IMPACT OF ELECTRON-ELECTRON SPIN-SPIN COUPLING ON ELECTRON-SPIN TURNING ANGLE IN A SPIN-LABELED COPPER(II) COMPLEX

The continuous wave EPR spectrum of copper bis(hexafluoro-acetylacetonate) complexed with 4-((2,2,6,6-tetramethyl-4-piperidinyl-1-oxy)iminomethyl)pyridine in 2:1 toluene:chloroform glass exhibits an electron-electron AB spin-coupled pattern with \J\ = 70 X 10(-4) cm(-1) and interspin distance = 12 Angstrom. In two-pulse field-swept echo-detected spectra, the relative intensities of the inner and outer lines of the AB pattern for this complex are dependent upon incident microwave power because of the dependence of turning angle on effective spin S. This observation confirms the impact of the electron-electron spin-spin interaction on effective S: the inner lines have effective S > 1/2 and the outer lines have effective S < 1/2. (C) 1995 Academic Press, Inc.