Tetraquinolinium ditelluro(VI)octavanadate(V) octahydrate

In the title compound, (C9H8N)4[Te2V8O28]·8H2O, the complete heteropolyanion is generated by a crystallographic inversion centre. One of the two quniolinium ions forms an N—H⋯Op (p = polyoxidometallate) hydrogen bond and the other an N—H⋯Ow (w = water) hydrogen bond. The water molecules further link the components by O—H⋯Op and O—H⋯Ow hydrogen bonds. A number of C—H⋯O interactions and aromatic π–π stacking interactions [shortest centroid–centroid separation = 3.541 (7) Å] are also observed. Together, these generate a three-dimensional network.

In the title compound, (C 9 H 8 N) 4 [Te 2 V 8 O 28 ]Á8H 2 O, the complete heteropolyanion is generated by a crystallographic inversion centre. One of the two quniolinium ions forms an N-HÁ Á ÁO p (p = polyoxidometallate) hydrogen bond and the other an N-HÁ Á ÁO w (w = water) hydrogen bond. The water molecules further link the components by O-HÁ Á ÁO p and O-HÁ Á ÁO w hydrogen bonds. A number of C-HÁ Á ÁO interactions and aromaticstacking interactions [shortest centroid-centroid separation = 3.541 (7) Å ] are also observed. Together, these generate a three-dimensional network.

Experimental
Crystal data (C 9
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HB7146).

Comment
The polyoxovanadate materials (POVs) are well established in magnetic, electric and biomedical fields because of their richness structural variety in relation with the vanadium element which can adopt different coordination geometries and variable oxidation states very interesting for redox applications in catalysis and materials science (Fukuda et al., 1997;Rajakumar et al., 2000;Folbergrova et al., 1987;Fantus et al.,1995). Furthermore, this family is dominated by the decavanadates, well known in their protonated forms [H x V 10 O 28 ] (6 -x)-. Nevertheless, incorporation of other elements besides vanadium into this structural type has not been reported yet. In particular, substitution of one or more vanadium atoms by Pt IV (Lee et al., 2008;Joo et al., 2011), Mo VI (Strukan et al., 1997 and Te VI (Konaka et al., 2008;Konaka et al., 2011) are investigated and resulted into novel materials with highly promising catalytic properties. To date in our knowledge, only two POVs incorporated one telluric, are known (Konaka et al., 2008). Here, we describe the synthesis and structure of the first ocatavanado-ditellurate ion, [Te 2 V 8 O 28 ] 4-, which was isolated as the hydrated quinolinium salt (C 9 H 8 N) 4 [Te 2 V 8 O 28 ]·8H 2 O (I). The asymmetric unit of (I) contains one half of a [Te 2 V 8 O 28 ] 4anion, two crystallographically independent quinolinium cations and four water molecules. Owing to the inversion symmetry, the whole polyanion is generated, resulting so to the title compound formulae (Fig. 1). The structure of the [Te 2 V 8 O 28 ] 4polyanion is basically the same as that of decavanadate, [V 10 O 28 ] 6- (Evans et al., 1966). In [Te 2 V 8 O 28 ] 4anion two of the central V atoms of [V 10 O 28 ] 6are replaced with two Te atoms. The valence bond calculation (Brown & Altermatt, 1985) gives effective bond valences of 6.1647 for Te cation and of 5.0743, 5.0068, 5.0574 and 5.063 for the four independent V cations, consistent with their oxidation states Te(+VI) and V(+V). Replacement of central V atom with a heteroatom, has also been observed for [H 2 PtV 9 O 28 ] 5- (Lee et al.,2008;Joo et al., 2011). As for the decavanadate anion, the [Te 2 V 8 O 28 ] 4anion is built up of 10 e dge sharing MO 6 (M = V or Te) octahedra. Within VO 6 octahedra, the V-O distances are also similar to those already observed and depend upon the type of oxo ligand: bond lengths to the terminal oxo oxygen V-Ot are between 1.602 (7) and 1.610 (6) Å, V-O2b bond lengths to the oxygen bonded to two V atoms vary from 1.767 (6) e t 1.864 (6) Å, V-O3b bond lengths to the oxygen bonded to three V atoms are 2.005 (7) and 2.039 (7) and finally, V-O6c bond lengths to the oxygen shared between six V atoms are 2.380 (7) and 2.387 (7) Å. The VO 6 octahedra are significantly distorted, with the bond angles at the V atoms ranging from 73.5 (3) to 176.5 (3)°. The TeO 6 octahedra are less distorted in comparison with VO 6 ocathedra since the Te-O distances vary from 1.765 (6) to 2.080 (7) Å. Similar trends are also observable for similar heteropolyanion (Konaka et al., 2008;Konaka et al., 2011). The quinolinium cations exhibit the typical ranges in bond lengths and angles as found in the related structures (Hemissi et al., 2010). polyanion sheets are linked thanks to O1W, O2W water molecules and terminal oxygen atoms (O1, O5 and O9) and bridged oxygen atoms (µ 2-O6, µ 2-O13, µ 2-O14 and µ 3-O4) of the polyanion, into a three dimensional network by N -H···O and C-H···O hydrogen bonds with donor-acceptor distances ranging from 2.700 (11) to 3.411 (13) Å.

Experimental
Vanadium (V) oxide (1.26 g, 6.93 mmol), quinoline (0.74 ml, 6.16 mmol) and telluric acid Te(OH) 6 (0.36 g, 1.55 mmol) were dissolved in a mixture of 30 ml of distilled water and 10 ml of ethanol and then stirred for 3 h. Yellow single crystals were obtained after one week by slow evaporation at room temperature.

Refinement
All H atoms attached to C and N atoms were fixed geometrically and treated as riding, with C-H = 0.

Tetraquinolinium ditelluro(VI)octavanadate(V) octahydrate
Crystal data (C 9  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 F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.