Ba2CaEr3(NiO5)2 crystallizes in the monoclinic C2 space group. Ba(1) is bonded in a distorted q6 geometry to one O(5), one O(6), two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. Ca(1) is bonded in a 7-coordinate geometry to one O(5), two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded in a 7-coordinate geometry to one O(6), two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to one O(5), two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms. In the third Er site, Er(3) is bonded in a 7-coordinate geometry to one O(6), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. Ni(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form corner-sharing NiO6 octahedra. The corner-sharing octahedral tilt angles range from 2-4°. There are six inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ba(1), one Ca(1), one Er(1), one Er(2), and one Ni(1) atom to form distorted OBa2CaEr2Ni octahedra that share  a cornercorner with one O(6)Ba2Er2Ni2 octahedra, corners with two equivalent O(1)Ba2CaEr2Ni octahedra, corners with two equivalent O(2)Ba2CaEr2Ni octahedra, corners with two equivalent O(3)Ba2CaEr2Ni octahedra, corners with two equivalent O(5)Ba2CaErNi2 octahedra, corners with seven equivalent O(4)Ba2Er3Ni octahedra,  an edgeedge with one O(4)Ba2Er3Ni octahedra, edges with two equivalent O(2)Ba2CaEr2Ni octahedra, edges with two equivalent O(3)Ba2CaEr2Ni octahedra,  a faceface with one O(1)Ba2CaEr2Ni octahedra,  a faceface with one O(2)Ba2CaEr2Ni octahedra,  a faceface with one O(3)Ba2CaEr2Ni octahedra,  a faceface with one O(5)Ba2CaErNi2 octahedra, and  a faceface with one O(6)Ba2Er2Ni2 octahedra. The corner-sharing octahedral tilt angles range from 2-69°. In the second O site, O(2) is bonded to two equivalent Ba(1), one Ca(1), one Er(1), one Er(3), and one Ni(1) atom to form distorted OBa2CaEr2Ni octahedra that share  a cornercorner with one O(5)Ba2CaErNi2 octahedra, corners with two equivalent O(1)Ba2CaEr2Ni octahedra, corners with two equivalent O(2)Ba2CaEr2Ni octahedra, corners with two equivalent O(6)Ba2Er2Ni2 octahedra, corners with two equivalent O(4)Ba2Er3Ni octahedra, corners with seven equivalent O(3)Ba2CaEr2Ni octahedra,  an edgeedge with one O(3)Ba2CaEr2Ni octahedra, edges with two equivalent O(1)Ba2CaEr2Ni octahedra, edges with two equivalent O(4)Ba2Er3Ni octahedra,  a faceface with one O(1)Ba2CaEr2Ni octahedra,  a faceface with one O(2)Ba2CaEr2Ni octahedra,  a faceface with one O(5)Ba2CaErNi2 octahedra,  a faceface with one O(6)Ba2Er2Ni2 octahedra, and  a faceface with one O(4)Ba2Er3Ni octahedra. The corner-sharing octahedral tilt angles range from 2-69°. In the third O site, O(3) is bonded to two equivalent Ba(1), one Ca(1), one Er(2), one Er(3), and one Ni(1) atom to form distorted OBa2CaEr2Ni octahedra that share  a cornercorner with one O(6)Ba2Er2Ni2 octahedra, corners with two equivalent O(1)Ba2CaEr2Ni octahedra, corners with two equivalent O(3)Ba2CaEr2Ni octahedra, corners with two equivalent O(5)Ba2CaErNi2 octahedra, corners with two equivalent O(4)Ba2Er3Ni octahedra, corners with seven equivalent O(2)Ba2CaEr2Ni octahedra,  an edgeedge with one O(2)Ba2CaEr2Ni octahedra, edges with two equivalent O(1)Ba2CaEr2Ni octahedra, edges with two equivalent O(4)Ba2Er3Ni octahedra,  a faceface with one O(1)Ba2CaEr2Ni octahedra,  a faceface with one O(3)Ba2CaEr2Ni octahedra,  a faceface with one O(5)Ba2CaErNi2 octahedra,  a faceface with one O(6)Ba2Er2Ni2 octahedra, and  a faceface with one O(4)Ba2Er3Ni octahedra. The corner-sharing octahedral tilt angles range from 2-68°. In the fourth O site, O(4) is bonded to two equivalent Ba(1), one Er(1), one Er(2), one Er(3), and one Ni(1) atom to form distorted OBa2Er3Ni octahedra that share  a cornercorner with one O(5)Ba2CaErNi2 octahedra, corners with two equivalent O(2)Ba2CaEr2Ni octahedra, corners with two equivalent O(3)Ba2CaEr2Ni octahedra, corners with two equivalent O(6)Ba2Er2Ni2 octahedra, corners with two equivalent O(4)Ba2Er3Ni octahedra, corners with seven equivalent O(1)Ba2CaEr2Ni octahedra,  an edgeedge with one O(1)Ba2CaEr2Ni octahedra, edges with two equivalent O(2)Ba2CaEr2Ni octahedra, edges with two equivalent O(3)Ba2CaEr2Ni octahedra,  a faceface with one O(2)Ba2CaEr2Ni octahedra,  a faceface with one O(3)Ba2CaEr2Ni octahedra,  a faceface with one O(5)Ba2CaErNi2 octahedra,  a faceface with one O(6)Ba2Er2Ni2 octahedra, and  a faceface with one O(4)Ba2Er3Ni octahedra. The corner-sharing octahedral tilt angles range from 2-68°. In the fifth O site, O(5) is bonded to two equivalent Ba(1), one Ca(1), one Er(2), and two equivalent Ni(1) atoms to form distorted OBa2CaErNi2 octahedra that share corners with two equivalent O(2)Ba2CaEr2Ni octahedra, corners with two equivalent O(4)Ba2Er3Ni octahedra, corners with four equivalent O(1)Ba2CaEr2Ni octahedra, corners with four equivalent O(3)Ba2CaEr2Ni octahedra, corners with four equivalent O(6)Ba2Er2Ni2 octahedra, faces with two equivalent O(1)Ba2CaEr2Ni octahedra, faces with two equivalent O(2)Ba2CaEr2Ni octahedra, faces with two equivalent O(3)Ba2CaEr2Ni octahedra, and faces with two equivalent O(4)Ba2Er3Ni octahedra. The corner-sharing octahedral tilt angles range from 1-59°. In the sixth O site, O(6) is bonded to two equivalent Ba(1), one Er(1), one Er(3), and two equivalent Ni(1) atoms to form distorted OBa2Er2Ni2 octahedra that share corners with two equivalent O(1)Ba2CaEr2Ni octahedra, corners with two equivalent O(3)Ba2CaEr2Ni octahedra, corners with four equivalent O(2)Ba2CaEr2Ni octahedra, corners with four equivalent O(5)Ba2CaErNi2 octahedra, corners with four equivalent O(4)Ba2Er3Ni octahedra, faces with two equivalent O(1)Ba2CaEr2Ni octahedra, faces with two equivalent O(2)Ba2CaEr2Ni octahedra, faces with two equivalent O(3)Ba2CaEr2Ni octahedra, and faces with two equivalent O(4)Ba2Er3Ni octahedra. The corner-sharing octahedral tilt angles range from 1-60°.
Ba2CaEr3(NiO5)2 crystallizes in the monoclinic C2 space group. Ba(1) is bonded in a distorted q6 geometry to one O(5), one O(6), two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. The Ba(1)-O(5) bond length is 2.88 Å. The Ba(1)-O(6) bond length is 2.92 Å. There is one shorter (2.87 Å) and one longer (2.95 Å) Ba(1)-O(1) bond length. There is one shorter (2.88 Å) and one longer (2.95 Å) Ba(1)-O(2) bond length. There is one shorter (2.93 Å) and one longer (2.94 Å) Ba(1)-O(3) bond length. There is one shorter (2.93 Å) and one longer (2.94 Å) Ba(1)-O(4) bond length. Ca(1) is bonded in a 7-coordinate geometry to one O(5), two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. The Ca(1)-O(5) bond length is 2.37 Å. Both Ca(1)-O(1) bond lengths are 2.49 Å. Both Ca(1)-O(2) bond lengths are 2.49 Å. Both Ca(1)-O(3) bond lengths are 2.32 Å. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded in a 7-coordinate geometry to one O(6), two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms. The Er(1)-O(6) bond length is 2.32 Å. Both Er(1)-O(1) bond lengths are 2.37 Å. Both Er(1)-O(2) bond lengths are 2.38 Å. Both Er(1)-O(4) bond lengths are 2.24 Å. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to one O(5), two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms. The Er(2)-O(5) bond length is 2.29 Å. Both Er(2)-O(1) bond lengths are 2.23 Å. Both Er(2)-O(3) bond lengths are 2.40 Å. Both Er(2)-O(4) bond lengths are 2.43 Å. In the third Er site, Er(3) is bonded in a 7-coordinate geometry to one O(6), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. The Er(3)-O(6) bond length is 2.31 Å. Both Er(3)-O(2) bond lengths are 2.25 Å. Both Er(3)-O(3) bond lengths are 2.39 Å. Both Er(3)-O(4) bond lengths are 2.42 Å. Ni(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form corner-sharing NiO6 octahedra. The corner-sharing octahedral tilt angles range from 2-4°. The Ni(1)-O(1) bond length is 2.15 Å. The Ni(1)-O(2) bond length is 2.15 Å. The Ni(1)-O(3) bond length is 2.09 Å. The Ni(1)-O(4) bond length is 2.20 Å. The Ni(1)-O(5) bond length is 1.87 Å. The Ni(1)-O(6) bond length is 1.87 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ba(1), one Ca(1), one Er(1), one Er(2), and one Ni(1) atom to form distorted OBa2CaEr2Ni octahedra that share  a cornercorner with one O(6)Ba2Er2Ni2 octahedra, corners with two equivalent O(1)Ba2CaEr2Ni octahedra, corners with two equivalent O(2)Ba2CaEr2Ni octahedra, corners with two equivalent O(3)Ba2CaEr2Ni octahedra, corners with two equivalent O(5)Ba2CaErNi2 octahedra, corners with seven equivalent O(4)Ba2Er3Ni octahedra,  an edgeedge with one O(4)Ba2Er3Ni octahedra, edges with two equivalent O(2)Ba2CaEr2Ni octahedra, edges with two equivalent O(3)Ba2CaEr2Ni octahedra,  a faceface with one O(1)Ba2CaEr2Ni octahedra,  a faceface with one O(2)Ba2CaEr2Ni octahedra,  a faceface with one O(3)Ba2CaEr2Ni octahedra,  a faceface with one O(5)Ba2CaErNi2 octahedra, and  a faceface with one O(6)Ba2Er2Ni2 octahedra. The corner-sharing octahedral tilt angles range from 2-69°. In the second O site, O(2) is bonded to two equivalent Ba(1), one Ca(1), one Er(1), one Er(3), and one Ni(1) atom to form distorted OBa2CaEr2Ni octahedra that share  a cornercorner with one O(5)Ba2CaErNi2 octahedra, corners with two equivalent O(1)Ba2CaEr2Ni octahedra, corners with two equivalent O(2)Ba2CaEr2Ni octahedra, corners with two equivalent O(6)Ba2Er2Ni2 octahedra, corners with two equivalent O(4)Ba2Er3Ni octahedra, corners with seven equivalent O(3)Ba2CaEr2Ni octahedra,  an edgeedge with one O(3)Ba2CaEr2Ni octahedra, edges with two equivalent O(1)Ba2CaEr2Ni octahedra, edges with two equivalent O(4)Ba2Er3Ni octahedra,  a faceface with one O(1)Ba2CaEr2Ni octahedra,  a faceface with one O(2)Ba2CaEr2Ni octahedra,  a faceface with one O(5)Ba2CaErNi2 octahedra,  a faceface with one O(6)Ba2Er2Ni2 octahedra, and  a faceface with one O(4)Ba2Er3Ni octahedra. The corner-sharing octahedral tilt angles range from 2-69°. In the third O site, O(3) is bonded to two equivalent Ba(1), one Ca(1), one Er(2), one Er(3), and one Ni(1) atom to form distorted OBa2CaEr2Ni octahedra that share  a cornercorner with one O(6)Ba2Er2Ni2 octahedra, corners with two equivalent O(1)Ba2CaEr2Ni octahedra, corners with two equivalent O(3)Ba2CaEr2Ni octahedra, corners with two equivalent O(5)Ba2CaErNi2 octahedra, corners with two equivalent O(4)Ba2Er3Ni octahedra, corners with seven equivalent O(2)Ba2CaEr2Ni octahedra,  an edgeedge with one O(2)Ba2CaEr2Ni octahedra, edges with two equivalent O(1)Ba2CaEr2Ni octahedra, edges with two equivalent O(4)Ba2Er3Ni octahedra,  a faceface with one O(1)Ba2CaEr2Ni octahedra,  a faceface with one O(3)Ba2CaEr2Ni octahedra,  a faceface with one O(5)Ba2CaErNi2 octahedra,  a faceface with one O(6)Ba2Er2Ni2 octahedra, and  a faceface with one O(4)Ba2Er3Ni octahedra. The corner-sharing octahedral tilt angles range from 2-68°. In the fourth O site, O(4) is bonded to two equivalent Ba(1), one Er(1), one Er(2), one Er(3), and one Ni(1) atom to form distorted OBa2Er3Ni octahedra that share  a cornercorner with one O(5)Ba2CaErNi2 octahedra, corners with two equivalent O(2)Ba2CaEr2Ni octahedra, corners with two equivalent O(3)Ba2CaEr2Ni octahedra, corners with two equivalent O(6)Ba2Er2Ni2 octahedra, corners with two equivalent O(4)Ba2Er3Ni octahedra, corners with seven equivalent O(1)Ba2CaEr2Ni octahedra,  an edgeedge with one O(1)Ba2CaEr2Ni octahedra, edges with two equivalent O(2)Ba2CaEr2Ni octahedra, edges with two equivalent O(3)Ba2CaEr2Ni octahedra,  a faceface with one O(2)Ba2CaEr2Ni octahedra,  a faceface with one O(3)Ba2CaEr2Ni octahedra,  a faceface with one O(5)Ba2CaErNi2 octahedra,  a faceface with one O(6)Ba2Er2Ni2 octahedra, and  a faceface with one O(4)Ba2Er3Ni octahedra. The corner-sharing octahedral tilt angles range from 2-68°. In the fifth O site, O(5) is bonded to two equivalent Ba(1), one Ca(1), one Er(2), and two equivalent Ni(1) atoms to form distorted OBa2CaErNi2 octahedra that share corners with two equivalent O(2)Ba2CaEr2Ni octahedra, corners with two equivalent O(4)Ba2Er3Ni octahedra, corners with four equivalent O(1)Ba2CaEr2Ni octahedra, corners with four equivalent O(3)Ba2CaEr2Ni octahedra, corners with four equivalent O(6)Ba2Er2Ni2 octahedra, faces with two equivalent O(1)Ba2CaEr2Ni octahedra, faces with two equivalent O(2)Ba2CaEr2Ni octahedra, faces with two equivalent O(3)Ba2CaEr2Ni octahedra, and faces with two equivalent O(4)Ba2Er3Ni octahedra. The corner-sharing octahedral tilt angles range from 1-59°. In the sixth O site, O(6) is bonded to two equivalent Ba(1), one Er(1), one Er(3), and two equivalent Ni(1) atoms to form distorted OBa2Er2Ni2 octahedra that share corners with two equivalent O(1)Ba2CaEr2Ni octahedra, corners with two equivalent O(3)Ba2CaEr2Ni octahedra, corners with four equivalent O(2)Ba2CaEr2Ni octahedra, corners with four equivalent O(5)Ba2CaErNi2 octahedra, corners with four equivalent O(4)Ba2Er3Ni octahedra, faces with two equivalent O(1)Ba2CaEr2Ni octahedra, faces with two equivalent O(2)Ba2CaEr2Ni octahedra, faces with two equivalent O(3)Ba2CaEr2Ni octahedra, and faces with two equivalent O(4)Ba2Er3Ni octahedra. The corner-sharing octahedral tilt angles range from 1-60°.