Materials Data on Ca19(Mg4H27)2 by Materials Project

Abstract

Ca19(Mg4H27)2 crystallizes in the cubic Im-3 space group. The structure is three-dimensional. there are three inequivalent Ca sites. In the first Ca site, Ca is bonded in a 8-coordinate geometry to eight H atoms. There are a spread of Ca–H bond distances ranging from 2.26–2.49 Å. In the second Ca site, Ca is bonded in a distorted q6 geometry to ten H atoms. There are four shorter (2.35 Å) and six longer (2.49 Å) Ca–H bond lengths. In the third Ca site, Ca is bonded to twelve equivalent H atoms to form CaH12 cuboctahedra that share faces with eight equivalent MgH6 octahedra. All Ca–H bond lengths are 2.50 Å. Mg is bonded to six H atoms to form MgH6 octahedra that share corners with three equivalent MgH6 octahedra and a faceface with one CaH12 cuboctahedra. The corner-sharing octahedral tilt angles are 35°. There is three shorter (1.95 Å) and three longer (2.02 Å) Mg–H bond length. There are four inequivalent H sites. In the first H site, H is bonded in a distorted see-saw-like geometry to four Ca atoms. In the second H site, H is bonded to four Ca atoms to form a mixture of edge and corner-sharing HCa4 tetrahedra. In the third H site, H is bonded to three Ca and one Mg atom to form a mixture of distorted edge and corner-sharing HCa3Mg tetrahedra. In the fourth H site, H is bonded to two Ca and two equivalent Mg atoms to form distorted HCa2Mg2 tetrahedra that share corners with fourteen HCa4 tetrahedra and edges with seven HCa2Mg2 tetrahedra.