Potential constants of Co(CO)3 NO from vibrational spectra of six isotopic species

Infrared and Raman spectra are reported for $\mathrm{Co}{(}^{12}{\mathrm{C}}^{16}\mathrm{O}{)}_3^{14}{\mathrm{N}}^{16}\mathrm{O},\mathrm{Co}{(}^{12}{\mathrm{C}}^{16}\mathrm{O}{)}_3^{15}{\mathrm{N}}^{18}\mathrm{O},\mathrm{Co}{(}^{12}{\mathrm{C}}^{18}\mathrm{O}{)}_3^{14}{\mathrm{N}}^{16}\mathrm{O},\mathrm{Co}{(}^{12}{\mathrm{C}}^{18}\mathrm{O}{)}_3^{15}{\mathrm{N}}^{18}\mathrm{O},\mathrm{Co}{(}^{13}{\mathrm{C}}^{16}\mathrm{O}{)}_3^{14}{\mathrm{N}}^{16}\mathrm{O}$ , and $\mathrm{Co}{(}^{13}{\mathrm{C}}^{16}\mathrm{O}{)}_3^{15}{\mathrm{N}}^{18}\mathrm{O}$ . All fundamentals have been assigned and anharmonicity corrections have been estimated for the C–O and N–O stretching frequencies. General quadratic potential constants have been calculated by constraining many of the interaction constants to values estimated from analogous constants of nickel carbonyl. Compared with $\mathrm{Ni}(\mathrm{CO}{)}_4,\mathrm{Co}(\mathrm{CO}{)}_3\mathrm{NO}$ exhibits slightly stronger backbonding of the metal d electrons to the carbonyl group. The NO, CoN interaction is surprisingly small, indicating that the effects of changes in pi backbonding and in Co–N sigma bonding nearly cancel each other.