Li2Fe2B2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded in a 4-coordinate geometry to one O(2), one O(4), one O(5), and one O(7) atom. In the second Li site, Li(2) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(4), one O(5), and one O(6) atom. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(6), one O(7), and two equivalent O(3) atoms. In the second Fe site, Fe(2) is bonded to one O(3), one O(4), one O(5), and one O(7) atom to form distorted FeO4 tetrahedra that share corners with two equivalent B(1)O4 tetrahedra and corners with two equivalent B(2)O4 tetrahedra. There are two inequivalent B sites. In the first B site, B(1) is bonded to one O(1), one O(2), one O(3), and one O(7) atom to form BO4 tetrahedra that share  a cornercorner with one B(2)O4 tetrahedra and corners with two equivalent Fe(2)O4 tetrahedra. In the second B site, B(2) is bonded to one O(1), one O(4), one O(5), and one O(6) atom to form BO4 tetrahedra that share  a cornercorner with one B(1)O4 tetrahedra and corners with two equivalent Fe(2)O4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Li(2), one Fe(1), one B(1), and one B(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Li(1), one Li(2), one Fe(1), and one B(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Fe(2), two equivalent Fe(1), and one B(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Li(1), one Li(2), one Fe(2), and one B(2) atom. In the fifth O site, O(5) is bonded to one Li(1), one Li(2), one Fe(2), and one B(2) atom to form corner-sharing OLi2FeB tetrahedra. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Li(2), one Fe(1), and one B(2) atom. In the seventh O site, O(7) is bonded to one Li(1), one Fe(1), one Fe(2), and one B(1) atom to form distorted corner-sharing OLiFe2B tetrahedra.
Li2Fe2B2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded in a 4-coordinate geometry to one O(2), one O(4), one O(5), and one O(7) atom. The Li(1)-O(2) bond length is 2.38 Å. The Li(1)-O(4) bond length is 2.13 Å. The Li(1)-O(5) bond length is 1.95 Å. The Li(1)-O(7) bond length is 2.07 Å. In the second Li site, Li(2) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(4), one O(5), and one O(6) atom. The Li(2)-O(1) bond length is 2.53 Å. The Li(2)-O(2) bond length is 2.01 Å. The Li(2)-O(4) bond length is 2.16 Å. The Li(2)-O(5) bond length is 2.10 Å. The Li(2)-O(6) bond length is 2.08 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(6), one O(7), and two equivalent O(3) atoms. The Fe(1)-O(1) bond length is 2.15 Å. The Fe(1)-O(2) bond length is 1.92 Å. The Fe(1)-O(6) bond length is 1.89 Å. The Fe(1)-O(7) bond length is 2.10 Å. There is one shorter (2.06 Å) and one longer (2.25 Å) Fe(1)-O(3) bond length. In the second Fe site, Fe(2) is bonded to one O(3), one O(4), one O(5), and one O(7) atom to form distorted FeO4 tetrahedra that share corners with two equivalent B(1)O4 tetrahedra and corners with two equivalent B(2)O4 tetrahedra. The Fe(2)-O(3) bond length is 1.96 Å. The Fe(2)-O(4) bond length is 1.91 Å. The Fe(2)-O(5) bond length is 1.88 Å. The Fe(2)-O(7) bond length is 1.93 Å. There are two inequivalent B sites. In the first B site, B(1) is bonded to one O(1), one O(2), one O(3), and one O(7) atom to form BO4 tetrahedra that share  a cornercorner with one B(2)O4 tetrahedra and corners with two equivalent Fe(2)O4 tetrahedra. The B(1)-O(1) bond length is 1.50 Å. The B(1)-O(2) bond length is 1.43 Å. The B(1)-O(3) bond length is 1.54 Å. The B(1)-O(7) bond length is 1.52 Å. In the second B site, B(2) is bonded to one O(1), one O(4), one O(5), and one O(6) atom to form BO4 tetrahedra that share  a cornercorner with one B(1)O4 tetrahedra and corners with two equivalent Fe(2)O4 tetrahedra. The B(2)-O(1) bond length is 1.52 Å. The B(2)-O(4) bond length is 1.51 Å. The B(2)-O(5) bond length is 1.50 Å. The B(2)-O(6) bond length is 1.46 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Li(2), one Fe(1), one B(1), and one B(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Li(1), one Li(2), one Fe(1), and one B(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Fe(2), two equivalent Fe(1), and one B(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Li(1), one Li(2), one Fe(2), and one B(2) atom. In the fifth O site, O(5) is bonded to one Li(1), one Li(2), one Fe(2), and one B(2) atom to form corner-sharing OLi2FeB tetrahedra. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Li(2), one Fe(1), and one B(2) atom. In the seventh O site, O(7) is bonded to one Li(1), one Fe(1), one Fe(2), and one B(1) atom to form distorted corner-sharing OLiFe2B tetrahedra.