Crystal forms of highly "dynamic" 18-crown[6] complexes with M[HSO4] and M[H2PO4] (M+ = NH4+, Rb+, Cs+): thermal behaviour and solid-state preparation

The hydrated complexes 18-crown[6]center dot[NH4][H2PO4](0.5)[HSO4](0.5)center dot H2O ( 1), 18-crown[6]center dot Rb[H(2)PO4](0.5)[HSO4](0.5)center dot 3H(2)O (2), 18-crown[6]center dot Cs[H2PO4](0.5)[HSO4](0.5)center dot 3H(2)O (3) and 18-crown[6]center dot Cs[HSO4]center dot 2H(2)O (4) have been quantitatively prepared by the mechanical mixing of crystalline 18-crown[6], 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 degrees 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 degrees C, decomplexation is observed, with formation of liquid crown ether and H3PO4, as well as crystalline [NH4](2)[SO4] and Rb-2[SO4], while on heating compound 3 to 140 degrees 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 degrees C by the extrusion of the crown ether from the complex, with formation of crystalline Cs[HSO4].