DOE OSTI2020
Mg13(NbH16)2 crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. there are four inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded in a body-centered cubic geometry to eight H+0.94- atoms. There are four shorter (2.04 Å) and four longer (2.08 Å) Mg–H bond lengths. In the second Mg2+ site, Mg2+ is bonded in a body-centered cubic geometry to eight H+0.94- atoms. There are four shorter (1.97 Å) and four longer (2.11 Å) Mg–H bond lengths. In the third Mg2+ site, Mg2+ is bonded in a body-centered cubic geometry to eight H+0.94- atoms. There are a spread of Mg–H bond distances ranging from 1.94–2.10 Å. In the fourth Mg2+ site, Mg2+ is bonded in a body-centered cubic geometry to eight equivalent H+0.94- atoms. All Mg–H bond lengths are 2.12 Å. There are two inequivalent Nb2+ sites. In the first Nb2+ site, Nb2+ is bonded in a body-centered cubic geometry to eight equivalent H+0.94- atoms. All Nb–H bond lengths are 1.93 Å. In the second Nb2+ site, Nb2+ is bonded in a body-centered cubic geometry to eight equivalent H+0.94- atoms. All Nb–H bond lengths are 1.94 Å. There are four inequivalent H+0.94- sites. In the first H+0.94- site, H+0.94- is bonded to three Mg2+ and one Nb2+ atom to form a mixture of edge and corner-sharing HMg3Nb tetrahedra. In the second H+0.94- site, H+0.94- is bonded to four Mg2+ atoms to form a mixture of edge and corner-sharing HMg4 tetrahedra. In the third H+0.94- site, H+0.94- is bonded in a trigonal planar geometry to three Mg2+ atoms. In the fourth H+0.94- site, H+0.94- is bonded to three Mg2+ and one Nb2+ atom to form HMg3Nb tetrahedra that share corners with twelve HMg3Nb tetrahedra and edges with four HMg4 tetrahedra.