After the profoundly experimental and theoretical investigations of the binuclear metallocenes, we prospected a new series of sandwich compounds, C6H6-M-M-C6H6 (M = Co, Ni, and Cu) using density functional theory. The cobalt complex has the stable coaxial structures, while the nickel and copper complexes have the new stable ones with the metal atom eta(2) bonding to the benzene ring. NBO analyses show that there exits a clear triple bond between the two cobalt atoms, and a single bond between the other two metal atoms in their complexes. For the cobalt complex, the multilayer sandwich clusters have also been studied. (c) 2006 Elsevier B.V. All rights reserved.