Homo- and hetero-halogen interaction based molecular associations in wheel–axle topology derived Sn(iv) porphyrin complexes: an experimental and theoretical analysis

Abstract

This paper describes our findings on the molecular association patterns of seven hexacoordinated Sn(IV)(axial-L)₂-(5,10,15,20-tetraiodophenylporphyrin) complexes [where L = F-substituted benzoate anions]. The systematic and progressive variation of the fluorine content on the molecular scaffold resembling a rigid wheel-and-axle duo demonstrates that it is possible to induce I⋯F hetero-halogen interactions among other weak interactions such as C–H⋯O, C–H⋯π, π⋯π etc. Hirshfeld surface analysis further supports the role of hetero-halogen interactions in the model compound 6. DFT-based electrostatic potential surface studies show the presence of a σ-hole on the iodine atom and thus vouch for its electrophilic nature in all the observed I⋯F halogen bonds. A homo-halogen I⋯I contact with much non-linearity is observed in 7, and, conspicuously, no F⋯F is found in any of the structures studied due to the hard nature of the fluorine atom. Quantum theory of atoms in molecules (QTAIM) analysis clearly reveals the presence of bond critical points, thus confirming the existence of homo- and hetero-halogen bonds within the studied dimer. Further support for the attractive nature of homo- and hetero-halogen bond interactions is gathered through noncovalent interaction-reduced density gradient (NCI-RDG) analysis, which shows the attractive nature of such interactions. Overall, the combined experimental and theoretical studies presented here showcase the occurrence of both homo- and hetero-halogen interactions and their role in the self-assembly process and associated photophysical properties of metalloporphyrin complexes.