The structures of cæsium and rubidium difluorophosphates

Abstract

Crystals of cæsium and rubidium difluorophosphates are orthorhombic, with a= 8·43₇, b= 6·79₆, c= 8·06 Å for the Cs salt, and a= 8·15, b= 6·45, c= 7·79 Å for the Rb salt, Z= 4, space-group Pnma. The structure of CsPO₂F₂ was determined by use of three-dimensional Mo-K_α scintillation counter data by comparison with potassium difluorophosphate, and refined by least-squares methods, the final R being 0·070 for 506 observed reflexions.

Potassium, rubidium, and cæsium difluorophosphates are isomorphous, and have the barium sulphate structure. The lattice parameters and interionic distances increase with increasing radius of the alkali-metal ion.