Crystal structure and magnetic properties of a copper(II) chloride nitronyl nitroxide complex containing six exchange-coupled S = 1/2 spins

A compound of formula CuCI2(NITpPy),, where NITpPy = 2-(4-pyridyl)-4,4,5,5-tetramethylimidazolinyIl--o xy1 3-oxide, was synthesized. It crystallizes in the triclinic Pi space group with a = 7.301 ( I ) A, b = 12.693 (2) A, c = 14.984 (2) A, a! = 79.79 (I)', 0 = 86.67 (I)', y = 83.92 (I)', and Z = 2. The structure consists of dinuclear [ C U C I ~ ( N I T ~ cPe~nt)ro~s]ym~m etric units. The copper atoms are square-pyramidally coordinated by two nitrogen atoms of the pyridine rings and three chlorine atoms, two of them bridging the copper ions. The N-0 groups of the radicals belonging to different mononuclear units are at a relatively short separation distance. The analysis of the magnetic susceptibility measurements and of the single-crystal EPR spectra at room and liquid-helium temperatures suggests that the six S = spins are antiferromagnetically coupled and that the interaction between copper and radical through the nitrogen of the pyridine ring dominates. The interaction between radicals is also significantly different from zero, and structural-magnetic correlations, based on the overlap of the magnetic orbitals, were attempted.