Ca2S2O9 crystallizes in the trigonal P3_121 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. In the second Ca site, Ca(2) is bonded in a 9-coordinate geometry to one O(1), two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. S(1) is bonded in a tetrahedral geometry to one O(2), one O(3), one O(4), and one O(5) atom. There are five inequivalent O sites. In the first O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one S(1) atom. In the second O site, O(1) is bonded in a single-bond geometry to one Ca(2) atom. In the third O site, O(2) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one S(1) atom. In the fourth O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one S(1) atom. In the fifth O site, O(4) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one S(1) atom.
Ca2S2O9 crystallizes in the trigonal P3_121 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. Both Ca(1)-O(2) bond lengths are 2.43 Å. Both Ca(1)-O(3) bond lengths are 2.42 Å. Both Ca(1)-O(4) bond lengths are 2.51 Å. Both Ca(1)-O(5) bond lengths are 2.67 Å. In the second Ca site, Ca(2) is bonded in a 9-coordinate geometry to one O(1), two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. The Ca(2)-O(1) bond length is 2.49 Å. Both Ca(2)-O(2) bond lengths are 2.55 Å. Both Ca(2)-O(3) bond lengths are 2.63 Å. Both Ca(2)-O(4) bond lengths are 2.46 Å. Both Ca(2)-O(5) bond lengths are 2.43 Å. S(1) is bonded in a tetrahedral geometry to one O(2), one O(3), one O(4), and one O(5) atom. The S(1)-O(2) bond length is 1.49 Å. The S(1)-O(3) bond length is 1.49 Å. The S(1)-O(4) bond length is 1.50 Å. The S(1)-O(5) bond length is 1.48 Å. There are five inequivalent O sites. In the first O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one S(1) atom. In the second O site, O(1) is bonded in a single-bond geometry to one Ca(2) atom. In the third O site, O(2) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one S(1) atom. In the fourth O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one S(1) atom. In the fifth O site, O(4) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one S(1) atom.