N-N bridged dinuclear complexes with Mn(II), Ni(II), Cu(II), Zn(II) and Cd(II); examples with antiferromagnetic and ferromagnetic coupling

A series of new complexes of some bis-bidentate N-4 ligands [picolinamide a zine (pahap), 2-pyrazinecarboxamide azine (pzhpz) and butanedione-monoxime picolinamide hydrazone (pahox)], based on a rotationally flexible N-N bridg ing 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 degrees M-N-N-M torsio nal angles, indicating `open' dinuclear structures. With weakly or non-coor dinating anions (e.g. ClO4-, ZnBr42-) 2 : 3 complexes are formed with small er torsional angles (39-43 degrees) in keeping with the presence of three N -N bridges and `closed' spiral structures. Antiferromagnetic exchange is ob served 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.