Co7(AsO6)2 crystallizes in the orthorhombic Imma space group. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(3), one O(5), and two equivalent O(1) atoms to form CoO4 tetrahedra that share corners with three equivalent Co(3)O6 octahedra, corners with three equivalent As(2)O6 octahedra, corners with four equivalent Co(2)O6 octahedra, and  a cornercorner with one As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-67°. In the second Co site, Co(2) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form CoO6 octahedra that share corners with two equivalent Co(4)O6 octahedra, corners with four equivalent Co(1)O4 tetrahedra,  an edgeedge with one Co(4)O6 octahedra, edges with two equivalent Co(2)O6 octahedra, edges with two equivalent Co(3)O6 octahedra, and edges with two equivalent As(2)O6 octahedra. The corner-sharing octahedral tilt angles are 13°. In the third Co site, Co(3) is bonded to one O(4), one O(5), two equivalent O(1), and two equivalent O(2) atoms to form CoO6 octahedra that share corners with three equivalent Co(1)O4 tetrahedra, corners with three equivalent As(1)O4 tetrahedra,  an edgeedge with one Co(3)O6 octahedra,  an edgeedge with one As(2)O6 octahedra, edges with two equivalent Co(2)O6 octahedra, and edges with two equivalent Co(4)O6 octahedra. In the fourth Co site, Co(4) is bonded to two equivalent O(2) and four equivalent O(4) atoms to form CoO6 octahedra that share corners with four equivalent Co(2)O6 octahedra, corners with two equivalent As(1)O4 tetrahedra, edges with two equivalent Co(2)O6 octahedra, edges with two equivalent Co(4)O6 octahedra, and edges with four equivalent Co(3)O6 octahedra. The corner-sharing octahedral tilt angles are 13°. There are two inequivalent As sites. In the first As site, As(1) is bonded to two equivalent O(2) and two equivalent O(5) atoms to form AsO4 tetrahedra that share corners with two equivalent Co(4)O6 octahedra, corners with six equivalent Co(3)O6 octahedra, and corners with two equivalent Co(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 53-57°. In the second As site, As(2) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form AsO6 octahedra that share corners with six equivalent Co(1)O4 tetrahedra, edges with two equivalent Co(3)O6 octahedra, and edges with four equivalent Co(2)O6 octahedra. There are five inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Co(1), one Co(2), one Co(3), and one As(2) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Co(4), two equivalent Co(3), and one As(1) atom. In the third O site, O(3) is bonded to one Co(1), two equivalent Co(2), and one As(2) atom to form distorted OCo3As tetrahedra that share corners with two equivalent O(4)Co5 square pyramids, corners with three equivalent O(3)Co3As tetrahedra, and  an edgeedge with one O(4)Co5 square pyramid. In the fourth O site, O(4) is bonded to one Co(3), two equivalent Co(2), and two equivalent Co(4) atoms to form OCo5 square pyramids that share corners with two equivalent O(4)Co5 square pyramids, corners with two equivalent O(3)Co3As tetrahedra, edges with three equivalent O(4)Co5 square pyramids, and  an edgeedge with one O(3)Co3As tetrahedra. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Co(1), one Co(3), and one As(1) atom.
Co7(AsO6)2 crystallizes in the orthorhombic Imma space group. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(3), one O(5), and two equivalent O(1) atoms to form CoO4 tetrahedra that share corners with three equivalent Co(3)O6 octahedra, corners with three equivalent As(2)O6 octahedra, corners with four equivalent Co(2)O6 octahedra, and  a cornercorner with one As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-67°. The Co(1)-O(3) bond length is 1.97 Å. The Co(1)-O(5) bond length is 2.03 Å. Both Co(1)-O(1) bond lengths are 1.98 Å. In the second Co site, Co(2) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form CoO6 octahedra that share corners with two equivalent Co(4)O6 octahedra, corners with four equivalent Co(1)O4 tetrahedra,  an edgeedge with one Co(4)O6 octahedra, edges with two equivalent Co(2)O6 octahedra, edges with two equivalent Co(3)O6 octahedra, and edges with two equivalent As(2)O6 octahedra. The corner-sharing octahedral tilt angles are 13°. Both Co(2)-O(1) bond lengths are 2.20 Å. Both Co(2)-O(3) bond lengths are 2.09 Å. Both Co(2)-O(4) bond lengths are 2.11 Å. In the third Co site, Co(3) is bonded to one O(4), one O(5), two equivalent O(1), and two equivalent O(2) atoms to form CoO6 octahedra that share corners with three equivalent Co(1)O4 tetrahedra, corners with three equivalent As(1)O4 tetrahedra,  an edgeedge with one Co(3)O6 octahedra,  an edgeedge with one As(2)O6 octahedra, edges with two equivalent Co(2)O6 octahedra, and edges with two equivalent Co(4)O6 octahedra. The Co(3)-O(4) bond length is 2.08 Å. The Co(3)-O(5) bond length is 2.10 Å. Both Co(3)-O(1) bond lengths are 2.10 Å. Both Co(3)-O(2) bond lengths are 2.20 Å. In the fourth Co site, Co(4) is bonded to two equivalent O(2) and four equivalent O(4) atoms to form CoO6 octahedra that share corners with four equivalent Co(2)O6 octahedra, corners with two equivalent As(1)O4 tetrahedra, edges with two equivalent Co(2)O6 octahedra, edges with two equivalent Co(4)O6 octahedra, and edges with four equivalent Co(3)O6 octahedra. The corner-sharing octahedral tilt angles are 13°. Both Co(4)-O(2) bond lengths are 2.22 Å. All Co(4)-O(4) bond lengths are 2.11 Å. There are two inequivalent As sites. In the first As site, As(1) is bonded to two equivalent O(2) and two equivalent O(5) atoms to form AsO4 tetrahedra that share corners with two equivalent Co(4)O6 octahedra, corners with six equivalent Co(3)O6 octahedra, and corners with two equivalent Co(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 53-57°. Both As(1)-O(2) bond lengths are 1.73 Å. Both As(1)-O(5) bond lengths are 1.74 Å. In the second As site, As(2) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form AsO6 octahedra that share corners with six equivalent Co(1)O4 tetrahedra, edges with two equivalent Co(3)O6 octahedra, and edges with four equivalent Co(2)O6 octahedra. Both As(2)-O(3) bond lengths are 1.88 Å. All As(2)-O(1) bond lengths are 1.88 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Co(1), one Co(2), one Co(3), and one As(2) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Co(4), two equivalent Co(3), and one As(1) atom. In the third O site, O(3) is bonded to one Co(1), two equivalent Co(2), and one As(2) atom to form distorted OCo3As tetrahedra that share corners with two equivalent O(4)Co5 square pyramids, corners with three equivalent O(3)Co3As tetrahedra, and  an edgeedge with one O(4)Co5 square pyramid. In the fourth O site, O(4) is bonded to one Co(3), two equivalent Co(2), and two equivalent Co(4) atoms to form OCo5 square pyramids that share corners with two equivalent O(4)Co5 square pyramids, corners with two equivalent O(3)Co3As tetrahedra, edges with three equivalent O(4)Co5 square pyramids, and  an edgeedge with one O(3)Co3As tetrahedra. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Co(1), one Co(3), and one As(1) atom.