CuBr2 AS A BROMINATION AGENT OF PYRAZOLE-BASED LIGAND: SYNTHESIS OF COPPER(II) COORDINATION COMPOUNDS BY OXIDATIVE DISSOLUTION OF COPPER POWDER IN ORGANIC SOLVENTS

Using the direct synthesis method, by oxidative dissolution of copper powder in the presence of CuBr2 and C5H8N2 (3,5-dimethyl-1H-pyrazole), three different types of crystals were formed, isolated, and identified. Three new coordination compounds, trinuclear [Cu3(mu 3-OH)(mu 2-C5H7N2Br)(mu 2-Br)3(C5H8N2)5Br]center dot CHCl3 (where C5H7N2Br - 4-bro-mo-3,5-dimethylpyrazole) (1) (orthorhombic, Pnma), binuclear [Cu2(mu 2-C5H7N2Br)(mu 2-Br)(C5H8N2)4Br2]center dot 2CHCl3 (2) (monoclinic, C2/c) and mononuclear [CuBr2(C5H8N2)3] (3) (triclinic, P1), have been obtained. According to the single-crystal X-ray diffraction analysis, the complex 1 is a trinuclear six-membered cycle, where copper atoms are connected by three types of bridges: mu 2-bromide ions, mu 2-4-bromo-3,5-dimethylpyrazole molecule, and mu 3-hydroxo group. The binuclear complex 2 is formed due to a connection between two copper atoms by a bidentate-bridging bromide ion and a bridged 4-brominated 3,5-dimethylpyrazole molecule. Coordination compound 3 is a mono-nuclear trigonal-bipyramidal copper(II) complex. During the reaction, some part of 3,5-dimethylpyrazole molecules was brominated in the 4th position of the pyrazole ring. The Hirshfeld surface analysis reveals that the inter-molecular H center dot center dot center dot H contacts have the highest contribution to the crystal packing of all compounds: 66.9 % for 1, 54.4 % for 2, and 66.5 % for 3.