Li2Cu2Si8O19 crystallizes in the monoclinic C2 space group. Li(1) is bonded in a distorted trigonal non-coplanar geometry to one O(10), one O(3), and one O(7) atom. Cu(1) is bonded to one O(4), one O(7), and two equivalent O(6) atoms to form CuO4 trigonal pyramids that share  a cornercorner with one Si(4)O4 tetrahedra, corners with three equivalent Si(3)O4 tetrahedra, and corners with two equivalent Cu(1)O4 trigonal pyramids. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(5), and one O(9) atom to form corner-sharing SiO4 tetrahedra. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(3), and one O(8) atom to form corner-sharing SiO4 tetrahedra. In the third Si site, Si(3) is bonded to one O(10), one O(3), one O(4), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with three equivalent Cu(1)O4 trigonal pyramids. In the fourth Si site, Si(4) is bonded to one O(5), one O(7), one O(8), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, and  a cornercorner with one Cu(1)O4 trigonal pyramid. There are ten inequivalent O sites. In the first O site, O(9) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(4) atom. In the second O site, O(10) is bonded in a distorted tetrahedral geometry to two equivalent Li(1) and two equivalent Si(3) atoms. In the third O site, O(1) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the fourth O site, O(2) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the fifth O site, O(3) is bonded in a 3-coordinate geometry to one Li(1), one Si(2), and one Si(3) atom. In the sixth O site, O(4) is bonded in a bent 120 degrees geometry to one Cu(1) and one Si(3) atom. In the seventh O site, O(5) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(4) atom. In the eighth O site, O(6) is bonded in a trigonal planar geometry to two equivalent Cu(1) and one Si(3) atom. In the ninth O site, O(7) is bonded in a distorted trigonal planar geometry to one Li(1), one Cu(1), and one Si(4) atom. In the tenth O site, O(8) is bonded in a linear geometry to one Si(2) and one Si(4) atom.
Li2Cu2Si8O19 crystallizes in the monoclinic C2 space group. Li(1) is bonded in a distorted trigonal non-coplanar geometry to one O(10), one O(3), and one O(7) atom. The Li(1)-O(10) bond length is 2.09 Å. The Li(1)-O(3) bond length is 2.18 Å. The Li(1)-O(7) bond length is 2.09 Å. Cu(1) is bonded to one O(4), one O(7), and two equivalent O(6) atoms to form CuO4 trigonal pyramids that share  a cornercorner with one Si(4)O4 tetrahedra, corners with three equivalent Si(3)O4 tetrahedra, and corners with two equivalent Cu(1)O4 trigonal pyramids. The Cu(1)-O(4) bond length is 1.93 Å. The Cu(1)-O(7) bond length is 1.93 Å. There is one shorter (2.00 Å) and one longer (2.06 Å) Cu(1)-O(6) bond length. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(5), and one O(9) atom to form corner-sharing SiO4 tetrahedra. The Si(1)-O(1) bond length is 1.64 Å. The Si(1)-O(2) bond length is 1.62 Å. The Si(1)-O(5) bond length is 1.63 Å. The Si(1)-O(9) bond length is 1.63 Å. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(3), and one O(8) atom to form corner-sharing SiO4 tetrahedra. The Si(2)-O(1) bond length is 1.63 Å. The Si(2)-O(2) bond length is 1.62 Å. The Si(2)-O(3) bond length is 1.64 Å. The Si(2)-O(8) bond length is 1.61 Å. In the third Si site, Si(3) is bonded to one O(10), one O(3), one O(4), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with three equivalent Cu(1)O4 trigonal pyramids. The Si(3)-O(10) bond length is 1.68 Å. The Si(3)-O(3) bond length is 1.66 Å. The Si(3)-O(4) bond length is 1.61 Å. The Si(3)-O(6) bond length is 1.64 Å. In the fourth Si site, Si(4) is bonded to one O(5), one O(7), one O(8), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, and  a cornercorner with one Cu(1)O4 trigonal pyramid. The Si(4)-O(5) bond length is 1.64 Å. The Si(4)-O(7) bond length is 1.63 Å. The Si(4)-O(8) bond length is 1.65 Å. The Si(4)-O(9) bond length is 1.65 Å. There are ten inequivalent O sites. In the first O site, O(9) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(4) atom. In the second O site, O(10) is bonded in a distorted tetrahedral geometry to two equivalent Li(1) and two equivalent Si(3) atoms. In the third O site, O(1) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the fourth O site, O(2) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the fifth O site, O(3) is bonded in a 3-coordinate geometry to one Li(1), one Si(2), and one Si(3) atom. In the sixth O site, O(4) is bonded in a bent 120 degrees geometry to one Cu(1) and one Si(3) atom. In the seventh O site, O(5) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(4) atom. In the eighth O site, O(6) is bonded in a trigonal planar geometry to two equivalent Cu(1) and one Si(3) atom. In the ninth O site, O(7) is bonded in a distorted trigonal planar geometry to one Li(1), one Cu(1), and one Si(4) atom. In the tenth O site, O(8) is bonded in a linear geometry to one Si(2) and one Si(4) atom.