Rb4CuSi2O7 crystallizes in the triclinic P-1 space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 7-coordinate geometry to one O(4), two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. In the second Rb site, Rb(2) is bonded in a 6-coordinate geometry to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms. Cu(1) is bonded in a square co-planar geometry to two equivalent O(1) and two equivalent O(2) atoms. Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form corner-sharing SiO4 tetrahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Rb(2), two equivalent Rb(1), one Cu(1), and one Si(1) atom. In the second O site, O(2) is bonded in a 6-coordinate geometry to two equivalent Rb(1), two equivalent Rb(2), one Cu(1), and one Si(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to two equivalent Rb(1), two equivalent Rb(2), and one Si(1) atom. In the fourth O site, O(4) is bonded in a linear geometry to two equivalent Rb(1), two equivalent Rb(2), and two equivalent Si(1) atoms.
Rb4CuSi2O7 crystallizes in the triclinic P-1 space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 7-coordinate geometry to one O(4), two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. The Rb(1)-O(4) bond length is 3.26 Å. There is one shorter (3.09 Å) and one longer (3.30 Å) Rb(1)-O(1) bond length. There is one shorter (3.05 Å) and one longer (3.07 Å) Rb(1)-O(2) bond length. There is one shorter (2.85 Å) and one longer (3.01 Å) Rb(1)-O(3) bond length. In the second Rb site, Rb(2) is bonded in a 6-coordinate geometry to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms. The Rb(2)-O(1) bond length is 2.88 Å. The Rb(2)-O(4) bond length is 3.22 Å. There is one shorter (2.87 Å) and one longer (2.99 Å) Rb(2)-O(2) bond length. There is one shorter (2.83 Å) and one longer (2.91 Å) Rb(2)-O(3) bond length. Cu(1) is bonded in a square co-planar geometry to two equivalent O(1) and two equivalent O(2) atoms. Both Cu(1)-O(1) bond lengths are 2.00 Å. Both Cu(1)-O(2) bond lengths are 1.99 Å. Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form corner-sharing SiO4 tetrahedra. The Si(1)-O(1) bond length is 1.66 Å. The Si(1)-O(2) bond length is 1.67 Å. The Si(1)-O(3) bond length is 1.61 Å. The Si(1)-O(4) bond length is 1.67 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Rb(2), two equivalent Rb(1), one Cu(1), and one Si(1) atom. In the second O site, O(2) is bonded in a 6-coordinate geometry to two equivalent Rb(1), two equivalent Rb(2), one Cu(1), and one Si(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to two equivalent Rb(1), two equivalent Rb(2), and one Si(1) atom. In the fourth O site, O(4) is bonded in a linear geometry to two equivalent Rb(1), two equivalent Rb(2), and two equivalent Si(1) atoms.