The hydrated complexes 18-crown·[NH4][H2PO4]0.5[HSO4]0.5·H2O (1), 18-crown·Rb[H2PO4]0.5[HSO4]0.5·3H2O (2), 18-crown·Cs[H2PO4]0.5[HSO4]0.5·3H2O (3) and 18-crown·Cs[HSO4]·2H2O (4) have been quantitatively prepared by the mechanical mixing of crystalline 18-crown, and M[H2PO4] and/or M[HSO4] inorganic salts. The structures of the four complexes have been determined from single crystals, obtained by recrystallization of the products from water. On heating the complexes to ca. 70 °C, water loss takes place. The dehydration processes have been investigated by DSC, TGA and variable temperature X-ray powder diffraction; in all of the compounds, water loss leads to the formation of their corresponding anhydrous phases. On further heating of complexes 1 and 2 to 120 °C, decomplexation is observed, with formation of liquid crown ether and H3PO4, as well as crystalline [NH4]2[SO4] and Rb2[SO4], while on heating compound 3 to 140 °C, decomplexation is observed, with formation of liquid crown ether and crystalline Cs[H2PO4]0.5[HSO4]0.5. On heating complex 4, the loss of water is followed by a reversible phase transition, that is very likely to be associated with the onset of a solid-state dynamic process, followed at 145 °C by the extrusion of the crown ether from the complex, with formation of crystalline Cs[HSO4].