Synthesis, Crystal Growth, Structural Characterization, Supramolecular Chemistry, and Theoretical Calculations of Methylenium Salts of Benzenesulfonates

Abstract

The current investigation describes the synthesis of four novel methylene blue (MB) salts of benzene sulfonate derivatives, featuring bulky anionic groups. The process involves treating chloride salt of MB with sodium salts of 4‐aminobenzene sulfonate, 4‐styrenebenzene sulfonate, 3,7‐naphthalene disulfonate, and anthraquinone‐1,5‐naphthalene disulfonate to substitute the chloride ion with benzoate sulfonate anion in MB‐chloride. The synthesis includes quaternizing MB‐chloride with the corresponding benzene sulfonate in minimal aqueous solvent to promote precipitation. The resultant precipitates were subsequently dissolved in an appropriate solvent to enable the crystallization of the ultimate product. The dissolution occurs either at ambient temperature or with heat. The crystals of the resultant salts were characterized using various analytical techniques like UV‐visible, and FT‐IR spectroscopy, TGA, single crystal X‐ray diffraction and powder X‐ray diffraction analysis. The UV‐visible spectroscopic results, frontier molecular orbital, density of states, molecular electrostatic potentials, and HOMO‐LUMO energy gaps were estimated by DFT. Structural analysis revealed that supramolecular structure of compounds achieved stabilization through electrostatic interactions, a diverse range of both conventional and non‐conventional hydrogen bonds, π–π stacking interactions, and other short‐range interactions. The investigation delves into intricate details and offers a thorough discussion of the fundamental principles that contribute to the formation and stabilization of supramolecular structures.