Novel coordination compounds of quinic acid. X-ray diffraction study of copper(II) complexes where the metal ion was a chiral centre

Abstract

The synthesis and characterization of the following coordination compounds derived from quinic acid (quin) (1): [Cu(quin)Cl(H2O)]n·(H2O)n(2); [Ni(quin)Cl(H2O)]n·(2H2O) n (3); [Co(quin) Cl(H2O)]n·(2H2O)n(4); [Cu(quin) (NO3)(H2O)]n·(2H2O)n(5); [Cu(quin)(AcO)(H2O)]n· (2H2O)n(6); [Cu(quin)H2O]2·2H2O(7); [Co(quin)2]n (8); [Zn(quin)2](9); [Cd(quin)2](10) and [Hg(quin)2]· 4H2O (11) is presented. All of the compounds were characterized by i.r. and u.v. spectroscopy; in addition, (9) and (10) were analysed by n.m.r., and (2), (5) and (7) by X-ray crystallography. Due to the polyfunctionality of quinic acid diverse structures were obtained: (2) –(6) and (8) were polymeric, (7) was dimeric and (9) –(11) were spiranic. In compound (2) the Cu had a distorted octahedral structure; it was a chiral centre with six different substituents and an optically active ligand. Only one stereoisomer (OC-6-25-A) of the 30 possible was observed in the crystal. Compound (5) was also polymeric, the hexacoordinated Cu atom was a chiral centre (OC-6-53C) and only one stereoisomer was observed. It was bonded to three quinic acid ligands in three different coordination modes and each quinic acid was in turn bonded to three different Cu atoms. Each chain was linked to another two chains giving a net structure. Compound (7) was a dimer with two square pyramidal Cu atoms. Two apical water molecules were found in acis arrangement. Each quinic acid ligand was bonded to two Cu atoms which were linked by two oxygen bridges and each Cu atom was bonded to two quinic acid moieties.