KTe_3O_6F: a new layer TeO_2 structure, stuffed with KF units

摘要

The crystal structure of a new tellurium IV oxyfluoride: KTe_3O_6F in the series MTe_3O_6F (M = K, Rb) has been determined on the basis of X-ray single crystal data (rhombohedral symmetry, R-3 space group, a = 948.60(10), c = 1377.4(2) pm, Z = 6, refinement program: SRFLXL-97, R_1 = 0.037). The structure is based on twisted Te_3O_6F sheets, separated by K layers, in which TeO_4F square pyramids share O corners and edges, forming hexagonal rings of the same nature as in hexagonal bronzes. The F anions are weakly bonded to Te cations (Te-F = 245.3 pm) and form quasi-independent KF units inserted inside a TeO_2 layer structure. The E lone pair is stereochemically active.