The compound described by CaSe2O7 crystallizes in the triclinic P-1 space group. Ca(1) is bonded to one O(3), one O(4), one O(5), one O(6), and two equivalent O(2) atoms to form distorted CaO6 octahedra that share corners with three equivalent Se(2)O4 tetrahedra and  an edgeedge with one Ca(1)O6 octahedra. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(3), and one O(7) atom. In the second Se site, Se(2) is bonded to one O(1), one O(4), one O(5), and one O(6) atom to form SeO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 35-55°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one Se(1) and one Se(2) 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 bent 150 degrees geometry to one Ca(1) and one Se(1) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to one Ca(1) and one Se(2) atom. In the fifth O site, O(5) is bonded in a bent 120 degrees geometry to one Ca(1) and one Se(2) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Ca(1) and one Se(2) atom. In the seventh O site, O(7) is bonded in a single-bond geometry to one Se(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_CaSe2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.245
_cell_length_b   7.269
_cell_length_c   7.293
_cell_angle_alpha   80.863
_cell_angle_beta   71.977
_cell_angle_gamma   85.067
_symmetry_Int_Tables_number   1
_cell_volume   360.306
_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  0.729  0.848  0.381  1.0
  Ca  Ca1  1  0.271  0.152  0.619  1.0
  Se  Se2  1  0.655  0.370  0.259  1.0
  Se  Se3  1  0.345  0.630  0.741  1.0
  Se  Se4  1  0.847  0.872  0.863  1.0
  Se  Se5  1  0.153  0.128  0.137  1.0
  O  O6  1  0.990  0.290  0.088  1.0
  O  O7  1  0.010  0.710  0.912  1.0
  O  O8  1  0.616  0.167  0.414  1.0
  O  O9  1  0.384  0.833  0.586  1.0
  O  O10  1  0.735  0.522  0.368  1.0
  O  O11  1  0.265  0.478  0.632  1.0
  O  O12  1  0.946  0.071  0.741  1.0
  O  O13  1  0.054  0.929  0.259  1.0
  O  O14  1  0.680  0.904  0.072  1.0
  O  O15  1  0.320  0.096  0.928  1.0
  O  O16  1  0.739  0.806  0.707  1.0
  O  O17  1  0.261  0.194  0.293  1.0
  O  O18  1  0.416  0.462  0.290  1.0
  O  O19  1  0.584  0.538  0.710  1.0
[/CIF]
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The compound described by CaSe2O7 crystallizes in the triclinic P-1 space group. Ca(1) is bonded to one O(3), one O(4), one O(5), one O(6), and two equivalent O(2) atoms to form distorted CaO6 octahedra that share corners with three equivalent Se(2)O4 tetrahedra and  an edgeedge with one Ca(1)O6 octahedra. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(3), and one O(7) atom. In the second Se site, Se(2) is bonded to one O(1), one O(4), one O(5), and one O(6) atom to form SeO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 35-55°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one Se(1) and one Se(2) 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 bent 150 degrees geometry to one Ca(1) and one Se(1) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to one Ca(1) and one Se(2) atom. In the fifth O site, O(5) is bonded in a bent 120 degrees geometry to one Ca(1) and one Se(2) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Ca(1) and one Se(2) atom. In the seventh O site, O(7) is bonded in a single-bond geometry to one Se(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_CaSe2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.245
_cell_length_b   7.269
_cell_length_c   7.293
_cell_angle_alpha   80.863
_cell_angle_beta   71.977
_cell_angle_gamma   85.067
_symmetry_Int_Tables_number   1
_cell_volume   360.306
_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  0.729  0.848  0.381  1.0
  Ca  Ca1  1  0.271  0.152  0.619  1.0
  Se  Se2  1  0.655  0.370  0.259  1.0
  Se  Se3  1  0.345  0.630  0.741  1.0
  Se  Se4  1  0.847  0.872  0.863  1.0
  Se  Se5  1  0.153  0.128  0.137  1.0
  O  O6  1  0.990  0.290  0.088  1.0
  O  O7  1  0.010  0.710  0.912  1.0
  O  O8  1  0.616  0.167  0.414  1.0
  O  O9  1  0.384  0.833  0.586  1.0
  O  O10  1  0.735  0.522  0.368  1.0
  O  O11  1  0.265  0.478  0.632  1.0
  O  O12  1  0.946  0.071  0.741  1.0
  O  O13  1  0.054  0.929  0.259  1.0
  O  O14  1  0.680  0.904  0.072  1.0
  O  O15  1  0.320  0.096  0.928  1.0
  O  O16  1  0.739  0.806  0.707  1.0
  O  O17  1  0.261  0.194  0.293  1.0
  O  O18  1  0.416  0.462  0.290  1.0
  O  O19  1  0.584  0.538  0.710  1.0
[/CIF]
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