NEW SULFIDO-BRIDGED DINIOBIUM(IV) AND DITANTALUM(IV) COMPLEXES AND A RELATED TETRANUCLEAR TANTALUM(IV) COMPOUND

Designed synthesis has led to the preparation of the compounds M2(mu-S)2Cl4(PMe3)4 (M = Nb, Ta) and an unexpected tetranuclear molecule, Ta4S4Cl8(PMe3)6, has been obtained in small yield. All three compounds have been conclusively identified and structurally characterized. The dinuclear compounds have Nb-Nb and Ta-Ta distances of 2.869(1) and 2.865(1) angstrom, respectively, indicative of single bonds between the metal atoms. Ta4S4Cl8(PMe3)6 has a central pair of Ta atoms bridged by four S atoms (Ta-Ta = 2.891(1) angstrom) with square-antiprismatic eight-coordination on each one completed by two trans Cl2(PMe3)2 sets of ligands. A TaCl2(PMe3) unit is then attached to each central Ta atom (Ta-Ta' = 3.091(1) angstrom) by two of the sulfur atoms and a terminal Cl atom, thus completing octahedral coordination about each Ta' atom.