Silver(I) Coordination Polymers Containing Heteroditopic Ureidopyridine Ligands: The Role of Ligand Isomerism, Hydrogen Bonding, and Stacking Interactions

Abstract

New silver (I) coordination polymers has been successfully designed and synthesized using heteroditopic ureidopyridine ligands 1 and 2 via a combination of coordinations bonds, hydrogen bonding, and π−π stacking interactions. This study shows an example of the orientation of the pyridine nitrogen relative to the urea moiety (4-substituted, 1, or 3-substituted, 2), used to control the packing of resulting crystalline coordination polymers. The ureidopyridine ligands present some flexibility because of the conformational rotation around the central urea moiety. The co-complexation of the silver(I) cation by two pyridine moieties and of the PF₆^- counteranion by the urea moiety results in the formation of discrete [1₂Ag]⁺PF₆^-, (3) and [2₂Ag]⁺PF₆^-, (4) complexes presenting restricted rotation around the central urea functionality. The geometrical information contained in the structures of ligands 1 and 2 and the heteroditopic complexation of silver hexafluorophosphate are fully exploited in an independent manner resulting in the emergence of quasi-rigidly preorganized linear and angular building blocks of 3 and 4, respectively. Additional π−π stacking contacts involving interactions between the π-donor benzene and the π-acceptor pyridine systems reinforce and direct the self-assembly of the above-described combined structural motifs in the solid state. Accordingly, linear and tubular arrays of π−π stacked architectures are generated in the solid state by synergistic and sequential metal ion complexation, hydrogen bonding, and π−π stacking interactions