A new polymorph with a layered structure ɛ-CaTe2O5

A new form of CaTe2O5 (ɛ) has been synthesized by hydrothermal method and its crystal structure has been solved and refined from single crystal X-ray diffraction data. ɛ-CaTe2O5 crystallizes in a monoclinic unit cell (P21/c; a = 9.4639(4) Å; b = 5.7566(3) Å; c = 11.2280(4) Å; β = 115.14(1)°) different from those already reported in the literature for four CaTe2O5 polymorphs. Its unique layered structure can be described by the stacking along the a-axis of [Te2O5]∞ layers interleaved with [Ca]∞ layers. Inside the [Te2O5]∞ layers, large tunnels extend along the [010], [011] and [011¯] directions, respectively. They result from the association of TeO4E distorted bipyramids where E denotes the Te(IV) electron lone pair. Ab initio density functional (DFT) calculations show that the electron lone pairs sit in the tunnels and in the tunnel walls along the [010], [011] and [011¯] directions.

Graphical abstractA new form of CaTe2O5 (ɛ) synthesized by hydrothermal method, with layered crystal structure.Figure optionsDownload full-size imageDownload as PowerPoint slide