PHOSPHORESCENCE AND ZERO-FIELD OPTICALLY DETECTED MAGNETIC-RESONANCE STUDIES OF (ND)10 TRANSITION-METAL COMPLEXES .1. ZNX2(PHEN) (X=CL, BR, I)

In order to elucidate the effect of (nd)10 central metal ions on the properties of the low-lying excited states of metal complexes, spectroscopic and optically detected magnetic resonance studies on the phenanthroline (phen) localized 3pi-pi* States of ZnX2(phen) (X - Cl, Br, I) were carried out. Comparison of the properties of the spin sublevels of ZnX2(phen) with those of the uncoordinated 1,10-phenanthroline yielded several noteworthy features: (a) the phosphorescence spectra of ZnX2(phen) complexes very closely resemble that of the uncoordinated phen molecule, (b) the magnitudes of the zero-field splittings follow the ordering phen > ZnCl2(phen) > ZnBr2(phen) > ZnI2(phen), and (c) the x sublevel (out-of-plane component) is the dominant decay channel in ZnX2(phen) replacing the z sublevel (in-plane component) as the dominant decay channel in uncoordinated phen. These experimental results have been interpreted systematically and satisfactorily by a model invoking Heitler-London type mixing of LLCT (halogen p-orbitals to phen charge transfer) electronic configurations with the phen locally excited electronic configuration.