Theoretical study of intermolecular interactions in meso-tetraphenylporphyrin diacid dimer (H4TPPCl2)2

Abstract

The intermolecular interactions between two meso-tetraphenylporphyrin diacid H₄TPPCl₂ monomers are investigated by density functional theory with the PBE1PBE functional and 6-31G* basis set. Structures of five stable isomers of (H₄TPPCl₂)₂ are determined. It is found that the interaction (IMHB-1) of Cl with orthoH atoms in two phenyl groups of H₄TPPCl₂ is unique in that it is the strongest interaction between two H₄TPPCl₂ monomers. Natural bond orbital analysis is carried out to explain the subtle differences of hydrogen bondings in these isomers. To understand the interactions of water molecule with H₄TPPCl₂ and (H₄TPPCl₂)₂, structures of H₄TPPCl₂·H₂O and nine isomers of (H₄TPPCl₂)₂·H₂O are also determined. The binding energy of H₄TPPCl₂·H₂O is 36.47 kJ mol⁻¹, less than that of the most stable structure of (H₄TPPCl₂)₂ dimers, 41.59 kJ mol⁻¹. The dimers containing the special IMHB-1 interactions may be the elementary building blocks for the aggregation of H₄TPPCl₂, which is supported by the crystal structure of H₄TPPCl₂·H₂O·2CH₃CN. Thus, study of the interactions between two or a small number of gas molecules can provide important information for understanding the main interactions and stable structures in related condensed-phase systems.