A combined electron paramagnetic resonance and Fourier transform infrared study of the Co(C6H6)1,2 complexes isolated in neat benzene or in cryogenic matrixes

The products obtained in the reaction of cobalt atoms in neat benzene or in a benzene/ argon mixture at low temperature have been reinvestigated. At least three cobalt-containing species were detected by IR, namely, Co(C6H6), Co(C6H6)(2), and Co-x(C6H6), x > 1. The IR bands were assigned to these complexes by monitoring their behavior as a function of (a) Co and C6H6 concentration, ( b) isotopic substitution, and ( c) photoirradiation. We were able to analyze the sample in neat benzene by both electron paramagnetic resonance (EPR) and IR spectroscopy and to determine the magnetic parameters ( g tensor and Co hyperfine interaction) for the Co(C6H6)(2) sandwich compound. The large number of fundamental bands observed in the IR spectrum of Co(C6H6)(2), the absorption pattern observed in the Co-ring stretching region of the IR spectrum of the mixed complex, Co(C6H6)(C6D6) and the orthorhombic g-values extracted from the EPR spectrum are most consistent with nonequivalent benzene ligands in Co(C6H6)(2), i. e., C-s symmetry. A bonding scheme consistent with both the EPR and IR data for Co(C6H6)(2) is discussed.