The calculation of energy-factored force constants for fac‑Re(CO)3(N‑N)(X) molecules and related complexes

Abstract

Our recently published "silent-CO" method is employed to enable energy-factored force fields (EFFF) to be estimated accurately for molecules of the type fac‑Re(CO)3(N‑N)(X), [fac‑Re(CO)3(N‑N)(L)]+ and [Re(CO)4(N‑N)]+ where there are fewer ν(CO) frequencies than force constants in the force field (where N‑N is a bidentate diimine ligand or similar, X is a halogen or pseudo-halogen and L is a ligand such as a phosphine or similar).The validity and reliability of the general method was tested on the accurately known force field of fac‑Re(CO)3(4,4'‑bpy)(Cl) and another set of Cs tricarbonyls, ten Fe(CO)3(diene) compounds, for which there exist force fields determined by 13CO substitution. The r.m.s. error in the force constants was under ±4 Nm-1 in both stretching force constants and interaction constants.Over 100 spectra have been re-examined to produce force constants for a range of rhenium tricarbonyl and tetracarbonyl species.