Tm2BaNiO5 crystallizes in the orthorhombic Immm space group. Ba(1) is bonded in a distorted q6 geometry to two equivalent O(1) and eight equivalent O(2) atoms. Tm(1) is bonded in a 7-coordinate geometry to one O(1) and six equivalent O(2) atoms. Ni(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form corner-sharing NiO6 octahedra. The corner-sharing octahedra are not tilted. There are two inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ba(1), two equivalent Tm(1), and two equivalent Ni(1) atoms to form distorted OBa2Tm2Ni2 octahedra that share corners with four equivalent O(1)Ba2Tm2Ni2 octahedra, corners with twelve equivalent O(2)Ba2Tm3Ni octahedra, and faces with eight equivalent O(2)Ba2Tm3Ni octahedra. The corner-sharing octahedral tilt angles range from 0-60°. In the second O site, O(2) is bonded to two equivalent Ba(1), three equivalent Tm(1), and one Ni(1) atom to form distorted OBa2Tm3Ni octahedra that share corners with three equivalent O(1)Ba2Tm2Ni2 octahedra, corners with thirteen equivalent O(2)Ba2Tm3Ni octahedra, edges with five equivalent O(2)Ba2Tm3Ni octahedra, faces with two equivalent O(1)Ba2Tm2Ni2 octahedra, and faces with three equivalent O(2)Ba2Tm3Ni octahedra. The corner-sharing octahedral tilt angles range from 0-71°.
Tm2BaNiO5 crystallizes in the orthorhombic Immm space group. Ba(1) is bonded in a distorted q6 geometry to two equivalent O(1) and eight equivalent O(2) atoms. Both Ba(1)-O(1) bond lengths are 2.87 Å. All Ba(1)-O(2) bond lengths are 2.95 Å. Tm(1) is bonded in a 7-coordinate geometry to one O(1) and six equivalent O(2) atoms. The Tm(1)-O(1) bond length is 2.30 Å. There are two shorter (2.21 Å) and four longer (2.40 Å) Tm(1)-O(2) bond lengths. Ni(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form corner-sharing NiO6 octahedra. The corner-sharing octahedra are not tilted. Both Ni(1)-O(1) bond lengths are 1.89 Å. All Ni(1)-O(2) bond lengths are 2.20 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ba(1), two equivalent Tm(1), and two equivalent Ni(1) atoms to form distorted OBa2Tm2Ni2 octahedra that share corners with four equivalent O(1)Ba2Tm2Ni2 octahedra, corners with twelve equivalent O(2)Ba2Tm3Ni octahedra, and faces with eight equivalent O(2)Ba2Tm3Ni octahedra. The corner-sharing octahedral tilt angles range from 0-60°. In the second O site, O(2) is bonded to two equivalent Ba(1), three equivalent Tm(1), and one Ni(1) atom to form distorted OBa2Tm3Ni octahedra that share corners with three equivalent O(1)Ba2Tm2Ni2 octahedra, corners with thirteen equivalent O(2)Ba2Tm3Ni octahedra, edges with five equivalent O(2)Ba2Tm3Ni octahedra, faces with two equivalent O(1)Ba2Tm2Ni2 octahedra, and faces with three equivalent O(2)Ba2Tm3Ni octahedra. The corner-sharing octahedral tilt angles range from 0-71°.