New aspects of rhodium(III)–dimethyl sulfoxide chemistry: synthesis and molecular structure of [NEt4][cis-RhCl4{(CH3)2SO}2] and chemical behaviour in aqueous solution of [RhCln{(CH3)2SO}6–n]3–n(n= 3 or 4) complexes

Abstract

A careful reinvestigation of the synthesis of the long known complex [H(dmso)₂][trans-RhCl₄(dmso-S)₂]2a has resulted in the isolation of the unprecedented cis isomer [H(dmso)₂][cis-RhCl₄(dmso-S)₂]2b. The new isomer has been characterized spectroscopically and the crystal structure of the anion determined as the tetraethylammonium salt. Crystal data: monoclinic, space group P2₁/c, Z= 4, a= 10.500(4), b= 17.054(3), c= 13.304(5)Å, β= 114.19(2)°. As in the case of the neutral isomers, mer,cis- and mer,trans-[RhCl₃(dmso-S)₂(dmso-O)]1a and 1b, respectively, the anionic trans derivative is thermodynamically unstable and isomerizes to the cis isomer in dmso solution with first order kinetics; the reverse cis to trans isomerization is promoted by visible light. A comparative investigation of the chemical behaviour of the two pairs of isomers 1 and 2 in aqueous solution, determined by ¹H and ¹³C NMR spectroscopy, has also been carried out. In both cases dissociation of the ligand trans to an S-bonded dmso ligand is the first step.