Self-Assembly of Tin(IV) Cyanophenyl Porphyrins into Hydrogen-Bonded Frameworks Reinforced by Halogen Bonding: Synthesis, Structure and Computational Perspectives

Abstract

This study presents a comprehensive investigation into the synthesis, structural organization, and optoelectronic properties of meso-tetrakis(4-cyanophenyl) porphyrin (CNP) (1) and their tin(IV) complexes Sn-CNP(IB)₂·2DMF (2), Sn-CNP(IP)₂·DMF (3) functionalized with axial linkers 4-iodobenzoic acid (IB) and 4-iodophenol (IP) respectively. Crystallographic analysis reveals the packing motifs are stabilized by directional CN···H–C hydrogen bonds in all compounds towards the formation of hydrogen bonded frameworks which are further reinforced by halogen–halogen contacts in compound 3. UV-Vis absorption, fluorescence data and electrochemical studies demonstrate that tin(IV) coordination and axial linkers significantly modulates the electronic structure of the porphyrin system. Density functional theory (DFT) and Reduced density gradient (RDG) analysis quantifies the strength and nature of non-covalent interactions that stabilize supramolecular assemblies. Spectroscopic and theoretical results demonstrate significant modulation of charge-transfer characteristics and band gap energies in response to metalation and axial ligand variation.