Sr2P7I crystallizes in the cubic P2_13 space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 13-coordinate geometry to six equivalent P(2), six equivalent P(3), and one I(1) atom. In the second Sr site, Sr(2) is bonded in a 7-coordinate geometry to one P(1), three equivalent P(2), and three equivalent I(1) atoms. There are three inequivalent P sites. In the first P site, P(1) is bonded to one Sr(2) and three equivalent P(2) atoms to form PSrP3 tetrahedra that share corners with three equivalent P(2)Sr3P2 square pyramids and corners with three equivalent I(1)Sr4 trigonal pyramids. In the second P site, P(2) is bonded to one Sr(2), two equivalent Sr(1), one P(1), and one P(3) atom to form distorted PSr3P2 square pyramids that share corners with six equivalent P(2)Sr3P2 square pyramids,  a cornercorner with one P(1)SrP3 tetrahedra, corners with three equivalent I(1)Sr4 trigonal pyramids, edges with four equivalent P(2)Sr3P2 square pyramids, and  an edgeedge with one I(1)Sr4 trigonal pyramid. In the third P site, P(3) is bonded in a 5-coordinate geometry to two equivalent Sr(1), one P(2), and two equivalent P(3) atoms. I(1) is bonded to one Sr(1) and three equivalent Sr(2) atoms to form ISr4 trigonal pyramids that share corners with nine equivalent P(2)Sr3P2 square pyramids, corners with three equivalent P(1)SrP3 tetrahedra, corners with six equivalent I(1)Sr4 trigonal pyramids, and edges with three equivalent P(2)Sr3P2 square pyramids.
Sr2P7I crystallizes in the cubic P2_13 space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 13-coordinate geometry to six equivalent P(2), six equivalent P(3), and one I(1) atom. There are three shorter (3.19 Å) and three longer (3.23 Å) Sr(1)-P(2) bond lengths. There are three shorter (3.37 Å) and three longer (3.38 Å) Sr(1)-P(3) bond lengths. The Sr(1)-I(1) bond length is 3.37 Å. In the second Sr site, Sr(2) is bonded in a 7-coordinate geometry to one P(1), three equivalent P(2), and three equivalent I(1) atoms. The Sr(2)-P(1) bond length is 3.18 Å. All Sr(2)-P(2) bond lengths are 3.24 Å. All Sr(2)-I(1) bond lengths are 3.59 Å. There are three inequivalent P sites. In the first P site, P(1) is bonded to one Sr(2) and three equivalent P(2) atoms to form PSrP3 tetrahedra that share corners with three equivalent P(2)Sr3P2 square pyramids and corners with three equivalent I(1)Sr4 trigonal pyramids. All P(1)-P(2) bond lengths are 2.18 Å. In the second P site, P(2) is bonded to one Sr(2), two equivalent Sr(1), one P(1), and one P(3) atom to form distorted PSr3P2 square pyramids that share corners with six equivalent P(2)Sr3P2 square pyramids,  a cornercorner with one P(1)SrP3 tetrahedra, corners with three equivalent I(1)Sr4 trigonal pyramids, edges with four equivalent P(2)Sr3P2 square pyramids, and  an edgeedge with one I(1)Sr4 trigonal pyramid. The P(2)-P(3) bond length is 2.15 Å. In the third P site, P(3) is bonded in a 5-coordinate geometry to two equivalent Sr(1), one P(2), and two equivalent P(3) atoms. Both P(3)-P(3) bond lengths are 2.27 Å. I(1) is bonded to one Sr(1) and three equivalent Sr(2) atoms to form ISr4 trigonal pyramids that share corners with nine equivalent P(2)Sr3P2 square pyramids, corners with three equivalent P(1)SrP3 tetrahedra, corners with six equivalent I(1)Sr4 trigonal pyramids, and edges with three equivalent P(2)Sr3P2 square pyramids.