Piperazine (and derivatives) Copper(II) compounds: 1,4-dimethylpiperazin-1,4-ium tetrachlorocuprate(II) and CuN bond formation in trichloro(1-methylpiperazin-1-ium-N4)copper(II) and trichloro(1,4-dimethylpiperazin-1-ium-N4)copper(II).