Tetrahalo and (mixed-tetrahalo)cuprates of the 1-methyl- and 2-methyl.pyperazinium dications. Hydrogen bonding effects on the coordination geometry of the CuX4 2- anions.

Some halo- and (mixed-halo) cuprates of the type (n-MepipzH2)CuXmY4-m (X=Cl; Y=Br; m=4,3,2,1,0; n=1 and 1-MepipzH2=1-methylpiperazinium dication; n=2 and 2-MepipzH2=2-methylpiperazinium dication) and (1-MepipzH·HX)2CuX4 (X=Cl,Br) (1-MepipzH·HX=1-methylpiperazinium monocation hydrohalide) were prepared and characterized by means of spectroscopic, magnetic, differential scanning calorimetric analysis and conductometric measurements. The compounds in the solid state may be divided in two categories: a) the (1-MepipzH2)CuXmY4-m (m=4,3,2,1,0) and (2-MepipzH2)CuXmY4-m (m=1,0) complexes, for which a distorted tetrahedral configuration is suggested from their room-temperature spectroscopic properties; b) the (2-MepipzH2)-CuXmY4-m (m=4,3,2) and (1-MepipzH·HX)2CuX4 complexes, for which an approximately square-planar geometry may be suggested. In particular the (1-MepipzH·HBr)2CuBr4 compound shows a thermochromic behaviour associable with a change in the coordination geometry like all the complexes in N,N′-dimethylformamide solution. The distortion from tetrahedral symmetry of the complexes is discussed on the basis of extensive N-H … X hydrogen bonding interactions, which are proposed as responsible for the planar geometry.