Charge density in the [Mo(NCS)6]3– ion in Cs3Mo(NCS)6

Abstract

High-quality X-ray data sets were collected on the new and simple molybdenum(III) complex Cs₃Mo(NCS)₆ at 295 and 115 K. The 1 102 unique data at 115 K were analysed using a multipole model of the charge density to give R(I) 0.015, χ² 1.38. The structure consists of [Mo(NCS)₆]^3– octahedra compressed down a three-fold axis along c. There is disorder over the two equivalent rotations of the octahedron about c. Deformation density maps show strong peaks at the Cs and Mo positions which probably arise from the disorder and/or anharmonic thermal motion. A valence-orbital analysis of the data restricted to (sin θ)/λ < 7 nm^–1 because of the disorder/anharmonicity is able to define the covalent charge transfers to and from the Mo atom and within it, the NCS group, and the Cs atoms. The Mo configuration is 4d^2.5(3) 5(s/p)^2.0(4), with a strong contraction of the 4d radius, to about 2/3 of the free-ion value. The high diffuse population and 4d orbital contraction are believed to reflect high covalence in the bonding to the NCS^– ion, which has comparable σ-donation and π-back-bonding components. The electronic structure of the NCS^– ion is well defined and shows good agreement with an ab initio calculation. The magnetic susceptibility of the compound shows evidence of substantial magnetic exchange [θ=–20.1(l) K] and a pathway for this is provided by the close intermolecular S ⋯ S contacts.