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 2-coordinate geometry to one O(2) and one O(3) atom. In the second Rb site, Rb(2) is bonded in a 4-coordinate geometry to one O(3), one O(4), and two equivalent O(1) atoms. Cu(1) is bonded in a linear geometry to two equivalent O(2) atoms. Si(1) is bonded in a distorted bent 120 degrees geometry to one O(1), one O(3), and one O(4) atom. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to two equivalent Rb(2), one Si(1), and one O(4) atom. In the second O site, O(2) is bonded in a distorted linear geometry to one Rb(1) and one Cu(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Rb(1), one Rb(2), and one Si(1) atom. In the fourth O site, O(4) is bonded in a distorted octahedral geometry to two equivalent Rb(2), two equivalent Si(1), and two equivalent O(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 2-coordinate geometry to one O(2) and one O(3) atom. The Rb(1)-O(2) bond length is 2.04 Å. The Rb(1)-O(3) bond length is 2.65 Å. In the second Rb site, Rb(2) is bonded in a 4-coordinate geometry to one O(3), one O(4), and two equivalent O(1) atoms. The Rb(2)-O(3) bond length is 2.71 Å. The Rb(2)-O(4) bond length is 3.11 Å. There is one shorter (2.95 Å) and one longer (3.15 Å) Rb(2)-O(1) bond length. Cu(1) is bonded in a linear geometry to two equivalent O(2) atoms. Both Cu(1)-O(2) bond lengths are 1.50 Å. Si(1) is bonded in a distorted bent 120 degrees geometry to one O(1), one O(3), and one O(4) atom. The Si(1)-O(1) bond length is 1.62 Å. The Si(1)-O(3) bond length is 1.69 Å. The Si(1)-O(4) bond length is 2.25 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to two equivalent Rb(2), one Si(1), and one O(4) atom. The O(1)-O(4) bond length is 2.01 Å. In the second O site, O(2) is bonded in a distorted linear geometry to one Rb(1) and one Cu(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Rb(1), one Rb(2), and one Si(1) atom. In the fourth O site, O(4) is bonded in a distorted octahedral geometry to two equivalent Rb(2), two equivalent Si(1), and two equivalent O(1) atoms.