Wheel-and-axle topology-driven halogen bonded supramolecular networks in six-coordinated Sn(iv)-porphyrins.

A direct influence of porphyrin's ring current on the sigma-hole potential of halogen atoms at the axial position of metalloporphyrins during halogen bonded self-assembly is determined in this study.

In this study, we report the first example of polymorphic Sn­(IV)-tetrapyridyl porphyrins axially armed with halogen (Cl, Br)-substituted carboxyphenyl ligands (structural formula [Sn­(tPyP)2+­(A−)2], where A is the axial ligand = 3,5-dichloro/dibromo benzoic acid). The two polymorphs of chloro-substituted Sn­(IV)-tetrapyridyl porphyrin (1α and 1β) display distinct photophysical and morphological properties in the solid state. X-ray diffraction study reveals that these polymorphs 1α and 1β greatly differ in supramolecular architecture and noncovalent interactions, which is responsible for their distinct solid-state properties. Molecules of the two polymorphs adopt different conformations of the axial carboxyphenyl ligand. Crystal packing of these polymorphs are dominated by intermolecular C–H···Npyridine, C–H···O, C–H···π, and Cl···Npyridin interactions. Theoretical study showed that the energy difference between the two polymorphs is ∼8 kcal/mol. In addition to these polymorphs, a reference compound 2 with an axial bromo-substituted carboxyphenyl ligand is also synthesized and structurally characterized.

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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, 1α), and the other stabilizes in monoclinic system (namely, 1β). The two 1α and 1β polymorphs display distinct photophysical and morphological properties in the solid state. X‐ray diffraction study reveals that these polymorphs 1α and 1β 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⋅⋅⋅F, C−H⋅⋅⋅π and C−Br⋅⋅⋅F interhalogen interactions. Furthermore, the solid‐state emission spectra of 1α showed red‐shifted emission bands with respect to 1β, in addition the redox behavior of 1α is slightly different in comparison to 1β. Complementary theoretical studies with Hirshfeld surface analysis show the definite role of Br⋅⋅⋅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 σ‐hole, a requisite feature to show halogen interactions in the crystalline state. In addition, lattice energy and single point energy calculation shows that 1α was found to be energetically more favorable and thermodynamically more stable compare to 1β.