Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270107017623/bc3043sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270107017623/bc3043Isup2.hkl |
A mixture of CdO (99.9%) and V2O5 (99.9%) in a 1:1 ratio was placed in a gold capsule and treated at 6 GPa and 1473 K in a belt-type high-pressure apparatus for 60 min (heating rate of 120 K min-1). After heat treatment, the sample was quenched to room temperature and the pressure was released slowly. The product consisted of small black single crystals suitable for X-ray crystal structure analysis. Powder X-ray diffraction revealed that the crystals are CdV2O6.
The structure was refined isotropically to R = 0.032 and anisotropically to R = 0.016. Difference Fourier syntheses revealed the highest residual peaks in the vicinity of the Cd and V sites. Anharmonic displacement parameters based on the Gram–Charlier expansion of the structure factor were refined up to the fourth order. Although the depths of negative regions in the probability density function maps were about 3–6%, only a few parameters had a significance level above 3σ and the reduction of the R factor was about 0.001. Therefore, in the final refinement cycles, all atoms were refined anisotropically. At the final stage, the occupancies of all sites were refined in turn, with deviations from unity less than 3σ in all cases. Fixed full occupancies were then used for all atoms. The use of the I > 2σ(I) cut-off instead of I > 3σ(I) added only eight extra observed reflections and raised the R index only slightly (0.018).
Data collection: CAD-4 Manual (Enraf–Nonius, 1988); cell refinement: CAD-4 Manual; data reduction: JANA2000 (Petříček & Dušek, 2000); program(s) used to solve structure: SIR2002 (Burla et al., 2000); program(s) used to refine structure: JANA2000; molecular graphics: ATOMS for Windows (Dowty, 1998); software used to prepare material for publication: JANA2000.
CdV2O6 | F(000) = 568 |
Mr = 310.29 | Dx = 5.159 Mg m−3 |
Orthorhombic, Pnab | Mo Kα radiation, λ = 0.71069 Å |
Hall symbol: -P 2bc 2n | Cell parameters from 23 reflections |
a = 4.9495 (6) Å | θ = 18.5–24.2° |
b = 5.6949 (7) Å | µ = 9.79 mm−1 |
c = 14.1692 (17) Å | T = 293 K |
V = 399.39 (8) Å3 | Plate, black |
Z = 4 | 0.22 × 0.11 × 0.06 mm |
Enraf–Nonius CAD-4 diffractometer | 1349 reflections with I > 3σ(I) |
Radiation source: X-ray sealed tube | Rint = 0.020 |
Equatorial mounted graphite monochromator | θmax = 46.0°, θmin = 2.9° |
ω scans | h = 0→10 |
Absorption correction: gaussian (JANA2000; Petříček & Dušek, 2000) | k = −3→11 |
Tmin = 0.314, Tmax = 0.565 | l = −20→28 |
4388 measured reflections | 2 standard reflections every 120 min |
1727 independent reflections | intensity decay: 0.0% |
Refinement on F | Weighting scheme based on measured s.u.'s w = 1/[σ2(F) + 0.000324F2] |
R[F2 > 2σ(F2)] = 0.016 | (Δ/σ)max = 0.002 |
wR(F2) = 0.028 | Δρmax = 0.58 e Å−3 |
S = 1.19 | Δρmin = −0.49 e Å−3 |
1349 reflections | Extinction correction: B-C type 1 Gaussian isotropic (Becker & Coppens, 1974) |
43 parameters | Extinction coefficient: 0.099926 |
CdV2O6 | V = 399.39 (8) Å3 |
Mr = 310.29 | Z = 4 |
Orthorhombic, Pnab | Mo Kα radiation |
a = 4.9495 (6) Å | µ = 9.79 mm−1 |
b = 5.6949 (7) Å | T = 293 K |
c = 14.1692 (17) Å | 0.22 × 0.11 × 0.06 mm |
Enraf–Nonius CAD-4 diffractometer | 1349 reflections with I > 3σ(I) |
Absorption correction: gaussian (JANA2000; Petříček & Dušek, 2000) | Rint = 0.020 |
Tmin = 0.314, Tmax = 0.565 | 2 standard reflections every 120 min |
4388 measured reflections | intensity decay: 0.0% |
1727 independent reflections |
R[F2 > 2σ(F2)] = 0.016 | 43 parameters |
wR(F2) = 0.028 | Δρmax = 0.58 e Å−3 |
S = 1.19 | Δρmin = −0.49 e Å−3 |
1349 reflections |
x | y | z | Uiso*/Ueq | ||
Cd | 0.75 | 0.77230 (3) | 1.0 | 0.00857 (4) | |
V | 0.72263 (5) | 0.31327 (4) | 0.833072 (15) | 0.00574 (4) | |
O1 | 0.5083 (2) | 0.57752 (18) | 0.89624 (6) | 0.00838 (19) | |
O2 | 0.3843 (2) | 0.35145 (19) | 0.75452 (6) | 0.00830 (18) | |
O3 | 0.6127 (2) | 0.11338 (19) | 0.90865 (7) | 0.00938 (19) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Cd | 0.00772 (6) | 0.01005 (7) | 0.00793 (6) | 0 | −0.00074 (3) | 0 |
V | 0.00534 (7) | 0.00615 (7) | 0.00572 (8) | 0.00057 (5) | 0.00023 (5) | −0.00066 (5) |
O1 | 0.0076 (3) | 0.0088 (4) | 0.0087 (3) | 0.0021 (3) | −0.0022 (3) | −0.0020 (3) |
O2 | 0.0076 (3) | 0.0093 (3) | 0.0080 (3) | −0.0002 (3) | −0.0023 (3) | −0.0010 (3) |
O3 | 0.0086 (3) | 0.0098 (4) | 0.0097 (3) | −0.0001 (3) | 0.0011 (3) | 0.0018 (3) |
Cd—O1 | 2.1961 (10) | V—O1 | 2.0472 (10) |
Cd—O1i | 2.1961 (10) | V—O1iv | 1.7853 (10) |
Cd—O3ii | 2.4311 (10) | V—O2 | 2.0225 (10) |
Cd—O3iii | 2.3071 (10) | V—O2vi | 1.7494 (10) |
Cd—O3iv | 2.3071 (10) | V—O2iv | 2.3505 (10) |
Cd—O3v | 2.4311 (10) | V—O3 | 1.6548 (10) |
O1—Cd—O1i | 119.32 (4) | O3v—Cd—O3iv | 81.71 (3) |
O1—Cd—O3ii | 83.97 (4) | O1—V—O1iv | 86.28 (4) |
O1—Cd—O3iii | 95.41 (4) | O1—V—O2 | 74.49 (4) |
O1—Cd—O3iv | 101.00 (3) | O1—V—O2vi | 160.28 (4) |
O1—Cd—O3v | 155.82 (4) | O1—V—O2iv | 77.66 (4) |
O1i—Cd—O1 | 119.32 (4) | O1—V—O3 | 93.01 (5) |
O1i—Cd—O3ii | 155.82 (4) | O1iv—V—O1 | 86.28 (4) |
O1i—Cd—O3iii | 101.00 (3) | O1iv—V—O2 | 153.41 (5) |
O1i—Cd—O3iv | 95.41 (4) | O1iv—V—O2vi | 100.38 (5) |
O1i—Cd—O3v | 83.97 (4) | O1iv—V—O2iv | 71.63 (4) |
O3ii—Cd—O3iii | 81.71 (3) | O1iv—V—O3 | 100.11 (5) |
O3ii—Cd—O3iv | 72.14 (3) | O2—V—O2vi | 92.63 (4) |
O3ii—Cd—O3v | 73.93 (3) | O2—V—O2iv | 86.21 (4) |
O3iii—Cd—O3ii | 81.71 (3) | O2—V—O3 | 99.09 (5) |
O3iii—Cd—O3iv | 147.22 (4) | O2vi—V—O2 | 92.63 (4) |
O3iii—Cd—O3v | 72.14 (3) | O2vi—V—O2iv | 86.79 (4) |
O3iv—Cd—O3ii | 72.14 (3) | O2vi—V—O3 | 103.92 (5) |
O3iv—Cd—O3iii | 147.22 (4) | O2iv—V—O2 | 86.21 (4) |
O3iv—Cd—O3v | 81.71 (3) | O2iv—V—O2vi | 86.79 (4) |
O3v—Cd—O3ii | 73.93 (3) | O2iv—V—O3 | 167.72 (4) |
O3v—Cd—O3iii | 72.14 (3) |
Symmetry codes: (i) −x+3/2, y, −z+2; (ii) x, y+1, z; (iii) −x+1, −y+1, −z+2; (iv) x+1/2, −y+1, z; (v) −x+3/2, y+1, −z+2; (vi) x+1/2, −y+1/2, −z+3/2. |
Experimental details
Crystal data | |
Chemical formula | CdV2O6 |
Mr | 310.29 |
Crystal system, space group | Orthorhombic, Pnab |
Temperature (K) | 293 |
a, b, c (Å) | 4.9495 (6), 5.6949 (7), 14.1692 (17) |
V (Å3) | 399.39 (8) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 9.79 |
Crystal size (mm) | 0.22 × 0.11 × 0.06 |
Data collection | |
Diffractometer | Enraf–Nonius CAD-4 diffractometer |
Absorption correction | Gaussian (JANA2000; Petříček & Dušek, 2000) |
Tmin, Tmax | 0.314, 0.565 |
No. of measured, independent and observed [I > 3σ(I)] reflections | 4388, 1727, 1349 |
Rint | 0.020 |
(sin θ/λ)max (Å−1) | 1.011 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.016, 0.028, 1.19 |
No. of reflections | 1349 |
No. of parameters | 43 |
No. of restraints | ? |
Δρmax, Δρmin (e Å−3) | 0.58, −0.49 |
Computer programs: CAD-4 Manual (Enraf–Nonius, 1988), CAD-4 Manual, JANA2000 (Petříček & Dušek, 2000), SIR2002 (Burla et al., 2000), JANA2000, ATOMS for Windows (Dowty, 1998).
Cd—O1 | 2.1961 (10) | V—O2 | 2.0225 (10) |
Cd—O3i | 2.4311 (10) | V—O2iv | 1.7494 (10) |
Cd—O3ii | 2.3071 (10) | V—O2iii | 2.3505 (10) |
V—O1 | 2.0472 (10) | V—O3 | 1.6548 (10) |
V—O1iii | 1.7853 (10) |
Symmetry codes: (i) x, y+1, z; (ii) −x+1, −y+1, −z+2; (iii) x+1/2, −y+1, z; (iv) x+1/2, −y+1/2, −z+3/2. |
Complex vanadium(V) oxides have received renewed interest as electrode materials and catalysts. A number of compounds with the general formula MV2O6 (M = Mg, Ca, Mn, Co, Ni, Cu, Zn and Cd) have been studied in the last decade (Rao & Palanna, 1996; Fuentes et al., 1999; Wei et al., 2005, 2006). Among these compounds, CuV2O6 (Cao et al., 2006) and CdV2O6 (Chen et al., 2004) have been shown to be promising cathode materials for rechargeable lithium batteries. Numerous MV2O6 oxides exist at ambient pressure (Rao & Palanna, 1996; Mocala & Ziolkowski, 1987; Tsuzuki et al., 1989) and their crystal structures have been reported by different authors for M = Mg (Ng & Calvo, 1972), Ca (Bouloux et al., 1972), Mn (Mueller-Buschbaum & Kobel, 1991a), Co (Jasper-Toennies & Mueller-Buschbaum, 1984; Mueller-Buschbaum & Kobel, 1991a), Ni (LeBail & Lafontaine, 1990; Mueller-Buschbaum & Kobel, 1991b), Cu (Lavaud & Galy, 1972; Calvo & Manolescu, 1973), Zn (Angenault & Rimsky, 1968; Andreetti et al.,1984) and Cd (Bouloux & Galy, 1969; Bouloux et al., 1972). Although the symmetry of the MV2O6 structures at ambient pressure is changed from orthorhombic to triclinic, all of them belong to the brannerite or thorutite (ThTi2O6) structure type. Except for M = Mn, MV2O6 transforms at high pressure to the orthorhombic columbite (FeNb2O6) structure type (Gondrand et al., 1974). The high-temperature polymorph of HgV2O6 also has a columbite-like structure (Mormann & Jeitschko, 2000), which is the only columbite-like MV2O6 vanadate stable at ambient pressure.
High-pressure polymorphs are usually denser (6–10% for MV2O6 phases) than their ambient pressure counterparts, and often have layered or close-packed structures. Layered structures are quite promising for applications as cathode materials. Therefore, the investigation of the high-pressure MV2O6 polymorphs in addition to the ambient pressure modifications may also be useful for their possible applications. However, the crystal structures of the MV2O6 compounds at high pressure have not been investigated yet, although their X-ray patterns have been reported (Gondrand et al., 1974). In this paper, we report the preparation of single crystals of a high-pressure modification of CdV2O6 and its crystal structure.
Two types of MO6 octahedra are present in the title CdV2O6 structure. The VO6 octahedra are connected via edge sharing and form zigzag chains running along the a direction (Fig. 1a). Octahedra in adjacent chains share corners and form corrugated layers separated by layers of Cd2+ cations. The VO6 octahedron is strongly distorted (Fig. 2b) and the V atom is shifted towards atom O3 away from atoms O1 and O2, due to the formation of a vanadyl bond [1.6548 (10) Å]. As a result, the V—O2 bond opposite the vanadyl bond is elongated to 2.3505 (10) Å. The O2—V—O3 angle is 167.72 (4)°. Bond-valence sum (BVS) calculations gave values of 5.23 and 4.87 for six- and five-coordinated V, respectively (Schindler et al., 2000). This type of distortion of the coordination polyhedron is typical for pentavalent V, and similar distances and angles for the VO6 octahedron were found, for instance, in the columbite-like structure of HgV2O6 (Mormann & Jeitschko, 2000). The CdO6 octahedra are linked by edge sharing into a zigzag chain running along the a direction. The chains are not connected to each other (Fig. 1b). The CdO6 octahedra are also strongly distorted (Fig. 2a) and have three pairs of Cd—O distances, 2.1961 (10), 2.3071 (10) and 2.4311 (10) Å. The largest O—Cd—O angle is 155.82 (4)°. BVS calculation (Brown & Altermatt, 1985; Brese & O'Keeffe, 1991) gives a value of 2.06, in spite of the strong distortion of the polyhedron. One may speculate that this distortion is a consequence of the almost pyramidal coordination of the V atom.
One may suggest that the strong distortion of the coordination polyhedra in the high-pressure structure is a reason for the instability of this modification at ambient pressure. In the brannerite-like structure, the Cd atom has an almost regular octahedral coordination with a small difference between the equatorial and apical Cd—O distances (2.287 and 2.199 Å, respectively). The coordination polyhedron of the V atom should be considered as a trigonal bipyramid with two vanadyl bonds of 1.687 and 1.708 Å (Zavalij & Whittingham, 1999). In the high-pressure structure, the V atoms have six O neighbours. However, the sixth V—O2 distance is 2.3505 (10) Å, and it is possible to use the τ parameter (Addison et al., 1984) to distinguish between the VO5 square-pyramidal and trigonal–bipyramidal geometries. The τ parameter is 0.12, indicating that, if the sixth O2 atom is ignored, the VO5 polyhedron is a square pyramid. In HgV2O6, the VO6 polyhedron (τ = 0.17) is very similar to that in CdV2O6 but the sixth V–O bond is longer (2.442 Å). The main difference between the two structures arises from the coordination of the Hg atom, with two very short (2.040 Å) and four long (2.643 and 2.677 Å) Hg—O distances. Such a coordination stabilizes a columbite-like structure, in spite of the square-pyramidal coordination of the V atom. One should note that, in other known columbite-like compounds, both cations have a nearly regular octahedral coordination. This is not the case for CdV2O6 and, although the cation–cation distances are very close in both modifications, the O environments for these cations are significantly different. Thus, one may conclude that the MV2O6 columbite-like structure results in a strong distortion of the MO6 octahedra which may be stabilized only at high pressure.