DOI: 10.17188/1716948
title: Materials Data on Ca4MgAs4O27 by Materials Project

description: Ca4MgAs4O27 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are four inequivalent Ca sites. In the first Ca site, Ca is bonded in a 7-coordinate geometry to seven O atoms. There are a spread of Ca–O bond distances ranging from 2.36–2.73 Å. In the second Ca site, Ca is bonded to six O atoms to form CaO6 octahedra that share corners with five AsO4 tetrahedra and an edgeedge with one CaO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.27–2.49 Å. In the third Ca site, Ca is bonded to seven O atoms to form distorted CaO7 pentagonal bipyramids that share corners with four AsO4 tetrahedra, an edgeedge with one CaO7 pentagonal bipyramid, and an edgeedge with one AsO4 tetrahedra. There are a spread of Ca–O bond distances ranging from 2.34–2.60 Å. In the fourth Ca site, Ca is bonded in a 7-coordinate geometry to seven O atoms. There are a spread of Ca–O bond distances ranging from 2.30–2.58 Å. Mg is bonded in a 5-coordinate geometry to six O atoms. There are a spread of Mg–O bond distances ranging from 2.01–2.71 Å. There are four inequivalent As sites. In the first As site, As is bonded to four O atoms to form AsO4 tetrahedra that share a cornercorner with one CaO6 octahedra, corners with two equivalent CaO7 pentagonal bipyramids, and an edgeedge with one CaO7 pentagonal bipyramid. The corner-sharing octahedral tilt angles are 50°. There are a spread of As–O bond distances ranging from 1.70–1.74 Å. In the second As site, As is bonded to four O atoms to form AsO4 tetrahedra that share corners with three equivalent CaO6 octahedra. The corner-sharing octahedra tilt angles range from 51–61°. There are a spread of As–O bond distances ranging from 1.72–1.74 Å. In the third As site, As is bonded to four O atoms to form AsO4 tetrahedra that share a cornercorner with one CaO6 octahedra and a cornercorner with one CaO7 pentagonal bipyramid. The corner-sharing octahedral tilt angles are 62°. There is three shorter (1.72 Å) and one longer (1.78 Å) As–O bond length. In the fourth As site, As is bonded to four O atoms to form AsO4 tetrahedra that share a cornercorner with one CaO7 pentagonal bipyramid. There are a spread of As–O bond distances ranging from 1.71–1.77 Å. There are twenty-seven inequivalent O sites. In the first O site, O is bonded in a bent 120 degrees geometry to one Ca and one As atom. In the second O site, O is bonded in a 3-coordinate geometry to two Ca and one As atom. In the third O site, O is bonded in a distorted trigonal non-coplanar geometry to two Ca and one As atom. In the fourth O site, O is bonded to three Ca and one As atom to form distorted edge-sharing OCa3As tetrahedra. In the fifth O site, O is bonded in a single-bond geometry to one As atom. In the sixth O site, O is bonded in a distorted bent 150 degrees geometry to one Ca and one As atom. In the seventh O site, O is bonded in a 4-coordinate geometry to three Ca and one As atom. In the eighth O site, O is bonded in a distorted trigonal non-coplanar geometry to two Ca and one As atom. In the ninth O site, O is bonded in a distorted trigonal planar geometry to two Ca and one As atom. In the tenth O site, O is bonded in a distorted trigonal planar geometry to two Ca and one As atom. In the eleventh O site, O is bonded in a distorted single-bond geometry to one As and one O atom. The O–O bond length is 1.76 Å. In the twelfth O site, O is bonded in a 2-coordinate geometry to one Ca, one Mg, and one As atom. In the thirteenth O site, O is bonded in a single-bond geometry to one As atom. In the fourteenth O site, O is bonded in a distorted trigonal planar geometry to one Ca, one Mg, and one As atom. In the fifteenth O site, O is bonded in a bent 120 degrees geometry to one Mg and one As atom. In the sixteenth O site, O is bonded in a distorted trigonal planar geometry to two Ca and one As atom. In the seventeenth O site, O is bonded in a bent 120 degrees geometry to one Ca and one O atom. The O–O bond length is 1.23 Å. In the eighteenth O site, O is bonded in a single-bond geometry to one Ca atom. In the nineteenth O site, O is bonded in a distorted single-bond geometry to one Ca atom. In the twentieth O site, O is bonded in a single-bond geometry to one Ca atom. In the twenty-first O site, O is bonded in a single-bond geometry to one Mg atom. In the twenty-second O site, O is bonded in a bent 120 degrees geometry to one Mg and one O atom. The O–O bond length is 1.22 Å. In the twenty-third O site, O is bonded in a distorted L-shaped geometry to one Ca and one Mg atom. In the twenty-fourth O site, O is bonded in a single-bond geometry to one O atom. In the twenty-fifth O site, O is bonded in a single-bond geometry to one O atom. The O–O bond length is 1.22 Å. In the twenty-sixth O site, O is bonded in a water-like geometry to two O atoms. In the twenty-seventh O site, O is bonded in a single-bond geometry to one O atom.