The material described by Ca2H2S2O9 crystallizes in the monoclinic C2 space group. There are four inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent O(1), two equivalent O(11), two equivalent O(5), and two equivalent O(9) atoms to form distorted CaO8 hexagonal bipyramids that share corners with two equivalent S(1)O4 tetrahedra, corners with two equivalent S(3)O4 tetrahedra, edges with two equivalent Ca(3)O8 hexagonal bipyramids, and edges with two equivalent S(2)O4 tetrahedra. In the second Ca site, Ca(2) is bonded in a 10-coordinate geometry to two equivalent H(1), two equivalent O(10), two equivalent O(12), two equivalent O(2), and two equivalent O(6) atoms. In the third Ca site, Ca(3) is bonded to one O(12), one O(2), one O(5), one O(9), two equivalent O(4), and two equivalent O(7) atoms to form distorted CaO8 hexagonal bipyramids that share corners with two equivalent S(2)O4 tetrahedra, corners with two equivalent S(3)O4 tetrahedra,  an edgeedge with one Ca(1)O8 hexagonal bipyramid, edges with two equivalent Ca(3)O8 hexagonal bipyramids,  an edgeedge with one S(1)O4 tetrahedra, and  an edgeedge with one S(3)O4 tetrahedra. In the fourth Ca site, Ca(4) is bonded in a 10-coordinate geometry to one H(2), one H(3), one O(1), one O(10), one O(11), one O(6), two equivalent O(3), and two equivalent O(8) atoms. There are three inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one Ca(2) and one O(13) atom. In the second H site, H(2) is bonded in a single-bond geometry to one Ca(4) and one O(14) atom. In the third H site, H(3) is bonded in a single-bond geometry to one Ca(4) and one O(14) atom. There are three inequivalent S sites. In the first S site, S(1) is bonded to one O(2), one O(3), one O(8), and one O(9) atom to form SO4 tetrahedra that share  a cornercorner with one Ca(1)O8 hexagonal bipyramid and  an edgeedge with one Ca(3)O8 hexagonal bipyramid. In the second S site, S(2) is bonded to one O(11), one O(12), one O(5), and one O(6) atom to form SO4 tetrahedra that share corners with two equivalent Ca(3)O8 hexagonal bipyramids and  an edgeedge with one Ca(1)O8 hexagonal bipyramid. In the third S site, S(3) is bonded to one O(1), one O(10), one O(4), and one O(7) atom to form SO4 tetrahedra that share  a cornercorner with one Ca(1)O8 hexagonal bipyramid, corners with two equivalent Ca(3)O8 hexagonal bipyramids, and  an edgeedge with one Ca(3)O8 hexagonal bipyramid. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(4), and one S(3) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ca(2), one Ca(3), and one S(1) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to two equivalent Ca(4) and one S(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Ca(3) and one S(3) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(3), and one S(2) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Ca(2), one Ca(4), and one S(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to two equivalent Ca(3) and one S(3) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to two equivalent Ca(4) and one S(1) atom. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(3), and one S(1) atom. In the tenth O site, O(10) is bonded in a 3-coordinate geometry to one Ca(2), one Ca(4), and one S(3) atom. In the eleventh O site, O(11) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(4), and one S(2) atom. In the twelfth O site, O(12) is bonded in a 3-coordinate geometry to one Ca(2), one Ca(3), and one S(2) atom. In the thirteenth O site, O(13) is bonded in a water-like geometry to two equivalent H(1) atoms. In the fourteenth O site, O(14) is bonded in a water-like geometry to one H(2) and one H(3) atom. is represented by the CIF file [CIF]
data_Ca2H2S2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.553
_cell_length_b   9.553
_cell_length_c   12.395
_cell_angle_alpha   49.602
_cell_angle_beta   49.602
_cell_angle_gamma   43.956
_symmetry_Int_Tables_number   1
_cell_volume   561.564
_cell_formula_units_Z   3
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  Ca  Ca0  1  0.464  0.536  0.000  1.0
  Ca  Ca1  1  0.004  0.996  0.500  1.0
  Ca  Ca2  1  0.096  0.566  0.432  1.0
  Ca  Ca3  1  0.434  0.904  0.568  1.0
  Ca  Ca4  1  0.917  0.413  0.083  1.0
  Ca  Ca5  1  0.587  0.083  0.917  1.0
  H  H6  1  0.647  0.351  0.437  1.0
  H  H7  1  0.649  0.353  0.563  1.0
  H  H8  1  0.997  0.336  0.875  1.0
  H  H9  1  0.664  0.003  0.125  1.0
  H  H10  1  0.188  0.144  0.939  1.0
  H  H11  1  0.856  0.812  0.061  1.0
  S  S12  1  0.191  0.644  0.811  1.0
  S  S13  1  0.356  0.809  0.189  1.0
  S  S14  1  0.206  0.296  0.250  1.0
  S  S15  1  0.704  0.794  0.750  1.0
  S  S16  1  0.855  0.313  0.689  1.0
  S  S17  1  0.687  0.145  0.311  1.0
  O  O18  1  0.700  0.263  0.152  1.0
  O  O19  1  0.737  0.300  0.848  1.0
  O  O20  1  0.213  0.760  0.649  1.0
  O  O21  1  0.240  0.787  0.351  1.0
  O  O22  1  0.588  0.710  0.146  1.0
  O  O23  1  0.290  0.412  0.854  1.0
  O  O24  1  0.089  0.216  0.641  1.0
  O  O25  1  0.784  0.911  0.359  1.0
  O  O26  1  0.159  0.477  0.255  1.0
  O  O27  1  0.523  0.841  0.745  1.0
  O  O28  1  0.656  0.977  0.754  1.0
  O  O29  1  0.023  0.344  0.246  1.0
  O  O30  1  0.458  0.228  0.415  1.0
  O  O31  1  0.772  0.542  0.585  1.0
  O  O32  1  0.959  0.725  0.910  1.0
  O  O33  1  0.275  0.041  0.090  1.0
  O  O34  1  0.316  0.704  0.168  1.0
  O  O35  1  0.296  0.684  0.832  1.0
  O  O36  1  0.821  0.196  0.674  1.0
  O  O37  1  0.804  0.179  0.326  1.0
  O  O38  1  0.745  0.603  0.891  1.0
  O  O39  1  0.397  0.255  0.109  1.0
  O  O40  1  0.256  0.100  0.386  1.0
  O  O41  1  0.900  0.744  0.614  1.0
  O  O42  1  0.568  0.432  0.500  1.0
  O  O43  1  0.134  0.201  0.867  1.0
  O  O44  1  0.799  0.866  0.133  1.0
[/CIF]
.
The material described by Ca2H2S2O9 crystallizes in the monoclinic C2 space group. There are four inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent O(1), two equivalent O(11), two equivalent O(5), and two equivalent O(9) atoms to form distorted CaO8 hexagonal bipyramids that share corners with two equivalent S(1)O4 tetrahedra, corners with two equivalent S(3)O4 tetrahedra, edges with two equivalent Ca(3)O8 hexagonal bipyramids, and edges with two equivalent S(2)O4 tetrahedra. In the second Ca site, Ca(2) is bonded in a 10-coordinate geometry to two equivalent H(1), two equivalent O(10), two equivalent O(12), two equivalent O(2), and two equivalent O(6) atoms. In the third Ca site, Ca(3) is bonded to one O(12), one O(2), one O(5), one O(9), two equivalent O(4), and two equivalent O(7) atoms to form distorted CaO8 hexagonal bipyramids that share corners with two equivalent S(2)O4 tetrahedra, corners with two equivalent S(3)O4 tetrahedra,  an edgeedge with one Ca(1)O8 hexagonal bipyramid, edges with two equivalent Ca(3)O8 hexagonal bipyramids,  an edgeedge with one S(1)O4 tetrahedra, and  an edgeedge with one S(3)O4 tetrahedra. In the fourth Ca site, Ca(4) is bonded in a 10-coordinate geometry to one H(2), one H(3), one O(1), one O(10), one O(11), one O(6), two equivalent O(3), and two equivalent O(8) atoms. There are three inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one Ca(2) and one O(13) atom. In the second H site, H(2) is bonded in a single-bond geometry to one Ca(4) and one O(14) atom. In the third H site, H(3) is bonded in a single-bond geometry to one Ca(4) and one O(14) atom. There are three inequivalent S sites. In the first S site, S(1) is bonded to one O(2), one O(3), one O(8), and one O(9) atom to form SO4 tetrahedra that share  a cornercorner with one Ca(1)O8 hexagonal bipyramid and  an edgeedge with one Ca(3)O8 hexagonal bipyramid. In the second S site, S(2) is bonded to one O(11), one O(12), one O(5), and one O(6) atom to form SO4 tetrahedra that share corners with two equivalent Ca(3)O8 hexagonal bipyramids and  an edgeedge with one Ca(1)O8 hexagonal bipyramid. In the third S site, S(3) is bonded to one O(1), one O(10), one O(4), and one O(7) atom to form SO4 tetrahedra that share  a cornercorner with one Ca(1)O8 hexagonal bipyramid, corners with two equivalent Ca(3)O8 hexagonal bipyramids, and  an edgeedge with one Ca(3)O8 hexagonal bipyramid. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(4), and one S(3) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ca(2), one Ca(3), and one S(1) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to two equivalent Ca(4) and one S(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Ca(3) and one S(3) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(3), and one S(2) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Ca(2), one Ca(4), and one S(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to two equivalent Ca(3) and one S(3) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to two equivalent Ca(4) and one S(1) atom. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(3), and one S(1) atom. In the tenth O site, O(10) is bonded in a 3-coordinate geometry to one Ca(2), one Ca(4), and one S(3) atom. In the eleventh O site, O(11) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(4), and one S(2) atom. In the twelfth O site, O(12) is bonded in a 3-coordinate geometry to one Ca(2), one Ca(3), and one S(2) atom. In the thirteenth O site, O(13) is bonded in a water-like geometry to two equivalent H(1) atoms. In the fourteenth O site, O(14) is bonded in a water-like geometry to one H(2) and one H(3) atom. is represented by the CIF file [CIF]
data_Ca2H2S2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.553
_cell_length_b   9.553
_cell_length_c   12.395
_cell_angle_alpha   49.602
_cell_angle_beta   49.602
_cell_angle_gamma   43.956
_symmetry_Int_Tables_number   1
_cell_volume   561.564
_cell_formula_units_Z   3
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  Ca  Ca0  1  0.464  0.536  0.000  1.0
  Ca  Ca1  1  0.004  0.996  0.500  1.0
  Ca  Ca2  1  0.096  0.566  0.432  1.0
  Ca  Ca3  1  0.434  0.904  0.568  1.0
  Ca  Ca4  1  0.917  0.413  0.083  1.0
  Ca  Ca5  1  0.587  0.083  0.917  1.0
  H  H6  1  0.647  0.351  0.437  1.0
  H  H7  1  0.649  0.353  0.563  1.0
  H  H8  1  0.997  0.336  0.875  1.0
  H  H9  1  0.664  0.003  0.125  1.0
  H  H10  1  0.188  0.144  0.939  1.0
  H  H11  1  0.856  0.812  0.061  1.0
  S  S12  1  0.191  0.644  0.811  1.0
  S  S13  1  0.356  0.809  0.189  1.0
  S  S14  1  0.206  0.296  0.250  1.0
  S  S15  1  0.704  0.794  0.750  1.0
  S  S16  1  0.855  0.313  0.689  1.0
  S  S17  1  0.687  0.145  0.311  1.0
  O  O18  1  0.700  0.263  0.152  1.0
  O  O19  1  0.737  0.300  0.848  1.0
  O  O20  1  0.213  0.760  0.649  1.0
  O  O21  1  0.240  0.787  0.351  1.0
  O  O22  1  0.588  0.710  0.146  1.0
  O  O23  1  0.290  0.412  0.854  1.0
  O  O24  1  0.089  0.216  0.641  1.0
  O  O25  1  0.784  0.911  0.359  1.0
  O  O26  1  0.159  0.477  0.255  1.0
  O  O27  1  0.523  0.841  0.745  1.0
  O  O28  1  0.656  0.977  0.754  1.0
  O  O29  1  0.023  0.344  0.246  1.0
  O  O30  1  0.458  0.228  0.415  1.0
  O  O31  1  0.772  0.542  0.585  1.0
  O  O32  1  0.959  0.725  0.910  1.0
  O  O33  1  0.275  0.041  0.090  1.0
  O  O34  1  0.316  0.704  0.168  1.0
  O  O35  1  0.296  0.684  0.832  1.0
  O  O36  1  0.821  0.196  0.674  1.0
  O  O37  1  0.804  0.179  0.326  1.0
  O  O38  1  0.745  0.603  0.891  1.0
  O  O39  1  0.397  0.255  0.109  1.0
  O  O40  1  0.256  0.100  0.386  1.0
  O  O41  1  0.900  0.744  0.614  1.0
  O  O42  1  0.568  0.432  0.500  1.0
  O  O43  1  0.134  0.201  0.867  1.0
  O  O44  1  0.799  0.866  0.133  1.0
[/CIF]
.