N–N Bridged dinuclear complexes with Mn(ii), Ni(ii), Cu(ii), Zn(ii) and Cd(ii); examples with antiferromagnetic and ferromagnetic coupling

Abstract

A series of new complexes of some bis-bidentate N₄ ligands [picolinamide azine (pahap), 2-pyrazinecarboxamide azine (pzhpz) and butanedione-monoxime picolinamide hydrazone (pahox)], based on a rotationally flexible N–N bridging unit, with Mn(II), Ni(II), Cu(II), Zn(II) and Cd(II) is reported. 2 ∶ 2 (M ∶ L) ratio complexes with Mn(II) and Cd(II), in which anionic ligands (Cl⁻, NO₃⁻) are bonded to the metals, have large >80° M–N–N–M torsional angles, indicating `open' dinuclear structures. With weakly or non-coordinating anions (e.g. ClO<sub>4</sub><sup>−</sup>, ZnBr<sub>4</sub><sup>2−</sup>) 2 ∶ 3 complexes are formed with smaller torsional angles (39–43°) in keeping with the presence of three N–N bridges and `closed' spiral structures. Antiferromagnetic exchange is observed bewteen Mn(II) and Ni(II) centres in both types of complex, whereas with Cu(II) small Cu–N–N–Cu angles lead to dominant ferromagnetic exchange coupling. Structural and magnetic data are discussed.