Er2SiO5 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 7-coordinate geometry to one O(4), three equivalent O(1), and three equivalent O(3) atoms. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to one O(1), two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms. Si(1) is bonded in a tetrahedral geometry to one O(2), one O(3), one O(4), and one O(5) atom. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Er(2) and three equivalent Er(1) atoms to form a mixture of corner and edge-sharing OEr4 tetrahedra. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Er(2) and one Si(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to three equivalent Er(1) and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Er(1), two equivalent Er(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Er(2) and one Si(1) atom.
Er2SiO5 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 7-coordinate geometry to one O(4), three equivalent O(1), and three equivalent O(3) atoms. The Er(1)-O(4) bond length is 2.29 Å. There are a spread of Er(1)-O(1) bond distances ranging from 2.18-2.25 Å. There are a spread of Er(1)-O(3) bond distances ranging from 2.31-2.56 Å. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to one O(1), two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms. The Er(2)-O(1) bond length is 2.22 Å. There is one shorter (2.29 Å) and one longer (2.36 Å) Er(2)-O(2) bond length. There is one shorter (2.21 Å) and one longer (2.42 Å) Er(2)-O(4) bond length. There is one shorter (2.23 Å) and one longer (2.31 Å) Er(2)-O(5) bond length. Si(1) is bonded in a tetrahedral geometry to one O(2), one O(3), one O(4), and one O(5) atom. The Si(1)-O(2) bond length is 1.60 Å. The Si(1)-O(3) bond length is 1.65 Å. The Si(1)-O(4) bond length is 1.66 Å. The Si(1)-O(5) bond length is 1.62 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Er(2) and three equivalent Er(1) atoms to form a mixture of corner and edge-sharing OEr4 tetrahedra. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Er(2) and one Si(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to three equivalent Er(1) and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Er(1), two equivalent Er(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Er(2) and one Si(1) atom.