NdNi4MgH4 crystallizes in the orthorhombic Pmn2_1 space group. Mg(1) is bonded in a 3-coordinate geometry to one H(2) and two equivalent H(1) atoms. Nd(1) is bonded in a 7-coordinate geometry to one H(3), two equivalent H(2), and four equivalent H(1) atoms. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a 3-coordinate geometry to one H(2) and two equivalent H(1) atoms. In the second Ni site, Ni(2) is bonded in a water-like geometry to one H(2) and one H(3) atom. In the third Ni site, Ni(3) is bonded in a water-like geometry to one H(1) and one H(3) atom. There are three inequivalent H sites. In the first H site, H(1) is bonded to one Mg(1), two equivalent Nd(1), one Ni(1), and one Ni(3) atom to form distorted HNd2MgNi2 trigonal bipyramids that share corners with three equivalent H(3)NdNi3 tetrahedra, corners with two equivalent H(2)Nd2MgNi2 trigonal bipyramids, corners with four equivalent H(1)Nd2MgNi2 trigonal bipyramids, edges with two equivalent H(1)Nd2MgNi2 trigonal bipyramids, and edges with two equivalent H(2)Nd2MgNi2 trigonal bipyramids. In the second H site, H(2) is bonded to one Mg(1), two equivalent Nd(1), one Ni(1), and one Ni(2) atom to form distorted HNd2MgNi2 trigonal bipyramids that share corners with three equivalent H(3)NdNi3 tetrahedra, corners with two equivalent H(2)Nd2MgNi2 trigonal bipyramids, corners with four equivalent H(1)Nd2MgNi2 trigonal bipyramids, and edges with four equivalent H(1)Nd2MgNi2 trigonal bipyramids. In the third H site, H(3) is bonded to one Nd(1), one Ni(2), and two equivalent Ni(3) atoms to form corner-sharing HNdNi3 tetrahedra.
NdNi4MgH4 crystallizes in the orthorhombic Pmn2_1 space group. Mg(1) is bonded in a 3-coordinate geometry to one H(2) and two equivalent H(1) atoms. The Mg(1)-H(2) bond length is 2.18 Å. Both Mg(1)-H(1) bond lengths are 2.20 Å. Nd(1) is bonded in a 7-coordinate geometry to one H(3), two equivalent H(2), and four equivalent H(1) atoms. The Nd(1)-H(3) bond length is 2.36 Å. Both Nd(1)-H(2) bond lengths are 2.53 Å. There are two shorter (2.48 Å) and two longer (2.49 Å) Nd(1)-H(1) bond lengths. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a 3-coordinate geometry to one H(2) and two equivalent H(1) atoms. The Ni(1)-H(2) bond length is 1.70 Å. Both Ni(1)-H(1) bond lengths are 1.65 Å. In the second Ni site, Ni(2) is bonded in a water-like geometry to one H(2) and one H(3) atom. The Ni(2)-H(2) bond length is 1.63 Å. The Ni(2)-H(3) bond length is 1.64 Å. In the third Ni site, Ni(3) is bonded in a water-like geometry to one H(1) and one H(3) atom. The Ni(3)-H(1) bond length is 1.68 Å. The Ni(3)-H(3) bond length is 1.63 Å. There are three inequivalent H sites. In the first H site, H(1) is bonded to one Mg(1), two equivalent Nd(1), one Ni(1), and one Ni(3) atom to form distorted HNd2MgNi2 trigonal bipyramids that share corners with three equivalent H(3)NdNi3 tetrahedra, corners with two equivalent H(2)Nd2MgNi2 trigonal bipyramids, corners with four equivalent H(1)Nd2MgNi2 trigonal bipyramids, edges with two equivalent H(1)Nd2MgNi2 trigonal bipyramids, and edges with two equivalent H(2)Nd2MgNi2 trigonal bipyramids. In the second H site, H(2) is bonded to one Mg(1), two equivalent Nd(1), one Ni(1), and one Ni(2) atom to form distorted HNd2MgNi2 trigonal bipyramids that share corners with three equivalent H(3)NdNi3 tetrahedra, corners with two equivalent H(2)Nd2MgNi2 trigonal bipyramids, corners with four equivalent H(1)Nd2MgNi2 trigonal bipyramids, and edges with four equivalent H(1)Nd2MgNi2 trigonal bipyramids. In the third H site, H(3) is bonded to one Nd(1), one Ni(2), and two equivalent Ni(3) atoms to form corner-sharing HNdNi3 tetrahedra.