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
crystallize in a trigonal space group

. The crystallographic parameters are C11H15Br2CuN4O2·0.3H2O, a =
28.172(2), c = 12.590(2) Å, V = 8653(2) Å3, and Z = 18 for 1, and C11H15Cl2CuN4O2·0.3H2O, a = 28.261(2),
c = 12.378(1) Å, and Z = 18 for 2. The hexanuclear arrays construct a perfect column perpendicular to the
molecular plane. The diameter of the resultant honeycomblike channel is ca. 11.5 Å defined by the interatomic
distance of two opposing copper ions. Their magnetic behavior is interpreted as the simultaneous presence of
ferro and antiferromagnetic couplings. The ferromagnetic couplings are attributed to the interactions between a
copper spin and the axially coordinated nitronyl nitroxide spin and between nitronyl nitroxide groups through
van der Waals contacts. The antiferromagnetic coupling is due to the interaction between copper ions across the
pyrimidine bridges.