NiAl2O4 is Spinel-like structured and crystallizes in the monoclinic Cm space group. There are six inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(13), one O(3), and two equivalent O(1) atoms to form NiO4 tetrahedra that share  a cornercorner with one Ni(6)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra, corners with two equivalent Al(7)O6 octahedra, corners with three equivalent Al(2)O6 octahedra, and corners with four equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 56-65°. In the second Ni site, Ni(2) is bonded to one O(4), one O(9), two equivalent O(5), and two equivalent O(6) atoms to form NiO6 octahedra that share corners with three equivalent Al(3)O4 tetrahedra, corners with three equivalent Al(6)O4 tetrahedra,  an edgeedge with one Ni(3)O6 octahedra,  an edgeedge with one Ni(5)O6 octahedra, edges with two equivalent Al(1)O6 octahedra, and edges with two equivalent Al(4)O6 octahedra. In the third Ni site, Ni(3) is bonded to one O(2), one O(7), two equivalent O(1), and two equivalent O(6) atoms to form NiO6 octahedra that share  a cornercorner with one Al(3)O4 tetrahedra,  a cornercorner with one Al(9)O4 tetrahedra, corners with two equivalent Ni(1)O4 tetrahedra, corners with two equivalent Al(6)O4 tetrahedra,  an edgeedge with one Ni(2)O6 octahedra,  an edgeedge with one Al(2)O6 octahedra, and edges with four equivalent Al(1)O6 octahedra. In the fourth Ni site, Ni(4) is bonded to one O(11), one O(15), two equivalent O(10), and two equivalent O(12) atoms to form NiO6 octahedra that share corners with three equivalent Al(5)O4 tetrahedra, corners with three equivalent Al(8)O4 tetrahedra,  an edgeedge with one Ni(5)O6 octahedra,  an edgeedge with one Ni(6)O6 octahedra, edges with two equivalent Al(4)O6 octahedra, and edges with two equivalent Al(7)O6 octahedra. In the fifth Ni site, Ni(5) is bonded to one O(14), one O(8), two equivalent O(12), and two equivalent O(5) atoms to form NiO6 octahedra that share  a cornercorner with one Al(5)O4 tetrahedra,  a cornercorner with one Al(6)O4 tetrahedra, corners with two equivalent Al(3)O4 tetrahedra, corners with two equivalent Al(8)O4 tetrahedra,  an edgeedge with one Ni(2)O6 octahedra,  an edgeedge with one Ni(4)O6 octahedra, and edges with four equivalent Al(4)O6 octahedra. In the sixth Ni site, Ni(6) is bonded to one O(13), one O(18), two equivalent O(10), and two equivalent O(17) atoms to form NiO6 octahedra that share  a cornercorner with one Ni(1)O4 tetrahedra,  a cornercorner with one Al(8)O4 tetrahedra, corners with two equivalent Al(5)O4 tetrahedra, corners with two equivalent Al(9)O4 tetrahedra,  an edgeedge with one Ni(4)O6 octahedra,  an edgeedge with one Al(2)O6 octahedra, and edges with four equivalent Al(7)O6 octahedra. There are nine inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(7) atom to form AlO6 octahedra that share  a cornercorner with one Al(3)O4 tetrahedra,  a cornercorner with one Al(9)O4 tetrahedra, corners with two equivalent Ni(1)O4 tetrahedra, corners with two equivalent Al(6)O4 tetrahedra,  an edgeedge with one Ni(2)O6 octahedra,  an edgeedge with one Al(2)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and edges with two equivalent Al(1)O6 octahedra. In the second Al site, Al(2) is bonded to one O(16), one O(3), two equivalent O(1), and two equivalent O(17) atoms to form AlO6 octahedra that share corners with three equivalent Ni(1)O4 tetrahedra, corners with three equivalent Al(9)O4 tetrahedra,  an edgeedge with one Ni(3)O6 octahedra,  an edgeedge with one Ni(6)O6 octahedra, edges with two equivalent Al(1)O6 octahedra, and edges with two equivalent Al(7)O6 octahedra. In the third Al site, Al(3) is bonded to one O(2), one O(9), and two equivalent O(5) atoms to form AlO4 tetrahedra that share  a cornercorner with one Ni(3)O6 octahedra, corners with two equivalent Ni(5)O6 octahedra, corners with two equivalent Al(1)O6 octahedra, corners with three equivalent Ni(2)O6 octahedra, and corners with four equivalent Al(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-59°. In the fourth Al site, Al(4) is bonded to one O(11), one O(12), one O(14), one O(5), one O(8), and one O(9) atom to form AlO6 octahedra that share  a cornercorner with one Al(5)O4 tetrahedra,  a cornercorner with one Al(6)O4 tetrahedra, corners with two equivalent Al(3)O4 tetrahedra, corners with two equivalent Al(8)O4 tetrahedra,  an edgeedge with one Ni(2)O6 octahedra,  an edgeedge with one Ni(4)O6 octahedra, edges with two equivalent Ni(5)O6 octahedra, and edges with two equivalent Al(4)O6 octahedra. In the fifth Al site, Al(5) is bonded to one O(15), one O(8), and two equivalent O(10) atoms to form AlO4 tetrahedra that share  a cornercorner with one Ni(5)O6 octahedra, corners with two equivalent Ni(6)O6 octahedra, corners with two equivalent Al(4)O6 octahedra, corners with three equivalent Ni(4)O6 octahedra, and corners with four equivalent Al(7)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-58°. In the sixth Al site, Al(6) is bonded to one O(14), one O(4), and two equivalent O(6) atoms to form AlO4 tetrahedra that share  a cornercorner with one Ni(5)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra, corners with two equivalent Al(4)O6 octahedra, corners with three equivalent Ni(2)O6 octahedra, and corners with four equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-59°. In the seventh Al site, Al(7) is bonded to one O(10), one O(13), one O(15), one O(16), one O(17), and one O(18) atom to form AlO6 octahedra that share  a cornercorner with one Ni(1)O4 tetrahedra,  a cornercorner with one Al(8)O4 tetrahedra, corners with two equivalent Al(5)O4 tetrahedra, corners with two equivalent Al(9)O4 tetrahedra,  an edgeedge with one Ni(4)O6 octahedra,  an edgeedge with one Al(2)O6 octahedra, edges with two equivalent Ni(6)O6 octahedra, and edges with two equivalent Al(7)O6 octahedra. In the eighth Al site, Al(8) is bonded to one O(11), one O(18), and two equivalent O(12) atoms to form AlO4 tetrahedra that share  a cornercorner with one Ni(6)O6 octahedra, corners with two equivalent Ni(5)O6 octahedra, corners with two equivalent Al(7)O6 octahedra, corners with three equivalent Ni(4)O6 octahedra, and corners with four equivalent Al(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-59°. In the ninth Al site, Al(9) is bonded to one O(16), one O(7), and two equivalent O(17) atoms to form AlO4 tetrahedra that share  a cornercorner with one Ni(3)O6 octahedra, corners with two equivalent Ni(6)O6 octahedra, corners with two equivalent Al(1)O6 octahedra, corners with three equivalent Al(2)O6 octahedra, and corners with four equivalent Al(7)O6 octahedra. The corner-sharing octahedral tilt angles range from 56-59°. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Ni(1), one Ni(3), one Al(1), and one Al(2) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Ni(3), one Al(3), and two equivalent Al(1) atoms. In the third O site, O(3) is bonded to one Ni(1), one Al(2), and two equivalent Al(1) atoms to form distorted corner-sharing OAl3Ni trigonal pyramids. In the fourth O site, O(4) is bonded in a rectangular see-saw-like geometry to one Ni(2), one Al(6), and two equivalent Al(1) atoms. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to one Ni(2), one Ni(5), one Al(3), and one Al(4) atom. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Ni(2), one Ni(3), one Al(1), and one Al(6) atom. In the seventh O site, O(7) is bonded in a rectangular see-saw-like geometry to one Ni(3), one Al(9), and two equivalent Al(1) atoms. In the eighth O site, O(8) is bonded in a rectangular see-saw-like geometry to one Ni(5), one Al(5), and two equivalent Al(4) atoms. In the ninth O site, O(9) is bonded in a rectangular see-saw-like geometry to one Ni(2), one Al(3), and two equivalent Al(4) atoms. In the tenth O site, O(10) is bonded in a rectangular see-saw-like geometry to one Ni(4), one Ni(6), one Al(5), and one Al(7) atom. In the eleventh O site, O(11) is bonded in a rectangular see-saw-like geometry to one Ni(4), one Al(8), and two equivalent Al(4) atoms. In the twelfth O site, O(12) is bonded in a rectangular see-saw-like geometry to one Ni(4), one Ni(5), one Al(4), and one Al(8) atom. In the thirteenth O site, O(13) is bonded to one Ni(1), one Ni(6), and two equivalent Al(7) atoms to form distorted corner-sharing OAl2Ni2 trigonal pyramids. In the fourteenth O site, O(14) is bonded in a rectangular see-saw-like geometry to one Ni(5), one Al(6), and two equivalent Al(4) atoms. In the fifteenth O site, O(15) is bonded in a rectangular see-saw-like geometry to one Ni(4), one Al(5), and two equivalent Al(7) atoms. In the sixteenth O site, O(16) is bonded in a distorted rectangular see-saw-like geometry to one Al(2), one Al(9), and two equivalent Al(7) atoms. In the seventeenth O site, O(17) is bonded in a rectangular see-saw-like geometry to one Ni(6), one Al(2), one Al(7), and one Al(9) atom. In the eighteenth O site, O(18) is bonded in a rectangular see-saw-like geometry to one Ni(6), one Al(8), and two equivalent Al(7) atoms.
NiAl2O4 is Spinel-like structured and crystallizes in the monoclinic Cm space group. There are six inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(13), one O(3), and two equivalent O(1) atoms to form NiO4 tetrahedra that share  a cornercorner with one Ni(6)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra, corners with two equivalent Al(7)O6 octahedra, corners with three equivalent Al(2)O6 octahedra, and corners with four equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 56-65°. The Ni(1)-O(13) bond length is 1.98 Å. The Ni(1)-O(3) bond length is 1.99 Å. Both Ni(1)-O(1) bond lengths are 1.94 Å. In the second Ni site, Ni(2) is bonded to one O(4), one O(9), two equivalent O(5), and two equivalent O(6) atoms to form NiO6 octahedra that share corners with three equivalent Al(3)O4 tetrahedra, corners with three equivalent Al(6)O4 tetrahedra,  an edgeedge with one Ni(3)O6 octahedra,  an edgeedge with one Ni(5)O6 octahedra, edges with two equivalent Al(1)O6 octahedra, and edges with two equivalent Al(4)O6 octahedra. The Ni(2)-O(4) bond length is 2.09 Å. The Ni(2)-O(9) bond length is 2.08 Å. Both Ni(2)-O(5) bond lengths are 2.05 Å. Both Ni(2)-O(6) bond lengths are 2.04 Å. In the third Ni site, Ni(3) is bonded to one O(2), one O(7), two equivalent O(1), and two equivalent O(6) atoms to form NiO6 octahedra that share  a cornercorner with one Al(3)O4 tetrahedra,  a cornercorner with one Al(9)O4 tetrahedra, corners with two equivalent Ni(1)O4 tetrahedra, corners with two equivalent Al(6)O4 tetrahedra,  an edgeedge with one Ni(2)O6 octahedra,  an edgeedge with one Al(2)O6 octahedra, and edges with four equivalent Al(1)O6 octahedra. The Ni(3)-O(2) bond length is 2.08 Å. The Ni(3)-O(7) bond length is 2.07 Å. Both Ni(3)-O(1) bond lengths are 2.02 Å. Both Ni(3)-O(6) bond lengths are 2.04 Å. In the fourth Ni site, Ni(4) is bonded to one O(11), one O(15), two equivalent O(10), and two equivalent O(12) atoms to form NiO6 octahedra that share corners with three equivalent Al(5)O4 tetrahedra, corners with three equivalent Al(8)O4 tetrahedra,  an edgeedge with one Ni(5)O6 octahedra,  an edgeedge with one Ni(6)O6 octahedra, edges with two equivalent Al(4)O6 octahedra, and edges with two equivalent Al(7)O6 octahedra. The Ni(4)-O(11) bond length is 2.07 Å. The Ni(4)-O(15) bond length is 2.10 Å. Both Ni(4)-O(10) bond lengths are 2.05 Å. Both Ni(4)-O(12) bond lengths are 2.04 Å. In the fifth Ni site, Ni(5) is bonded to one O(14), one O(8), two equivalent O(12), and two equivalent O(5) atoms to form NiO6 octahedra that share  a cornercorner with one Al(5)O4 tetrahedra,  a cornercorner with one Al(6)O4 tetrahedra, corners with two equivalent Al(3)O4 tetrahedra, corners with two equivalent Al(8)O4 tetrahedra,  an edgeedge with one Ni(2)O6 octahedra,  an edgeedge with one Ni(4)O6 octahedra, and edges with four equivalent Al(4)O6 octahedra. The Ni(5)-O(14) bond length is 2.07 Å. The Ni(5)-O(8) bond length is 2.07 Å. Both Ni(5)-O(12) bond lengths are 2.05 Å. Both Ni(5)-O(5) bond lengths are 2.04 Å. In the sixth Ni site, Ni(6) is bonded to one O(13), one O(18), two equivalent O(10), and two equivalent O(17) atoms to form NiO6 octahedra that share  a cornercorner with one Ni(1)O4 tetrahedra,  a cornercorner with one Al(8)O4 tetrahedra, corners with two equivalent Al(5)O4 tetrahedra, corners with two equivalent Al(9)O4 tetrahedra,  an edgeedge with one Ni(4)O6 octahedra,  an edgeedge with one Al(2)O6 octahedra, and edges with four equivalent Al(7)O6 octahedra. The Ni(6)-O(13) bond length is 2.02 Å. The Ni(6)-O(18) bond length is 2.07 Å. Both Ni(6)-O(10) bond lengths are 2.05 Å. Both Ni(6)-O(17) bond lengths are 2.07 Å. There are nine inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(7) atom to form AlO6 octahedra that share  a cornercorner with one Al(3)O4 tetrahedra,  a cornercorner with one Al(9)O4 tetrahedra, corners with two equivalent Ni(1)O4 tetrahedra, corners with two equivalent Al(6)O4 tetrahedra,  an edgeedge with one Ni(2)O6 octahedra,  an edgeedge with one Al(2)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and edges with two equivalent Al(1)O6 octahedra. The Al(1)-O(1) bond length is 1.87 Å. The Al(1)-O(2) bond length is 1.98 Å. The Al(1)-O(3) bond length is 1.91 Å. The Al(1)-O(4) bond length is 1.96 Å. The Al(1)-O(6) bond length is 1.90 Å. The Al(1)-O(7) bond length is 1.98 Å. In the second Al site, Al(2) is bonded to one O(16), one O(3), two equivalent O(1), and two equivalent O(17) atoms to form AlO6 octahedra that share corners with three equivalent Ni(1)O4 tetrahedra, corners with three equivalent Al(9)O4 tetrahedra,  an edgeedge with one Ni(3)O6 octahedra,  an edgeedge with one Ni(6)O6 octahedra, edges with two equivalent Al(1)O6 octahedra, and edges with two equivalent Al(7)O6 octahedra. The Al(2)-O(16) bond length is 2.00 Å. The Al(2)-O(3) bond length is 1.90 Å. Both Al(2)-O(1) bond lengths are 1.86 Å. Both Al(2)-O(17) bond lengths are 1.97 Å. In the third Al site, Al(3) is bonded to one O(2), one O(9), and two equivalent O(5) atoms to form AlO4 tetrahedra that share  a cornercorner with one Ni(3)O6 octahedra, corners with two equivalent Ni(5)O6 octahedra, corners with two equivalent Al(1)O6 octahedra, corners with three equivalent Ni(2)O6 octahedra, and corners with four equivalent Al(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-59°. The Al(3)-O(2) bond length is 1.80 Å. The Al(3)-O(9) bond length is 1.84 Å. Both Al(3)-O(5) bond lengths are 1.80 Å. In the fourth Al site, Al(4) is bonded to one O(11), one O(12), one O(14), one O(5), one O(8), and one O(9) atom to form AlO6 octahedra that share  a cornercorner with one Al(5)O4 tetrahedra,  a cornercorner with one Al(6)O4 tetrahedra, corners with two equivalent Al(3)O4 tetrahedra, corners with two equivalent Al(8)O4 tetrahedra,  an edgeedge with one Ni(2)O6 octahedra,  an edgeedge with one Ni(4)O6 octahedra, edges with two equivalent Ni(5)O6 octahedra, and edges with two equivalent Al(4)O6 octahedra. The Al(4)-O(11) bond length is 1.98 Å. The Al(4)-O(12) bond length is 1.91 Å. The Al(4)-O(14) bond length is 1.96 Å. The Al(4)-O(5) bond length is 1.89 Å. The Al(4)-O(8) bond length is 1.96 Å. The Al(4)-O(9) bond length is 1.96 Å. In the fifth Al site, Al(5) is bonded to one O(15), one O(8), and two equivalent O(10) atoms to form AlO4 tetrahedra that share  a cornercorner with one Ni(5)O6 octahedra, corners with two equivalent Ni(6)O6 octahedra, corners with two equivalent Al(4)O6 octahedra, corners with three equivalent Ni(4)O6 octahedra, and corners with four equivalent Al(7)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-58°. The Al(5)-O(15) bond length is 1.82 Å. The Al(5)-O(8) bond length is 1.82 Å. Both Al(5)-O(10) bond lengths are 1.78 Å. In the sixth Al site, Al(6) is bonded to one O(14), one O(4), and two equivalent O(6) atoms to form AlO4 tetrahedra that share  a cornercorner with one Ni(5)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra, corners with two equivalent Al(4)O6 octahedra, corners with three equivalent Ni(2)O6 octahedra, and corners with four equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-59°. The Al(6)-O(14) bond length is 1.85 Å. The Al(6)-O(4) bond length is 1.84 Å. Both Al(6)-O(6) bond lengths are 1.79 Å. In the seventh Al site, Al(7) is bonded to one O(10), one O(13), one O(15), one O(16), one O(17), and one O(18) atom to form AlO6 octahedra that share  a cornercorner with one Ni(1)O4 tetrahedra,  a cornercorner with one Al(8)O4 tetrahedra, corners with two equivalent Al(5)O4 tetrahedra, corners with two equivalent Al(9)O4 tetrahedra,  an edgeedge with one Ni(4)O6 octahedra,  an edgeedge with one Al(2)O6 octahedra, edges with two equivalent Ni(6)O6 octahedra, and edges with two equivalent Al(7)O6 octahedra. The Al(7)-O(10) bond length is 1.90 Å. The Al(7)-O(13) bond length is 1.86 Å. The Al(7)-O(15) bond length is 1.98 Å. The Al(7)-O(16) bond length is 2.02 Å. The Al(7)-O(17) bond length is 1.96 Å. The Al(7)-O(18) bond length is 1.96 Å. In the eighth Al site, Al(8) is bonded to one O(11), one O(18), and two equivalent O(12) atoms to form AlO4 tetrahedra that share  a cornercorner with one Ni(6)O6 octahedra, corners with two equivalent Ni(5)O6 octahedra, corners with two equivalent Al(7)O6 octahedra, corners with three equivalent Ni(4)O6 octahedra, and corners with four equivalent Al(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-59°. The Al(8)-O(11) bond length is 1.84 Å. The Al(8)-O(18) bond length is 1.85 Å. Both Al(8)-O(12) bond lengths are 1.79 Å. In the ninth Al site, Al(9) is bonded to one O(16), one O(7), and two equivalent O(17) atoms to form AlO4 tetrahedra that share  a cornercorner with one Ni(3)O6 octahedra, corners with two equivalent Ni(6)O6 octahedra, corners with two equivalent Al(1)O6 octahedra, corners with three equivalent Al(2)O6 octahedra, and corners with four equivalent Al(7)O6 octahedra. The corner-sharing octahedral tilt angles range from 56-59°. The Al(9)-O(16) bond length is 1.91 Å. The Al(9)-O(7) bond length is 1.80 Å. Both Al(9)-O(17) bond lengths are 1.84 Å. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Ni(1), one Ni(3), one Al(1), and one Al(2) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Ni(3), one Al(3), and two equivalent Al(1) atoms. In the third O site, O(3) is bonded to one Ni(1), one Al(2), and two equivalent Al(1) atoms to form distorted corner-sharing OAl3Ni trigonal pyramids. In the fourth O site, O(4) is bonded in a rectangular see-saw-like geometry to one Ni(2), one Al(6), and two equivalent Al(1) atoms. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to one Ni(2), one Ni(5), one Al(3), and one Al(4) atom. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Ni(2), one Ni(3), one Al(1), and one Al(6) atom. In the seventh O site, O(7) is bonded in a rectangular see-saw-like geometry to one Ni(3), one Al(9), and two equivalent Al(1) atoms. In the eighth O site, O(8) is bonded in a rectangular see-saw-like geometry to one Ni(5), one Al(5), and two equivalent Al(4) atoms. In the ninth O site, O(9) is bonded in a rectangular see-saw-like geometry to one Ni(2), one Al(3), and two equivalent Al(4) atoms. In the tenth O site, O(10) is bonded in a rectangular see-saw-like geometry to one Ni(4), one Ni(6), one Al(5), and one Al(7) atom. In the eleventh O site, O(11) is bonded in a rectangular see-saw-like geometry to one Ni(4), one Al(8), and two equivalent Al(4) atoms. In the twelfth O site, O(12) is bonded in a rectangular see-saw-like geometry to one Ni(4), one Ni(5), one Al(4), and one Al(8) atom. In the thirteenth O site, O(13) is bonded to one Ni(1), one Ni(6), and two equivalent Al(7) atoms to form distorted corner-sharing OAl2Ni2 trigonal pyramids. In the fourteenth O site, O(14) is bonded in a rectangular see-saw-like geometry to one Ni(5), one Al(6), and two equivalent Al(4) atoms. In the fifteenth O site, O(15) is bonded in a rectangular see-saw-like geometry to one Ni(4), one Al(5), and two equivalent Al(7) atoms. In the sixteenth O site, O(16) is bonded in a distorted rectangular see-saw-like geometry to one Al(2), one Al(9), and two equivalent Al(7) atoms. In the seventeenth O site, O(17) is bonded in a rectangular see-saw-like geometry to one Ni(6), one Al(2), one Al(7), and one Al(9) atom. In the eighteenth O site, O(18) is bonded in a rectangular see-saw-like geometry to one Ni(6), one Al(8), and two equivalent Al(7) atoms.