Sr3Ir2O7 crystallizes in the monoclinic C2/m space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to four equivalent O(2) and eight equivalent O(3) atoms to form distorted SrO12 cuboctahedra that share corners with four equivalent Sr(1)O12 cuboctahedra, faces with four equivalent Sr(1)O12 cuboctahedra, and faces with eight equivalent Ir(1)O6 octahedra. In the second Sr site, Sr(2) is bonded in a 9-coordinate geometry to four equivalent O(3) and five equivalent O(1) atoms. Ir(1) is bonded to one O(1), one O(2), and four equivalent O(3) atoms to form IrO6 octahedra that share corners with five equivalent Ir(1)O6 octahedra and faces with four equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-16°. There are three inequivalent O sites. In the first O site, O(1) is bonded to five equivalent Sr(2) and one Ir(1) atom to form distorted OSr5Ir octahedra that share  a cornercorner with one O(2)Sr4Ir2 octahedra, corners with four equivalent O(1)Sr5Ir octahedra, and edges with eight equivalent O(1)Sr5Ir octahedra. The corner-sharing octahedral tilt angles range from 1-10°. In the second O site, O(2) is bonded to four equivalent Sr(1) and two equivalent Ir(1) atoms to form distorted OSr4Ir2 octahedra that share corners with two equivalent O(1)Sr5Ir octahedra, corners with four equivalent O(2)Sr4Ir2 octahedra, and edges with four equivalent O(2)Sr4Ir2 octahedra. The corner-sharing octahedral tilt angles range from 0-1°. In the third O site, O(3) is bonded in a 6-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Ir(1) atoms.
Sr3Ir2O7 crystallizes in the monoclinic C2/m space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to four equivalent O(2) and eight equivalent O(3) atoms to form distorted SrO12 cuboctahedra that share corners with four equivalent Sr(1)O12 cuboctahedra, faces with four equivalent Sr(1)O12 cuboctahedra, and faces with eight equivalent Ir(1)O6 octahedra. There are two shorter (2.75 Å) and two longer (2.90 Å) Sr(1)-O(2) bond lengths. There are four shorter (2.64 Å) and four longer (3.07 Å) Sr(1)-O(3) bond lengths. In the second Sr site, Sr(2) is bonded in a 9-coordinate geometry to four equivalent O(3) and five equivalent O(1) atoms. There are two shorter (2.53 Å) and two longer (2.88 Å) Sr(2)-O(3) bond lengths. There are a spread of Sr(2)-O(1) bond distances ranging from 2.47-2.91 Å. Ir(1) is bonded to one O(1), one O(2), and four equivalent O(3) atoms to form IrO6 octahedra that share corners with five equivalent Ir(1)O6 octahedra and faces with four equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-16°. The Ir(1)-O(1) bond length is 2.03 Å. The Ir(1)-O(2) bond length is 2.04 Å. There are two shorter (2.00 Å) and two longer (2.04 Å) Ir(1)-O(3) bond lengths. There are three inequivalent O sites. In the first O site, O(1) is bonded to five equivalent Sr(2) and one Ir(1) atom to form distorted OSr5Ir octahedra that share  a cornercorner with one O(2)Sr4Ir2 octahedra, corners with four equivalent O(1)Sr5Ir octahedra, and edges with eight equivalent O(1)Sr5Ir octahedra. The corner-sharing octahedral tilt angles range from 1-10°. In the second O site, O(2) is bonded to four equivalent Sr(1) and two equivalent Ir(1) atoms to form distorted OSr4Ir2 octahedra that share corners with two equivalent O(1)Sr5Ir octahedra, corners with four equivalent O(2)Sr4Ir2 octahedra, and edges with four equivalent O(2)Sr4Ir2 octahedra. The corner-sharing octahedral tilt angles range from 0-1°. In the third O site, O(3) is bonded in a 6-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Ir(1) atoms.