Mg2Ta2Ni2O9 is Corundum-derived structured and crystallizes in the trigonal P-3c1 space group. Mg(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted MgO6 octahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with three equivalent Ta(1)O6 octahedra, corners with three equivalent Ni(1)O6 octahedra, edges with three equivalent Ta(1)O6 octahedra, and  a faceface with one Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-65°. Ta(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted TaO6 octahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with six equivalent Ni(1)O6 octahedra, edges with three equivalent Mg(1)O6 octahedra, and  a faceface with one Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-58°. Ni(1) is bonded to six equivalent O(1) atoms to form NiO6 octahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with six equivalent Ta(1)O6 octahedra, edges with three equivalent Ni(1)O6 octahedra, and  a faceface with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-58°. There are two inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Ta(1), and two equivalent Ni(1) atoms to form distorted OMgTaNi2 trigonal pyramids that share corners with four equivalent O(2)Mg2Ta2 trigonal pyramids, corners with eight equivalent O(1)MgTaNi2 trigonal pyramids,  an edgeedge with one O(2)Mg2Ta2 trigonal pyramid, and edges with three equivalent O(1)MgTaNi2 trigonal pyramids. In the second O site, O(2) is bonded to two equivalent Mg(1) and two equivalent Ta(1) atoms to form distorted OMg2Ta2 trigonal pyramids that share corners with four equivalent O(2)Mg2Ta2 trigonal pyramids, corners with eight equivalent O(1)MgTaNi2 trigonal pyramids, edges with two equivalent O(2)Mg2Ta2 trigonal pyramids, and edges with two equivalent O(1)MgTaNi2 trigonal pyramids.
Mg2Ta2Ni2O9 is Corundum-derived structured and crystallizes in the trigonal P-3c1 space group. Mg(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted MgO6 octahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with three equivalent Ta(1)O6 octahedra, corners with three equivalent Ni(1)O6 octahedra, edges with three equivalent Ta(1)O6 octahedra, and  a faceface with one Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-65°. All Mg(1)-O(1) bond lengths are 2.20 Å. All Mg(1)-O(2) bond lengths are 2.04 Å. Ta(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted TaO6 octahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with six equivalent Ni(1)O6 octahedra, edges with three equivalent Mg(1)O6 octahedra, and  a faceface with one Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-58°. All Ta(1)-O(1) bond lengths are 1.92 Å. All Ta(1)-O(2) bond lengths are 2.13 Å. Ni(1) is bonded to six equivalent O(1) atoms to form NiO6 octahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with six equivalent Ta(1)O6 octahedra, edges with three equivalent Ni(1)O6 octahedra, and  a faceface with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-58°. There are three shorter (2.09 Å) and three longer (2.13 Å) Ni(1)-O(1) bond lengths. There are two inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Ta(1), and two equivalent Ni(1) atoms to form distorted OMgTaNi2 trigonal pyramids that share corners with four equivalent O(2)Mg2Ta2 trigonal pyramids, corners with eight equivalent O(1)MgTaNi2 trigonal pyramids,  an edgeedge with one O(2)Mg2Ta2 trigonal pyramid, and edges with three equivalent O(1)MgTaNi2 trigonal pyramids. In the second O site, O(2) is bonded to two equivalent Mg(1) and two equivalent Ta(1) atoms to form distorted OMg2Ta2 trigonal pyramids that share corners with four equivalent O(2)Mg2Ta2 trigonal pyramids, corners with eight equivalent O(1)MgTaNi2 trigonal pyramids, edges with two equivalent O(2)Mg2Ta2 trigonal pyramids, and edges with two equivalent O(1)MgTaNi2 trigonal pyramids.