Synthesis of a mixed cluster/binuclear compound. Electrochemical properties and X-ray diffraction structure of CO3(CO)(9)[mu(3)-CCO2CH2CCH{Co-2(CO)(6)}]

The tetrahedrane cluster Co-3(CO)(9)(mu(3)-CCO2CH2C=CH) reacts with Co-2(CO )(6) to furnish the pentacobalt compound Co-3(CO)(9)[mu(3)-CCO2CH2CCH{Co-2( CO)(6)}] in high yield. Functionalization of the pendant alkyne group by Co 2(CO)6 was ascertained by IR and NMR spectroscopies (H-1 and C-13), and the solid-state structure of Co-3(CO)(9)[mu(3)-CCO2CH2CCH{Co-2(CO)(6)}] was un equivocally established by X-ray diffraction analysis. Co-3(CO)(9)[mu(3)-CC O2CH2CCH {Co-2(CO)(6)}] crystallizes in the triclinic space group <P(1)over bar>, a = 7.9674(5), b = 13.208(1), c = 13.3094(9) Angstrom, alpha = 76.25 7(6), beta = 79.123(6), gamma = 86.403(6)degrees, V = 1335.8(2) Angstrom(3) , Z = 2, and d(calc) = 2.016 g/cm(3). The electrochemical properties of Co- 3(CO)(9)[mu(3)-CCO2CH2CCH {Co-2(CO)(6)}] were examined by cyclic voltammetr y and the first reduction wave was found to be a reversible, one-electron r eduction associated with the tricobalt moiety. No evidence for electronic c ommunication between the Co-3 and Co-2 portions of the complex was observed . The results of extended Huckel MO calculations on Co-3(CO)(9)[mu(3)-CCO2C H2CCH{Co-2(CO)(6)}] establish the nature of the LUMO in Co-3(CO)(9)[mu(3)-C CO2CH2CCH{Co-2(CO)(6)}].