Polarized FT-IR Spectra of Transition Metal Carbonyl Complexes Oriented in Nematic Liquid Crystal Solvents

Abstract

The polarized FT-IR spectra of Mn₂(CO)₁₀, M(CO)₆ (M = Cr, W), and CpM′(CO)₃ (Cp = η⁵-C₅H₅; M′ = Mn, Re) dissolved in a nematic liquid crystal solvent (Merck 1132 TNC) have been recorded at room temperature. Definitive vibrational assignments have been made for the CO stretching modes of the complexes on the basis of their observed polarization behavior. For Mn₂(CO)₁₀, assignments are also proposed for MnCO bending modes. The group VIB metal hexacarbonyls are shown to be tetragonally distorted in Merck 1132 TNC. Dichroic spectra were obtained for the CO stretching modes of the CpM′(CO)₃ complexes with the use of both Merck 1132 TNC and Kodak X11643 liquid crystal solvents. The complexes orient perpendicularly to the long axes of the components of the Merck liquid crystal and parallel to those of the Kodak one. The dichroic spectra show that the known distortions of the Cp′ rings in these complexes are apparently accompanied by deformation of the M′(CO)₃ moieties.