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Complexes of oxovanadium(IV)
1. lnorg. Nucl. Chem., 1962, Vol. 24, pp. 1111 to 1119. Pergamon Press Ltd. Printed in England
COMPLEXES OF OXOVANADIUM (IV)* J . SELBIN AND L . H . HOLMES J R .
Coates Chemical Laboratories, Louisiana State University, Baton Rouge, Louisiana (Received 1 February 1962; in revised form 12 March 1962)
Abstract--The preparation and partial characterization of a number of new complexes of the oxovanadium(IV) ion are reported. Cationic, neutral and anionic complexes in which the vanadium(IV) is either five- or six-co-ordinated are included. Conductivity studies have generally allowed the assignment of groups to the first co-ordination sphere and the presence of the vanadium-oxygen multiple bond in each compound has been established by infrared spectra. MONONUCLEAR oxycations of the types MO n+ and MO2 n+ are found mainly among the lighter transition elements (in their high oxidation states) of a given period, e.g., in Groups IV, V, and VI. They are almost non-existent with the latergroup metals, although exceptions, such as OsO 2÷ and RuO 2 +, may be noted. The most extensively studied and best characterized oxycation is the dioxouranium (VI) or uranyl ion, U O 2 + . (1'2) The next best characterized and most studied oxycation is the oxovanadium (IV) or vanadyl ion, VO 2+.(3-12) The strongly bound oxygens of such species present additional means for studying the complexes of the oxycations beyond those normally available with transition metal complexes. Thus, for example, vibrational motions of the "central (polyatomic) ion" can be studied as they are perturbed by the additional ligated species. Indeed it has been shown (1, 13) that a ligand series strikingly similar to the spectrochemical series may be established from the shifts observed in the symmetric and antisymmetric vibrations of the O-U-O entity in a series ofuranyl complexes. A similar study of vanadyl * Based in part upon a thesis submitted in partial fulfilment of the requirements for the Ph.D. degree at Louisiana State University, 1961. (~) S. P. McGLYNN, J. K. SMITH and W. C. NEELY,J. Chem. Phys. 35, 105 (1961), and references contained therein. izl R. L. BELFORDand G. BELFORD,J. Phys. Chem. 34, 1330 (1961). (3) F. J. C. ROSSOTTIand H. S. ROSSOTTI,Acta Chem. Scand. 9, 1177 (1955). 141 M. M. JONES,Z. Naturforsch, 12 b, 595 (1957). (5i Q. TRUJILLO et aL, series of papers in Anales real. soc. espan, fiz, y quim (Madrid), 1956-1958. (6) C. K. JORGENSEN, Acta Chem. Scand. 11, 73 (1957). (7) C. FURLANI, Ricerca Sci. 27, 1141 (1957). (8) M. n. PALMA-VITTORELLI,M. U. PALMA,D. PALUMBOand F. SGARLATA,Nuovo cimento 3, 718 (1956). c,)l J. SELmN, L. H. HOLMES,JR. and S. P. McGLYNN, Chem. and Industry, 746 (1961). c10/C. J. BALLHAUSENand H. B. GRAY, Inorg. Chem. 1, 111 (1962). (11) R. D. FELTHAM. Thesis, University of California, U.S.A.E.C. Report UCRL-3867 (1957). (121 R. P. DODGE, U.S.A.E.C. Report UCRL-8225 (1958). (13) B. SHAMBURGER and J. SELBIN. Unpublished results. 1111
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J. SELBINand L. H. HOLMES,JR.
complexes~9, 14) has utilized the V-O stretching vibration as the probe to establish certain ligand series and has uncovered a very interesting correlation between infra-red spectral data and electronic spectral data~ 14). The oxygen(s) attached to the central metal produce one (or more) additional electronic (electron transfer) absorption bands, which, again, are perturbed to varying degrees by the particular set of ligands. Information from this source is more difficult to unravel and interpret, but, in principle, it should provide independent data concerning the nature of the complexes.~14) In order to have a wide variety of complexes available for such studies as mentioned above, we have prepared and partially characterized a large number of complexes of the oxovanadium(IV) cation. These include cationic, neutral and anionic complexes in which the vanadium is either five-or six-co-ordinated. Complex types in which the vanadium is five-co-ordinated include [VO(AAAA)]*, [VO(ABBA)], [VO(AA)2], [VO(AA) (BB)] and [VO(AA)a2]. Complex types in which the vanadium is sixco-ordinated include [VOas], [VOa4b], [VOa3b2], [VO(AA)a3] and [VO(AA)2a ]. Conductivity studies of many of these complexes in nitrobenzene generally allowed the assignment of groups to the first co-ordination sphere and the determination of a definite co-ordination number. For example, with VO(AA)2X2 compounds (where AA----o-phen or dipy) the formulation as [VO(AA)2X]X is found for X=C1 or Br, whereas the formulation [VO(AA)2]X 2 holds for X~---CIO4. If X2----SO4, an intermediate conductivity value is observed, indicating, perhaps, ion-pair association in this case. The infra-red spectrum of this compound indicates that in the solid state the sulphate ion is co-ordinated as a unidentate ligand. Two complexes having empirical formulas VO(AA)I.5(NCS)2 (where AA----o-phen or dipy) are formulated as [VO(AA)2NCS] [VO(AA) (NCS)3 ] on the basis of their mode of formation, conductivity data and infra-red spectra. The assignment of the absorption bands due to the V-O (vanadyl) stretching vibration has been made for over fifty complexes, including a few vanadium (V) compounds.t9,14) They are found to fall in the range 932-1035 cm -1. Several ligand series may be deduced from these results, and the series have been interpreted in terms of ligand a and n bonding.t14) The persistence of the vanadium-oxygen multiple bond in all of the complexes may be considered to be established from the infrared spectra of the compounds. BARRACLOUGH,et aL ~15) have concluded that the presence of a metal-oxygen multiple bond can be correlated with a stretching frequency in the range 900-1100 cm -1. We have verified this conclusion with a large number of compounds of MOO3+, MoO 2+ and WO22÷ as well as VO 2÷ and UO 2÷, although we could find no evidence for a TiO2+ or a ZrO2+ mononuclear species in certain so-called titanyl or zireonyl compounds. The formation of multiple bonds to oxygen by metals in this region of the periodic table has been explained theoretically for UO 2÷ 1,VO2+ (10,14)and MoO 3+ and CrO 3+ c16) However, qualitatively this situation may be traced to the ability or tendency for * Abbreviations used in this paper are: AAAA = symmetrical quadridentate ligand; AB = unsymmetrical bidentate ligand; a, b = unidentate ligands, etc. ; o-phen = orthophenanthroline; dipy = dipyridyl; DMSO = dimethylsulphoxide. c14~j. SELBIN,S. P. McGLYNN and L. H. HOLMES. In preparation for publication. C15JC. G. BARRACLOUGH,J. LEWISand R. S. NYHOLM,~. Chem. Soc. 3552 (1959). t16) H. B. GRAYand C. R. HARE. Inorg. Chem. 1, 363 (1962).
Complexes of oxovanadium(IV)
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oxygen to delocalize itspn- electrons away from its highly compact valence sheell, forming n-bonds by this means. GILLESVIECI7)has accumulated a great deal of stereochemical evidence to support the hypothesis that oxygen (and fluorine) will form multiple bonds with atoms or groups which can readily accept n-bonding electrons available in the compact 2p level. The early transition elements in their high oxidation states, in which they achieve d o or d 1 configurations, are apparently good n-electron acceptors. In fact, it is well known that the metals at the beginning of the transition series form their most stable complexes with oxygen-donor ligands and that their halide complexes follow the stability order F >>C I > B r > I. The formation and great stability of multiple bonds with oxygen by the metals in this region of the periodic table is thus not unexpected. EXPERIMENTAL
A. Preparation of Compounds The starting vanadium materials included VOSO4"5H20, V205, and VOC12(syrupy), all commercial reagent grade products, and VO(C104)2"xH20, prepared as described below.
Vanadyl perchlorate Three methods were found to be satisfactory for obtaining pure aqueous solutions of this compound. (a) VOSO4 is treated with sodium hydroxide and the precipitated VO(OH)2 is filtered and washed until free of sodium sulphate. An excess of alkali should be avoided due to the amphoterism exhibited by the VO2+ ion. Ammonia may be used, providing all of the ammonia is washed from the precipitated hydroxide. The hydroxide is then dissolved in perchloric acid to give a vanadyl perchlorate solution which is stable for many days at room temperature or below. Heating causes show oxidation of the vanadyl to V205 by the perchlorate. (b) Vanadium pentoxide is suspended in perchloric acid and electrolysed at a constant potential of 0.55 V (vs. Ag-AgC1 electrode). Complete dissolution and reduction is slow; the solution is then filtered, yielding a vanadyl perchlorate solution. (c) Perchloric acid is added to a solution of VOC12 and the resulting solution heated on a steam bath to drive off HC1. Oxidation of the vanadyl ion by the perchlorate ion can be reversed by adding small amounts of ethanol to the solution. Ethanol in acid solution will reduce vanadium pentoxide to VO2+. A blue solution is finally obtained which gives a negative test for chloride ion with silver nitrate. Filtration improves the purity of the solution, but this is the least satisfactory of the three methods. Solid hydrated vanadyl perchlorate may be obtained as large clear blue crystals by slow vacuum evaporation of the above solutions at room temperature. The crystals are extremely hygroscopic, making precise analysis difficult. (Found: VO, 18.5; CIO4, 27-2. Calc. for VO(CIO4)2-5H20: VO, 18-8; CIO4, 27.9 and for VO(C104)2"6H20: VO, 17.9; C104, 26-6%). Vanadyl chloride and vanadyl bromide These compounds are prepared in aqueous solution by heating a mixture of vanadium pentoxide, ethyl alcohol, water and the appropriate acid until all of the vanadium pentoxide has reacted. Evaporation yields syrupy liquids and the vanadyl halides contain an indeterminate amount of water. Continued heating results in partial hydrolysis. Vanadyl fluoride (a) An aqueous solution of vanadium pentoxide and HF is electrolysed at constant potential and the filtered solution is evaporated to a blue solid: VOF2.xH20; (b) a solution of VOCI2 is treated with a solution of AgF in HF (prepared from silver oxide and HF) and the AgCI removed by filtration. Evaporation of the filtrate yields VOF2-xH20. (Found: VO, 40"1. Calc. for VOF2-3H20: VO, 42.1, and for VOF2.4H20: VO, 37.8 %). (17) R. J. GILLESPIE,J. Amer. Chem. Soe. 82, 5978 (1960).
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J. SELBINand L. H. HOLMES,JR.
Pentacyano-oxovanadate(1V) ion (a) Tetraethylammonium salt. VOSO4"5H20is dissolved in ca. 6M NaCN; the initial precipitate of hydroxide dissolves with stirring. The dark green solution is cooled in ice and filtered. The clear green filtrate is mixed with an aqueous solution of Et4NBr and the mixture evaporated in an air stream at room temperature. After several hours, green crystals separate and they are filtered, washed with alcohol and ether and dried in vacuo. Acetone cannot be used as wash solution since it appears to cause decomposition of the product. The product is insoluble in organic solvents and dissolves with decomposition in water. (Found: VO, 12.25; CN, 22.2. Calc. for [(C2Hs)4N]3[VO(CN)5]: VO, 11"41; CN, 22"2 ~o). The analysis for vanadyl was made by precipitating the cyanide with an equivalent amount of silver nitrate and titrating the filtrate with permanganate. The high analysis for vanadyl may perhaps be explained as due to some soluble Ag(CN)z- which would be oxidized by permanganate. (b) Tetramethylammonium salt. VOSO4.5HzO is dissolved in ca. 6M NaCN solution and a hot aqueous solution of Me4NI is added. A precipitate forms immediately and after cooling in ice, a light green powder is filtered and washed with alcohol and ether and vacuum-dried. (Found: VO, 16-80; CN, 32-2. Calc. for [(CH3)4N]a[VO(CN)s]: VO, 16.00; CN, 31.25 %). (c) Cesium salt. To a solution of VOSO4"5H20 dissolved in ca. 6M NaCN is added a solution of CsCI. An aqua coloured precipitate forms which is cooled in ice and filtered. It is washed with ca. 6M NaCN in order to remove Na2SO4 which may be coprecipitated. The cyanide solution is used for washing because the cyano complexes are unstable in water but stable in excess cyanide. Finally alcohol and ether are used to wash the product and it is air-dried. (Found: VO, 20.70; CN, 21.07. Calc. for Cs3[VO(CN)s]: VO, 20.36; CN, 21.80 ~). Pentaisothiocyanato-oxovanadate( IV) ion (a) Tetraeth,ylammonium salt. Vanadyl sulphate is dissolved in ca. 8 M NH4NCS. An aqueous solution of Et4NBr is added, yielding an immediate precipitate. The solution is heated and the precipitate dissolves; on cooling slowly to ice temperature the solution yields blue needles. They are recrystallized from absolute alcohol, filtered, washed with alcohol and ether and vacuum-dried. (Found: NCS, 40.70; C, 42.39, 42.01; H, 7.25, 7.27; N, 14.48, 14.50. Calc. for [(C2Hs)4N]3[VO(NCS)5]: NCS, 38-90; C, 46.50; H, 8.08; N, 16.05~. Found: C/H, 5.68; C/N, 2.92. Calc. C/H, 5.75; C/N, 2.90.) It is possible that this compound was not fully decomposed in the analysis for C, H and N, as the ratios would indicate. The crystals recrystallize nicely and are well formed. They appear to be quite pure under a microscope and the analysis for NCS run in this laboratory is satisfactory. There is also the possibility that some bromide ion (from the Et4NBr) is present: it would lower the C, H and N percentages and raise the thiocyanate percentage which was determined as AgNCS. This last possibility finds support in the superior analysis found with the tetramethylammonium compound prepared from (CHa)4NI and described below. (b) Tetramethylammonium salt. Vanadyl sulphate is dissolved in ca. 8 M NH4NCS and a hot aqueous solution of Me4NI is added. On cooling, a precipitate of sparkling blue crystals is obtained. These crystals are filtered, recrystallized from absolute alcohol, washed with alcohol and ether and air-dried. A hot solution of the Me4NI is used here as previously because of the lower solubility of this compound at lower temperatures. (Found: NCS, 49.50; C, 34.53; 34-20; H, 6.51, 6.66; N, 19.00, 19.21. Calc. for [(CH3)4N]3[VO(NCS)s]: NCS, 50"01; C, 34"61; H, 6"26; N, 20"50~). Sulphatodipyridylo xovanadium( I I1) Vanadyl sulphate is dissolved in warm dimethylformamide (DMF) and then added to a solution of ~,ct'-dipyridyl in DMF. A green solution is obtained at first, but upon further addition of vanadyl sulphate, a green powder deposits. The powder is refluxed in absolute ethanol, filtered, washed with ether and dried in vacuo. (Found: VO, 21"40; SO4, 31.0. Calc. for [VO(CloHsNz)SO4]:VO, 21.00; SO4, 30-10 ~).
Complexes of oxovanadium(1V)
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Sulphato(orthophenanthroline)oxovanadium(l V) Vanadyl sulphate is dissolved in D M F and added to o-phen dissolved in DMF. A yellow solid forms immediately which on further addition of vanadyl sulphate dissolves to produce a green solution. When this solution is heated just below the boiling point, a greenish powder precipitates. It is refluxed in absolute ethanol, filtered, washed with ether and dried in vacuo. (Found: VO, 19.35; 504, 28"70. Calc. for [VO(C12HsN2)SO4]: VO, 19-50; SO4, 28'00%) Bis(orthophenanthroline)-oxovanadium(1V) sulphate Vanadyl sulphate is dissolved in ethanol (containing enough water to cause dissolution) and added in a one to two mole ratio to o-phen dissolved in ethanol. A gummy precipitate is obtained which dissolves if the solution is heated. Upon cooling, a yellow-brown powder is deposited which is not very soluble in ethanol after drying. It is washed with acetone and ether and dried in vacuo. (Found: VO, 14.20; SO4, 18.20. Calc. for VO(C12HsN2)2SO4: VO, 12.80; SO4, 18.35~). Tetramethylammonium tetrachloro-oxovanadate( I V) monoethanolate Syrupy vanadyl chloride is mixed with a very concentrated solution of (CH3)4NC] and ethanol is added. Upon addition of acetone and ether to this solution a blue oil separates. This oil is washed with successive portions of absolute ethanol-acetone mixtures (enough acetone to prevent redissolving the oil) and then dissolved in a small volume of absolute ethanol. Acetone addition to this solution gives a greenish-blue gummy solid which is washed repeatedly with acetone. The product can then be recrystallized from absolute ethanol by dissolving it and then evaporating some of the solvent, followed by cooling. An aqua coloured powder is obtained which is ether-washed and dried in vacuo. (Found: VO, 16.42; C1, 35.00. Calc. for [(CH3)4N2][VOC14(C2HsOH)]: VO, 16.62; CI, 35.25°<0). Bis( dil~yridyl)--o xo vanadium( I V ) perchlorate Vanadyl perchlorate (aqueous or solid) is dissolved in acetone and added to cq~'-dipyridyl dissolved in acetone. A greenish-brown solution results which is evaporated to dryness in a vacuum at room temperature. The solid obtained is washed several times with a 1]1 mixture of acetone-ether and again evaporated to dryness under vacuum at room temperature. Washing with acetone-ether mixtures may produce an oil. The final product is a greenishbrown powder which is washed with ether and dried in vacuo. ~Found: VO, 11 "24; C, 42"48 ; H, 3"38; N, 9"60. Calc. for [VO(C10HsNz)2](C104)2 :VO, l 1.58; C, 41-60; H, 2.80; N, 9"69 °/k). Bis(orthophenanthroline)-oxovanadium(IV) perchlorate Vanadyl perchlorate in acetone is added to o-phen dissolved in acetone. After the solution is stirred for several minutes a green precipitate begins to appear and precipitation is complete after cooling in ice. It is filtered, washed with ether and vacuum-dried. (Found: VO, 10"75; C, 45.82; H, 2.98; N, 8.45. Calc. for [VO(ClEHsN2)2](C104)2: VO, 10.70; C, 46.00; H, 2.58; N, 8.96~). Bromobis(orthophenanthroline)-oxovanadium(1 V) bromide l-hydrate Aqueous vanadyl bromide in acetone is added dropwise with stirring to o-phen dissolved in acetone. A chartreuse precipitate appears at once and increases in amount as the VOBr2 is added. The solution above the precipitate is nearly colourless as long as excess o-phen is present; if excess VOBrz is added it becomes greenish. The precipitate is refluxed for some minutes in a 1 ~1 ethanol-acetone mixture and filtered, washed with ether and vacuum-dried. (Found: Br, 26.4; C, 46-44; H, 2.96; N, 9.10. Calc. for [VO(C~2HsNz)2Br]Br-H20: Br, 26.40; C, 48-00; H, 3"00; N, 9"33 ~). Bromobis(dipyridyl)-oxovanadium(IV) bromide 1-hydrate A solution of hydrated VOBr2 in acetone is added dropwise with stirring to a solution of dipy dissolved in acetone. A green precipitate separates at once, increasing in quantity as VOBr2 is added. The solution remains colourless if an excess of dipy is present, greenish, if not. The precipitate is filtered and dissolved in a 1~1 ethanol-acetone mixture. Upon cooling for several hours in ice the solution deposits a dark green powder, which is washed with ether and vacuum-dried. (Found: Br, 28-20; C, 42"38; H, 3.56; N, 10.08. Calc. for [VO(CloH8Nz)zBr]Br'H20: Br, 28"70; C, 43 -20; H, 3-24; N, 10-09 ~).
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J. SELBINand L. H. HOLMES,JR.
Chlorobis(orthophenanthroline)-oxovanadiurn(IV) chloride Syrupy VOClz dissolved in acetone is added dropwise with stirring to o-phen dissolved in acetone. A light greenish-yellow fluffy precipitate forms at first, but on further addition of VOC12 the precipitate becomes green and heavier, settling out very readily. When the supernatant liquid becomes green the addition is stopped and the mixture heated to boiling for several minutes, filtered and the green powder washed with ether and vacuum-dried. (Found: VO, 13.98; C1, 14.08. Calc. for [VO(C12HaN2)2C1]Cl: VO, 13.42; C1, 14.24%). Chlorobis(dipyridyl)-oxovanadium(IV) chloride Syrupy VOC12 dissolved in acetone is added dropwise with stirring to dipy dissolved in acetone. A green precipitate is obtained immediately and VOC12 addition is stopped when the solution turns green. The mixture is boiled for several minutes, the solid filtered and refluxed in fresh acetone for several more minutes, then filtered, washed with ether and dried in vacuo. (Found: VO, 15.01; C1, 14.51. Calc. for [VO(C10HsN2)2CI]CI: VO, 14.12; C1, 14.95 ~).
VOC204"H2C204"3H20 Aqueous VOCI2 is mixed with excess oxalic acid and the solution is heated on the steam bath for several hours, water being added as it evaporates. Finally the mixture is evaporated to dryness, leaving a blue solid. This solid is broken up and heated with 95 per cent ethanol. It is filtered hot, yielding a blue powder, which is repeatedly washed with hot 95 per cent ethanol until a negative test for chloride ion is obtained when the powder is dissolved in water. Then the product is washed with ether and dried in vacuo. The vanadyl and oxalate were analysed by titrating a sample with permanganate and calculating the per cent VO using 1 of the volume and the C204 using 4 of the volume required. (Found: VO, 22.20; C204, 58.40; C, 16.26; H, 2.00. Calc. for VOC204-HzC204"3H20: VO, 22.38; C204, 58.90; C, 17.05; H, 2.67%).
Oxalato(dipyridyl)-oxovanadium(1V) The product just described, VOC204.H2C204"3HzO, is dissolved in ethanol (containing just enough water to effect dissolution) and added dropwise with stirring to dipy dissolved in alcohol. The solution immediately turns yellow, then darkens to green, and finally a green precipitate deposits. The vanadyl solution is added until there is a 2: I mole ratio (VO:dipy) present. The mixture is boiled for several minutes, cooled, filtered and the green product washed with acetone and ether and air-dried. (Found: VO, 20.65; C204, 27.10; C, 43.95; H, 3.17; N, 8-51; C/N, 5.18. Calc. for [VO(CIoHsN2)C204]: VO, 21-60; C204, 28"30; C, 46"40; H, 2.58; N, 9-00; C/N, 5"169/o). Oxalato(orthophenanthroline)-oxovanadium(IV) VOCEO4"HECEOg'3H20 is dissolved in warm dimethylformamide and added dropwise with stirring to o-phen dissolved in ethanol. Immediate precipitation of a yellow-green solid occurs and the addition is stopped when the mole ratio (VO:o-phen) is near 2~1. The mixture is boiled for several minutes, cooled in ice, filtered and the product washed with acetone and dried in vacuo. (Found: VO, 19.10; C204, 26.40; C, 47.36; H, 3-22; N, 9.49. Calc. for [VO(C12HaN2)C204]: VO, 20"00; C204, 26.25; C, 50"20; H, 2.39; N, 8.38 %). Difluoro(orthophenathroline)-oxovanadium(IV) An aqueous solution of vanadyl fluoride (or solid vanadyl fluoride) is dissolved in a 1 : 1 ethanol-water mixture and then added dropwise with stirring to o-phen dissolved in ethanol. A green powder is obtained which, after boiling in the mother liquor for a few minutes, is filtered, washed with several portions of 95 per cent ethanol, acetone and then vacuum-dried. (Found: VO, 23.50; C, 41.85; H, 3.85; N, 7.36; C/N, 5.67. Calc. for [VO(C12HaN2)F2]: VO, 23.45; C, 50"60; H, 2"91; N, 10.01 ~ ; C/N, 5"05). The reasons for the poor agreement on the C, H and N analyses are unknown; however the compound appears to be pure (e.g., under the microscope) and our own analysis for vanadyl is quite satisfactory. The C, H and N were determined by a commercial laboratory.
Complexes of oxovanadium(IV)
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Difluoro(dipyridyl)-oxovanadium(IV) A solution of vanadyl fluoride in a 1 ~1 water-ethanol mixture is added dropwise with stirring to dipy dissolved in ethanol. The green precipitate obtained is heated to boiling in the mother liquor for several minutes then filtered. It is then refluxed in acetone for several minutes, filtered, washed with ether and vacuum-dried. (Found: VO, 27.18; C, 45-35; H, 3"63; N, 10-76. Calc. for [VO(C10HnN2)F2]: VO, 25.63; C, 46.00; H, 3.07; N, 10.72 ~,,). (VO)2(o-phen)3(NCS)4 A solution of vanadyl thiocyanate in ethanol is prepared as follows. Syrupy VOCI2 is dissolved in absolute ethanol and treated with about 3 moles of NHaNCS for each mole of VOCI2. The solution is heated on a hot plate for about 30 min and then cooled for several hours in ice. The precipitated NH4C1 is filtered off, leaving vanadyl thiocyanate (and some NH4NCS) in solution. This is added dropwise with stirring to a solution of o-phen in ethanol. A chartreuse precipitate separates out and the mixture is boiled for several minutes. After cooling in ice, it is filtered, washed with acetone and vacuum-dried. (Found: C, 52.30; H, 2-73; N, 14-68. Calc. for VO(C12HaN2)I.s(NCS)2: C, 53.00; H, 2"65; N, 15"45~). (VO)2(dipy)3(NCS)4 This compound is prepared by the same procedure used to obtain the previous compound. It is a green powder, which is refluxed in acetone for several minutes, filtered and washed with ether and air-dried. (Found: C, 48.79; H, 2.70; N, 17.00. Calc. for VO(C10H8N2h.s(NCS)z: C, 48.99; H, 2.16; N, 16-79~).
Bis(8-hydroxyquinolinate)-oxovanadium(l V) This compound is prepared by the method of BIEUG and BAVER.t18) Vanadyl sulphate and oxine are heated in water solution for an hour or so on a steam bath. The brown vanadyl oxinate separates as a solid and is filtered, washed free of SO4 with hot water and dried in vacuo. It is anhydrous. A mmonium pentafluoro-oxovanadate(l V) This compound is prepared by the method of MUETTERTIES.(j9) Ammonium bifluoride is added to an aqueous solution of vanadyl fluoride and a light blue powder precipitates. It is recrystallized from water and air-dried. It is anhydrous. The same compound can be obtained using vanadyl sulphate in aqueous H F to which ammonium bifluoride is added. (Found: VO, 30.90. Calc. for (NH4)3[VOF5]: VO, 31.00%). Vanadyl phthalocyanine This compound was prepared from VzO5 and phthalonitrile according to the method of BARRETT et al.(2o) Pentakis(dimethylsulphoxide)-oxovanadium( IV) perchlorate An aqueous solution of VO(CIO4)2 is added to pure dimethylsulphoxide (DMSO): the solution becomes hot and subsequently blue crystals are deposited. The VO(C104)2 must be added to the DMSO; addition of DMSO to a VO(C104)2 solution did not yield a crystalline product. The crystals are washed with ether and vacuum-dried. (Found: C104, 31.0; C, 18.55; H, 4.64. Calc. for [VO{(CH3)zSO}5](CIO4)z: C104, 30"4; C, 18'65; H, 4"57~). Sulphatotris(dimethylsulphoxide)-oxovanadium( I V) VOSO4"5HzO in pure DMSO is heated to dissolution of the salt, then cooled, yielding blue crystals. These are filtered, washed with acetone and ether and vacuum-dried. (Found: SO4, 25.4; C, 18.38; H, 4.78. Calc. for [VO((CH3)zSO}3SO4]: SO4, 24.2; C, 18.15; H, 4.54%). 1~8) H. J. BIELtG and E. BAYER, Ann. 584, 96 (1953). (19) E. MLIETTERTIES,J. Amer. Chem. Soc. 82, 1082 (1960). (201 p. A. BARRETX,C. E. DENT, R. P. LrNSTEAD,J. Chem. Soc. 1719 (1936).
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J. SELB1Nand L. H. HOLMES,JR.
D ich loro tris(dimet hy lsulpho x ide)-o xo vanadium(I V ) Syrupy VOC12 is dissolved in DMSO with the liberation of heat. On cooling, the solution becomes syrupy and it does not yield a precipitate. It is heated to remove some of the DMSO, then added to ethanol. To this solution at its boiling point, acetone is added and then the mixture is cooled in ice. A light blue powder is obtained. It is recrystallized from a 1Z1 ethanol-acetone mixture, filtered, washed with ether and vacuum-dried. (Found: C1, 19.39; C, 19.48; H, 5.34. Calc. for [VO((CH3)2SO}aC12]: CI, 19.20; C, 19.35; H, 4.88 ~). Pentakis(dimethylsulphoxide)-oxovanadium(IV) bromide (a) Aqueous VOBr2 and DMSO are mixed in acetone and ether is added to precipitate a green-blue solid. The product is recrystallized from absolute ethanol, filtered, washed with ether and dried in vacuo. (b) Aqueous VOBr2 is dissolved in pure DMSO and after cooling to 0°C, blue crystals are deposited. They are recrystallized as described in (a). (Found: Br, 26.03; C, 19.24; H, 4-95. Calc. for [VO((CH3)2SO}5]Br2: Br, 25-93; C, 19.49; H, 4.87~). Vanadyl bis(acetylacetonate) This compound was obtained as a commercial product from K and K Laboratories. B. Physical Measurements 1. Conductance Equivalent conductances of the vanadyl complexes were obtained in nitrobenzene. Concentrations ranged from 10-4 to 10-3 M. According to previously published data{211 for the conductances of complexes in nitrobenzene, the range for equivalent conductances in ohm-1 cm 2 were taken as follows: four ions, 70-90; three ions, 40-60; two ions, 20-30. In Table 1 the conductance data are collected. These data allow the assignment of ligands to the first co-ordination sphere in all but three of the compounds listed. (That some of the compounds may be polymeric with ligands other than the oxygen acting as bridging groups cannot be completely ruled out at the present time; however, molecular weight determinations have proven VO(acac)2 and VO(oxine)2 to be monomeric in benzene.) The low value (7-6) for the equivalent conductance of VO(o-phen)2SO4 may result from partial dissociation of the sulphate ion or from strong ion-pair interaction between the divalent cation and anion. A value of ten was obtained for the equivalent conductance of the compounds having empirical formulas of VO(dipy)l.5(NCS)2 and VO(o-phen)l.5(NCS)2. If these formulas are doubled a value of twenty is obtained, which is in the range for a one to one electrolyte. We tentatively suggest that these compounds should be formulated as [VO(dipy)2NCS][VO(dipy)(NCS)3] and [VO(o-phen)2NCS][VO(o-phen)(NCS)3]. The method of preparation of these compounds is such that it would not be unreasonable to anticipate these products. Thus the addition of the chelating agent (AA) to a solution containing the [VO(NCS)5]3species would be expected to form [VO(AA)(NCS)3]- initially. This species would then react with additional (AA) to give [VO(AA)2NCS] +, which may then be precipitated by the anionic complex species to yield [VO(AA)2NCS][VO(AA)(NCS)3], a uni-univalent electrolyte. Attempts to get NCS- to add to [VO(AA)2]2+ to give the cationic complex or to add and displace an AA group to give the anionic complex were unsuccessful. 2. Infra-red spectra The infra-red spectra of the vanadyl complexes were obtained in the 4000-650 cm-I region using a Perkin-Elmer Model 21 spectrophotometer and a Beckman IR-7 spectrophotometer* each equipped with NaC1 optics. Nujol mulls were employed since some of the compounds appeared to have been altered in the preparation of KBr pellets. The spectra of all of the ligands were obtained so that ligand bands could be more easily identified in the spectra of the complexes. Generally there was no difficulty in identifying the strong band * The Beckman IR-7 infra-red spectrophotometer was purchased with funds obtained in part from the National Science Foundation, grants numbers NSF-15242 and NSF-16724 and in part from a grant to one of us (J. S.) by the Research Corporation. c211F. A. COTTONand D. GOODGAME,J. Chem. Soc. 5267 (1960).
Complexes of oxovanadium(IV)
1119
(or bands) due to the vanadium-oxygen multiple bond in the infra-red spectra. The frequencies of the V-O stretching vibration ranged from 1020 cm-1 to 932 cm-1, depending upon the particular set of ligands which surrounded the VO z+ entity. TABLE 1.--EQUIVALENT CONDUCTANCESOF VANADYLCOMPLEXESIN NITROBENZENE Compound 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.
VO(DMSO)s(C104)2 VO(DMSO)sBr2 VO(DMSO)3C12 VO(DMSO)3SO4 VO(dipy)SO4 VO(o-phen)SO4 VO(dipy)(ox) VO(o-phen)(ox) VO(dipy)F2 VO(o-phen)F2 VO(oxine)2 VO(o-phen)2Br2"H20 VO(dipy)zBr2-H20 VO(o-phen)2C12 VO(dipy)2Cl2 VO(o-phen)2SO4 (VO)2(dipy)3(NCS)4 (VO)2(o-phen)3(NCS)4 VO(o-phen)2(C104)2 VO(dipy)2(C104)2 (Et4N)3VO(NCS)5 (MeaN)3VO(NCS)s VO(acac)2
Equiv. cond. £)- 1 cm 2
No. of ions indicated
48"5 18'4 0 0 0 0 0 0 0 0 0 26.2 25"2 23.7 18"2 7"6 20 20 56.5 56 69.1 86 0
3 2 0 0 0 0 0 0 0 0 0 2 2 2 2 0-2 2 2 3 3 4 4 0
Acknowledgement--The authors are grateful to the National Science Foundation for financial support received under a grant number NSF-G15242.
COMPLEXES OF OXOVANADIUM (IV)* J . SELBIN AND L . H . HOLMES J R .
Coates Chemical Laboratories, Louisiana State University, Baton Rouge, Louisiana (Received 1 February 1962; in revised form 12 March 1962)
Abstract--The preparation and partial characterization of a number of new complexes of the oxovanadium(IV) ion are reported. Cationic, neutral and anionic complexes in which the vanadium(IV) is either five- or six-co-ordinated are included. Conductivity studies have generally allowed the assignment of groups to the first co-ordination sphere and the presence of the vanadium-oxygen multiple bond in each compound has been established by infrared spectra. MONONUCLEAR oxycations of the types MO n+ and MO2 n+ are found mainly among the lighter transition elements (in their high oxidation states) of a given period, e.g., in Groups IV, V, and VI. They are almost non-existent with the latergroup metals, although exceptions, such as OsO 2÷ and RuO 2 +, may be noted. The most extensively studied and best characterized oxycation is the dioxouranium (VI) or uranyl ion, U O 2 + . (1'2) The next best characterized and most studied oxycation is the oxovanadium (IV) or vanadyl ion, VO 2+.(3-12) The strongly bound oxygens of such species present additional means for studying the complexes of the oxycations beyond those normally available with transition metal complexes. Thus, for example, vibrational motions of the "central (polyatomic) ion" can be studied as they are perturbed by the additional ligated species. Indeed it has been shown (1, 13) that a ligand series strikingly similar to the spectrochemical series may be established from the shifts observed in the symmetric and antisymmetric vibrations of the O-U-O entity in a series ofuranyl complexes. A similar study of vanadyl * Based in part upon a thesis submitted in partial fulfilment of the requirements for the Ph.D. degree at Louisiana State University, 1961. (~) S. P. McGLYNN, J. K. SMITH and W. C. NEELY,J. Chem. Phys. 35, 105 (1961), and references contained therein. izl R. L. BELFORDand G. BELFORD,J. Phys. Chem. 34, 1330 (1961). (3) F. J. C. ROSSOTTIand H. S. ROSSOTTI,Acta Chem. Scand. 9, 1177 (1955). 141 M. M. JONES,Z. Naturforsch, 12 b, 595 (1957). (5i Q. TRUJILLO et aL, series of papers in Anales real. soc. espan, fiz, y quim (Madrid), 1956-1958. (6) C. K. JORGENSEN, Acta Chem. Scand. 11, 73 (1957). (7) C. FURLANI, Ricerca Sci. 27, 1141 (1957). (8) M. n. PALMA-VITTORELLI,M. U. PALMA,D. PALUMBOand F. SGARLATA,Nuovo cimento 3, 718 (1956). c,)l J. SELmN, L. H. HOLMES,JR. and S. P. McGLYNN, Chem. and Industry, 746 (1961). c10/C. J. BALLHAUSENand H. B. GRAY, Inorg. Chem. 1, 111 (1962). (11) R. D. FELTHAM. Thesis, University of California, U.S.A.E.C. Report UCRL-3867 (1957). (121 R. P. DODGE, U.S.A.E.C. Report UCRL-8225 (1958). (13) B. SHAMBURGER and J. SELBIN. Unpublished results. 1111
1112
J. SELBINand L. H. HOLMES,JR.
complexes~9, 14) has utilized the V-O stretching vibration as the probe to establish certain ligand series and has uncovered a very interesting correlation between infra-red spectral data and electronic spectral data~ 14). The oxygen(s) attached to the central metal produce one (or more) additional electronic (electron transfer) absorption bands, which, again, are perturbed to varying degrees by the particular set of ligands. Information from this source is more difficult to unravel and interpret, but, in principle, it should provide independent data concerning the nature of the complexes.~14) In order to have a wide variety of complexes available for such studies as mentioned above, we have prepared and partially characterized a large number of complexes of the oxovanadium(IV) cation. These include cationic, neutral and anionic complexes in which the vanadium is either five-or six-co-ordinated. Complex types in which the vanadium is five-co-ordinated include [VO(AAAA)]*, [VO(ABBA)], [VO(AA)2], [VO(AA) (BB)] and [VO(AA)a2]. Complex types in which the vanadium is sixco-ordinated include [VOas], [VOa4b], [VOa3b2], [VO(AA)a3] and [VO(AA)2a ]. Conductivity studies of many of these complexes in nitrobenzene generally allowed the assignment of groups to the first co-ordination sphere and the determination of a definite co-ordination number. For example, with VO(AA)2X2 compounds (where AA----o-phen or dipy) the formulation as [VO(AA)2X]X is found for X=C1 or Br, whereas the formulation [VO(AA)2]X 2 holds for X~---CIO4. If X2----SO4, an intermediate conductivity value is observed, indicating, perhaps, ion-pair association in this case. The infra-red spectrum of this compound indicates that in the solid state the sulphate ion is co-ordinated as a unidentate ligand. Two complexes having empirical formulas VO(AA)I.5(NCS)2 (where AA----o-phen or dipy) are formulated as [VO(AA)2NCS] [VO(AA) (NCS)3 ] on the basis of their mode of formation, conductivity data and infra-red spectra. The assignment of the absorption bands due to the V-O (vanadyl) stretching vibration has been made for over fifty complexes, including a few vanadium (V) compounds.t9,14) They are found to fall in the range 932-1035 cm -1. Several ligand series may be deduced from these results, and the series have been interpreted in terms of ligand a and n bonding.t14) The persistence of the vanadium-oxygen multiple bond in all of the complexes may be considered to be established from the infrared spectra of the compounds. BARRACLOUGH,et aL ~15) have concluded that the presence of a metal-oxygen multiple bond can be correlated with a stretching frequency in the range 900-1100 cm -1. We have verified this conclusion with a large number of compounds of MOO3+, MoO 2+ and WO22÷ as well as VO 2÷ and UO 2÷, although we could find no evidence for a TiO2+ or a ZrO2+ mononuclear species in certain so-called titanyl or zireonyl compounds. The formation of multiple bonds to oxygen by metals in this region of the periodic table has been explained theoretically for UO 2÷ 1,VO2+ (10,14)and MoO 3+ and CrO 3+ c16) However, qualitatively this situation may be traced to the ability or tendency for * Abbreviations used in this paper are: AAAA = symmetrical quadridentate ligand; AB = unsymmetrical bidentate ligand; a, b = unidentate ligands, etc. ; o-phen = orthophenanthroline; dipy = dipyridyl; DMSO = dimethylsulphoxide. c14~j. SELBIN,S. P. McGLYNN and L. H. HOLMES. In preparation for publication. C15JC. G. BARRACLOUGH,J. LEWISand R. S. NYHOLM,~. Chem. Soc. 3552 (1959). t16) H. B. GRAYand C. R. HARE. Inorg. Chem. 1, 363 (1962).
Complexes of oxovanadium(IV)
1113
oxygen to delocalize itspn- electrons away from its highly compact valence sheell, forming n-bonds by this means. GILLESVIECI7)has accumulated a great deal of stereochemical evidence to support the hypothesis that oxygen (and fluorine) will form multiple bonds with atoms or groups which can readily accept n-bonding electrons available in the compact 2p level. The early transition elements in their high oxidation states, in which they achieve d o or d 1 configurations, are apparently good n-electron acceptors. In fact, it is well known that the metals at the beginning of the transition series form their most stable complexes with oxygen-donor ligands and that their halide complexes follow the stability order F >>C I > B r > I. The formation and great stability of multiple bonds with oxygen by the metals in this region of the periodic table is thus not unexpected. EXPERIMENTAL
A. Preparation of Compounds The starting vanadium materials included VOSO4"5H20, V205, and VOC12(syrupy), all commercial reagent grade products, and VO(C104)2"xH20, prepared as described below.
Vanadyl perchlorate Three methods were found to be satisfactory for obtaining pure aqueous solutions of this compound. (a) VOSO4 is treated with sodium hydroxide and the precipitated VO(OH)2 is filtered and washed until free of sodium sulphate. An excess of alkali should be avoided due to the amphoterism exhibited by the VO2+ ion. Ammonia may be used, providing all of the ammonia is washed from the precipitated hydroxide. The hydroxide is then dissolved in perchloric acid to give a vanadyl perchlorate solution which is stable for many days at room temperature or below. Heating causes show oxidation of the vanadyl to V205 by the perchlorate. (b) Vanadium pentoxide is suspended in perchloric acid and electrolysed at a constant potential of 0.55 V (vs. Ag-AgC1 electrode). Complete dissolution and reduction is slow; the solution is then filtered, yielding a vanadyl perchlorate solution. (c) Perchloric acid is added to a solution of VOC12 and the resulting solution heated on a steam bath to drive off HC1. Oxidation of the vanadyl ion by the perchlorate ion can be reversed by adding small amounts of ethanol to the solution. Ethanol in acid solution will reduce vanadium pentoxide to VO2+. A blue solution is finally obtained which gives a negative test for chloride ion with silver nitrate. Filtration improves the purity of the solution, but this is the least satisfactory of the three methods. Solid hydrated vanadyl perchlorate may be obtained as large clear blue crystals by slow vacuum evaporation of the above solutions at room temperature. The crystals are extremely hygroscopic, making precise analysis difficult. (Found: VO, 18.5; CIO4, 27-2. Calc. for VO(CIO4)2-5H20: VO, 18-8; CIO4, 27.9 and for VO(C104)2"6H20: VO, 17.9; C104, 26-6%). Vanadyl chloride and vanadyl bromide These compounds are prepared in aqueous solution by heating a mixture of vanadium pentoxide, ethyl alcohol, water and the appropriate acid until all of the vanadium pentoxide has reacted. Evaporation yields syrupy liquids and the vanadyl halides contain an indeterminate amount of water. Continued heating results in partial hydrolysis. Vanadyl fluoride (a) An aqueous solution of vanadium pentoxide and HF is electrolysed at constant potential and the filtered solution is evaporated to a blue solid: VOF2.xH20; (b) a solution of VOCI2 is treated with a solution of AgF in HF (prepared from silver oxide and HF) and the AgCI removed by filtration. Evaporation of the filtrate yields VOF2-xH20. (Found: VO, 40"1. Calc. for VOF2-3H20: VO, 42.1, and for VOF2.4H20: VO, 37.8 %). (17) R. J. GILLESPIE,J. Amer. Chem. Soe. 82, 5978 (1960).
1114
J. SELBINand L. H. HOLMES,JR.
Pentacyano-oxovanadate(1V) ion (a) Tetraethylammonium salt. VOSO4"5H20is dissolved in ca. 6M NaCN; the initial precipitate of hydroxide dissolves with stirring. The dark green solution is cooled in ice and filtered. The clear green filtrate is mixed with an aqueous solution of Et4NBr and the mixture evaporated in an air stream at room temperature. After several hours, green crystals separate and they are filtered, washed with alcohol and ether and dried in vacuo. Acetone cannot be used as wash solution since it appears to cause decomposition of the product. The product is insoluble in organic solvents and dissolves with decomposition in water. (Found: VO, 12.25; CN, 22.2. Calc. for [(C2Hs)4N]3[VO(CN)5]: VO, 11"41; CN, 22"2 ~o). The analysis for vanadyl was made by precipitating the cyanide with an equivalent amount of silver nitrate and titrating the filtrate with permanganate. The high analysis for vanadyl may perhaps be explained as due to some soluble Ag(CN)z- which would be oxidized by permanganate. (b) Tetramethylammonium salt. VOSO4.5HzO is dissolved in ca. 6M NaCN solution and a hot aqueous solution of Me4NI is added. A precipitate forms immediately and after cooling in ice, a light green powder is filtered and washed with alcohol and ether and vacuum-dried. (Found: VO, 16-80; CN, 32-2. Calc. for [(CH3)4N]a[VO(CN)s]: VO, 16.00; CN, 31.25 %). (c) Cesium salt. To a solution of VOSO4"5H20 dissolved in ca. 6M NaCN is added a solution of CsCI. An aqua coloured precipitate forms which is cooled in ice and filtered. It is washed with ca. 6M NaCN in order to remove Na2SO4 which may be coprecipitated. The cyanide solution is used for washing because the cyano complexes are unstable in water but stable in excess cyanide. Finally alcohol and ether are used to wash the product and it is air-dried. (Found: VO, 20.70; CN, 21.07. Calc. for Cs3[VO(CN)s]: VO, 20.36; CN, 21.80 ~). Pentaisothiocyanato-oxovanadate( IV) ion (a) Tetraeth,ylammonium salt. Vanadyl sulphate is dissolved in ca. 8 M NH4NCS. An aqueous solution of Et4NBr is added, yielding an immediate precipitate. The solution is heated and the precipitate dissolves; on cooling slowly to ice temperature the solution yields blue needles. They are recrystallized from absolute alcohol, filtered, washed with alcohol and ether and vacuum-dried. (Found: NCS, 40.70; C, 42.39, 42.01; H, 7.25, 7.27; N, 14.48, 14.50. Calc. for [(C2Hs)4N]3[VO(NCS)5]: NCS, 38-90; C, 46.50; H, 8.08; N, 16.05~. Found: C/H, 5.68; C/N, 2.92. Calc. C/H, 5.75; C/N, 2.90.) It is possible that this compound was not fully decomposed in the analysis for C, H and N, as the ratios would indicate. The crystals recrystallize nicely and are well formed. They appear to be quite pure under a microscope and the analysis for NCS run in this laboratory is satisfactory. There is also the possibility that some bromide ion (from the Et4NBr) is present: it would lower the C, H and N percentages and raise the thiocyanate percentage which was determined as AgNCS. This last possibility finds support in the superior analysis found with the tetramethylammonium compound prepared from (CHa)4NI and described below. (b) Tetramethylammonium salt. Vanadyl sulphate is dissolved in ca. 8 M NH4NCS and a hot aqueous solution of Me4NI is added. On cooling, a precipitate of sparkling blue crystals is obtained. These crystals are filtered, recrystallized from absolute alcohol, washed with alcohol and ether and air-dried. A hot solution of the Me4NI is used here as previously because of the lower solubility of this compound at lower temperatures. (Found: NCS, 49.50; C, 34.53; 34-20; H, 6.51, 6.66; N, 19.00, 19.21. Calc. for [(CH3)4N]3[VO(NCS)s]: NCS, 50"01; C, 34"61; H, 6"26; N, 20"50~). Sulphatodipyridylo xovanadium( I I1) Vanadyl sulphate is dissolved in warm dimethylformamide (DMF) and then added to a solution of ~,ct'-dipyridyl in DMF. A green solution is obtained at first, but upon further addition of vanadyl sulphate, a green powder deposits. The powder is refluxed in absolute ethanol, filtered, washed with ether and dried in vacuo. (Found: VO, 21"40; SO4, 31.0. Calc. for [VO(CloHsNz)SO4]:VO, 21.00; SO4, 30-10 ~).
Complexes of oxovanadium(1V)
1115
Sulphato(orthophenanthroline)oxovanadium(l V) Vanadyl sulphate is dissolved in D M F and added to o-phen dissolved in DMF. A yellow solid forms immediately which on further addition of vanadyl sulphate dissolves to produce a green solution. When this solution is heated just below the boiling point, a greenish powder precipitates. It is refluxed in absolute ethanol, filtered, washed with ether and dried in vacuo. (Found: VO, 19.35; 504, 28"70. Calc. for [VO(C12HsN2)SO4]: VO, 19-50; SO4, 28'00%) Bis(orthophenanthroline)-oxovanadium(1V) sulphate Vanadyl sulphate is dissolved in ethanol (containing enough water to cause dissolution) and added in a one to two mole ratio to o-phen dissolved in ethanol. A gummy precipitate is obtained which dissolves if the solution is heated. Upon cooling, a yellow-brown powder is deposited which is not very soluble in ethanol after drying. It is washed with acetone and ether and dried in vacuo. (Found: VO, 14.20; SO4, 18.20. Calc. for VO(C12HsN2)2SO4: VO, 12.80; SO4, 18.35~). Tetramethylammonium tetrachloro-oxovanadate( I V) monoethanolate Syrupy vanadyl chloride is mixed with a very concentrated solution of (CH3)4NC] and ethanol is added. Upon addition of acetone and ether to this solution a blue oil separates. This oil is washed with successive portions of absolute ethanol-acetone mixtures (enough acetone to prevent redissolving the oil) and then dissolved in a small volume of absolute ethanol. Acetone addition to this solution gives a greenish-blue gummy solid which is washed repeatedly with acetone. The product can then be recrystallized from absolute ethanol by dissolving it and then evaporating some of the solvent, followed by cooling. An aqua coloured powder is obtained which is ether-washed and dried in vacuo. (Found: VO, 16.42; C1, 35.00. Calc. for [(CH3)4N2][VOC14(C2HsOH)]: VO, 16.62; CI, 35.25°<0). Bis( dil~yridyl)--o xo vanadium( I V ) perchlorate Vanadyl perchlorate (aqueous or solid) is dissolved in acetone and added to cq~'-dipyridyl dissolved in acetone. A greenish-brown solution results which is evaporated to dryness in a vacuum at room temperature. The solid obtained is washed several times with a 1]1 mixture of acetone-ether and again evaporated to dryness under vacuum at room temperature. Washing with acetone-ether mixtures may produce an oil. The final product is a greenishbrown powder which is washed with ether and dried in vacuo. ~Found: VO, 11 "24; C, 42"48 ; H, 3"38; N, 9"60. Calc. for [VO(C10HsNz)2](C104)2 :VO, l 1.58; C, 41-60; H, 2.80; N, 9"69 °/k). Bis(orthophenanthroline)-oxovanadium(IV) perchlorate Vanadyl perchlorate in acetone is added to o-phen dissolved in acetone. After the solution is stirred for several minutes a green precipitate begins to appear and precipitation is complete after cooling in ice. It is filtered, washed with ether and vacuum-dried. (Found: VO, 10"75; C, 45.82; H, 2.98; N, 8.45. Calc. for [VO(ClEHsN2)2](C104)2: VO, 10.70; C, 46.00; H, 2.58; N, 8.96~). Bromobis(orthophenanthroline)-oxovanadium(1 V) bromide l-hydrate Aqueous vanadyl bromide in acetone is added dropwise with stirring to o-phen dissolved in acetone. A chartreuse precipitate appears at once and increases in amount as the VOBr2 is added. The solution above the precipitate is nearly colourless as long as excess o-phen is present; if excess VOBrz is added it becomes greenish. The precipitate is refluxed for some minutes in a 1 ~1 ethanol-acetone mixture and filtered, washed with ether and vacuum-dried. (Found: Br, 26.4; C, 46-44; H, 2.96; N, 9.10. Calc. for [VO(C~2HsNz)2Br]Br-H20: Br, 26.40; C, 48-00; H, 3"00; N, 9"33 ~). Bromobis(dipyridyl)-oxovanadium(IV) bromide 1-hydrate A solution of hydrated VOBr2 in acetone is added dropwise with stirring to a solution of dipy dissolved in acetone. A green precipitate separates at once, increasing in quantity as VOBr2 is added. The solution remains colourless if an excess of dipy is present, greenish, if not. The precipitate is filtered and dissolved in a 1~1 ethanol-acetone mixture. Upon cooling for several hours in ice the solution deposits a dark green powder, which is washed with ether and vacuum-dried. (Found: Br, 28-20; C, 42"38; H, 3.56; N, 10.08. Calc. for [VO(CloH8Nz)zBr]Br'H20: Br, 28"70; C, 43 -20; H, 3-24; N, 10-09 ~).
1116
J. SELBINand L. H. HOLMES,JR.
Chlorobis(orthophenanthroline)-oxovanadiurn(IV) chloride Syrupy VOClz dissolved in acetone is added dropwise with stirring to o-phen dissolved in acetone. A light greenish-yellow fluffy precipitate forms at first, but on further addition of VOC12 the precipitate becomes green and heavier, settling out very readily. When the supernatant liquid becomes green the addition is stopped and the mixture heated to boiling for several minutes, filtered and the green powder washed with ether and vacuum-dried. (Found: VO, 13.98; C1, 14.08. Calc. for [VO(C12HaN2)2C1]Cl: VO, 13.42; C1, 14.24%). Chlorobis(dipyridyl)-oxovanadium(IV) chloride Syrupy VOC12 dissolved in acetone is added dropwise with stirring to dipy dissolved in acetone. A green precipitate is obtained immediately and VOC12 addition is stopped when the solution turns green. The mixture is boiled for several minutes, the solid filtered and refluxed in fresh acetone for several more minutes, then filtered, washed with ether and dried in vacuo. (Found: VO, 15.01; C1, 14.51. Calc. for [VO(C10HsN2)2CI]CI: VO, 14.12; C1, 14.95 ~).
VOC204"H2C204"3H20 Aqueous VOCI2 is mixed with excess oxalic acid and the solution is heated on the steam bath for several hours, water being added as it evaporates. Finally the mixture is evaporated to dryness, leaving a blue solid. This solid is broken up and heated with 95 per cent ethanol. It is filtered hot, yielding a blue powder, which is repeatedly washed with hot 95 per cent ethanol until a negative test for chloride ion is obtained when the powder is dissolved in water. Then the product is washed with ether and dried in vacuo. The vanadyl and oxalate were analysed by titrating a sample with permanganate and calculating the per cent VO using 1 of the volume and the C204 using 4 of the volume required. (Found: VO, 22.20; C204, 58.40; C, 16.26; H, 2.00. Calc. for VOC204-HzC204"3H20: VO, 22.38; C204, 58.90; C, 17.05; H, 2.67%).
Oxalato(dipyridyl)-oxovanadium(1V) The product just described, VOC204.H2C204"3HzO, is dissolved in ethanol (containing just enough water to effect dissolution) and added dropwise with stirring to dipy dissolved in alcohol. The solution immediately turns yellow, then darkens to green, and finally a green precipitate deposits. The vanadyl solution is added until there is a 2: I mole ratio (VO:dipy) present. The mixture is boiled for several minutes, cooled, filtered and the green product washed with acetone and ether and air-dried. (Found: VO, 20.65; C204, 27.10; C, 43.95; H, 3.17; N, 8-51; C/N, 5.18. Calc. for [VO(CIoHsN2)C204]: VO, 21-60; C204, 28"30; C, 46"40; H, 2.58; N, 9-00; C/N, 5"169/o). Oxalato(orthophenanthroline)-oxovanadium(IV) VOCEO4"HECEOg'3H20 is dissolved in warm dimethylformamide and added dropwise with stirring to o-phen dissolved in ethanol. Immediate precipitation of a yellow-green solid occurs and the addition is stopped when the mole ratio (VO:o-phen) is near 2~1. The mixture is boiled for several minutes, cooled in ice, filtered and the product washed with acetone and dried in vacuo. (Found: VO, 19.10; C204, 26.40; C, 47.36; H, 3-22; N, 9.49. Calc. for [VO(C12HaN2)C204]: VO, 20"00; C204, 26.25; C, 50"20; H, 2.39; N, 8.38 %). Difluoro(orthophenathroline)-oxovanadium(IV) An aqueous solution of vanadyl fluoride (or solid vanadyl fluoride) is dissolved in a 1 : 1 ethanol-water mixture and then added dropwise with stirring to o-phen dissolved in ethanol. A green powder is obtained which, after boiling in the mother liquor for a few minutes, is filtered, washed with several portions of 95 per cent ethanol, acetone and then vacuum-dried. (Found: VO, 23.50; C, 41.85; H, 3.85; N, 7.36; C/N, 5.67. Calc. for [VO(C12HaN2)F2]: VO, 23.45; C, 50"60; H, 2"91; N, 10.01 ~ ; C/N, 5"05). The reasons for the poor agreement on the C, H and N analyses are unknown; however the compound appears to be pure (e.g., under the microscope) and our own analysis for vanadyl is quite satisfactory. The C, H and N were determined by a commercial laboratory.
Complexes of oxovanadium(IV)
1117
Difluoro(dipyridyl)-oxovanadium(IV) A solution of vanadyl fluoride in a 1 ~1 water-ethanol mixture is added dropwise with stirring to dipy dissolved in ethanol. The green precipitate obtained is heated to boiling in the mother liquor for several minutes then filtered. It is then refluxed in acetone for several minutes, filtered, washed with ether and vacuum-dried. (Found: VO, 27.18; C, 45-35; H, 3"63; N, 10-76. Calc. for [VO(C10HnN2)F2]: VO, 25.63; C, 46.00; H, 3.07; N, 10.72 ~,,). (VO)2(o-phen)3(NCS)4 A solution of vanadyl thiocyanate in ethanol is prepared as follows. Syrupy VOCI2 is dissolved in absolute ethanol and treated with about 3 moles of NHaNCS for each mole of VOCI2. The solution is heated on a hot plate for about 30 min and then cooled for several hours in ice. The precipitated NH4C1 is filtered off, leaving vanadyl thiocyanate (and some NH4NCS) in solution. This is added dropwise with stirring to a solution of o-phen in ethanol. A chartreuse precipitate separates out and the mixture is boiled for several minutes. After cooling in ice, it is filtered, washed with acetone and vacuum-dried. (Found: C, 52.30; H, 2-73; N, 14-68. Calc. for VO(C12HaN2)I.s(NCS)2: C, 53.00; H, 2"65; N, 15"45~). (VO)2(dipy)3(NCS)4 This compound is prepared by the same procedure used to obtain the previous compound. It is a green powder, which is refluxed in acetone for several minutes, filtered and washed with ether and air-dried. (Found: C, 48.79; H, 2.70; N, 17.00. Calc. for VO(C10H8N2h.s(NCS)z: C, 48.99; H, 2.16; N, 16-79~).
Bis(8-hydroxyquinolinate)-oxovanadium(l V) This compound is prepared by the method of BIEUG and BAVER.t18) Vanadyl sulphate and oxine are heated in water solution for an hour or so on a steam bath. The brown vanadyl oxinate separates as a solid and is filtered, washed free of SO4 with hot water and dried in vacuo. It is anhydrous. A mmonium pentafluoro-oxovanadate(l V) This compound is prepared by the method of MUETTERTIES.(j9) Ammonium bifluoride is added to an aqueous solution of vanadyl fluoride and a light blue powder precipitates. It is recrystallized from water and air-dried. It is anhydrous. The same compound can be obtained using vanadyl sulphate in aqueous H F to which ammonium bifluoride is added. (Found: VO, 30.90. Calc. for (NH4)3[VOF5]: VO, 31.00%). Vanadyl phthalocyanine This compound was prepared from VzO5 and phthalonitrile according to the method of BARRETT et al.(2o) Pentakis(dimethylsulphoxide)-oxovanadium( IV) perchlorate An aqueous solution of VO(CIO4)2 is added to pure dimethylsulphoxide (DMSO): the solution becomes hot and subsequently blue crystals are deposited. The VO(C104)2 must be added to the DMSO; addition of DMSO to a VO(C104)2 solution did not yield a crystalline product. The crystals are washed with ether and vacuum-dried. (Found: C104, 31.0; C, 18.55; H, 4.64. Calc. for [VO{(CH3)zSO}5](CIO4)z: C104, 30"4; C, 18'65; H, 4"57~). Sulphatotris(dimethylsulphoxide)-oxovanadium( I V) VOSO4"5HzO in pure DMSO is heated to dissolution of the salt, then cooled, yielding blue crystals. These are filtered, washed with acetone and ether and vacuum-dried. (Found: SO4, 25.4; C, 18.38; H, 4.78. Calc. for [VO((CH3)zSO}3SO4]: SO4, 24.2; C, 18.15; H, 4.54%). 1~8) H. J. BIELtG and E. BAYER, Ann. 584, 96 (1953). (19) E. MLIETTERTIES,J. Amer. Chem. Soc. 82, 1082 (1960). (201 p. A. BARRETX,C. E. DENT, R. P. LrNSTEAD,J. Chem. Soc. 1719 (1936).
1118
J. SELB1Nand L. H. HOLMES,JR.
D ich loro tris(dimet hy lsulpho x ide)-o xo vanadium(I V ) Syrupy VOC12 is dissolved in DMSO with the liberation of heat. On cooling, the solution becomes syrupy and it does not yield a precipitate. It is heated to remove some of the DMSO, then added to ethanol. To this solution at its boiling point, acetone is added and then the mixture is cooled in ice. A light blue powder is obtained. It is recrystallized from a 1Z1 ethanol-acetone mixture, filtered, washed with ether and vacuum-dried. (Found: C1, 19.39; C, 19.48; H, 5.34. Calc. for [VO((CH3)2SO}aC12]: CI, 19.20; C, 19.35; H, 4.88 ~). Pentakis(dimethylsulphoxide)-oxovanadium(IV) bromide (a) Aqueous VOBr2 and DMSO are mixed in acetone and ether is added to precipitate a green-blue solid. The product is recrystallized from absolute ethanol, filtered, washed with ether and dried in vacuo. (b) Aqueous VOBr2 is dissolved in pure DMSO and after cooling to 0°C, blue crystals are deposited. They are recrystallized as described in (a). (Found: Br, 26.03; C, 19.24; H, 4-95. Calc. for [VO((CH3)2SO}5]Br2: Br, 25-93; C, 19.49; H, 4.87~). Vanadyl bis(acetylacetonate) This compound was obtained as a commercial product from K and K Laboratories. B. Physical Measurements 1. Conductance Equivalent conductances of the vanadyl complexes were obtained in nitrobenzene. Concentrations ranged from 10-4 to 10-3 M. According to previously published data{211 for the conductances of complexes in nitrobenzene, the range for equivalent conductances in ohm-1 cm 2 were taken as follows: four ions, 70-90; three ions, 40-60; two ions, 20-30. In Table 1 the conductance data are collected. These data allow the assignment of ligands to the first co-ordination sphere in all but three of the compounds listed. (That some of the compounds may be polymeric with ligands other than the oxygen acting as bridging groups cannot be completely ruled out at the present time; however, molecular weight determinations have proven VO(acac)2 and VO(oxine)2 to be monomeric in benzene.) The low value (7-6) for the equivalent conductance of VO(o-phen)2SO4 may result from partial dissociation of the sulphate ion or from strong ion-pair interaction between the divalent cation and anion. A value of ten was obtained for the equivalent conductance of the compounds having empirical formulas of VO(dipy)l.5(NCS)2 and VO(o-phen)l.5(NCS)2. If these formulas are doubled a value of twenty is obtained, which is in the range for a one to one electrolyte. We tentatively suggest that these compounds should be formulated as [VO(dipy)2NCS][VO(dipy)(NCS)3] and [VO(o-phen)2NCS][VO(o-phen)(NCS)3]. The method of preparation of these compounds is such that it would not be unreasonable to anticipate these products. Thus the addition of the chelating agent (AA) to a solution containing the [VO(NCS)5]3species would be expected to form [VO(AA)(NCS)3]- initially. This species would then react with additional (AA) to give [VO(AA)2NCS] +, which may then be precipitated by the anionic complex species to yield [VO(AA)2NCS][VO(AA)(NCS)3], a uni-univalent electrolyte. Attempts to get NCS- to add to [VO(AA)2]2+ to give the cationic complex or to add and displace an AA group to give the anionic complex were unsuccessful. 2. Infra-red spectra The infra-red spectra of the vanadyl complexes were obtained in the 4000-650 cm-I region using a Perkin-Elmer Model 21 spectrophotometer and a Beckman IR-7 spectrophotometer* each equipped with NaC1 optics. Nujol mulls were employed since some of the compounds appeared to have been altered in the preparation of KBr pellets. The spectra of all of the ligands were obtained so that ligand bands could be more easily identified in the spectra of the complexes. Generally there was no difficulty in identifying the strong band * The Beckman IR-7 infra-red spectrophotometer was purchased with funds obtained in part from the National Science Foundation, grants numbers NSF-15242 and NSF-16724 and in part from a grant to one of us (J. S.) by the Research Corporation. c211F. A. COTTONand D. GOODGAME,J. Chem. Soc. 5267 (1960).
Complexes of oxovanadium(IV)
1119
(or bands) due to the vanadium-oxygen multiple bond in the infra-red spectra. The frequencies of the V-O stretching vibration ranged from 1020 cm-1 to 932 cm-1, depending upon the particular set of ligands which surrounded the VO z+ entity. TABLE 1.--EQUIVALENT CONDUCTANCESOF VANADYLCOMPLEXESIN NITROBENZENE Compound 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.
VO(DMSO)s(C104)2 VO(DMSO)sBr2 VO(DMSO)3C12 VO(DMSO)3SO4 VO(dipy)SO4 VO(o-phen)SO4 VO(dipy)(ox) VO(o-phen)(ox) VO(dipy)F2 VO(o-phen)F2 VO(oxine)2 VO(o-phen)2Br2"H20 VO(dipy)zBr2-H20 VO(o-phen)2C12 VO(dipy)2Cl2 VO(o-phen)2SO4 (VO)2(dipy)3(NCS)4 (VO)2(o-phen)3(NCS)4 VO(o-phen)2(C104)2 VO(dipy)2(C104)2 (Et4N)3VO(NCS)5 (MeaN)3VO(NCS)s VO(acac)2
Equiv. cond. £)- 1 cm 2
No. of ions indicated
48"5 18'4 0 0 0 0 0 0 0 0 0 26.2 25"2 23.7 18"2 7"6 20 20 56.5 56 69.1 86 0
3 2 0 0 0 0 0 0 0 0 0 2 2 2 2 0-2 2 2 3 3 4 4 0
Acknowledgement--The authors are grateful to the National Science Foundation for financial support received under a grant number NSF-G15242.