Ca(2)Te(3)O(8), a new phase in the CaO–TeO(2) system

Single crystals of dicalcium octa­oxidotritellurate(IV), Ca(2)Te(3)O(8), were obtained from a CsCl/NaCl melt with CaO and TeO(2) as educts in the molar ratio of 1:2. Ca(2)Te(3)O(8) crystallizes isotypically with Pb(3)Te(2)O(8) and is comprised of two unique Ca, four Te and eight O sites. One calcium cation has eight and the other nine coordination partners. Both coordination polyhedra are considerably distorted. Two kinds of oxotellurate(IV) anions with the same formula [Te(3)O(8)](4−) are present. One is an infinite zigzag chain anion consisting of pairs of [TeO(4)] bis­phenoids linked to a trigonal–pyramidal [TeO(3)] group with a connectivity of [(TeO(1/1)O(2/2))(TeO(2/1)O(2/2))(2)](n), while the other is a finite anion made up of one central [TeO(4)] bis­phenoid linked to two [TeO(3)] trigonal pyramids and has a connectivity of [(TeO(2/1)O(1/2))(2)(TeO(2/2)O(2/1))]. In the crystal, the anions are organized in layers extending parallel to (100). Adjacent layers are held together by the calcium cations to define a three-dimensional framework structure.