Ba2ErInSe5 crystallizes in the orthorhombic Cmc2_1 space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 8-coordinate geometry to one Se(3), one Se(5), two equivalent Se(1), two equivalent Se(2), and two equivalent Se(4) atoms. In the second Ba site, Ba(2) is bonded in a 8-coordinate geometry to one Se(2), one Se(5), two equivalent Se(1), two equivalent Se(3), and two equivalent Se(4) atoms. Er(1) is bonded to one Se(1), one Se(5), two equivalent Se(2), and two equivalent Se(3) atoms to form ErSe6 octahedra that share edges with two equivalent Er(1)Se6 octahedra and edges with two equivalent In(1)Se4 trigonal pyramids. In(1) is bonded to one Se(3), one Se(4), and two equivalent Se(5) atoms to form InSe4 trigonal pyramids that share corners with two equivalent In(1)Se4 trigonal pyramids and edges with two equivalent Er(1)Se6 octahedra. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Ba(1), two equivalent Ba(2), and one Er(1) atom to form SeBa4Er square pyramids that share corners with two equivalent Se(3)Ba3Er2In octahedra, corners with four equivalent Se(4)Ba4In square pyramids, corners with two equivalent Se(2)Ba3Er2 trigonal bipyramids, edges with three equivalent Se(3)Ba3Er2In octahedra, edges with two equivalent Se(1)Ba4Er square pyramids, edges with two equivalent Se(4)Ba4In square pyramids, and edges with three equivalent Se(2)Ba3Er2 trigonal bipyramids. The corner-sharing octahedral tilt angles are 31°. In the second Se site, Se(2) is bonded to one Ba(2), two equivalent Ba(1), and two equivalent Er(1) atoms to form distorted SeBa3Er2 trigonal bipyramids that share corners with two equivalent Se(3)Ba3Er2In octahedra, corners with two equivalent Se(1)Ba4Er square pyramids, corners with four equivalent Se(4)Ba4In square pyramids, edges with three equivalent Se(3)Ba3Er2In octahedra,  an edgeedge with one Se(4)Ba4In square pyramid, edges with three equivalent Se(1)Ba4Er square pyramids, and edges with two equivalent Se(2)Ba3Er2 trigonal bipyramids. The corner-sharing octahedral tilt angles are 10°. In the third Se site, Se(3) is bonded to one Ba(1), two equivalent Ba(2), two equivalent Er(1), and one In(1) atom to form distorted SeBa3Er2In octahedra that share corners with two equivalent Se(1)Ba4Er square pyramids, corners with four equivalent Se(4)Ba4In square pyramids, corners with two equivalent Se(2)Ba3Er2 trigonal bipyramids, edges with two equivalent Se(3)Ba3Er2In octahedra, edges with three equivalent Se(1)Ba4Er square pyramids, edges with three equivalent Se(2)Ba3Er2 trigonal bipyramids, and  a faceface with one Se(4)Ba4In square pyramid. In the fourth Se site, Se(4) is bonded to two equivalent Ba(1), two equivalent Ba(2), and one In(1) atom to form SeBa4In square pyramids that share corners with four equivalent Se(3)Ba3Er2In octahedra, corners with four equivalent Se(1)Ba4Er square pyramids, corners with four equivalent Se(2)Ba3Er2 trigonal bipyramids, edges with two equivalent Se(1)Ba4Er square pyramids, edges with two equivalent Se(4)Ba4In square pyramids,  an edgeedge with one Se(2)Ba3Er2 trigonal bipyramid, and  a faceface with one Se(3)Ba3Er2In octahedra. The corner-sharing octahedral tilt angles range from 40-67°. In the fifth Se site, Se(5) is bonded in a 5-coordinate geometry to one Ba(1), one Ba(2), one Er(1), and two equivalent In(1) atoms.
Ba2ErInSe5 crystallizes in the orthorhombic Cmc2_1 space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 8-coordinate geometry to one Se(3), one Se(5), two equivalent Se(1), two equivalent Se(2), and two equivalent Se(4) atoms. The Ba(1)-Se(3) bond length is 3.51 Å. The Ba(1)-Se(5) bond length is 3.86 Å. Both Ba(1)-Se(1) bond lengths are 3.32 Å. Both Ba(1)-Se(2) bond lengths are 3.35 Å. Both Ba(1)-Se(4) bond lengths are 3.31 Å. In the second Ba site, Ba(2) is bonded in a 8-coordinate geometry to one Se(2), one Se(5), two equivalent Se(1), two equivalent Se(3), and two equivalent Se(4) atoms. The Ba(2)-Se(2) bond length is 3.31 Å. The Ba(2)-Se(5) bond length is 3.67 Å. Both Ba(2)-Se(1) bond lengths are 3.29 Å. Both Ba(2)-Se(3) bond lengths are 3.60 Å. Both Ba(2)-Se(4) bond lengths are 3.37 Å. Er(1) is bonded to one Se(1), one Se(5), two equivalent Se(2), and two equivalent Se(3) atoms to form ErSe6 octahedra that share edges with two equivalent Er(1)Se6 octahedra and edges with two equivalent In(1)Se4 trigonal pyramids. The Er(1)-Se(1) bond length is 2.74 Å. The Er(1)-Se(5) bond length is 3.07 Å. Both Er(1)-Se(2) bond lengths are 2.84 Å. Both Er(1)-Se(3) bond lengths are 2.95 Å. In(1) is bonded to one Se(3), one Se(4), and two equivalent Se(5) atoms to form InSe4 trigonal pyramids that share corners with two equivalent In(1)Se4 trigonal pyramids and edges with two equivalent Er(1)Se6 octahedra. The In(1)-Se(3) bond length is 2.72 Å. The In(1)-Se(4) bond length is 2.55 Å. Both In(1)-Se(5) bond lengths are 2.64 Å. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Ba(1), two equivalent Ba(2), and one Er(1) atom to form SeBa4Er square pyramids that share corners with two equivalent Se(3)Ba3Er2In octahedra, corners with four equivalent Se(4)Ba4In square pyramids, corners with two equivalent Se(2)Ba3Er2 trigonal bipyramids, edges with three equivalent Se(3)Ba3Er2In octahedra, edges with two equivalent Se(1)Ba4Er square pyramids, edges with two equivalent Se(4)Ba4In square pyramids, and edges with three equivalent Se(2)Ba3Er2 trigonal bipyramids. The corner-sharing octahedral tilt angles are 31°. In the second Se site, Se(2) is bonded to one Ba(2), two equivalent Ba(1), and two equivalent Er(1) atoms to form distorted SeBa3Er2 trigonal bipyramids that share corners with two equivalent Se(3)Ba3Er2In octahedra, corners with two equivalent Se(1)Ba4Er square pyramids, corners with four equivalent Se(4)Ba4In square pyramids, edges with three equivalent Se(3)Ba3Er2In octahedra,  an edgeedge with one Se(4)Ba4In square pyramid, edges with three equivalent Se(1)Ba4Er square pyramids, and edges with two equivalent Se(2)Ba3Er2 trigonal bipyramids. The corner-sharing octahedral tilt angles are 10°. In the third Se site, Se(3) is bonded to one Ba(1), two equivalent Ba(2), two equivalent Er(1), and one In(1) atom to form distorted SeBa3Er2In octahedra that share corners with two equivalent Se(1)Ba4Er square pyramids, corners with four equivalent Se(4)Ba4In square pyramids, corners with two equivalent Se(2)Ba3Er2 trigonal bipyramids, edges with two equivalent Se(3)Ba3Er2In octahedra, edges with three equivalent Se(1)Ba4Er square pyramids, edges with three equivalent Se(2)Ba3Er2 trigonal bipyramids, and  a faceface with one Se(4)Ba4In square pyramid. In the fourth Se site, Se(4) is bonded to two equivalent Ba(1), two equivalent Ba(2), and one In(1) atom to form SeBa4In square pyramids that share corners with four equivalent Se(3)Ba3Er2In octahedra, corners with four equivalent Se(1)Ba4Er square pyramids, corners with four equivalent Se(2)Ba3Er2 trigonal bipyramids, edges with two equivalent Se(1)Ba4Er square pyramids, edges with two equivalent Se(4)Ba4In square pyramids,  an edgeedge with one Se(2)Ba3Er2 trigonal bipyramid, and  a faceface with one Se(3)Ba3Er2In octahedra. The corner-sharing octahedral tilt angles range from 40-67°. In the fifth Se site, Se(5) is bonded in a 5-coordinate geometry to one Ba(1), one Ba(2), one Er(1), and two equivalent In(1) atoms.