Co2As2O7 crystallizes in the triclinic P1 space group. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(2), one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form distorted CoO6 pentagonal pyramids that share corners with three equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra, and edges with three equivalent Co(2)O6 pentagonal pyramids. In the second Co site, Co(2) is bonded to one O(2), one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form distorted CoO6 pentagonal pyramids that share corners with three equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra, and edges with three equivalent Co(1)O6 pentagonal pyramids. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form AsO4 tetrahedra that share corners with three equivalent Co(1)O6 pentagonal pyramids, corners with three equivalent Co(2)O6 pentagonal pyramids, and  a cornercorner with one As(2)O4 tetrahedra. In the second As site, As(2) is bonded to one O(1), one O(3), one O(6), and one O(7) atom to form AsO4 tetrahedra that share corners with three equivalent Co(1)O6 pentagonal pyramids, corners with three equivalent Co(2)O6 pentagonal pyramids, and  a cornercorner with one As(1)O4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to one As(1) and one As(2) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Co(1), one Co(2), and one As(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Co(1), one Co(2), and one As(2) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Co(1), one Co(2), and one As(1) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Co(1), one Co(2), and one As(1) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Co(1), one Co(2), and one As(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Co(1), one Co(2), and one As(2) atom.
Co2As2O7 crystallizes in the triclinic P1 space group. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(2), one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form distorted CoO6 pentagonal pyramids that share corners with three equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra, and edges with three equivalent Co(2)O6 pentagonal pyramids. The Co(1)-O(2) bond length is 2.14 Å. The Co(1)-O(3) bond length is 2.14 Å. The Co(1)-O(4) bond length is 2.19 Å. The Co(1)-O(5) bond length is 2.09 Å. The Co(1)-O(6) bond length is 2.20 Å. The Co(1)-O(7) bond length is 2.06 Å. In the second Co site, Co(2) is bonded to one O(2), one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form distorted CoO6 pentagonal pyramids that share corners with three equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra, and edges with three equivalent Co(1)O6 pentagonal pyramids. The Co(2)-O(2) bond length is 2.13 Å. The Co(2)-O(3) bond length is 2.15 Å. The Co(2)-O(4) bond length is 2.07 Å. The Co(2)-O(5) bond length is 2.20 Å. The Co(2)-O(6) bond length is 2.09 Å. The Co(2)-O(7) bond length is 2.21 Å. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form AsO4 tetrahedra that share corners with three equivalent Co(1)O6 pentagonal pyramids, corners with three equivalent Co(2)O6 pentagonal pyramids, and  a cornercorner with one As(2)O4 tetrahedra. The As(1)-O(1) bond length is 1.74 Å. The As(1)-O(2) bond length is 1.72 Å. The As(1)-O(4) bond length is 1.72 Å. The As(1)-O(5) bond length is 1.71 Å. In the second As site, As(2) is bonded to one O(1), one O(3), one O(6), and one O(7) atom to form AsO4 tetrahedra that share corners with three equivalent Co(1)O6 pentagonal pyramids, corners with three equivalent Co(2)O6 pentagonal pyramids, and  a cornercorner with one As(1)O4 tetrahedra. The As(2)-O(1) bond length is 1.74 Å. The As(2)-O(3) bond length is 1.73 Å. The As(2)-O(6) bond length is 1.71 Å. The As(2)-O(7) bond length is 1.72 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to one As(1) and one As(2) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Co(1), one Co(2), and one As(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Co(1), one Co(2), and one As(2) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Co(1), one Co(2), and one As(1) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Co(1), one Co(2), and one As(1) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Co(1), one Co(2), and one As(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Co(1), one Co(2), and one As(2) atom.