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

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 nu(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 C-s tricarbonyls, ten Fe(CO)(3)(diene) compounds, for which there exist force fields determined by (CO)-C-13 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.