Synthesis of copper(II) complexes with 3,5-bis(4,6-dimethylpyrimidin-2-yl)-4H-1,2,4-triazol-4-amine (L). Molecular and crystal structures of L and [Cu2L2Cl4]·2MeCN

A series of copper(II) complexes, i.e. Cu2LCl4, CuLCl2·H2O and [Cu2L2Cl4]·2MeCN (8), based on a new potentially polytopic ligand, 3,5-bis(4,6-dimethylpyrimidin-2-yl)-4H-1,2,4-triazol-4-amine (3b, L), have been synthesized. The crystal structures of L and [Cu2L2Cl4]·2MeCN were studied by X-ray single crystal analysis. The dinuclear compound [Cu2L2Cl4]·2MeCN represents the first example of structurally characterized metal complexes with 3,5-di(pyrimidin-2-yl)-4H-1,2,4-triazol-4-amines. Both copper atoms have distorted tetragonal–pyramidal 3N + 2Cl environment. Surprisingly, in contrast to the complexes based on 3,5-di(pyridin-2-yl)-4H-1,2,4-triazol-4-amine (pyridinyl analog of L), the compound [Cu2L2Cl4]·2MeCN adopts a dinuclear trans-(N′,N1,N2)2 double bridging binding mode which is due to tridentate coordination of two L molecules linking two copper atoms through N1,N2-triazole and N′-pyrimidine atoms. It seems to be reasonable that it is methyl groups in pyrimidinyl moiety that obstruct the expected dinuclear (N′,N1,N2,N″)2 double bridging coordination being one of the most common for 4-substituted 3,5-di(pyridin-2-yl)-4H-1,2,4-triazoles and 3,5-di(pyridin-2-yl)-1,2,4-triazolates. Due to π–π stacking interactions, molecules of Cu2L2Cl4 in the structure of [Cu2L2Cl4]·2MeCN form 1D chains.