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

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The reactions of fac(S)-[M(aet)3] (M = IrIII or RhIII; aet = 2-aminoethanethiolate) with [NH4]2[MoCl5(H2O)] in both anaerobic and aerobic atmospheres gave linear-type S-bridged trinuclear complexes, [MoIV{Ir(aet)3}2]4+1 and [MoIII{Rh(aet)3}2]3+2. Complex 2 was spontaneously oxidized by exposure to air and converted into a novel S-bridged pentanuclear complex, [MoV2O2(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.