Thermodynamic behaviour of bistable NH+–N hydrogen bonds in monosalts of 1,4-diazabicyclo[2.2.2]octane

Proton dynamics in NH+–N hydrogen bonds is characterized by high-pressure dielectric and calorimetric studies of ferroelectric/paraelectric phase transitions in perchlorate and tetrafluoroborate mono-salts of 1,4-diazabicyclo[2.2.2]octane (DABCO), [C6H13N2]+·ClO4− and [C6H13N2]+·BF4−. The p–T phase diagrams of these ferroelectrics have been determined and described. The positive pressure dependences of Tc testify to the strong coupling of the ionic dynamics with the proton disordering in the NH+–N hydrogen bonds. Close isostructurality of the crystals provides a unique opportunity for analysing the proton disordering at varied crystal environments.