Molecular structures of inorganic compounds of low volatility: I. Salts of oxygen acids of the type M2XO4

We report an electron diffraction study of the molecular structure of gaseous cesium and thallium sulphates and cesium molybdate and tungstate. The average structure found for the M₂XO₄ molecules is described by a model (symmetry D_2d) in which the metal atoms bridge two edges of an XO₄ tetrahedron to form two 4-membered mutually perpendicular planar MO₂X rings.The data lead to conclusions on the complex nature of intramolecular motion. This motion may roughly correspond to great displacements of metal atoms on the surface of an imaginary sphere described near the tetrahedral acid residue.