ErAlB4 crystallizes in the orthorhombic Pbam space group. Er(1) is bonded in a 14-coordinate geometry to two equivalent B(1), four equivalent B(2), four equivalent B(3), and four equivalent B(4) atoms. Al(1) is bonded in a 10-coordinate geometry to two equivalent B(2), two equivalent B(3), two equivalent B(4), and four equivalent B(1) atoms. There are four inequivalent B sites. In the first B site, B(1) is bonded in a 9-coordinate geometry to two equivalent Er(1), four equivalent Al(1), one B(1), one B(2), and one B(3) atom. In the second B site, B(2) is bonded in a 9-coordinate geometry to four equivalent Er(1), two equivalent Al(1), one B(1), one B(2), and one B(4) atom. In the third B site, B(3) is bonded in a 9-coordinate geometry to four equivalent Er(1), two equivalent Al(1), one B(1), and two equivalent B(4) atoms. In the fourth B site, B(4) is bonded in a 9-coordinate geometry to four equivalent Er(1), two equivalent Al(1), one B(2), and two equivalent B(3) atoms.
ErAlB4 crystallizes in the orthorhombic Pbam space group. Er(1) is bonded in a 14-coordinate geometry to two equivalent B(1), four equivalent B(2), four equivalent B(3), and four equivalent B(4) atoms. Both Er(1)-B(1) bond lengths are 2.61 Å. All Er(1)-B(2) bond lengths are 2.72 Å. There are two shorter (2.69 Å) and two longer (2.74 Å) Er(1)-B(3) bond lengths. There are two shorter (2.71 Å) and two longer (2.74 Å) Er(1)-B(4) bond lengths. Al(1) is bonded in a 10-coordinate geometry to two equivalent B(2), two equivalent B(3), two equivalent B(4), and four equivalent B(1) atoms. Both Al(1)-B(2) bond lengths are 2.33 Å. Both Al(1)-B(3) bond lengths are 2.33 Å. Both Al(1)-B(4) bond lengths are 2.27 Å. There are two shorter (2.36 Å) and two longer (2.37 Å) Al(1)-B(1) bond lengths. There are four inequivalent B sites. In the first B site, B(1) is bonded in a 9-coordinate geometry to two equivalent Er(1), four equivalent Al(1), one B(1), one B(2), and one B(3) atom. The B(1)-B(1) bond length is 1.73 Å. The B(1)-B(2) bond length is 1.74 Å. The B(1)-B(3) bond length is 1.75 Å. In the second B site, B(2) is bonded in a 9-coordinate geometry to four equivalent Er(1), two equivalent Al(1), one B(1), one B(2), and one B(4) atom. The B(2)-B(2) bond length is 1.73 Å. The B(2)-B(4) bond length is 1.86 Å. In the third B site, B(3) is bonded in a 9-coordinate geometry to four equivalent Er(1), two equivalent Al(1), one B(1), and two equivalent B(4) atoms. There is one shorter (1.75 Å) and one longer (1.87 Å) B(3)-B(4) bond length. In the fourth B site, B(4) is bonded in a 9-coordinate geometry to four equivalent Er(1), two equivalent Al(1), one B(2), and two equivalent B(3) atoms.