DOE OSTI2020
Mg2Al4Si5O18 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with six SiO4 tetrahedra, an edgeedge with one SiO4 tetrahedra, and edges with two AlO4 tetrahedra. There are a spread of Mg–O bond distances ranging from 2.04–2.24 Å. In the second Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with six SiO4 tetrahedra and edges with three AlO4 tetrahedra. There are a spread of Mg–O bond distances ranging from 2.09–2.18 Å. In the third Mg2+ site, Mg2+ is bonded to six O2- atoms to form distorted MgO6 octahedra that share corners with three AlO4 tetrahedra, corners with three SiO4 tetrahedra, an edgeedge with one SiO4 tetrahedra, and edges with two AlO4 tetrahedra. There are a spread of Mg–O bond distances ranging from 1.99–2.22 Å. In the fourth Mg2+ site, Mg2+ is bonded to six O2- atoms to form distorted MgO6 octahedra that share corners with three AlO4 tetrahedra, corners with three SiO4 tetrahedra, and edges with three AlO4 tetrahedra. There are a spread of Mg–O bond distances ranging from 2.00–2.28 Å. There are eight inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to four O2- atoms to form distorted AlO4 tetrahedra that share corners with two AlO4 tetrahedra, corners with two SiO4 tetrahedra, and edges with two MgO6 octahedra. There are a spread of Al–O bond distances ranging from 1.74–1.82 Å. In the second Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with four SiO4 tetrahedra and edges with two MgO6 octahedra. There are a spread of Al–O bond distances ranging from 1.76–1.78 Å. In the third Al3+ site, Al3+ is bonded to four O2- atoms to form distorted AlO4 tetrahedra that share corners with four SiO4 tetrahedra and edges with two MgO6 octahedra. There are a spread of Al–O bond distances ranging from 1.76–1.78 Å. In the fourth Al3+ site, Al3+ is bonded to four O2- atoms to form distorted AlO4 tetrahedra that share a cornercorner with one AlO4 tetrahedra, corners with three SiO4 tetrahedra, and edges with two MgO6 octahedra. There are a spread of Al–O bond distances ranging from 1.73–1.79 Å. In the fifth Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share a cornercorner with one AlO4 tetrahedra, corners with three SiO4 tetrahedra, and edges with two MgO6 octahedra. There are a spread of Al–O bond distances ranging from 1.72–1.79 Å. In the sixth Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with two MgO6 octahedra, a cornercorner with one AlO4 tetrahedra, and corners with three SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 41–50°. There are a spread of Al–O bond distances ranging from 1.72–1.80 Å. In the seventh Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with two MgO6 octahedra, corners with two AlO4 tetrahedra, and corners with two SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 45–47°. There are a spread of Al–O bond distances ranging from 1.73–1.76 Å. In the eighth Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with two MgO6 octahedra, a cornercorner with one AlO4 tetrahedra, and corners with three SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 42–50°. There are a spread of Al–O bond distances ranging from 1.72–1.79 Å. There are ten inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two MgO6 octahedra, a cornercorner with one AlO4 tetrahedra, and corners with three SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 41–48°. There are a spread of Si–O bond distances ranging from 1.63–1.69 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two MgO6 octahedra, a cornercorner with one SiO4 tetrahedra, and corners with three AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 43–44°. There are a spread of Si–O bond distances ranging from 1.59–1.66 Å. In the third Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two MgO6 octahedra, corners with two AlO4 tetrahedra, and corners with two SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 41–49°. There are a spread of Si–O bond distances ranging from 1.58–1.72 Å. In the fourth Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two MgO6 octahedra, a cornercorner with one SiO4 tetrahedra, and corners with three AlO4 tetrahedra. The corner-sharing octahedral tilt angles are 43°. There are a spread of Si–O bond distances ranging from 1.58–1.66 Å. In the fifth Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two MgO6 octahedra, a cornercorner with one SiO4 tetrahedra, and corners with three AlO4 tetrahedra. The corner-sharing octahedral tilt angles are 41°. There are a spread of Si–O bond distances ranging from 1.59–1.66 Å. In the sixth Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two MgO6 octahedra, corners with two AlO4 tetrahedra, and corners with two SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 43–44°. There is one shorter (1.62 Å) and three longer (1.65 Å) Si–O bond length. In the seventh Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two MgO6 octahedra and corners with four AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 43–44°. There are a spread of Si–O bond distances ranging from 1.59–1.67 Å. In the eighth Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two MgO6 octahedra, corners with two AlO4 tetrahedra, and corners with two SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 41–42°. There are a spread of Si–O bond distances ranging from 1.62–1.66 Å. In the ninth Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two MgO6 octahedra, corners with two AlO4 tetrahedra, and corners with two SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 43–44°. There are a spread of Si–O bond distances ranging from 1.63–1.65 Å. In the tenth Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two AlO4 tetrahedra, corners with two SiO4 tetrahedra, and edges with two MgO6 octahedra. There is two shorter (1.62 Å) and two longer (1.69 Å) Si–O bond length. There are thirty-six inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to one Al3+ and one Si4+ atom. In the second O2- site, O2- is bonded in a linear geometry to two Si4+ atoms. In the third O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+ and two Si4+ atoms. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one Al3+, and one Si4+ atom. In the fifth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mg2+ and two Si4+ atoms. In the sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mg2+, one Al3+, and one Si4+ atom. In the seventh O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one Al3+, and one Si4+ atom. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one Al3+, and one Si4+ atom. In the ninth O2- site, O2- is bonded in a linear geometry to one Al3+ and one Si4+ atom. In the tenth O2- site, O2- is bonded in a linear geometry to two Si4+ atoms. In the eleventh O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mg2+, one Al3+, and one Si4+ atom. In the twelfth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one Al3+, and one Si4+ atom. In the thirteenth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one Al3+, and one Si4+ atom. In the fourteenth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one Al3+, and one Si4+ atom. In the fifteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mg2+, one Al3+, and one Si4+ atom. In the sixteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mg2+, one Al3+, and one Si4+ atom. In the seventeenth O2- site, O2- is bonded in a linear geometry to two Si4+ atoms. In the eighteenth O2- site, O2- is bonded in a linear geometry to one Al3+ and one Si4+ atom. In the nineteenth O2- site, O2- is bonded in a linear geometry to two Si4+ atoms. In the twentieth O2- site, O2- is bonded in a linear geometry to two Si4+ atoms. In the twenty-first O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one Al3+, and one Si4+ atom. In the twenty-second O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one Al3+, and one Si4+ atom. In the twenty-third O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one Al3+, and one Si4+ atom. In the twenty-fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one Al3+, and one Si4+ atom. In the twenty-fifth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one Al3+, and one Si4+ atom. In the twenty-sixth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one Al3+, and one Si4+ atom. In the twenty-seventh O2- site, O2- is bonded in a linear geometry to one Al3+ and one Si4+ atom. In the twenty-eighth O2- site, O2- is bonded in a linear geometry to two Si4+ atoms. In the twenty-ninth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mg2+ and two Al3+ atoms. In the thirtieth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mg2+ and two Al3+ atoms. In the thirty-first O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one Al3+, and one Si4+ atom. In the thirty-second O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+ and two Al3+ atoms. In the thirty-third O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one Al3+, and one Si4+ atom. In the thirty-fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+ and two Al3+ atoms. In the thirty-fifth O2- site, O2- is bonded in a linear geometry to one Al3+ and one Si4+ atom. In the thirty-sixth O2- site, O2- is bonded in a linear geometry to one Al3+ and one Si4+ atom.