Preparation, molecular structure, and stereochemical properties of copper(II) complexes co-ordinated to (3S)- and (RS)-3-aminopiperidine: effect of ring size on stereochromism

Abstract

A series of copper(II) complexes co-ordinated to a chiral heterocyclic diamine 3-aminopiperidine (apip) has been prepared. The complexes obtained from the racemic and optically active forms of apip with BF₄^– or ClO₄^– as the counter anions differ significantly in their spectroscopic properties. Such differences are discussed in comparison with those observed in the related copper(II) complexes of 3-aminohexahydroazepine. Mixed-anion complexes Cu(apip)₂X(ClO₄) have been prepared, and the X-ray crystallographic analysis of [Cu(NCS)(S-apip)₂][ClO₄] revealed that the thiocyanate occupies the fifth co-ordination site yielding a complex having square-pyramidal geometry. The anion dependency of the reflectance spectra revealed that the spectral change in the apip complexes is caused by steric rather than electronic effects of the anion.