MAGNETIC-PROPERTIES OF BINUCLEAR MANGANESE(II), COBALT(II), NICKEL(II) AND COPPER(II) COMPLEXES OF A MACROCYCLIC LIGAND DERIVED FROM PYRIDINE-N-OXIDE, AND CRYSTAL-STRUCTURE OF THE NICKEL-COMPLEX

The preparation of complexes M(2)L(NO3)(4) . 2CH(3)OH . nH(2)O (4a-d) (M = Mn, Co, Ni, Cu; L=C18H22N6O4 (3); n = 0.5 or 1) from pyridine-1-oxide-2,6-dialdehyde, 1,2-diaminoethane and the metal(II) nitrate is reported. The complex [Ni(2)L(H2O)(4)](NO3)(4) . 2H(2)O (5) was also prepared and its crystal structure determined. 5 is monoclinic, space group P2(1)/n, a = 11.831(8), b = 12.168(8), c = 12.329(7) Angstrom, beta = 114.26(5)degrees, Z = 2. In the cyclic ligand 3, the pyridine-l-oxide rings are linked by CH(OH).NH.(CH2)(2).N:CH groups, showing that partial hydrolysis of the expected Schiff-base ligand has occurred during synthesis of the complex. In the centrosymmetric complex 5, the Ni2+ ions are bridged in a planar Ni2O2 unit by the N-oxide oxygen atoms, the ligand adopting a non-planar 'stepped' conformation with pyramidal stereochemistry at the bridging O atoms. Six-fold coordination of each Ni2+ ion is completed by two N atoms and two cis water molecules. The magnetic susceptibilities of 4a-d were measured between 5 and 300 K and analysed to obtain values of the parameter J in the exchange Hamiltonian -2JS(1) . S-2: J = -1.15, -5.0, -15.5 and +3.3 cm(-1), respectively. These values are discussed in terms of the contributing orbital pathways.