Synthesis, characterization and reactivity of linear-type S-bridged trinuclear complexes containing vanadium(III) ion. Crystal structures of [VIII{M(aet)3}2](ClO4)3 (M = RhIII, IrIII; aet = 2-aminoethanethiolate)†

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Reactions of fac(S)-[M(aet)3] (M = RhIII, IrIII; aet = 2-aminoethanethiolate) with an excess of VCl3 gave linear-type S-bridged trinuclear complexes [VIII{M(aet)3}2]3+ (M = RhIII 1, IrIII 2). The ΔΛ isomers (1a(ClO4)3 and 2a(ClO4)3) were selectively crystallized and their structures were determined by X-ray diffraction. Both the complex cations consist of two terminal fac(S)-[M(aet)3] units and a central vanadium atom, which is situated in an octahedral environment with a VIIIS6 chromophore. The Ir complex 2a was also formed by using VIVOCl2 instead of VIIICl3 in a redox reaction, whereas the Rh complex 1a was not formed by a similar method. The optically active isomer (ΛΛ-1b) of the Rh complex was selectively obtained by using Λ-fac(S)-[Rh(aet)3], and characterized by IR, UV-VIS absorption and CD spectra. All the obtained complexes exhibit a unique strong absorption band at ca. 18 × 103 cm−1. Stability and reactivity relating to V–S bond cleavage for the complexes were investigated using UV-VIS absorption spectroscopic methods. These studies show first order decomposition or metal exchange. While 2a has weaker V–S bonds than 1a (from the X-ray analyses), the former is considerably more stable in water than the latter. Cyclic voltammograms of 1a and 2a in water show only irreversible oxidation and reduction waves including VIV/III and VIII/II processes. The V(III) ions in the S-bridged trinuclear structures exhibit a lower magnetic moment (2.59 μB for 1a and 2.27 μB for 2a) at room temperature than the spin-only value for a d2 electronic configuration.