MgTb2(NiO3)2 crystallizes in the trigonal R3 space group. Mg(1) is bonded in a distorted trigonal non-coplanar geometry to three equivalent O(1) and three equivalent O(2) atoms. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form TbO6 octahedra that share corners with three equivalent Ni(1)O6 octahedra and  a faceface with one Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 46°. In the second Tb site, Tb(2) is bonded in a 6-coordinate geometry to three equivalent O(1) and three equivalent O(2) atoms. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form NiO6 octahedra that share corners with three equivalent Tb(1)O6 octahedra and  a faceface with one Tb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 46°. In the second Ni site, Ni(2) is bonded in a trigonal planar geometry to three equivalent O(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Tb(1), one Tb(2), and one Ni(1) atom to form a mixture of distorted edge and corner-sharing OTb2MgNi trigonal pyramids. In the second O site, O(2) is bonded in a 5-coordinate geometry to one Mg(1), one Tb(1), one Tb(2), one Ni(1), and one Ni(2) atom.
MgTb2(NiO3)2 crystallizes in the trigonal R3 space group. Mg(1) is bonded in a distorted trigonal non-coplanar geometry to three equivalent O(1) and three equivalent O(2) atoms. All Mg(1)-O(1) bond lengths are 1.99 Å. All Mg(1)-O(2) bond lengths are 2.72 Å. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form TbO6 octahedra that share corners with three equivalent Ni(1)O6 octahedra and  a faceface with one Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 46°. All Tb(1)-O(1) bond lengths are 2.28 Å. All Tb(1)-O(2) bond lengths are 2.27 Å. In the second Tb site, Tb(2) is bonded in a 6-coordinate geometry to three equivalent O(1) and three equivalent O(2) atoms. All Tb(2)-O(1) bond lengths are 2.20 Å. All Tb(2)-O(2) bond lengths are 2.49 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form NiO6 octahedra that share corners with three equivalent Tb(1)O6 octahedra and  a faceface with one Tb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 46°. All Ni(1)-O(1) bond lengths are 2.19 Å. All Ni(1)-O(2) bond lengths are 2.12 Å. In the second Ni site, Ni(2) is bonded in a trigonal planar geometry to three equivalent O(2) atoms. All Ni(2)-O(2) bond lengths are 1.94 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Tb(1), one Tb(2), and one Ni(1) atom to form a mixture of distorted edge and corner-sharing OTb2MgNi trigonal pyramids. In the second O site, O(2) is bonded in a 5-coordinate geometry to one Mg(1), one Tb(1), one Tb(2), one Ni(1), and one Ni(2) atom.