A new approach to predicting the carbonyl stretching frequencies of Co₂(CO)₈ with D₃d symmetry

Abstract

This paper describes a method for determining C-O stretching frequencies of dicobalt octacarbonyl belonging to D₃d point group. The method is based on the variation of fundamental C-O stretching frequencies and C-O stretching force constants of axially substituted X₃MCo(CO)₄ (M=Si, Ge, Sn and Pb; X=Cl, Ph and Et) molecules with the dipole moment of X₃M-Co(CO)₄ bond. Frequencies of a1ɡ⁽¹⁾, a₂ս⁽²⁾ and ℯս modes have been evaluated from the graph of frequency versus dipole moment, and the frequencies of a1g⁽²⁾ and ℯɡ modes determined from the equations derived by using the CO-factored force field. The calculated frequencies have been found to be consistent with the experimental values. With the use of the calculated frequencies, the C-O factored force constants of Co₂(CO)₈ with D₃d symmetry have been calculated. In addition, frequencies of mono-¹³CO substituted species of Co₂(CO)₈ have been estimated and compared with observed frequencies of the species.