AB-INITIO CALCULATIONS OF ISOTROPIC HYPERFINE COUPLING-CONSTANTS IN BETA-KETOENOLYL RADICALS

Ab initio unrestricted Hartree-Fock (UHF), unrestricted second-order M oller-Plesset (UMP2) perturbation, unrestricted coupled cluster (UCCD) , and unrestricted quadratic configuration interaction (UQCISD) calcul ations have been performed on the organic radicals CH3, CH3CH2, CH2CHC H2, CH3CHCOO-, HCOCHCOH, CH3COCHCOH, CH3COCHCOCH3, and CH3COC(CH3)COCH 3, using double-zeta and split-valence-plus-polarization basis sets. T hese radicals are derived from common organic ligands and have been ob served in recent experimental work on tris(beta-ketoenolato)cobalt(III ) complexes. Their geometry has been optimized at the UHF level using the two mentioned basis sets. From these calculations, values for the isotropic hyperfine coupling constants at the hydrogen atoms are predi cted and compared with the experimental results. The usefulness of sem iempirical extrapolations based on limited basis sets and treatment of electron correlation effects is carefully analyzed in the examples co nsidered. (C) 1994 John Wiley & Sons, Inc.