Supramolecular cocrystals of dispiro-P3N3-dicarboxylic acid: Synthesis, structural characterization and hirshfeld surface analysis

Abstract

The design of cocrystals for a particular molecule begins with examining that molecule's functional group and selecting a complementary functional group that would generate the foreseeable supramolecular synthons. In this work, the cyclotriphosphazene-based compound Dispiro-P3N3-dicarboxylic acid (L) was identified to produce two cocrystals with two different N-donor compounds such as 4,4′-bipyridine and piperazine by slow evaporation technique. These compounds 1 and 2 were characterized by single-crystal X-ray diffraction, PXRD, FT-IR, NMR, UV–Vis spectroscopy, TG analysis, computational analysis of pKa and Hirshfeld surface analysis. The ΔpKa value of compounds 1 (-0.180) and 2 (0.191) indicates that both are cocrystals in nature. Compounds 1 and 2 have the same triclinic crystal system with space group Pī. X-ray diffraction analysis displays that both compounds were formed with the coformer through complementary hydrogen bonding with an alternating sequence of Dispiro-P3N3-dicarboxylic acid and N-donor compounds. Compound 1 exhibits O-H···N and C-H···O hydrogen bonding interactions between Dispiro-P3N3-dicarboxylic acid and 4,4′-bipyridine that results in the formation of one-dimensional polymeric chains A and B. In addition, the adjacent one-dimensional polymeric chains A and B in compound 1 are further held together by π···π interactions between phenyl groups of Dispiro-P3N3-dicarboxylic acids from two different set of one-dimensional polymeric chains A and B. In compound 2, the recognition between Dispiro-P3N3-dicarboxylic acid and piperazine is established via O-H···N, N-H···O hydrogen bondings and π···π interactions which leads to the formation of one-dimensional polymeric chains. Furthermore, the one-dimensional polymeric chains are interconnected with each other via C-H···N hydrogen bondings which results to the formation of two-dimensional sheet like structure in compound 2. Hirshfeld surface analysis confirmed that the O-H···N hydrogen bondings are major interactions in compound 1; in contrast, N-H···O hydrogen bondings are more prominent interactions than the O-H···N hydrogen bondings in compound 2.