Liquid Co-crystals of Dual-Active Phenothiazine–NSAID Drugs: Synthesis, Spectroscopic, and Thermal Characterization

[Image: see text] Four aliphatic phenothiazine cations (promazinium, promethazinium, chlorpromazinium, and triflupromazinium) were each paired with docusate anions and three different NSAID anions (ibuprofen, salicylate, and naproxen) to form fifteen glassy materials and one solid. The compounds were prepared via the metathesis reaction between the corresponding phenothiazine hydrochloride salts and sodium docusate or sodium NSAID salts and were obtained as liquid co-crystals with various degrees of ionization. The self-diffusion coefficients of several derivatives in 0.06 M DMSO-d(6) solutions were determined using DOSY NMR spectroscopy. The influence of the size, shape of the compounds, and intermolecular forces has been investigated by using the four promazine and the four ibuprofen co-crystals. The ion pairs (or aggregates) were found to be maintained in six out of the seven compounds examined. All fifteen glassy compounds showed reversible glass transitions in the −25 to 10 °C range with the docusate derivatives exhibiting the highest thermal stability (T(onset) values being at least 40 °C higher than those of the corresponding phenothiazine hydrochlorides).