Ba3NdIr2O9 crystallizes in the monoclinic C2/c space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded to two equivalent O(1), two equivalent O(2), two equivalent O(3), two equivalent O(4), and four equivalent O(5) atoms to form distorted BaO12 cuboctahedra that share corners with six equivalent Ba(1)O12 cuboctahedra, faces with two equivalent Nd(1)O6 octahedra, and faces with six equivalent Ir(1)O6 octahedra. In the second Ba site, Ba(2) is bonded in a 12-coordinate geometry to one O(3), two equivalent O(5), three equivalent O(1), three equivalent O(2), and three equivalent O(4) atoms. Nd(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form NdO6 octahedra that share corners with six equivalent Ir(1)O6 octahedra and faces with two equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 7-11°. Ir(1) is bonded to one O(1), one O(2), one O(3), one O(4), and two equivalent O(5) atoms to form IrO6 octahedra that share corners with three equivalent Nd(1)O6 octahedra, faces with three equivalent Ba(1)O12 cuboctahedra, and  a faceface with one Ir(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 7-11°. There are five inequivalent O sites. In the first O site, O(3) is bonded to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Ir(1) atoms to form a mixture of distorted face and corner-sharing OBa4Ir2 octahedra. The corner-sharing octahedral tilt angles range from 5-60°. In the second O site, O(4) is bonded in a 2-coordinate geometry to one Ba(1), three equivalent Ba(2), one Nd(1), and one Ir(1) atom. In the third O site, O(5) is bonded to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Ir(1) atoms to form a mixture of distorted face and corner-sharing OBa4Ir2 octahedra. The corner-sharing octahedral tilt angles range from 6-60°. In the fourth O site, O(1) is bonded in a 2-coordinate geometry to one Ba(1), three equivalent Ba(2), one Nd(1), and one Ir(1) atom. In the fifth O site, O(2) is bonded in a 2-coordinate geometry to one Ba(1), three equivalent Ba(2), one Nd(1), and one Ir(1) atom.
Ba3NdIr2O9 crystallizes in the monoclinic C2/c space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded to two equivalent O(1), two equivalent O(2), two equivalent O(3), two equivalent O(4), and four equivalent O(5) atoms to form distorted BaO12 cuboctahedra that share corners with six equivalent Ba(1)O12 cuboctahedra, faces with two equivalent Nd(1)O6 octahedra, and faces with six equivalent Ir(1)O6 octahedra. Both Ba(1)-O(1) bond lengths are 2.98 Å. Both Ba(1)-O(2) bond lengths are 2.82 Å. Both Ba(1)-O(3) bond lengths are 3.00 Å. Both Ba(1)-O(4) bond lengths are 3.33 Å. There are two shorter (2.98 Å) and two longer (3.02 Å) Ba(1)-O(5) bond lengths. In the second Ba site, Ba(2) is bonded in a 12-coordinate geometry to one O(3), two equivalent O(5), three equivalent O(1), three equivalent O(2), and three equivalent O(4) atoms. The Ba(2)-O(3) bond length is 2.90 Å. There is one shorter (2.76 Å) and one longer (3.09 Å) Ba(2)-O(5) bond length. There are a spread of Ba(2)-O(1) bond distances ranging from 2.87-3.33 Å. There are a spread of Ba(2)-O(2) bond distances ranging from 2.93-3.45 Å. There are a spread of Ba(2)-O(4) bond distances ranging from 2.96-3.08 Å. Nd(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form NdO6 octahedra that share corners with six equivalent Ir(1)O6 octahedra and faces with two equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 7-11°. Both Nd(1)-O(1) bond lengths are 2.30 Å. Both Nd(1)-O(2) bond lengths are 2.30 Å. Both Nd(1)-O(4) bond lengths are 2.32 Å. Ir(1) is bonded to one O(1), one O(2), one O(3), one O(4), and two equivalent O(5) atoms to form IrO6 octahedra that share corners with three equivalent Nd(1)O6 octahedra, faces with three equivalent Ba(1)O12 cuboctahedra, and  a faceface with one Ir(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 7-11°. The Ir(1)-O(1) bond length is 1.98 Å. The Ir(1)-O(2) bond length is 1.98 Å. The Ir(1)-O(3) bond length is 2.07 Å. The Ir(1)-O(4) bond length is 1.98 Å. There is one shorter (2.06 Å) and one longer (2.07 Å) Ir(1)-O(5) bond length. There are five inequivalent O sites. In the first O site, O(3) is bonded to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Ir(1) atoms to form a mixture of distorted face and corner-sharing OBa4Ir2 octahedra. The corner-sharing octahedral tilt angles range from 5-60°. In the second O site, O(4) is bonded in a 2-coordinate geometry to one Ba(1), three equivalent Ba(2), one Nd(1), and one Ir(1) atom. In the third O site, O(5) is bonded to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Ir(1) atoms to form a mixture of distorted face and corner-sharing OBa4Ir2 octahedra. The corner-sharing octahedral tilt angles range from 6-60°. In the fourth O site, O(1) is bonded in a 2-coordinate geometry to one Ba(1), three equivalent Ba(2), one Nd(1), and one Ir(1) atom. In the fifth O site, O(2) is bonded in a 2-coordinate geometry to one Ba(1), three equivalent Ba(2), one Nd(1), and one Ir(1) atom.