DOE OSTI2020
Mo2Al2O7 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Mo4+ sites. In the first Mo4+ site, Mo4+ is bonded in a 6-coordinate geometry to six O2- atoms. There are four shorter (1.99 Å) and two longer (2.09 Å) Mo–O bond lengths. In the second Mo4+ site, Mo4+ is bonded to six O2- atoms to form MoO6 octahedra that share corners with two equivalent MoO6 octahedra, corners with two equivalent AlO6 octahedra, and edges with two equivalent AlO6 octahedra. The corner-sharing octahedra tilt angles range from 54–64°. There are a spread of Mo–O bond distances ranging from 1.97–2.16 Å. In the third Mo4+ site, Mo4+ is bonded to six O2- atoms to form distorted MoO6 octahedra that share corners with two equivalent MoO6 octahedra, corners with two equivalent AlO6 octahedra, and edges with two equivalent AlO6 octahedra. The corner-sharing octahedra tilt angles range from 54–58°. There are a spread of Mo–O bond distances ranging from 1.94–2.27 Å. In the fourth Mo4+ site, Mo4+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Mo–O bond distances ranging from 1.97–2.43 Å. There are four inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Al–O bond distances ranging from 1.96–2.38 Å. In the second Al3+ site, Al3+ is bonded to six O2- atoms to form distorted AlO6 octahedra that share corners with four AlO6 octahedra and edges with two equivalent MoO6 octahedra. The corner-sharing octahedra tilt angles range from 66–75°. There are a spread of Al–O bond distances ranging from 1.97–2.35 Å. In the third Al3+ site, Al3+ is bonded to six O2- atoms to form distorted AlO6 octahedra that share corners with two equivalent MoO6 octahedra and corners with four AlO6 octahedra. The corner-sharing octahedra tilt angles range from 63–75°. There are a spread of Al–O bond distances ranging from 1.94–2.28 Å. In the fourth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent MoO6 octahedra, corners with four AlO6 octahedra, and edges with two equivalent MoO6 octahedra. The corner-sharing octahedra tilt angles range from 58–66°. There are a spread of Al–O bond distances ranging from 1.91–2.05 Å. There are fourteen inequivalent O2- sites. In the first O2- site, O2- is bonded to four Al3+ atoms to form distorted OAl4 tetrahedra that share corners with six OAl4 tetrahedra and an edgeedge with one OAl2Mo2 tetrahedra. In the second O2- site, O2- is bonded to four Al3+ atoms to form distorted OAl4 tetrahedra that share corners with six OAl4 tetrahedra and an edgeedge with one OAl2Mo2 tetrahedra. In the third O2- site, O2- is bonded in a 4-coordinate geometry to two Mo4+ and two Al3+ atoms. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Mo4+ and one Al3+ atom. In the fifth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Mo4+ and one Al3+ atom. In the sixth O2- site, O2- is bonded to two Mo4+ and two Al3+ atoms to form a mixture of distorted corner and edge-sharing OAl2Mo2 tetrahedra. In the seventh O2- site, O2- is bonded in a trigonal planar geometry to two Mo4+ and one Al3+ atom. In the eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Mo4+ and one Al3+ atom. In the ninth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Mo4+ and one Al3+ atom. In the tenth O2- site, O2- is bonded in a trigonal planar geometry to two Mo4+ and one Al3+ atom. In the eleventh O2- site, O2- is bonded to two Mo4+ and two Al3+ atoms to form a mixture of distorted corner and edge-sharing OAl2Mo2 tetrahedra. In the twelfth O2- site, O2- is bonded in a 4-coordinate geometry to two Mo4+ and two Al3+ atoms. In the thirteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Mo4+ and one Al3+ atom. In the fourteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Mo4+ and one Al3+ atom.