Chelation of a diphosphine ligand at FeCo2(CO)(9)(mu(3)-S): Spectroscopic and X-ray diffraction data for FeCo2(CO)(7)(bpcd)(mu(3)-S)

The tetrahedrane cluster, FeCo2(CO)(9)(mu(3)-S), reacts with the redox-acti ve ligand, 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd), to gi ve the disubstituted cluster, FeCo2 (CO)(7)(bpcd)(mu(3)-S), as the sole pro duct. This diphosphine-substituted cluster contains a cobalt-bound, chelati ng bpcd ligand. Both IR and P-31 NMR spectroscopies have been employed in t he solution characterization of FeCo2(CO)(7)(bpcd)(mu(3)-S), and the solid- state structure has been unequivocally established by X-ray diffraction ana lysis, FeCo2(CO)(7)(bpcd)(mu(3)-S) crystallizes in the monoclinic space gro up C2/c, a = 34.494(3) Angstrom, b = 11.4194(9) Angstrom, c = 18.634(2) Ang strom, beta = 98.103(7)degrees, V = 7266.7(9) Angstrom(3), Z = 8, and d(cal c) = 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 re dox couples has been examined by carrying out extended Huckel MO calculatio ns on the model complex FeCo2(CO)(7)(H-4-bpcd)(mu(3)-S), with the results b eing compared to related cluster compounds.