Coordination chemistry of molybdenum with novel thiolate ligands. The crystal and molecular structures of a binuclear complex with a MoMo triple bond [Mo2(SC6H4oPPh2)3Cl3] and of [Mo(SC6H3-2-SiMe3-6-P(O)Ph2)2Cl2], a species exhibiting [MoO2S2Cl2] coordination