Transition metal complexes with pyrazole-based ligands. Part 28. Synthesis, structural, DFT and thermal studies of cadmium(II) halides and zinc(II) chloride complexes with 3,5-dimethylpyrazole-1-carboxamidine

Abstract

The complex formation of 3,5-dimethylpyrazole-1-carboxamidinium nitrate, HL center dot HNO(3) with ammine complexes of cadmium(II) halides (Cl, Br, I) and zinc(II) chloride has been investigated under self-controlled reaction conditions. The complexes have been characterized by X-ray diffraction, FT-IR spectroscopy, thermal analysis and quantum chemical calculations. In the case of cadmium bromide and iodide salts, isostructural complexes with composition of [CdX(2)(HL)(2)] were formed. With CdCl(2) a binuclear octahedral [Cd(2)(HL)(4)(mu-Cl)(2)](NO(3))(2) complex is obtained. Zinc(II) chloride with HL center dot HNO(3) gives [Zn(HL)(2)Cl]NO(3), the zinc center exhibiting severely distorted five-coordinate stereochemistry, intermediate between an ideal trigonal bipyramid and a square pyramid. The course of complex formation as well as the thermal properties of the compounds has been explained using the HSAB principle. The assignment of the FT-IR spectra was supported by DFT computations. (C) 2009 Elsevier Ltd. All rights reserved.