Piperazine (and derivatives) copper(II) compounds: 1,4-dimethylpiperazine-1,4-ium tetrachlorocuprate(II) and Cu-N bond formation in trichloro(1-methylpiperazin-1-ium-N4)copper(II) and trichloro(1,4-dimethylpiperazin-1-ium-N4)copper(II)

The ionic salt (H2Me2ppz)2- [CuCl4]2- (1), the pseudotetrahedral zwitterionic [CuCl3(HMe2ppz)] (2) and [CuCl3(H2Meppz)] (3) complexes of copper(II) have been synthesized and characterized, [(H2Me2ppz)2 =1,4-dimethyl-piperazin-1,4-ium; (HMe2ppz)+ =1,4-dimethylpiperazin-1-ium; (H2Meppz)+ =1-methylpiperazin-1-ium]. The X-ray diffraction analysis of compound (1) shows that the [CuCl4]2- anion possesses a flattened tetrahedral geometry with the two largest Cl-Cu-Cl angles being 125.90(5) and 131.41(5)°. The Cu-Cl distances range from 2.215(1) to 2.267(1) A, and all the chlorine atoms are involved in bifurcated hydrogen bonds. Physico-chemical measurements, UV–Vis, IR and especially X-ray analysis, prove that complex 2 is the first example of a Cu(II) ion bonded to one nitrogen atom of the piperazinium ring which is not constrained into a macrocyclic ligand. In fact, the -CuCl3 group is coordinated to the (HMe2ppz)- cation in the unusual axial position similar to the Co(II) derivative. The CuCl3N coordination polyhedron exhibits a pseudotetrahedral geometry with the two largest Cl-Cu-Cl angles being 132.17(12) and 135.38(7)°. Complex 3 shows the same physico-chemical behaviour as complex 2 confirming that this complex also contains a Cu(II-N bond in a pseudo-tetrahedral environment.