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 pentastrontium tetrakis[oxotellurate(IV)] dihydroxide}, comprises three Sr-II cations (one with site symmetry 2) and two Te-IV atoms, as well as seven O atoms. The coordination numbers of the alkaline earth cations to nearby O atoms range from seven (2 x) to eight, and the Te-IV atoms are surrounded by three oxygen partners in the form of trigonal pyramids. The SrOx polyhedra share corners and edges to build up a three-dimensional framework structure encapsulating channels propagating along [010]. The Te-IV atoms flank the framework O atoms and are situated at the outer array of the channels with the 5s(2) lone electron pairs protruding into the empty space of the channels (diameter similar or equal to 4 angstrom). Although the H atom of the OH group could not be located, bond-valence-sum calculations and typical O center dot center dot center dot O distances (range 2.81-3.06 angstrom) clearly indicate hydrogen bonding of medium to weak strengths.