Co2As2O7 crystallizes in the triclinic P1 space group. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(12), one O(13), one O(4), one O(6), one O(8), and one O(9) atom to form distorted CoO6 octahedra that share  a cornercorner with one As(3)O4 tetrahedra, corners with two equivalent As(4)O4 tetrahedra,  a cornercorner with one As(1)O5 trigonal bipyramid,  a cornercorner with one As(2)O5 trigonal bipyramid,  an edgeedge with one Co(2)O6 octahedra, edges with two equivalent Co(4)O6 octahedra, and  an edgeedge with one As(2)O5 trigonal bipyramid. In the second Co site, Co(2) is bonded to one O(10), one O(11), one O(14), one O(4), one O(6), and one O(7) atom to form distorted CoO6 octahedra that share  a cornercorner with one As(3)O4 tetrahedra, corners with two equivalent As(4)O4 tetrahedra,  a cornercorner with one As(1)O5 trigonal bipyramid,  a cornercorner with one As(2)O5 trigonal bipyramid,  an edgeedge with one Co(1)O6 octahedra, edges with two equivalent Co(3)O6 octahedra, and  an edgeedge with one As(2)O5 trigonal bipyramid. In the third Co site, Co(3) is bonded to one O(10), one O(11), one O(14), one O(3), one O(5), and one O(7) atom to form distorted CoO6 octahedra that share  a cornercorner with one As(4)O4 tetrahedra, corners with two equivalent As(3)O4 tetrahedra,  a cornercorner with one As(1)O5 trigonal bipyramid,  a cornercorner with one As(2)O5 trigonal bipyramid,  an edgeedge with one Co(4)O6 octahedra, edges with two equivalent Co(2)O6 octahedra, and  an edgeedge with one As(1)O5 trigonal bipyramid. In the fourth Co site, Co(4) is bonded to one O(12), one O(13), one O(3), one O(5), one O(8), and one O(9) atom to form distorted CoO6 octahedra that share  a cornercorner with one As(4)O4 tetrahedra, corners with two equivalent As(3)O4 tetrahedra,  a cornercorner with one As(1)O5 trigonal bipyramid,  a cornercorner with one As(2)O5 trigonal bipyramid,  an edgeedge with one Co(3)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, and  an edgeedge with one As(1)O5 trigonal bipyramid. There are four inequivalent As sites. In the first As site, As(1) is bonded to one O(2), one O(3), one O(5), one O(7), and one O(9) atom to form distorted AsO5 trigonal bipyramids that share  a cornercorner with one Co(1)O6 octahedra,  a cornercorner with one Co(2)O6 octahedra,  a cornercorner with one Co(3)O6 octahedra,  a cornercorner with one Co(4)O6 octahedra, corners with two equivalent As(3)O4 tetrahedra,  an edgeedge with one Co(3)O6 octahedra, and  an edgeedge with one Co(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 45-52°. In the second As site, As(2) is bonded to one O(1), one O(10), one O(4), one O(6), and one O(8) atom to form distorted AsO5 trigonal bipyramids that share  a cornercorner with one Co(1)O6 octahedra,  a cornercorner with one Co(2)O6 octahedra,  a cornercorner with one Co(3)O6 octahedra,  a cornercorner with one Co(4)O6 octahedra, corners with two equivalent As(4)O4 tetrahedra,  an edgeedge with one Co(1)O6 octahedra, and  an edgeedge with one Co(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-53°. In the third As site, As(3) is bonded to one O(11), one O(13), one O(2), and one O(5) atom to form AsO4 tetrahedra that share  a cornercorner with one Co(1)O6 octahedra,  a cornercorner with one Co(2)O6 octahedra, corners with two equivalent Co(3)O6 octahedra, corners with two equivalent Co(4)O6 octahedra, and corners with two equivalent As(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 44-64°. In the fourth As site, As(4) is bonded to one O(1), one O(12), one O(14), and one O(6) atom to form AsO4 tetrahedra that share  a cornercorner with one Co(3)O6 octahedra,  a cornercorner with one Co(4)O6 octahedra, corners with two equivalent Co(1)O6 octahedra, corners with two equivalent Co(2)O6 octahedra, and corners with two equivalent As(2)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 44-64°. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one As(2) and one As(4) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one As(1) and one As(3) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Co(3), one Co(4), and one As(1) 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(2) atom. In the fifth O site, O(5) is bonded in a distorted rectangular see-saw-like geometry to one Co(3), one Co(4), one As(1), and one As(3) atom. In the sixth O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to one Co(1), one Co(2), one As(2), and one As(4) atom. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to one Co(2), one Co(3), and one As(1) atom. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Co(1), one Co(4), and one As(2) atom. In the ninth O site, O(9) is bonded in a distorted trigonal non-coplanar geometry to one Co(1), one Co(4), and one As(1) atom. In the tenth O site, O(10) is bonded in a distorted trigonal non-coplanar geometry to one Co(2), one Co(3), and one As(2) atom. In the eleventh O site, O(11) is bonded in a distorted trigonal planar geometry to one Co(2), one Co(3), and one As(3) atom. In the twelfth O site, O(12) is bonded in a distorted trigonal planar geometry to one Co(1), one Co(4), and one As(4) atom. In the thirteenth O site, O(13) is bonded in a 3-coordinate geometry to one Co(1), one Co(4), and one As(3) atom. In the fourteenth O site, O(14) is bonded in a 3-coordinate geometry to one Co(2), one Co(3), and one As(4) atom.
Co2As2O7 crystallizes in the triclinic P1 space group. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(12), one O(13), one O(4), one O(6), one O(8), and one O(9) atom to form distorted CoO6 octahedra that share  a cornercorner with one As(3)O4 tetrahedra, corners with two equivalent As(4)O4 tetrahedra,  a cornercorner with one As(1)O5 trigonal bipyramid,  a cornercorner with one As(2)O5 trigonal bipyramid,  an edgeedge with one Co(2)O6 octahedra, edges with two equivalent Co(4)O6 octahedra, and  an edgeedge with one As(2)O5 trigonal bipyramid. The Co(1)-O(12) bond length is 2.20 Å. The Co(1)-O(13) bond length is 2.00 Å. The Co(1)-O(4) bond length is 2.11 Å. The Co(1)-O(6) bond length is 2.16 Å. The Co(1)-O(8) bond length is 2.08 Å. The Co(1)-O(9) bond length is 2.07 Å. In the second Co site, Co(2) is bonded to one O(10), one O(11), one O(14), one O(4), one O(6), and one O(7) atom to form distorted CoO6 octahedra that share  a cornercorner with one As(3)O4 tetrahedra, corners with two equivalent As(4)O4 tetrahedra,  a cornercorner with one As(1)O5 trigonal bipyramid,  a cornercorner with one As(2)O5 trigonal bipyramid,  an edgeedge with one Co(1)O6 octahedra, edges with two equivalent Co(3)O6 octahedra, and  an edgeedge with one As(2)O5 trigonal bipyramid. The Co(2)-O(10) bond length is 2.08 Å. The Co(2)-O(11) bond length is 2.03 Å. The Co(2)-O(14) bond length is 2.31 Å. The Co(2)-O(4) bond length is 2.09 Å. The Co(2)-O(6) bond length is 2.17 Å. The Co(2)-O(7) bond length is 2.06 Å. In the third Co site, Co(3) is bonded to one O(10), one O(11), one O(14), one O(3), one O(5), and one O(7) atom to form distorted CoO6 octahedra that share  a cornercorner with one As(4)O4 tetrahedra, corners with two equivalent As(3)O4 tetrahedra,  a cornercorner with one As(1)O5 trigonal bipyramid,  a cornercorner with one As(2)O5 trigonal bipyramid,  an edgeedge with one Co(4)O6 octahedra, edges with two equivalent Co(2)O6 octahedra, and  an edgeedge with one As(1)O5 trigonal bipyramid. The Co(3)-O(10) bond length is 2.08 Å. The Co(3)-O(11) bond length is 2.17 Å. The Co(3)-O(14) bond length is 2.03 Å. The Co(3)-O(3) bond length is 2.11 Å. The Co(3)-O(5) bond length is 2.13 Å. The Co(3)-O(7) bond length is 2.10 Å. In the fourth Co site, Co(4) is bonded to one O(12), one O(13), one O(3), one O(5), one O(8), and one O(9) atom to form distorted CoO6 octahedra that share  a cornercorner with one As(4)O4 tetrahedra, corners with two equivalent As(3)O4 tetrahedra,  a cornercorner with one As(1)O5 trigonal bipyramid,  a cornercorner with one As(2)O5 trigonal bipyramid,  an edgeedge with one Co(3)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, and  an edgeedge with one As(1)O5 trigonal bipyramid. The Co(4)-O(12) bond length is 2.01 Å. The Co(4)-O(13) bond length is 2.30 Å. The Co(4)-O(3) bond length is 2.11 Å. The Co(4)-O(5) bond length is 2.19 Å. The Co(4)-O(8) bond length is 2.05 Å. The Co(4)-O(9) bond length is 2.07 Å. There are four inequivalent As sites. In the first As site, As(1) is bonded to one O(2), one O(3), one O(5), one O(7), and one O(9) atom to form distorted AsO5 trigonal bipyramids that share  a cornercorner with one Co(1)O6 octahedra,  a cornercorner with one Co(2)O6 octahedra,  a cornercorner with one Co(3)O6 octahedra,  a cornercorner with one Co(4)O6 octahedra, corners with two equivalent As(3)O4 tetrahedra,  an edgeedge with one Co(3)O6 octahedra, and  an edgeedge with one Co(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 45-52°. The As(1)-O(2) bond length is 1.77 Å. The As(1)-O(3) bond length is 1.70 Å. The As(1)-O(5) bond length is 2.20 Å. The As(1)-O(7) bond length is 1.71 Å. The As(1)-O(9) bond length is 1.70 Å. In the second As site, As(2) is bonded to one O(1), one O(10), one O(4), one O(6), and one O(8) atom to form distorted AsO5 trigonal bipyramids that share  a cornercorner with one Co(1)O6 octahedra,  a cornercorner with one Co(2)O6 octahedra,  a cornercorner with one Co(3)O6 octahedra,  a cornercorner with one Co(4)O6 octahedra, corners with two equivalent As(4)O4 tetrahedra,  an edgeedge with one Co(1)O6 octahedra, and  an edgeedge with one Co(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-53°. The As(2)-O(1) bond length is 1.77 Å. The As(2)-O(10) bond length is 1.70 Å. The As(2)-O(4) bond length is 1.71 Å. The As(2)-O(6) bond length is 2.19 Å. The As(2)-O(8) bond length is 1.71 Å. In the third As site, As(3) is bonded to one O(11), one O(13), one O(2), and one O(5) atom to form AsO4 tetrahedra that share  a cornercorner with one Co(1)O6 octahedra,  a cornercorner with one Co(2)O6 octahedra, corners with two equivalent Co(3)O6 octahedra, corners with two equivalent Co(4)O6 octahedra, and corners with two equivalent As(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 44-64°. The As(3)-O(11) bond length is 1.69 Å. The As(3)-O(13) bond length is 1.68 Å. The As(3)-O(2) bond length is 1.70 Å. The As(3)-O(5) bond length is 1.72 Å. In the fourth As site, As(4) is bonded to one O(1), one O(12), one O(14), and one O(6) atom to form AsO4 tetrahedra that share  a cornercorner with one Co(3)O6 octahedra,  a cornercorner with one Co(4)O6 octahedra, corners with two equivalent Co(1)O6 octahedra, corners with two equivalent Co(2)O6 octahedra, and corners with two equivalent As(2)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 44-64°. The As(4)-O(1) bond length is 1.70 Å. The As(4)-O(12) bond length is 1.69 Å. The As(4)-O(14) bond length is 1.68 Å. The As(4)-O(6) bond length is 1.72 Å. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one As(2) and one As(4) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one As(1) and one As(3) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Co(3), one Co(4), and one As(1) 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(2) atom. In the fifth O site, O(5) is bonded in a distorted rectangular see-saw-like geometry to one Co(3), one Co(4), one As(1), and one As(3) atom. In the sixth O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to one Co(1), one Co(2), one As(2), and one As(4) atom. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to one Co(2), one Co(3), and one As(1) atom. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Co(1), one Co(4), and one As(2) atom. In the ninth O site, O(9) is bonded in a distorted trigonal non-coplanar geometry to one Co(1), one Co(4), and one As(1) atom. In the tenth O site, O(10) is bonded in a distorted trigonal non-coplanar geometry to one Co(2), one Co(3), and one As(2) atom. In the eleventh O site, O(11) is bonded in a distorted trigonal planar geometry to one Co(2), one Co(3), and one As(3) atom. In the twelfth O site, O(12) is bonded in a distorted trigonal planar geometry to one Co(1), one Co(4), and one As(4) atom. In the thirteenth O site, O(13) is bonded in a 3-coordinate geometry to one Co(1), one Co(4), and one As(3) atom. In the fourteenth O site, O(14) is bonded in a 3-coordinate geometry to one Co(2), one Co(3), and one As(4) atom.