BaCu2SnSe4 crystallizes in the orthorhombic Ama2 space group. Ba(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent Se(2), and four equivalent Se(3) atoms. Cu(1) is bonded to one Se(1), one Se(2), and two equivalent Se(3) atoms to form distorted CuSe4 tetrahedra that share corners with two equivalent Cu(1)Se4 tetrahedra, corners with four equivalent Sn(1)Se4 tetrahedra, and  an edgeedge with one Cu(1)Se4 tetrahedra. Sn(1) is bonded to one Se(1), one Se(2), and two equivalent Se(3) atoms to form SnSe4 tetrahedra that share corners with eight equivalent Cu(1)Se4 tetrahedra. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Ba(1), two equivalent Cu(1), and one Sn(1) atom to form distorted corner-sharing SeBa2Cu2Sn trigonal bipyramids. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to two equivalent Ba(1), two equivalent Cu(1), and one Sn(1) atom. In the third Se site, Se(3) is bonded in a 5-coordinate geometry to two equivalent Ba(1), two equivalent Cu(1), and one Sn(1) atom.
BaCu2SnSe4 crystallizes in the orthorhombic Ama2 space group. Ba(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent Se(2), and four equivalent Se(3) atoms. Both Ba(1)-Se(1) bond lengths are 3.37 Å. Both Ba(1)-Se(2) bond lengths are 3.44 Å. There are two shorter (3.39 Å) and two longer (3.45 Å) Ba(1)-Se(3) bond lengths. Cu(1) is bonded to one Se(1), one Se(2), and two equivalent Se(3) atoms to form distorted CuSe4 tetrahedra that share corners with two equivalent Cu(1)Se4 tetrahedra, corners with four equivalent Sn(1)Se4 tetrahedra, and  an edgeedge with one Cu(1)Se4 tetrahedra. The Cu(1)-Se(1) bond length is 2.48 Å. The Cu(1)-Se(2) bond length is 2.49 Å. There is one shorter (2.45 Å) and one longer (2.50 Å) Cu(1)-Se(3) bond length. Sn(1) is bonded to one Se(1), one Se(2), and two equivalent Se(3) atoms to form SnSe4 tetrahedra that share corners with eight equivalent Cu(1)Se4 tetrahedra. The Sn(1)-Se(1) bond length is 2.61 Å. The Sn(1)-Se(2) bond length is 2.59 Å. Both Sn(1)-Se(3) bond lengths are 2.60 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Ba(1), two equivalent Cu(1), and one Sn(1) atom to form distorted corner-sharing SeBa2Cu2Sn trigonal bipyramids. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to two equivalent Ba(1), two equivalent Cu(1), and one Sn(1) atom. In the third Se site, Se(3) is bonded in a 5-coordinate geometry to two equivalent Ba(1), two equivalent Cu(1), and one Sn(1) atom.