Crystal structure of Sr5Te4O12(OH)2, the first basic strontium oxotellurate(IV)

The asymmetric unit of the title basic strontium oxotellurate(IV), Sr5Te4O12(OH)2 {systematic name penta-strontium tetra-kis-[oxotellurate(IV)] di-hydroxide}, comprises three SrII cations (one with site symmetry 2) and two TeIV atoms, as well as seven O atoms. The coordination numbers of the alkaline earth cations to nearby O atoms range from seven (2 ×) to eight, and the TeIV atoms are surrounded by three oxygen partners in the form of trigonal pyramids. The SrO x polyhedra share corners and edges to build up a three-dimensional framework structure encapsulating channels propagating along [010]. The TeIV atoms flank the framework O atoms and are situated at the outer array of the channels with the 5s2 lone electron pairs protruding into the empty space of the channels (diameter ≃ 4 Å). Although the H atom of the OH group could not be located, bond-valence-sum calculations and typical O⋯O distances (range 2.81-3.06 Å) clearly indicate hydrogen bonding of medium to weak strengths.