CoAl2O4 is Spinel-like structured and crystallizes in the monoclinic Cm space group. There are six inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(17), one O(9), and two equivalent O(16) atoms to form CoO4 tetrahedra that share  a cornercorner with one Al(3)O6 octahedra, corners with two equivalent Al(2)O6 octahedra, corners with two equivalent Al(9)O6 octahedra, corners with three equivalent Co(3)O6 octahedra, and corners with four equivalent Al(7)O6 octahedra. The corner-sharing octahedral tilt angles range from 55-64°. In the second Co site, Co(2) is bonded to one O(14), one O(6), and two equivalent O(4) atoms to form CoO4 tetrahedra that share  a cornercorner with one Al(6)O6 octahedra, corners with two equivalent Al(3)O6 octahedra, corners with two equivalent Al(4)O6 octahedra, corners with three equivalent Al(5)O6 octahedra, and corners with four equivalent Al(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 59-60°. In the third Co site, Co(3) is bonded to one O(17), one O(3), two equivalent O(1), and two equivalent O(16) atoms to form CoO6 octahedra that share corners with three equivalent Co(1)O4 tetrahedra, corners with three equivalent Al(1)O4 tetrahedra,  an edgeedge with one Al(3)O6 octahedra,  an edgeedge with one Al(9)O6 octahedra, edges with two equivalent Al(2)O6 octahedra, and edges with two equivalent Al(7)O6 octahedra. In the fourth Co site, Co(4) is bonded to one O(2), one O(8), and two equivalent O(5) atoms to form CoO4 tetrahedra that share  a cornercorner with one Al(3)O6 octahedra, corners with two equivalent Al(2)O6 octahedra, corners with two equivalent Al(6)O6 octahedra, corners with three equivalent Al(5)O6 octahedra, and corners with four equivalent Al(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 59-62°. In the fifth Co site, Co(5) is bonded to one O(12), one O(18), and two equivalent O(11) atoms to form CoO4 tetrahedra that share  a cornercorner with one Al(9)O6 octahedra, corners with two equivalent Al(6)O6 octahedra, corners with two equivalent Al(7)O6 octahedra, corners with three equivalent Al(8)O6 octahedra, and corners with four equivalent Al(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 58-60°. In the sixth Co site, Co(6) is bonded to one O(15), one O(7), and two equivalent O(10) atoms to form CoO4 tetrahedra that share  a cornercorner with one Al(6)O6 octahedra, corners with two equivalent Al(4)O6 octahedra, corners with two equivalent Al(9)O6 octahedra, corners with three equivalent Al(8)O6 octahedra, and corners with four equivalent Al(7)O6 octahedra. The corner-sharing octahedral tilt angles range from 59-61°. There are nine inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(13), one O(3), and two equivalent O(1) atoms to form AlO4 tetrahedra that share  a cornercorner with one Al(9)O6 octahedra, corners with two equivalent Al(3)O6 octahedra, corners with two equivalent Al(7)O6 octahedra, corners with three equivalent Co(3)O6 octahedra, and corners with four equivalent Al(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 54-62°. In the second Al site, Al(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(9) atom to form AlO6 octahedra that share  a cornercorner with one Co(1)O4 tetrahedra,  a cornercorner with one Co(4)O4 tetrahedra, corners with two equivalent Co(2)O4 tetrahedra, corners with two equivalent Al(1)O4 tetrahedra,  an edgeedge with one Co(3)O6 octahedra,  an edgeedge with one Al(5)O6 octahedra, edges with two equivalent Al(2)O6 octahedra, and edges with two equivalent Al(3)O6 octahedra. In the third Al site, Al(3) is bonded to one O(2), one O(9), two equivalent O(1), and two equivalent O(4) atoms to form AlO6 octahedra that share  a cornercorner with one Co(1)O4 tetrahedra,  a cornercorner with one Co(4)O4 tetrahedra, corners with two equivalent Co(2)O4 tetrahedra, corners with two equivalent Al(1)O4 tetrahedra,  an edgeedge with one Co(3)O6 octahedra,  an edgeedge with one Al(5)O6 octahedra, and edges with four equivalent Al(2)O6 octahedra. In the fourth Al site, Al(4) is bonded to one O(11), one O(12), one O(14), one O(5), one O(7), and one O(8) atom to form AlO6 octahedra that share  a cornercorner with one Co(2)O4 tetrahedra,  a cornercorner with one Co(6)O4 tetrahedra, corners with two equivalent Co(4)O4 tetrahedra, corners with two equivalent Co(5)O4 tetrahedra,  an edgeedge with one Al(5)O6 octahedra,  an edgeedge with one Al(8)O6 octahedra, edges with two equivalent Al(4)O6 octahedra, and edges with two equivalent Al(6)O6 octahedra. In the fifth Al site, Al(5) is bonded to one O(6), one O(8), two equivalent O(4), and two equivalent O(5) atoms to form AlO6 octahedra that share corners with three equivalent Co(2)O4 tetrahedra, corners with three equivalent Co(4)O4 tetrahedra,  an edgeedge with one Al(3)O6 octahedra,  an edgeedge with one Al(6)O6 octahedra, edges with two equivalent Al(2)O6 octahedra, and edges with two equivalent Al(4)O6 octahedra. In the sixth Al site, Al(6) is bonded to one O(14), one O(7), two equivalent O(11), and two equivalent O(5) atoms to form AlO6 octahedra that share  a cornercorner with one Co(2)O4 tetrahedra,  a cornercorner with one Co(6)O4 tetrahedra, corners with two equivalent Co(4)O4 tetrahedra, corners with two equivalent Co(5)O4 tetrahedra,  an edgeedge with one Al(5)O6 octahedra,  an edgeedge with one Al(8)O6 octahedra, and edges with four equivalent Al(4)O6 octahedra. 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 Co(5)O4 tetrahedra,  a cornercorner with one Al(1)O4 tetrahedra, corners with two equivalent Co(1)O4 tetrahedra, corners with two equivalent Co(6)O4 tetrahedra,  an edgeedge with one Co(3)O6 octahedra,  an edgeedge with one Al(8)O6 octahedra, edges with two equivalent Al(7)O6 octahedra, and edges with two equivalent Al(9)O6 octahedra. In the eighth Al site, Al(8) is bonded to one O(12), one O(15), two equivalent O(10), and two equivalent O(11) atoms to form AlO6 octahedra that share corners with three equivalent Co(5)O4 tetrahedra, corners with three equivalent Co(6)O4 tetrahedra,  an edgeedge with one Al(6)O6 octahedra,  an edgeedge with one Al(9)O6 octahedra, edges with two equivalent Al(4)O6 octahedra, and edges with two equivalent Al(7)O6 octahedra. In the ninth Al site, Al(9) is bonded to one O(13), one O(18), two equivalent O(10), and two equivalent O(16) atoms to form AlO6 octahedra that share  a cornercorner with one Co(5)O4 tetrahedra,  a cornercorner with one Al(1)O4 tetrahedra, corners with two equivalent Co(1)O4 tetrahedra, corners with two equivalent Co(6)O4 tetrahedra,  an edgeedge with one Co(3)O6 octahedra,  an edgeedge with one Al(8)O6 octahedra, and edges with four equivalent Al(7)O6 octahedra. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Co(3), one Al(1), one Al(2), and one Al(3) atom. In the second O site, O(2) is bonded to one Co(4), one Al(3), and two equivalent Al(2) atoms to form corner-sharing OAl3Co tetrahedra. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Co(3), one Al(1), and two equivalent Al(2) atoms. In the fourth O site, O(4) is bonded to one Co(2), one Al(2), one Al(3), and one Al(5) atom to form a mixture of distorted edge and corner-sharing OAl3Co trigonal pyramids. In the fifth O site, O(5) is bonded to one Co(4), one Al(4), one Al(5), and one Al(6) atom to form a mixture of distorted edge and corner-sharing OAl3Co trigonal pyramids. In the sixth O site, O(6) is bonded to one Co(2), one Al(5), and two equivalent Al(2) atoms to form a mixture of distorted edge and corner-sharing OAl3Co trigonal pyramids. In the seventh O site, O(7) is bonded to one Co(6), one Al(6), and two equivalent Al(4) atoms to form a mixture of distorted edge and corner-sharing OAl3Co tetrahedra. In the eighth O site, O(8) is bonded to one Co(4), one Al(5), and two equivalent Al(4) atoms to form a mixture of distorted edge and corner-sharing OAl3Co tetrahedra. In the ninth O site, O(9) is bonded to one Co(1), one Al(3), and two equivalent Al(2) atoms to form a mixture of distorted edge and corner-sharing OAl3Co trigonal pyramids. In the tenth O site, O(10) is bonded to one Co(6), one Al(7), one Al(8), and one Al(9) atom to form a mixture of distorted edge and corner-sharing OAl3Co tetrahedra. In the eleventh O site, O(11) is bonded to one Co(5), one Al(4), one Al(6), and one Al(8) atom to form a mixture of distorted edge and corner-sharing OAl3Co tetrahedra. In the twelfth O site, O(12) is bonded to one Co(5), one Al(8), and two equivalent Al(4) atoms to form a mixture of distorted edge and corner-sharing OAl3Co tetrahedra. In the thirteenth O site, O(13) is bonded in a rectangular see-saw-like geometry to one Al(1), one Al(9), and two equivalent Al(7) atoms. In the fourteenth O site, O(14) is bonded to one Co(2), one Al(6), and two equivalent Al(4) atoms to form a mixture of distorted edge and corner-sharing OAl3Co trigonal pyramids. In the fifteenth O site, O(15) is bonded to one Co(6), one Al(8), and two equivalent Al(7) atoms to form a mixture of distorted edge and corner-sharing OAl3Co tetrahedra. In the sixteenth O site, O(16) is bonded in a rectangular see-saw-like geometry to one Co(1), one Co(3), one Al(7), and one Al(9) atom. In the seventeenth O site, O(17) is bonded in a distorted rectangular see-saw-like geometry to one Co(1), one Co(3), and two equivalent Al(7) atoms. In the eighteenth O site, O(18) is bonded to one Co(5), one Al(9), and two equivalent Al(7) atoms to form distorted corner-sharing OAl3Co trigonal pyramids.
CoAl2O4 is Spinel-like structured and crystallizes in the monoclinic Cm space group. There are six inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(17), one O(9), and two equivalent O(16) atoms to form CoO4 tetrahedra that share  a cornercorner with one Al(3)O6 octahedra, corners with two equivalent Al(2)O6 octahedra, corners with two equivalent Al(9)O6 octahedra, corners with three equivalent Co(3)O6 octahedra, and corners with four equivalent Al(7)O6 octahedra. The corner-sharing octahedral tilt angles range from 55-64°. The Co(1)-O(17) bond length is 1.93 Å. The Co(1)-O(9) bond length is 2.00 Å. Both Co(1)-O(16) bond lengths are 1.96 Å. In the second Co site, Co(2) is bonded to one O(14), one O(6), and two equivalent O(4) atoms to form CoO4 tetrahedra that share  a cornercorner with one Al(6)O6 octahedra, corners with two equivalent Al(3)O6 octahedra, corners with two equivalent Al(4)O6 octahedra, corners with three equivalent Al(5)O6 octahedra, and corners with four equivalent Al(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 59-60°. The Co(2)-O(14) bond length is 1.97 Å. The Co(2)-O(6) bond length is 1.98 Å. Both Co(2)-O(4) bond lengths are 1.98 Å. In the third Co site, Co(3) is bonded to one O(17), one O(3), two equivalent O(1), and two equivalent O(16) atoms to form CoO6 octahedra that share corners with three equivalent Co(1)O4 tetrahedra, corners with three equivalent Al(1)O4 tetrahedra,  an edgeedge with one Al(3)O6 octahedra,  an edgeedge with one Al(9)O6 octahedra, edges with two equivalent Al(2)O6 octahedra, and edges with two equivalent Al(7)O6 octahedra. The Co(3)-O(17) bond length is 2.09 Å. The Co(3)-O(3) bond length is 2.18 Å. Both Co(3)-O(1) bond lengths are 2.08 Å. Both Co(3)-O(16) bond lengths are 1.98 Å. In the fourth Co site, Co(4) is bonded to one O(2), one O(8), and two equivalent O(5) atoms to form CoO4 tetrahedra that share  a cornercorner with one Al(3)O6 octahedra, corners with two equivalent Al(2)O6 octahedra, corners with two equivalent Al(6)O6 octahedra, corners with three equivalent Al(5)O6 octahedra, and corners with four equivalent Al(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 59-62°. The Co(4)-O(2) bond length is 2.02 Å. The Co(4)-O(8) bond length is 1.98 Å. Both Co(4)-O(5) bond lengths are 1.98 Å. In the fifth Co site, Co(5) is bonded to one O(12), one O(18), and two equivalent O(11) atoms to form CoO4 tetrahedra that share  a cornercorner with one Al(9)O6 octahedra, corners with two equivalent Al(6)O6 octahedra, corners with two equivalent Al(7)O6 octahedra, corners with three equivalent Al(8)O6 octahedra, and corners with four equivalent Al(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 58-60°. The Co(5)-O(12) bond length is 1.97 Å. The Co(5)-O(18) bond length is 1.95 Å. Both Co(5)-O(11) bond lengths are 1.97 Å. In the sixth Co site, Co(6) is bonded to one O(15), one O(7), and two equivalent O(10) atoms to form CoO4 tetrahedra that share  a cornercorner with one Al(6)O6 octahedra, corners with two equivalent Al(4)O6 octahedra, corners with two equivalent Al(9)O6 octahedra, corners with three equivalent Al(8)O6 octahedra, and corners with four equivalent Al(7)O6 octahedra. The corner-sharing octahedral tilt angles range from 59-61°. The Co(6)-O(15) bond length is 1.99 Å. The Co(6)-O(7) bond length is 2.00 Å. Both Co(6)-O(10) bond lengths are 1.98 Å. There are nine inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(13), one O(3), and two equivalent O(1) atoms to form AlO4 tetrahedra that share  a cornercorner with one Al(9)O6 octahedra, corners with two equivalent Al(3)O6 octahedra, corners with two equivalent Al(7)O6 octahedra, corners with three equivalent Co(3)O6 octahedra, and corners with four equivalent Al(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 54-62°. The Al(1)-O(13) bond length is 1.83 Å. The Al(1)-O(3) bond length is 1.81 Å. Both Al(1)-O(1) bond lengths are 1.83 Å. In the second Al site, Al(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(9) atom to form AlO6 octahedra that share  a cornercorner with one Co(1)O4 tetrahedra,  a cornercorner with one Co(4)O4 tetrahedra, corners with two equivalent Co(2)O4 tetrahedra, corners with two equivalent Al(1)O4 tetrahedra,  an edgeedge with one Co(3)O6 octahedra,  an edgeedge with one Al(5)O6 octahedra, edges with two equivalent Al(2)O6 octahedra, and edges with two equivalent Al(3)O6 octahedra. The Al(2)-O(1) bond length is 1.98 Å. The Al(2)-O(2) bond length is 1.91 Å. The Al(2)-O(3) bond length is 1.96 Å. The Al(2)-O(4) bond length is 1.93 Å. The Al(2)-O(6) bond length is 1.93 Å. The Al(2)-O(9) bond length is 1.92 Å. In the third Al site, Al(3) is bonded to one O(2), one O(9), two equivalent O(1), and two equivalent O(4) atoms to form AlO6 octahedra that share  a cornercorner with one Co(1)O4 tetrahedra,  a cornercorner with one Co(4)O4 tetrahedra, corners with two equivalent Co(2)O4 tetrahedra, corners with two equivalent Al(1)O4 tetrahedra,  an edgeedge with one Co(3)O6 octahedra,  an edgeedge with one Al(5)O6 octahedra, and edges with four equivalent Al(2)O6 octahedra. The Al(3)-O(2) bond length is 1.91 Å. The Al(3)-O(9) bond length is 1.92 Å. Both Al(3)-O(1) bond lengths are 1.98 Å. Both Al(3)-O(4) bond lengths are 1.93 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(7), and one O(8) atom to form AlO6 octahedra that share  a cornercorner with one Co(2)O4 tetrahedra,  a cornercorner with one Co(6)O4 tetrahedra, corners with two equivalent Co(4)O4 tetrahedra, corners with two equivalent Co(5)O4 tetrahedra,  an edgeedge with one Al(5)O6 octahedra,  an edgeedge with one Al(8)O6 octahedra, edges with two equivalent Al(4)O6 octahedra, and edges with two equivalent Al(6)O6 octahedra. The Al(4)-O(11) bond length is 1.93 Å. The Al(4)-O(12) bond length is 1.92 Å. The Al(4)-O(14) bond length is 1.93 Å. The Al(4)-O(5) bond length is 1.94 Å. The Al(4)-O(7) bond length is 1.93 Å. The Al(4)-O(8) bond length is 1.94 Å. In the fifth Al site, Al(5) is bonded to one O(6), one O(8), two equivalent O(4), and two equivalent O(5) atoms to form AlO6 octahedra that share corners with three equivalent Co(2)O4 tetrahedra, corners with three equivalent Co(4)O4 tetrahedra,  an edgeedge with one Al(3)O6 octahedra,  an edgeedge with one Al(6)O6 octahedra, edges with two equivalent Al(2)O6 octahedra, and edges with two equivalent Al(4)O6 octahedra. The Al(5)-O(6) bond length is 1.93 Å. The Al(5)-O(8) bond length is 1.93 Å. Both Al(5)-O(4) bond lengths are 1.92 Å. Both Al(5)-O(5) bond lengths are 1.93 Å. In the sixth Al site, Al(6) is bonded to one O(14), one O(7), two equivalent O(11), and two equivalent O(5) atoms to form AlO6 octahedra that share  a cornercorner with one Co(2)O4 tetrahedra,  a cornercorner with one Co(6)O4 tetrahedra, corners with two equivalent Co(4)O4 tetrahedra, corners with two equivalent Co(5)O4 tetrahedra,  an edgeedge with one Al(5)O6 octahedra,  an edgeedge with one Al(8)O6 octahedra, and edges with four equivalent Al(4)O6 octahedra. The Al(6)-O(14) bond length is 1.94 Å. The Al(6)-O(7) bond length is 1.94 Å. Both Al(6)-O(11) bond lengths are 1.93 Å. Both Al(6)-O(5) bond lengths are 1.94 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 Co(5)O4 tetrahedra,  a cornercorner with one Al(1)O4 tetrahedra, corners with two equivalent Co(1)O4 tetrahedra, corners with two equivalent Co(6)O4 tetrahedra,  an edgeedge with one Co(3)O6 octahedra,  an edgeedge with one Al(8)O6 octahedra, edges with two equivalent Al(7)O6 octahedra, and edges with two equivalent Al(9)O6 octahedra. The Al(7)-O(10) bond length is 1.93 Å. The Al(7)-O(13) bond length is 2.04 Å. The Al(7)-O(15) bond length is 1.93 Å. The Al(7)-O(16) bond length is 1.90 Å. The Al(7)-O(17) bond length is 1.87 Å. The Al(7)-O(18) bond length is 1.93 Å. In the eighth Al site, Al(8) is bonded to one O(12), one O(15), two equivalent O(10), and two equivalent O(11) atoms to form AlO6 octahedra that share corners with three equivalent Co(5)O4 tetrahedra, corners with three equivalent Co(6)O4 tetrahedra,  an edgeedge with one Al(6)O6 octahedra,  an edgeedge with one Al(9)O6 octahedra, edges with two equivalent Al(4)O6 octahedra, and edges with two equivalent Al(7)O6 octahedra. The Al(8)-O(12) bond length is 1.94 Å. The Al(8)-O(15) bond length is 1.93 Å. Both Al(8)-O(10) bond lengths are 1.92 Å. Both Al(8)-O(11) bond lengths are 1.93 Å. In the ninth Al site, Al(9) is bonded to one O(13), one O(18), two equivalent O(10), and two equivalent O(16) atoms to form AlO6 octahedra that share  a cornercorner with one Co(5)O4 tetrahedra,  a cornercorner with one Al(1)O4 tetrahedra, corners with two equivalent Co(1)O4 tetrahedra, corners with two equivalent Co(6)O4 tetrahedra,  an edgeedge with one Co(3)O6 octahedra,  an edgeedge with one Al(8)O6 octahedra, and edges with four equivalent Al(7)O6 octahedra. The Al(9)-O(13) bond length is 2.05 Å. The Al(9)-O(18) bond length is 1.93 Å. Both Al(9)-O(10) bond lengths are 1.92 Å. Both Al(9)-O(16) bond lengths are 1.89 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 Co(3), one Al(1), one Al(2), and one Al(3) atom. In the second O site, O(2) is bonded to one Co(4), one Al(3), and two equivalent Al(2) atoms to form corner-sharing OAl3Co tetrahedra. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Co(3), one Al(1), and two equivalent Al(2) atoms. In the fourth O site, O(4) is bonded to one Co(2), one Al(2), one Al(3), and one Al(5) atom to form a mixture of distorted edge and corner-sharing OAl3Co trigonal pyramids. In the fifth O site, O(5) is bonded to one Co(4), one Al(4), one Al(5), and one Al(6) atom to form a mixture of distorted edge and corner-sharing OAl3Co trigonal pyramids. In the sixth O site, O(6) is bonded to one Co(2), one Al(5), and two equivalent Al(2) atoms to form a mixture of distorted edge and corner-sharing OAl3Co trigonal pyramids. In the seventh O site, O(7) is bonded to one Co(6), one Al(6), and two equivalent Al(4) atoms to form a mixture of distorted edge and corner-sharing OAl3Co tetrahedra. In the eighth O site, O(8) is bonded to one Co(4), one Al(5), and two equivalent Al(4) atoms to form a mixture of distorted edge and corner-sharing OAl3Co tetrahedra. In the ninth O site, O(9) is bonded to one Co(1), one Al(3), and two equivalent Al(2) atoms to form a mixture of distorted edge and corner-sharing OAl3Co trigonal pyramids. In the tenth O site, O(10) is bonded to one Co(6), one Al(7), one Al(8), and one Al(9) atom to form a mixture of distorted edge and corner-sharing OAl3Co tetrahedra. In the eleventh O site, O(11) is bonded to one Co(5), one Al(4), one Al(6), and one Al(8) atom to form a mixture of distorted edge and corner-sharing OAl3Co tetrahedra. In the twelfth O site, O(12) is bonded to one Co(5), one Al(8), and two equivalent Al(4) atoms to form a mixture of distorted edge and corner-sharing OAl3Co tetrahedra. In the thirteenth O site, O(13) is bonded in a rectangular see-saw-like geometry to one Al(1), one Al(9), and two equivalent Al(7) atoms. In the fourteenth O site, O(14) is bonded to one Co(2), one Al(6), and two equivalent Al(4) atoms to form a mixture of distorted edge and corner-sharing OAl3Co trigonal pyramids. In the fifteenth O site, O(15) is bonded to one Co(6), one Al(8), and two equivalent Al(7) atoms to form a mixture of distorted edge and corner-sharing OAl3Co tetrahedra. In the sixteenth O site, O(16) is bonded in a rectangular see-saw-like geometry to one Co(1), one Co(3), one Al(7), and one Al(9) atom. In the seventeenth O site, O(17) is bonded in a distorted rectangular see-saw-like geometry to one Co(1), one Co(3), and two equivalent Al(7) atoms. In the eighteenth O site, O(18) is bonded to one Co(5), one Al(9), and two equivalent Al(7) atoms to form distorted corner-sharing OAl3Co trigonal pyramids.