) monomeric complexes; B. W(V) and W(IV) dimeric complexes. A. W V onomeric om lexes 1. Preparation of Complexes The reaction of WC15 with neutral, acidic (with HCl) and basic (with alkoxide ion) alcohol solutions was in- vestigated. At -78°, WC15 formed a bane-black mixture with the alcohols studied. When the temperature of the solution was increased to 0°, dark green solutions were ob- tained. The addition of a pyridine—alcohol mixture or a pyridinium chloride solution resulted in the formation of the light green tetrachlorodialkoxotungstate(V) complexes, C5H6NW(OR)3C14, R = CH3. C2H5. When larger cations, such as tetraethylammonium chloride, were added to this WC15 alcohol solution, a mixture cf salts of the anions W(OR)C15- andW(OR)2Cl‘- was isolated.81 Only mixed oxoalkoxo complexes were isolated from the reaction of WC15 with 1 or 2~propanol. The light blue- green complex, (C5H3N)2WOC15, was prepared by the addition of pyridinium chloride to a solution of WC15 in 2—propanol 39 40 saturated with HCl. The method of preparation of this com— pound repOrted by Funk62 could not be successfully repeated. Funk added pyridinium chloride to a hot solution of WCl5 in methanol. In acidic (with HCl) alcohol solutions, WCl5 formed an unstable anion, W(OR)Cl5-. The size of the cation was critical in the isolation of this species. -No solid com- plex was obtained withtie pyridinium cation. However, the yellow complexes, (C2H5)3NHW(OR)C15, R = CH3, C2H5, were prepared by the use of the triethylammonium cation. The pentachloroalkoxotungstate(V) complexes were unstable and decomposed in the solid state with evolution of alkyl halide vapor. One of the solid products of this decomposition re- action was identified as the tetrachlorooxotungstate(V) complex. Rillema72 found that the rate of alkyl halide evolution decreased as the sizes of the cation and the alkoxide ligand were increased. Attempts to prepare monomeric complexes of the type, W(OR)nCl;_n with n > 2 were unsuccessful. The green WCl5 alcohol solutions were made basic with alkoxide ion. When alcohol solutions of the cations, (C2H5)4NC1 or (C2H5)4NOR. were added to this reaction solution with the OR-/W ratio greater than 2:1, the precipitate was contaminated with dark red or brown crystalline material. These highly colored complexes were diamagnetic dimers (see Results and Discussion, Part B). In these basic alcohol solutions, di- merization appeared to be the dominant reaction. 41 Several new thiocyanate complexes of W(V) were also prepared. The reaction of WC15 with (C2H5)4NSCN in chloro- form yielded the dark brown (C2H5)4NW@mSXnfi. .Attempts to prepare other substituted chlorothiocyanate complexes of W(V) were unsuccessful. The mixed alkoxo-thiocyanate com- pound, (C2H5)4NW(OC2H5)(NCS)C14, was prepared by the addi- tion of (C3H5)4NSCN to an ethanol solution of WCl5 which had been treated with NH4SCN. This compound decomposed with evolution of ethyl chloride. The solid complex gradu- ally changed from a light yellow-green to dark green. However, the solid residue was unidentified. The esr and far ir spectra of these W(V) monomers indicated that the compounds possessed axial symmetry. 2. Electron Spin Resonance Spectra The esr spectra were determined for solid samples and solutions of the W(V) complexes at 77°K and at room tempera- ture. These results are listed in Table I and representative spectra are shown in Figures 1 and 2. The frozen solution spectra of the W(V) complexes could be resolved into parallel and perpendicular components. Thus, axial symmetry is indicated--D4h symmetry for the dialkoxide complexes and C4v symmetry for (C5H3N)2WOC15 and for (C3H5)4NW(OC¢H5)(NCS)C14. In each case, 9|! was found to be greater than 9 1.. A similar observation is reported for WOX5=, X = Cl, Br, complexes.19 The spectra of the solid samples and solutions of the complexes at room 42 Table I. ESR parameters for W(V) complexes.a . Temp. Com ound Medium 9 °I< <9> 9| l 91 (C5H3N)2WOC15 Solid 297 1.76 CH3NO2 77 (1.78) 1.79 1.77 C5H5NW(OCH3)3Cl4 Solid 297 1.73 CH30H 77 (1.72) 1.75 1.70 CHgNOa 77 (1.74) 1.78 1.72 C5H5NW(OC3H5)3C14 Solid 297 1.75 C2H50H 297 1.76 77 1.76 1.70 CH3NO2 77 (1.75) 1.79 1.73 (C2H5)4Nw(OC2H5)(Ncs)Cl4 Solid 297 1.79 1.72 CH3NO2 77 (1.75) 1.78 1.73 (C3H5)4NW(NCS)C15 Solid 297 1.78 a( ) = calculated values. 43 increasing 'magneEic fihld Figure 1. Electron spin resonance spectrum of solid C5H5NW(OCH3)3C14 at 2979K. increasing - magnatrc-rreid Figure 2. Electron spin resonance spectrum of C5H6NW(OCH3)3C14 in CH3N02 at 77°K. 44 temperature consisted of a single broad absorption (half width ~v100 gauss). No suitable solvent was found for (C2H5 )4NW(NCS)C15 . An absorption in the frozen solution spectra of these compounds was thought to be the hyperfine component of the parallel band due to 133W (I = 1/2, 14.28%). However, the broad absorptions of the isotopes with I = 0 prevented any definite assignment. 3. Ipfrared Spectra The infrared absorptions of these complexes are listed in Table II. rRepresentative traces of the spectra are shown in Figures 3 to 7. The evidence of C4v or D4h point group symmetry for these complexes was indicated by the position and number of the observed far ir vibrations. The dialkoxo compounds ex- hibited a trans alkoxide arrangement (D4 This symmetry h)' required only five normal modes. The cis configuration (C2 ) “‘ v would require a large number (13) of normal modes. The metal-chlorine stretching frequency at about 300'Cm-1 and the metal-chlorine deformation vibrations at 165 cm-1 were assigned by comparison with tungsten hexachloro‘9 and oxochloro32 complexes. Absorptions of the tungsten alkoxide complexes in the region 500-600 cm_1 are probably M-O-C stretching vibrations. 1A band at 400 cm-1 in the ethoxide complexes may be an O-C-C deformation. 45 a Table II. Infrared absorption frequencies of W(V) monomers. (With possible assignment.) (C5H6N)2WOC15 C5H3Nw(OCH3)2c14 606 (s) 559,542-(8) v(W-O) 387 (s) 389,360 (w) 309,294 (s) v(W-Cl) 317 (sh)' 231,238 (8) 289 (s) v(W-Cl) 197,203 (8) 255 (s) 161 (s) V(C14W-Cl) 1060 (S) V(C-0) 970 (s) v(W = O) C5H6NW(OC2H5)3C14 (C2H5)4NW(OC2H5)(NCS)C14 594 (s) v(W-O) 595 (s) v(W-O) 416 (m) v(C-c-O) 480 (w) 0(N-C-S) 286 (s) (broad) vCW-Cl) 410 (m) 231 (m) 350 (m) 154 (s) v(C14W-Cl) 315 (sh) 1060,1095 v(C-O) 285 (s) v(w-C1) 2020 (s) V (C2H5)4NW(NCS)015 2085 (m) v(c-N) 500 (w) 5(N-C-S) 1990 (sh) 320 (s) v(W-Cl) 900 (w) v(C-S) 2120 (m) 1060,1090 v(C-O) 1980 (s) v(C-N) 2020 (sh) 1920 (m) 1830 (w) 890 (w) v(C-S) aPlus all cation bands; w = weak; m = medium; s = strong; sh shoulder. 46 A l I l l I 5000 3000 2000 1800 _1 1400 1000 800 2000 cm L 1 L l 1 J 600 500 400cm—1 300 200 100 Figure 3. Infrared spectrum of (C5H3N)3WOC15. 47 1 1 1 I A 1 1 1 4 n 4 5000 3000 2000 1800 _1 1400 1000 800 2000 cm 1 L 1 t _ 1 J 600 500 400 cm31300 200 100 Figure 4. Infrared spectrum of C5H5NW(OCH3)2C14. 48 A. L _4__l L 1 u. A L . 5000 3000 2000 1800 1400 1000 800 -1 2000 cm I L 1 1 1 I 600 500 400 _1 300 200 100 cm Figure 5. Infrared spectrum of C5H3NW(OC2H5)2C14. 49 . . U ' 1 g 1 4 1 l n 2000 1800 1600 1400 1200 1000 800 600 400 250 —1 cm Figure 6. Infrared spectrum of (C2H5)4NWKNCS)C15. I L I I L I I I I ‘000 1800 1600 1400 1200 _1 1000 800 600 400 250 cm Figure 7. Infrared spectrum of (C2H5)4NW(OC2H5)(NCS)C14. 50 Near ir spectra (5000—650 cm-l) of the tetrachlorodialkoxo- tungstate(v) and pentachlorooxotungstate(V) complexes indicated that pyridinium ion was present rather than pyridine ligand. Cation bands due to (C2H5)4N+ were also identified in the spectra of tetraethylammonium salts. The alkoxide complexes have strong bands in the region (1000-1100 cm-l) where the C-0 stretching vibration occurs.82 No OeH vibration at 3500 cm.1 was observed, as one would expect with alkoxide rather than alcohol ligands bound to the metal. The C-N stretching,83 the C—N-S bending84 and C-S stretch- ing85 vibrations at 2150-2050, 500-400 and 880-690 cm-l, respectively, have been used to differentiate between thio- cyanato (S—bonded) and isothiocyanato (N—bonded) complexes. For an N-bonded complex, an increase in the covalent char- acter of the coordinate bond results in a decrease of the c—N stretching frequency and an increase in both the C-S stretching and N-C-S bending vibrations from those observed for the free thiocyanate ion. The ir spectra of the W(V) complexes indicated the presence of N-bonded thiocyanate ligands. The C-N stretching frequencies of the W(V) compounds are located at 2000—1950 cmdf These bands are lower than the free thiocyanate value (2050 cm-l). Weak absorptions near 900 cm“1 and 500 cm.1 are believed to be the C—S stretch- ing and N-C—S bending vibrations. These bands are at higher frequencies than the free thiocyanate values. Similar re— sults were reported for the N-bonded niobium and tantalum 51 hexaisothiocyanates, K2M(NCS)6.34 The presence of more than one absorption band in the C-N region for these W(V) complexes can be explained by assuming the M-N-C bond to be bent rather than linear. An interesting comparison can be made between the C-N stretching frequencies of (C2H5)4NW(NCS)(OC3H5)C14 at 2020 cm"1 and (C3H5)4NW(NCS)C15 at 1970 cm-1. The lower value for the latter complex is an indication of a more covalent nitrogen bond to the tungsten atom. -The mixed alkoxo-thiocyanate complex apparently has a more ionic M-N bond. Its ir spectrum in the C-N region is similar to that for WO(NCS)5=. For this reason, the ethoxide and thio- cyanate ligands are probably in a trans configuration. 4. .Magpetic Moments The magnetic susceptibilities of the W(V) complexes were measured at room temperature, at 77°K and in some cases at 195°K. These results are listed in Table III. The compounds exhibited normal field independent paramag- netism. The weak temperature dependence of the magnetic moments is reflected in the small negative values of the Weiss constant. .Ir and esr spectra of these complexes suggest that the degeneracy of the ground state was removed by axial dis— tortion to give tetragonal symmetry. This is the basic requirement for the use of the Figgis calculations.3° Because of the nearly constant magnetic moments, only 52 Table III. Magnetic properties of W(V)-compounds. Compound Temp. X; x 106 u 6 (°K) cgs units (B.M.) (°K) (C5H3N)2WOC15 297 1000.4 1.54 -2 77 3834.0 1.54 C5H3NW(OCH3)2C14 297 913.9 1.48 -1 195 1358 1.46 77 3166 1.40 caner(Oc,H5),c1, 297 957 1.51 +1 195 1501 1.53 77 3775 ' 1.50 (C5H3)4NW(NCS)C15 297 417.5 1.00 —35 77 1244 0.88 (C,H,).NW(OC,H5)(NCS)C14 297 919.7 1.49 -1 77 3544 1.48 53 qualitative conclusions were obtained. For the oxychloride and dialkoxide complexes, v is greater than 10, A ranges from 8,000 to 11,000 cm-1 and A is approximately 500 cm-1. Other workers86 have found similar values for other oxyhalide compounds. V The low value of the magnetic moment for (C2H5)4NW(NCS)C15 is a reflection of the weak ligand field of the thiocyanate ion. The weak axial component of the ligand field does not increase the spacing of the degenerate t2g orbitals and the large spin-orbit coupling constant leads to a magnetic moment well below the spin-only value. The magnetic moments of the other complexes increase as the number of alkoxide groups increases. By analogy with the oxo complexes, a strong tungsten oxygen multiple bond would provide a strong axial distortion to increase the spacing of the t29 orbi- tals. Then, the spin~orbit contribution to the magnetic moment is lowered. 5. Visible and Reflectance Spectra The electronic spectra in solution and the reflectance spectra of the solid complexes were determined. ‘The results are listed in Table IV. Sketches of the spectra are shown in Figures 8 to 11. The symmetry of the compounds can be used to assign the absorption bands. The splitting of the d orbitals by either C or D4h symmetry result in the same arrangement 4V of the orbitals. The ordering of the orbitals from lowest 54 Table IV. Electronic absorption spectra of W(V) compounds. Electronic Absorptions Compound Medium maxima x 103 cm (s in parentheses) (C5H5N)2WOCls solid 12.8,14.1,15.6 (sh), 17.3 (sh), 23.8 C5H6Nw(OCH3)2c14 solid 11.1,13.9,24.1 methanol 11.2(12), 14.3(15),25.0 (~15), 30.8(>103), 35.0 (>103) c5H6Nw(Oc2H5)2c14 solid 12.4,14.5,25.6 ethanol 11.4(12),13.9(13), 25.0(60),30.8(600), 34.5(~103) (C2H5)4NW(NCS)C15 solid 17.8,19.6,24.1 (02H5)4NW(OC2H5)(NCS)C14 solid 17.1,18.5,23.5,26.0 (sh) solid (after two 14.3,17.2,18.2 weeks) 55 2.0 0) U C. (U ,0 H O U) .-Q u< 0.0 l L 1 l 1 n L L 50.0 40.0 _1 33 .3 28.6 25.0 cm x103 2.0 Q) U (2 f0 .0 H O U) ,Q '42 / 4‘1 0.0 _l I I I L L J I 22 .2 18 .2_ 15 .4 13 .3. 11.8 cm x103 Figure 8. Solution spectrum of C5H6NW(OC§H5)2C14 in ethanol. 56 .Hocmsum as M v «HesflnmnooVSZomso one “Hocmsums CH A IIIIII V «HUNAmmoovzz moo mo Esnuoomm coausaom .m musmflm monH|EU mo.m o.oH H.HH m.NH m.vH ®.mH o.om o.mN 0.0 I I: .\.II. I. \. / ./ l \. / \ l I. \ / I \ III-‘1‘", \ I.:l.|.\ V. a. s o I 0.. e U o e ’ a I I a .x I. a a 57 .A uuuuuu V .HOAAnmaOOVEZomno ocm aéllllllv VHUNAemUOvzzemmo mo Esuuoomm mocmuooammu oHHom moneIEU mo.m o.oH H.HH m.NH man m.mH o.om o.mm c a 4 - J- - 4 u ’I’ I l. _\.l I s I .x I , I x , a \ I x a x a 1’ s I x , c D 4 a , x I I I ’ \ 1:. z a /l\ I A / \ I \ .OH onsmflh 58 .A|~I.I I.a I9 mxmmB 03» Hmumm «HUA onAmmuoovzszmmuuv flaw . vHuAmUZVAmmuoovzz A ..... v .HH wusmflm 2.0mm“: XIIIIV maoAmnzvzzAmm 8 mo 833QO mocmuomflmu cfiom monHIEU mo.m o.oH H.HH n.mfi m.vH o.mH o.om o.mu - q - u q d d J /O /I 59 to highest energy are the b2 (dxy), the degenerate e (dxz, dyz), the b1 (dxz-yz) and the al (dzz). Thus three d-d transitions are spin allowed. Molar absorptivities for these Laporte forbidden bands should be low (~10). For the tungsten oxo or dialkoxo compounds, the bands at ~12.0 x 103 cm“1 and «14.0 x 103 cm—1 are prob- ably the Bz-——> E transition. The two transitions are probably due to a removal of the degeneracy of the E state. The Ba —-> 81 transition may be located at «23.0 x 103 cm-l. The other d-d transition is probably ob- scured by the charge-transfer bands at higher energy. The absorption bands for the thiocyanate complexes are located at about 16.0 x 103 cm"1 and also indicate the low ligand field strength of the thiocyanate ion. The t29 orbital is not split to a great extent since these values are close to the 10Dq -value for WCls- at 21.7 x 103 cm-l. After the compound had stood in a sealed tube for two weeks, the spectrum of (C2H5)4NW(NCS)(OC2H5)C14 showed a strong band in the region of 14.0 x 103 cm-l. This band was ab— sent from the spectrum of a freshly prepared sample and is probably due to the presence of oxychloride decomposition products. 60 B. W(V) and WQTV) Dimeric Complexes 1. Preparation of Complexes Color changes were observed during the titration of WC15 alcohol solutions with alkoxide ion solutions. Table V summarizes these results for an ethanol solution. Similar changes occurred in methanol and 1-propanol. No further colors were noted for alkoxide to tungsten ratios greater than 6:1. The visible spectra of these solutions were char- acterized by intense charge transfer bands which gradually shifted into the visible region with greater alkoxide con- centration. Table V. WC15 in basic ethanol solutions. 1— Ratio —OC2H5/W Color 0 green 2:1 red-brown 4:1 dark—brown 6:1 blue A new preparative method was developed to isolate the complexes present in these basic alcdhol solutions. A WC15 sample was allowed to react with the neutral alcohol, then a stoichiometric amount of alkoxide ion dissolved in alcohol was added. After filtration to remove the sodium or potassium 61 chloride that was formed, the resulting solution was allowed to reflux for 1-2 hours. -The complex crystallized after the reaction solution was allowed to cool to -10°. The red, diamagnetic complexes, W2Cl4(OR)6, R = C2H5, 1-C3H7 were isolated from solutions with an alkoxide to tungsten ratio of 2:1. The ethoxide complex, W2Cl4(OC2H5)6, was previously prepared by the prolonged alcoholysis of WC16.57 Brown, diamagnetic complexes W2C12(OR)8, R = C2H5, 1-C3H7, were prepared when the WC15 alcohol solution was treated with an alkoxide solution where -OR/W = 4:1. A red-black liquid, W(OC2H5)5, was obtained after a WC15 ethanol solution was treated with an ethoxide solution with -0C2H5/W = 5:1. Vacuum distillation was necessary to obtain this compound in a pure form. A yellow, paramagnetic solid, probably NaW(OC2H5)6, was isolated after an alkoxide solution with -0C2H5/W = 6:1 was added to the neutral WC15 ethanol solution. This complex was unstable and satisfactory elemental analyses were not obtained. -Solid W(IV) chloride alkoxides, W2Cl4(OR)4(ROH)2, and solutions containing W(V) species were obtained when WCl4 was allowed to react with the various alcohols. No evidence for W(III) or W(II) species was found. Therefore, a normal disproportionation reaction is unlikely. The nature of the oxidizing agent is unknown. The possibility that the start- ing material was contaminated with WC15 can be discounted. The WCl4 was purified by heating under vacuum at 325°. Under these conditions, WC15 would have sublimed away from the tetrahalide. 62 The compounds, W2Cl4(OR)4(ROH)2, were the only stable W(IV) Species prepared in this work. The black compound, W2C12(0C2H5)6(C2H5OH)2, decomposed slowly in a sealed tube, and W(OC2H5)4 could not be isolated. The reason for the instability of the tetraethoxide may be similar to that postu- lated for the niobium analogue. Bradley87 has suggested the cause for the instability of the tetraalkoxide of niobium in the presence of alcohol, 2 Nb(0R)4 + ZROH > 2 Nb(OR)5 + H2. A similar reaction may be involved in the tungsten tetra- ethoxide decomposition. The main product from attempts to prepare W(OC2H5)4 was the pentavalent derivative, W(OC2H5)5. However, Wentworth and Brubaker88 successfully prepared Nb(002H5)4, which may indicate that Bradley's argument is not valid. 2 The W(IV) alkoxoalcohol complexes are very similar to the W(III) compounds, W2Cl4(OR)2(ROH)4, R = CH3, chs, C3H7, prepared by Clark and Wentworth.64 However, products dif- ferent from those reported by Clark and Wentworth were isolated from the reaction of the ethoxo-ethanol compounds with pyridine. A brown, air-sensitive material was reported64 as the result of the reaction of the W(III) complex with pyridine. An orange compounds, W2C14(OC2H5)4(C5H5N)2, was isolated from the analogous reaction of the W(IV) ethoxo- ethanol compound. 63 The dimeric formulation for these W(V) and W(IV) com- pounds is supported by mass spectra and molecular weight deternunations. The diamagnetism and far ir and pmr spectra of the chloro-alkoxo compounds suggest that the structure of these complexes may be a chloride bridged bioctahedron. 2. Mass §pectra and Molecular Weight Determinations Mass spectroscopic data for W2Cl4(OC3H7)6, .W2C14(OC2H5)4(C2H5OH)2 and W2C14(OC2H5)4(C5H5N)2 have con— firmed the dimeric nature of these compounds. The same formulation for the other compounds is suggested by the similarity of their chemical and physical properties. -Molecular weight determinations in benzene (cryoscopic method) were performed by Galbraith Laboratories,Inc. The results for the compounds, W2Cl4(OC3H7)6 (1040) and for WgCl4(OC3H7)4(C3H7OH)2 (1013) were higher than the calcu- lated molecular weights, 864 and 866, respectively. Partial dissociation of the complexes in solution is a possible ex- planation of these results. Conductivity data were not ob- tained for these solutions. 3. Magnetic Susceptibility and Oxidation State Deter- minations All of the compounds formulated as dimers were diamag- netic. A chloride bridged bioctahedral structure was pro- posed for W2Cl4(OC2H5)6 by Klejnot.57 The other W(V) and .W(IV) dimeric compounds prepared in this study probably have similar structures. Thus, the diamagnetism can be ex- plained in terms of metal-metal bonding resulting from overlap of orbitals on adjacent tungsten atoms. If the 64 tungsten ions are shifted from the centers of their octa- hedra toward each other, as is observed for the niobium and tungsten tetrahalides, then overlap would be even more favorable. The oxidation state determinations confirmed the formulation of these complexes as W(V) or W(IV) deriva- tives. 4. (Infrared Spectra The infrared features of the W(V) and W(IV) dimers are listed in Tables VI and VII. Sketches of the spectra are given in Figures 12 to 19. These compounds have near ir absorptions characteristic of bound alkoxide in the 1000-1100 cm.1 region. The complex- ity of the spectra in this region may be an indication of non-equivalent alkoxide groups and has been interpreted as evidence for bridging and terminal alkoxide groups.82 However, the far ir spectra of these compounds tend to sup- port a chloride bridged formulation. An absorption at about 250 cm.1 may be a W—Cl bridge vibration in these W(V) and W(IV) dimers. Similar bands for the dimers, WC15 (246 cm-1) and WCl4 (237 cm-1) have been assigned as bridging chloride vibrationsfl:3 The term- inal W-Cl vibration at about 300 cm-1 is in the same region as the W(V) monomers. The presence of a bridging metal- chlorine vibration about 50 cm.1 below the terminal vibra- tion was also noted for polymeric cobalt complexes.8 65 Table VI. Infrared absorption frequencies (cm-1) of dimeric tungsten species (with possible assignment). W2C12(0C2H5)8 W(0C2H5)5 600(s) v(W-O) 615(3) v(W-O) 519(3) v(W-O) 582(3) v(W-O)- 387 (m) v ‘(o—w—o) 550 (Sh) 282(3) V(W-Cl) 228(m) v(W-Cl) w,,c14 (OC3H7)6 w,,c:1,(ocH;,)4 (CH3OH)2 652(m) 575(m) v(W-O) 619(3) v(W-O) 532(3) v(W-0) 575(3) v(W-O) 476(3) ' 515(3) 460(3) 449(m) 412(w) 418(m) 332(W) 377(m) 306,299(v3) v(W-Cl) 297,301(vs) v(W-Cl) 245(m) v(W-Cl) 266(3h) 203(w) 229(m) v(W-Cl) 188(m) W2C14(0C2H5)4(C2H5OH)2 W2014(1-OC3H7)4(C3H7OH-1)2 586(3) v(W-O) 615(3) v(W-O) 526(3) v(W+O) 561(3) v(W-O) 478(m) v(O-W-O) 455(m) v(O-W-O) 379(m) 412(m) 319(3) v(W-Cl) 305(3) v(W-Cl) 302(3) v(W—Cl) 255(m) v(W-Cl) 290(sh) 265(m) 245(m) V(W-C1) 66 Table VI. (Continued) W2Cl4 (2-0C3H7) 4 (C3H7OH-2 ) 2 W2Cl4 (OC2H5 ) 4 (C5H5N) 2 258 (m) 617(3) v (W-O) 648 (s) 586(3) v(W-O) 609(3) v(W-O) 486 (m) v '(o-w-o) 559 '(s) '(w-o) 449(m) 476(m) v(O¥W-O) 407(m) 449(w) ' 307(3h) v(W-Cl) 397(w) 294(3) ' 315(sh) v(W-Cl) 250(m) v(W-Cl) 291,296(v3) v(W-N) 194(w) 280(8) ' I 230(m) v(W-Cl) wzcl4 (oczn5 ) 6 205 '(w) ' 617 (s) v (w-o) 185 (W) 515,497 (3) v'(W-O) ' 395(m) ' v(04w—0) 304(3) v(W-Cl) 284(8) ' v(W-Cl) 67 Table VII. Features of infrared spectra of W(V), W(IV) compounds (1000-1100 cm-l). . , Compound W3Cl4(OC3H5)3 984(3), 1050(3), 1078(sh), 1100(m) W2C12(OC2H5)8 1020(sh), 1060(3), 1075(3), 1100(m) - W(OC3H5)5 1040(3h), 1060(s), 1095(m). W2C14<0C3H7)6 980(8), 1010(8), 1070(8), 1100(m) W2C12<0C3H7)3 985(8), 1005(8), 1080(8), 1100(m) W2014kxafl5)4(C2H50H)2 1010 3), 1095 3) CHCl 1020 s , 1060 3h), 1095(m) $01,: W2C14(1-0C3H7)4(C3H7OH-1)2 1040(m), 1060(3) W2C14(OC2H5)4(C5H5N)2 1000(m), 1045(8), 1095(m) Pyridine bands: 1610(w), 690(3), 755(3) W2C12(OC3H5)6(C2H50H)2 1045(3), 1060(3), 1095(3) NaW(OC2H5)6 1060(s), 1095(m) 68 ///)” U 1400 j A I 5000 3000 2000 1800 1000 800 2000 cm- 600 500 400 _1 300 200 100 cm Figure 12. Infrared spectrum of W2Cl4(OC2H5)6. 69 V‘w U “A?“ J 5000 ‘ 3000 Lzooo 1600 ' 1400 1000 800 -1 2000 cm 600 500 400 _1 300 200 100 cm Figure 13. Infrared spectrum of W2C12(0C2H5)8. 7O MW 4 . .U .. U 5000 3000 2000 1800 _ 1400 1000 800 2000 cm 600 500 400 300 200 100 -1 cm Figure 14. Infrared spectrum of W2Cl4(OC3H7)6. 71 V? d A l «Mn L m 2000 1800 1400 1000 800 5000 3000 _ 2000 cm sdb 50b 400 _1 300 200 100 cm Figure 15. Infrared spectrum of W(OC3H5)5. 72 /\ 5000 3000 .2000 1800 _ 1400 1000 800 2000 cm 1 l l - l !_-—_I_. L 600 500 400 _1 300 200 100 cm Figure 16. Infrared spectrum of W2Cl4 (0CH3)4(CH3OH)2 . 73 f/w 5000 3000 2000 1800 1400 1000 800 -1 2000 cm 600 500 400 _1 300 260 160 cm Figure 17. Infrared spectrum of W2C14(0C2H5)4(C3H50H)2. 74 fl 1 U 5000 3000 2000 1800_ 1100 1000 800 2000 cm 660 500 400 _1 300 200 100 cm Figure 18. Infrared spectrum of W2Cl4(OC2H5)4(C5H5N)2. 75 *4”) 1L 4)) 5000 3000 2000 1800 _ '1400 1000 300 2000 cm 600 500 400 300 200 100 -'1 cm Figure 19. Infrared spectrum of W2Cl4(1-OC3H7)4(C3H7OH-1)2. 76 Attempts were made to displace the chloride ions from’- the chloro alkoxide dimers. .Samples were dissolved in alcohol and a saturated solution of KI in alcohol was added. No precipitation occurred even after heating. The relative inertness of the chloride ions to solvolysis and precipita- tion of KCl may be an indication of chloride bridging. On the basis of similar chemical evidence, Wentworth and Brubaker88 suggested a chloride bridged structure for the dimer,Nb2C12(OC2H5)5(C5H5N)2. Tentative assignments of the far ir absorptions were based on previous work with monomeric W(V) alkoxides (see this section Part A). In general, the W-O stretching fre- quency was observed between 600-500 cm.1 and the W-Cl and w—N stretch about 300 cm-1. As the alkoxide increased in size, the metal oxygen stretch increased in frequency. This trend was also noted for monomeric W(V) alkoxides.90 No apparent change in the W-Cl stretching frequency occurred when the oxidation state changed. A saturated CHc13 solution of W2Cl4(OC2H5)4(C2H50H)2 showed bands assigned to bound ethoxide only. No O-H stretch at 3500 cm-1 was observed. Some type of proton exchange is apparently present in these W(IV) alkoxoalcohol complexes. 5. Proton Magnetic Resonance Spectra The pmr absorptions of the dimers are listed in Table VIII. The spectra are presented in Figures 20 to 25. 77 Table VIII. PMR spectra of W(V) and W(IV) dimers.a (Relative intensities in brackets). T Compound Solvent -CH3 -CH2 ppm ppm W2C14(OC2H5)5 col4 1.03(2) 4.57(2) 1.38(1) 5.83(1) W2C12(OC2H5)3 col4 .98 5.22(1) 1.38 5.23(1) W(OC2H5)5 CCl, 1.22 4.75 W2Cl4(OC3H7)6 CC14 Complex 4.47(2) 5.58(1) W2Cl4(OC2H5)4(C2H50H)2 CHCl3 1.25(2) 4.56(2) 1.38(1) 5.47(1) W2Cl4(OC3H5)4(C5H5N)2b CHC13 1.42~ 5.88 W2C14(1-OC3H7)4(C3H70H-1)2 CHC13' Complex 4.35(2) 5.17(1) W2C14(2-0C3H7 )4 (C3H7OH-2 )2 CHCl3 1 .22 1.75 aTMS used as internal standard, all spectra were run at 35°. b Reacted with TMS; resonance measured again3t CHC13 (7.27 ppm). 78 M "JAM 7 6 5 4. 3 2711 o PPm Figure 20. Proton magnetic resonance spectrum of W2Cl4(0C2H5)6 ‘ in CC14. l d n n n 1 l I 1 J 7 6 5 4 3 2 1 0 PPm Figure 21. Proton magnetic resonance spectrum of W2C12(OC2H5)3 in CCl4. 79 11) ml) 1 j l J J J L fi’ 7 6 5 4 3 2 1 ' 0 PPm Figure 22. Proton magnetic resonance spectrum of W2C14 (0C3H7 )6 in CC14 o A 7 6 5 4 3 1 0 ppm . Figure 23. Proton magnetic resonance spectrum ch(OC2H5)5 in CCl4. m) 80 D D A A A j I 7 5 5 4 3' 2 1 0 ppm Figure 24. Proton magnetic resonance spectrum of Wgcl4(OC2H5)4(C2H50H)2 in CHC13. A B A L J L I A l l V 6 5 ppm 4 3 6 £5 ppm 44 3 Figure 25. A. Low field pmr spectrum of W3Cl4(OC2H5) 4(C2H50H)2 B. with DMSO after 15 minutes. 81 Klejnot57 reported that the pmr spectrum of W2Cl4(OC2H5)6 showed two groups of signals with an intensity ratio of 2:1, indicating four and two ethoxide groups in two different environments. These results were confirmed in this work and a similar 2:1 intensity ratio was observed for all other complexes with six alkoxide or alcohol and four chloride ligands. The chloride-bridged bioctahedral structure pro- posed by Klejnot is shown in Figure 26. An interesting comparison can be made between W3Cl4(OC2H5)6 and W3C12(OC2H5)3. The relatively simple spec- trum of W2C12(OC2H5)8, consisting of two closely spaced quartets of equal intensity, would be compatible with a sym- metrical structure and chloride bridging. A possible struc- ture for W3Clz(oczH5)3 is shown in Figure 27. A comparison of the propoxide derivatives was not possible because pure W2C13(OC3H7)8 was not obtained. The pmr and ir spectra are not sufficiently diagnostic to decide absolutely on the nature of the bridging groups. An X-ray structure determina- tion would be required to resolve this question. rThe small effect of the oxidation state upon physical properties is evident from the close similarities of the pmr and ir spectra of the compounds, W2Cl4(OC2H5)6,57 W2Cl4(OC3H5)4(C2H50H)2 and W2Cl4(OC2H5)2(C2H5OH)4.64 The pmr spectra of the W(III)64 and W(IV) alkoxoalcohol complexes did not show a resonance due to the hydroxyl pro- tons of the bound alcohol. Presumably, the lack of an ob- servable signal in the pmr spectrum is the result of proton 82 C) C) /O‘—" ‘———Cl—- 0 Cl | en 6! O o O = OC2H5 Figure 26. Proposed structure for W2Cl4(OC2H5)3. ° C! o 0 = 0C2H5 ‘Figure 27. Proposed structure for W2C12(OC2H5)8. 83 exchange occurring at a very fast rate. The presence of the alcohol ligands in the W(IV) eth- oxoethanol compound was demonstrated by an exchange experi- ment with dimethylsulfoxide (DMSO). .With excess DMSO, the bound alcohol of W3Cl4(OC2H5)4(C2H5OH)2 is replaced, result- ing in appropriate shifts in the spectrum. (As the unbound alcohol appears, the signal due to its hydroxyl proton be- comes apparent (Figure 25). Quantitative correlations of signal intensity to possible structures of the complex were not made because the reaction and the equilibria involved are not understood. Bradley and Holloway54 have proposed an edge—shared bioctahedral structure for niobium and tantalum pentaalk- oxides. The pmr spectrum of [Ta(OCH3)5]2 above 40° gave one peak at 5.78 ppmwAt —58°, the single methyl resonance splits into 3 peaks (5.78, 5.68, 5.97 ppm) with intensity ratios of 2:2:1. These results were interpreted as evidence for the three types of alkoxide groups in the edge-shared bioctahedron. Uranium pentaethoxide91 was similar. -At 35°, W(OC2H5)5 has a simple pmr spectrum, probably due to rapid intramolecular exchange between terminal and bridging eth- oxide groups. Low temperature studies (to -80°) in carbon disulfide or gfpentane failed to resolve the expected split- ting of the methylene quartet. vUntil molecular weight or mass spectral data can be obtained, the structure of W(OC2H5)5 will remain uncertain. The diamagnetism of the complex sug- gests a dimer or higher polymer. Attempts to convert this 84 compound into a monomer were also unsuccessful.