VIBRATIONAL-SPECTRA AND STRUCTURE OF STAIRCASE CARBONYL PI-COMPLEXES OF TRANSITION-METALS .1. ELECTRONIC EFFECTS

FTIR spectra have been studied for ''staircase'' cyclopentadienyl comp lexes comprising two or three metal carbonyl fragments bound by the me tal-carbon bond Cp(CO)(2)Fe-CpmMn(CO)(3) (1), Cp(CO)(2)Fe-CpmFe(CO)(2) CH(2)Ph (2), Cp(CO)(2)Fe-Cpm(CO)(2)Fe-CpmMn(CO)(3) (3), Cp(CO)(2)Mo-Cp m(CO)(2)Fe-CpmMn(CO)(3) (4), Cp(CO)(3)W-Cpm(CO)(2)Fe-CpmMn(CO)(3) (5), Cp(CO)(2)Fe-Cpm(CO)(2)Fe-BmCr(CO)(3) (6), Cr(CO)(3)Bm-CpmFe(CO)(2)CH( 2)Ph (7), where Cp = eta(5)-C5H5, Cpm = eta(1):eta(5)-C5H4, Bm = eta(1 ):eta(6)-C6H5, as well as mononuclear model complexes Cp(CO)(2)Fe(CH)( 2)Ph (8), CpMn(CO)(3) (9), and (eta(6)-C6H6)Cr(CO)(3) (10). The spectr a were interpreted on the basis of the local symmetry of each metal ca rbonyl center. The positions of vCOs are determined by the mutual elec tronic effect of each center. CpmM(CO)(n) groups are strong electron a ccepters and cause an increase in vCOs of adjacent M(CO)(n) groups. Cp (CO)(n)M groups, being electron donors, cause a decrease in the freque ncies of neighboring groups. In trinuclear complexes, the frequencies of the central Fe(CO)(2) group are not changed much due to the compens ation of donor and acceptor influences of two neighboring substituents .