Mg6HfNiO8 is Caswellsilverite-derived structured and crystallizes in the tetragonal P4/mmm space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1) and four equivalent O(4) atoms to form MgO6 octahedra that share corners with two equivalent Ni(1)O6 octahedra, corners with four equivalent Mg(1)O6 octahedra, edges with four equivalent Mg(2)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. In the second Mg site, Mg(2) is bonded to two equivalent O(2) and four equivalent O(4) atoms to form MgO6 octahedra that share corners with two equivalent Hf(1)O6 octahedra, corners with four equivalent Mg(2)O6 octahedra, edges with four equivalent Mg(1)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. In the third Mg site, Mg(3) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form MgO6 octahedra that share corners with six equivalent Mg(3)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Hf(1)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, and edges with four equivalent Mg(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-7°. Hf(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form HfO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra, corners with four equivalent Hf(1)O6 octahedra, edges with four equivalent Ni(1)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. Ni(1) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form NiO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with four equivalent Ni(1)O6 octahedra, edges with four equivalent Hf(1)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), four equivalent Mg(3), and one Ni(1) atom to form distorted OMg5Ni octahedra that share corners with six equivalent O(1)Mg5Ni octahedra, edges with four equivalent O(3)Hf2Mg2Ni2 octahedra, edges with four equivalent O(2)HfMg5 octahedra, and edges with four equivalent O(4)Mg6 octahedra. The corner-sharing octahedral tilt angles range from 0-6°. In the second O site, O(2) is bonded to one Mg(2), four equivalent Mg(3), and one Hf(1) atom to form OHfMg5 octahedra that share corners with six equivalent O(2)HfMg5 octahedra, edges with four equivalent O(3)Hf2Mg2Ni2 octahedra, edges with four equivalent O(1)Mg5Ni octahedra, and edges with four equivalent O(4)Mg6 octahedra. The corner-sharing octahedral tilt angles range from 0-7°. In the third O site, O(3) is bonded to two equivalent Mg(3), two equivalent Hf(1), and two equivalent Ni(1) atoms to form OHf2Mg2Ni2 octahedra that share corners with two equivalent O(4)Mg6 octahedra, corners with four equivalent O(3)Hf2Mg2Ni2 octahedra, edges with four equivalent O(3)Hf2Mg2Ni2 octahedra, edges with four equivalent O(2)HfMg5 octahedra, and edges with four equivalent O(1)Mg5Ni octahedra. The corner-sharing octahedra are not tilted. In the fourth O site, O(4) is bonded to two equivalent Mg(1), two equivalent Mg(2), and two equivalent Mg(3) atoms to form OMg6 octahedra that share corners with two equivalent O(3)Hf2Mg2Ni2 octahedra, corners with four equivalent O(4)Mg6 octahedra, edges with four equivalent O(2)HfMg5 octahedra, edges with four equivalent O(1)Mg5Ni octahedra, and edges with four equivalent O(4)Mg6 octahedra. The corner-sharing octahedra are not tilted.
Mg6HfNiO8 is Caswellsilverite-derived structured and crystallizes in the tetragonal P4/mmm space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1) and four equivalent O(4) atoms to form MgO6 octahedra that share corners with two equivalent Ni(1)O6 octahedra, corners with four equivalent Mg(1)O6 octahedra, edges with four equivalent Mg(2)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. Both Mg(1)-O(1) bond lengths are 2.06 Å. All Mg(1)-O(4) bond lengths are 2.13 Å. In the second Mg site, Mg(2) is bonded to two equivalent O(2) and four equivalent O(4) atoms to form MgO6 octahedra that share corners with two equivalent Hf(1)O6 octahedra, corners with four equivalent Mg(2)O6 octahedra, edges with four equivalent Mg(1)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. Both Mg(2)-O(2) bond lengths are 2.29 Å. All Mg(2)-O(4) bond lengths are 2.13 Å. In the third Mg site, Mg(3) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form MgO6 octahedra that share corners with six equivalent Mg(3)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Hf(1)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, and edges with four equivalent Mg(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-7°. The Mg(3)-O(3) bond length is 2.39 Å. The Mg(3)-O(4) bond length is 2.17 Å. Both Mg(3)-O(1) bond lengths are 2.13 Å. Both Mg(3)-O(2) bond lengths are 2.13 Å. Hf(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form HfO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra, corners with four equivalent Hf(1)O6 octahedra, edges with four equivalent Ni(1)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. Both Hf(1)-O(2) bond lengths are 2.26 Å. All Hf(1)-O(3) bond lengths are 2.13 Å. Ni(1) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form NiO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with four equivalent Ni(1)O6 octahedra, edges with four equivalent Hf(1)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. Both Ni(1)-O(1) bond lengths are 2.50 Å. All Ni(1)-O(3) bond lengths are 2.13 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), four equivalent Mg(3), and one Ni(1) atom to form distorted OMg5Ni octahedra that share corners with six equivalent O(1)Mg5Ni octahedra, edges with four equivalent O(3)Hf2Mg2Ni2 octahedra, edges with four equivalent O(2)HfMg5 octahedra, and edges with four equivalent O(4)Mg6 octahedra. The corner-sharing octahedral tilt angles range from 0-6°. In the second O site, O(2) is bonded to one Mg(2), four equivalent Mg(3), and one Hf(1) atom to form OHfMg5 octahedra that share corners with six equivalent O(2)HfMg5 octahedra, edges with four equivalent O(3)Hf2Mg2Ni2 octahedra, edges with four equivalent O(1)Mg5Ni octahedra, and edges with four equivalent O(4)Mg6 octahedra. The corner-sharing octahedral tilt angles range from 0-7°. In the third O site, O(3) is bonded to two equivalent Mg(3), two equivalent Hf(1), and two equivalent Ni(1) atoms to form OHf2Mg2Ni2 octahedra that share corners with two equivalent O(4)Mg6 octahedra, corners with four equivalent O(3)Hf2Mg2Ni2 octahedra, edges with four equivalent O(3)Hf2Mg2Ni2 octahedra, edges with four equivalent O(2)HfMg5 octahedra, and edges with four equivalent O(1)Mg5Ni octahedra. The corner-sharing octahedra are not tilted. In the fourth O site, O(4) is bonded to two equivalent Mg(1), two equivalent Mg(2), and two equivalent Mg(3) atoms to form OMg6 octahedra that share corners with two equivalent O(3)Hf2Mg2Ni2 octahedra, corners with four equivalent O(4)Mg6 octahedra, edges with four equivalent O(2)HfMg5 octahedra, edges with four equivalent O(1)Mg5Ni octahedra, and edges with four equivalent O(4)Mg6 octahedra. The corner-sharing octahedra are not tilted.