EXCHANGE INTERACTIONS IN BIS(HEXAFLUOROACETYLACETONATO)(4-HYDROXY-2,2,6,6-TETRAMETHYLPIPERIDINYL-N-OXY)COPPER(II) - A NITROXYL RADICAL COMPLEX OF COPPER(II)

The single-crystal EPR spectra and the temperature dependence of the magnetic susceptibility of bis(hexafluoroacetylacetonato)(4-hydroxy-2,2,6,6-tetramethylpiperidinyl-N-oxy)copper(II) (Cu(hfac)2(TEMPOL)) were measured. The compound has a linear chain structure, with a TEMPOL ligand bridging 2 Cu(hfac)2 moieties, but the EPR spectra are typical of a triplet state, showing that magnetically the compound is a chain of weakly coupled metal-radical pairs. The magnetic coupling between the 2 spins is ferromagnetic with a single-triplet separation of -13 .+-. 5 cm-1. The single-crystal EPR spectra show that g and D are practically parallel to each other. The principal values are the following: gx = 2.057, gy = 2.013, gz = 2.157, Dx = 88 .times. 10-4 cm-1, Dy = 1140 .times. 10-4 cm-1, Dz = 1052 .times. 10-4 cm-1, with z roughly parallel to the Cu-O(TEMPOL) bond direction. The g tensor was decomposed into the Cu and radical contributions, yielding information on the nature of the magnetic orbital localized on Cu. The 0-field splitting tensor was decomposed into the sum of a dipolar and an exchange component.