Er7IrI12 is trigonal omega-derived structured and crystallizes in the trigonal R-3 space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to one Ir(1), two equivalent I(2), and three equivalent I(1) atoms to form distorted ErIrI5 octahedra that share corners with three equivalent Er(1)IrI5 octahedra,  an edgeedge with one Er(2)I6 octahedra, and edges with five equivalent Er(1)IrI5 octahedra. The corner-sharing octahedral tilt angles range from 0-9°. In the second Er site, Er(2) is bonded to six equivalent I(2) atoms to form edge-sharing ErI6 octahedra. Ir(1) is bonded in an octahedral geometry to six equivalent Er(1) atoms. There are two inequivalent I sites. In the first I site, I(1) is bonded in a distorted T-shaped geometry to three equivalent Er(1) atoms. In the second I site, I(2) is bonded in a distorted T-shaped geometry to one Er(2) and two equivalent Er(1) atoms.
Er7IrI12 is trigonal omega-derived structured and crystallizes in the trigonal R-3 space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to one Ir(1), two equivalent I(2), and three equivalent I(1) atoms to form distorted ErIrI5 octahedra that share corners with three equivalent Er(1)IrI5 octahedra,  an edgeedge with one Er(2)I6 octahedra, and edges with five equivalent Er(1)IrI5 octahedra. The corner-sharing octahedral tilt angles range from 0-9°. The Er(1)-Ir(1) bond length is 2.65 Å. There is one shorter (3.18 Å) and one longer (3.21 Å) Er(1)-I(2) bond length. There are a spread of Er(1)-I(1) bond distances ranging from 3.08-3.36 Å. In the second Er site, Er(2) is bonded to six equivalent I(2) atoms to form edge-sharing ErI6 octahedra. All Er(2)-I(2) bond lengths are 3.00 Å. Ir(1) is bonded in an octahedral geometry to six equivalent Er(1) atoms. There are two inequivalent I sites. In the first I site, I(1) is bonded in a distorted T-shaped geometry to three equivalent Er(1) atoms. In the second I site, I(2) is bonded in a distorted T-shaped geometry to one Er(2) and two equivalent Er(1) atoms.