Ca2Cu2Si3(HO3)4 crystallizes in the monoclinic P2_1/m space group. Ca(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(4), one O(6), and two equivalent O(5) atoms. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(4), two equivalent O(3), and two equivalent O(7) atoms to form distorted CuO5 trigonal bipyramids that share  a cornercorner with one Si(2)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. In the second Cu site, Cu(2) is bonded in a 5-coordinate geometry to one O(1), two equivalent O(3), and two equivalent O(7) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(2), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra and  a cornercorner with one Cu(1)O5 trigonal bipyramid. In the second Si site, Si(2) is bonded to one O(1), one O(4), and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra and  a cornercorner with one Cu(1)O5 trigonal bipyramid. There are two inequivalent H sites. In the first H site, H(1) is bonded in a distorted linear geometry to one O(5) and one O(7) atom. In the second H site, H(2) is bonded in a single-bond geometry to one O(7) atom. There are seven inequivalent O sites. In the first O site, O(4) is bonded to two equivalent Ca(1), one Cu(1), and one Si(2) atom to form distorted corner-sharing OCa2CuSi trigonal pyramids. In the second O site, O(5) is bonded to two equivalent Ca(1), one Si(1), and one H(1) atom to form distorted OCa2SiH tetrahedra that share corners with two equivalent O(4)Ca2CuSi trigonal pyramids and  an edgeedge with one O(5)Ca2SiH tetrahedra. In the third O site, O(6) is bonded in a bent 150 degrees geometry to one Ca(1) and one Si(1) atom. In the fourth O site, O(7) is bonded in a distorted water-like geometry to one Cu(1), one Cu(2), one H(1), and one H(2) atom. In the fifth O site, O(1) is bonded in a distorted single-bond geometry to two equivalent Ca(1), one Cu(2), and one Si(2) atom. In the sixth O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Ca(1), one Si(1), and one Si(2) atom. In the seventh O site, O(3) is bonded in a distorted trigonal planar geometry to one Cu(1), one Cu(2), and one Si(1) atom.
Ca2Cu2Si3(HO3)4 crystallizes in the monoclinic P2_1/m space group. Ca(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(4), one O(6), and two equivalent O(5) atoms. The Ca(1)-O(1) bond length is 2.50 Å. The Ca(1)-O(2) bond length is 2.80 Å. The Ca(1)-O(4) bond length is 2.34 Å. The Ca(1)-O(6) bond length is 2.23 Å. There is one shorter (2.43 Å) and one longer (2.46 Å) Ca(1)-O(5) bond length. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(4), two equivalent O(3), and two equivalent O(7) atoms to form distorted CuO5 trigonal bipyramids that share  a cornercorner with one Si(2)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. The Cu(1)-O(4) bond length is 2.21 Å. Both Cu(1)-O(3) bond lengths are 1.93 Å. Both Cu(1)-O(7) bond lengths are 2.24 Å. In the second Cu site, Cu(2) is bonded in a 5-coordinate geometry to one O(1), two equivalent O(3), and two equivalent O(7) atoms. The Cu(2)-O(1) bond length is 2.44 Å. Both Cu(2)-O(3) bond lengths are 1.92 Å. Both Cu(2)-O(7) bond lengths are 2.06 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(2), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra and  a cornercorner with one Cu(1)O5 trigonal bipyramid. The Si(1)-O(2) bond length is 1.67 Å. The Si(1)-O(3) bond length is 1.69 Å. The Si(1)-O(5) bond length is 1.65 Å. The Si(1)-O(6) bond length is 1.59 Å. In the second Si site, Si(2) is bonded to one O(1), one O(4), and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra and  a cornercorner with one Cu(1)O5 trigonal bipyramid. The Si(2)-O(1) bond length is 1.61 Å. The Si(2)-O(4) bond length is 1.63 Å. Both Si(2)-O(2) bond lengths are 1.66 Å. There are two inequivalent H sites. In the first H site, H(1) is bonded in a distorted linear geometry to one O(5) and one O(7) atom. The H(1)-O(5) bond length is 1.58 Å. The H(1)-O(7) bond length is 1.05 Å. In the second H site, H(2) is bonded in a single-bond geometry to one O(7) atom. The H(2)-O(7) bond length is 0.99 Å. There are seven inequivalent O sites. In the first O site, O(4) is bonded to two equivalent Ca(1), one Cu(1), and one Si(2) atom to form distorted corner-sharing OCa2CuSi trigonal pyramids. In the second O site, O(5) is bonded to two equivalent Ca(1), one Si(1), and one H(1) atom to form distorted OCa2SiH tetrahedra that share corners with two equivalent O(4)Ca2CuSi trigonal pyramids and  an edgeedge with one O(5)Ca2SiH tetrahedra. In the third O site, O(6) is bonded in a bent 150 degrees geometry to one Ca(1) and one Si(1) atom. In the fourth O site, O(7) is bonded in a distorted water-like geometry to one Cu(1), one Cu(2), one H(1), and one H(2) atom. In the fifth O site, O(1) is bonded in a distorted single-bond geometry to two equivalent Ca(1), one Cu(2), and one Si(2) atom. In the sixth O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Ca(1), one Si(1), and one Si(2) atom. In the seventh O site, O(3) is bonded in a distorted trigonal planar geometry to one Cu(1), one Cu(2), and one Si(1) atom.