Co2Al2O7 crystallizes in the triclinic P-1 space group. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(6) atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedral tilt angles range from 56-58°. In the second Co site, Co(2) is bonded to two equivalent O(2), two equivalent O(6), and two equivalent O(7) atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedral tilt angles range from 54-56°. In the third Co site, Co(3) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(7) atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedral tilt angles range from 54-56°. In the fourth Co site, Co(4) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedral tilt angles range from 56-58°. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded in a distorted body-centered cubic geometry to two equivalent O(1), two equivalent O(2), two equivalent O(5), and two equivalent O(7) atoms. In the second Al site, Al(2) is bonded in a distorted body-centered cubic geometry to two equivalent O(1), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. In the third Al site, Al(3) is bonded in a body-centered cubic geometry to two equivalent O(1), two equivalent O(2), two equivalent O(4), and two equivalent O(6) atoms. In the fourth Al site, Al(4) is bonded in a body-centered cubic geometry to two equivalent O(1), two equivalent O(3), two equivalent O(6), and two equivalent O(7) atoms. There are seven inequivalent O sites. In the first O site, O(1) is bonded to one Al(1), one Al(2), one Al(3), and one Al(4) atom to form OAl4 tetrahedra that share corners with two equivalent O(2)Al2Co2 tetrahedra, corners with two equivalent O(3)Al2Co2 tetrahedra, corners with two equivalent O(4)Al2Co2 tetrahedra, corners with two equivalent O(5)Al2Co2 tetrahedra, corners with two equivalent O(6)Al2Co2 tetrahedra, corners with four equivalent O(1)Al4 tetrahedra,  an edgeedge with one O(2)Al2Co2 tetrahedra,  an edgeedge with one O(3)Al2Co2 tetrahedra,  an edgeedge with one O(4)Al2Co2 tetrahedra,  an edgeedge with one O(5)Al2Co2 tetrahedra, and  an edgeedge with one O(6)Al2Co2 tetrahedra. In the second O site, O(2) is bonded to one Co(2), one Co(4), one Al(1), and one Al(3) atom to form distorted OAl2Co2 tetrahedra that share corners with two equivalent O(4)Al2Co2 tetrahedra, corners with two equivalent O(5)Al2Co2 tetrahedra, corners with two equivalent O(6)Al2Co2 tetrahedra, corners with two equivalent O(1)Al4 tetrahedra, corners with four equivalent O(2)Al2Co2 tetrahedra,  an edgeedge with one O(4)Al2Co2 tetrahedra,  an edgeedge with one O(5)Al2Co2 tetrahedra,  an edgeedge with one O(6)Al2Co2 tetrahedra, and  an edgeedge with one O(1)Al4 tetrahedra. In the third O site, O(3) is bonded to one Co(1), one Co(3), one Al(2), and one Al(4) atom to form distorted OAl2Co2 tetrahedra that share corners with two equivalent O(4)Al2Co2 tetrahedra, corners with two equivalent O(5)Al2Co2 tetrahedra, corners with two equivalent O(6)Al2Co2 tetrahedra, corners with two equivalent O(1)Al4 tetrahedra, corners with four equivalent O(3)Al2Co2 tetrahedra,  an edgeedge with one O(4)Al2Co2 tetrahedra,  an edgeedge with one O(5)Al2Co2 tetrahedra,  an edgeedge with one O(6)Al2Co2 tetrahedra, and  an edgeedge with one O(1)Al4 tetrahedra. In the fourth O site, O(4) is bonded to one Co(1), one Co(4), one Al(2), and one Al(3) atom to form OAl2Co2 tetrahedra that share corners with two equivalent O(2)Al2Co2 tetrahedra, corners with two equivalent O(3)Al2Co2 tetrahedra, corners with two equivalent O(5)Al2Co2 tetrahedra, corners with two equivalent O(6)Al2Co2 tetrahedra, corners with two equivalent O(1)Al4 tetrahedra, corners with four equivalent O(4)Al2Co2 tetrahedra,  an edgeedge with one O(2)Al2Co2 tetrahedra,  an edgeedge with one O(3)Al2Co2 tetrahedra,  an edgeedge with one O(5)Al2Co2 tetrahedra,  an edgeedge with one O(6)Al2Co2 tetrahedra, and  an edgeedge with one O(1)Al4 tetrahedra. In the fifth O site, O(5) is bonded to one Co(3), one Co(4), one Al(1), and one Al(2) atom to form distorted OAl2Co2 tetrahedra that share corners with two equivalent O(2)Al2Co2 tetrahedra, corners with two equivalent O(3)Al2Co2 tetrahedra, corners with two equivalent O(4)Al2Co2 tetrahedra, corners with two equivalent O(1)Al4 tetrahedra, corners with four equivalent O(5)Al2Co2 tetrahedra,  an edgeedge with one O(2)Al2Co2 tetrahedra,  an edgeedge with one O(3)Al2Co2 tetrahedra,  an edgeedge with one O(4)Al2Co2 tetrahedra, and  an edgeedge with one O(1)Al4 tetrahedra. In the sixth O site, O(6) is bonded to one Co(1), one Co(2), one Al(3), and one Al(4) atom to form distorted OAl2Co2 tetrahedra that share corners with two equivalent O(2)Al2Co2 tetrahedra, corners with two equivalent O(3)Al2Co2 tetrahedra, corners with two equivalent O(4)Al2Co2 tetrahedra, corners with two equivalent O(1)Al4 tetrahedra, corners with four equivalent O(6)Al2Co2 tetrahedra,  an edgeedge with one O(2)Al2Co2 tetrahedra,  an edgeedge with one O(3)Al2Co2 tetrahedra,  an edgeedge with one O(4)Al2Co2 tetrahedra, and  an edgeedge with one O(1)Al4 tetrahedra. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Co(2), one Co(3), one Al(1), and one Al(4) atom.
Co2Al2O7 crystallizes in the triclinic P-1 space group. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(6) atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedral tilt angles range from 56-58°. Both Co(1)-O(3) bond lengths are 1.83 Å. Both Co(1)-O(4) bond lengths are 1.93 Å. Both Co(1)-O(6) bond lengths are 1.83 Å. In the second Co site, Co(2) is bonded to two equivalent O(2), two equivalent O(6), and two equivalent O(7) atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedral tilt angles range from 54-56°. Both Co(2)-O(2) bond lengths are 1.83 Å. Both Co(2)-O(6) bond lengths are 1.89 Å. Both Co(2)-O(7) bond lengths are 1.81 Å. In the third Co site, Co(3) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(7) atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedral tilt angles range from 54-56°. Both Co(3)-O(3) bond lengths are 1.88 Å. Both Co(3)-O(5) bond lengths are 1.82 Å. Both Co(3)-O(7) bond lengths are 1.81 Å. In the fourth Co site, Co(4) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedral tilt angles range from 56-58°. Both Co(4)-O(2) bond lengths are 1.87 Å. Both Co(4)-O(4) bond lengths are 1.86 Å. Both Co(4)-O(5) bond lengths are 1.86 Å. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded in a distorted body-centered cubic geometry to two equivalent O(1), two equivalent O(2), two equivalent O(5), and two equivalent O(7) atoms. Both Al(1)-O(1) bond lengths are 2.00 Å. Both Al(1)-O(2) bond lengths are 2.07 Å. Both Al(1)-O(5) bond lengths are 2.07 Å. Both Al(1)-O(7) bond lengths are 2.41 Å. In the second Al site, Al(2) is bonded in a distorted body-centered cubic geometry to two equivalent O(1), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. Both Al(2)-O(1) bond lengths are 2.01 Å. Both Al(2)-O(3) bond lengths are 2.13 Å. Both Al(2)-O(4) bond lengths are 2.12 Å. Both Al(2)-O(5) bond lengths are 2.33 Å. In the third Al site, Al(3) is bonded in a body-centered cubic geometry to two equivalent O(1), two equivalent O(2), two equivalent O(4), and two equivalent O(6) atoms. Both Al(3)-O(1) bond lengths are 2.01 Å. Both Al(3)-O(2) bond lengths are 2.30 Å. Both Al(3)-O(4) bond lengths are 2.14 Å. Both Al(3)-O(6) bond lengths are 2.13 Å. In the fourth Al site, Al(4) is bonded in a body-centered cubic geometry to two equivalent O(1), two equivalent O(3), two equivalent O(6), and two equivalent O(7) atoms. Both Al(4)-O(1) bond lengths are 1.99 Å. Both Al(4)-O(3) bond lengths are 2.23 Å. Both Al(4)-O(6) bond lengths are 2.21 Å. Both Al(4)-O(7) bond lengths are 2.10 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded to one Al(1), one Al(2), one Al(3), and one Al(4) atom to form OAl4 tetrahedra that share corners with two equivalent O(2)Al2Co2 tetrahedra, corners with two equivalent O(3)Al2Co2 tetrahedra, corners with two equivalent O(4)Al2Co2 tetrahedra, corners with two equivalent O(5)Al2Co2 tetrahedra, corners with two equivalent O(6)Al2Co2 tetrahedra, corners with four equivalent O(1)Al4 tetrahedra,  an edgeedge with one O(2)Al2Co2 tetrahedra,  an edgeedge with one O(3)Al2Co2 tetrahedra,  an edgeedge with one O(4)Al2Co2 tetrahedra,  an edgeedge with one O(5)Al2Co2 tetrahedra, and  an edgeedge with one O(6)Al2Co2 tetrahedra. In the second O site, O(2) is bonded to one Co(2), one Co(4), one Al(1), and one Al(3) atom to form distorted OAl2Co2 tetrahedra that share corners with two equivalent O(4)Al2Co2 tetrahedra, corners with two equivalent O(5)Al2Co2 tetrahedra, corners with two equivalent O(6)Al2Co2 tetrahedra, corners with two equivalent O(1)Al4 tetrahedra, corners with four equivalent O(2)Al2Co2 tetrahedra,  an edgeedge with one O(4)Al2Co2 tetrahedra,  an edgeedge with one O(5)Al2Co2 tetrahedra,  an edgeedge with one O(6)Al2Co2 tetrahedra, and  an edgeedge with one O(1)Al4 tetrahedra. In the third O site, O(3) is bonded to one Co(1), one Co(3), one Al(2), and one Al(4) atom to form distorted OAl2Co2 tetrahedra that share corners with two equivalent O(4)Al2Co2 tetrahedra, corners with two equivalent O(5)Al2Co2 tetrahedra, corners with two equivalent O(6)Al2Co2 tetrahedra, corners with two equivalent O(1)Al4 tetrahedra, corners with four equivalent O(3)Al2Co2 tetrahedra,  an edgeedge with one O(4)Al2Co2 tetrahedra,  an edgeedge with one O(5)Al2Co2 tetrahedra,  an edgeedge with one O(6)Al2Co2 tetrahedra, and  an edgeedge with one O(1)Al4 tetrahedra. In the fourth O site, O(4) is bonded to one Co(1), one Co(4), one Al(2), and one Al(3) atom to form OAl2Co2 tetrahedra that share corners with two equivalent O(2)Al2Co2 tetrahedra, corners with two equivalent O(3)Al2Co2 tetrahedra, corners with two equivalent O(5)Al2Co2 tetrahedra, corners with two equivalent O(6)Al2Co2 tetrahedra, corners with two equivalent O(1)Al4 tetrahedra, corners with four equivalent O(4)Al2Co2 tetrahedra,  an edgeedge with one O(2)Al2Co2 tetrahedra,  an edgeedge with one O(3)Al2Co2 tetrahedra,  an edgeedge with one O(5)Al2Co2 tetrahedra,  an edgeedge with one O(6)Al2Co2 tetrahedra, and  an edgeedge with one O(1)Al4 tetrahedra. In the fifth O site, O(5) is bonded to one Co(3), one Co(4), one Al(1), and one Al(2) atom to form distorted OAl2Co2 tetrahedra that share corners with two equivalent O(2)Al2Co2 tetrahedra, corners with two equivalent O(3)Al2Co2 tetrahedra, corners with two equivalent O(4)Al2Co2 tetrahedra, corners with two equivalent O(1)Al4 tetrahedra, corners with four equivalent O(5)Al2Co2 tetrahedra,  an edgeedge with one O(2)Al2Co2 tetrahedra,  an edgeedge with one O(3)Al2Co2 tetrahedra,  an edgeedge with one O(4)Al2Co2 tetrahedra, and  an edgeedge with one O(1)Al4 tetrahedra. In the sixth O site, O(6) is bonded to one Co(1), one Co(2), one Al(3), and one Al(4) atom to form distorted OAl2Co2 tetrahedra that share corners with two equivalent O(2)Al2Co2 tetrahedra, corners with two equivalent O(3)Al2Co2 tetrahedra, corners with two equivalent O(4)Al2Co2 tetrahedra, corners with two equivalent O(1)Al4 tetrahedra, corners with four equivalent O(6)Al2Co2 tetrahedra,  an edgeedge with one O(2)Al2Co2 tetrahedra,  an edgeedge with one O(3)Al2Co2 tetrahedra,  an edgeedge with one O(4)Al2Co2 tetrahedra, and  an edgeedge with one O(1)Al4 tetrahedra. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Co(2), one Co(3), one Al(1), and one Al(4) atom.