THE AFFINITY OF THE VANADYL(IV) ION FOR NITROGEN DONOR LIGANDS

The affinity of the VO2+ ion for nitrogen donor ligands is discussed in terms of predictions made previously. A dual basicity equation predicts logK1(NH3) = 3.0 for VO2+. Equations that model the chelate effect are used to show that this is a reasonable prediction. In accord with experience, the vanadyl ammines should be hydrolyzed in aqueous solution, as should also the ethylenediamine complexes. The formation constants of VO2+ with a variety of more hydrolysis-resistant chelating nitrogen donor ligands, 2,2'-bipyridyl, 1,10-phenathroline, o-aminomethyl-pyridine, 2-(2-pyridyl)-imidazole, N,N,N'N'-tetrakis(2-hydroxypropyl)ethylenediamine, di-2-pyridyl-amine, 2,2',2''-terpyridyl, and picolinic acid, are reported, determined by glass electrode potentiometry. It is shown that these formation constants are consistent with the predicted logK1(NH3) for VO2+, supporting the validity of the dual basicity equation use.