Li2LuSiO5 crystallizes in the triclinic P-1 space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form distorted LiO4 tetrahedra that share corners with four equivalent Lu(1)O6 octahedra,  a cornercorner with one Li(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra,  an edgeedge with one Li(1)O4 tetrahedra, and  an edgeedge with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 62-78°. In the second Li site, Li(2) is bonded to one O(2), one O(5), and two equivalent O(4) atoms to form distorted LiO4 tetrahedra that share corners with five equivalent Lu(1)O6 octahedra,  a cornercorner with one Li(1)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra,  an edgeedge with one Li(2)O4 tetrahedra, and  an edgeedge with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-68°. Lu(1) is bonded to one O(1), one O(2), one O(3), one O(4), and two equivalent O(5) atoms to form LuO6 octahedra that share corners with four equivalent Li(1)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, corners with five equivalent Li(2)O4 tetrahedra, and  an edgeedge with one Lu(1)O6 octahedra. Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share corners with four equivalent Lu(1)O6 octahedra,  a cornercorner with one Li(2)O4 tetrahedra, corners with two equivalent Li(1)O4 tetrahedra,  an edgeedge with one Li(1)O4 tetrahedra, and  an edgeedge with one Li(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 40-57°. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Li(1), one Lu(1), and one Si(1) atom. In the second O site, O(2) is bonded to one Li(1), one Li(2), one Lu(1), and one Si(1) atom to form a mixture of distorted corner and edge-sharing OLi2LuSi trigonal pyramids. In the third O site, O(3) is bonded to two equivalent Li(1), one Lu(1), and one Si(1) atom to form a mixture of distorted corner and edge-sharing OLi2LuSi trigonal pyramids. In the fourth O site, O(4) is bonded to two equivalent Li(2), one Lu(1), and one Si(1) atom to form a mixture of distorted corner and edge-sharing OLi2LuSi trigonal pyramids. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Li(2) and two equivalent Lu(1) atoms.
Li2LuSiO5 crystallizes in the triclinic P-1 space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form distorted LiO4 tetrahedra that share corners with four equivalent Lu(1)O6 octahedra,  a cornercorner with one Li(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra,  an edgeedge with one Li(1)O4 tetrahedra, and  an edgeedge with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 62-78°. The Li(1)-O(1) bond length is 1.93 Å. The Li(1)-O(2) bond length is 1.99 Å. There is one shorter (1.94 Å) and one longer (2.13 Å) Li(1)-O(3) bond length. In the second Li site, Li(2) is bonded to one O(2), one O(5), and two equivalent O(4) atoms to form distorted LiO4 tetrahedra that share corners with five equivalent Lu(1)O6 octahedra,  a cornercorner with one Li(1)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra,  an edgeedge with one Li(2)O4 tetrahedra, and  an edgeedge with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-68°. The Li(2)-O(2) bond length is 2.03 Å. The Li(2)-O(5) bond length is 2.04 Å. There is one shorter (2.01 Å) and one longer (2.14 Å) Li(2)-O(4) bond length. Lu(1) is bonded to one O(1), one O(2), one O(3), one O(4), and two equivalent O(5) atoms to form LuO6 octahedra that share corners with four equivalent Li(1)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, corners with five equivalent Li(2)O4 tetrahedra, and  an edgeedge with one Lu(1)O6 octahedra. The Lu(1)-O(1) bond length is 2.14 Å. The Lu(1)-O(2) bond length is 2.21 Å. The Lu(1)-O(3) bond length is 2.20 Å. The Lu(1)-O(4) bond length is 2.24 Å. There is one shorter (2.23 Å) and one longer (2.25 Å) Lu(1)-O(5) bond length. Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share corners with four equivalent Lu(1)O6 octahedra,  a cornercorner with one Li(2)O4 tetrahedra, corners with two equivalent Li(1)O4 tetrahedra,  an edgeedge with one Li(1)O4 tetrahedra, and  an edgeedge with one Li(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 40-57°. The Si(1)-O(1) bond length is 1.63 Å. The Si(1)-O(2) bond length is 1.66 Å. The Si(1)-O(3) bond length is 1.65 Å. The Si(1)-O(4) bond length is 1.65 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Li(1), one Lu(1), and one Si(1) atom. In the second O site, O(2) is bonded to one Li(1), one Li(2), one Lu(1), and one Si(1) atom to form a mixture of distorted corner and edge-sharing OLi2LuSi trigonal pyramids. In the third O site, O(3) is bonded to two equivalent Li(1), one Lu(1), and one Si(1) atom to form a mixture of distorted corner and edge-sharing OLi2LuSi trigonal pyramids. In the fourth O site, O(4) is bonded to two equivalent Li(2), one Lu(1), and one Si(1) atom to form a mixture of distorted corner and edge-sharing OLi2LuSi trigonal pyramids. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Li(2) and two equivalent Lu(1) atoms.