A comparison of the coordination geometries of some 4-methylimidazole-5-carbaldehyde complexes with Zn(II), Cd(II) and Co(II) ions in the solid state and aqueous solution

摘要

Reactions of Zn(II), Cd(II) and Co(II) ions with 4-methylimidazole-5-carbaldehyde (4-Me-5-CHOIm) afforded four novel complexes [Zn(4-Me-5-CHOIm)(4)](NO3)(2) (1), [Cd(4-Me-5-CHOIm)(4)](NO3)(2)(H2O) (2), [Co(4-Me-5-CHOIm)(2)(H2O)(2)](NO3)(2) (3) and [Co(4-Me-5-CHOIm)2(NO3)(2)] (4). Compounds 1-3 were characterized by X-ray diffraction, establishing tetrahedral (I4), distorted dodecahedral (C2/c) and octahedral (PI) coordinating geometries of the metal ions, respectively. The crystal structure of 3 includes in the unit cell two symmetry-independent cations: [Co(1)L-2(H2O)(2)](2+) and [Co(2)L-2(H2O)(2)](2+) which differ slightly in bond lengths and valence angles. In solution, NMR and potentiometric methods have confirmed the preference of the central ions not only to adopt a specific coordination number and geometry of coordination polyhedra, but also the function of the ligands which can be either monodentate (ZnN4) or bidentate (CdN4O4 and CoN2O4). (c) 2005 Elsevier Ltd. All rights reserved.