Li2CuSiO4 is beta beryllia-derived structured and crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form LiO4 tetrahedra that share corners with two equivalent Cu(1)O4 tetrahedra, corners with four equivalent Li(2)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Li(1)O4 tetrahedra. In the second Li site, Li(2) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form LiO4 tetrahedra that share corners with four equivalent Li(1)O4 tetrahedra, corners with four equivalent Cu(1)O4 tetrahedra, and corners with four equivalent Si(1)O4 tetrahedra. Cu(1) is bonded to one O(2), one O(3), and two equivalent O(4) atoms to form CuO4 tetrahedra that share corners with two equivalent Li(1)O4 tetrahedra, corners with four equivalent Li(2)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Cu(1)O4 tetrahedra. 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 Li(1)O4 tetrahedra, corners with four equivalent Li(2)O4 tetrahedra, and corners with four equivalent Cu(1)O4 tetrahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Li(2), two equivalent Li(1), and one Si(1) atom to form distorted OLi3Si tetrahedra that share corners with four equivalent O(2)Li2CuSi tetrahedra, corners with four equivalent O(3)Li2CuSi tetrahedra, and  an edgeedge with one O(1)Li3Si tetrahedra. In the second O site, O(2) is bonded to one Li(1), one Li(2), one Cu(1), and one Si(1) atom to form OLi2CuSi tetrahedra that share corners with four equivalent O(3)Li2CuSi tetrahedra and corners with four equivalent O(1)Li3Si tetrahedra. In the third O site, O(3) is bonded to one Li(1), one Li(2), one Cu(1), and one Si(1) atom to form OLi2CuSi tetrahedra that share corners with four equivalent O(2)Li2CuSi tetrahedra and corners with four equivalent O(1)Li3Si tetrahedra. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Li(2), two equivalent Cu(1), and one Si(1) atom.
Li2CuSiO4 is beta beryllia-derived structured and crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form LiO4 tetrahedra that share corners with two equivalent Cu(1)O4 tetrahedra, corners with four equivalent Li(2)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Li(1)O4 tetrahedra. The Li(1)-O(2) bond length is 2.03 Å. The Li(1)-O(3) bond length is 2.01 Å. There is one shorter (1.96 Å) and one longer (2.00 Å) Li(1)-O(1) bond length. In the second Li site, Li(2) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form LiO4 tetrahedra that share corners with four equivalent Li(1)O4 tetrahedra, corners with four equivalent Cu(1)O4 tetrahedra, and corners with four equivalent Si(1)O4 tetrahedra. The Li(2)-O(1) bond length is 1.94 Å. The Li(2)-O(2) bond length is 1.98 Å. The Li(2)-O(3) bond length is 1.97 Å. The Li(2)-O(4) bond length is 2.17 Å. Cu(1) is bonded to one O(2), one O(3), and two equivalent O(4) atoms to form CuO4 tetrahedra that share corners with two equivalent Li(1)O4 tetrahedra, corners with four equivalent Li(2)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Cu(1)O4 tetrahedra. The Cu(1)-O(2) bond length is 1.97 Å. The Cu(1)-O(3) bond length is 1.91 Å. There is one shorter (1.95 Å) and one longer (2.19 Å) Cu(1)-O(4) 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 Li(1)O4 tetrahedra, corners with four equivalent Li(2)O4 tetrahedra, and corners with four equivalent Cu(1)O4 tetrahedra. The Si(1)-O(1) bond length is 1.62 Å. The Si(1)-O(2) bond length is 1.66 Å. The Si(1)-O(3) bond length is 1.67 Å. The Si(1)-O(4) bond length is 1.68 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Li(2), two equivalent Li(1), and one Si(1) atom to form distorted OLi3Si tetrahedra that share corners with four equivalent O(2)Li2CuSi tetrahedra, corners with four equivalent O(3)Li2CuSi tetrahedra, and  an edgeedge with one O(1)Li3Si tetrahedra. In the second O site, O(2) is bonded to one Li(1), one Li(2), one Cu(1), and one Si(1) atom to form OLi2CuSi tetrahedra that share corners with four equivalent O(3)Li2CuSi tetrahedra and corners with four equivalent O(1)Li3Si tetrahedra. In the third O site, O(3) is bonded to one Li(1), one Li(2), one Cu(1), and one Si(1) atom to form OLi2CuSi tetrahedra that share corners with four equivalent O(2)Li2CuSi tetrahedra and corners with four equivalent O(1)Li3Si tetrahedra. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Li(2), two equivalent Cu(1), and one Si(1) atom.