ErNbO4 crystallizes in the monoclinic P2/c space group. Er(1) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(1) atoms. Nb(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form distorted edge-sharing NbO6 octahedra. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Er(1) and one Nb(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Er(1) and two equivalent Nb(1) atoms.
ErNbO4 crystallizes in the monoclinic P2/c space group. Er(1) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(1) atoms. Both Er(1)-O(2) bond lengths are 2.22 Å. There are two shorter (2.25 Å) and two longer (2.36 Å) Er(1)-O(1) bond lengths. Nb(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form distorted edge-sharing NbO6 octahedra. Both Nb(1)-O(1) bond lengths are 1.91 Å. There are two shorter (2.01 Å) and two longer (2.20 Å) Nb(1)-O(2) bond lengths. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Er(1) and one Nb(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Er(1) and two equivalent Nb(1) atoms.