Crystal Spectrum of Chromium Acetylacetonate and the Ligand Field in Trigonal Coordination Compounds

The optical crystal spectrum of chromium acetylacetonate has been measured. The trigonal field splitting K is found to be +530 cm—1. The ionic model can account for the sign of the trigonal field and intensity ratios of Cr(C2O4)3—3 but not of the acetylacetonate. This failure is ascribed to covalency, particularly π covalency in the acetylacetonate ring.