New framework hydrous silicate K3Sc[Si3O9] • H2O related to the high-temperature anhydrous silicate K3Ho[Si3O9] and symmetry analysis of a phase transition with prediction of structures

Crystals of a new framework silicate K3Sc[Si3O9] center dot H2O, space group Pm2(1) n (nonstandard setting of space group Pmn2(1) = C (2v) (7)), are obtained under hydrothermal conditions. The structure is determined without preliminary knowledge of the chemical formula. The absolute configuration is determined. The structure is close to that of the high-temperature K3Ho[Si3O9] phase, which was obtained upon the heating of K3HoSi3O8(OH)(2). This structural similarity is due to the specific conditions of synthesis and an analogous formula, where holmium is replaced by scandium. A symmetry analysis shows that the high local symmetry of a block (rod) is responsible for the first-order phase transition of both the order-disorder (OD) and displacement type. The number of structures in which the simplest and high-symmetry layers are multiplied by different symmetry elements are predicted.