Rb4P21I crystallizes in the orthorhombic Cmcm space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 8-coordinate geometry to one P(1), one P(6), one P(7), two equivalent P(3), two equivalent P(5), and one I(1) atom. In the second Rb site, Rb(2) is bonded in a 8-coordinate geometry to two equivalent P(2), two equivalent P(4), two equivalent P(8), and two equivalent I(1) atoms. There are eight inequivalent P sites. In the first P site, P(5) is bonded in a 5-coordinate geometry to two equivalent Rb(1), one P(1), and two equivalent P(8) atoms. In the second P site, P(6) is bonded to one Rb(1), one P(2), and two equivalent P(4) atoms to form PRbP3 tetrahedra that share  a cornercorner with one I(1)Rb6 pentagonal pyramid, corners with two equivalent P(7)RbP3 tetrahedra, corners with two equivalent P(4)RbP3 trigonal pyramids, and corners with four equivalent P(3)RbP3 trigonal pyramids. In the third P site, P(7) is bonded to one Rb(1), one P(2), and two equivalent P(3) atoms to form PRbP3 tetrahedra that share  a cornercorner with one I(1)Rb6 pentagonal pyramid, corners with two equivalent P(6)RbP3 tetrahedra, corners with two equivalent P(8)RbP3 tetrahedra, corners with two equivalent P(3)RbP3 trigonal pyramids, and corners with two equivalent P(4)RbP3 trigonal pyramids. In the fourth P site, P(8) is bonded to one Rb(2), one P(3), one P(5), and one P(8) atom to form PRbP3 tetrahedra that share corners with two equivalent I(1)Rb6 pentagonal pyramids,  a cornercorner with one P(7)RbP3 tetrahedra, corners with two equivalent P(8)RbP3 tetrahedra,  a cornercorner with one P(3)RbP3 trigonal pyramid,  a cornercorner with one P(4)RbP3 trigonal pyramid, corners with two equivalent P(2)Rb2P2 trigonal pyramids, and  an edgeedge with one P(4)RbP3 trigonal pyramid. In the fifth P site, P(1) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Rb(1) and two equivalent P(5) atoms. In the sixth P site, P(2) is bonded to two equivalent Rb(2), one P(6), and one P(7) atom to form PRb2P2 trigonal pyramids that share corners with two equivalent I(1)Rb6 pentagonal pyramids, corners with four equivalent P(8)RbP3 tetrahedra, corners with two equivalent P(2)Rb2P2 trigonal pyramids, corners with two equivalent P(3)RbP3 trigonal pyramids, corners with six equivalent P(4)RbP3 trigonal pyramids, and  an edgeedge with one I(1)Rb6 pentagonal pyramid. In the seventh P site, P(3) is bonded to one Rb(1), one P(4), one P(7), and one P(8) atom to form PRbP3 trigonal pyramids that share  a cornercorner with one I(1)Rb6 pentagonal pyramid,  a cornercorner with one P(7)RbP3 tetrahedra,  a cornercorner with one P(8)RbP3 tetrahedra, corners with two equivalent P(6)RbP3 tetrahedra,  a cornercorner with one P(2)Rb2P2 trigonal pyramid,  a cornercorner with one P(4)RbP3 trigonal pyramid, and corners with two equivalent P(3)RbP3 trigonal pyramids. In the eighth P site, P(4) is bonded to one Rb(2), one P(3), one P(4), and one P(6) atom to form distorted PRbP3 trigonal pyramids that share corners with two equivalent I(1)Rb6 pentagonal pyramids,  a cornercorner with one P(6)RbP3 tetrahedra,  a cornercorner with one P(7)RbP3 tetrahedra,  a cornercorner with one P(8)RbP3 tetrahedra,  a cornercorner with one P(3)RbP3 trigonal pyramid, corners with two equivalent P(4)RbP3 trigonal pyramids, corners with three equivalent P(2)Rb2P2 trigonal pyramids, and  an edgeedge with one P(8)RbP3 tetrahedra. I(1) is bonded to two equivalent Rb(1) and four equivalent Rb(2) atoms to form distorted IRb6 pentagonal pyramids that share corners with two equivalent P(6)RbP3 tetrahedra, corners with two equivalent P(7)RbP3 tetrahedra, corners with eight equivalent P(8)RbP3 tetrahedra, corners with four equivalent P(2)Rb2P2 trigonal pyramids, corners with four equivalent P(3)RbP3 trigonal pyramids, corners with eight equivalent P(4)RbP3 trigonal pyramids, edges with two equivalent I(1)Rb6 pentagonal pyramids, and edges with two equivalent P(2)Rb2P2 trigonal pyramids.
Rb4P21I crystallizes in the orthorhombic Cmcm space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 8-coordinate geometry to one P(1), one P(6), one P(7), two equivalent P(3), two equivalent P(5), and one I(1) atom. The Rb(1)-P(1) bond length is 3.37 Å. The Rb(1)-P(6) bond length is 3.38 Å. The Rb(1)-P(7) bond length is 3.55 Å. Both Rb(1)-P(3) bond lengths are 3.53 Å. Both Rb(1)-P(5) bond lengths are 3.84 Å. The Rb(1)-I(1) bond length is 3.81 Å. In the second Rb site, Rb(2) is bonded in a 8-coordinate geometry to two equivalent P(2), two equivalent P(4), two equivalent P(8), and two equivalent I(1) atoms. Both Rb(2)-P(2) bond lengths are 3.59 Å. Both Rb(2)-P(4) bond lengths are 3.85 Å. Both Rb(2)-P(8) bond lengths are 3.71 Å. Both Rb(2)-I(1) bond lengths are 3.88 Å. There are eight inequivalent P sites. In the first P site, P(5) is bonded in a 5-coordinate geometry to two equivalent Rb(1), one P(1), and two equivalent P(8) atoms. The P(5)-P(1) bond length is 2.13 Å. Both P(5)-P(8) bond lengths are 2.22 Å. In the second P site, P(6) is bonded to one Rb(1), one P(2), and two equivalent P(4) atoms to form PRbP3 tetrahedra that share  a cornercorner with one I(1)Rb6 pentagonal pyramid, corners with two equivalent P(7)RbP3 tetrahedra, corners with two equivalent P(4)RbP3 trigonal pyramids, and corners with four equivalent P(3)RbP3 trigonal pyramids. The P(6)-P(2) bond length is 2.15 Å. Both P(6)-P(4) bond lengths are 2.21 Å. In the third P site, P(7) is bonded to one Rb(1), one P(2), and two equivalent P(3) atoms to form PRbP3 tetrahedra that share  a cornercorner with one I(1)Rb6 pentagonal pyramid, corners with two equivalent P(6)RbP3 tetrahedra, corners with two equivalent P(8)RbP3 tetrahedra, corners with two equivalent P(3)RbP3 trigonal pyramids, and corners with two equivalent P(4)RbP3 trigonal pyramids. The P(7)-P(2) bond length is 2.13 Å. Both P(7)-P(3) bond lengths are 2.24 Å. In the fourth P site, P(8) is bonded to one Rb(2), one P(3), one P(5), and one P(8) atom to form PRbP3 tetrahedra that share corners with two equivalent I(1)Rb6 pentagonal pyramids,  a cornercorner with one P(7)RbP3 tetrahedra, corners with two equivalent P(8)RbP3 tetrahedra,  a cornercorner with one P(3)RbP3 trigonal pyramid,  a cornercorner with one P(4)RbP3 trigonal pyramid, corners with two equivalent P(2)Rb2P2 trigonal pyramids, and  an edgeedge with one P(4)RbP3 trigonal pyramid. The P(8)-P(3) bond length is 2.18 Å. The P(8)-P(8) bond length is 2.26 Å. In the fifth P site, P(1) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Rb(1) and two equivalent P(5) atoms. In the sixth P site, P(2) is bonded to two equivalent Rb(2), one P(6), and one P(7) atom to form PRb2P2 trigonal pyramids that share corners with two equivalent I(1)Rb6 pentagonal pyramids, corners with four equivalent P(8)RbP3 tetrahedra, corners with two equivalent P(2)Rb2P2 trigonal pyramids, corners with two equivalent P(3)RbP3 trigonal pyramids, corners with six equivalent P(4)RbP3 trigonal pyramids, and  an edgeedge with one I(1)Rb6 pentagonal pyramid. In the seventh P site, P(3) is bonded to one Rb(1), one P(4), one P(7), and one P(8) atom to form PRbP3 trigonal pyramids that share  a cornercorner with one I(1)Rb6 pentagonal pyramid,  a cornercorner with one P(7)RbP3 tetrahedra,  a cornercorner with one P(8)RbP3 tetrahedra, corners with two equivalent P(6)RbP3 tetrahedra,  a cornercorner with one P(2)Rb2P2 trigonal pyramid,  a cornercorner with one P(4)RbP3 trigonal pyramid, and corners with two equivalent P(3)RbP3 trigonal pyramids. The P(3)-P(4) bond length is 2.22 Å. In the eighth P site, P(4) is bonded to one Rb(2), one P(3), one P(4), and one P(6) atom to form distorted PRbP3 trigonal pyramids that share corners with two equivalent I(1)Rb6 pentagonal pyramids,  a cornercorner with one P(6)RbP3 tetrahedra,  a cornercorner with one P(7)RbP3 tetrahedra,  a cornercorner with one P(8)RbP3 tetrahedra,  a cornercorner with one P(3)RbP3 trigonal pyramid, corners with two equivalent P(4)RbP3 trigonal pyramids, corners with three equivalent P(2)Rb2P2 trigonal pyramids, and  an edgeedge with one P(8)RbP3 tetrahedra. The P(4)-P(4) bond length is 2.24 Å. I(1) is bonded to two equivalent Rb(1) and four equivalent Rb(2) atoms to form distorted IRb6 pentagonal pyramids that share corners with two equivalent P(6)RbP3 tetrahedra, corners with two equivalent P(7)RbP3 tetrahedra, corners with eight equivalent P(8)RbP3 tetrahedra, corners with four equivalent P(2)Rb2P2 trigonal pyramids, corners with four equivalent P(3)RbP3 trigonal pyramids, corners with eight equivalent P(4)RbP3 trigonal pyramids, edges with two equivalent I(1)Rb6 pentagonal pyramids, and edges with two equivalent P(2)Rb2P2 trigonal pyramids.