Crystal chemistry of Te(IV) fluorinated compounds

After a short review of the main results of our activities in the field of fluorinated compounds, a comparison of the crystal structures of the MxTey(IV)Fz compounds is developed. ering only the shortest bonds (in the range 1.80–2.10 Å) the co-ordination polyhedra for Te atoms are quasi systematically TeF5E square pyramids or more rarely TeF4E disphenoids. With increasing M/Te ratio, the fluorinated network changes from bi-dimensional Te1.5F6.5 layers of corner-sharing TeF4E and TeF5E polyhedra in RbTe3F13, to independent TeF5E units in the MTeF5 compounds, via finite Te4F18 groups of four basic units, in KTe2F9. Such an evolution emphasises the depolymerising character of the M atoms. these structures the electronic lone pairs E of Te atoms are stereochemically active, pointing towards the empty spaces of the various networks: cavities, tunnels or inter-sheet spaces.