AIC5037 11Divalent 3d metal complexes with nicotinate N-oxide (N-nicO), of the type M(N-nicO)rxHzO (M = Mn-Zn; x = 4 or 5 ) , were synthesized by reaction of the corresponding metal(I1) acetates or ferrous ammonium sulfate with ammonium nicotinate N-oxide. The characterization of the new metal complexes was based on spectral, magnetic, and x-ray powder diffraction studies and their solubility characteristics. These compounds appear to be hexacoordinated, linear, polynuclear complexes of the type [M(N-nic0)2(0H2)2],.mH20 (m = 2n for M = Mn, Fe, Co, Ni, Cu; m = 3n for M = Zn), probably involving double M(N-nicO)zM bridges. The N-nicO ligands coordinate through the N-0 oxygen and one of the COO oxygens, while the other carboxylate oxygen is hydrogen bonded to water. Lattice water is also present in these complexes.Desiccation of the preceding compounds over PzOs, under reduced pressure, leads to their partial or complete dehydration.Under these conditions, only lattice water is eliminated from the Mn(II), Ni(II), and Cu(I1) complexes, without occurrence of any structural change. The Fe(I1) and Co(I1) complexes are completely dehydrated, while the Zn(I1) complex loses the lattice water and one aquo ligand per Zn2+ ion. Co(N-nic0)z seems to maintain coordination number 6, by the function of N-nicO as a tridentate bridging ligand, in a highly cross-linked polymeric structure. Fe(N-nic0)2 and Zn(N-nicO)yHzO appear to be pentacoordinated, comprising chemically nonequivalent carboxylate groups; evidence favors the presence of both bi-and tridentate N-nicO bridging ligands in the Fe(I1) complex and hydrogen-bonding of the uncomplexed COO oxygen of part of the bidentate ligands in the Zn(I1) complex. N-nicO is a ligand of strength about equal to that of picolinate N-oxide.
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