The crystal structure of a new CdTeO polymorph, isotypic with ∊-CaTeO.

Single crystals of cadmium penta-oxidoditellurate(IV), CdTeO, were obtained as by-products in a hydro-thermal reaction of Cd(NO)·4HO, TeO, HTeO and NH (molar ratios 2:1:1:6) at 483 K for seven days. The crystals represent a different polymorph (henceforth referred to as the -form) than the -CdTeO crystals grown from the melt, and are isotypic with hydro-thermally grown -CaTeO. The asymmetric unit of -CdTeO comprises one Cd, two Te and five O sites, all of which are located in general positions (Wyckoff position 4 ). The cadmium(II) atom is coordinated by seven oxygen atoms, forming [CdOO] (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 bis-phenoidal [TeO] units also form layers propagating parallel to (100) by sharing edges with each other. The stereochemically active 5 lone pair of the Te atoms leads to the formation of large channels extending along [011] and smaller ones along [010]. A qu-anti-tative comparison between the crystal structures of -CdTeO and ∊-CaTeO is made.