Rb4MgCuSi2O7 crystallizes in the triclinic P1 space group. There are four inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(3), one O(4), and one O(5) atom. In the second Rb site, Rb(2) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(4), one O(5), and one O(7) atom. In the third Rb site, Rb(3) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(3), and one O(4) atom. In the fourth Rb site, Rb(4) is bonded in a 6-coordinate geometry to one Cu(1), one O(2), one O(3), one O(4), one O(5), and one O(7) atom. Mg(1) is bonded in a distorted trigonal planar geometry to one O(2), one O(5), and one O(6) atom. Cu(1) is bonded in a distorted linear geometry to one Rb(4), one O(1), and one O(6) atom. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(5), and one O(7) atom to form corner-sharing SiO4 tetrahedra. In the second Si site, Si(2) is bonded to one O(2), one O(4), one O(6), and one O(7) atom to form corner-sharing SiO4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted water-like geometry to one Rb(1), one Rb(2), one Rb(3), one Cu(1), and one Si(1) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Rb(3), one Rb(4), one Mg(1), and one Si(2) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Rb(1), one Rb(2), one Rb(3), one Rb(4), and one Si(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one Rb(1), one Rb(2), one Rb(3), one Rb(4), and one Si(2) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Rb(1), one Rb(2), one Rb(4), one Mg(1), and one Si(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Mg(1), one Cu(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Rb(2), one Rb(4), one Si(1), and one Si(2) atom.
Rb4MgCuSi2O7 crystallizes in the triclinic P1 space group. There are four inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(3), one O(4), and one O(5) atom. The Rb(1)-O(1) bond length is 3.05 Å. The Rb(1)-O(2) bond length is 3.06 Å. The Rb(1)-O(3) bond length is 2.79 Å. The Rb(1)-O(4) bond length is 2.79 Å. The Rb(1)-O(5) bond length is 3.08 Å. In the second Rb site, Rb(2) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(4), one O(5), and one O(7) atom. The Rb(2)-O(1) bond length is 3.03 Å. The Rb(2)-O(3) bond length is 2.89 Å. The Rb(2)-O(4) bond length is 2.86 Å. The Rb(2)-O(5) bond length is 2.79 Å. The Rb(2)-O(7) bond length is 2.97 Å. In the third Rb site, Rb(3) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(3), and one O(4) atom. The Rb(3)-O(1) bond length is 2.95 Å. The Rb(3)-O(2) bond length is 3.12 Å. The Rb(3)-O(3) bond length is 2.69 Å. The Rb(3)-O(4) bond length is 2.73 Å. In the fourth Rb site, Rb(4) is bonded in a 6-coordinate geometry to one Cu(1), one O(2), one O(3), one O(4), one O(5), and one O(7) atom. The Rb(4)-Cu(1) bond length is 3.47 Å. The Rb(4)-O(2) bond length is 3.20 Å. The Rb(4)-O(3) bond length is 2.78 Å. The Rb(4)-O(4) bond length is 3.49 Å. The Rb(4)-O(5) bond length is 3.22 Å. The Rb(4)-O(7) bond length is 2.93 Å. Mg(1) is bonded in a distorted trigonal planar geometry to one O(2), one O(5), and one O(6) atom. The Mg(1)-O(2) bond length is 2.00 Å. The Mg(1)-O(5) bond length is 1.97 Å. The Mg(1)-O(6) bond length is 2.07 Å. Cu(1) is bonded in a distorted linear geometry to one Rb(4), one O(1), and one O(6) atom. The Cu(1)-O(1) bond length is 1.90 Å. The Cu(1)-O(6) bond length is 1.91 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(5), and one O(7) atom to form corner-sharing SiO4 tetrahedra. The Si(1)-O(1) bond length is 1.66 Å. The Si(1)-O(3) bond length is 1.62 Å. The Si(1)-O(5) bond length is 1.65 Å. The Si(1)-O(7) bond length is 1.71 Å. In the second Si site, Si(2) is bonded to one O(2), one O(4), one O(6), and one O(7) atom to form corner-sharing SiO4 tetrahedra. The Si(2)-O(2) bond length is 1.65 Å. The Si(2)-O(4) bond length is 1.62 Å. The Si(2)-O(6) bond length is 1.69 Å. The Si(2)-O(7) bond length is 1.70 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted water-like geometry to one Rb(1), one Rb(2), one Rb(3), one Cu(1), and one Si(1) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Rb(3), one Rb(4), one Mg(1), and one Si(2) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Rb(1), one Rb(2), one Rb(3), one Rb(4), and one Si(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one Rb(1), one Rb(2), one Rb(3), one Rb(4), and one Si(2) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Rb(1), one Rb(2), one Rb(4), one Mg(1), and one Si(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Mg(1), one Cu(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Rb(2), one Rb(4), one Si(1), and one Si(2) atom.