Synthesis, crystal and molecular structure of pseudotetrahedral Zn(II) zwitterionic complexes: trichloro(1-methylpiperazin-1-ium-N 4)zinc(II) and trichloro(1,4-dimethylpiperazin-1-ium-N 4)zinc(II)

Abstract

The synthesis and the X-ray structure of the two pseudotetrahedral Zn(II) zwitterionic complexes: trichloro(1-methylpiperazin-1-ium-N 4)zinc(II), [ZnCl 3(H 2Meppz)], and trichloro(1,4-dimethylpiperazin-1-ium-N 4)zinc(II), [ZnCl 3(HMe 2ppz)], are described [(H 2Meppz) +=1-methylpiperazin-1-ium monocation and (HMe 2ppz) +=1,4-dimethylpiperazin-1-ium monocation]. [ZnCl 3(H 2Meppz)] and [ZnCl 3(HMe 2ppz)] complexes are isomorphous and isostructural, respectively, to the [CoCl 3(H 2Meppz)] and [CoCl 3(HMe 2ppz)] complexes, already reported in literature by us. Both complexes present a very uncommon and distorted tetrahedral aminotrichlorozinc(II), NZnCl 3, group, where N is a nitrogen atom of an aliphatic amine. So far this group has been found only in the (1,3,5,7-tetraazaadamantane)trichloro-zincate(II) anion [{(CH 2) 6N 4}ZnCl 3] −. The bulky ZnCl 3 group present in [ZnCl 3(HMe 2ppz)], is coordinated to the axial position of the piperazine ring instead of the less hindered equatorial position, as found in the analogous [CoCl 3(HMe 2ppz)] complex. An extended hydrogen bond network is present in the crystals of both the complexes but, while the [ZnCl 3(H 2Meppz)] complex shows nearly linear N +H⋯Cl intermolecular hydrogen bonds, the [ZnCl 3(HMe 2ppz)] complex shows a perfectly symmetrical (imposed by space group symmetry) ZnNCl three-centre intermolecular hydrogen bond. The solid state infrared spectra of both the compounds are discussed in agreement with the hydrogen bond network present in the crystals.