Spectroscopic and DFT study of tris(beta-diketonato)cobalt(III) complexes

Nuclear magnetic resonance measurements confirm that, as expected, the mer isomer of tris(beta-diketonato) cobalt(III) complexes is more stable (mer isomers are more stable because they are less affected by steric hindrance and they have lower dipoles). An excess of the mer isomer or only the mer isomer is experimentally observed. The existence of both fac and mer isomers is predicted by density functional theory calculations. At room temperature, the nuclear magnetic resonance peaks of phenyl-containing mer complexes are broad due to the intermediate rotation of bulky phenyl groups resulting in only the average orientation of the non-equivalent protons in the mer complexes. However, upon heating to 55 degrees C (thus speeding up the rotation) or cooling to -50 degrees C (slowing down the rotation), this broad peak is resolved into three sets of carbon peaks appearing in the C-13 NMR spectrum, as well as splitting of the H-1 NMR peaks for the non-equivalent protons in the mer isomer. In solid-state C-13 NMR the aromatic rings do not rotate, resulting in the splitting of all the C-13 NMR peaks. Two sets of well-defined peaks are observed for the fluorine-containing compound [Co(CF3COCHCOCPh)(3)] in both the C-13 and F-19 NMR spectra, indicating that both the fac and mer isomers are present with a ratio of fac:mer = 0.1:1. The X-ray photoelectron spectroscopy measured binding energy of the Co(2)p(3/2) photoelectron lines are influenced by the subtle electronic (electron-donating or electron-withdrawing) properties of the R groups on the beta-diketonato ligands. Various relationships are established between the binding energy of Co(2)p(3/2) and several physical and density functional theory-calculated properties, confirming good electronic communication (the measurable electronic effect that a molecular fragment has on the physical properties of another molecular fragment in the molecule) of the substituent groups through the pseudo aromatic system of the beta-diketonato backbones to the metal.