BaCo2Si2O7 crystallizes in the monoclinic C2/c space group. Ba(1) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(4), one O(5), two equivalent O(1), and two equivalent O(7) atoms. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(4), one O(6), and two equivalent O(5) atoms to form distorted CoO5 trigonal bipyramids that share  a cornercorner with one Co(2)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra,  an edgeedge with one Si(1)O4 tetrahedra, and  an edgeedge with one Co(1)O5 trigonal bipyramid. In the second Co site, Co(2) is bonded to two equivalent O(2) and two equivalent O(4) atoms to form CoO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and corners with two equivalent Co(1)O5 trigonal bipyramids. In the third Co site, Co(3) is bonded in a 4-coordinate geometry to two equivalent O(2), two equivalent O(6), and two equivalent O(7) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(3), one O(4), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Co(2)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Co(1)O5 trigonal bipyramid, and  an edgeedge with one Co(1)O5 trigonal bipyramid. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Co(2)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Co(1)O5 trigonal bipyramids. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Co(3), and one Si(1) atom. In the second O site, O(1) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Co(1), and one Si(2) atom. In the third O site, O(2) is bonded in a 4-coordinate geometry to one Ba(1), one Co(2), one Co(3), and one Si(2) atom. In the fourth O site, O(6) is bonded in a distorted trigonal planar geometry to one Co(1), one Co(3), and one Si(2) atom. In the fifth O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Si(1), and one Si(2) atom. In the sixth O site, O(4) is bonded in a 3-coordinate geometry to one Ba(1), one Co(1), one Co(2), and one Si(1) atom. In the seventh O site, O(5) is bonded in a 4-coordinate geometry to one Ba(1), two equivalent Co(1), and one Si(1) atom.
BaCo2Si2O7 crystallizes in the monoclinic C2/c space group. Ba(1) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(4), one O(5), two equivalent O(1), and two equivalent O(7) atoms. The Ba(1)-O(2) bond length is 2.73 Å. The Ba(1)-O(3) bond length is 2.90 Å. The Ba(1)-O(4) bond length is 3.05 Å. The Ba(1)-O(5) bond length is 2.77 Å. There is one shorter (2.80 Å) and one longer (3.10 Å) Ba(1)-O(1) bond length. There is one shorter (2.74 Å) and one longer (3.17 Å) Ba(1)-O(7) bond length. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(4), one O(6), and two equivalent O(5) atoms to form distorted CoO5 trigonal bipyramids that share  a cornercorner with one Co(2)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra,  an edgeedge with one Si(1)O4 tetrahedra, and  an edgeedge with one Co(1)O5 trigonal bipyramid. The Co(1)-O(1) bond length is 2.01 Å. The Co(1)-O(4) bond length is 2.07 Å. The Co(1)-O(6) bond length is 2.00 Å. There is one shorter (2.02 Å) and one longer (2.36 Å) Co(1)-O(5) bond length. In the second Co site, Co(2) is bonded to two equivalent O(2) and two equivalent O(4) atoms to form CoO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and corners with two equivalent Co(1)O5 trigonal bipyramids. Both Co(2)-O(2) bond lengths are 1.99 Å. Both Co(2)-O(4) bond lengths are 1.99 Å. In the third Co site, Co(3) is bonded in a 4-coordinate geometry to two equivalent O(2), two equivalent O(6), and two equivalent O(7) atoms. Both Co(3)-O(2) bond lengths are 2.69 Å. Both Co(3)-O(6) bond lengths are 2.04 Å. Both Co(3)-O(7) bond lengths are 2.05 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(3), one O(4), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Co(2)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Co(1)O5 trigonal bipyramid, and  an edgeedge with one Co(1)O5 trigonal bipyramid. The Si(1)-O(3) bond length is 1.68 Å. The Si(1)-O(4) bond length is 1.66 Å. The Si(1)-O(5) bond length is 1.64 Å. The Si(1)-O(7) bond length is 1.62 Å. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Co(2)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Co(1)O5 trigonal bipyramids. The Si(2)-O(1) bond length is 1.63 Å. The Si(2)-O(2) bond length is 1.64 Å. The Si(2)-O(3) bond length is 1.68 Å. The Si(2)-O(6) bond length is 1.65 Å. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Co(3), and one Si(1) atom. In the second O site, O(1) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Co(1), and one Si(2) atom. In the third O site, O(2) is bonded in a 4-coordinate geometry to one Ba(1), one Co(2), one Co(3), and one Si(2) atom. In the fourth O site, O(6) is bonded in a distorted trigonal planar geometry to one Co(1), one Co(3), and one Si(2) atom. In the fifth O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Si(1), and one Si(2) atom. In the sixth O site, O(4) is bonded in a 3-coordinate geometry to one Ba(1), one Co(1), one Co(2), and one Si(1) atom. In the seventh O site, O(5) is bonded in a 4-coordinate geometry to one Ba(1), two equivalent Co(1), and one Si(1) atom.