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 M2L(NO3)4·2CH3OH·nH2O (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 [Ni2L(H2O)4](NO3)4· 2H2O (5) was also prepared and its crystal structure determined. 5 is monoclinic, space group P21/n, a = 11.831(8), b = 12.168(8), c = 12.329(7) A ̊, β = 114.26(5)°, Z = 2. In the cyclic ligand 3, the pyridine-1-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 -2JS1·S2: J = - -1.15, -5.0, -15.5 and +3.3 cm-1, respectively. These values are discussed in terms of the contributing orbital pathways. © 1995.



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