ErCO4 crystallizes in the orthorhombic P2_12_12_1 space group. Er(1) is bonded in a 9-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(4), and three equivalent O(3) atoms. C(1) is bonded in a trigonal planar geometry to one O(2), one O(3), and one O(4) atom. There are four inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to two equivalent Er(1) atoms. In the second O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Er(1) and one C(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to three equivalent Er(1) and one C(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to two equivalent Er(1) and one C(1) atom.
ErCO4 crystallizes in the orthorhombic P2_12_12_1 space group. Er(1) is bonded in a 9-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(4), and three equivalent O(3) atoms. There is one shorter (2.19 Å) and one longer (2.21 Å) Er(1)-O(1) bond length. There is one shorter (2.42 Å) and one longer (2.58 Å) Er(1)-O(2) bond length. There is one shorter (2.37 Å) and one longer (2.40 Å) Er(1)-O(4) bond length. There are a spread of Er(1)-O(3) bond distances ranging from 2.47-2.86 Å. C(1) is bonded in a trigonal planar geometry to one O(2), one O(3), and one O(4) atom. The C(1)-O(2) bond length is 1.28 Å. The C(1)-O(3) bond length is 1.31 Å. The C(1)-O(4) bond length is 1.29 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to two equivalent Er(1) atoms. In the second O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Er(1) and one C(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to three equivalent Er(1) and one C(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to two equivalent Er(1) and one C(1) atom.