Li2CuSiO4 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 distorted LiO4 tetrahedra that share corners with two equivalent Li(1)O4 tetrahedra and corners with four equivalent Si(1)O4 tetrahedra. In the second Li site, Li(2) is bonded in a see-saw-like geometry to one O(1), one O(2), one O(3), and one O(4) atom. Cu(1) is bonded in a distorted rectangular see-saw-like geometry to one O(2), one O(3), and two equivalent O(4) atoms. 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. 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 two equivalent O(2)Li2CuSi tetrahedra, corners with two equivalent O(1)Li3Si tetrahedra, corners with two equivalent O(3)Li2CuSi trigonal pyramids,  an edgeedge with one O(2)Li2CuSi tetrahedra, and  an edgeedge with one O(3)Li2CuSi trigonal pyramid. 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 distorted OLi2CuSi tetrahedra that share corners with two equivalent O(1)Li3Si tetrahedra, corners with four equivalent O(3)Li2CuSi trigonal pyramids, and  an edgeedge with one 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 distorted OLi2CuSi trigonal pyramids that share corners with two equivalent O(1)Li3Si tetrahedra, corners with four equivalent O(2)Li2CuSi tetrahedra, and  an edgeedge with one O(1)Li3Si tetrahedra. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Li(2), two equivalent Cu(1), and one Si(1) atom.
Li2CuSiO4 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 distorted LiO4 tetrahedra that share corners with two equivalent Li(1)O4 tetrahedra and corners with four equivalent Si(1)O4 tetrahedra. The Li(1)-O(2) bond length is 1.98 Å. The Li(1)-O(3) bond length is 2.00 Å. Both Li(1)-O(1) bond lengths are 1.98 Å. In the second Li site, Li(2) is bonded in a see-saw-like geometry to one O(1), one O(2), one O(3), and one O(4) atom. The Li(2)-O(1) bond length is 1.94 Å. The Li(2)-O(2) bond length is 2.06 Å. The Li(2)-O(3) bond length is 1.97 Å. The Li(2)-O(4) bond length is 2.21 Å. Cu(1) is bonded in a distorted rectangular see-saw-like geometry to one O(2), one O(3), and two equivalent O(4) atoms. The Cu(1)-O(2) bond length is 1.89 Å. The Cu(1)-O(3) bond length is 1.90 Å. There is one shorter (2.05 Å) and one longer (2.14 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. The Si(1)-O(1) bond length is 1.61 Å. The Si(1)-O(2) bond length is 1.67 Å. The Si(1)-O(3) bond length is 1.66 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 two equivalent O(2)Li2CuSi tetrahedra, corners with two equivalent O(1)Li3Si tetrahedra, corners with two equivalent O(3)Li2CuSi trigonal pyramids,  an edgeedge with one O(2)Li2CuSi tetrahedra, and  an edgeedge with one O(3)Li2CuSi trigonal pyramid. 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 distorted OLi2CuSi tetrahedra that share corners with two equivalent O(1)Li3Si tetrahedra, corners with four equivalent O(3)Li2CuSi trigonal pyramids, and  an edgeedge with one 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 distorted OLi2CuSi trigonal pyramids that share corners with two equivalent O(1)Li3Si tetrahedra, corners with four equivalent O(2)Li2CuSi tetrahedra, and  an edgeedge with one O(1)Li3Si tetrahedra. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Li(2), two equivalent Cu(1), and one Si(1) atom.