Be2CoTl2(O3F4)2 crystallizes in the monoclinic P2_1/c space group. Be(1) is bonded to one F(1), one F(2), one F(3), and one F(4) atom to form BeF4 tetrahedra that share corners with four equivalent Tl(1)OF4 trigonal bipyramids. Co(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form CoO6 octahedra that share corners with two equivalent Tl(1)OF4 trigonal bipyramids. Tl(1) is bonded to one O(3), one F(1), one F(2), one F(3), and one F(4) atom to form TlOF4 trigonal bipyramids that share  a cornercorner with one Co(1)O6 octahedra and corners with four equivalent Be(1)F4 tetrahedra. The corner-sharing octahedral tilt angles are 55°. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Co(1) and one O(2) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Co(1) and one O(1) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one Co(1) and one Tl(1) atom. There are four inequivalent F sites. In the first F site, F(4) is bonded in a distorted bent 150 degrees geometry to one Be(1) and one Tl(1) atom. In the second F site, F(1) is bonded in a distorted bent 150 degrees geometry to one Be(1) and one Tl(1) atom. In the third F site, F(2) is bonded in a distorted bent 150 degrees geometry to one Be(1) and one Tl(1) atom. In the fourth F site, F(3) is bonded in a distorted bent 150 degrees geometry to one Be(1) and one Tl(1) atom.
Be2CoTl2(O3F4)2 crystallizes in the monoclinic P2_1/c space group. Be(1) is bonded to one F(1), one F(2), one F(3), and one F(4) atom to form BeF4 tetrahedra that share corners with four equivalent Tl(1)OF4 trigonal bipyramids. The Be(1)-F(1) bond length is 1.56 Å. The Be(1)-F(2) bond length is 1.58 Å. The Be(1)-F(3) bond length is 1.60 Å. The Be(1)-F(4) bond length is 1.55 Å. Co(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form CoO6 octahedra that share corners with two equivalent Tl(1)OF4 trigonal bipyramids. Both Co(1)-O(1) bond lengths are 1.90 Å. Both Co(1)-O(2) bond lengths are 1.91 Å. Both Co(1)-O(3) bond lengths are 1.80 Å. Tl(1) is bonded to one O(3), one F(1), one F(2), one F(3), and one F(4) atom to form TlOF4 trigonal bipyramids that share  a cornercorner with one Co(1)O6 octahedra and corners with four equivalent Be(1)F4 tetrahedra. The corner-sharing octahedral tilt angles are 55°. The Tl(1)-O(3) bond length is 2.07 Å. The Tl(1)-F(1) bond length is 2.31 Å. The Tl(1)-F(2) bond length is 2.17 Å. The Tl(1)-F(3) bond length is 2.20 Å. The Tl(1)-F(4) bond length is 2.31 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Co(1) and one O(2) atom. The O(1)-O(2) bond length is 1.31 Å. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Co(1) and one O(1) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one Co(1) and one Tl(1) atom. There are four inequivalent F sites. In the first F site, F(4) is bonded in a distorted bent 150 degrees geometry to one Be(1) and one Tl(1) atom. In the second F site, F(1) is bonded in a distorted bent 150 degrees geometry to one Be(1) and one Tl(1) atom. In the third F site, F(2) is bonded in a distorted bent 150 degrees geometry to one Be(1) and one Tl(1) atom. In the fourth F site, F(3) is bonded in a distorted bent 150 degrees geometry to one Be(1) and one Tl(1) atom.