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.