V1.42In1.83Mo15Se19

The structure of the title compound, vanadium indium pentadecamolybdenum nonadecaselenide, V1.42In1.83Mo15Se19, is isotypic with In2.9Mo15Se19 [Grüttner et al. (1979 ▶). Acta Cryst. B35, 285–292]. It is characterized by two cluster units Mo6Sei 8Sea 6 and Mo9Sei 11Sea 6 (where i represents inner and a apical atoms) that are present in a 1:1 ratio. The cluster units are centered at Wyckoff positions 2b and 2c and have point-group symmetry and , respectively. The clusters are interconnected through additional Mo—Se bonds. In the title compound, the V3+ cations replace the trivalent indium atoms present in In2.9Mo15Se19, and a deficiency is observed on the monovalent indium site. One Mo, one Se and the V atom are situated on mirror planes, and two other Se atoms and the In atom are situated on threefold rotation axes.

The structure of the title compound, vanadium indium pentadecamolybdenum nonadecaselenide, V 1.42 In 1.83 Mo 15 -Se 19 , is isotypic with In 2.9 Mo 15 Se 19 . Acta Cryst. B35, [285][286][287][288][289][290][291][292]. It is characterized by two cluster units Mo 6 Se i 8 Se a 6 and Mo 9 Se i 11 Se a 6 (where i represents inner and a apical atoms) that are present in a 1:1 ratio. The cluster units are centered at Wyckoff positions 2b and 2c and have pointgroup symmetry 3 and 6, respectively. The clusters are interconnected through additional Mo-Se bonds. In the title compound, the V 3+ cations replace the trivalent indium atoms present in In 2.9 Mo 15 Se 19 , and a deficiency is observed on the monovalent indium site. One Mo, one Se and the V atom are situated on mirror planes, and two other Se atoms and the In atom are situated on threefold rotation axes.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: WM2403).  (Grüttner et al., 1979) constitute an interesting family of compounds. Indeed, their crystal structure contains an equal mixture of Mo 6 and Mo 9 cluster units and the In atoms occupy two crystallographically different positions depending on their formal oxidation state of +1 or +3. Recently, we have shown that the In 3+ cation can be replaced by other trivalent cations such as Ho 3+ (Salloum et al., 2006) and the In + cation by K + (Salloum et al., 2007). Interest in these Mo cluster compounds also lies in their physical properties, because they become superconductors with high critical magnetic fields at about 4 K . We present here the crystal structure of V 1.42 In 1.83 Mo 15 Se 19 in which a 3d element replaces the trivalent indium atom.
The Mo-Se framework of the title compound consists of the cluster units Mo 6 Se i 8 Se a 6 and Mo 9 Se i 11 Se a 6 in a 1:1 ratio (for details of the i-and a-type ligand notation, see: Schäfer & von Schnering (1964)). Both cluster units are interconnected through additional Mo-Se bonds ( Figs. 1 and 2). The first unit can be described as an Mo 6 octahedron surrounded by eight face-capping inner Se i and six apical Se a ligands. The Mo 9 cluster is surrounded by 11 Se i atoms capping one or two faces of the bioctahedron and six Se a ligands above the apical Mo atoms. The Mo 6 Se i 8 Se a 6 and Mo 9 Se i 11 Se a 6 units are centered at Wyckoff positions 2b and 2c and have point-group symmetry 3 and 6, respectively. The Mo-Mo distances within the Mo 6 cluster are 2.6992 (7) Å for the distances of the Mo triangles formed by the Mo1 atoms related through the threefold axis, and 2.7223 (8) Å for the distances between these triangles. The Mo-Mo distances within the Mo 9 clusters are 2.6474 (7) and 2.7056 (10) Å in the triangles formed by the atoms Mo2 and Mo3, respectively, and 2.7136 (5) and 2.7557 (5) Å for those between the Mo2 3 and Mo3 3 triangles. The Se atoms bridge either one (Se1, Se2, Se4 and Se5) or two (Se3) triangular faces of the Mo clusters. Moreover, atoms Se1 and Se2 are linked to an Mo atom of a neighboring cluster. The Mo-Se bond lengths range from 2.5467 (7) to 2.6378 (7)  flowing gas at 1273 K during ten hours in order to eliminate any trace of oxygen. The binaries V 2 Se 3 , MoSe 2 , InSe were obtained by heating stoichioetric mixtures of the elements in sealed evacuated silica tubes during about 2 days. All handlings of materials were done in an argon-filled glove box. The initial mixture (ca. 5 g) was cold pressed and loaded into a molybdenum crucible, which was sealed under a low argon pressure using an arc welding system. The charge was heated at the rate of 300 K/h up to 1773 K, the temperature which was held for 48 hours, then cooled at 100 K/h down to 1373 K and finally furnace cooled.

Refinement
The highest peak and the deepest hole are located 1.56 Å and 0.66 Å from Mo3, respectively. Refinement of the occupancy factors of the V and In atoms led to the final composition V 1.42 (2) In 1.832 (8) Mo 15 Se 19 . Fig. 1

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.