Electron-sponge behavior and electronic structures in cobalt-centered pentagonal prismatic Co11Te7(CO)10 and Co11Te5(CO)15 cluster anions

The novel cluster anion Co(11)Te(5)(CO)15]- (3]-) has been isolated and structurally characterized as part of the salt Cp*(2)Nb(CO)2]3] (Cp* = C(5)Me(5)). The cobalt-centered Co10 pentagonal prism is surrounded by a shell of two mu5-Te, three mu4-Te ligands, and 15 CO groups in terminal, symmetrical, and sigma-semibridging bonding modes. The hybrid carbonyl-telluride character of the ligand shell is reflected in the solid state by a one-dimensional assembly of polyhedral prisms along a backbone of Cp*(2)Nb(CO)2]+ cations. Electrochemical studies reveal the presence of four redox couples of 3]n (n = -1 to -5). The electronic structures of various metal-centered and empty pentagonal-prismatic (PP) M10 clusters (M = Co, Ni) are calculated and compared to those of pentagonal-antiprismatic (PA) M10 structures. Closed-shells of 152 and 156 metal valence electrons, respectively, are found to determine the electronic structures and chemical properties of these geometries. From these considerations, magnetic properties have been predicted. They have been verified for the Co(11)Te(7)(CO)10]- cluster anion, which exhibits a singlet-triplet gap of 0.318 kcal/mol.