Reactions of co-ordinated molecules. Part 9. Calculation of carbonyl-stretching force constants of metallo-acetylacetonate molecules: evidence supporting intramolecular π bonding

Abstract

The carbonyl-stretching force constants of three complexes containing the metallo-acetylacetonate moiety, cis-[Al{(OCMe)₂M(CO)₄}₃] and cis-[Re(MeCO ⋯ H ⋯ OCMe)(CO)₄](M = Mn or Re), have been calculated using the Cotton–Kraihanzel approximation. The results permit the assignment of the normal modes of the carbonyl ligands of the metallo-acetylacetonate group to the experimentally observed stretching frequencies. The values of the force constants, k₂, are related to the magnitude of the intramolecular bonding between the two axial-carbonyl ligands and the metallo-acetylacetonate ligand. Laser Raman data are presented to support the band assignment.