Materials Data on KNaMg2Si4(O5F)2 by Materials Project
KNaMg2Si4(O5F)2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. K1+ is bonded to twelve O2- atoms to form KO12 cuboctahedra that share edges with six equivalent KO12 cuboctahedra and edges with twelve equivalent SiO4 tetrahedra. There are a spread of K–O bond distances ranging from 3.12–3.26 Å. Na1+ is bonded to four equivalent O2- and two equivalent F1- atoms to form NaO4F2 octahedra that share corners with four equivalent SiO4 tetrahedra and edges with six equivalent MgO4F2 octahedra. All Na–O bond lengths are 2.28 Å. Both Na–F bond lengths are 2.24 Å. Mg2+ is bonded to four equivalent O2- and two equivalent F1- atoms to form MgO4F2 octahedra that share corners with four equivalent SiO4 tetrahedra, edges with three equivalent NaO4F2 octahedra, and edges with three equivalent MgO4F2 octahedra. There are two shorter (2.07 Å) and two longer (2.09 Å) Mg–O bond lengths. Both Mg–F bond lengths are 2.01 Å. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share a cornercorner with one NaO4F2 octahedra, corners with two equivalent MgO4F2 octahedra, corners with three equivalent SiO4 tetrahedra, and edges with three equivalent KO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 52–62°. There are a spread of Si–O bond distances ranging from 1.60–1.67 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Na1+, two equivalent Mg2+, and one Si4+ atom. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent K1+ and two equivalent Si4+ atoms. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent K1+ and two equivalent Si4+ atoms. F1- is bonded in a 3-coordinate geometry to one Na1+ and two equivalent Mg2+ atoms.