The Infrared Spectra and Normal Coordinate Treatments of X3M–Mn(CO)5(X=Cl, Br, and I; M=Si, Ge, and Sn). II.

Abstract

Abstract The infrared absorption spectra (2200–50 cm−1) have been measured for four metal-metal bonded molecules, Cl3Si–Mn(CO)5, Cl3Ge–Mn(CO)5, Br3Ge–Mn(CO)5, and I3Sn–Mn(CO)5. Vibrational normal coordinate analyses have been made for each of these molecules on the basis of a modified Urey-Bradley force-field. The calculated frequencies agree closely with validly-assigned frequencies. The metal-metal stretching force constant, K(M–Mn), or the F-matrix element, f(M–Mn), varies with the halogen atom, and increases as the electronegativity of X increases. The force constant, K(M–Mn), or f(M–Mn) depends also on the IVb metal atom, and increases in the order of: K(Si–Mn)≥K(Ge–Mn)>(Sn–Mn), or f(Si–Mn)≥f(Ge–Mn)>f(Sn–Mn). However, there is no clear relationship between the electronegativity of M and the K(M–Mn) or (M–Mn). These dependences of K(M–Mn) or f(M–Mn) on X and M are discussed, along with the bonding implications of the M–Mn bonds, on the basis of the sets of the force constants, or the sets of the F-matrix elements, and are interpreted in terms of the predominant σ-bonding framework of the M–Mn bonds.