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 pentagonal pyramids that share corners with two equivalent As(1)O4 tetrahedra, corners with two equivalent As(3)O4 tetrahedra, edges with two equivalent Co(4)O6 octahedra,  an edgeedge with one Co(2)O6 pentagonal pyramid,  an edgeedge with one As(2)O5 trigonal bipyramid, and  an edgeedge with one As(4)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 pentagonal pyramids that share corners with two equivalent As(1)O4 tetrahedra, corners with two equivalent As(3)O4 tetrahedra, edges with two equivalent Co(3)O6 octahedra,  an edgeedge with one Co(1)O6 pentagonal pyramid,  an edgeedge with one As(2)O5 trigonal bipyramid, and  an edgeedge with one As(4)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(1)O4 tetrahedra,  a cornercorner with one As(3)O4 tetrahedra, corners with two equivalent As(2)O5 trigonal bipyramids, corners with two equivalent As(4)O5 trigonal bipyramids,  an edgeedge with one Co(4)O6 octahedra, and edges with two equivalent Co(2)O6 pentagonal pyramids. 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(1)O4 tetrahedra,  a cornercorner with one As(3)O4 tetrahedra, corners with two equivalent As(2)O5 trigonal bipyramids, corners with two equivalent As(4)O5 trigonal bipyramids,  an edgeedge with one Co(3)O6 octahedra, and edges with two equivalent Co(1)O6 pentagonal pyramids. There are four inequivalent As sites. In the first As site, As(1) is bonded to one O(2), one O(4), one O(7), and one O(9) 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 pentagonal pyramids, corners with two equivalent Co(2)O6 pentagonal pyramids, and corners with two equivalent As(4)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 62-65°. In the second As site, As(2) is bonded to one O(1), one O(10), one O(3), one O(6), and one O(8) atom to form distorted AsO5 trigonal bipyramids that share corners with two equivalent Co(3)O6 octahedra, corners with two equivalent Co(4)O6 octahedra, corners with two equivalent As(3)O4 tetrahedra,  an edgeedge with one Co(1)O6 pentagonal pyramid, and  an edgeedge with one Co(2)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 45-51°. In the third As site, As(3) is bonded to one O(1), one O(11), one O(13), 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 pentagonal pyramids, corners with two equivalent Co(2)O6 pentagonal pyramids, and corners with two equivalent As(2)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 63-64°. In the fourth As site, As(4) is bonded to one O(12), one O(14), one O(2), one O(4), and one O(5) atom to form distorted AsO5 trigonal bipyramids that share corners with two equivalent Co(3)O6 octahedra, corners with two equivalent Co(4)O6 octahedra, corners with two equivalent As(1)O4 tetrahedra,  an edgeedge with one Co(1)O6 pentagonal pyramid, and  an edgeedge with one Co(2)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 44-51°. 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(3) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one As(1) and one As(4) 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(2) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Co(1), one Co(2), one As(1), and one As(4) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Co(3), one Co(4), and one As(4) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Co(1), one Co(2), one As(2), and one As(3) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar 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 3-coordinate 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 non-coplanar geometry to one Co(1), one Co(4), and one As(4) atom. In the thirteenth O site, O(13) is bonded in a distorted trigonal planar geometry to one Co(1), one Co(4), and one As(3) atom. In the fourteenth O site, O(14) is bonded in a distorted trigonal non-coplanar 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 pentagonal pyramids that share corners with two equivalent As(1)O4 tetrahedra, corners with two equivalent As(3)O4 tetrahedra, edges with two equivalent Co(4)O6 octahedra,  an edgeedge with one Co(2)O6 pentagonal pyramid,  an edgeedge with one As(2)O5 trigonal bipyramid, and  an edgeedge with one As(4)O5 trigonal bipyramid. The Co(1)-O(12) bond length is 2.10 Å. The Co(1)-O(13) bond length is 2.10 Å. The Co(1)-O(4) bond length is 2.15 Å. The Co(1)-O(6) bond length is 2.15 Å. The Co(1)-O(8) bond length is 2.11 Å. The Co(1)-O(9) bond length is 2.10 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 pentagonal pyramids that share corners with two equivalent As(1)O4 tetrahedra, corners with two equivalent As(3)O4 tetrahedra, edges with two equivalent Co(3)O6 octahedra,  an edgeedge with one Co(1)O6 pentagonal pyramid,  an edgeedge with one As(2)O5 trigonal bipyramid, and  an edgeedge with one As(4)O5 trigonal bipyramid. The Co(2)-O(10) bond length is 2.11 Å. The Co(2)-O(11) bond length is 2.10 Å. The Co(2)-O(14) bond length is 2.13 Å. The Co(2)-O(4) bond length is 2.14 Å. The Co(2)-O(6) bond length is 2.15 Å. The Co(2)-O(7) bond length is 2.10 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(1)O4 tetrahedra,  a cornercorner with one As(3)O4 tetrahedra, corners with two equivalent As(2)O5 trigonal bipyramids, corners with two equivalent As(4)O5 trigonal bipyramids,  an edgeedge with one Co(4)O6 octahedra, and edges with two equivalent Co(2)O6 pentagonal pyramids. The Co(3)-O(10) bond length is 2.09 Å. The Co(3)-O(11) bond length is 2.27 Å. The Co(3)-O(14) bond length is 2.08 Å. The Co(3)-O(3) bond length is 2.14 Å. The Co(3)-O(5) bond length is 2.14 Å. The Co(3)-O(7) bond length is 2.21 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(1)O4 tetrahedra,  a cornercorner with one As(3)O4 tetrahedra, corners with two equivalent As(2)O5 trigonal bipyramids, corners with two equivalent As(4)O5 trigonal bipyramids,  an edgeedge with one Co(3)O6 octahedra, and edges with two equivalent Co(1)O6 pentagonal pyramids. The Co(4)-O(12) bond length is 2.10 Å. The Co(4)-O(13) bond length is 2.23 Å. The Co(4)-O(3) bond length is 2.15 Å. The Co(4)-O(5) bond length is 2.14 Å. The Co(4)-O(8) bond length is 2.07 Å. The Co(4)-O(9) bond length is 2.29 Å. There are four inequivalent As sites. In the first As site, As(1) is bonded to one O(2), one O(4), one O(7), and one O(9) 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 pentagonal pyramids, corners with two equivalent Co(2)O6 pentagonal pyramids, and corners with two equivalent As(4)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 62-65°. The As(1)-O(2) bond length is 1.73 Å. The As(1)-O(4) bond length is 1.75 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(3), one O(6), and one O(8) atom to form distorted AsO5 trigonal bipyramids that share corners with two equivalent Co(3)O6 octahedra, corners with two equivalent Co(4)O6 octahedra, corners with two equivalent As(3)O4 tetrahedra,  an edgeedge with one Co(1)O6 pentagonal pyramid, and  an edgeedge with one Co(2)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 45-51°. The As(2)-O(1) bond length is 1.80 Å. The As(2)-O(10) bond length is 1.73 Å. The As(2)-O(3) bond length is 1.72 Å. The As(2)-O(6) bond length is 2.23 Å. The As(2)-O(8) bond length is 1.74 Å. In the third As site, As(3) is bonded to one O(1), one O(11), one O(13), 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 pentagonal pyramids, corners with two equivalent Co(2)O6 pentagonal pyramids, and corners with two equivalent As(2)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 63-64°. The As(3)-O(1) bond length is 1.73 Å. The As(3)-O(11) bond length is 1.70 Å. The As(3)-O(13) bond length is 1.70 Å. The As(3)-O(6) bond length is 1.75 Å. In the fourth As site, As(4) is bonded to one O(12), one O(14), one O(2), one O(4), and one O(5) atom to form distorted AsO5 trigonal bipyramids that share corners with two equivalent Co(3)O6 octahedra, corners with two equivalent Co(4)O6 octahedra, corners with two equivalent As(1)O4 tetrahedra,  an edgeedge with one Co(1)O6 pentagonal pyramid, and  an edgeedge with one Co(2)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 44-51°. The As(4)-O(12) bond length is 1.73 Å. The As(4)-O(14) bond length is 1.73 Å. The As(4)-O(2) bond length is 1.79 Å. The As(4)-O(4) bond length is 2.26 Å. The As(4)-O(5) 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(3) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one As(1) and one As(4) 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(2) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Co(1), one Co(2), one As(1), and one As(4) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Co(3), one Co(4), and one As(4) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Co(1), one Co(2), one As(2), and one As(3) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar 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 3-coordinate 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 non-coplanar geometry to one Co(1), one Co(4), and one As(4) atom. In the thirteenth O site, O(13) is bonded in a distorted trigonal planar geometry to one Co(1), one Co(4), and one As(3) atom. In the fourteenth O site, O(14) is bonded in a distorted trigonal non-coplanar geometry to one Co(2), one Co(3), and one As(4) atom.