Electrochemical, Photophysical, Morphological and DFT Study of Polymorphic Sn(IV)-Porphyrins Containing Fluorinated Axial Ligand

In this study, we report the polymorphism of six coordinated Sn(IV)-tetrabromophenyl porphyrins axially armed with fluorine-substituted phenolate ligands (structural formula [Sn(TBrPP)(2+)(A(-))(2)], where A is the axial ligand=3,5-difluoro phenol, compound 1). One form stabilizes in triclinic system (namely, 1 alpha), and the other stabilizes in monoclinic system (namely, 1 beta). The two 1 alpha and 1 beta polymorphs display distinct photophysical and morphological properties in the solid state. X-ray diffraction study reveals that these polymorphs 1 alpha and 1 beta significantly differ in their supramolecular architecture, different axial phenolate conformations, and noncovalent interactions, which are responsible for their distinct solid-state properties. The crystal packing of these polymorphs dominates by intermolecular C-H center dot center dot center dot center dot F, C-H center dot center dot center dot pi and C-Br center dot center dot center dot F interhalogen interactions. Furthermore, the solid-state emission spectra of 1 alpha showed red-shifted emission bands with respect to 1 beta, in addition the redox behavior of 1 alpha is slightly different in comparison to 1 beta. Complementary theoretical studies with Hirshfeld surface analysis show the definite role of Br center dot center dot center dot F interhalogen interactions in the overall stability. Mapping the electrostatic potential isosurfaces with the aid of density functional theory in compound 1 clearly shows the presence of sigma-hole, a requisite feature to show halogen interactions in the crystalline state. In addition, lattice energy and single point energy calculation shows that 1 alpha was found to be energetically more favorable and thermodynamically more stable compare to 1 beta.

Automated summary

In this study, the polymorphism of six coordinated Sn(IV)-tetrabromophenyl porphyrins with fluorine-substituted phenolate ligands was investigated. The two polymorphs, 1 alpha and 1 beta, displayed distinct properties in terms of their supramolecular architecture, axial phenolate conformations, and noncovalent interactions. The emission spectra and redox behavior also differed between 1 alpha and 1 beta.