PERIPHERAL BONDING OF MERCURY(II) IODIDE TO TRINUCLEAR MOLYBDENUM-SULFUR-DITHIOPHOSPHINATO CLUSTERS - [MO3S4(R2PS2)4HGI2] (R = ET, PR)

Reaction of Mo3S4(R2PS2)4 1 (a: R = Et, b: R = Pr) with HgI2 in THF yields the diamagnetic title complexes [Mo3S4(R2PS2)4HgI2]3. The crystal structure of [3a (H2O)] . 2CH2Cl2 shows the complexes to consist of a triangular array of Mo atoms which are bridged by mu2-S atoms and capped by a mu3-S atom. Each of the Mo atoms is chelated by a dithiophosphinato ligand Et2PS2- and in addition two Mo atoms are bridged by a Et2PS2- ligand while the H2O molecule is bonded weakly to the third Mo atom. Thus, all Mo atoms reveal a distorted octahedral coordination sphere. HgI2 is ''peripherally'' bonded to the cluster via two S atoms, one of which belongs to a chelating ligand and the other one to the bridging ligand. Space group P1BAR, lattice constants a = 12.157(2), b = 15.284(3), c = 16.049(3) angstrom, alpha = 115.56(1), beta = 107.35(1), and gamma = 94.62(1)degrees; Z = 2, d(calc) = 2.23 mg/mm3; 4236 observed reflections, R = 0.068. In organic solvents complexes 3 are strong electrolytes. VT-P-31 NMR data suggest a stepwise dissociation of 3 with formation of [Mo3S4(R2PS2)3]+[(R2PS2)HgI2]- and elimination of the bridging ligand from the cluster.