Binuclear cyclopentadienylcobalt sulfur and phosphinidene complexes Cp2Co2E2 (EÂ =Â S, PX): Comparison with their Iron carbonyl analogues

Studies on a series of Cp2Co2E2 derivatives (E = S and PX; X = H, Cl, OH, OMe, NH2, NMe2) predict butterfly structures with a Co-Co bond for the “body” to be the lowest energy structures in all cases. Such butterfly structures for Cp2Co2(PX)2 can either be symmetrical singlet diradicals with one X group and a single electron on each phosphorus, or unsymmetrical structures with both X groups on one phosphorus and a lone pair on the other phosphorus. Tetrahedrane and rhombus structures have significantly higher energies than any of the butterfly structures.