Er5Si4 crystallizes in the monoclinic P2_1/c space group. There are five inequivalent Er sites. In the first Er site, Er(1) is bonded in a 6-coordinate geometry to one Si(3), two equivalent Si(4), and three equivalent Si(1) atoms. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to one Si(3), two equivalent Si(4), and three equivalent Si(2) atoms. In the third Er site, Er(3) is bonded to one Si(4), two equivalent Si(3), and three equivalent Si(1) atoms to form a mixture of distorted corner, face, and edge-sharing ErSi6 octahedra. The corner-sharing octahedral tilt angles range from 40-44°. In the fourth Er site, Er(4) is bonded in a 7-coordinate geometry to one Si(4), two equivalent Si(3), and four equivalent Si(2) atoms. In the fifth Er site, Er(5) is bonded to one Si(1), one Si(2), two equivalent Si(3), and two equivalent Si(4) atoms to form a mixture of distorted corner and face-sharing ErSi6 octahedra. The corner-sharing octahedral tilt angles range from 42-55°. There are four inequivalent Si sites. In the first Si site, Si(4) is bonded in a 9-coordinate geometry to one Er(3), one Er(4), two equivalent Er(1), two equivalent Er(2), two equivalent Er(5), and one Si(3) atom. In the second Si site, Si(1) is bonded in a 8-coordinate geometry to one Er(5), three equivalent Er(1), three equivalent Er(3), and one Si(1) atom. In the third Si site, Si(2) is bonded in a 8-coordinate geometry to one Er(5), three equivalent Er(2), and four equivalent Er(4) atoms. In the fourth Si site, Si(3) is bonded in a 9-coordinate geometry to one Er(1), one Er(2), two equivalent Er(3), two equivalent Er(4), two equivalent Er(5), and one Si(4) atom.
Er5Si4 crystallizes in the monoclinic P2_1/c space group. There are five inequivalent Er sites. In the first Er site, Er(1) is bonded in a 6-coordinate geometry to one Si(3), two equivalent Si(4), and three equivalent Si(1) atoms. The Er(1)-Si(3) bond length is 2.99 Å. There is one shorter (2.87 Å) and one longer (2.90 Å) Er(1)-Si(4) bond length. There are a spread of Er(1)-Si(1) bond distances ranging from 2.82-2.94 Å. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to one Si(3), two equivalent Si(4), and three equivalent Si(2) atoms. The Er(2)-Si(3) bond length is 2.97 Å. There is one shorter (2.93 Å) and one longer (2.98 Å) Er(2)-Si(4) bond length. There are a spread of Er(2)-Si(2) bond distances ranging from 2.81-2.93 Å. In the third Er site, Er(3) is bonded to one Si(4), two equivalent Si(3), and three equivalent Si(1) atoms to form a mixture of distorted corner, face, and edge-sharing ErSi6 octahedra. The corner-sharing octahedral tilt angles range from 40-44°. The Er(3)-Si(4) bond length is 3.09 Å. There is one shorter (2.97 Å) and one longer (3.07 Å) Er(3)-Si(3) bond length. There are a spread of Er(3)-Si(1) bond distances ranging from 3.01-3.11 Å. In the fourth Er site, Er(4) is bonded in a 7-coordinate geometry to one Si(4), two equivalent Si(3), and four equivalent Si(2) atoms. The Er(4)-Si(4) bond length is 3.14 Å. There is one shorter (3.01 Å) and one longer (3.17 Å) Er(4)-Si(3) bond length. There are a spread of Er(4)-Si(2) bond distances ranging from 2.93-3.40 Å. In the fifth Er site, Er(5) is bonded to one Si(1), one Si(2), two equivalent Si(3), and two equivalent Si(4) atoms to form a mixture of distorted corner and face-sharing ErSi6 octahedra. The corner-sharing octahedral tilt angles range from 42-55°. The Er(5)-Si(1) bond length is 3.08 Å. The Er(5)-Si(2) bond length is 2.97 Å. There is one shorter (2.90 Å) and one longer (3.01 Å) Er(5)-Si(3) bond length. There is one shorter (2.89 Å) and one longer (3.17 Å) Er(5)-Si(4) bond length. There are four inequivalent Si sites. In the first Si site, Si(4) is bonded in a 9-coordinate geometry to one Er(3), one Er(4), two equivalent Er(1), two equivalent Er(2), two equivalent Er(5), and one Si(3) atom. The Si(4)-Si(3) bond length is 2.56 Å. In the second Si site, Si(1) is bonded in a 8-coordinate geometry to one Er(5), three equivalent Er(1), three equivalent Er(3), and one Si(1) atom. The Si(1)-Si(1) bond length is 2.46 Å. In the third Si site, Si(2) is bonded in a 8-coordinate geometry to one Er(5), three equivalent Er(2), and four equivalent Er(4) atoms. In the fourth Si site, Si(3) is bonded in a 9-coordinate geometry to one Er(1), one Er(2), two equivalent Er(3), two equivalent Er(4), two equivalent Er(5), and one Si(4) atom.