Interesting organic supramolecular structures constructed by piperazine/N,N′-dimethylpiperazine with aromatic multicomponent acids: synthon cooperation and structural diversity

Abstract

Crystallographic studies reveal that organic supramolecular structures 1–7 constructed by piperazine/N,N′-dimethylpiperazine with aromatic multicomponent acids are organic salts formed due to the proton transfer from the carboxylic group of the aromatic multicomponent acids to the nitrogen atom of the piperazine/N,N′-dimethylpiperazine. In all salts, the cations and anions are associated via N–H⋯O(–COO⁻) charge-assisted hydrogen bonds, leading to ionic synthons. Competition and cooperation among –COOH, –COO⁻, –OH, –NO₂, –NH⁺– and –NH²⁺– functional groups for the observed hydrogen bond synthons are examined in the seven structures. It is noted that C–H⋯O hydrogen bonds increase the dimensionality of the supramolecular architectures of the seven salts. The number of acids involved in the complex equals to the number of N-protonated binding sites in the piperazine/N,N′-dimethylpiperazine. Water molecules play a significant role in the formation of the supramolecular architectures. The supramolecular structures of the seven piperazine/N,N′-dimethylpiperazine salts were determined by single-crystal X-ray diffraction, respectively, to understand how variations in their molecular structures and intermolecular interactions influence their supramolecular assemblies. After the formation of salts of 1–7, the melting points are dramatically different, and thermal stability of these compounds were investigated by thermogravimetric analysis (TGA).