Solution and solid-state preparation of 18-crown[6] complexes with M[HSO₄]_n Salts (M = NH₄⁺, K ⁺, Sr²⁺ and n = 1, 2) and an investigation of solvation/desolvation processes and crystal polymorphism

18-Crown[6] ether has been used to prepare a new class of organic-inorganic complexes of general formula 18-crown[6]·M[HSO₄]_n (where M = NH₄⁺, K⁺, Sr²⁺ and n = 1, 2) by reacting directly in solution or in the solid state the crown ether 18-crown[6] with inorganic salts such as [NH₄][HSO₄], K[HSO₄], and Sr[HSO₄]₂. The structures of 18-crown[6]·[NH₄][HSO₄]·2H₂O (1·2 H₂O), 18-crown[6]·[NH₄][HSO ₄] (1), 18-crown[6]·K[HSO₄]·2H₂O (2·2 H₂O), 18-crown[6]·K[HSO₄] (2), and 18-crown[6]·Sr[HSO₄]₂ (3) have been characterized by single-crystal X-ray diffraction. The reversible water loss in compounds 1·2 H₂O and 2·2 H₂O leads to formation of the corresponding anhydrous phases 18-crown[6]·[NH₄]-[HSO ₄] (1), and 18-crown[6]·K[HSO₄] (2), which undergo, on further heating, enantiotropic solid-solid transitions very likely associated with the on-set of a solid state dynamical process. Similar high-temperature behavior is shown by 18-crown[6]·Sr[HSO ₄]₂ (3). The dehydration and phase-transition processes have been investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and variable temperature X-ray powder diffraction.