The cadmium oxidotellurates(IV) Cd₅(TeO₃)₄(NO₃)₂ and Cd₄Te₅O₁₄

Abstract

Monoclinic single crystals of Cd5(TeO3)4(NO3)2 (space group P21/c), pentacadmium tetrakis[oxidotellurate(IV)] dinitrate, and of Cd4Te5O14 (space group C2/c), tetracadmium pentaoxidotellurate(IV), were obtained under the same hydrothermal conditions. Whereas the crystal structure of Cd5(TeO3)4(NO3)2 is distinctively layered, that of Cd4Te5O14 exhibits a tri-periodic framework. In Cd5(TeO3)4(NO3)2, the three CdII atoms have coordination numbers (CN) of 7, 6 and 6. The two types of [CdO6] and the [CdO7] polyhedra [bond lengths range from 2.179 (3) to 2.658 (2) Å] share corners and edges, resulting in layers extending parallel to (100). Both TeIV atoms are coordinated by three oxygen atoms in a trigonal–pyramidal shape. The oxygen atoms of the isolated [TeO3] groups [bond lengths range from 1.847 (3) to 1.886 (3) Å] all are part of the cadmium–oxygen layer. The electron lone pairs ψ of the TeIV atoms are directed away from the layer on both sides. The available interlayer space is co-occupied by the nitrate group, which is directly connected with two of its O atoms to the layer whereas the third O atom is solely bonded to the N atom and points towards the adjacent layer. In Cd4Te5O14, all three unique CdII atoms are coordinated by six oxygen atoms, considering Cd—O distances from 2.235 (2) to 2.539 (2) Å. By edge- and corner-sharing, the distorted [CdO6] polyhedra form an open framework that is partially filled with three different stereochemically active TeIV atoms. All of them exhibit a CN of 4, with Te—O bonds in a range from 1.859 (2) to 2.476 (2) Å. The corresponding [TeO4] units are linked to each other by corner- and edge-sharing, forming infinite helical 1 ∞[Te10O28] chains extending parallel to [203]. The connectivity in the chains can be described as (...–⋄–⋄=⋄–⋄–⋄–⋄–⋄=⋄–⋄–⋄–...) n where ‘⋄’ denotes a [TeO4] unit, ‘–’ a linkage via corners and ‘=’ a linkage via edges. Such a structural motif is unprecedented in the crystal chemistry of oxidotellurate(IV) compounds.