ErRh4B4 crystallizes in the orthorhombic Ccce space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 24-coordinate geometry to two equivalent Rh(3), four equivalent Rh(2), six equivalent Rh(1), two equivalent B(3), four equivalent B(1), and six equivalent B(2) atoms. In the second Er site, Er(2) is bonded in a 24-coordinate geometry to four equivalent Rh(2), eight equivalent Rh(3), four equivalent B(1), and eight equivalent B(3) atoms. There are three inequivalent Rh sites. In the first Rh site, Rh(2) is bonded in a 6-coordinate geometry to one Er(2), two equivalent Er(1), one B(2), one B(3), and three equivalent B(1) atoms. In the second Rh site, Rh(3) is bonded in a 5-coordinate geometry to one Er(1), two equivalent Er(2), one B(1), and four equivalent B(3) atoms. In the third Rh site, Rh(1) is bonded in a 5-coordinate geometry to three equivalent Er(1), one B(1), and four equivalent B(2) atoms. There are three inequivalent B sites. In the first B site, B(1) is bonded in a 6-coordinate geometry to one Er(2), two equivalent Er(1), one Rh(1), one Rh(3), three equivalent Rh(2), and one B(3) atom. In the second B site, B(2) is bonded in a 6-coordinate geometry to three equivalent Er(1), one Rh(2), four equivalent Rh(1), and one B(2) atom. In the third B site, B(3) is bonded in a 6-coordinate geometry to one Er(1), two equivalent Er(2), one Rh(2), four equivalent Rh(3), and one B(1) atom.
ErRh4B4 crystallizes in the orthorhombic Ccce space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 24-coordinate geometry to two equivalent Rh(3), four equivalent Rh(2), six equivalent Rh(1), two equivalent B(3), four equivalent B(1), and six equivalent B(2) atoms. Both Er(1)-Rh(3) bond lengths are 3.17 Å. There are two shorter (2.90 Å) and two longer (3.27 Å) Er(1)-Rh(2) bond lengths. There are a spread of Er(1)-Rh(1) bond distances ranging from 2.91-3.26 Å. Both Er(1)-B(3) bond lengths are 2.99 Å. There are two shorter (2.95 Å) and two longer (3.30 Å) Er(1)-B(1) bond lengths. There are a spread of Er(1)-B(2) bond distances ranging from 2.96-3.23 Å. In the second Er site, Er(2) is bonded in a 24-coordinate geometry to four equivalent Rh(2), eight equivalent Rh(3), four equivalent B(1), and eight equivalent B(3) atoms. All Er(2)-Rh(2) bond lengths are 3.15 Å. There are four shorter (2.95 Å) and four longer (3.17 Å) Er(2)-Rh(3) bond lengths. All Er(2)-B(1) bond lengths are 2.97 Å. There are four shorter (3.02 Å) and four longer (3.20 Å) Er(2)-B(3) bond lengths. There are three inequivalent Rh sites. In the first Rh site, Rh(2) is bonded in a 6-coordinate geometry to one Er(2), two equivalent Er(1), one B(2), one B(3), and three equivalent B(1) atoms. The Rh(2)-B(2) bond length is 2.17 Å. The Rh(2)-B(3) bond length is 2.23 Å. There are a spread of Rh(2)-B(1) bond distances ranging from 2.18-2.29 Å. In the second Rh site, Rh(3) is bonded in a 5-coordinate geometry to one Er(1), two equivalent Er(2), one B(1), and four equivalent B(3) atoms. The Rh(3)-B(1) bond length is 2.25 Å. There are a spread of Rh(3)-B(3) bond distances ranging from 2.18-2.25 Å. In the third Rh site, Rh(1) is bonded in a 5-coordinate geometry to three equivalent Er(1), one B(1), and four equivalent B(2) atoms. The Rh(1)-B(1) bond length is 2.22 Å. There are a spread of Rh(1)-B(2) bond distances ranging from 2.17-2.27 Å. There are three inequivalent B sites. In the first B site, B(1) is bonded in a 6-coordinate geometry to one Er(2), two equivalent Er(1), one Rh(1), one Rh(3), three equivalent Rh(2), and one B(3) atom. The B(1)-B(3) bond length is 1.76 Å. In the second B site, B(2) is bonded in a 6-coordinate geometry to three equivalent Er(1), one Rh(2), four equivalent Rh(1), and one B(2) atom. The B(2)-B(2) bond length is 1.77 Å. In the third B site, B(3) is bonded in a 6-coordinate geometry to one Er(1), two equivalent Er(2), one Rh(2), four equivalent Rh(3), and one B(1) atom.