supplementary materials


Acta Cryst. (2013). E69, i79    [ doi:10.1107/S1600536813028869 ]

A triclinic polymorph of dicadmium divanadate(V)

A. Ould Saleck, A. Assani, M. Saadi and L. El Ammari

Abstract top

The title compound, Cd2V2O7, was obtained under hydro­thermal conditions. Different from the known monoclinic form, the new polymorph of Cd2V2O7 has triclinic symmetry and is isotypic with Ca2V2O7. The building units of the crystal structure are two Cd2+ cations, with coordination numbers of six and seven, and two V atoms with a tetra­hedral and a significantly distorted trigonal-pyramidal coordination environment, respectively. Two VO5 pyramids share an edge and each pyramid is connected to one VO4 tetra­hedron via a corner atom, forming an isolated V4O148- anion. These anions are arranged in sheets parallel to (-211) and are linked through the Cd2+ cations into a three-dimensional framework structure.

Comment top

Vanadate-based compounds have received a great extent of interest and still remain promising functional materials. Their structural diversity, mainly associated with the ability of vanadium to form different anions like (VO4)3-, (V2O7)4-, (V4O12)4-, (V10O28)6-, is strongly required for catalysis applications (Jin et al., 2013; Valverde et al., 2012).

A bibliographic analysis revealed that pyrovanadates with the (V2O7)4- anion can adopt different symmetries. For example, Cu2V2O7, Mn2V2O7 and Mg2V2O7 are polymorphic and exhibit both monoclinic and triclinic varieties, the Cu-member additionally an orthorhombic form. In the case of Co2V2O7, Ni2V2O7, and Cd2V2O7 only one monoclinic form is yet known, for Zn2V2O7 two monoclinic forms are reported. Ca2V2O7 and Ba2V2O7 crystallize in the triclinic system, Sr2V2O7 is likewise polymorphic, with triclinic and tetragonal varieties. We report here on the crystal structure determination of a new form of Cd2V2O7 that was hydrothermally synthesized. In contrast to the known monoclinic polymorph (Au & Calvo, 1967) that is stable from ambient temperature to 1173 K (Krasnenko et al., 2010), this new form has triclinic symmetry and is isotypic with Ca2V2O7 (Trunov et al., 1983).

The structure of the title compound is built up from two types of vanadium sites and two types of cadmium sites, each with a different oxygen coordination as shown in Fig. 1. The coordination environment of V1 is tetrahedral with V1–O distances in the range 1.6882 (13) Å - 1.7708 (13) Å. V2 is surrounded by five oxygen atoms with four V2—O distances ranging from 1.6612 (14) Å to 1.8535 (13) Å and the fifth O atom at a longer distance V2–O1 = 2.0348 (13) Å, forming a distorted trigonal V2O55- pyramid. The bond valence sum calculation (Brown & Altermatt, 1985) for V1 and V2 are as expected, viz. 4.99 and 5.11 valence units, respectively. This result confirms the involvement of O1 in the V2 environment. The V2O55- pyramids build a dimeric unit (V2)2O86- by sharing an edge. A corner atom (O1) of each of the pyramids is also part of a V1O4 tetrahedron. This linkeage leads to the formation of a centrosymmetric (V4O14)8- anion. This type of anion is rarely encountered in the crystal chemistry of pyrovanadates. Like in the monoclinic Cd2V2O7 variety (Au and Calvo, 1967), (V2O7)4- groups made up from two corner-sharing VO4 tetrahedra are more commonly observed.

The two independent cadmium sites Cd1 and Cd2 are surrounded by six and seven oxygen atoms, respectively, in the form of distorted polyhedra. The Cd—O distance range from 2.2401 (13) Å to 2.5300 (13) Å for Cd1O7 and from 2.2449 (14) Å to 2.4562 (14) Å for Cd2O6. As shown in Fig. 2, edge-sharing CdO6 and CdO7 polyhedra built up sheets parallel to (211) with 8-membered open rings. Two adjacent layers are linked by the (V4O14)8- groups into a three-dimensional framework (Fig. 3). In the monoclinic Cd2V2O7 polymorph, the CdO6 octahedra share edges and form sheets with six-membered rings that are linked by (V2O7)4- groups.

Related literature top

For Ca2V2O7, isotypic with the title compound, see: Trunov et al. (1983). For the structure of the monoclinic polymorph of Cd2V2O7, see: Au & Calvo (1967). For the thermal stability of the monoclinic polymorph, see: Krasnenko & Rotermel (2010). For applications of vanadates, see: Jin et al. (2013); Valverde et al. (2012). For bond-valence analysis, see: Brown & Altermatt (1985).

Experimental top

Crystals of the title compound were isolated from the hydrothermal treatment of cadmium oxide, ammonium metavanadate and zinc oxide in a molar ratio Cd:V:Zn = 11:8:1. Zinc oxide, not present in the obtained crystals, presumably acted as a mineralizing agent. The hydrothermal reaction was conducted in a 23 ml Teflon-lined autoclave, filled to 50% with distilled water and under autogeneous pressure at 493 K for four days. After being filtered off, washed with deionized water and air dried, the reaction product consists of colourless sheet-shaped crystals corresponding to the title compound.

Refinement top

The highest peak and the deepest hole in the final Fourier map are at 1.69 Å and 0.08 Å, from O2 and Cd2, respectively. Reflections (200) and (020) were omitted from the refinement due to large differences between observed and calculated intensities.

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top
[Figure 1] Fig. 1. The coordination environment of the Cd and V sites in the crystal structure of the title compound, triclinic Cd2V2O7. Displacement ellipsoids are drawn at the 70% probability level. [Symmetry codes: (i) -x, -y + 1, -z + 1; (ii) -x + 1, -y, -z + 1; (iii) -x + 1, -y + 1, -z + 1; (iv) x - 1, y, z + 1; (v) x, y, z + 1; (vi) -x + 2, -y, -z + 1.]
[Figure 2] Fig. 2. Polyhedral representation of triclinic Cd2V2O7, showing the sheets of cadmium- and vanadium-oxygen polyhedra.
[Figure 3] Fig. 3. A three dimensional view of the crystal structure of triclinic Cd2V2O7 showing the stacking of the cadium and vanadium layers that extend parallel to (211).
Dicadmium divanadate(V) top
Crystal data top
Cd2V2O7Z = 2
Mr = 438.68F(000) = 396
Triclinic, P1Dx = 5.176 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 6.5974 (2) ÅCell parameters from 2717 reflections
b = 6.8994 (2) Åθ = 3.0–33.1°
c = 6.9961 (2) ŵ = 10.65 mm1
α = 83.325 (1)°T = 296 K
β = 63.898 (1)°Block, colourless
γ = 80.145 (1)°0.29 × 0.17 × 0.12 mm
V = 281.45 (1) Å3
Data collection top
Bruker X8 APEX
diffractometer
2134 independent reflections
Radiation source: fine-focus sealed tube2077 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.025
φ and ω scansθmax = 33.1°, θmin = 3.0°
Absorption correction: multi-scan
(SADABS; Bruker, 2009)
h = 1010
Tmin = 0.164, Tmax = 0.376k = 1010
10113 measured reflectionsl = 1010
Refinement top
Refinement on F20 restraints
Least-squares matrix: fullPrimary atom site location: structure-invariant direct methods
R[F2 > 2σ(F2)] = 0.016Secondary atom site location: difference Fourier map
wR(F2) = 0.037 w = 1/[σ2(Fo2) + (0.0148P)2 + 0.2572P]
where P = (Fo2 + 2Fc2)/3
S = 1.21(Δ/σ)max = 0.001
2134 reflectionsΔρmax = 0.70 e Å3
100 parametersΔρmin = 1.53 e Å3
Crystal data top
Cd2V2O7γ = 80.145 (1)°
Mr = 438.68V = 281.45 (1) Å3
Triclinic, P1Z = 2
a = 6.5974 (2) ÅMo Kα radiation
b = 6.8994 (2) ŵ = 10.65 mm1
c = 6.9961 (2) ÅT = 296 K
α = 83.325 (1)°0.29 × 0.17 × 0.12 mm
β = 63.898 (1)°
Data collection top
Bruker X8 APEX
diffractometer
2134 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2009)
2077 reflections with I > 2σ(I)
Tmin = 0.164, Tmax = 0.376Rint = 0.025
10113 measured reflectionsθmax = 33.1°
Refinement top
R[F2 > 2σ(F2)] = 0.016Δρmax = 0.70 e Å3
wR(F2) = 0.037Δρmin = 1.53 e Å3
S = 1.21Absolute structure: ?
2134 reflectionsAbsolute structure parameter: ?
100 parametersRogers parameter: ?
0 restraints
Special details top

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 > 2σ(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 (Å2) top
xyzUiso*/Ueq
Cd10.24214 (2)0.336697 (18)0.83258 (2)0.00767 (4)
Cd20.74980 (2)0.034380 (18)0.75748 (2)0.00845 (4)
V10.71038 (5)0.16450 (4)0.25864 (4)0.00469 (5)
V20.22836 (5)0.45517 (4)0.34409 (5)0.00542 (5)
O10.8612 (2)0.3328 (2)0.0816 (2)0.0100 (2)
O20.8622 (2)0.0439 (2)0.3907 (2)0.0099 (2)
O30.4592 (2)0.2893 (2)0.4363 (2)0.0092 (2)
O40.6546 (2)0.00638 (19)0.1233 (2)0.0086 (2)
O50.2714 (2)0.29481 (19)0.1660 (2)0.0093 (2)
O60.3839 (2)0.6438 (2)0.2436 (2)0.0104 (2)
O70.0496 (2)0.5892 (2)0.3678 (2)0.0100 (2)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cd10.00672 (6)0.00774 (6)0.00900 (6)0.00006 (4)0.00431 (4)0.00047 (4)
Cd20.00779 (6)0.00795 (6)0.00808 (6)0.00031 (4)0.00277 (4)0.00069 (4)
V10.00423 (11)0.00515 (11)0.00483 (11)0.00033 (8)0.00222 (9)0.00007 (9)
V20.00472 (11)0.00635 (12)0.00446 (11)0.00089 (9)0.00115 (9)0.00065 (9)
O10.0089 (5)0.0096 (5)0.0098 (5)0.0031 (4)0.0025 (5)0.0023 (4)
O20.0080 (5)0.0124 (6)0.0090 (5)0.0009 (4)0.0044 (4)0.0003 (4)
O30.0070 (5)0.0116 (6)0.0079 (5)0.0021 (4)0.0032 (4)0.0013 (4)
O40.0110 (6)0.0068 (5)0.0095 (5)0.0012 (4)0.0054 (5)0.0014 (4)
O50.0128 (6)0.0079 (5)0.0083 (5)0.0002 (4)0.0057 (5)0.0015 (4)
O60.0081 (5)0.0079 (5)0.0147 (6)0.0021 (4)0.0046 (5)0.0014 (4)
O70.0056 (5)0.0157 (6)0.0064 (5)0.0026 (4)0.0020 (4)0.0004 (4)
Geometric parameters (Å, º) top
Cd1—O7i2.2401 (13)Cd2—O4ii2.4562 (14)
Cd1—O4ii2.2898 (13)V1—O11.6882 (13)
Cd1—O6iii2.3083 (14)V1—O21.7028 (14)
Cd1—O1iii2.3345 (14)V1—O31.7265 (13)
Cd1—O1iv2.3476 (13)V1—O41.7708 (13)
Cd1—O5v2.4043 (13)V2—O51.6612 (14)
Cd1—O32.5300 (13)V2—O61.6885 (14)
Cd2—O6iii2.2449 (14)V2—O71.8530 (13)
Cd2—O5ii2.2858 (13)V2—O7i1.8535 (13)
Cd2—O2vi2.2894 (14)V2—O32.0348 (13)
Cd2—O22.3327 (14)V2—V2i2.8482 (6)
Cd2—O4v2.3459 (13)
O7i—Cd1—O4ii114.29 (5)O2vi—Cd2—O274.71 (5)
O7i—Cd1—O6iii131.24 (5)O6iii—Cd2—O4v96.72 (5)
O4ii—Cd1—O6iii83.66 (5)O5ii—Cd2—O4v75.42 (5)
O7i—Cd1—O1iii85.81 (5)O2vi—Cd2—O4v102.17 (5)
O4ii—Cd1—O1iii157.35 (5)O2—Cd2—O4v174.49 (5)
O6iii—Cd1—O1iii90.73 (5)O6iii—Cd2—O4ii81.30 (5)
O7i—Cd1—O1iv76.73 (5)O5ii—Cd2—O4ii75.69 (5)
O4ii—Cd1—O1iv94.46 (5)O2vi—Cd2—O4ii160.52 (5)
O6iii—Cd1—O1iv149.98 (5)O2—Cd2—O4ii98.40 (5)
O1iii—Cd1—O1iv79.55 (5)O4v—Cd2—O4ii83.09 (5)
O7i—Cd1—O5v153.49 (5)O1—V1—O2109.38 (7)
O4ii—Cd1—O5v74.22 (5)O1—V1—O3107.57 (7)
O6iii—Cd1—O5v73.06 (5)O2—V1—O3109.85 (7)
O1iii—Cd1—O5v83.15 (5)O1—V1—O4109.71 (7)
O1iv—Cd1—O5v77.60 (5)O2—V1—O4109.65 (7)
O7i—Cd1—O362.10 (5)O3—V1—O4110.65 (6)
O4ii—Cd1—O386.49 (5)O5—V2—O6114.25 (7)
O6iii—Cd1—O375.19 (5)O5—V2—O799.11 (7)
O1iii—Cd1—O3113.31 (5)O6—V2—O798.25 (7)
O1iv—Cd1—O3134.73 (5)O5—V2—O7i121.64 (7)
O5v—Cd1—O3144.28 (4)O6—V2—O7i123.74 (7)
O6iii—Cd2—O5ii156.37 (5)O7—V2—O7i79.57 (6)
O6iii—Cd2—O2vi116.20 (5)O5—V2—O392.06 (6)
O5ii—Cd2—O2vi87.38 (5)O6—V2—O393.85 (6)
O6iii—Cd2—O288.75 (5)O7—V2—O3158.40 (6)
O5ii—Cd2—O299.75 (5)O7i—V2—O378.83 (6)
Symmetry codes: (i) x, y+1, z+1; (ii) x+1, y, z+1; (iii) x+1, y+1, z+1; (iv) x1, y, z+1; (v) x, y, z+1; (vi) x+2, y, z+1.

Experimental details

Crystal data
Chemical formulaCd2V2O7
Mr438.68
Crystal system, space groupTriclinic, P1
Temperature (K)296
a, b, c (Å)6.5974 (2), 6.8994 (2), 6.9961 (2)
α, β, γ (°)83.325 (1), 63.898 (1), 80.145 (1)
V3)281.45 (1)
Z2
Radiation typeMo Kα
µ (mm1)10.65
Crystal size (mm)0.29 × 0.17 × 0.12
Data collection
DiffractometerBruker X8 APEX
diffractometer
Absorption correctionMulti-scan
(SADABS; Bruker, 2009)
Tmin, Tmax0.164, 0.376
No. of measured, independent and
observed [I > 2σ(I)] reflections
10113, 2134, 2077
Rint0.025
(sin θ/λ)max1)0.769
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.016, 0.037, 1.21
No. of reflections2134
No. of parameters100
No. of restraints0
Δρmax, Δρmin (e Å3)0.70, 1.53

Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg, 2006), publCIF (Westrip, 2010).

Acknowledgements top

The authors thank the Unit of Support for Technical and Scientific Research (UATRS, CNRST) for the X-ray measurements.

references
References top

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