Triaqua(oxalato-O,O')oxovanadium(IV) dihydrate

In the structure of the title compound, [VO(C₂O₄)(H₂O)₃]·2H₂O, the V atom of the oxovanadium(IV) cation is coordinated to one bidentate oxalate anion and three water mol­ecules, resulting in a neutral complex. Two more water mol­ecules are not coordinated to the V atoms but are involved in the hydrogen-bonding network, which consists of ten different hydrogen bonds.

S1. Comment

Several different types of coordination complexes of the oxovanadium(IV) cation with oxalate ligands (and also in some cases water) have been isolated so far. In each of the five structurally characterized compounds found in the Cambridge Crystallographic Database (CCD; Allen & Kennard, 1993) the V atom has a distorted octahedral coordination sphere. This is formed by two oxalate ligands and one water ligand in (NH₄)₂[VO(C₂O₄)₂H₂O]·H₂O (Oughtred et al., 1976) and in [(terpy)Cu(C₂O₄)VO(C₂O₄)H₂O]·H₂O (Cortes et al., 1994) (terpy = ?), by two oxalate ligands and one oxalate ligand bridging two VO(C₂O₄)₂ units in K₆[(VO)₂(C₂O₄)₅]·4H₂O (Zhou et al., 1983), or by one bidentate oxalate, one water and a tetradentate oxalate ligand bridging two [VO(C₂O₄)H₂O] units in (Ph₄P)₂[(VO)₂(C₂O₄)₃(H₂O)₂]·4H₂O (Salta et al., 1996) and in (Ph₄P)₂[(VO)₂(C₂O₄)₃(H₂O)₂]·8H₂O (Zheng et al., 1998). In all these compounds, cations neutralize the charge of the anionic complexes. In this context, we have established the crystal structure of the title compound, (I). \sch

In (I), in contrast to the above-mentioned compounds, the five free coordination sites of the V atom of the oxovanadium(IV) cation are occupied by one bidentate oxalate anion and three water ligands, resulting in a neutral complex (Fig. 1). Two further water molecules are not coordinated to the V atoms. The four O1—V1—O angles are distinctly larger than 90°, and this is presumably attributable to repulsion between the π electrons and the σ bonding pairs. The distance between V1 and O4, situated trans to O1, is markedly larger than between V1 and the other four ligands, due to the trans influence. Similar features are observed in the five oxovanadium(IV) oxalates found in the CCD.

The oxalate anion is considerably twisted [11.74 (9)°] around the C—C bond, leading to an elongated C—C bond length of 1.539 (2) Å. A search of the CCD for oxalates resulted in a mean torsion angle of 4.4 (2)° [standard deviation of the sample = 3.8°] and an even larger mean C—C bond length of 1.546 (1) Å.

The hydrogen-bonding system in (I) (Fig. 2) consists of ten different hydrogen bonds involving all ten H atoms of the water molecules. The acceptors of these hydrogen bonds are the O atoms of the two water molecules not coordinated to the V atom and the O atoms of the oxalate ligand (Fig. 2). The O atoms of the three water molecules coordinated to the V atom and atom O1 do not act as acceptor atoms of hydrogen bonds. The metal complexes are not connected amongst themselves but are only mediated via water molecules.

S2. Experimental

To a suspension of vanadium pentoxide (310 g) in water (900 g), oxalic acid dihydrate (645 g) was added and the mixture stirred at 333–353 K for 12 h, during which a vigorous evolution of CO₂ was observed. Large intensely blue single crystals of (I) separated on cooling.

S3. Refinement

H atoms were refined with individual isotropic displacement parameters. The highest peak (0.59 e Å⁻³) and the deepest hole (−0.35 e Å⁻³) in the difference Fourier map were situated less than 0.9 Å from the V atom.

Computing details

Data collection: local software; cell refinement: local software; data reduction: local software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP (Johnson, 1965); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. ORTEP (Johnson, 1965) drawing of the asymmetric unit of (I) showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. A stereoscopic packing diagram of the crystal structure of (I). The atoms are drawn as spheres of arbitrary radii, and covalent bonds are shown as full bonds, the five contacts to the VO^2+ ions as dashed bonds and hydrogen bonds as dotted bonds.

Triaqua(oxalato-O,O')oxovanadium(IV) dihydrate

Crystal data

[VO(C2O4)(H2O)3]·2H2O	F(000) = 500
Mr = 245.04	Dx = 1.854 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71069 Å
a = 7.152 (2) Å	Cell parameters from 31 reflections
b = 8.806 (3) Å	θ = 3.7–8.1°
c = 14.004 (4) Å	µ = 1.16 mm^−1
β = 95.60 (2)°	T = 293 K
V = 877.8 (5) Å^3	Block, intense blue
Z = 4	0.5 × 0.3 × 0.3 mm

Data collection

Stoe 4-circle diffractometer	Rint = 0.038
Radiation source: fine-focus sealed tube	θmax = 30.0°, θmin = 2.9°
Graphite monochromator	h = −10→10
ω scans	k = −1→12
3570 measured reflections	l = −1→19
2555 independent reflections	3 standard reflections every 100 reflections
2268 reflections with I > 2σ(I)	intensity decay: 0.2%

Refinement

Refinement on F^2	Hydrogen site location: difference Fourier map
Least-squares matrix: full	All H-atom parameters refined
R[F^2 > 2σ(F^2)] = 0.031	Calculated w = 1/[σ^2(Fo^2) + (0.0401P)^2 + 0.1639P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.081	(Δ/σ)max = 0.001
S = 1.06	Δρmax = 0.59 e Å^−3
2555 reflections	Δρmin = −0.36 e Å^−3
159 parameters	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.038 (2)
Primary atom site location: structure-invariant direct methods

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

The H-atoms were refined unconstrained with individual isotropic displacement parameters.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
V1	0.69101 (3)	0.23279 (3)	1.011215 (18)	0.01970 (10)
O1	0.6774 (2)	0.07947 (16)	1.06842 (10)	0.0400 (3)
C1	0.3489 (2)	0.24579 (17)	0.89664 (11)	0.0204 (3)
O11	0.41590 (15)	0.28023 (13)	0.98177 (8)	0.0230 (2)
O12	0.18368 (16)	0.25336 (14)	0.86472 (9)	0.0280 (3)
C2	0.4959 (2)	0.18958 (18)	0.83150 (11)	0.0220 (3)
O21	0.65671 (15)	0.15923 (13)	0.87479 (8)	0.0252 (2)
O22	0.45245 (16)	0.17608 (17)	0.74501 (8)	0.0338 (3)
O2	0.70923 (18)	0.37928 (15)	1.12290 (8)	0.0286 (3)
H21	0.635 (4)	0.366 (3)	1.1646 (19)	0.047 (7)*
H22	0.820 (4)	0.397 (3)	1.1502 (17)	0.047 (7)*
O3	0.97186 (18)	0.2378 (2)	1.01112 (11)	0.0390 (4)
H31	1.024 (4)	0.247 (3)	0.970 (2)	0.044 (7)*
H32	1.039 (4)	0.204 (3)	1.051 (2)	0.057 (8)*
O4	0.7211 (2)	0.45260 (15)	0.93104 (10)	0.0324 (3)
H41	0.783 (3)	0.475 (3)	0.889 (2)	0.050 (7)*
H42	0.698 (3)	0.528 (3)	0.9518 (17)	0.040 (6)*
O5	0.0442 (2)	0.0325 (2)	0.71390 (10)	0.0349 (3)
H51	0.001 (4)	−0.033 (4)	0.738 (2)	0.076 (11)*
H52	0.094 (5)	0.086 (4)	0.748 (2)	0.067 (10)*
O6	0.17664 (19)	0.37958 (17)	0.65774 (9)	0.0313 (3)
H61	0.258 (4)	0.318 (3)	0.6810 (18)	0.044 (7)*
H62	0.233 (3)	0.450 (3)	0.6434 (18)	0.049 (7)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
V1	0.01762 (14)	0.02305 (15)	0.01830 (14)	0.00068 (9)	0.00111 (9)	0.00011 (9)
O1	0.0448 (8)	0.0315 (7)	0.0423 (8)	−0.0022 (6)	−0.0021 (6)	0.0105 (6)
C1	0.0192 (6)	0.0225 (7)	0.0198 (6)	0.0010 (5)	0.0038 (5)	0.0021 (5)
O11	0.0185 (5)	0.0301 (5)	0.0207 (5)	0.0014 (4)	0.0029 (4)	−0.0051 (4)
O12	0.0187 (5)	0.0410 (7)	0.0243 (5)	0.0039 (5)	0.0013 (4)	0.0010 (5)
C2	0.0202 (6)	0.0254 (7)	0.0208 (7)	0.0017 (5)	0.0037 (5)	−0.0026 (5)
O21	0.0191 (5)	0.0313 (6)	0.0251 (5)	0.0054 (4)	0.0011 (4)	−0.0076 (4)
O22	0.0254 (6)	0.0562 (8)	0.0199 (5)	0.0057 (5)	0.0021 (4)	−0.0063 (5)
O2	0.0245 (6)	0.0413 (7)	0.0206 (5)	−0.0075 (5)	0.0057 (4)	−0.0064 (5)
O3	0.0179 (6)	0.0741 (11)	0.0253 (6)	0.0096 (6)	0.0035 (5)	0.0104 (7)
O4	0.0436 (7)	0.0242 (6)	0.0317 (7)	0.0005 (5)	0.0160 (6)	0.0025 (5)
O5	0.0316 (6)	0.0433 (8)	0.0292 (6)	−0.0074 (6)	0.0006 (5)	0.0009 (6)
O6	0.0313 (6)	0.0313 (6)	0.0302 (6)	−0.0051 (5)	−0.0030 (5)	0.0033 (5)

Geometric parameters (Å, º)

V1—O1	1.5778 (14)	O2—H21	0.83 (3)
V1—O2	2.0218 (13)	O2—H22	0.86 (3)
V1—O3	2.0093 (14)	O3—H31	0.72 (3)
V1—O4	2.2585 (14)	O3—H32	0.76 (3)
V1—O11	2.0144 (12)	O4—H41	0.79 (3)
V1—O21	2.0096 (12)	O4—H42	0.75 (3)
C1—C2	1.539 (2)	O5—H51	0.75 (4)
C1—O11	1.2771 (19)	O5—H52	0.74 (4)
C1—O12	1.2240 (19)	O6—H61	0.84 (3)
C2—O21	1.2749 (18)	O6—H62	0.77 (3)
C2—O22	1.2265 (19)
O1—V1—O4	178.03 (6)	O12—C1—O11	126.07 (14)
O3—V1—O11	162.16 (6)	O21—C2—C1	114.97 (13)
O21—V1—O2	159.04 (5)	O22—C2—C1	119.64 (13)
O1—V1—O21	101.48 (7)	O22—C2—O21	125.39 (14)
O1—V1—O11	100.03 (6)	C1—O11—V1	114.31 (9)
O1—V1—O2	98.96 (7)	C2—O21—V1	113.90 (9)
O1—V1—O3	97.48 (7)	V1—O2—H21	117.2 (18)
O3—V1—O21	92.05 (6)	V1—O2—H22	116.6 (17)
O11—V1—O2	90.80 (5)	H21—O2—H22	109 (2)
O3—V1—O2	89.86 (6)	V1—O3—H31	127 (2)
O11—V1—O4	81.89 (5)	V1—O3—H32	123 (2)
O21—V1—O11	81.14 (5)	H31—O3—H32	107 (3)
O3—V1—O4	80.63 (6)	V1—O4—H41	132 (2)
O2—V1—O4	80.54 (6)	V1—O4—H42	122.2 (18)
O21—V1—O4	79.18 (5)	H41—O4—H42	103 (3)
O11—C1—C2	114.46 (13)	H51—O5—H52	113 (3)
O12—C1—C2	119.47 (14)	H61—O6—H62	105 (2)
O11—C1—C2—O21	11.9 (2)	O3—V1—O11—C1	68.3 (2)
O12—C1—C2—O21	−167.83 (14)	O21—V1—O11—C1	−0.27 (11)
O11—C1—C2—O22	−168.72 (15)	O2—V1—O11—C1	160.29 (11)
O12—C1—C2—O22	11.6 (2)	O4—V1—O11—C1	79.96 (11)
C1—C2—O21—V1	−11.86 (17)	O1—V1—O21—C2	105.73 (12)
C2—C1—O11—V1	−5.53 (16)	O3—V1—O21—C2	−156.22 (12)
O12—C1—O11—V1	174.16 (13)	O11—V1—O21—C2	7.20 (11)
O22—C2—O21—V1	168.79 (14)	O2—V1—O21—C2	−61.25 (19)
O1—V1—O11—C1	−100.47 (12)	O4—V1—O21—C2	−76.16 (11)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H21···O22^i	0.83 (3)	1.84 (3)	2.6735 (18)	173 (3)
O2—H22···O5^ii	0.86 (3)	1.87 (3)	2.715 (2)	170 (2)
O3—H31···O12^iii	0.72 (3)	1.96 (3)	2.669 (2)	174 (3)
O3—H32···O6^ii	0.76 (3)	1.86 (3)	2.616 (2)	173 (3)
O4—H41···O5^iv	0.79 (3)	2.05 (3)	2.846 (2)	177 (3)
O4—H42···O11^v	0.75 (3)	2.12 (3)	2.8670 (19)	169 (2)
O5—H51···O6^vi	0.75 (4)	2.16 (3)	2.845 (2)	151 (4)
O5—H52···O12	0.74 (4)	2.25 (4)	2.971 (2)	167 (3)
O6—H61···O22	0.84 (3)	2.02 (3)	2.851 (2)	176 (2)
O6—H62···O21^iv	0.77 (3)	2.03 (3)	2.7926 (19)	167 (3)

Symmetry codes: (i) x, −y+1/2, z+1/2; (ii) x+1, −y+1/2, z+1/2; (iii) x+1, y, z; (iv) −x+1, y+1/2, −z+3/2; (v) −x+1, −y+1, −z+2; (vi) −x, y−1/2, −z+3/2.