Chelation of a diphosphine ligand at FeCo2(CO)9(μ3-S):: Spectroscopic and X-ray diffraction data for FeCo2(CO)7(bpcd)(μ3-S)

The tetrahedrane cluster, FeCo2(CO)(9)(mu(3)-S), reacts with the redox-active ligand, 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd), to give the disubstituted cluster, FeCo2 (CO)(7)(bpcd)(mu(3)-S), as the sole product. This diphosphine-substituted cluster contains a cobalt-bound, chelating bpcd ligand. Both IR and P-31 NMR spectroscopies have been employed in the solution characterization of FeCo2(CO)(7)(bpcd)(mu(3)-S), and the solid-state structure has been unequivocally established by X-ray diffraction analysis, FeCo2(CO)(7)(bpcd)(mu(3)-S) crystallizes in the monoclinic space group C2/c, a = 34.494(3) Angstrom, b = 11.4194(9) Angstrom, c = 18.634(2) Angstrom, beta = 98.103(7)degrees, V = 7266.7(9) Angstrom(3), Z = 8, and d(calc) = 1.584 g/cm(3). Cyclic voltammetric studies on FeCo2(CO)(7)(bpcd)(mu(3)-S) reveal the presence of two quasireversible redox responses assigned to the 0/1(-) and 1(-)/2(-) redox couples. The orbital composition of these redox couples has been examined by carrying out extended Huckel MO calculations on the model complex FeCo2(CO)(7)(H-4-bpcd)(mu(3)-S), with the results being compared to related cluster compounds.