Metal-nitroxyl interactions. 23. Dinitroxyl adducts of paramagnetic metal complexes

Abstract

The characteristic EPR spectrum of a nitroxyl biradical with intermediate electron-electron exchange, changed to a three-line mononitroxyl EPR spectrum upon coordination of a nitroxyl oxygen to the spin- 1 2 metal complexes Cu(tfac) 2 Cu(hfac) 2, VO(tfac) 2, or VO(hfac) 2. Similar behavior was observed for a nitroxyl biradical with large electron-electron exchange when a nitroxyl oxygen was coordinated to VO(tfac) 2 or VO(hfac) 2. One electron from the dinitroxyl couples with the metal unpaired electron, yielding a net spin of 1 2 . Thus the dinitroxyl-paramagnetic metal complex becomes a mononitroxyl. Approximate equilibrium constants were obtained for these Lewis acid-Lewis base interactions.