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

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 ortho H 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 center dot H2O and nine isomers of (H4TPPCl2)(2)center dot H2O are also determined. The binding energy of H4TPPCl2 center dot 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 center dot H2O center dot 2CH(3)CN. 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.