DOI: 10.17188/1712336
title: Materials Data on MgAl2As2(HO)18 by Materials Project

description: MgAl2As2(H7O8)2(H2O)2 crystallizes in the triclinic P-1 space group. The structure is three-dimensional and consists of two water molecules and one MgAl2As2(H7O8)2 framework. In the MgAl2As2(H7O8)2 framework, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with two equivalent AsO4 tetrahedra. There are a spread of Mg–O bond distances ranging from 2.07–2.13 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent AlO6 octahedra and corners with two equivalent AsO4 tetrahedra. The corner-sharing octahedral tilt angles are 42°. There are a spread of Al–O bond distances ranging from 1.88–2.00 Å. In the second Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent AlO6 octahedra and corners with four equivalent AsO4 tetrahedra. The corner-sharing octahedral tilt angles are 42°. There are a spread of Al–O bond distances ranging from 1.89–1.95 Å. As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share a cornercorner with one MgO6 octahedra and corners with three AlO6 octahedra. The corner-sharing octahedra tilt angles range from 45–56°. There is three shorter (1.72 Å) and one longer (1.73 Å) As–O bond length. There are seven inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a distorted single-bond geometry to two O2- atoms. There is one shorter (1.02 Å) and one longer (1.61 Å) H–O bond length. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the third H1+ site, H1+ is bonded in a distorted single-bond geometry to one O2- atom. The H–O bond length is 1.01 Å. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to two O2- atoms. There is one shorter (1.00 Å) and one longer (1.73 Å) H–O bond length. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted water-like geometry to one Al3+ and two H1+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to one Mg2+ and two H1+ atoms. In the third O2- site, O2- is bonded in a distorted water-like geometry to one Mg2+ and two H1+ atoms. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to two Al3+ and one H1+ atom. In the fifth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Al3+, one As5+, and one H1+ atom. In the sixth O2- site, O2- is bonded in a bent 120 degrees geometry to one Al3+ and one As5+ atom. In the seventh O2- site, O2- is bonded in a trigonal planar geometry to one Al3+, one As5+, and one H1+ atom. In the eighth O2- site, O2- is bonded in a 2-coordinate geometry to one Mg2+ and one As5+ atom.