Materials Data on RbNaMg6O7 by Materials Project
RbNaMg6O7 crystallizes in the tetragonal P4mm space group. The structure is three-dimensional. Rb1+ is bonded in a 5-coordinate geometry to five O2- atoms. There are four shorter (2.73 Å) and one longer (2.98 Å) Rb–O bond lengths. Na1+ is bonded to six O2- atoms to form NaO6 octahedra that share corners with four equivalent NaO6 octahedra, edges with four equivalent MgO5 square pyramids, and edges with four equivalent MgO5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 6°. There are a spread of Na–O bond distances ranging from 2.12–2.44 Å. There are four inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to five O2- atoms to form MgO5 square pyramids that share corners with four equivalent MgO5 square pyramids, edges with four equivalent NaO6 octahedra, and edges with four equivalent MgO5 trigonal bipyramids. There are one shorter (2.05 Å) and four longer (2.13 Å) Mg–O bond lengths. In the second Mg2+ site, Mg2+ is bonded in a rectangular see-saw-like geometry to four equivalent O2- atoms. All Mg–O bond lengths are 2.13 Å. In the third Mg2+ site, Mg2+ is bonded in a square co-planar geometry to four O2- atoms. There are a spread of Mg–O bond distances ranging from 2.02–2.14 Å. In the fourth Mg2+ site, Mg2+ is bonded to five O2- atoms to form MgO5 trigonal bipyramids that share corners with four equivalent MgO5 trigonal bipyramids, edges with two equivalent NaO6 octahedra, edges with two equivalent MgO5 square pyramids, and edges with four equivalent MgO5 trigonal bipyramids. There are a spread of Mg–O bond distances ranging from 2.12–2.18 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded to one Na1+ and four equivalent Mg2+ atoms to form ONaMg4 square pyramids that share a cornercorner with one ORbNaMg4 octahedra, corners with four equivalent ONaMg4 square pyramids, corners with four equivalent ORb2Mg3 trigonal bipyramids, and edges with four equivalent ONa2Mg4 octahedra. The corner-sharing octahedral tilt angles are 0°. In the second O2- site, O2- is bonded to one Rb1+, one Na1+, and four equivalent Mg2+ atoms to form distorted ORbNaMg4 octahedra that share corners with four equivalent ORbNaMg4 octahedra, a cornercorner with one ONaMg4 square pyramid, corners with four equivalent ORb2Mg3 trigonal bipyramids, edges with four equivalent ONa2Mg4 octahedra, and edges with four equivalent OMg5 square pyramids. The corner-sharing octahedral tilt angles are 20°. In the third O2- site, O2- is bonded to five Mg2+ atoms to form OMg5 square pyramids that share corners with four equivalent OMg5 square pyramids and edges with eight ORbNaMg4 octahedra. In the fourth O2- site, O2- is bonded to two equivalent Na1+ and four Mg2+ atoms to form ONa2Mg4 octahedra that share corners with four equivalent ONa2Mg4 octahedra, a cornercorner with one ORb2Mg3 trigonal bipyramid, edges with six ORbNaMg4 octahedra, and edges with four ONaMg4 square pyramids. The corner-sharing octahedra tilt angles range from 6–11°. In the fifth O2- site, O2- is bonded to two equivalent Rb1+ and three Mg2+ atoms to form distorted ORb2Mg3 trigonal bipyramids that share corners with three ORbNaMg4 octahedra, corners with two equivalent ONaMg4 square pyramids, corners with four equivalent ORb2Mg3 trigonal bipyramids, and edges with four equivalent ORb2Mg3 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 0–51°.