A new aqua­hydroxido­copper(II) oxo­vanadium(IV) vanadate, Cu(H₂O)(OH)VO(VO₄)

Single crystals of the title compound have been prepared hydro­thermally. Vanadate tetrahedra and distorted oxovanadium octahedra form layers, linked by two independent Cu atoms located on inversion centres. Each Cu atom is surrounded by six O atoms, forming an octahedron distorted by Jahn-Teller elongation. One of the two independent interlayer spaces bridged by the Cu atoms is significantly more compact than the other.

S1. Comment

Many examples are known of anhydrous copper(II) vanadium compounds in which the V atom can be V^V, V^IV or of mixed valence (Zavaly & Whittingham, 1999, and references therein). However, hydrated or hydroxyl compounds of the same elements are less numerous (Fleury, 1966; Leblanc & Férey, 1990, and references therein). Among these compounds, there exists a natural mineral, Cu₃(V₂O₇)(OH)₂·2H₂O, called volborthite, whose structure has been determined from X-ray and neutron powder diffraction (Lafontaine et al., 1990). Since this compound has interesting magnetic properties owing to the peculiar Cu^II arrangement characteristic of the kagomè lattice (Hiroi et al., 2001), we attempted to obtain single crystals by the hydrothermal technique. This experiment failed; however, tiny crystallites were isolated and identified from X-ray powder diffraction as Cu₄V_2.15O_9.38 (Christian & Muller-Buschbaum, 1975). During attempts to grow single crystals of this latter compound, a new phase was isolated. X-ray single-crystal techniques were used to determine its detailed structure and hence its chemical composition.

In the title compound, the independent non-H atoms are two Cu atoms, located on inversion centers, and two V and seven O atoms, located in general positions. Calculations of bond valence sums of atoms Cu1, Cu2, V1 and V2 gives values of 2.15, 2.10, 5.01 and 4.19, respectively (Altermatt & Brown, 1985). The excess negative charge is compensated by the presence of three H atoms, belonging to one water molecule (O7) and one hydroxyl group (O6). The Cu atoms are centred in the (001) and (100) faces of the triclinic cell. A projection view along [100] is given in Fig. 1.

Atom V1 is surrounded by four O atoms that form an almost regular tetrahedron, indicating that the V atom is in the pentavalent state. The V1—O bond distances and the O—V1—O bond angles are in the ranges 1.690 (4)–1.763 (4) Å and 108.3 (2)–110.9 (2)°, respectively (Table 1). Atom V2 exhibits [5 + 1] coordination, the O atoms of the hydroxyl groups (O6—H6) completing a distorted octahedron. One of the axial V—O bonds of this octahedron is characteristic of an oxovanadium(IV) or a vanadyl group, VO²⁺ (V2═O5 = 1.617 (4) Å), with V2 displaced by 0.362 (2) Å from the O2^v/O3/O6/O4^vi square plane. (Throughout this discussion, superscripts appended to atom names refer to the symmetry operations given in Table 1.) The sixth axial distance, V2—O6^vii, is correspondingly longer, i.e. 2.309 (4) Å. Such distances confirm that atom V2 is in the V^IV state, whiich has a well known tendency to be located in a square pyramid (SP) of O atoms. The V2O₅ SP is nearly regular, with V2—O distances of 1.959 (4)–2.025 (4) Å in the basal plane and cis O—V2—O angles between these bonds in the range 85.8 (2)–90.4 (2)°.

The V2O₅ SPs and V1O₄ tetrahedra, which share corners at atoms O2, O3 and O4, form a layer roughly parallel to (001), as shown in Fig. 2. Two such layers, related by the symmetry center where atom Cu2 is located, are firmly connected via four strong Cu—O bonds (two Cu2—O4 and two Cu2—O6 bonds) and two weaker bonds (two Cu2—O3), the axial Cu2—O3 bond being rather long (2.534 (4) Å; Table 1). Cu2 exhibits a sixfold O-atom coordination, which forms an elongated octahedron with a classic Jahn–Teller distortion. If the longest distance (V2—O6^vii) is considered, two V2 atoms, related by a symmetry center, share the O6—O6^vii edge, giving rise to a vanadyl dimer (see Fig. 1), the V2—V2^vii distance being 3.492 (2) Å. Note that the vanadyl groups point outward from the thick double layers. Atom O5 of the vanadyl group is linked to atom Cu1, on the symmetry centre 0 1/2 1/2, at a distance of 2.359 (4) Å. The sixfold coordination around atom Cu1 is completed by atoms O1 and O7. Note again the Jahn–Teller distortion of the Cu1O₆ octahedron; the square equatorial plane contains atoms O1 and O7 with short bonds [1.965 (4) and 1.967 (4) Å, respectively], with atom O5 assuming the long axial bonds.

The Cu—O distances within the basal planes are similar for the two Cu atoms, but the angles are slightly different. While the O—Cu1—O angles do not depart from 90° by more than 1°, the O—Cu2—O angles range from 84.4 (2) to 95.6 (2)° (Table 1). The opening of the O4ⁱⁱ—Cu2—O6 angle is due mainly to the fact that the two layers of V atoms related by Cu2 are so close [3.049 (1) Å]. The compactness of the space between the two layers can be understood by considering that atoms O3, O4 and O6, localized in this space, are µ₃ and concomitantly that the distances between these atoms and the mean plane of the layer are relatively small [0.705 (4) Å, 0.955 (4) Å and 0.907 (4) Å, respectively]. Atoms O1, O2 and O5, located outside this space, are µ₂, corresponding to larger distances between atoms O1 and O5 and the mean plane of the layer [1.584 (4) Å and 1.587 (4) Å respectively]. Consequently, the layers connected by Cu1 atoms are more distant than those related by Cu2 atoms.

The H atom of the hydroxyl group (O6/H6) is approximately in a tetrahedral position with respect to the three metal atoms bound to O6 (Fig 1); the angles about O6 are in the range 108.6–120.1°. (Note that H6 was refined as a riding atom.) Atom H6 forms a bifurcated hydrogen bond with O2^vi and O3ⁱⁱ. H atoms of the water molecule interact with O1 at −x, 1 − y, −z, O2^v and O1^v, with O7—O distances ranging from 2.812 (6)–3.138 (6) Å.

S2. Experimental

A few bluish-black single crystals were obtained from an aqueous suspension (50 ml) of Cu(SO₄)·5H₂O, CuO and V₂O₅ in the molar ratio 2:2:1. These reactants were sealed in a Teflon-lined steel bomb (autogeneous pressure) and heated at 473 K for 20 d. After cooling, the precipitate was filtered off, washed with distilled water and dried at room temperature. The X-ray powder pattern of the whole material shows mainly the presence of a major phase, volborthite Cu₃(V₂O₇)(OH)₂·2H₂O, and a minor phase, antlerite Cu₃(SO₄)(OH)₄.

S3. Refinement

Direct methods associated with the Patterson function revealed not only the heavy atoms but also, after the first Fourier synthesis, the O atom sites, leading to a chemical formulation of CuV₂O₇. The analysis of Cu and V coordination showed that the charge on the metal atoms was [Cu²⁺] [V⁵⁺,V⁴⁺], implying an electronic imbalance. From difference Fourier syntheses, it was then possible to locate three H atoms, localized on a hydroxyl group (O6) and on a water molecule (O7). The H atoms were refined as riding. Refinement of the positional and anisotropic displacement parameters gave a good R factor, the formula Cu²⁺V⁵⁺V⁴⁺O₅(OH)(H₂O) being well established, with Z = 2 formula units per cell.

Computing details

Data collection: COLLECT (Nonius 1998); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN; program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1966); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A projection onto (100) of the structure of Cu(H2O)(OH)VO(VO4). Displacement ellipsoids are shown at the 50% probability level. The symmetry codes are given in Table 1.
	Fig. 2. A view of a layer formed by the vanadate tetrahedra and oxovanadium square pyramids. The symmetry codes are given in Table 1.

'aqua hydroxyl copper(II) oxo-vanadium(IV) vanadate'

Crystal data

Cu(H2O)(OH)VO(VO4)	Z = 2
Mr = 280.45	F(000) = 268
Triclinic, P1	Dx = 3.521 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 5.1290 (7) Å	Cell parameters from 914 reflections
b = 5.307 (1) Å	θ = 6.2–29.4°
c = 10.3590 (14) Å	µ = 7.42 mm^−1
α = 99.902 (14)°	T = 293 K
β = 101.139 (14)°	Parallelepiped, blue-black
γ = 101.495 (13)°	0.15 × 0.08 × 0.05 mm
V = 264.53 (8) Å^3

Data collection

Enraf-Nonius KappaCCD area-detector diffractometer	914 independent reflections
Radiation source: fine-focus sealed tube	819 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.049
ϕ and ω scans	θmax = 25.0°, θmin = 6.2°
Absorption correction: multi-scan SORTAV, Blessing, 1995	h = −6→6
Tmin = 0.490, Tmax = 0.690	k = −6→6
1972 measured reflections	l = −12→12

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.032	H-atom parameters constrained
wR(F^2) = 0.089	w = 1/[σ^2(Fo^2) + (0.0373P)^2 + 1.2774P] where P = (Fo^2 + 2Fc^2)/3
S = 1.12	(Δ/σ)max < 0.001
914 reflections	Δρmax = 0.98 e Å^−3
95 parameters	Δρmin = −0.77 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.012 (3)

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.

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

	x	y	z	Uiso*/Ueq
Cu1	0.5000	0.5000	0.0000	0.0171 (3)
Cu2	1.0000	0.5000	0.5000	0.0112 (3)
V1	0.35925 (17)	0.33092 (16)	0.28053 (8)	0.0097 (3)
V2	0.82209 (17)	0.92354 (16)	0.33112 (8)	0.0097 (3)
O1	0.2810 (8)	0.3489 (8)	0.1168 (4)	0.0189 (9)
O2	0.5000 (8)	0.0682 (8)	0.2915 (4)	0.0173 (8)
O3	0.5815 (8)	0.6165 (7)	0.3739 (4)	0.0149 (8)
O4	0.0589 (8)	0.2818 (7)	0.3413 (4)	0.0127 (8)
O5	0.8394 (9)	0.7799 (8)	0.1833 (4)	0.0203 (9)
O6	1.1342 (7)	0.8373 (7)	0.4541 (4)	0.0114 (8)
H6	1.2927	0.8542	0.4126	0.016*
O7	0.2872 (9)	0.7689 (8)	−0.0090 (4)	0.0218 (9)
H7a	0.1252	0.7420	−0.0650	0.030*
H7b	0.3161	0.8945	0.0630	0.030*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0196 (5)	0.0194 (5)	0.0163 (5)	0.0053 (4)	0.0106 (4)	0.0064 (4)
Cu2	0.0150 (5)	0.0084 (5)	0.0119 (5)	0.0024 (3)	0.0081 (4)	0.0016 (3)
V1	0.0096 (5)	0.0099 (5)	0.0110 (5)	0.0021 (3)	0.0064 (3)	0.0016 (3)
V2	0.0098 (5)	0.0078 (5)	0.0125 (5)	0.0015 (3)	0.0056 (3)	0.0025 (3)
O1	0.018 (2)	0.028 (2)	0.0121 (19)	0.0016 (17)	0.0073 (16)	0.0075 (16)
O2	0.0163 (19)	0.0128 (18)	0.024 (2)	0.0033 (15)	0.0084 (16)	0.0040 (15)
O3	0.0151 (19)	0.0150 (19)	0.0151 (19)	−0.0006 (15)	0.0073 (15)	0.0054 (15)
O4	0.0152 (19)	0.0118 (17)	0.0128 (18)	0.0030 (15)	0.0077 (15)	0.0029 (14)
O5	0.025 (2)	0.020 (2)	0.016 (2)	0.0036 (17)	0.0107 (17)	0.0009 (16)
O6	0.0120 (18)	0.0100 (17)	0.0150 (18)	0.0026 (14)	0.0084 (15)	0.0045 (14)
O7	0.023 (2)	0.017 (2)	0.024 (2)	0.0062 (17)	0.0059 (17)	0.0015 (16)

Geometric parameters (Å, º)

Cu1—O7	1.965 (4)	V1—O2	1.704 (4)
Cu1—O7^i	1.966 (4)	V1—O3	1.707 (4)
Cu1—O1^i	1.967 (4)	V1—O4	1.763 (4)
Cu1—O1	1.967 (4)	V2—O5	1.617 (4)
Cu1—O5	2.359 (4)	V2—O2^v	1.959 (4)
Cu1—O5^i	2.359 (4)	V2—O3	2.008 (4)
Cu2—O4^ii	1.953 (3)	V2—O4^vi	2.016 (4)
Cu2—O4^iii	1.953 (3)	V2—O6	2.025 (4)
Cu2—O6	1.958 (3)	V2—O6^vii	2.309 (4)
Cu2—O6^iv	1.958 (3)	O6—H6	0.9866
Cu2—O3^iv	2.534 (4)	O7—H7a	0.8866
Cu2—O3	2.534 (4)	O7—H7b	0.8767
V1—O1	1.690 (4)
O7—Cu1—O7^i	180.0	O3—V1—O4	109.19 (18)
O7—Cu1—O1^i	90.59 (17)	O5—V2—O2^v	102.8 (2)
O7^i—Cu1—O1^i	89.41 (17)	O5—V2—O3	97.96 (18)
O7—Cu1—O1	89.41 (17)	O2^v—V2—O3	88.13 (16)
O7^i—Cu1—O1	90.59 (17)	O5—V2—O4^vi	98.45 (18)
O1^i—Cu1—O1	180.0	O2^v—V2—O4^vi	88.55 (16)
O7—Cu1—O5	91.72 (16)	O3—V2—O4^vi	163.58 (15)
O7^i—Cu1—O5	88.28 (16)	O5—V2—O6	102.55 (19)
O1^i—Cu1—O5	86.52 (15)	O2^v—V2—O6	154.52 (16)
O1—Cu1—O5	93.48 (15)	O3—V2—O6	85.76 (15)
O7—Cu1—O5^i	88.28 (16)	O4^vi—V2—O6	90.38 (15)
O7^i—Cu1—O5^i	91.72 (16)	O5—V2—O6^vii	171.22 (17)
O1^i—Cu1—O5^i	93.48 (15)	O2^v—V2—O6^vii	82.41 (15)
O1—Cu1—O5^i	86.52 (15)	O3—V2—O6^vii	89.21 (14)
O5—Cu1—O5^i	180.0	O4^vi—V2—O6^vii	74.42 (13)
O4^ii—Cu2—O4^iii	180.000 (1)	O6—V2—O6^vii	72.80 (15)
O4^ii—Cu2—O6	95.63 (15)	V1—O1—Cu1	132.6 (2)
O4^iii—Cu2—O6	84.37 (15)	V1—O2—V2^viii	150.3 (2)
O4^ii—Cu2—O6^iv	84.37 (15)	V1—O3—V2	134.8 (2)
O4^iii—Cu2—O6^iv	95.63 (15)	V1—O3—Cu2	108.03 (18)
O6—Cu2—O6^iv	179.999 (2)	V2—O3—Cu2	90.26 (14)
O4^ii—Cu2—O3^iv	84.89 (14)	V1—O4—Cu2^ix	125.8 (2)
O4^iii—Cu2—O3^iv	95.11 (14)	V1—O4—V2^x	123.7 (2)
O6—Cu2—O3^iv	105.92 (13)	Cu2^ix—O4—V2^x	103.27 (15)
O6^iv—Cu2—O3^iv	74.08 (13)	V2—O5—Cu1	131.5 (2)
O4^ii—Cu2—O3	95.11 (14)	Cu2—O6—V2	108.90 (17)
O4^iii—Cu2—O3	84.89 (14)	Cu2—O6—V2^vii	93.28 (14)
O6—Cu2—O3	74.08 (13)	V2—O6—V2^vii	107.20 (15)
O6^iv—Cu2—O3	105.92 (13)	Cu2—O6—H6	117.5
O3^iv—Cu2—O3	180.00 (15)	V2—O6—H6	108.6
O1—V1—O2	108.3 (2)	V2^vii—O6—H6	120.1
O1—V1—O3	109.85 (19)	Cu1—O7—H7a	123.6
O2—V1—O3	110.95 (19)	Cu1—O7—H7b	118.1
O1—V1—O4	109.78 (18)	H7a—O7—H7b	113.9
O2—V1—O4	108.75 (18)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O6—H6···O2^vi	0.99	2.13	2.979 (5)	144
O6—H6···O3^ii	0.99	2.18	2.967 (5)	136
O7—H7a···O1^xi	0.89	1.98	2.812 (6)	155
O7—H7b···O2^v	0.88	2.32	3.114 (6)	151
O7—H7b···O1^v	0.88	2.43	3.138 (6)	138

Symmetry codes: (ii) x+1, y, z; (v) x, y+1, z; (vi) x+1, y+1, z; (xi) −x, −y+1, −z.