Two novel cyclic dimer M2L2 complexes constructed from 2-[(4-carboxyl)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3 oxide: Crystal structure and magnetic properties

Two novel complexes derived from 2-[(4-carboxyl)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxy-3-oxide (NITPBAH), [Mn(hfac)(2)(NITPBAH)](2) (1) and [Co(hfac)(2)(NITPBAH)](2) (2) (hfac = hexafluoroacetylacetonate), have been synthesized as well as characterized structurally and magnetically. The X-ray crystal structure analyses show that the structures of the two compounds are isomorphic and both consist of cyclic dimer units bridged by NITPBAH ligands, in which metal ion Mn(II) or Co(II) is coordinated by four oxygen atoms from two hfac ligands, one oxygen atom from nitronyl nitroxide and one oxygen atom from carboxyl group of another radical ligand. The magnetic studies show that the manganese(II) or cobalt(II) ion strong antiferromagnetically interacts with the directly coordinated nitroxide group. There exists a weak antiferromagnetic coupling between the metal ion and the nitroxide through phenyl ring and carboxyl group of the radical ligand, which is agreement with spin polarization mechanism. (C) 2012 Elsevier Ltd. All rights reserved.