Er4BO7Cl crystallizes in the monoclinic P2_1/c space group. There are four inequivalent Er sites. In the first Er site, Er(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(5), one O(6), one O(7), and one Cl(1) atom. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), one O(5), two equivalent O(4), and one Cl(1) atom. In the third Er site, Er(3) is bonded in a 7-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(7), two equivalent O(1), and one Cl(1) atom. In the fourth Er site, Er(4) is bonded in a 5-coordinate geometry to one O(2), one O(3), one O(4), one O(6), one O(7), and two equivalent Cl(1) atoms. B(1) is bonded in a trigonal planar geometry to one O(5), one O(6), and one O(7) atom. There are seven inequivalent O sites. In the first O site, O(3) is bonded to one Er(1), one Er(2), one Er(3), and one Er(4) atom to form a mixture of corner and edge-sharing OEr4 tetrahedra. In the second O site, O(4) is bonded to one Er(3), one Er(4), and two equivalent Er(2) atoms to form a mixture of corner and edge-sharing OEr4 tetrahedra. In the third O site, O(5) is bonded in a 4-coordinate geometry to one Er(1), one Er(2), one Er(3), and one B(1) atom. In the fourth O site, O(6) is bonded in a distorted trigonal planar geometry to one Er(1), one Er(4), and one B(1) atom. In the fifth O site, O(7) is bonded in a distorted single-bond geometry to one Er(1), one Er(3), one Er(4), and one B(1) atom. In the sixth O site, O(1) is bonded to one Er(1), one Er(2), and two equivalent Er(3) atoms to form a mixture of corner and edge-sharing OEr4 tetrahedra. In the seventh O site, O(2) is bonded to one Er(1), one Er(2), one Er(3), and one Er(4) atom to form a mixture of corner and edge-sharing OEr4 tetrahedra. Cl(1) is bonded in a 5-coordinate geometry to one Er(1), one Er(2), one Er(3), and two equivalent Er(4) atoms.
Er4BO7Cl crystallizes in the monoclinic P2_1/c space group. There are four inequivalent Er sites. In the first Er site, Er(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(5), one O(6), one O(7), and one Cl(1) atom. The Er(1)-O(1) bond length is 2.19 Å. The Er(1)-O(2) bond length is 2.25 Å. The Er(1)-O(3) bond length is 2.28 Å. The Er(1)-O(5) bond length is 2.26 Å. The Er(1)-O(6) bond length is 2.21 Å. The Er(1)-O(7) bond length is 2.31 Å. The Er(1)-Cl(1) bond length is 3.12 Å. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), one O(5), two equivalent O(4), and one Cl(1) atom. The Er(2)-O(1) bond length is 2.27 Å. The Er(2)-O(2) bond length is 2.27 Å. The Er(2)-O(3) bond length is 2.24 Å. The Er(2)-O(5) bond length is 2.33 Å. There is one shorter (2.22 Å) and one longer (2.27 Å) Er(2)-O(4) bond length. The Er(2)-Cl(1) bond length is 2.92 Å. In the third Er site, Er(3) is bonded in a 7-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(7), two equivalent O(1), and one Cl(1) atom. The Er(3)-O(2) bond length is 2.26 Å. The Er(3)-O(3) bond length is 2.27 Å. The Er(3)-O(4) bond length is 2.22 Å. The Er(3)-O(5) bond length is 2.53 Å. The Er(3)-O(7) bond length is 2.73 Å. There is one shorter (2.24 Å) and one longer (2.28 Å) Er(3)-O(1) bond length. The Er(3)-Cl(1) bond length is 3.27 Å. In the fourth Er site, Er(4) is bonded in a 5-coordinate geometry to one O(2), one O(3), one O(4), one O(6), one O(7), and two equivalent Cl(1) atoms. The Er(4)-O(2) bond length is 2.23 Å. The Er(4)-O(3) bond length is 2.19 Å. The Er(4)-O(4) bond length is 2.17 Å. The Er(4)-O(6) bond length is 2.23 Å. The Er(4)-O(7) bond length is 2.31 Å. There is one shorter (2.83 Å) and one longer (3.24 Å) Er(4)-Cl(1) bond length. B(1) is bonded in a trigonal planar geometry to one O(5), one O(6), and one O(7) atom. The B(1)-O(5) bond length is 1.38 Å. The B(1)-O(6) bond length is 1.36 Å. The B(1)-O(7) bond length is 1.37 Å. There are seven inequivalent O sites. In the first O site, O(3) is bonded to one Er(1), one Er(2), one Er(3), and one Er(4) atom to form a mixture of corner and edge-sharing OEr4 tetrahedra. In the second O site, O(4) is bonded to one Er(3), one Er(4), and two equivalent Er(2) atoms to form a mixture of corner and edge-sharing OEr4 tetrahedra. In the third O site, O(5) is bonded in a 4-coordinate geometry to one Er(1), one Er(2), one Er(3), and one B(1) atom. In the fourth O site, O(6) is bonded in a distorted trigonal planar geometry to one Er(1), one Er(4), and one B(1) atom. In the fifth O site, O(7) is bonded in a distorted single-bond geometry to one Er(1), one Er(3), one Er(4), and one B(1) atom. In the sixth O site, O(1) is bonded to one Er(1), one Er(2), and two equivalent Er(3) atoms to form a mixture of corner and edge-sharing OEr4 tetrahedra. In the seventh O site, O(2) is bonded to one Er(1), one Er(2), one Er(3), and one Er(4) atom to form a mixture of corner and edge-sharing OEr4 tetrahedra. Cl(1) is bonded in a 5-coordinate geometry to one Er(1), one Er(2), one Er(3), and two equivalent Er(4) atoms.