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Diazine-bridged coordination polymers of copper and nickel : synthesis and thermal, spectral, structural, and magnetic properties Otieno, Tom


A large number of coordination compounds of copper(I), copper (II) and nickel (II) have been prepared and characterized by thermal, spectroscopic and X-ray diffraction methods as well as by elemental analysis and magnetic susceptibility measurements. The neutral ligands used in the study were pyrazine (1,4-diazine), pyridazine (1,2-diazine), methylpyrazine, 2,5-dimethylpyrazine, pyridine and 4,4'-bipyridine. Anionic ligands of a range of coordinating abilities were employed. These include cyanate, nitrate, methanesulfonate, hexafluoroarsenate, hexafluorophosphate, chloride and thiocyanate anions. Polymeric and mononuclear compounds were isolated. The polymeric materials were found to be of three basic structural types: one-dimensional extended chains, two-dimensional square lattices or infinite three-dimensional lattices. These include the novel copper(I) complexes,[Cu₂(2,5-me₂pyz)₃][PF₆]₂ and [Cu(2,5-me₂pyz)₂][PF₆], which have graphite-related and diamond-related cationic lattices, respectively. Cu(mepyz)₂(NCO)₂, a two-dimensional polymer, represents the first compound containing methylpyrazine to be structurally characterized by single crystal X-ray diffraction. Magneto-structural correlations were made for all the compounds. Whenever possible the magnetic susceptibility data of the complexes were analyzed by theoretical models. The trimeric compound, [Cu(pdz)₂(NO₃)₂]₃, was found to exhibit the largest antiferromagnetic exchange coupling, with a J value of -139 cm⁻¹. The copper ions in another pyridazine complex, Cu(pdz)(NCO)₂, were also found to be strongly coupled antiferromagnetically, with a J value of -44 cm⁻¹. Five nickel compounds, Ni(py)₂(NCS)₂, Ni(py)Cl₂, Ni(pyz)Cl₂, Ni(pyz)(NCO)₂ and Ni(pyz)(NCS)₂, exhibited metamagnetic behaviour. All the other copper (II) and nickel (II) complexes studied were found to be magnetically dilute or to involve only weakly antiferromagnetically coupled metal centres.

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