A One-Dimensional Helical Copper(II) Imino Nitroxide

The reaction of [CuI(CH3CN)4](PF6) with a biradical of imino nitroxide in methanol yielded a copper(II) complex [CuII(imapy)](PF6) (2) (Himapy = 2-(1‘-oxy-4‘,4‘,5‘,5‘-tetramethyl-4‘,5‘-dihydro-1‘H-imidazol-2‘-yl)-6-(1‘‘-oxyl-4‘‘,4‘‘,5‘‘,5‘‘-tetramethyl-4‘‘,5‘‘-dihydro-1‘‘H-imidazol-2‘‘-yl)pyridine)). In 2 one of the nitroxides in the ligand was reduced to a hydroxyamino anion and the CuI ion was oxidized. Complex 2 crystallizes in tetragonal space group P43212 with a = 14.341(3) Å, c = 24.282(5) Å, V = 4993(1) Å3, and Z = 8, and the absolute structure for this crystal was determined by using Flack's parameter. Square planar coordination sites of the CuII ion are occupied by two nitrogen and two oxygen atoms, where one of the coordinated oxygen atoms comes from the hydroxyamino group in the next molecule. The CuII ions are bridged by the imino−hydroxyamino anion to form a one-dimensional structure with each CuII ion having the coordinated imino nitroxide. Complex molecules locate on the 4-fold screw axis, which results in a counterclockwise helical arrangement of the imino nitroxides. Magnetic susceptibility measurements revealed that antiferromagnetic interactions are operative. The system was treated as the one-dimensional chain of the CuII−radical species, and coupling constants J 1 and J 2 for the intrachain and CuII−radical interactions were estimated to be −6 and −23 cm-1, respectively.