Copper(II) complexes based on a new chelating 4-(3,5-diphenyl-1H-pyrazol-1-yl)-6-(piperidin-1-yl)pyrimidine ligand: Synthesis and crystal structures. Lone pair-π, C-H•••π, π-π and C-H•••A (A = N, Cl) non-covalent interactions

A new bidentate chelating pyrazolylpyrimidine ligand bearing a strong electron-donating substituent, i.e. 4-(3,5-diphenyl-1H-pyrazol-1-yl)-6-(piperidin-1-yl) pyrimidine (L) (Scheme 1), has been synthesized and used to obtain the copper(II) complexes by reaction with CuCl2. The molar ratio Cu:L = 1: 2 leads to isolation of a complex having CuL2Cl2 empirical formula, while the molar ratio Cu:L = 1:1 gives a complex with CuLCl2 empirical formula. The crystal structure of L as well as the structures of both complexes were studied by single crystal X-ray diffraction. The crystal structure of CuL2Cl2 compound is formed by trans-[CuL2Cl2] mononuclear molecules. Surprisingly, in contrast to the previous compound having molecular structure, the crystal structure of CuLCl2 consists of mononuclear [CuL2Cl](+) complex cations and dinuclear [Cu2Cl6](2) anions. Thus, formula of CuLCl2 complex can be represented as [CuL2Cl](2)[Cu2Cl6]. In both complexes molecules of L adopt bidentate chelating coordination mode through N-2 atom of pyrazole and N-3 atom of pyrimidine rings forming five-membered CuN3C metallocycles. Owing to C-H center dot center dot center dot N interactions and pi-pi-stacking L molecules form 2D network. In the structure of trans-[CuL2Cl2] there exist double lone pair(N(piperidine))-pi(pyrimidine) interactions and C-H center dot center dot center dot Cl contacts resulting in the formation of 1D chains. Layered 2D structure of [CuL2Cl](2)[Cu2Cl6] results from C-H center dot center dot center dot Cl, C-H center dot center dot center dot pi and double lone pair (Cl([CuL2Cl](+) complex cation)-pi(pyrimidine) interactions. (C) 2010 Elsevier B.V. All rights reserved.