Energetic features of antiparallel stacking and hydrogen bonding interactions in two coordination complexes bearing 1,10-phenanthroline-2,9-dicarboxylic acid

Abstract

Two new metal–organic complexes, [Co(phen)(PDA)H2O]·CH3CN·H2O (1), (phen = 1,10-phenanthroline, PDA = 1,10-phenanthroline-2,9-dicarboxylate) and [Ce2(PDA)3(H2O)2]·3H2O (2) have been synthesized and characterized by elemental analysis, infrared spectroscopy, and single-crystal X-ray crystallography. Structural characterization by single-crystal X-ray diffraction shows that in 1 the cobalt ion forms a discrete seven-coordinated complex with a distorted pentagonal bipyramidal geometry around the metal centre. These discrete units are further packed into 3-D supramolecular assemblies by different kinds of the noncovalent interactions. Complex 2 consists of a 1D coordination polymeric structure with the cerium ion coordinated by PDA and water in the form of left-handed and right-handed helices. The extended aromatic systems of PDA and phen have a strong tendency to establish antiparallel π···π stacking interactions generating interesting assemblies in the solid state of 1. They have been studied theoretically using DFT calculations and characterized by means of the quantum theory of “atoms-in-molecules” (QTAIM) and the noncovalent interaction (NCI) plot methods. This study is useful to understand in more detail the energetic and structural stability of these categories of metal-organic complexes. The results reported herein suggest that the antiparallel π-stacking interactions involving the neutral and, in principle innocent, phen auxiliary ligand are energetically very relevant in the solid state of 1.