Materials Data on K2Mg2Be3F12 by Materials Project
K2Mg2Be3F12 crystallizes in the cubic P2_13 space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 9-coordinate geometry to nine F1- atoms. There are a spread of K–F bond distances ranging from 2.81–3.26 Å. In the second K1+ site, K1+ is bonded in a 12-coordinate geometry to twelve F1- atoms. There are a spread of K–F bond distances ranging from 2.91–3.23 Å. There are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six F1- atoms to form MgF6 octahedra that share corners with six equivalent BeF4 tetrahedra. All Mg–F bond lengths are 2.01 Å. In the second Mg2+ site, Mg2+ is bonded to six F1- atoms to form MgF6 octahedra that share corners with six equivalent BeF4 tetrahedra. There are three shorter (1.99 Å) and three longer (2.01 Å) Mg–F bond lengths. Be2+ is bonded to four F1- atoms to form BeF4 tetrahedra that share corners with four MgF6 octahedra. The corner-sharing octahedra tilt angles range from 16–49°. There are a spread of Be–F bond distances ranging from 1.55–1.57 Å. There are four inequivalent F1- sites. In the first F1- site, F1- is bonded in a 2-coordinate geometry to two K1+, one Mg2+, and one Be2+ atom. In the second F1- site, F1- is bonded in a distorted bent 150 degrees geometry to three K1+, one Mg2+, and one Be2+ atom. In the third F1- site, F1- is bonded in a distorted bent 150 degrees geometry to one K1+, one Mg2+, and one Be2+ atom. In the fourth F1- site, F1- is bonded in a 3-coordinate geometry to one K1+, one Mg2+, and one Be2+ atom.