Li2B2Se5 crystallizes in the monoclinic C2/c space group. Li(1) is bonded to one Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form LiSe5 square pyramids that share  a cornercorner with one Li(1)Se5 square pyramid, corners with eight equivalent B(1)Se4 tetrahedra, and edges with two equivalent Li(1)Se5 square pyramids. B(1) is bonded to one Se(1), one Se(3), and two equivalent Se(2) atoms to form BSe4 tetrahedra that share corners with eight equivalent Li(1)Se5 square pyramids and corners with three equivalent B(1)Se4 tetrahedra. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Li(1) and two equivalent B(1) atoms to form corner-sharing SeLi2B2 tetrahedra. In the second Se site, Se(2) is bonded to two equivalent Li(1) and two equivalent B(1) atoms to form a mixture of distorted edge and corner-sharing SeLi2B2 tetrahedra. In the third Se site, Se(3) is bonded in a 3-coordinate geometry to two equivalent Li(1) and one B(1) atom.
Li2B2Se5 crystallizes in the monoclinic C2/c space group. Li(1) is bonded to one Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form LiSe5 square pyramids that share  a cornercorner with one Li(1)Se5 square pyramid, corners with eight equivalent B(1)Se4 tetrahedra, and edges with two equivalent Li(1)Se5 square pyramids. The Li(1)-Se(1) bond length is 2.62 Å. There is one shorter (2.56 Å) and one longer (2.84 Å) Li(1)-Se(2) bond length. There is one shorter (2.67 Å) and one longer (2.70 Å) Li(1)-Se(3) bond length. B(1) is bonded to one Se(1), one Se(3), and two equivalent Se(2) atoms to form BSe4 tetrahedra that share corners with eight equivalent Li(1)Se5 square pyramids and corners with three equivalent B(1)Se4 tetrahedra. The B(1)-Se(1) bond length is 2.06 Å. The B(1)-Se(3) bond length is 2.07 Å. There is one shorter (2.05 Å) and one longer (2.08 Å) B(1)-Se(2) bond length. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Li(1) and two equivalent B(1) atoms to form corner-sharing SeLi2B2 tetrahedra. In the second Se site, Se(2) is bonded to two equivalent Li(1) and two equivalent B(1) atoms to form a mixture of distorted edge and corner-sharing SeLi2B2 tetrahedra. In the third Se site, Se(3) is bonded in a 3-coordinate geometry to two equivalent Li(1) and one B(1) atom.