Solid state transformations in stoichiometric hydrogen bonded molecular salts: ionic interconversion and dehydration processes

Abstract

We report structural aspects of three new stoichiometric 5-sulfosalicylate benzimidazolium (A₁B₁), 5-sulfonatosalicylate bis(benzimidazolium) monohydrate (A₁B₂·H₂O) and 5-sulfonatosalicylate bis(benzimidazolium) (A₁B₂) molecular salts. Using single crystal and powder X-ray diffraction, we describe the reversible solid state ionic interconversion between A₁B₁ and A₁B₂·H₂O upon neat grinding by adding one equivalent of benzimidazole or 5-sulfosalicilic acid dihydrate (B or A·2H₂O), respectively. In the process water molecules are included/excluded upon grinding suggesting that water could mediate the proton transfer. We have also studied the hydrogen bond network rearrangement after the dehydration of A₁B₂·H₂O by growing single crystals of the anhydrous salt using the seeding method. X-ray powder diffraction analysis confirmed that the product obtained directly upon heating corresponds to the structure obtained by the seeding method. In order to rationalize the experimental results and to gain insights into the role of water molecules in the formation of crystalline salts, the relative stabilities of the crystalline phases were compared by quantum mechanics calculations which are specific for solid state systems.