Caesium vanadium selenite, Cs(VO₂)₃(SeO₃)₂

Caesium vanadium(V) selenite contains infinite sheets of distorted vertex-sharing VO₆ octahedra, capped by selenite groups [d_av(V-O) = 1.927 (4) Å and d_av(Se-O) = 1.709 (3) Å]. Interlayer caesium cations complete the structure [d_av(Cs-O) = 3.365 (4) Å].

S1. Comment

The title compound is another member of the family of layered phases (Harrison et al., 1996) structurally related to hexagonal tungsten oxide, hex-WO₃ (Gérand et al., 1979). It is built up from vertex sharing VO₆ octahedra and SeO₃ pyramids, fused together via V—O—V (θ_av = 141.5°) and V—O—Se (θ_av = 129.5°) bonds. Interlayer Cs⁺ cations complete the packing in Cs(VO₂)₃(SeO₃)₂ which is isostructural with NH₄(VO₂)₃(SeO₃)₂ (Vaughey et al., 1994), K(VO₂)₃(SeO₃)₂ (Harrison et al., 1995), and Cs(VO₂)₃(TeO₃)₂ (Harrison & Buttery, 2000).

The VO₆ grouping shows a distinctive distortion mode with the vanadium atom displaced by 0.36 Å from the geometric best centre (Balic Zunic & Makovicky, 1996) of its octahedron, essentially towards an octahedral edge (Harrison et al., 1996). This situation results in two short (d < 1.67 Å) V–O vertices, each of which is trans to a long (d > 2.16 Å) V—O bond. The two remaining V—O bonds are of intermediate length. The short and long bonds are involved in V—O—V links and the intermediate length bonds participate in V—O—Se connections. A bond valence sum (BVS; Brown, 1996) of 5.05 results for vanadium (expected value = 5.00 for V^V). The two Se atoms have threefold symmetry and their expected pyramidal geometry [BVS(Se1) = 3.95, BVS(Se2) = 3.96, expected = 4.00]. The 12-coordinate [d_av = 3.365 (4) Å] caesium cation, with site symmetry 3, serves to link adjacent anionic sheets by way of O—Cs—O bonds.

S2. Experimental

Initially, `H₂SeO₃' (dissolved SeO₂; 8 ml 0.5 M), water (4 ml), VOSO₄·H₂O (0.532 g) and CsCl (0.673 g)(starting ratio of Cs:V:Se = 1:1:1) were heated to 423 K in a 23-ml-capacity teflon-lined hydrothermal bomb for two days, resulting in a green plug, which was discarded, and a blue solution. –The solution was evaporated to dryness to result in a blue-green glass (amorphous by X-rays) which was returned to the bomb with H₂O (5 ml) and heated to 423 K for a further four days. Product recovery by vacuum filtration and washing with water and acetone led to a mass of well faceted, pleochroic (dark orange–brown along the hexagonal axis; yellow–green normal to the hexagonal axis) hexagonal prisms of the title compound. These prisms varied in shape from plate-like to rod-like.

S3. Refinement

The largest difference peak is 0.82 Å from Cs1. Friedel pairs were not merged during data reduction to enable determination of the absolute structure by refinement of the Flack parameter. The structure has pseudosymmetry comparable with space group P6₃mc. However, the systematic absences are not consistent with P6₃mc, and the merging R factor of 0.131 for Laue group 6/mmm is significantly larger than that for 6/m (0.048). Structurally, P6₃mc appears to involve the vanadium atom being placed at the centre of its octahedron, which is a very unlikely situation for a vanadium(V) system.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SMART; data reduction: SMART; program(s) used to solve structure: starting coordinates from isostructural material; program(s) used to refine structure: SHELXL97 (Sheldrick, 1997).

(I)

Crystal data

Cs·(VO2)3·(SeO3)2	Dx = 4.091 Mg m^−3
Mr = 635.65	Melting point: decomposes before melting K
Hexagonal, P63	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 6c	Cell parameters from 1888 reflections
a = 7.1613 (5) Å	θ = 3.3–29.4°
c = 11.6184 (8) Å	µ = 13.25 mm^−1
V = 516.01 (6) Å^3	T = 298 K
Z = 2	Hexagonal column, yellow–green
F(000) = 576	0.27 × 0.08 × 0.08 mm

Data collection

Bruker SMART 1000 diffractometer	966 independent reflections
Radiation source: fine-focus sealed tube	895 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.048
ω scans	θmax = 30°, θmin = 3.3°
Absorption correction: multi-scan (SADABS; Bruker, 1999)	h = −9→7
Tmin = 0.172, Tmax = 0.346	k = −6→9
3428 measured reflections	l = −16→16

Refinement

Refinement on F^2	Secondary atom site location: none
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0336P)^2] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.029	(Δ/σ)max < 0.001
wR(F^2) = 0.063	Δρmax = 2.23 e Å^−3
S = 1.01	Δρmin = −0.80 e Å^−3
966 reflections	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
57 parameters	Extinction coefficient: 0.0030 (6)
1 restraint	Absolute structure: Flack (1983)
Primary atom site location: from isostructural material	Absolute structure parameter: 0.00 (2)

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
Cs1	0.3333	0.6667	0.98245 (5)	0.02018 (18)
V1	0.78873 (16)	0.12114 (15)	0.79392 (8)	0.00958 (19)
Se1	0.6667	0.3333	1.01597 (7)	0.0105 (2)
Se2	1.0000	0.0000	0.57510 (9)	0.00937 (19)
O1	0.8021 (6)	0.2192 (6)	0.9539 (3)	0.0129 (8)
O2	0.8868 (6)	0.1348 (6)	0.6387 (3)	0.0124 (8)
O3	0.5441 (6)	0.0792 (7)	0.7650 (4)	0.0152 (8)
O4	0.7461 (6)	−0.1225 (7)	0.8265 (4)	0.0130 (8)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cs1	0.0165 (2)	0.0165 (2)	0.0275 (3)	0.00825 (12)	0.000	0.000
V1	0.0071 (5)	0.0071 (5)	0.0138 (4)	0.0030 (4)	0.0003 (3)	0.0003 (3)
Se1	0.0108 (3)	0.0108 (3)	0.0099 (4)	0.00541 (16)	0.000	0.000
Se2	0.0094 (3)	0.0094 (3)	0.0093 (3)	0.00471 (13)	0.000	0.000
O1	0.014 (2)	0.016 (2)	0.0121 (19)	0.0107 (17)	−0.0007 (13)	−0.0006 (13)
O2	0.012 (2)	0.0105 (19)	0.0156 (19)	0.0061 (16)	0.0016 (14)	0.0001 (13)
O3	0.0084 (18)	0.0146 (19)	0.024 (2)	0.0067 (15)	−0.0013 (16)	−0.0013 (18)
O4	0.0124 (19)	0.0124 (19)	0.0164 (17)	0.0079 (16)	0.0032 (17)	0.0031 (15)

Geometric parameters (Å, º)

Cs1—O4^i	3.137 (4)	V1—O3	1.657 (4)
Cs1—O4^ii	3.137 (4)	V1—O4	1.658 (4)
Cs1—O4^iii	3.137 (4)	V1—O2	1.920 (4)
Cs1—O2^iv	3.169 (4)	V1—O1	1.972 (4)
Cs1—O2^v	3.169 (4)	V1—O4^x	2.176 (4)
Cs1—O2^vi	3.169 (4)	V1—O3^ix	2.178 (4)
Cs1—O1^vii	3.558 (4)	Se1—O1	1.709 (4)
Cs1—O1^viii	3.558 (4)	Se1—O1^ii	1.709 (4)
Cs1—O1^ix	3.558 (4)	Se1—O1^ix	1.709 (4)
Cs1—O3^i	3.596 (4)	Se2—O2^x	1.708 (4)
Cs1—O3^iii	3.596 (4)	Se2—O2^xi	1.708 (4)
Cs1—O3^ii	3.596 (4)	Se2—O2	1.708 (4)
O4^i—Cs1—O4^ii	89.96 (11)	O1^ix—Cs1—O3^iii	91.69 (9)
O4^i—Cs1—O4^iii	89.96 (11)	O3^i—Cs1—O3^iii	76.07 (12)
O4^ii—Cs1—O4^iii	89.96 (11)	O4^i—Cs1—O3^ii	100.05 (12)
O4^i—Cs1—O2^iv	70.25 (10)	O4^ii—Cs1—O3^ii	44.85 (9)
O4^ii—Cs1—O2^iv	130.95 (11)	O4^iii—Cs1—O3^ii	46.88 (9)
O4^iii—Cs1—O2^iv	132.49 (11)	O2^iv—Cs1—O3^ii	170.13 (10)
O4^i—Cs1—O2^v	130.95 (11)	O2^v—Cs1—O3^ii	97.63 (10)
O4^ii—Cs1—O2^v	132.49 (11)	O2^vi—Cs1—O3^ii	95.15 (10)
O4^iii—Cs1—O2^v	70.25 (10)	O1^vii—Cs1—O3^ii	91.69 (9)
O2^iv—Cs1—O2^v	90.44 (10)	O1^viii—Cs1—O3^ii	119.67 (9)
O4^i—Cs1—O2^vi	132.49 (11)	O1^ix—Cs1—O3^ii	43.87 (9)
O4^ii—Cs1—O2^vi	70.25 (10)	O3^i—Cs1—O3^ii	76.07 (12)
O4^iii—Cs1—O2^vi	130.95 (11)	O3^iii—Cs1—O3^ii	76.07 (12)
O2^iv—Cs1—O2^vi	90.44 (10)	O1—Se1—O1^ii	103.47 (15)
O2^v—Cs1—O2^vi	90.44 (10)	O1—Se1—O1^ix	103.47 (15)
O4^i—Cs1—O1^vii	79.45 (10)	O1^ii—Se1—O1^ix	103.47 (14)
O4^ii—Cs1—O1^vii	46.83 (9)	O2^x—Se2—O2^xi	102.67 (16)
O4^iii—Cs1—O1^vii	134.87 (10)	O2^x—Se2—O2	102.67 (16)
O2^iv—Cs1—O1^vii	84.82 (10)	O2^xi—Se2—O2	102.67 (16)
O2^v—Cs1—O1^vii	145.18 (10)	O3—V1—O4	103.5 (2)
O2^vi—Cs1—O1^vii	55.22 (9)	O3—V1—O2	98.3 (2)
O4^i—Cs1—O1^viii	46.83 (9)	O4—V1—O2	97.95 (19)
O4^ii—Cs1—O1^viii	134.87 (10)	O3—V1—O1	96.6 (2)
O4^iii—Cs1—O1^viii	79.45 (9)	O4—V1—O1	96.3 (2)
O2^iv—Cs1—O1^viii	55.22 (9)	O2—V1—O1	156.29 (17)
O2^v—Cs1—O1^viii	84.82 (9)	O3—V1—O4^x	166.77 (19)
O2^vi—Cs1—O1^viii	145.18 (10)	O4—V1—O4^x	89.7 (2)
O1^vii—Cs1—O1^viii	119.141 (19)	O2—V1—O4^x	80.63 (17)
O4^i—Cs1—O1^ix	134.87 (10)	O1—V1—O4^x	80.63 (16)
O4^ii—Cs1—O1^ix	79.45 (9)	O3—V1—O3^ix	89.8 (3)
O4^iii—Cs1—O1^ix	46.83 (9)	O4—V1—O3^ix	166.6 (2)
O2^iv—Cs1—O1^ix	145.18 (10)	O2—V1—O3^ix	81.73 (17)
O2^v—Cs1—O1^ix	55.22 (9)	O1—V1—O3^ix	80.02 (17)
O2^vi—Cs1—O1^ix	84.82 (9)	O4^x—V1—O3^ix	77.02 (16)
O1^vii—Cs1—O1^ix	119.141 (19)	Se1—O1—V1	129.0 (2)
O1^viii—Cs1—O1^ix	119.14 (2)	Se1—O1—Cs1^xii	97.87 (16)
O4^i—Cs1—O3^i	44.85 (9)	V1—O1—Cs1^xii	104.38 (14)
O4^ii—Cs1—O3^i	46.88 (9)	Se1—O1—Cs1^xiii	92.58 (14)
O4^iii—Cs1—O3^i	100.05 (12)	V1—O1—Cs1^xiii	81.22 (12)
O2^iv—Cs1—O3^i	95.15 (10)	Cs1^xii—O1—Cs1^xiii	160.46 (12)
O2^v—Cs1—O3^i	170.13 (10)	V1—O3—V1^ii	142.4 (3)
O2^vi—Cs1—O3^i	97.63 (10)	V1—O3—Cs1^xiii	88.73 (16)
O1^vii—Cs1—O3^i	43.87 (9)	V1^ii—O3—Cs1^xiii	98.67 (15)
O1^viii—Cs1—O3^i	91.69 (8)	V1—O3—Cs1^xiv	97.11 (18)
O1^ix—Cs1—O3^i	119.67 (9)	V1^ii—O3—Cs1^xiv	88.18 (13)
O4^i—Cs1—O3^iii	46.88 (9)	Cs1^xiii—O3—Cs1^xiv	160.27 (14)
O4^ii—Cs1—O3^iii	100.05 (12)	V1—O4—V1^xi	140.6 (2)
O4^iii—Cs1—O3^iii	44.85 (9)	V1—O4—Cs1^xiii	105.77 (17)
O2^iv—Cs1—O3^iii	97.63 (10)	V1^xi—O4—Cs1^xiii	113.58 (16)
O2^v—Cs1—O3^iii	95.15 (10)	Se2—O2—V1	130.0 (2)
O2^vi—Cs1—O3^iii	170.13 (10)	Se2—O2—Cs1^xiv	119.26 (18)
O1^vii—Cs1—O3^iii	119.67 (9)	V1—O2—Cs1^xiv	108.04 (16)
O1^viii—Cs1—O3^iii	43.87 (9)

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