Saddle-shaped macrocycle distortion and symmetry decrease in cobalt (II) meso-tetraphenylporphyrin: structure of a dichloromethane solvate and DFT calculations

Abstract

Many studies about porphyrins have emerged in recent years, including studies using porphyrins as building blocks for supramolecular assemblies. Understanding new solid state forms of porphyrins and the elucidation of their structures can have remarkable benefits for nanoscience and synthetic biology. In this study, a new pseudopolymorph of cobalt (II) meso-tetraphenylporphyrin, (CoTPP), was synthesized in a known one-pot reaction, rather than using many-step conventional methods, was isolated and was characterized for the first time by low-temperature single crystal X-ray diffraction. It is a nonstoichiometric solvate assembled into dichloromethane channels. The most striking feature of this structure is the conformation adopted by the porphyrin macrocycle. In contrast to the non-solvated form of CoTPP that exhibits a ruffled core distortion and crystallizes in the tetragonal space group I-42d, this solvated form has been crystallized in the triclinic space group Pī and shows a distinct saddle-shaped macrocycle distortion. In the triclinic form, the conformation of one of the four phenyl rings is remarkably different from the others. A potential energy surface scan of the torsional angles around the bonds between this phenyl moiety and the macrocycle of CoTPP in both the non-solvated and the solvate forms demonstrates that the saddle-shaped macrocycle distortion depends on the unusual phenyl conformation. The distortion is responsible for the symmetry decrease in the channel solvate form, causing a loss of the 4-fold rotoinversion axis observed in the non-solvated tetragonal phase, which has identical phenyl conformations.