The structure described by CaH4Se2O7 crystallizes in the triclinic P-1 space group. Ca(1) is bonded in a 8-coordinate geometry to one O(3), one O(4), one O(5), one O(6), two equivalent O(1), and two equivalent O(2) atoms. There are four inequivalent H sites. In the first H site, H(1) is bonded in a linear geometry to one O(3) and one O(7) atom. In the second H site, H(2) is bonded in a distorted linear geometry to one O(5) and one O(6) atom. In the third H site, H(3) is bonded in a single-bond geometry to one O(4) and one O(7) atom. In the fourth H site, H(4) is bonded in a single-bond geometry to one O(7) atom. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a trigonal non-coplanar geometry to one O(1), one O(2), and one O(3) atom. In the second Se site, Se(2) is bonded in a distorted trigonal non-coplanar geometry to one O(4), one O(5), and one O(6) atom. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Ca(1) and one Se(1) atom. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Ca(1) and one Se(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Ca(1), one H(1), and one Se(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Ca(1), one H(3), and one Se(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Ca(1), one H(2), and one Se(2) atom. In the sixth O site, O(6) is bonded in a distorted single-bond geometry to one Ca(1), one H(2), and one Se(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to one H(1), one H(3), and one H(4) atom. is represented by the CIF file [CIF]
data_CaH4Se2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.861
_cell_length_b   7.034
_cell_length_c   7.457
_cell_angle_alpha   71.707
_cell_angle_beta   89.045
_cell_angle_gamma   88.399
_symmetry_Int_Tables_number   1
_cell_volume   341.539
_cell_formula_units_Z   2
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  0.125  0.771  0.925  1.0
  Ca  Ca1  1  0.875  0.229  0.075  1.0
  H  H2  1  0.531  0.760  0.735  1.0
  H  H3  1  0.469  0.240  0.265  1.0
  H  H4  1  0.016  0.545  0.655  1.0
  H  H5  1  0.984  0.455  0.345  1.0
  H  H6  1  0.699  0.792  0.479  1.0
  H  H7  1  0.301  0.208  0.521  1.0
  H  H8  1  0.654  0.572  0.601  1.0
  H  H9  1  0.346  0.428  0.399  1.0
  Se  Se10  1  0.659  0.750  0.038  1.0
  Se  Se11  1  0.341  0.250  0.962  1.0
  Se  Se12  1  0.131  0.821  0.396  1.0
  Se  Se13  1  0.869  0.179  0.604  1.0
  O  O14  1  0.797  0.958  0.954  1.0
  O  O15  1  0.203  0.042  0.046  1.0
  O  O16  1  0.815  0.586  0.984  1.0
  O  O17  1  0.185  0.414  0.016  1.0
  O  O18  1  0.474  0.787  0.856  1.0
  O  O19  1  0.526  0.213  0.144  1.0
  O  O20  1  0.101  0.082  0.645  1.0
  O  O21  1  0.899  0.918  0.355  1.0
  O  O22  1  0.141  0.638  0.286  1.0
  O  O23  1  0.859  0.362  0.714  1.0
  O  O24  1  0.110  0.659  0.641  1.0
  O  O25  1  0.890  0.341  0.359  1.0
  O  O26  1  0.592  0.708  0.555  1.0
  O  O27  1  0.408  0.292  0.445  1.0
[/CIF]
.
The structure described by CaH4Se2O7 crystallizes in the triclinic P-1 space group. Ca(1) is bonded in a 8-coordinate geometry to one O(3), one O(4), one O(5), one O(6), two equivalent O(1), and two equivalent O(2) atoms. There are four inequivalent H sites. In the first H site, H(1) is bonded in a linear geometry to one O(3) and one O(7) atom. In the second H site, H(2) is bonded in a distorted linear geometry to one O(5) and one O(6) atom. In the third H site, H(3) is bonded in a single-bond geometry to one O(4) and one O(7) atom. In the fourth H site, H(4) is bonded in a single-bond geometry to one O(7) atom. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a trigonal non-coplanar geometry to one O(1), one O(2), and one O(3) atom. In the second Se site, Se(2) is bonded in a distorted trigonal non-coplanar geometry to one O(4), one O(5), and one O(6) atom. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Ca(1) and one Se(1) atom. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Ca(1) and one Se(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Ca(1), one H(1), and one Se(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Ca(1), one H(3), and one Se(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Ca(1), one H(2), and one Se(2) atom. In the sixth O site, O(6) is bonded in a distorted single-bond geometry to one Ca(1), one H(2), and one Se(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to one H(1), one H(3), and one H(4) atom. is represented by the CIF file [CIF]
data_CaH4Se2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.861
_cell_length_b   7.034
_cell_length_c   7.457
_cell_angle_alpha   71.707
_cell_angle_beta   89.045
_cell_angle_gamma   88.399
_symmetry_Int_Tables_number   1
_cell_volume   341.539
_cell_formula_units_Z   2
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  0.125  0.771  0.925  1.0
  Ca  Ca1  1  0.875  0.229  0.075  1.0
  H  H2  1  0.531  0.760  0.735  1.0
  H  H3  1  0.469  0.240  0.265  1.0
  H  H4  1  0.016  0.545  0.655  1.0
  H  H5  1  0.984  0.455  0.345  1.0
  H  H6  1  0.699  0.792  0.479  1.0
  H  H7  1  0.301  0.208  0.521  1.0
  H  H8  1  0.654  0.572  0.601  1.0
  H  H9  1  0.346  0.428  0.399  1.0
  Se  Se10  1  0.659  0.750  0.038  1.0
  Se  Se11  1  0.341  0.250  0.962  1.0
  Se  Se12  1  0.131  0.821  0.396  1.0
  Se  Se13  1  0.869  0.179  0.604  1.0
  O  O14  1  0.797  0.958  0.954  1.0
  O  O15  1  0.203  0.042  0.046  1.0
  O  O16  1  0.815  0.586  0.984  1.0
  O  O17  1  0.185  0.414  0.016  1.0
  O  O18  1  0.474  0.787  0.856  1.0
  O  O19  1  0.526  0.213  0.144  1.0
  O  O20  1  0.101  0.082  0.645  1.0
  O  O21  1  0.899  0.918  0.355  1.0
  O  O22  1  0.141  0.638  0.286  1.0
  O  O23  1  0.859  0.362  0.714  1.0
  O  O24  1  0.110  0.659  0.641  1.0
  O  O25  1  0.890  0.341  0.359  1.0
  O  O26  1  0.592  0.708  0.555  1.0
  O  O27  1  0.408  0.292  0.445  1.0
[/CIF]
.