Crystal structure of a chloride-bridged copper(II) dimer: piperazine-1,4-dium bis-(di-μ-chlorido-bis[(4-carboxypyridine-2-carboxyl-ato-κ,)chlorido-cuprate(II)].

Crystals of a new dimeric chloride-bridged cuprate(II) derived from pyridine-2,4-di-carb-oxy-lic acid were obtained solvothermally in the presence of piperazine and hydro-chloric acid. The crystal structure determination of the title salt, (CHN)[Cu(CHNO)Cl], revealed one of the carboxyl groups of the original pyridine-2,4-di-carb-oxy-lic acid ligand to be protonated, whereas the other is deprotonated and binds together with the pyridine N atom to the Cu atom. The coordination environment of the Cu atom is distorted square-pyramidal.