Transition metal complexes with sulfur ligands. 97. Coordinatively and electronically unsaturated and saturated chromium, molybdenum, and tungsten dithiolate complexes of the type [M(CO)3('S2')]2- and [M2(CO)7('S2')]2- {'S2'2- = S2C6R42- (R = H, Cl, Me); S2C2H42-}