Syntheses, characterization and crystal structure of copper(II) α,β-unsaturated carboxylate complexes with imidazole

Four copper(II) α,β-unsaturated carboxylate complexes with imidazole, Cu(CH2=CH-COO)2(imH)2 (1), Cu2(CH2=CH-COO)4(imH)2 (2), Cu[CH2=C(CH3)-COO]2(imH)2 (3) and Cu2[CH2=C(CH3)-COO]4(imH)2 (4) (where imH=imidazole) have been prepared and characterized by elemental analyses, IR, ESR and electronic reflectance spectroscopies. The single crystal X-ray diffraction study of complex 3 shows that the copper(II) atom is in a symmetric centre of a square planar environment completed by two monodentate α-methacrylate groups and two imidazole ligands displayed in trans position. Each molecular unit is linked with four neighbouring units by hydrogen-bond interactions forming a two-dimensional supramolecular compound (dN⋯O=2.781 Å). Complex 1 has a similar structure as complex 3, while complexes 2 and 4 have a binuclear cage structure. The ESR spectra show that the spin coupling between the unpaired electrons of Cu(II) atoms present in complexes 2 and 4, is not observed in complexes 1 and 3. The electronic reflectance spectra suggest that the d-d transitions of complexes 1 and 3 are in a square planar ligand field, while that of complexes 2 and 4 are in a tetragonal ligand field, and the ligand field strength of acrylate group and α-methacrylate group is similar. Complexes 1 and 2 as well as 3 and 4, were produced simultaneously in the reaction of the corresponding copper(II) α,β-unsaturated carboxylate with imidazole in methanol solution.