Complex Formation Between Imidazole and Nickel(II) Salts

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Abstract
Coordination compounds of formula Ni(Iz)nX2(H2O)m, in which Iz=imidazole, n = 1, 2, 4, 6, m = 0-4, and X = Cl-, Br-, I- and NCS-, are described. The anhydrous compounds are prepared from ethanolic solutions of Iz and nickel(II) salts in stoichiometric amounts in the presence of the dehydrating agent triethylorthoformate. Without this dehydrating agent hydrates are isolated for n = 2,4 and 6 with X = Cl, Br. The compounds were identified by means of infrared spectra (4000-25 cm-1), ligand-field spectra (35000-4000 cm-1) and X-ray powder diagrams. Compounds of formula [Ni(Iz)6]X2 all contain octahedrally coordinated Ni2+, for which the spectrochemical parameters were obtained. Tetragonal Ni2+ ions occur in [Ni(Iz)4X2] in which X = Cl and NCS, and in [Ni(Iz)4(H2O)2]X2 in which X = Cl and Br. These compounds are paramagnetic and the crystal-field parameters for tetragonal symmetry have been calculated. In [Ni(Iz)4]X2 with X = I and Br, the Ni2+ ions are square-planar coordinated with anions in the second coordination sphere, resulting in orange-coloured diamagnetic compounds. Anion-bridged distorted octahedrally coordinated Ni2+ ions probably occur in the compounds of formula Ni(Iz)2X2, in which Iz takes the axial positions. Similar structures are suggested for the mono-imidazole compounds, NiIzX2.

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