Polarization and Dipole Moment Effects on Sigma-Hole Potential in Tin(IV)-Porphyrins.

Abstract

This study investigates how electron-withdrawing substitution, molecular polarization, and dipole moment influence the σ-hole potential in six-coordinate metalloporphyrins. To evaluate halogen bonding tendencies, we synthesized a series of five Sn(IV)-5,10,15,20-meso-tetrakis(4-iodophenyl)porphyrin complexes with various fluorinated phenolate axial ligands. Single-crystal X-ray diffraction analysis revealed distinct halogen-bonded supramolecular motifs, which vary depending on the degree of fluorination at the axial ligands. Our findings highlight the critical role of ligand-induced polarization and dipole moment variations in modulating the σ-hole characteristics of the equatorial iodine atoms. Computational modelling showed that increased fluorine substitution reduces both the atomic dipole moments of fluorine and the polarizability of the central tin ion. However, despite these changes, the axial fluorination has a negligible effect on the σ-hole potential at the iodine atoms. This limited influence is attributed to the orthogonal orientation between the porphyrin core and the peripheral phenyl rings, which suppresses resonance interactions. Overall, this work emphasizes the importance of understanding electronic effects at the molecular level, particularly in the design and formation of halogen-bonded supramolecular architectures.