Hexaaquadodeca-μ2-chlorido-octahedro-hexaniobium diiodide

The crystal structure of the cluster complex [Nb6Cl12(H2O)6]I2 is described. The octahedral Nb6 cluster core is coordinated by twelve chlorido and six water ligands. The two iodide ions are not bonded to the cluster unit but are present in the crystal structure as the counter-anion to the cluster cation.

The title compound, [Nb 6 Cl 12 (H 2 O) 6 ]I 2 , consists of the niobium cluster cation [Nb 6 Cl 12 (H 2 O) 6 ] 2+ and two non-coordinating, charge-balancing iodide ions. The edges of the Nb 6 octahedron are bridged by chlorido ligands. Each Nb atom is further coordinated by a water ligand. The cluster cation has a charge of +2, which is balanced by that of two iodide anions.

Structure description
Cluster complexes of transition metals have been an interesting research area for many years (Cotton, 1964;Simon, 1988). Ligand-exchange reactions in solvents have opened up a wide field of new cluster compounds (Lemoine et al., 2019), of which so far iodides have been investigated much less than chlorides.
The title compound crystallizes in the trigonal space group P31m. The asymmetric unit consists of an [NbCl 2 (H 2 O)] 0.5 unit, which is located close to the Wyckoff site 1a with 3m symmetry, and one-sixth of an iodide ion. The Nb 6 unit is a metal atom octahedron with an Nb-Nb bond length of 2.8960 (4) Å . The twelve 2 bridging positions of the inner ligand sphere are occupied by chlorido ligands. An average Nb-Cl bonding length of 2.456 Å and an average Nb-Cl-Nb angle of 72.31 are present. The six positions of the outer ligand sphere are occupied by water ligands, reaching Nb-O bond lengths of 2.250 (2) Å . The structure of the cluster cation and the packing are shown in Figs. 1 and 2. The charge of the two iodide anions are counter-balanced by that of the doubly positive charged cluster cation [Nb 6 Cl 12 (H 2 O) 6 ] 2+ . Based on the ion ratio and Nb-Nb bond lengths of comparable structures, 16 cluster-based electrons (CBE) are present. Even though six water molecules are present per formula unit, hydrogen bonding is essentially not present in crystals of the title compound, because the large iodide anions separate the cluster units such that the shortest OÁ Á ÁO distance is 4.432 (2) Å . The only weak data reports hydrogen-type bonding contact exists between I1 and O1 with an O1-H1AÁ Á ÁO1 distance of 3.501 (1) Å .

Figure 1
Perspective view of the title compound with atom labelling for the asymmetric unit. Displacement ellipsoids are shown at the 50% probability level.

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. The H atom was located in a difference maps, but refined using a riding model with O-H = 0.85 Å and with U(H) = 1.5 U eq (O).