Stereochemistry and electrochemical properties of molybdenum ions incorporated into S-bridged polynuclear structures

Abstract

The reactions of fac(S)-[M(aet)₃] (M = Ir^III or Rh^III; aet = 2-aminoethanethiolate) with [NH₄]₂[MoCl₅(H₂O)] in both anaerobic and aerobic atmospheres gave linear-type S-bridged trinuclear complexes, [Mo^IV{Ir(aet)₃}₂]⁴⁺1 and [Mo^III{Rh(aet)₃}₂]³⁺2. Complex 2 was spontaneously oxidized by exposure to air and converted into a novel S-bridged pentanuclear complex, [Mo^V₂O₂(μ-O){Rh(aet)₃}₃]⁴⁺3, and the structural change from 2 to 3 was monitored by UV-vis spectroscopy. The crystal structures of 1Br₄·4H₂O, 2Br₃·H₂O, and 3Br₄·6H₂O were determined by X-ray diffraction. In the complex cations 1 and 2, Mo⁴⁺ and Mo³⁺ ions are co-ordinated by the six thiolato sulfur atoms from two fac(S)-[M(aet)₃] units and relatively short metal–metal distances (2.7469(7) and 2.860(3) Å) are observed, respectively. In 3 the Mo–O–Mo angle (157.0(4)°) in the Mo₂O₂(μ-O)⁴⁺ core is unique and the core is co-ordinated by the eight thiolato sulfur atoms of three fac(S)-[Rh(aet)₃] units. The cyclic voltammograms for 1 and 2 indicate that the oxidation states of the molybdenum ions, which are incorporated into the S-bridged polynuclear structures, and stability of the complexes, depend upon the metal ions in the terminal building blocks, fac(S)-[M(aet)₃]. The absorption spectrum of each complex exhibited characteristic intense bands in the visible region, which relate to the molybdenum ions.