Metastable crystalline phases of D5O2+ClO4−: Selective stabilization by addition of the light hydrogen isotope

The crystallization products from the liquid phase of DClO4·2D2O (99 at.% D) on a silver chloride substrate were investigated by IR absorption spectroscopy. The conditions of crystallization and heat treatment of the resulting crystal film of D5O 2 + ClO 4 − (I) were varied to detect signs of polymorphism. The results of the study indicate the existence of four metastable crystalline phases for I. It is shown that the chain of transformations of the metastable phases initiated by heat treatment is accompanied by disturbances of the symmetry of the symmetry of the D2O 2 + cation. The detected phase transformations are irreversible. The most stable metastable phase is isostructural with the well-known orthorhombic phase of D5O 2 + ClO 4 − . The metastable nature of the orthorhombic phase is confirmed by the presence of a monotropic transition, which dramatically reduces the symmetry of the D5O 2 + cation. The polymorphism typical of I disappears with the addition of more than 10 at.% of protium. Instead of the four metastable phases found for the deutertaed sample, only one orthorhombic phase crystallizes. Extraordinary stabilization by the addition of the protium isotope prevents polymorphic transition.