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Dinuclear oxovanadium(IV) compound with alkoxyalcohol: synthesis and structural study of {VOCl[OCH(CH3)CH2OCH3]}2
0277-5387/93 $6.00+ .Ml Cc) 1993 Pergamon Press Ltd
Polyhedron Vol. 12, No. 20, pp. 2507-251 I, 1993 Printed in Great Britain
DINUCLEAR OXOVANADIUM(IV) COMPOUND ALKOXYALCOHOL: SYNTHESIS AND STRUCTURAL (VOCl[OCH(CH,)CH,OCH,1), GISELE FOULON, Laboratoire
JEAN-DOMINIQUE
FOULON
and NADINE
WITH STUDY OF
HOVNANIAN*
de Physicochimie des Materiaux, URA 1312, ENSCM 8 rue Ecole Not-male, 34053 Montpellier Ctdex 1, France (Received 21 April 1993 ; accepted 4 June 1993)
Abstract-The
reaction between VOC13 and 3 equivalents of sodium 1-methoxy-2-propanoxide in a mixture of toluene/l-methoxy-Zpropanol leads, after removal of the salt and crystallization of the concentrated filtrate, to a vanadium(IV) compound which has been characterized by the usual techniques (elemental analysis, IR, MS, EPR, ‘H and “V NMR) and X-ray diffraction as a dimeric five-coordinate oxovanadium(IV) chloride dialkoxide, {VOC1[OCH(CH3)CH20CH3]}2. Th is compound can also be obtained from VOC13 with I-methoxy-2-propanol in THF using ammonia gas. One of the two oxygen atoms from each methoxyalkoxo group bridges the vanadium centres yielding a planar V202 core. Surprisingly, a cis configuration around the V-O-V-O ring is adopted both by 0x0 groups and chlorine atoms.
Oxoalkoxovanadium complexes are attractive sources of molecular oxide precursors for sol-gel processes. ’ They can lead also to vanadium alkoxo compounds of high interest in catalytic and biological applications. 2 A number of vanadium oxoalkoxides derived from primary, secondary and tertiary monoalcohols have been synthesized from V205, NH4V03, VOC13 or by ester-exchange reactions3. Some of them have been structurally characterized as polymeric species such as [vO(OMe)3]a4 or fivecoordinate complexes such as VO(OCH2CH2C1)3S and [VO(cyclo-C,H90)3]26; the main character is that alkoxide ligands often act as bridging groups. The literature also mentions crystallographic data for derivatives with potential polydentate alcohols, particularly diols in dimeric or tetrameric associatioils. These polymerizations are achieved by two different bridging structural arrangements between the vanadium centre and the diols: either one of the oxygen atoms of each of the diol moieties bridges two vanadium centres7 or each alkoxide oxygen atom is coordinated to only one metal atom.8 Note that recently a hydrothermal synthesis based on polyols such as CH3C(CH20H), *Author to whom correspondence
should be addressed.
or CH 3CH 2C(CH20H) 3 yielded hexavanadium polyoxo alkoxide anion clusters. 9 We have decided to study the reactivity of VOCl, towards alkoxyalcohols, since these derivatives are used as additives in sol-gel techniques, yielding multicomponent oxides, in order to avoid formation of heterogeneous media, to slow down hydrolysis rates and/or stabilize gels. lo Alkoxyalcohols have proved to react easily with various transition metals, main group elements or lanthanides yielding stable and highly soluble alkoxide derivatives. ’ ’ In this paper we describe the synthesis, X-ray crystallographic characterization and spectroscopic study of {VOCl[OCH(CH3)CH20CH3]}2, a fivecoordinate oxovanadium (IV) chloride dialkoxide compound obtained from 1-methoxy-Zpropanol.
EXPERIMENTAL All manipulations were routinely performed under argon using Schlenk tubes and vacuum-line techniques with solvents purified by standard methods. VOCl, was used as received. ‘H and “V NMR and IR spectra were run on Bruker AC-250 and IR FT Nicolet ZDX spectrometers, respectively. 6(5’V) values are quoted relative to VOC13 and the
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G. FOULON et al.
spectra in non-deuterated solvents (parent alcohol) were recorded with external lock (D,O). IR spectra were obtained as Nujol mulls between KBr plates. Mass spectra were recorded on a 300 DX JEOL by Electronic Impact. EPR spectra were recorded on a Bruker ER 200D spectrometer, operating at Xband with 100 KHz field modulation ; the measurements were made on a solid sample at room temperature. Analytical data were obtained from the Centre de Microanalyses du CNRS. Synthesis of{VOCl[OCH(CH3)CH,0CHJ),
(1)
Pieces of sodium metal rods (1.52 g, 66 mmol) were slowly added under vigorous stirring to a solution of I-methoxy-2-propanol (8 cm3, 79.2 mmol) in toluene (15 cm’). The solution was heated as the reaction slowed down. The mixture was stirred at room temperature overnight until all the sodium metal was consumed. The solution was then cooled at 0°C and vanadium oxytrichloride (2 cm3, 21.2 mmol) was added dropwise under a slow argon flow. The reaction was exothermic and the colorless solution turned brown-red. The mixture was stirred for 12 h at room temperature and then filtered. After concentration the brown-red filtrate was left to crystallize at 5°C over a few days. Dark blue needle-shaped crystals were formed. Yield : 40% based on vanadium. Found : C, 25.2 ; H, 4.6 ; Cl, 17.9; V, 26.3. Calc. for CsH1806C12V2: C, 25.0; H, 4.7; Cl, 18.5; V, 26.6.%. IR (cm-‘): 1307, 1258, 1159, 1089, 1019,962,864,801,723,674,541,462, 354. SM (m/z, EI), OR = OCH(CH,)CH,OMe: [vOCl(OR)], (12%), V202Cl(OR), (lo%), V10CI(OR)2 (7%), V02Cl(OR)2 (13%), VO(OR) CI(CHCH,OMe) (6%), VO(OR)(CHCH,OMe) (5%), VO(OR) (5%), OMeCH,CH(CH,) (lOO%), OMeCH, (30%). ‘H NMR (CD,C12, ppm) : 1.09 m (CH,, 3H); 3.15 m-3.31 m (CH, and CH3, 5H); 3.9 m (CH, 1H). “V NMR (I-methoxy-2-propanol, ppm): -573.1 (1); -573.9 (1).
Crystallographic studies
A suitable crystal of {VOCl[OCH(CH,) CH20CH3])Z was mounted onto a Siemens P3 automatic diffractometer. Unit cell parameters were obtained from least-squares fit to the automatically centred settings for 20 reflections. The crystal parameters and basic information related to data collection and structure refinement are summarized in Table 1. The profile fitting option of the XDISK programI was used during data reduction in order to correct 25% of decay. No correction for absorption was made. All calculations were performed on a VAX 3100. Complex neutral-atom scattering factors were employed. Anomalous dispersion terms were used. Positions for the vanadium and chlorine atoms were obtained from a Patterson syn-
Table 1. Crystallographic data of {VOCl[OCH(CH,)
CHWH,I,} Compound Molecular weight Crystal system Space group a (A) b (A) c (A) B(“) V(A’) Z D (talc.) (g cm- ‘) F(OO0) (e-) Temperature (K)
Radiation Scan type Scan width hkl limits Reference reflections Intensity
stability
Data collected Unique data used
Alternative synthesis of 1
VOCl, (2 cm3, 21 mmol) was added to THF (40 cm’) immediately yielding a dark red solution. After addition of 1-methoxy-2-propanol (8 cm3, 79.2 mmol) the dark red solution was stirred. Then ammonia gas was bubbled at intermittent intervals of 2-5 min until the white fog formed above the reaction mixture disappeared. The solution became bright orange, then orange-white. After removal of NH&l by filtration the bright orange filtrate was concentrated and left to crystallize at 5°C. Dark blue crystals were formed.
PII2 > 3g(FrJ2) F (cm- ‘) R” R,” Weight (A/o) max” Residual electron density (e A-‘)
‘33
I .@&l,V,
382.9 Monoclinic P2,lc 14.104(7) 10.356(4) 11.388(8) 111.75(5) 1544(l) 4 1.647 776 293 MO-K, ce28 1.2+0.35 tan 8 +h, +k, +I 3 every 100 reflections 25% of decay (during data collection) 1432 940 15.7 0.0463 0.0545 w = 1/[d(F) + O.O009P] 0.001 f0.4
“The quantity minimized in the least-squares prois : cedure wWol--IFcl>‘. R = Wl~oI-~cll/Wol; R, = [Xw(jFol - IFcl)*/I;w(Fo)‘] I”. h Maximum ratio of the rms shift to standard deviation observed for the last cycle of refinement.
Synthesis and structural study of {VOCl[OCH(CH,)CH20CH3]}2 thesis using SHELXS-8613 and were confirmed by subsequent development of the structure. All remaining non-hydrogen atoms were found by successive electron density map calculations using SHELX 76. I4 Anisotropic temperature factors were introduced for all non-hydrogen atoms. Hydrogen atoms were placed in calculated positions (C-H = 1.08 A) and were no further refined, but recalculated after each cycle. Positional parameters and anisotropic thermal parameters are given as supplementary material. RESULTS
AND DISCUSSION
The exothermic reaction of VOC13 with 3 equivalents of sodium I-methoxy-2-propanoxide in a mixture of toluene/l-methoxy-2-propanol yielded a dark blue solid, (VOC1[OCH(CH3)CH20CH3]}2 (1). This compound was also obtained by reaction between VOC13 and 1-methoxy-2-propanol in THF using ammonia gas. This compound crystallized from the concentrated reaction medium after removal of NaCl or NH,Cl. Despite the bubbling of NH3 through the solution or the reaction with an alkali alkoxide, chloride ligands are still present and a reaction of reduction has occurred. Since solutions of light-sensitive vanadium(V) compounds when they are exposed to diffuse daylight or UV turn to light blue vanadium(IV) simultaneously with a black powder precipitate, we have carried out the syntheses in the dark and reproducible quantities of {VOClOCH (CH,)CH@CHd)z were obtained. According to the literature no reduction products are formed by reaction of VOC13 with functionalized alcohols when methylene chloride is used as a solvent of reaction or of recrystallization.” However, some reduction reactions occurred when vanadium(III) and (IV) carboxylates were previously prepared from VOC13.‘6 {VOC1[OCH(CH3)CH20CH3]}Z is soluble in polar organic solvents such as parent alcohol or DMSO and insoluble in pentane. Its dissolution in chlorinated solvents (CH,Cl,) or in toluene or THF is slow and results in a partially clear and blue solution. The oxidation degree of this oxovanadium chloride alkoxide correlates well with its colour, either in the solid state or in solution. Sol-gel investigations have shown us that in the presence of low or high water concentration, in the parent alcohol, compound I yields clear and limpid yellow or green solutions without any precipitation. These solutions become blue after many weeks. This observation (stability towards hydrolysis which seems to generate soluble materials) appears at first surprising, considering the known sensitivity of alkoxides
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towards water. The study of hydrolysis of this oxoalkoxide (by “V NMR and IR spectroscopies) is in progress. In order to confirm the vanadium(IV) oxidation state assignment for the bulk sample of 1 an EPR spectrum of 1 was carried out. It consists of an intense and symmetric broad signal, showing a partially resolved hyperfine structure due to the coupling with the vanadium nucleus (I = 7/2; eight lines are distinguishable. The direct measurement of g from the EPR spectrum gives a value of 1.95, which is similar to those previously recorded for a number of oxovanadate(IV) complexes. ’ 7 IR spectroscopy for 1 is consistent with the formulation provided by the X-ray analysis ; it exhibits in particular two bands at 1159 and 1089 cm- ’ which can be assigned to v(C-O-V) vibrations, while an intense band at 1019 cn- ’ is attributed to v(V=O). In the low energy range the peaks located at 674, 541, 462 and 354 cm- ’ are typical of v(V-OR) and v(C-Cl) vibrations, respectively. Despite the paramagnetism of compound 1, a ‘H NMR spectrum reveals the characteristic chemical shifts of the alkoxide groups. Nevertheless, no structural information can be provided because of the broadening of the signals due to quadrupolar and paramagnetic effects. The 5’V NMR spectrum of 1 shows two very close signals at - 573.1 and - 573.9 ppm in a ratio l:l, which reveals a nonabsolute equivalence for the “V resonances. We note that the weak half-line width of these resonances (45 Hz) is not affected by paramagnetic effects. Due to the lack of “V NMR information about oxovanadium(IV) compounds, ’ ’ conversely to oxovanadium(V) species, no comparison is possible. The dimeric nature of the compound was first suggested by mass spectral data, which exhibit the parent molecular ion without any ion of higher molecular mass. It has been definitively confirmed by an X-ray structural study. The X-ray crystal structure of 1 is shown in Fig. 1. Relevant bond lengths and angles are collected in Table 2. The complex consists of a dimeric unit in which the two independent VOCI[OCH(CH,) CH20CH3] units are held together by the bridging pZ-O(1) and p*-O(2) oxygen atoms. Although no crystallographic symmetry is imposed, a molecule of 1 exhibits an overall symmetry close to CZ, with the approximate C2 axis passing through the midpoint of a line joining the vanadium atoms and perpendicular to the V-O-V-O plane. Thus, both 0x0 groups and chlorine atoms adopt a cis configuration around the V-O-V-O ring. Such a configuration is rather rare since the tram configuration is more often encountered as
G. FOULON
2510
et al.
CC8
C(4)
molecule, showing the atomic numbering Fig. 1. ORTEP view of the {VOCl[OCH(CH,)CH20CHJ}2 scheme (thermal ellipsoids drawn at 40% probability level).
in the related
vanadium(V) complex {VOCl[OC Moreover, the C2 symmetry of the V-WZ)Z.~~ molecule leads to a boat-like configuration, as evidenced by Fig. 2,. This configuration tends to reduce the intramolecular interactions between the alkoxide ligand and both 0x0 group and chlorine atom. The vanadium atoms are five-coordinate, defining a distorted trigonal bipyramid. Actually, this
environment can alternatively be described as a distorted square pyramid. Although important shifts between the ideal angle values and the observed ones are noticed in both descriptions, we tend to prefer the trigonal bipyramid model in the way that deviation from planarity (+ 0.17 A) of the square base in the pyramidal model appear to be consequent. Nevertheless, these two types of environment
Table 2. Selected bond lengths (A) and angles (“) (standard parentheses)
WFW) V(lFO(2) V(l)-O(3) V(lbO(5) V(l)-Cl(l)
O(1F--W) C(l)--C(2) C(2)-C(3) C(3)-O(3) 0(3)-C(4)
deviations
1.952(7) 1.966(7) 2.052(7) 1.590(7) 2.282(3)
V(2)-O(2) V(2)_-0(1) V(2)--o(4) V(2)_-0(6) V(2)-Cl(2)
1.964(7) 1.948(7) 2.065(7) 1.584(7) 2.281(3)
1.454(11) 1.547(14) 1.484( 14) 1.452( 12) 1.424(11)
0(2)-C(6) C(5)-C(6) C(6)-C(7) C(7)_-0(4) 0(4)-C(8)
1.428(11) 1.536(14) 1.496(14) 1.455(11) 1.435(11)
in
V . V interaction V(l)-V(2) 3.084(3) V(2)--Wl)-V(1) O(l)---V(l)--o(2) WtV(l)--o(3) O(ltiV(l)---o(5) O(l)--V(l)-Cl(l) o(2)-V(l)--o(3) o(2)-V(l)--o(5) 0(2)-v(1)--c1(1) 0(3tV(lto(5) 0(3)-v(l)--Cl(l) o(5)---V(ltCl(l)
104.5(3) 76.0(3) 78.5(3) 113.8(3) 138.0(2) 148.0(3) 106.2(3) 94.7(2) 101.5(3) 91.5(2) 108.2(3)
V(l)--0(2)-V(2) O(2)-V(2W( 1) o(2)-V(2to(4) O(2)-V(2W(6) O(2)-V(2tcl(2) o(l)-V(2to(4) O(1 )-V(2tW6) O(l)-V(2)--cl(2) O(4)-V(2)--0(6) o(4)-V(2t-c1(2) O(6)-V(2)---Cl(2)
103.4(3) 76.1(3) 77.6(3) 114.2(3) 136.7(2) 147.2(3) 106.2(3) 95.6(2) 102.3(3) 90.2(2) 108.9(3)
Synthesis and structural study of {VOCl[OCH(CH,)CH,0CHj]}2
2511
6. F. Hillerns, F. Olbrich, U. Behrens and D. Reher, Angew. Chem, Int. Edn Engl. 1992,31,447. 7. (a) D. C. Crans, R. A. Felty and M. M. Miller, J.
Fig. 2. View of 1 perpendicular to the V--O-V4 showing the boat-like configuration.
ring,
Am. Chem. Sot. 1991, 113, 265 ; (b) D. C. Crans, R. W. Marshman, M. S. Gottlieb, 0. P. Anderson and M. M. Miller, Znorg. Chem. 1992,31,4939. 8. D. C. Crans, R. A. Felty, 0. P. Anderson and M. M. Miller, Inorg. Chem. 1993, 32,247. 9. D. L. Clark, J. G. Watkin and J. C. Huffman, fnorg. Chem. 1992,31,
1556.
10. (a) D. J. Eichorst and D. A. Payne, Better Ceramics are currently encountered in vanadium(IV) complexes. 16~3,I7a, I9 The V-O and V-Cl bond lengths fall in the range of values previously reported in the literature. 7a.7b,‘7a.Worthy of mention is the V---p ,--0 bond length, which is significantly longer than the V-p,0 one [average 2.058(7) and 1.957(7) A”, respectively]. This is clearly explained by the fact that the ~~-0 atoms [O(l) and O(2)] are negatively charged, whereas the ~~-0 atoms of the methoxy groups [O(3) and O(4)] are uncharged, allowing a weaker px-dn donation. The value of the intermetallic distance [V(l). . . V(2) = 3.084(3) A] is in good agreement with the V . . _V distance observed in the related oxovanadium compounds.7”~‘7”~20 At this distance a V-V bonding should not be expected and consequently, the two unpaired electrons should be mainly localized on one V=O unit. The presence of remaining chloride ligands in complex 1 makes the metal atom functionalizable and may permit the introduction of a second metal (by reaction with a species such as K[M(OR),] with salt elimination, for example). Further investigations towards the reactivity of 1 are in progress in this way. REFERENCES 1. M. Nabavi, C. Sanchez and J. Livage, Eur. J. Solid State Inorg. Gem. 1991,28, 1173. 2. S. I. Zones, M. R. Palmer, J. G. Palmer, J. M. Doemeny and G. N. Schrauzer, J. Am. Chem. Sot. 1978, loo, 2113. 3. (a) D. C. Crans, H. Chen and R. A. Felty, J. Am. Chem. Sot. 1992, 114, 4543 ; (b) F. Hillerns and D. Rehder, Chem. Ber. 1991,124,2249; (c) R. K. Mittal and R. C. Mehrotra, Z. Anorg. Allg. Chem. 1964, 327,311; (d) N. F. Orlov and M. G. Voronkov, Bull. Acad. Sci URSS, Div. Chem. Sci. 1959,933 ; (e) Von H. Funk, W. Weiss and M. Zeising, 2. Anorg. Allg. Chem. 1958,2%,36.
4. C. N. Caughlan, H. M. Smith and K. Watenpaugh, Inorg. Chem. 1966, 5, 2131.
5. W. Priebsch and D. Rehder, Znorg. Chem. 1990, 29, 3013.
Through Chemistry III, Material Research Society Symp. hoc. 1988, 121, 773 ; (b) J. T. J. Davies, H. C. Winterton and N. N. Hughes, Better Ceramics Through Chemistry II 1986,73, 111.
11. (a) 0. Poncelet, L. Hubert-Pfalzgraf, J.-C. Daran and R. Astier, J. Chem. Sot., Chem. Commun. 1989, 1846; (b) K. G. Caulton, M. H. Chisholm, S. R. Drake and J. C. Huffman, J. Chem. Sot., Chem. Commun. 1990, 1498 ; (c) M.-C. Massiani, R. Papiernik, L. Hubert-Pfalzgraf and J-C. Daran, J. Chem. Sot., Chem. Commun. 1990, 301; (d) S. C. Goel, M. A. Matchett, M. Y. Chiang and W. E. Buhro, J. Am. Chem. Sot. 1991, 113, 1844; (e) S. Boulmaaz, R. Papiemik, L. Hubert-Pfalzgraf, J. Vaissermann and J.-C. Daran, Polyhedron 1992, 11, 1331; (f) S. C. Goel, M. Y. Chiang and W. E. Buhro, Inorg. Chem. 1990,29,4640.
12. Program XDISK from the commercial package SHELXTL PLUS distributed by Siemens. 13. G. M. Sheldrick, SHELXS-86, Program for the Solution of Crystal Structures. University of Giittingen, F.R.G. (1987). 14. G. M. Sheldrick, SHELX 76, Program for Crystal Structure Determination. University of Cambridge, U.K. (1976). 15. It seems that this solvent stabilizes the oxovanadium(V) alkoxide species. Further reactions in CH,Cl, are, at present, being investigated to confirm this hypothesis. 16. (a) D. Rehder, W. Priebsch and M. von Oeynhausen, Angew. Chem., Int. Edn Engl. 1989,28, 1221; (b) H. J. Seifert, 2. Anorg. Ailg. Chem. 1962, 317, 123 ; (c) R. C. Paul and A. Kumar, J. Inorg. Nucl. Chem. 1965,27,2537.
17. (a) F. A. Cotton, G. E. Lewis and G. N. Mott, Znorg. Chem. 1983, 22, 378 ; (b) R. R. Reeder and P. H. Rieger, Znorg. Chem. 1971, 6, 1258; (c) N. D. Chasteen and M. W. Hanna, J. Phys. Chem. 1972, 76, 3951; (d) A. T. Casey, B. S. Morris, E. Sinn and J. R. Thackeray, Aust. J. Chem. 1972, 25, 1195. 18. To our knowledge, the only “V data of vanadium (IV) compounds are published by F. Preuss and L. Ogger in Z. Naturforsch. 1982,37b, 957. 19. G. Barr-David, T. W. Hambley, J. A. Irwin, R. J. Judd, P. A. Lay, B. D. Martin, R. Bramley, N. E. Dixon, P. Hendry, J.-Y. Ji, R. S. U. Baker and A. M. Bonin, Znorg. Chem. 1992, 31,4906. 20. S. Gambarotta, F. van Bolhuis and M. Y. Chiang, Znorg. Chem. 1987, 26,430l.
Polyhedron Vol. 12, No. 20, pp. 2507-251 I, 1993 Printed in Great Britain
DINUCLEAR OXOVANADIUM(IV) COMPOUND ALKOXYALCOHOL: SYNTHESIS AND STRUCTURAL (VOCl[OCH(CH,)CH,OCH,1), GISELE FOULON, Laboratoire
JEAN-DOMINIQUE
FOULON
and NADINE
WITH STUDY OF
HOVNANIAN*
de Physicochimie des Materiaux, URA 1312, ENSCM 8 rue Ecole Not-male, 34053 Montpellier Ctdex 1, France (Received 21 April 1993 ; accepted 4 June 1993)
Abstract-The
reaction between VOC13 and 3 equivalents of sodium 1-methoxy-2-propanoxide in a mixture of toluene/l-methoxy-Zpropanol leads, after removal of the salt and crystallization of the concentrated filtrate, to a vanadium(IV) compound which has been characterized by the usual techniques (elemental analysis, IR, MS, EPR, ‘H and “V NMR) and X-ray diffraction as a dimeric five-coordinate oxovanadium(IV) chloride dialkoxide, {VOC1[OCH(CH3)CH20CH3]}2. Th is compound can also be obtained from VOC13 with I-methoxy-2-propanol in THF using ammonia gas. One of the two oxygen atoms from each methoxyalkoxo group bridges the vanadium centres yielding a planar V202 core. Surprisingly, a cis configuration around the V-O-V-O ring is adopted both by 0x0 groups and chlorine atoms.
Oxoalkoxovanadium complexes are attractive sources of molecular oxide precursors for sol-gel processes. ’ They can lead also to vanadium alkoxo compounds of high interest in catalytic and biological applications. 2 A number of vanadium oxoalkoxides derived from primary, secondary and tertiary monoalcohols have been synthesized from V205, NH4V03, VOC13 or by ester-exchange reactions3. Some of them have been structurally characterized as polymeric species such as [vO(OMe)3]a4 or fivecoordinate complexes such as VO(OCH2CH2C1)3S and [VO(cyclo-C,H90)3]26; the main character is that alkoxide ligands often act as bridging groups. The literature also mentions crystallographic data for derivatives with potential polydentate alcohols, particularly diols in dimeric or tetrameric associatioils. These polymerizations are achieved by two different bridging structural arrangements between the vanadium centre and the diols: either one of the oxygen atoms of each of the diol moieties bridges two vanadium centres7 or each alkoxide oxygen atom is coordinated to only one metal atom.8 Note that recently a hydrothermal synthesis based on polyols such as CH3C(CH20H), *Author to whom correspondence
should be addressed.
or CH 3CH 2C(CH20H) 3 yielded hexavanadium polyoxo alkoxide anion clusters. 9 We have decided to study the reactivity of VOCl, towards alkoxyalcohols, since these derivatives are used as additives in sol-gel techniques, yielding multicomponent oxides, in order to avoid formation of heterogeneous media, to slow down hydrolysis rates and/or stabilize gels. lo Alkoxyalcohols have proved to react easily with various transition metals, main group elements or lanthanides yielding stable and highly soluble alkoxide derivatives. ’ ’ In this paper we describe the synthesis, X-ray crystallographic characterization and spectroscopic study of {VOCl[OCH(CH3)CH20CH3]}2, a fivecoordinate oxovanadium (IV) chloride dialkoxide compound obtained from 1-methoxy-Zpropanol.
EXPERIMENTAL All manipulations were routinely performed under argon using Schlenk tubes and vacuum-line techniques with solvents purified by standard methods. VOCl, was used as received. ‘H and “V NMR and IR spectra were run on Bruker AC-250 and IR FT Nicolet ZDX spectrometers, respectively. 6(5’V) values are quoted relative to VOC13 and the
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G. FOULON et al.
spectra in non-deuterated solvents (parent alcohol) were recorded with external lock (D,O). IR spectra were obtained as Nujol mulls between KBr plates. Mass spectra were recorded on a 300 DX JEOL by Electronic Impact. EPR spectra were recorded on a Bruker ER 200D spectrometer, operating at Xband with 100 KHz field modulation ; the measurements were made on a solid sample at room temperature. Analytical data were obtained from the Centre de Microanalyses du CNRS. Synthesis of{VOCl[OCH(CH3)CH,0CHJ),
(1)
Pieces of sodium metal rods (1.52 g, 66 mmol) were slowly added under vigorous stirring to a solution of I-methoxy-2-propanol (8 cm3, 79.2 mmol) in toluene (15 cm’). The solution was heated as the reaction slowed down. The mixture was stirred at room temperature overnight until all the sodium metal was consumed. The solution was then cooled at 0°C and vanadium oxytrichloride (2 cm3, 21.2 mmol) was added dropwise under a slow argon flow. The reaction was exothermic and the colorless solution turned brown-red. The mixture was stirred for 12 h at room temperature and then filtered. After concentration the brown-red filtrate was left to crystallize at 5°C over a few days. Dark blue needle-shaped crystals were formed. Yield : 40% based on vanadium. Found : C, 25.2 ; H, 4.6 ; Cl, 17.9; V, 26.3. Calc. for CsH1806C12V2: C, 25.0; H, 4.7; Cl, 18.5; V, 26.6.%. IR (cm-‘): 1307, 1258, 1159, 1089, 1019,962,864,801,723,674,541,462, 354. SM (m/z, EI), OR = OCH(CH,)CH,OMe: [vOCl(OR)], (12%), V202Cl(OR), (lo%), V10CI(OR)2 (7%), V02Cl(OR)2 (13%), VO(OR) CI(CHCH,OMe) (6%), VO(OR)(CHCH,OMe) (5%), VO(OR) (5%), OMeCH,CH(CH,) (lOO%), OMeCH, (30%). ‘H NMR (CD,C12, ppm) : 1.09 m (CH,, 3H); 3.15 m-3.31 m (CH, and CH3, 5H); 3.9 m (CH, 1H). “V NMR (I-methoxy-2-propanol, ppm): -573.1 (1); -573.9 (1).
Crystallographic studies
A suitable crystal of {VOCl[OCH(CH,) CH20CH3])Z was mounted onto a Siemens P3 automatic diffractometer. Unit cell parameters were obtained from least-squares fit to the automatically centred settings for 20 reflections. The crystal parameters and basic information related to data collection and structure refinement are summarized in Table 1. The profile fitting option of the XDISK programI was used during data reduction in order to correct 25% of decay. No correction for absorption was made. All calculations were performed on a VAX 3100. Complex neutral-atom scattering factors were employed. Anomalous dispersion terms were used. Positions for the vanadium and chlorine atoms were obtained from a Patterson syn-
Table 1. Crystallographic data of {VOCl[OCH(CH,)
CHWH,I,} Compound Molecular weight Crystal system Space group a (A) b (A) c (A) B(“) V(A’) Z D (talc.) (g cm- ‘) F(OO0) (e-) Temperature (K)
Radiation Scan type Scan width hkl limits Reference reflections Intensity
stability
Data collected Unique data used
Alternative synthesis of 1
VOCl, (2 cm3, 21 mmol) was added to THF (40 cm’) immediately yielding a dark red solution. After addition of 1-methoxy-2-propanol (8 cm3, 79.2 mmol) the dark red solution was stirred. Then ammonia gas was bubbled at intermittent intervals of 2-5 min until the white fog formed above the reaction mixture disappeared. The solution became bright orange, then orange-white. After removal of NH&l by filtration the bright orange filtrate was concentrated and left to crystallize at 5°C. Dark blue crystals were formed.
PII2 > 3g(FrJ2) F (cm- ‘) R” R,” Weight (A/o) max” Residual electron density (e A-‘)
‘33
I .@&l,V,
382.9 Monoclinic P2,lc 14.104(7) 10.356(4) 11.388(8) 111.75(5) 1544(l) 4 1.647 776 293 MO-K, ce28 1.2+0.35 tan 8 +h, +k, +I 3 every 100 reflections 25% of decay (during data collection) 1432 940 15.7 0.0463 0.0545 w = 1/[d(F) + O.O009P] 0.001 f0.4
“The quantity minimized in the least-squares prois : cedure wWol--IFcl>‘. R = Wl~oI-~cll/Wol; R, = [Xw(jFol - IFcl)*/I;w(Fo)‘] I”. h Maximum ratio of the rms shift to standard deviation observed for the last cycle of refinement.
Synthesis and structural study of {VOCl[OCH(CH,)CH20CH3]}2 thesis using SHELXS-8613 and were confirmed by subsequent development of the structure. All remaining non-hydrogen atoms were found by successive electron density map calculations using SHELX 76. I4 Anisotropic temperature factors were introduced for all non-hydrogen atoms. Hydrogen atoms were placed in calculated positions (C-H = 1.08 A) and were no further refined, but recalculated after each cycle. Positional parameters and anisotropic thermal parameters are given as supplementary material. RESULTS
AND DISCUSSION
The exothermic reaction of VOC13 with 3 equivalents of sodium I-methoxy-2-propanoxide in a mixture of toluene/l-methoxy-2-propanol yielded a dark blue solid, (VOC1[OCH(CH3)CH20CH3]}2 (1). This compound was also obtained by reaction between VOC13 and 1-methoxy-2-propanol in THF using ammonia gas. This compound crystallized from the concentrated reaction medium after removal of NaCl or NH,Cl. Despite the bubbling of NH3 through the solution or the reaction with an alkali alkoxide, chloride ligands are still present and a reaction of reduction has occurred. Since solutions of light-sensitive vanadium(V) compounds when they are exposed to diffuse daylight or UV turn to light blue vanadium(IV) simultaneously with a black powder precipitate, we have carried out the syntheses in the dark and reproducible quantities of {VOClOCH (CH,)CH@CHd)z were obtained. According to the literature no reduction products are formed by reaction of VOC13 with functionalized alcohols when methylene chloride is used as a solvent of reaction or of recrystallization.” However, some reduction reactions occurred when vanadium(III) and (IV) carboxylates were previously prepared from VOC13.‘6 {VOC1[OCH(CH3)CH20CH3]}Z is soluble in polar organic solvents such as parent alcohol or DMSO and insoluble in pentane. Its dissolution in chlorinated solvents (CH,Cl,) or in toluene or THF is slow and results in a partially clear and blue solution. The oxidation degree of this oxovanadium chloride alkoxide correlates well with its colour, either in the solid state or in solution. Sol-gel investigations have shown us that in the presence of low or high water concentration, in the parent alcohol, compound I yields clear and limpid yellow or green solutions without any precipitation. These solutions become blue after many weeks. This observation (stability towards hydrolysis which seems to generate soluble materials) appears at first surprising, considering the known sensitivity of alkoxides
2509
towards water. The study of hydrolysis of this oxoalkoxide (by “V NMR and IR spectroscopies) is in progress. In order to confirm the vanadium(IV) oxidation state assignment for the bulk sample of 1 an EPR spectrum of 1 was carried out. It consists of an intense and symmetric broad signal, showing a partially resolved hyperfine structure due to the coupling with the vanadium nucleus (I = 7/2; eight lines are distinguishable. The direct measurement of g from the EPR spectrum gives a value of 1.95, which is similar to those previously recorded for a number of oxovanadate(IV) complexes. ’ 7 IR spectroscopy for 1 is consistent with the formulation provided by the X-ray analysis ; it exhibits in particular two bands at 1159 and 1089 cm- ’ which can be assigned to v(C-O-V) vibrations, while an intense band at 1019 cn- ’ is attributed to v(V=O). In the low energy range the peaks located at 674, 541, 462 and 354 cm- ’ are typical of v(V-OR) and v(C-Cl) vibrations, respectively. Despite the paramagnetism of compound 1, a ‘H NMR spectrum reveals the characteristic chemical shifts of the alkoxide groups. Nevertheless, no structural information can be provided because of the broadening of the signals due to quadrupolar and paramagnetic effects. The 5’V NMR spectrum of 1 shows two very close signals at - 573.1 and - 573.9 ppm in a ratio l:l, which reveals a nonabsolute equivalence for the “V resonances. We note that the weak half-line width of these resonances (45 Hz) is not affected by paramagnetic effects. Due to the lack of “V NMR information about oxovanadium(IV) compounds, ’ ’ conversely to oxovanadium(V) species, no comparison is possible. The dimeric nature of the compound was first suggested by mass spectral data, which exhibit the parent molecular ion without any ion of higher molecular mass. It has been definitively confirmed by an X-ray structural study. The X-ray crystal structure of 1 is shown in Fig. 1. Relevant bond lengths and angles are collected in Table 2. The complex consists of a dimeric unit in which the two independent VOCI[OCH(CH,) CH20CH3] units are held together by the bridging pZ-O(1) and p*-O(2) oxygen atoms. Although no crystallographic symmetry is imposed, a molecule of 1 exhibits an overall symmetry close to CZ, with the approximate C2 axis passing through the midpoint of a line joining the vanadium atoms and perpendicular to the V-O-V-O plane. Thus, both 0x0 groups and chlorine atoms adopt a cis configuration around the V-O-V-O ring. Such a configuration is rather rare since the tram configuration is more often encountered as
G. FOULON
2510
et al.
CC8
C(4)
molecule, showing the atomic numbering Fig. 1. ORTEP view of the {VOCl[OCH(CH,)CH20CHJ}2 scheme (thermal ellipsoids drawn at 40% probability level).
in the related
vanadium(V) complex {VOCl[OC Moreover, the C2 symmetry of the V-WZ)Z.~~ molecule leads to a boat-like configuration, as evidenced by Fig. 2,. This configuration tends to reduce the intramolecular interactions between the alkoxide ligand and both 0x0 group and chlorine atom. The vanadium atoms are five-coordinate, defining a distorted trigonal bipyramid. Actually, this
environment can alternatively be described as a distorted square pyramid. Although important shifts between the ideal angle values and the observed ones are noticed in both descriptions, we tend to prefer the trigonal bipyramid model in the way that deviation from planarity (+ 0.17 A) of the square base in the pyramidal model appear to be consequent. Nevertheless, these two types of environment
Table 2. Selected bond lengths (A) and angles (“) (standard parentheses)
WFW) V(lFO(2) V(l)-O(3) V(lbO(5) V(l)-Cl(l)
O(1F--W) C(l)--C(2) C(2)-C(3) C(3)-O(3) 0(3)-C(4)
deviations
1.952(7) 1.966(7) 2.052(7) 1.590(7) 2.282(3)
V(2)-O(2) V(2)_-0(1) V(2)--o(4) V(2)_-0(6) V(2)-Cl(2)
1.964(7) 1.948(7) 2.065(7) 1.584(7) 2.281(3)
1.454(11) 1.547(14) 1.484( 14) 1.452( 12) 1.424(11)
0(2)-C(6) C(5)-C(6) C(6)-C(7) C(7)_-0(4) 0(4)-C(8)
1.428(11) 1.536(14) 1.496(14) 1.455(11) 1.435(11)
in
V . V interaction V(l)-V(2) 3.084(3) V(2)--Wl)-V(1) O(l)---V(l)--o(2) WtV(l)--o(3) O(ltiV(l)---o(5) O(l)--V(l)-Cl(l) o(2)-V(l)--o(3) o(2)-V(l)--o(5) 0(2)-v(1)--c1(1) 0(3tV(lto(5) 0(3)-v(l)--Cl(l) o(5)---V(ltCl(l)
104.5(3) 76.0(3) 78.5(3) 113.8(3) 138.0(2) 148.0(3) 106.2(3) 94.7(2) 101.5(3) 91.5(2) 108.2(3)
V(l)--0(2)-V(2) O(2)-V(2W( 1) o(2)-V(2to(4) O(2)-V(2W(6) O(2)-V(2tcl(2) o(l)-V(2to(4) O(1 )-V(2tW6) O(l)-V(2)--cl(2) O(4)-V(2)--0(6) o(4)-V(2t-c1(2) O(6)-V(2)---Cl(2)
103.4(3) 76.1(3) 77.6(3) 114.2(3) 136.7(2) 147.2(3) 106.2(3) 95.6(2) 102.3(3) 90.2(2) 108.9(3)
Synthesis and structural study of {VOCl[OCH(CH,)CH,0CHj]}2
2511
6. F. Hillerns, F. Olbrich, U. Behrens and D. Reher, Angew. Chem, Int. Edn Engl. 1992,31,447. 7. (a) D. C. Crans, R. A. Felty and M. M. Miller, J.
Fig. 2. View of 1 perpendicular to the V--O-V4 showing the boat-like configuration.
ring,
Am. Chem. Sot. 1991, 113, 265 ; (b) D. C. Crans, R. W. Marshman, M. S. Gottlieb, 0. P. Anderson and M. M. Miller, Znorg. Chem. 1992,31,4939. 8. D. C. Crans, R. A. Felty, 0. P. Anderson and M. M. Miller, Inorg. Chem. 1993, 32,247. 9. D. L. Clark, J. G. Watkin and J. C. Huffman, fnorg. Chem. 1992,31,
1556.
10. (a) D. J. Eichorst and D. A. Payne, Better Ceramics are currently encountered in vanadium(IV) complexes. 16~3,I7a, I9 The V-O and V-Cl bond lengths fall in the range of values previously reported in the literature. 7a.7b,‘7a.Worthy of mention is the V---p ,--0 bond length, which is significantly longer than the V-p,0 one [average 2.058(7) and 1.957(7) A”, respectively]. This is clearly explained by the fact that the ~~-0 atoms [O(l) and O(2)] are negatively charged, whereas the ~~-0 atoms of the methoxy groups [O(3) and O(4)] are uncharged, allowing a weaker px-dn donation. The value of the intermetallic distance [V(l). . . V(2) = 3.084(3) A] is in good agreement with the V . . _V distance observed in the related oxovanadium compounds.7”~‘7”~20 At this distance a V-V bonding should not be expected and consequently, the two unpaired electrons should be mainly localized on one V=O unit. The presence of remaining chloride ligands in complex 1 makes the metal atom functionalizable and may permit the introduction of a second metal (by reaction with a species such as K[M(OR),] with salt elimination, for example). Further investigations towards the reactivity of 1 are in progress in this way. REFERENCES 1. M. Nabavi, C. Sanchez and J. Livage, Eur. J. Solid State Inorg. Gem. 1991,28, 1173. 2. S. I. Zones, M. R. Palmer, J. G. Palmer, J. M. Doemeny and G. N. Schrauzer, J. Am. Chem. Sot. 1978, loo, 2113. 3. (a) D. C. Crans, H. Chen and R. A. Felty, J. Am. Chem. Sot. 1992, 114, 4543 ; (b) F. Hillerns and D. Rehder, Chem. Ber. 1991,124,2249; (c) R. K. Mittal and R. C. Mehrotra, Z. Anorg. Allg. Chem. 1964, 327,311; (d) N. F. Orlov and M. G. Voronkov, Bull. Acad. Sci URSS, Div. Chem. Sci. 1959,933 ; (e) Von H. Funk, W. Weiss and M. Zeising, 2. Anorg. Allg. Chem. 1958,2%,36.
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11. (a) 0. Poncelet, L. Hubert-Pfalzgraf, J.-C. Daran and R. Astier, J. Chem. Sot., Chem. Commun. 1989, 1846; (b) K. G. Caulton, M. H. Chisholm, S. R. Drake and J. C. Huffman, J. Chem. Sot., Chem. Commun. 1990, 1498 ; (c) M.-C. Massiani, R. Papiernik, L. Hubert-Pfalzgraf and J-C. Daran, J. Chem. Sot., Chem. Commun. 1990, 301; (d) S. C. Goel, M. A. Matchett, M. Y. Chiang and W. E. Buhro, J. Am. Chem. Sot. 1991, 113, 1844; (e) S. Boulmaaz, R. Papiemik, L. Hubert-Pfalzgraf, J. Vaissermann and J.-C. Daran, Polyhedron 1992, 11, 1331; (f) S. C. Goel, M. Y. Chiang and W. E. Buhro, Inorg. Chem. 1990,29,4640.
12. Program XDISK from the commercial package SHELXTL PLUS distributed by Siemens. 13. G. M. Sheldrick, SHELXS-86, Program for the Solution of Crystal Structures. University of Giittingen, F.R.G. (1987). 14. G. M. Sheldrick, SHELX 76, Program for Crystal Structure Determination. University of Cambridge, U.K. (1976). 15. It seems that this solvent stabilizes the oxovanadium(V) alkoxide species. Further reactions in CH,Cl, are, at present, being investigated to confirm this hypothesis. 16. (a) D. Rehder, W. Priebsch and M. von Oeynhausen, Angew. Chem., Int. Edn Engl. 1989,28, 1221; (b) H. J. Seifert, 2. Anorg. Ailg. Chem. 1962, 317, 123 ; (c) R. C. Paul and A. Kumar, J. Inorg. Nucl. Chem. 1965,27,2537.
17. (a) F. A. Cotton, G. E. Lewis and G. N. Mott, Znorg. Chem. 1983, 22, 378 ; (b) R. R. Reeder and P. H. Rieger, Znorg. Chem. 1971, 6, 1258; (c) N. D. Chasteen and M. W. Hanna, J. Phys. Chem. 1972, 76, 3951; (d) A. T. Casey, B. S. Morris, E. Sinn and J. R. Thackeray, Aust. J. Chem. 1972, 25, 1195. 18. To our knowledge, the only “V data of vanadium (IV) compounds are published by F. Preuss and L. Ogger in Z. Naturforsch. 1982,37b, 957. 19. G. Barr-David, T. W. Hambley, J. A. Irwin, R. J. Judd, P. A. Lay, B. D. Martin, R. Bramley, N. E. Dixon, P. Hendry, J.-Y. Ji, R. S. U. Baker and A. M. Bonin, Znorg. Chem. 1992, 31,4906. 20. S. Gambarotta, F. van Bolhuis and M. Y. Chiang, Znorg. Chem. 1987, 26,430l.