DOE OSTI2020
Mg5B3O9F crystallizes in the orthorhombic Pna2_1 space group. The structure is three-dimensional. there are five inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with six MgO6 octahedra and edges with three MgO5F octahedra. The corner-sharing octahedra tilt angles range from 56–69°. There are a spread of Mg–O bond distances ranging from 2.07–2.24 Å. In the second Mg2+ site, Mg2+ is bonded to five O2- and one F1- atom to form a mixture of corner and edge-sharing MgO5F octahedra. The corner-sharing octahedra tilt angles range from 50–69°. There are a spread of Mg–O bond distances ranging from 2.08–2.13 Å. The Mg–F bond length is 2.00 Å. In the third Mg2+ site, Mg2+ is bonded to six O2- atoms to form a mixture of corner and edge-sharing MgO6 octahedra. The corner-sharing octahedra tilt angles range from 56–69°. There are a spread of Mg–O bond distances ranging from 2.07–2.24 Å. In the fourth Mg2+ site, Mg2+ is bonded to five O2- and one F1- atom to form distorted MgO5F octahedra that share corners with eight MgO6 octahedra and edges with two MgO5F octahedra. The corner-sharing octahedra tilt angles range from 49–62°. There are a spread of Mg–O bond distances ranging from 2.07–2.18 Å. The Mg–F bond length is 2.01 Å. In the fifth Mg2+ site, Mg2+ is bonded to five O2- and one F1- atom to form a mixture of corner and edge-sharing MgO5F octahedra. The corner-sharing octahedra tilt angles range from 49–69°. There are a spread of Mg–O bond distances ranging from 2.08–2.14 Å. The Mg–F bond length is 2.01 Å. There are three inequivalent B3+ sites. In the first B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of B–O bond distances ranging from 1.39–1.41 Å. In the second B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.38 Å) and two longer (1.40 Å) B–O bond length. In the third B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of B–O bond distances ranging from 1.39–1.41 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Mg2+ and one B3+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to three Mg2+ and one B3+ atom. In the third O2- site, O2- is bonded in a 4-coordinate geometry to three Mg2+ and one B3+ atom. In the fourth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Mg2+ and one B3+ atom. In the fifth O2- site, O2- is bonded to three Mg2+ and one B3+ atom to form distorted corner-sharing OMg3B trigonal pyramids. In the sixth O2- site, O2- is bonded to three Mg2+ and one B3+ atom to form distorted corner-sharing OMg3B trigonal pyramids. In the seventh O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Mg2+ and one B3+ atom. In the eighth O2- site, O2- is bonded in a 4-coordinate geometry to three Mg2+ and one B3+ atom. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to three Mg2+ and one B3+ atom. F1- is bonded in a distorted trigonal planar geometry to three Mg2+ atoms.