DOI: 10.17188/1262416
title: Materials Data on CaAl2Si2(H2O5)2 by Materials Project

description: CaAl2Si2(H2O5)2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ca2+ is bonded to six O2- atoms to form distorted CaO6 octahedra that share corners with four AlO6 octahedra and corners with six SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 63–64°. There are a spread of Ca–O bond distances ranging from 2.40–2.51 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 CaO6 octahedra, corners with four SiO4 tetrahedra, and edges with two equivalent AlO6 octahedra. The corner-sharing octahedral tilt angles are 63°. There are a spread of Al–O bond distances ranging from 1.89–1.97 Å. In the second Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent CaO6 octahedra, corners with four SiO4 tetrahedra, and edges with two equivalent AlO6 octahedra. The corner-sharing octahedral tilt angles are 64°. There are a spread of Al–O bond distances ranging from 1.90–2.00 Å. There are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with three equivalent CaO6 octahedra, corners with four AlO6 octahedra, and a cornercorner with one SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 49–67°. There are a spread of Si–O bond distances ranging from 1.63–1.67 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with three equivalent CaO6 octahedra, corners with four AlO6 octahedra, and a cornercorner with one SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 48–68°. There are a spread of Si–O bond distances ranging from 1.64–1.67 Å. There are four inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.97 Å. In the second H1+ site, H1+ is bonded in a distorted linear geometry to two O2- atoms. There is one shorter (1.01 Å) and one longer (1.60 Å) H–O bond length. In the third 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 fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded to two equivalent Al3+ and two H1+ atoms to form distorted corner-sharing OAl2H2 tetrahedra. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ca2+ and two Si4+ atoms. In the third O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent Al3+ and one H1+ atom. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ca2+, one Al3+, and one Si4+ atom. In the fifth O2- site, O2- is bonded in a distorted water-like geometry to one Ca2+ and two H1+ atoms. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Al3+ and one Si4+ atom. In the seventh O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ca2+, one Al3+, and one Si4+ atom. In the eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Al3+ and one Si4+ atom.