Effect of non-covalent interaction on the diastereoselective self-assembly of Cu(ii) complexes containing a racemic Schiff base in a chiral self-discriminating process

Abstract

The diastereoselective self-assembly of five Cu(II) heterochiral complexes containing a racemic Schiff base ligand LH (where LH = (R,S) 2-((1-(2-pyridyl)ethylimino)methyl)phenol in a chiral self-discriminating process is reported. Complexes 1–5 are synthesized using ligand LH, Cu(NO₃)₂·3H₂O, Cu(ClO₄)₂·6H₂O, and co-ligands such as N₃⁻, NCS⁻, NCO⁻, and are conclusively structurally characterized. Determination of the molecular structures of 1–5 confirmed the presence of a di-copper core with an inversion centre located directly between the two copper ions. In 1–5, each ligand in the di-copper core discriminates its own chirality and results in heterochiral dimerization in a chiral self-discriminating manner. The crystal packing pattern of compounds 1–5 are analyzed in terms of non-covalent C–H⋯O, C–H⋯N, C–H⋯π, and parallel displaced π⋯π interactions. In the crystal structure of compounds 1–4, there is a parallel displaced π⋯π interaction between the pyridine and benzene rings in the two adjacent heterochiral dimers, which act cooperatively with other different non-covalent interactions. In 2, the coordinated water molecule acts as a bifurcated H-bond donor to phenoxo-O and perchlorate-O in a diastereoselective and enantioselective manner, respectively. The results described here address new examples of the rarely occurring chiral self-discriminating process.