Materials Data on KCr12Si8BrO28 by Materials Project

KCr12Si8O28Br crystallizes in the tetragonal I4mm space group. The structure is three-dimensional. K1+ is bonded in a 4-coordinate geometry to eight O2- atoms. There are four shorter (2.63 Å) and four longer (3.00 Å) K–O bond lengths. There are three inequivalent Cr2+ sites. In the first Cr2+ site, Cr2+ is bonded in a distorted square co-planar geometry to four O2- and one Br1- atom. All Cr–O bond lengths are 2.06 Å. The Cr–Br bond length is 3.37 Å. In the second Cr2+ site, Cr2+ is bonded in a rectangular see-saw-like geometry to four O2- atoms. There are two shorter (2.06 Å) and two longer (2.08 Å) Cr–O bond lengths. In the third Cr2+ site, Cr2+ is bonded in a rectangular see-saw-like geometry to four O2- atoms. All Cr–O bond lengths are 2.06 Å. There are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. There is three shorter (1.64 Å) and one longer (1.66 Å) Si–O bond length. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form corner-sharing SiO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.64–1.66 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two Cr2+ and one Si4+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to one K1+ and two Si4+ atoms. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to one K1+, two equivalent Cr2+, and one Si4+ atom. In the fourth O2- site, O2- is bonded in a trigonal planar geometry to two equivalent Cr2+ and one Si4+ atom. In the fifth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Cr2+ and one Si4+ atom. Br1- is bonded in a distorted square co-planar geometry to four equivalent Cr2+ atoms.