Radical-copper wheels: Structure and magnetism of hexanuclear hybrid arrays

Complexation of copper(II) bromide and chloride with 4-pyrimidinyl nitronyl nitroxide (4PMNN) as a bridging ligand gave discrete hexanuclear complexes carrying 12 spins, [CuX2. (4PMNN)](6) [X = Br (1), Cl (2)], which crystall ize in a trigonal space group R-3(-). The crystallographic parameters are C 11H15Br2CuN4O2.0.3H(2)O, a = 28.172(2), c = 12.590(2) Angstrom, V = 8653(2) Angstrom (3), and Z = 18 for 1, and C11H15Cl2CuN4O2.0.3H(2)O, a = 28.261(2 ), c = 12.378(1) Angstrom, and Z = 18 for 2. The hexanuclear arrays constru ct a perfect column perpendicular to the molecular plane. The diameter of t he resultant honeycomblike channel is ca. 11.5 Angstrom defined by the inte ratomic distance of two opposing copper ions. Their magnetic behavior is in terpreted as the simultaneous presence of ferro and antiferromagnetic coupl ings. The ferromagnetic couplings are attributed to the interactions betwee n a copper spin and the axially coordinated nitronyl nitroxide spin and bet ween nitronyl nitroxide groups through van der Waals contacts. The antiferr omagnetic coupling is due to the interaction between copper ions across the pyrimidine bridges.