Intermolecular Ferromagnetic and Antiferromagnetic Interactions in Halogen-Bridged Copper(I) Imino Nitroxides: Crystal Structures and Magnetic Properties of [CuI(π-X)(imino nitroxide)]2 (X = I or Br)

Abstract

Reaction of CuI or CuBr with some imino nitroxides in methanol gave the halogen bridged dinuclear Cu(I) complexes [Cu(μ-I)(impy)]2 (1), [Cu(μ-I)(immepy)]2 (2), [Cu(μ-Br)(immepy)]2 (3), and [Cu(μ-Br)(imph-NO2)]2 (4), respectively (impy = 2-(2′-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-l-oxyl, immepy = 2-(6′-methyl-2′-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H- imidazolyl-1-oxyl, imph-NO2 = 2-(4′-nitrophenyl)-4,4,5,5-tetramethyl-4,6-dihydro-1H-imidazolyl-1-oxyl). Crystal structures and magnetic properties have been studied. Complexes 1-4 have dimeric structures where two copper ions are doubly bridged by halide ions in μ2 fashion. In 1-3, each copper ion is tetrahedral with a bidentate imino nitroxide and two halide ions, and the two copper ions are separated by 2.592(2), 2.6869(8), and 2.7357(6) Å, respectively. In 4, triangular coordination sites of the copper ions are completed with a nitrogen atom from the imino nitroxide and two bromide ions bridging the two copper ions with a separation of 3.074(2) Å. Ligand imino nitroxides in 1-4 form one-dimensional radical chains, and the chains are linked with halocuprate dimer units. Structural and magnetic susceptibility data support that radicals in 1 and 4 are ferromagnetically stacked, while radicals in 2 and 3 form an antiferromagnetic chain. The magnetic behaviors are discussed in connection with the stacking modes of the radicals and bridging conformations. Crystal data (Mo Ka, A = 0.71069 Å): 1, orthorhombic, space group P212121, a = 17.807(2) Å, b = 8.595(2) Å, c = 19.336(6) Å, and Z = 4; 2, monoclinic, space group P21/c, a = 9.941(2) Å, b = 18.482(2) Å, c = 8.337(2) Å, β= 96.41(2)°, and Z = 2; 3, monoclinic, space group P21/c, a = 9.964(6) Å, b = 18.167(4) A, c = 8.009(7) Å, β= 95.81(6)°, and Z = 2; 4, monoclinic, space group P21/c, a = 11.991(7) Åb= 17.998(8) Å, c = 7.215(6) ̊, beta;= 104.07(6)°, and Z = 2.