BaErAl3SiN4O3 crystallizes in the hexagonal P6_3mc space group. Ba(1) is bonded to six equivalent N(2) and six equivalent O(1) atoms to form BaN6O6 cuboctahedra that share corners with twelve equivalent Ba(1)N6O6 cuboctahedra, edges with three equivalent Si(1)N4 tetrahedra, edges with nine equivalent Al(1)N2O2 tetrahedra, and faces with four equivalent Er(1)N3O3 octahedra. Er(1) is bonded to three equivalent N(2) and three equivalent O(1) atoms to form ErN3O3 octahedra that share corners with three equivalent Si(1)N4 tetrahedra, corners with nine equivalent Al(1)N2O2 tetrahedra, and faces with four equivalent Ba(1)N6O6 cuboctahedra. Al(1) is bonded to one N(1), one N(2), and two equivalent O(1) atoms to form AlN2O2 tetrahedra that share corners with three equivalent Er(1)N3O3 octahedra, corners with two equivalent Si(1)N4 tetrahedra, corners with four equivalent Al(1)N2O2 tetrahedra, and edges with three equivalent Ba(1)N6O6 cuboctahedra. The corner-sharing octahedral tilt angles range from 58-61°. Si(1) is bonded to one N(1) and three equivalent N(2) atoms to form SiN4 tetrahedra that share corners with three equivalent Er(1)N3O3 octahedra, corners with six equivalent Al(1)N2O2 tetrahedra, and edges with three equivalent Ba(1)N6O6 cuboctahedra. The corner-sharing octahedral tilt angles are 52°. There are two inequivalent N sites. In the first N site, N(1) is bonded in a tetrahedral geometry to three equivalent Al(1) and one Si(1) atom. In the second N site, N(2) is bonded in a distorted trigonal planar geometry to two equivalent Ba(1), one Er(1), one Al(1), and one Si(1) atom. O(1) is bonded in a 3-coordinate geometry to two equivalent Ba(1), one Er(1), and two equivalent Al(1) atoms.
BaErAl3SiN4O3 crystallizes in the hexagonal P6_3mc space group. Ba(1) is bonded to six equivalent N(2) and six equivalent O(1) atoms to form BaN6O6 cuboctahedra that share corners with twelve equivalent Ba(1)N6O6 cuboctahedra, edges with three equivalent Si(1)N4 tetrahedra, edges with nine equivalent Al(1)N2O2 tetrahedra, and faces with four equivalent Er(1)N3O3 octahedra. All Ba(1)-N(2) bond lengths are 3.07 Å. There are three shorter (3.08 Å) and three longer (3.12 Å) Ba(1)-O(1) bond lengths. Er(1) is bonded to three equivalent N(2) and three equivalent O(1) atoms to form ErN3O3 octahedra that share corners with three equivalent Si(1)N4 tetrahedra, corners with nine equivalent Al(1)N2O2 tetrahedra, and faces with four equivalent Ba(1)N6O6 cuboctahedra. All Er(1)-N(2) bond lengths are 2.26 Å. All Er(1)-O(1) bond lengths are 2.39 Å. Al(1) is bonded to one N(1), one N(2), and two equivalent O(1) atoms to form AlN2O2 tetrahedra that share corners with three equivalent Er(1)N3O3 octahedra, corners with two equivalent Si(1)N4 tetrahedra, corners with four equivalent Al(1)N2O2 tetrahedra, and edges with three equivalent Ba(1)N6O6 cuboctahedra. The corner-sharing octahedral tilt angles range from 58-61°. The Al(1)-N(1) bond length is 1.94 Å. The Al(1)-N(2) bond length is 1.84 Å. Both Al(1)-O(1) bond lengths are 1.81 Å. Si(1) is bonded to one N(1) and three equivalent N(2) atoms to form SiN4 tetrahedra that share corners with three equivalent Er(1)N3O3 octahedra, corners with six equivalent Al(1)N2O2 tetrahedra, and edges with three equivalent Ba(1)N6O6 cuboctahedra. The corner-sharing octahedral tilt angles are 52°. The Si(1)-N(1) bond length is 1.84 Å. All Si(1)-N(2) bond lengths are 1.74 Å. There are two inequivalent N sites. In the first N site, N(1) is bonded in a tetrahedral geometry to three equivalent Al(1) and one Si(1) atom. In the second N site, N(2) is bonded in a distorted trigonal planar geometry to two equivalent Ba(1), one Er(1), one Al(1), and one Si(1) atom. O(1) is bonded in a 3-coordinate geometry to two equivalent Ba(1), one Er(1), and two equivalent Al(1) atoms.