BaEr2CoO5 crystallizes in the orthorhombic Pnma space group. Ba(1) is bonded in a 11-coordinate geometry to three equivalent O(1), four equivalent O(2), and four equivalent O(3) atoms. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(1), two equivalent O(2), and four equivalent O(3) atoms to form distorted ErO7 pentagonal bipyramids that share corners with five equivalent Co(1)O5 trigonal bipyramids, edges with two equivalent Er(1)O7 pentagonal bipyramids, and  an edgeedge with one Co(1)O5 trigonal bipyramid. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to one O(1), two equivalent O(3), and four equivalent O(2) atoms. Co(1) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted CoO5 trigonal bipyramids that share corners with five equivalent Er(1)O7 pentagonal bipyramids and  an edgeedge with one Er(1)O7 pentagonal bipyramid. There are three inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Ba(1), one Er(1), one Er(2), and one Co(1) atom to form distorted OBa3Er2Co octahedra that share corners with two equivalent O(1)Ba3Er2Co octahedra, corners with eight equivalent O(2)Ba2Er3Co octahedra, edges with two equivalent O(1)Ba3Er2Co octahedra, and faces with four equivalent O(2)Ba2Er3Co octahedra. The corner-sharing octahedral tilt angles range from 1-64°. In the second O site, O(2) is bonded to two equivalent Ba(1), one Er(1), two equivalent Er(2), and one Co(1) atom to form distorted OBa2Er3Co octahedra that share corners with four equivalent O(2)Ba2Er3Co octahedra, corners with four equivalent O(1)Ba3Er2Co octahedra, edges with two equivalent O(2)Ba2Er3Co octahedra, faces with two equivalent O(2)Ba2Er3Co octahedra, and faces with two equivalent O(1)Ba3Er2Co octahedra. The corner-sharing octahedral tilt angles range from 25-78°. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Er(2), two equivalent Er(1), and one Co(1) atom.
BaEr2CoO5 crystallizes in the orthorhombic Pnma space group. Ba(1) is bonded in a 11-coordinate geometry to three equivalent O(1), four equivalent O(2), and four equivalent O(3) atoms. There is one shorter (2.73 Å) and two longer (2.86 Å) Ba(1)-O(1) bond lengths. There are two shorter (2.90 Å) and two longer (3.00 Å) Ba(1)-O(2) bond lengths. There are two shorter (3.08 Å) and two longer (3.30 Å) Ba(1)-O(3) bond lengths. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(1), two equivalent O(2), and four equivalent O(3) atoms to form distorted ErO7 pentagonal bipyramids that share corners with five equivalent Co(1)O5 trigonal bipyramids, edges with two equivalent Er(1)O7 pentagonal bipyramids, and  an edgeedge with one Co(1)O5 trigonal bipyramid. The Er(1)-O(1) bond length is 2.32 Å. Both Er(1)-O(2) bond lengths are 2.36 Å. There are two shorter (2.30 Å) and two longer (2.34 Å) Er(1)-O(3) bond lengths. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to one O(1), two equivalent O(3), and four equivalent O(2) atoms. The Er(2)-O(1) bond length is 2.34 Å. Both Er(2)-O(3) bond lengths are 2.29 Å. There are two shorter (2.33 Å) and two longer (2.38 Å) Er(2)-O(2) bond lengths. Co(1) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted CoO5 trigonal bipyramids that share corners with five equivalent Er(1)O7 pentagonal bipyramids and  an edgeedge with one Er(1)O7 pentagonal bipyramid. The Co(1)-O(1) bond length is 2.01 Å. Both Co(1)-O(2) bond lengths are 2.11 Å. Both Co(1)-O(3) bond lengths are 2.04 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Ba(1), one Er(1), one Er(2), and one Co(1) atom to form distorted OBa3Er2Co octahedra that share corners with two equivalent O(1)Ba3Er2Co octahedra, corners with eight equivalent O(2)Ba2Er3Co octahedra, edges with two equivalent O(1)Ba3Er2Co octahedra, and faces with four equivalent O(2)Ba2Er3Co octahedra. The corner-sharing octahedral tilt angles range from 1-64°. In the second O site, O(2) is bonded to two equivalent Ba(1), one Er(1), two equivalent Er(2), and one Co(1) atom to form distorted OBa2Er3Co octahedra that share corners with four equivalent O(2)Ba2Er3Co octahedra, corners with four equivalent O(1)Ba3Er2Co octahedra, edges with two equivalent O(2)Ba2Er3Co octahedra, faces with two equivalent O(2)Ba2Er3Co octahedra, and faces with two equivalent O(1)Ba3Er2Co octahedra. The corner-sharing octahedral tilt angles range from 25-78°. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Er(2), two equivalent Er(1), and one Co(1) atom.