Materials Data on Na2Mg2NiH6 by Materials Project

Abstract

Na2Mg2NiH6 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Na sites. In the first Na site, Na is bonded in a 1-coordinate geometry to five H atoms. There are a spread of Na–H bond distances ranging from 2.33–2.64 Å. In the second Na site, Na is bonded to six H atoms to form distorted NaH6 pentagonal pyramids that share corners with four equivalent MgH6 octahedra, corners with two equivalent NiH4 tetrahedra, edges with four equivalent MgH6 octahedra, and an edgeedge with one NiH4 tetrahedra. The corner-sharing octahedra tilt angles range from 8–81°. There are a spread of Na–H bond distances ranging from 2.32–2.48 Å. Mg is bonded to six H atoms to form distorted MgH6 octahedra that share corners with four equivalent MgH6 octahedra, corners with two equivalent NaH6 pentagonal pyramids, an edgeedge with one MgH6 octahedra, edges with two equivalent NaH6 pentagonal pyramids, and edges with two equivalent NiH4 tetrahedra. The corner-sharing octahedra tilt angles range from 24–33°. There are a spread of Mg–H bond distances ranging from 1.98–2.21 Å. Ni is bonded to four H atoms to form NiH4 tetrahedra that share corners with two equivalent NaH6 pentagonal pyramids, edges with four equivalent MgH6 octahedra, and an edgeedge with one NaH6 pentagonal pyramid. There is two shorter (1.58 Å) and two longer (1.59 Å) Ni–H bond length. There are four inequivalent H sites. In the first H site, H is bonded to two Na, two equivalent Mg, and one Ni atom to form a mixture of distorted edge and corner-sharing HNa2Mg2Ni trigonal bipyramids. In the second H site, H is bonded in a 4-coordinate geometry to two Na and two equivalent Mg atoms. In the third H site, H is bonded in a distorted rectangular see-saw-like geometry to one Na, two equivalent Mg, and one Ni atom. In the fourth H site, H is bonded to two Na, two equivalent Mg, and one Ni atom to form a mixture of distorted edge, face, and corner-sharing HNa2Mg2Ni square pyramids.