The crystal structure of a new CdTe2O5 polymorph, isotypic with ∊-CaTe2O5

Single crystals of cadmium penta­oxidoditellurate(IV), CdTe2O5, were obtained as by-products in a hydro­thermal reaction of Cd(NO3)2·4H2O, TeO2, H6TeO6 and NH3 (molar ratios 2:1:1:6) at 483 K for seven days. The crystals represent a different polymorph (henceforth referred to as the β-form) than the α-CdTe2O5 crystals grown from the melt, and are isotypic with hydro­thermally grown ∊-CaTe2O5. The asymmetric unit of β-CdTe2O5 comprises one Cd, two Te and five O sites, all of which are located in general positions (Wyckoff position 4 e). The cadmium(II) atom is coordinated by seven oxygen atoms, forming 2∞[CdO6/2O1/1] (100) layers. Both tellurium sites are surrounded by four oxygen atoms with one of them being at a significantly longer distance than the other three. The resulting bis­phenoidal [TeO4] units also form layers propagating parallel to (100) by sharing edges with each other. The stereochemically active 5s2 lone pair of the TeIV atoms leads to the formation of large channels extending along [011] and smaller ones along [010]. A qu­anti­tative comparison between the crystal structures of β-CdTe2O5 and ∊-CaTe2O5 is made.