LIGAND NUCLEAR HYPERFINE COUPLING CONSTANTS IN VANADYL(4)-AQUO COMPLEX - EVIDENCE FOR METAL-LIGAND PI BONDING

Ligand hyperfine coupling constants in the vanadyl(IV )-aquo complex have been determined from nmr chemical shift studies. The values obtained are (A/h)17o = +(4.4 ± 1.5) × 106 Hz and (A/h)2H = +(4.9 ± 0.8) × 105 Hz. From the latter the proton hyperfine coupling is calculated to be (A/h)1H = + (3.2 ± 0.5) × 106 Hz corresponding to a spin density of (2.3 ± 0.3) X 10-3 on the hydrogen atoms. The results are interpreted in terms of currently accepted schemes of unpaired electron delocalization in transition metal-aquo complexes. It appears that metal-ligand π bonding is the major path of spin delocalization to the four equatorial water molecules in the vanadyl(IV)-aquo complex and that the effective charge of the VO2+ ion with respect to the ligands is greater than that of divalent transition metal ions. © 1969, American Chemical Society. All rights reserved.