Four new Cu-coordination compounds based on different nitronyl nitroxide radicals: Structural design and magneto-structural correlations

Four new copper(II) complexes containing different nitronyl nitroxide radicals have been synthesized, characterized structurally and magnetically: [(Cu(hfac)2)3(NITPh-3-Br-4-OMe)2] (1), [(Cu(hfac)2)3(NITPyOMe)2] (2), [Cu(hfac)2(2-QNNN)] (3) and [Cu(hfac)2(NITmNO2)2] (4) (hfac = hexafluoro-acetylacetonate; and NITPh-3-Br-4-OMe = 2-3′-Br-4′-methoxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, NITPyOMe = 2-4′-methoxy-3′-pyridyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide, 2-QNNN = 2-2′-quinolyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, NITmNO2 = 2-(3-nitrophenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide). The X-ray crystal structure analyses show that complexes 1 and 2 have similar centrosymmetric five-spin structures built by three Cu(hfac)2 units bridged by two nitroxide ligands through their NO groups. While complex 3 consists of isolated molecule where the nitronyl nitroxide radical acts as chelating ligand towards copper(II), and complex 4 is a rare mononuclear tri-spin compound, in which central Cu(II) ion is coordinated by two hfac and two NITmNO2 radicals. The variable-temperature magnetic susceptibility studies reveal strong antiferromagnetic interactions between Cu(II) ions and radicals in complexes 1–2, practically diamagnetic in complex 3 and weak ferromagnetic interaction in complex 4.

Graphical abstractFour novel Cu(hfac)2 complexes based on different nitronyl-nitroxide radicals have been synthesized, and steric hinderance greatly affects the structure of complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide