Ca2IrO4 crystallizes in the hexagonal P-62m space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to six equivalent O(1) atoms to form distorted CaO6 pentagonal pyramids that share corners with six equivalent Ir(1)O6 octahedra, edges with three equivalent Ir(1)O6 octahedra, and faces with two equivalent Ca(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 7°. In the second Ca site, Ca(2) is bonded in a 9-coordinate geometry to three equivalent O(2) and six equivalent O(3) atoms. In the third Ca site, Ca(3) is bonded in a 7-coordinate geometry to one O(2), two equivalent O(1), and four equivalent O(3) atoms. Ir(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form IrO6 octahedra that share corners with two equivalent Ca(1)O6 pentagonal pyramids, edges with two equivalent Ir(1)O6 octahedra, and  an edgeedge with one Ca(1)O6 pentagonal pyramid. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ca(1), two equivalent Ca(3), and two equivalent Ir(1) atoms to form OCa4Ir2 octahedra that share corners with four equivalent O(1)Ca4Ir2 octahedra, corners with four equivalent O(3)Ca4Ir trigonal bipyramids, edges with two equivalent O(1)Ca4Ir2 octahedra, edges with four equivalent O(3)Ca4Ir trigonal bipyramids, and faces with two equivalent O(1)Ca4Ir2 octahedra. The corner-sharing octahedral tilt angles are 43°. In the second O site, O(2) is bonded in a 5-coordinate geometry to one Ca(3), two equivalent Ca(2), and two equivalent Ir(1) atoms. In the third O site, O(3) is bonded to two equivalent Ca(2), two equivalent Ca(3), and one Ir(1) atom to form distorted OCa4Ir trigonal bipyramids that share corners with two equivalent O(1)Ca4Ir2 octahedra, corners with seven equivalent O(3)Ca4Ir trigonal bipyramids, edges with two equivalent O(1)Ca4Ir2 octahedra, and edges with five equivalent O(3)Ca4Ir trigonal bipyramids. The corner-sharing octahedral tilt angles are 61°.
Ca2IrO4 crystallizes in the hexagonal P-62m space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to six equivalent O(1) atoms to form distorted CaO6 pentagonal pyramids that share corners with six equivalent Ir(1)O6 octahedra, edges with three equivalent Ir(1)O6 octahedra, and faces with two equivalent Ca(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 7°. All Ca(1)-O(1) bond lengths are 2.38 Å. In the second Ca site, Ca(2) is bonded in a 9-coordinate geometry to three equivalent O(2) and six equivalent O(3) atoms. All Ca(2)-O(2) bond lengths are 2.82 Å. All Ca(2)-O(3) bond lengths are 2.47 Å. In the third Ca site, Ca(3) is bonded in a 7-coordinate geometry to one O(2), two equivalent O(1), and four equivalent O(3) atoms. The Ca(3)-O(2) bond length is 2.29 Å. Both Ca(3)-O(1) bond lengths are 2.65 Å. All Ca(3)-O(3) bond lengths are 2.34 Å. Ir(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form IrO6 octahedra that share corners with two equivalent Ca(1)O6 pentagonal pyramids, edges with two equivalent Ir(1)O6 octahedra, and  an edgeedge with one Ca(1)O6 pentagonal pyramid. Both Ir(1)-O(1) bond lengths are 2.10 Å. Both Ir(1)-O(2) bond lengths are 2.02 Å. Both Ir(1)-O(3) bond lengths are 2.04 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ca(1), two equivalent Ca(3), and two equivalent Ir(1) atoms to form OCa4Ir2 octahedra that share corners with four equivalent O(1)Ca4Ir2 octahedra, corners with four equivalent O(3)Ca4Ir trigonal bipyramids, edges with two equivalent O(1)Ca4Ir2 octahedra, edges with four equivalent O(3)Ca4Ir trigonal bipyramids, and faces with two equivalent O(1)Ca4Ir2 octahedra. The corner-sharing octahedral tilt angles are 43°. In the second O site, O(2) is bonded in a 5-coordinate geometry to one Ca(3), two equivalent Ca(2), and two equivalent Ir(1) atoms. In the third O site, O(3) is bonded to two equivalent Ca(2), two equivalent Ca(3), and one Ir(1) atom to form distorted OCa4Ir trigonal bipyramids that share corners with two equivalent O(1)Ca4Ir2 octahedra, corners with seven equivalent O(3)Ca4Ir trigonal bipyramids, edges with two equivalent O(1)Ca4Ir2 octahedra, and edges with five equivalent O(3)Ca4Ir trigonal bipyramids. The corner-sharing octahedral tilt angles are 61°.