Interplay of coordinative and supramolecular interactions in engineering unusual crystalline architectures of low-dimensional metal–pamoate complexes under co-ligand intervention

Abstract

This work presents a systematic investigation on coordination chemistry of a pharmaceutical agent pamoic acid (H₂PA), and also reveals the significant function of supramolecular interactions in managing the resultant crystalline networks with the incorporation of secondary co-ligands. Assemblies of pamoic acid with transition metal ions under similar conditions yield a series of eleven Mn^II, Cu^II, Zn^II, and Cd^II complexes, in the absence/presence of the organonitrogen ligands such as 2,2′-bipyridyl (2,2′-bipy), 1,10-phenanthroline (phen), and 4,4′-bipyridyl (4,4′-bipy). These compounds, together with the DMF solvate of pamoic acid, have been characterized by IR, elemental analysis, and single-crystal X-ray diffraction techniques. Generally, these complexes display similar 1-D pamoate-bridged coordination arrays (or 2-D coordination layers by introducing bridging 4,4′-bipy). Remarkably, distinct extended network architectures are further constructed with the aid of weak secondary interactions especially aromatic stacking. Amongst them, complexes 6, 8, 9, and 12, which exhibit unusual interpenetrating networks of (6,3) layers or 3-D 5-connected frameworks regulated by stacking forces, are representative paradigms of this research. Structural evolution under the co-ligand intervention in this series of complexes, as well as the general coordination rule of pamoate, has been further discussed. Thermal stability of these crystalline materials and fluorescent properties of the polymeric Zn^II and Cd^II complexes have also been explored.