Mixed-ligand tris chelated complexes of Mo(IV) and W(IV): a comparative study

Two hitherto unknown mixed-ligand tris chelated complexes containing 2-aminothiophenolate, [Et<SUB>4</SUB>N]<SUB>2</SUB>[M<SUP>IV</SUP>(NH-(C<SUB>6</SUB>H<SUB>4</SUB>)-S)(mnt)2] (M=Mo, 1a; W, 2a) and two mixed-ligand tris chelate complex containing N,N-diethyldithiocarbamate, [Et<SUB>4</SUB>N]<SUB>2</SUB>[M<SUP>IV</SUP>(Et<SUB>2</SUB>NS<SUB>2</SUB>)(mnt)<SUB>2</SUB>] (M=Mo, 1b; W, 2b) have been synthesized and characterized structurally. Although these complexes are supposed to be quite similar to the well-known symmetric tris chelate complexes of maleonitriledithiolate (mnt), [Et<SUB>4</SUB>N]<SUB>2</SUB>[M<SUP>IV</SUP>(mnt)<SUB>3</SUB>] (M= Mo, 1c; W, 2c), but display both trigonal prismatic and distorted trigonal prismatic geometry in their crystal structure indicating the possibility of an equilibrium between these two structural possibilities in solution. Unlike extreme stability of 1b, 2b, 1c and 2c, both 1a and 2a are highly unstable in solution. In contrast to one reversible reduction in case of 1b and 2b, 1a and 2a exhibited no possible reduction up to &#8722;1.2 V and two sequential oxidation steps which have been further investigated with EPR study. Differences in stability and electrochemical behavior of 1a, 1b, 2a and 2b have been correlated with theoretical calculations at DFT level in comparison with long known 1c and 2c