Thermoanalytical characterization of pseudopolymorphs of sulphadimidine and sulphadimidine–trimethoprim molecular complexes

Abstract

In recrystallization experiments of sulphadimidine from water, dioxane and their mixtures aimed at preparing the unstable hydrate, a non-stoichiometric solvate with dioxane C 12H 14N 4O 2S· 1 5 C 4H 8O 2 and a pseudopolymorph with similar X-ray powder diffraction and infrared absorption properties but different thermal behaviour (DSC, TG) were isolated. In co-crystallization experiments of trimethoprim and sulphadimidine, a monohydrate of the respective 1 : 2 molecular complex and a methanol solvate of the equimolecular complex were obtained from aqueous ethanol and anhydrous methanol, respectively. The thermal stability of both pseudopolymorphic complexes is reflected by the high DSC and TG onset temperatures of solvent escape from the crystal lattice ( T e≈163°C and T e≈144°C, respectively, for water and methanol) and is consistent with the important role of water in the hydrated crystal packing and the very strong hydrogen-bonding interaction of methanol with a sulphonamido oxygen atom in the methanol solvate crystal.