Materials Data on CaAl2Si2(H2O5)2 by Materials Project

Abstract

CaAl2Si2O7(OH)2H2O crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional and consists of four water molecules and one CaAl2Si2O7(OH)2 framework. In the CaAl2Si2O7(OH)2 framework, Ca2+ is bonded to five O2- atoms to form distorted CaO5 trigonal bipyramids that share corners with four equivalent AlO6 octahedra and corners with six equivalent SiO4 tetrahedra. The corner-sharing octahedral tilt angles are 44°. There are four shorter (2.37 Å) and one longer (2.57 Å) Ca–O bond lengths. Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent CaO5 trigonal bipyramids, edges with two equivalent AlO6 octahedra, and edges with two equivalent SiO4 tetrahedra. There are a spread of Al–O bond distances ranging from 1.91–2.05 Å. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share a cornercorner with one SiO4 tetrahedra, corners with three equivalent CaO5 trigonal bipyramids, and edges with two equivalent AlO6 octahedra. There are a spread of Si–O bond distances ranging from 1.63–1.67 Å. H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.97 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ca2+ and two equivalent Si4+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Ca2+, one Al3+, and one Si4+ atom. In the third O2- site, O2- is bonded in a distorted T-shaped geometry to two equivalent Al3+ and one Si4+ atom. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent Al3+ and one H1+ atom.