Synthesis, structure and spectroscopic characterization of sodium tetrabutylammonium tris(thiobenzilato)-molybdate(IV)

Abstract

The synthesis, structure and spectroscopic properties of the mixed salt [NBuⁿ₄]Na[Mo{O₂CC(S)Ph₂}₃]·H₂O·MeOH are reported. It crystallizes in the space group Pbca, with a= 19.369(6), b= 25.175(6), c= 24.273(6)Å, and Z= 8. The molybdenum atom is six-co-ordinated and bonded to both the thiolate sulfur and carboxylate oxygen atoms of each of the three co-ordinated thiobenzilate ligands. The average Mo–S and Mo–O distances are 2.291(4) and 2.076(9)Å, respectively, the former being the shortest observed for any tris(chelate)molybdenum complex. Contrary to the result predicted from previous molecular orbital calculations, the co-ordination polyhedron around the molybdenum atom is essentially trigonal prismatic. The two triangular faces, formed by three sulfur and three oxygen atoms from the thiolate and carboxylate groups, respectively, are nearly parallel and twisted by ca. 4.7° with respect to a regular prism. Sodium cations are intercalated between Mo(S₃O₃) units and are also subject to a trigonal-prismatic co-ordination by three carboxylate oxygen atoms, two water and one methanol molecule. Cyclic voltammetry indicates that [Mo{O₂CC(S)Ph₂}₃]^2– undergoes a reversible one-electron oxidation to [Mo{O₂CC(S)Ph₂}₃]^– at –0.26 V (ESR parameters 〈g〉= 1.968, 〈A〉= 36 × 10^–4 cm^–1). The latter species can also be generated in solution by chemical oxidation.