LAUSR

Abstract The stereochemistry of n s 2 n p 4 ( n  = 4, 5) lone pair LP characterizing noble gas Kr and Xe (labeled M*) in M*F 2 difluorides is examined within coherent crystal chemistry and ab initio visualizations. M* 2+ in such oxidation state brings three lone pairs (E) and difluorides are formulated M*F 2 E 3 . The analyses use electron localization function (ELF) obtained within density functional theory calculations showing the development of the LP triplets whirling {E 3 } quantified in the relevant chemical systems. Detailed ELF data analyses allowed showing that in α KrF 2 E 3 and isostructural XeF 2 E 3 difluorides the three E electronic clouds merge or hybridize into a torus and adopt a perfect gyration circle with an elliptical section, while in β KrF 2 the network architecture deforms the whole torus into an ellipsoid shape. Original precise metrics are provided for the torus in the different compounds under study. In KrF 2 the geometric changes upon β → α phase transition is schematized and mechanisms for the transformation with temperature or pressure are proposed. The results are further highlighted by electronic band structure calculations which show similar features of equal band gaps of 3 eV in both α and β KrF 2 and a reorganization of frontier orbitals due to the different orientations of the F-Kr-F linear molecule in the two tetragonal structures.