ROLE OF PI-BONDING FOR TRIGONAL LEVEL SPLITTINGS IN CHROMIUM(III) COMPLEXES .4. DOUBLET STATES AND ZEEMAN LEVEL SPLITTINGS IN [CR(BPY)(3)](3+)

A detailed analysis of Zeeman splittings of highly resolved spin-forbi dden transitions in [Cr(bpy)(3)](PF6)(3) is presented. Assignments of vibronic bands are made based on low-temperature absorption, emission, and infrared spectra. The pattern of doublet states, obtained for H = 0 and H = 5 T, is consistent with angular overlap model (AOM) calcula tions, which allow one to consider sigma- and pi-interactions between the metal-d and relevant ligand orbitals and the particular angular ge ometry of the chromoshore simultaneously. The observed level splitting s are found to result from the combined effect of trigonal distortion and contributions of the symmetry adapted d(pi)-orbitals involved due to coupling with corresponding counterparts from the bidentate ligand (phase coupling). The larger splitting of the lowest excited state (2) E(g)(O-h) in the analogous ClO4- salt is due to the more distorted geo metry of the [CrN6] moiety. Related properties of the bipyridine ligan d, which turn out to show donor behavior in the present compounds, and the acetylacetonate ligand are discussed, and AOM parameters for the metal-ligand pi-interaction are correlated with results of MO calculat ions.