Thermochemistry of amine-templated open frameworks

The thermochemistry of pure-silica zeolites and other microporous compounds was extensively reported in the literature: high-temperature calorimetry experiments revealed that the enthalpy of formation of the molecular sieves is on the order of twice the thermal energy available at the synthesis temperature. However, a better knowledge of the role that the structuring agents used in the hydrothermal synthesis play in the stability and the selection of the structures is necessary. In this paper, the stability of hybrid organic-inorganic composites, precursors of microporous structures, is investigated. Amine-templated gallophosphates of the ULM-n series have been studied by high-temperature calorimetry combining transposed temperature drop and drop solution experiments. The heats of formation of the composites are about - 1 and - 10 kJ/mol GaPO₄ for ULM-4 and ULM-5 templated with diaminopropane and diaminohexane, respectively, and -202 kJ/mol GaPO₄ for ULM-3 where the template is the monohydrate of diaminopropane. The results for the ULM-n materials suggest an enthalpy of stabilization by the structuring agents on the order of what was found in the case of stabilization by adsorption of water in hydrated microporous aluminophosphates.