Coordination Polymers of Copper(II) and Zinc(II) with 1-ethyl-1H-imidazole Incorporating Maleato or Malonato and Study of their Spectroscopic and Thermal Properties

Polymer carboxylates coordination complexes formulated as [Cu(malea)(1-Etim)2]n (1) and [Zn(malon)(1-Etim)2]n (2) (malea = maleato, malon = malonato and 1-Etim = 1-ethyl-1H-imidazole) were prepared from maleic acid and malonic acid in the presence of 2-ethylimidazole as co-ligand. The complexes were characterized by elemental analysis, UV-visible and FTIR spectroscopies, thermogravimetry analysis (TGA), differential scanning calorimetry (DSC) analysis and X-ray diffraction. Complex 1 crystallizes in the tetragonal system space group I41cd with a = 16.0188 (14) Å, c = 26.1287 (4) Å, V = 6704.67(13) Å3 and Z= 16 whereas 2 crystallizes in the monoclinic system space group P21/n with a = 7.2539(2) Å, b = 25.1372(7) Å, c = 9.0422(3) Å, b = 111.8405(8) °, V = 1530.43 (8) Å3 and Z= 4. In complex 1, the copper (II) is situated in a N2O3 site, and its coordination sphere is best described as strongly distorted square pyramidal. The Cu(II) ion is linked to two nitrogen atom from two 1-ethyl-1H-imidazole molecules and one oxygen atom from a maleate dianion. The coordination sphere is completed by two oxygen atoms from a maleate group of a neighboring complex molecule. In complex 2, the Zn(II) center is coordinated by two nitrogen atom from two 1-ethyl-1H-imidazole molecules and one oxygen atom from malonate dianion. The fourth position is occupied by an oxygen atom of a maleate unit of a neighboring complex molecule. The environment around Zn(II) is described as distorted tetrahedral geometry. For both complexes, adjacent polymers chains are linked together by numerous intermolecular hydrogen bonds C—H···O, leading to a 3D network structure. Thermogravimetric analysis of the complexes was carried out at 25–700 °C and showed that the complex 1 decomposes in the temperature range 138-438 °C while complex 2 decomposes between 118 and 415 °C.