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)

Abstract

Reactions of fac(S)-[M(aet)₃] (M = Rh^III, Ir^III; aet = 2-aminoethanethiolate) with an excess of VCl₃ gave linear-type S-bridged trinuclear complexes [V^III{M(aet)₃}₂]³⁺ (M = Rh^III  1, Ir^III  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 V^IIIS₆ chromophore. The Ir complex 2a was also formed by using V^IVOCl₂ instead of V^IIICl₃ 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 V^IV/III and V^III/II processes. The V(III) ions in the S-bridged trinuclear structures exhibit a lower magnetic moment (2.59 μ_B for 1a and 2.27 μ_B for 2a) at room temperature than the spin-only value for a d² electronic configuration.