LEWIS ACIDITY OF BIS(1,1,1,5,5,5-HEXAFLUOROPENTANE-2,4-DIONATO)OXOVANADIUM(IV) - SPIN PAIRING OF ELECTRONS IN THE 2,2,6,6-TETRAMETHYLPIPERIDINYL-N-OXY ADDUCT

Thermodynamic data for the reaction of the title Lewis acid with several Lewis bases is presented. Its Lewis acidity is interpreted in terms of its EKand CAparameters and is compared to that of other transition metal ion complexes. As was the case with the analogous Cu(II) complex, large donor atoms such as sulfur experience flanking-atom charge repulsion with this acid. In the adduct with the free radical base TMPO, a strong exchange interaction occurs between the odd electrons on the metal and the nitroxide. This spin pairing does not make a contribution to the measured enthalpy of adduct formation. The relevance of this conclusion to the general problem of describing antiferromagnetically coupled systems is discussed. © 1979, American Chemical Society. All rights reserved.