Novel organic–inorganic molecular assembly: a copper(I) and copper(II) mixed-valent cluster with bromide bridges and paramagnetic ligands

Complex pbt2Cu8Br12 [pbt=pyridine-2,6-diylbis(methyleneamino-TEMPO)] was synthesized from CuBr2 and a new ligand pbt, and characterized by means of X-ray crystal structure analysis and magnetic measurements. The centrosymmetric molecule consists of a Cu6Br10 cluster sandwiched with two pbt·CuBr complexes. Detailed geometrical analysis and magnetic analysis reveal the presence of four copper(I) and four copper(II) ions in a molecule. Antiferromagnetic couplings observed can be attributed to the intermolecular radical⋯radical and intramolecular copper(II)⋯copper(II) interactions.