Hydration studies of a simple molecular solid

This paper presents novel information on the thermal dehydration and rehydration of the molecular\udsolid, Oxalic Acid Dihydrate. Although the procedure of the overall decomposition process is welldefined,\udthe structural basis and mechanism of the dehydration process has been poorly studied. We\udshow that the dehydration occurs in a planar manner, with a resultant semi-topotactic relationship\udbetween hydrated and dehydrated structures, reflected in the molecular packing. During rehydration,\udthe reconstruction of the phase can be seen to occur at a 3-dimensional phase boundary reaction front,\udi.e. a recrystallisation of the dihydrate on the surface of the reactant product, with the topotactic\udrelationship leading to texturing and possibly epitaxial relationships between partially dehydrated and\udrehydrated structures. The proposed mechanism is shown to be consistent with the measured kinetics of\udthe process