The alkali metal copper(II) oxidotellurates(IV) Li₂Cu₂Te₃O₉, Li₂Cu₃Te₄O₁₂, Rb₂Cu₃Te₆O₁₆ and Cs₂Cu₃Te₆O₁₆ – four new structure types

Abstract

Four new MI/CuII/TeIV/O phases were obtained under hydrothermal conditions or with water as a mineralizer, and their crystal structures determined by single‐crystal X‐ray diffraction. Li2Cu2Te3O9 comprises trigonal‐pyramidal [TeO3], distorted tetrahedral [LiO4] and distorted square‐pyramidal [CuO5] units, forming a framework penetrated by channels into which the electron lone pairs of the TeIV atoms are directed. Li2Cu3Te4O12 contains isolated trigonal‐pyramidal [TeO3] units, tetrahedral [LiO4] groups forming [Li2O6] dimers by sharing an edge, as well as square‐planar [CuO4] and square‐pyramidal [CuO5] units, forming ∞1 ${_\infty ^1 }$ [Cu3O10] chains oriented parallel to [100]. These units also form a framework structure with channels where the electron lone pairs reside. Rb2Cu3Te6O16 and Cs2Cu3Te6O16 have isopointal crystal structures containing isolated [TeO3] groups and ∞1 ${_\infty ^1 }$ [Te4O10] chains oriented parallel to [010]. While in Rb2Cu3Te6O16 both Cu sites are 4‐coordinate in form of nearly square‐planar [CuO4] units, in Cs2Cu3Te6O16 one Cu site has a fifth oxygen contact resulting in a distorted square‐pyramidal [CuO5] polyhedron. Both crystal structures are made up from two alternating layer types stacked along [100]. The differences between Rb2Cu3Te6O16 and Cs2Cu3Te6O16 originate almost exclusively from the layer type consisting of the 5‐coordinate Cu site in Cs2Cu3Te6O16, while the other layer type shows almost no difference. A quantitative comparison between the two crystal structures is given.