The structure described by Li2Se2O7 crystallizes in the orthorhombic Pnma space group. Li(1) is bonded to one O(1), one O(2), one O(4), and two equivalent O(3) atoms to form LiO5 trigonal bipyramids that share corners with two equivalent Se(1)O4 tetrahedra, corners with three equivalent Se(2)O4 tetrahedra, and edges with two equivalent Li(1)O5 trigonal bipyramids. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to one O(2), one O(5), and two equivalent O(1) atoms to form SeO4 tetrahedra that share  a cornercorner with one Se(2)O4 tetrahedra and corners with four equivalent Li(1)O5 trigonal bipyramids. In the second Se site, Se(2) is bonded to one O(4), one O(5), and two equivalent O(3) atoms to form SeO4 tetrahedra that share  a cornercorner with one Se(1)O4 tetrahedra and corners with six equivalent Li(1)O5 trigonal bipyramids. There are five inequivalent O sites. In the first O site, O(4) is bonded in a distorted trigonal planar geometry to two equivalent Li(1) and one Se(2) atom. In the second O site, O(5) is bonded in a bent 120 degrees geometry to one Se(1) and one Se(2) atom. In the third O site, O(1) is bonded in a bent 120 degrees geometry to one Li(1) and one Se(1) atom. In the fourth O site, O(2) is bonded in a distorted trigonal planar geometry to two equivalent Li(1) and one Se(1) atom. In the fifth O site, O(3) is bonded in a trigonal planar geometry to two equivalent Li(1) and one Se(2) atom. is represented by the CIF file [CIF]
data_Li2Se2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.216
_cell_length_b   8.672
_cell_length_c   14.150
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   639.986
_cell_formula_units_Z   4
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
  Li  Li0  1  0.409  0.433  0.102  1.0
  Li  Li1  1  0.091  0.067  0.602  1.0
  Li  Li2  1  0.591  0.933  0.898  1.0
  Li  Li3  1  0.909  0.567  0.398  1.0
  Li  Li4  1  0.591  0.567  0.898  1.0
  Li  Li5  1  0.909  0.933  0.398  1.0
  Li  Li6  1  0.409  0.067  0.102  1.0
  Li  Li7  1  0.091  0.433  0.602  1.0
  Se  Se8  1  0.237  0.750  0.219  1.0
  Se  Se9  1  0.263  0.750  0.719  1.0
  Se  Se10  1  0.763  0.250  0.781  1.0
  Se  Se11  1  0.737  0.250  0.281  1.0
  Se  Se12  1  0.390  0.750  0.503  1.0
  Se  Se13  1  0.110  0.750  0.003  1.0
  Se  Se14  1  0.610  0.250  0.497  1.0
  Se  Se15  1  0.890  0.250  0.997  1.0
  O  O16  1  0.399  0.590  0.205  1.0
  O  O17  1  0.101  0.910  0.705  1.0
  O  O18  1  0.601  0.090  0.795  1.0
  O  O19  1  0.899  0.410  0.295  1.0
  O  O20  1  0.601  0.410  0.795  1.0
  O  O21  1  0.899  0.090  0.295  1.0
  O  O22  1  0.399  0.910  0.205  1.0
  O  O23  1  0.101  0.590  0.705  1.0
  O  O24  1  0.049  0.750  0.312  1.0
  O  O25  1  0.451  0.750  0.812  1.0
  O  O26  1  0.951  0.250  0.688  1.0
  O  O27  1  0.549  0.250  0.188  1.0
  O  O28  1  0.219  0.590  0.492  1.0
  O  O29  1  0.281  0.910  0.992  1.0
  O  O30  1  0.781  0.090  0.508  1.0
  O  O31  1  0.719  0.410  0.008  1.0
  O  O32  1  0.781  0.410  0.508  1.0
  O  O33  1  0.719  0.090  0.008  1.0
  O  O34  1  0.219  0.910  0.492  1.0
  O  O35  1  0.281  0.590  0.992  1.0
  O  O36  1  0.659  0.750  0.442  1.0
  O  O37  1  0.841  0.750  0.942  1.0
  O  O38  1  0.341  0.250  0.558  1.0
  O  O39  1  0.159  0.250  0.058  1.0
  O  O40  1  0.991  0.750  0.123  1.0
  O  O41  1  0.509  0.750  0.623  1.0
  O  O42  1  0.009  0.250  0.877  1.0
  O  O43  1  0.491  0.250  0.377  1.0
[/CIF]
.
The structure described by Li2Se2O7 crystallizes in the orthorhombic Pnma space group. Li(1) is bonded to one O(1), one O(2), one O(4), and two equivalent O(3) atoms to form LiO5 trigonal bipyramids that share corners with two equivalent Se(1)O4 tetrahedra, corners with three equivalent Se(2)O4 tetrahedra, and edges with two equivalent Li(1)O5 trigonal bipyramids. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to one O(2), one O(5), and two equivalent O(1) atoms to form SeO4 tetrahedra that share  a cornercorner with one Se(2)O4 tetrahedra and corners with four equivalent Li(1)O5 trigonal bipyramids. In the second Se site, Se(2) is bonded to one O(4), one O(5), and two equivalent O(3) atoms to form SeO4 tetrahedra that share  a cornercorner with one Se(1)O4 tetrahedra and corners with six equivalent Li(1)O5 trigonal bipyramids. There are five inequivalent O sites. In the first O site, O(4) is bonded in a distorted trigonal planar geometry to two equivalent Li(1) and one Se(2) atom. In the second O site, O(5) is bonded in a bent 120 degrees geometry to one Se(1) and one Se(2) atom. In the third O site, O(1) is bonded in a bent 120 degrees geometry to one Li(1) and one Se(1) atom. In the fourth O site, O(2) is bonded in a distorted trigonal planar geometry to two equivalent Li(1) and one Se(1) atom. In the fifth O site, O(3) is bonded in a trigonal planar geometry to two equivalent Li(1) and one Se(2) atom. is represented by the CIF file [CIF]
data_Li2Se2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.216
_cell_length_b   8.672
_cell_length_c   14.150
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   639.986
_cell_formula_units_Z   4
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
  Li  Li0  1  0.409  0.433  0.102  1.0
  Li  Li1  1  0.091  0.067  0.602  1.0
  Li  Li2  1  0.591  0.933  0.898  1.0
  Li  Li3  1  0.909  0.567  0.398  1.0
  Li  Li4  1  0.591  0.567  0.898  1.0
  Li  Li5  1  0.909  0.933  0.398  1.0
  Li  Li6  1  0.409  0.067  0.102  1.0
  Li  Li7  1  0.091  0.433  0.602  1.0
  Se  Se8  1  0.237  0.750  0.219  1.0
  Se  Se9  1  0.263  0.750  0.719  1.0
  Se  Se10  1  0.763  0.250  0.781  1.0
  Se  Se11  1  0.737  0.250  0.281  1.0
  Se  Se12  1  0.390  0.750  0.503  1.0
  Se  Se13  1  0.110  0.750  0.003  1.0
  Se  Se14  1  0.610  0.250  0.497  1.0
  Se  Se15  1  0.890  0.250  0.997  1.0
  O  O16  1  0.399  0.590  0.205  1.0
  O  O17  1  0.101  0.910  0.705  1.0
  O  O18  1  0.601  0.090  0.795  1.0
  O  O19  1  0.899  0.410  0.295  1.0
  O  O20  1  0.601  0.410  0.795  1.0
  O  O21  1  0.899  0.090  0.295  1.0
  O  O22  1  0.399  0.910  0.205  1.0
  O  O23  1  0.101  0.590  0.705  1.0
  O  O24  1  0.049  0.750  0.312  1.0
  O  O25  1  0.451  0.750  0.812  1.0
  O  O26  1  0.951  0.250  0.688  1.0
  O  O27  1  0.549  0.250  0.188  1.0
  O  O28  1  0.219  0.590  0.492  1.0
  O  O29  1  0.281  0.910  0.992  1.0
  O  O30  1  0.781  0.090  0.508  1.0
  O  O31  1  0.719  0.410  0.008  1.0
  O  O32  1  0.781  0.410  0.508  1.0
  O  O33  1  0.719  0.090  0.008  1.0
  O  O34  1  0.219  0.910  0.492  1.0
  O  O35  1  0.281  0.590  0.992  1.0
  O  O36  1  0.659  0.750  0.442  1.0
  O  O37  1  0.841  0.750  0.942  1.0
  O  O38  1  0.341  0.250  0.558  1.0
  O  O39  1  0.159  0.250  0.058  1.0
  O  O40  1  0.991  0.750  0.123  1.0
  O  O41  1  0.509  0.750  0.623  1.0
  O  O42  1  0.009  0.250  0.877  1.0
  O  O43  1  0.491  0.250  0.377  1.0
[/CIF]
.