Beschreibung:
<jats:p> Thermogravimetry, differential scanning calorimetry, and FT-IR vibrational spectral studies on the 1:1:1 18-crown-6: dichloropicric acid: water complex reveal that it remains unaltered when heated to melting. On the other hand, one molecule of water is expelled from the 1:2:2 complex by heating prior to melting. This results in an ionic microcrystalline product of undetermined crystal structure, in which the conformation of the crown is lower than D<jats:sub>3d</jats:sub> in symmetry. The enthalpy accompanying this process, which involves rupturing of two water–crown hydrogen bonds, is −44 to −55 kJ mol<jats:sup>−1</jats:sup>. The original 1:2:2 complex is regenerated by exposure of the heated adduct to water vapor. It was found that H<jats:sub>2</jats:sub>O in the structure of the solid 1:2:2 adduct was partially replaced by D<jats:sub>2</jats:sub>O at room temperature upon exposure to D<jats:sub>2</jats:sub>O vapor. The crown–H<jats:sub>2</jats:sub>O OH stretch in the IR exhibits a small or negligible positive isotope effect on deuteration. Keywords: crown ether, hydrogen bonding, water, dichloropicric acid. </jats:p>