Synthesis and structure of new cobalt-carbonyl complexes containing tellurium atoms

Co-2(CO)(8) and Te2O react to form the well known Co-4(CO)(10)Te-2, Co-4(CO )(11)Te-2 complexes and the two new cluster complexes CCo6(CO)(12)Te-2 (1), and CCo6(CO)(10)Te-2(Te-3) (2). The structures of 1 and 2 were determined by X-ray analysis, together with the triphenylphosphine derivative of 1, CC o6(CO)(11)(PPh3)Te-2 (3), which was analyzed to clarify the disordered stru cture of the parent compound. Complex 1 is formed by a prismatic cluster of cobalt atoms with a carbon embedded in the cage. two tellurium atoms cap t he triangular faces of the prism and each cobalt atom links two terminal ca rbonyl groups. The complex 2 has a similar prismatic cage CCo6; two mu(4)-T e atoms cap two rectangular faces of the prism, while other two Te atoms br idge two edges of the triangular faces and are linked each other through a third Te atom. Electron counting gives for complex 2 92 electrons: the pres ence of two long Go-Co distances suggests that the two excess electrons are located on Go-Co antibonding orbitals. Crystal data for 1, space group C2/ c, a = 12.845(2) Angstrom, b = 13.449(2) Angstrom, c = 13.246(2) Angstrom, beta = 91.95(2)degrees, Z = 4, R = 0.097 for 2555 reflections; for 2, space group Pnna, a = 17.219(5) Angstrom, b = 14.969(6) Angstrom; c = 9.178(4) A ngstrom, Z = 4, R = 0.037 for 3103 reflections; for 3, space group P2(1)/c, a = 9.288(2) Angstrom, b = 14.920(6) Angstrom,= 26.300(9) Angstrom, beta = 99.99(2)degrees, Z = 4, R = 0.037 for 4300 reflections. The vibrational an alysis of the complex 1 was performed and most of the v(CO), v(mu(6)(-)C-Co ), v(Co-Te) and v(Co-Co) modes were assigned. The v(Co-Te) modes were inter preted on the basis of the intermolecular coupling, due to the close contac t between neighboring clusters in one distinct direction in the crystal.