Synthesis and structural characterization of some selenoruthenates and telluroruthenates.

The reaction of solid [RuClCp(PPh(3))(2)] with TeSe(3)(2-) or Se(n)(2-) in DMF leads to the formation of RuCp(PPh(3))(mu(2)-Se(2)) (1). In the structure of this compound the two bridging Se(2) groups lead to a six-membered Ru(2)Se(4) ring in a chair conformation. Attached to each Ru center is a PPh(3) ligand in an equatorial position and a Cp ring in an axial position. The compound is diamagnetic. The compound Ru(2)Cp(2)(mu(3)-Se(2))(mu(3)-Se) (2) is obtained under similar conditions in the presence of air. This structure comprises a centrosymmetric Ru(4)Se(6) dimer formed from the two bridging Se groups and the two bridging Se(2) groups. Each Ru center is pi-bonded to a Cp ring. The reaction of solid [RuClCp(PPh(3))(2)] with a Te(n)(2-) polytelluride solution in DMF leads to the diamagnetic compound [(RuCp(PPh(3)))(2)(mu(2)-(1,4-eta:3,6-eta)Te(6))] (3). Here the Ru centers are bound to a bridging Te(6) chain at the 1, 4, 3, and 6 positions, leading to a bicyclic Ru(2)Te(6) ring. Each Ru atom is bound to a Cp ring and a PPh(3) group. This dimer possesses a center of symmetry. The structure of 3 is the first example of a bicyclic complex where fusion occurs along a Te-Te bond. If the same reaction is carried out in DMF/CH(2)Cl(2), rather than DMF, then [(RuCp(PPh(3)))(2)(mu(2)-(1,4-eta:3,6-eta)Te(6))].CH(2)Cl(2) (4) is obtained. In the solid state it possesses the same Ru(2)Te(6) structural unit as does 3, but the unit lacks a crystallographically imposed center of symmetry. The electronic structures of 3 and 4 have been analyzed with the use of first principles density functional theory. Bond order analysis indicates that the Te-Te bond where fusion occurs has a shared bonding charge of about (2)/(3) of that found for Te-Te single bonds.