Rb4Co(PO4)6 crystallizes in the monoclinic C2/m space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 8-coordinate geometry to two equivalent O(3), two equivalent O(4), two equivalent O(6), and two equivalent O(8) atoms. In the second Rb site, Rb(2) is bonded in a 9-coordinate geometry to one O(6), two equivalent O(1), two equivalent O(3), two equivalent O(4), and two equivalent O(7) atoms. Co(1) is bonded to two equivalent O(5) and four equivalent O(7) atoms to form CoO6 octahedra that share corners with two equivalent P(2)O4 tetrahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form corner-sharing PO4 tetrahedra. In the second P site, P(2) is bonded to one O(5), one O(6), and two equivalent O(2) atoms to form PO4 tetrahedra that share  a cornercorner with one Co(1)O6 octahedra and corners with two equivalent P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 46°. There are eight inequivalent O sites. In the first O site, O(4) is bonded in a distorted single-bond geometry to one Rb(1), one Rb(2), and one P(1) atom. In the second O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Co(1) and one P(2) atom. In the third O site, O(6) is bonded in a single-bond geometry to one Rb(2), two equivalent Rb(1), and one P(2) atom. In the fourth O site, O(7) is bonded in a distorted single-bond geometry to one Rb(2) and one Co(1) atom. In the fifth O site, O(8) is bonded in a 3-coordinate geometry to two equivalent Rb(1) and one O(8) atom. In the sixth O site, O(1) is bonded in a 2-coordinate geometry to two equivalent Rb(2) and two equivalent P(1) atoms. In the seventh O site, O(2) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the eighth O site, O(3) is bonded in a single-bond geometry to one Rb(1), one Rb(2), and one P(1) atom.
Rb4Co(PO4)6 crystallizes in the monoclinic C2/m space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 8-coordinate geometry to two equivalent O(3), two equivalent O(4), two equivalent O(6), and two equivalent O(8) atoms. Both Rb(1)-O(3) bond lengths are 3.12 Å. Both Rb(1)-O(4) bond lengths are 2.90 Å. Both Rb(1)-O(6) bond lengths are 3.12 Å. Both Rb(1)-O(8) bond lengths are 3.19 Å. In the second Rb site, Rb(2) is bonded in a 9-coordinate geometry to one O(6), two equivalent O(1), two equivalent O(3), two equivalent O(4), and two equivalent O(7) atoms. The Rb(2)-O(6) bond length is 3.11 Å. There is one shorter (2.99 Å) and one longer (3.33 Å) Rb(2)-O(1) bond length. Both Rb(2)-O(3) bond lengths are 3.34 Å. Both Rb(2)-O(4) bond lengths are 2.99 Å. Both Rb(2)-O(7) bond lengths are 2.93 Å. Co(1) is bonded to two equivalent O(5) and four equivalent O(7) atoms to form CoO6 octahedra that share corners with two equivalent P(2)O4 tetrahedra. Both Co(1)-O(5) bond lengths are 1.96 Å. All Co(1)-O(7) bond lengths are 1.76 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form corner-sharing PO4 tetrahedra. The P(1)-O(1) bond length is 1.64 Å. The P(1)-O(2) bond length is 1.63 Å. The P(1)-O(3) bond length is 1.49 Å. The P(1)-O(4) bond length is 1.50 Å. In the second P site, P(2) is bonded to one O(5), one O(6), and two equivalent O(2) atoms to form PO4 tetrahedra that share  a cornercorner with one Co(1)O6 octahedra and corners with two equivalent P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 46°. The P(2)-O(5) bond length is 1.53 Å. The P(2)-O(6) bond length is 1.49 Å. Both P(2)-O(2) bond lengths are 1.62 Å. There are eight inequivalent O sites. In the first O site, O(4) is bonded in a distorted single-bond geometry to one Rb(1), one Rb(2), and one P(1) atom. In the second O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Co(1) and one P(2) atom. In the third O site, O(6) is bonded in a single-bond geometry to one Rb(2), two equivalent Rb(1), and one P(2) atom. In the fourth O site, O(7) is bonded in a distorted single-bond geometry to one Rb(2) and one Co(1) atom. In the fifth O site, O(8) is bonded in a 3-coordinate geometry to two equivalent Rb(1) and one O(8) atom. The O(8)-O(8) bond length is 1.24 Å. In the sixth O site, O(1) is bonded in a 2-coordinate geometry to two equivalent Rb(2) and two equivalent P(1) atoms. In the seventh O site, O(2) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the eighth O site, O(3) is bonded in a single-bond geometry to one Rb(1), one Rb(2), and one P(1) atom.