Novel square planar copper(II) complexes with imino or nitronyl nitroxide radicals exhibiting large ferro- and antiferromagnetic interactions

This paper reports the synthesis, crystal structures, and magnetic properti es of two copper(II) complexes (1, 2) of general formula Cu(tfac)(2)(radica l)(2) (tfac = trifluoroacetate; radical = (1) 2-phenyl-4,4,5,5-tetramethyli midazoline-1-oxyl-3-oxide (NITPh) or (2) 2-phenyl-4,4,5,5-tetramethyl-4,5-d ihydro-1H-imidazoline-1-oxyl (IMPh)). They crystallize in the monoclinic P2 (1)/n space group with the following parameters: (1) a = 13.212(2) Angstrom , b = 9.136(1) Angstrom, c = 15.587(2) Angstrom, beta = 114.61(1)degrees, Z = 2; (2) a = 11.059(2) Angstrom, b = 15.289(1) Angstrom, c = 10.694(2) Ang strom, beta = 114.20(1)degrees, Z = 2. In both complexes the copper(II) ion is coordinated to two radicals in a slightly distorted square planar surro unding. The copper(II)-radical exchange couplings are antiferromagnetic for the nitronyl nitroxide (NITPh) complex (1) and ferromagnetic in the case o f the imino nitroxide (IMPh) analogue (2). The ground state has been found to be a spin-doublet for 1 and the spin-quartet for 2. No thermal populatio n of the highest states has been observed, indicating copper(II)-radical co uplings of \J \ > 500 cm(-1).