Crystal chemistry of Te(IV) fluorinated compounds

Abstract 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 M x Te y (IV) F z compounds is developed. Considering only the shortest bonds (in the range 1.80–2.10 A) the co-ordination polyhedra for Te atoms are quasi systematically TeF 5 E square pyramids or more rarely TeF 4 E disphenoids. With increasing M/Te ratio, the fluorinated network changes from bi-dimensional Te 1.5 F 6.5 layers of corner-sharing TeF 4 E and TeF 5 E polyhedra in RbTe 3 F 13 , to independent TeF 5 E units in the MTeF 5 compounds, via finite Te 4 F 18 groups of four basic units, in KTe 2 F 9 . Such an evolution emphasises the depolymerising character of the M atoms. In all 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.