Structure and redox properties of the molybdenum(IV) metal cluster K₅[Mo₃S₄(CN)₉].7H₂O

Abstract

The anionic molybdenum(IV) cluster [Mo₃S₄(CN)₉]^5- has been subjected to X-ray crystal structure analysis. The potassium salt crystallized in the triclinic space group P1, a 10.634(1), b 11.888(3), c 24.892(2) Å, α 89.56(2), β 79.86(1), γ 76.53(2)º, Z 4. The three Mo^IV atoms in each unit of approximately CSL_3v symmetry are situated at the corners of an equilateral triangle with Mo-Mo distance 2.765(7) Å. There are three S²- ligands bridging between pairs of Mo atoms, and a unique S²- ligand located uniformly above the plane of the equilateral triangle. Distorted octahedral coordination of each Mo^IV is completed by three CN- ligands to each of the three metal centres. The ion is structurally similar to the [MO₃S(S₂)₆]^2- precursor, and to [Mo₃O₄X₉]^n- analogues. In dimethyl sulfoxide, the cluster is irreversibly reduced in a single step near -2 V (v. saturated calomel electrode), but exhibits a quasi-reversible oxidation at + 0.51 V. On the coulometric time scale, the complex is irreversibly oxidized to Mo^V monomer.