Reactions of copper(II) bromide with 2,6-diacetylpyridine bis(phenyl-hydrazone) (L) – Molecular and crystal structure of L and its mixed-valence complex [CuIIL2][CuI2Br4] Scientific paper

Abstract

Utilizing X-ray crystallography, the crystal and molecular structures of 2,6-diacetylpyridine bis(phenylhydrazone) (L) were determined. The ener­getics of the intermolecular interactions in the crystal structure were assessed with computational methods, revealing that dispersion interactions are domin­ant. The basic structural unit of the crystal packing was revealed to be the her­ring-bone type arrangement of L molecules. Assignation of the IR spectrum of L with the aid of DFT calculations was performed. Furthermore, new reactions of L with CuBr₂ in different solvents are described, which led to the synthesis of the mixed Cu(II)–Cu(I) complex with the formula [Cu^IIL₂][Cu^I₂Br₄] (1), and its structural characterization. In the complex cation, two molecules of triden­tate N3 ligand are meridionally arranged in a very distorted octahedral environ­ment of a Cu(II) ion. In [Cu₂Br₄]^2-, the bromide ions are arranged in a trigonal-planar geometry around each copper(I) atom. Finally, for ligand, 1, and the previously synthesized com­plex [CuL₂]Br₂, the thermal properties were exam­ined. The thermal stability of the complexes were lower than that of the ligand and decrease in the order: L (250 °C) > [CuL₂]Br₂ (221 °C) > [Cu^IIL₂][CuI₂Br₄] (212 °C). The differences in thermal stability of the com­plexes are due to differences in the packing efficacy of the constitutional ions.