Polymorphism in Sn(IV)-Tetrapyridyl Porphyrins with a Halogenated Axial Ligand: Structural, Photophysical, and Morphological Study

Abstract

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.