The crystal structure described by Ba(As2O7)2 crystallizes in the orthorhombic Pmna space group. Ba(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(3), and four equivalent O(5) atoms. There are two inequivalent As sites. In the first As site, As(1) is bonded to two equivalent O(1), two equivalent O(4), and two equivalent O(5) atoms to form AsO6 octahedra that share corners with two equivalent As(2)O4 tetrahedra and  an edgeedge with one As(1)O6 octahedra. In the second As site, As(2) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form corner-sharing AsO4 tetrahedra. The corner-sharing octahedral tilt angles are 66°. There are five inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one As(1) and one As(2) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Ba(1) and one As(2) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Ba(1) and one As(2) atom. In the fourth O site, O(4) is bonded in a water-like geometry to two equivalent As(1) atoms. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to one Ba(1) and one As(1) atom. is represented by the CIF file [CIF]
data_Ba(As2O7)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.791
_cell_length_b   8.911
_cell_length_c   11.585
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   597.887
_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
  Ba  Ba0  1  0.000  0.000  0.500  1.0
  Ba  Ba1  1  0.000  0.500  0.000  1.0
  As  As2  1  0.500  0.658  0.500  1.0
  As  As3  1  0.500  0.842  0.000  1.0
  As  As4  1  0.500  0.342  0.500  1.0
  As  As5  1  0.500  0.158  0.000  1.0
  As  As6  1  0.790  0.500  0.688  1.0
  As  As7  1  0.210  0.500  0.312  1.0
  As  As8  1  0.790  0.000  0.812  1.0
  As  As9  1  0.210  0.000  0.188  1.0
  O  O10  1  0.758  0.662  0.605  1.0
  O  O11  1  0.242  0.662  0.395  1.0
  O  O12  1  0.758  0.838  0.895  1.0
  O  O13  1  0.242  0.838  0.105  1.0
  O  O14  1  0.242  0.338  0.395  1.0
  O  O15  1  0.758  0.338  0.605  1.0
  O  O16  1  0.242  0.162  0.105  1.0
  O  O17  1  0.758  0.162  0.895  1.0
  O  O18  1  0.652  0.500  0.821  1.0
  O  O19  1  0.348  0.500  0.179  1.0
  O  O20  1  0.652  0.000  0.679  1.0
  O  O21  1  0.348  0.000  0.321  1.0
  O  O22  1  0.056  0.500  0.754  1.0
  O  O23  1  0.944  0.500  0.246  1.0
  O  O24  1  0.056  0.000  0.746  1.0
  O  O25  1  0.944  0.000  0.254  1.0
  O  O26  1  0.378  0.500  0.587  1.0
  O  O27  1  0.622  0.500  0.413  1.0
  O  O28  1  0.378  0.000  0.913  1.0
  O  O29  1  0.622  0.000  0.087  1.0
  O  O30  1  0.366  0.687  0.927  1.0
  O  O31  1  0.634  0.687  0.073  1.0
  O  O32  1  0.366  0.813  0.573  1.0
  O  O33  1  0.634  0.813  0.427  1.0
  O  O34  1  0.634  0.313  0.073  1.0
  O  O35  1  0.366  0.313  0.927  1.0
  O  O36  1  0.634  0.187  0.427  1.0
  O  O37  1  0.366  0.187  0.573  1.0
[/CIF]
.
The crystal structure described by Ba(As2O7)2 crystallizes in the orthorhombic Pmna space group. Ba(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(3), and four equivalent O(5) atoms. There are two inequivalent As sites. In the first As site, As(1) is bonded to two equivalent O(1), two equivalent O(4), and two equivalent O(5) atoms to form AsO6 octahedra that share corners with two equivalent As(2)O4 tetrahedra and  an edgeedge with one As(1)O6 octahedra. In the second As site, As(2) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form corner-sharing AsO4 tetrahedra. The corner-sharing octahedral tilt angles are 66°. There are five inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one As(1) and one As(2) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Ba(1) and one As(2) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Ba(1) and one As(2) atom. In the fourth O site, O(4) is bonded in a water-like geometry to two equivalent As(1) atoms. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to one Ba(1) and one As(1) atom. is represented by the CIF file [CIF]
data_Ba(As2O7)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.791
_cell_length_b   8.911
_cell_length_c   11.585
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   597.887
_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
  Ba  Ba0  1  0.000  0.000  0.500  1.0
  Ba  Ba1  1  0.000  0.500  0.000  1.0
  As  As2  1  0.500  0.658  0.500  1.0
  As  As3  1  0.500  0.842  0.000  1.0
  As  As4  1  0.500  0.342  0.500  1.0
  As  As5  1  0.500  0.158  0.000  1.0
  As  As6  1  0.790  0.500  0.688  1.0
  As  As7  1  0.210  0.500  0.312  1.0
  As  As8  1  0.790  0.000  0.812  1.0
  As  As9  1  0.210  0.000  0.188  1.0
  O  O10  1  0.758  0.662  0.605  1.0
  O  O11  1  0.242  0.662  0.395  1.0
  O  O12  1  0.758  0.838  0.895  1.0
  O  O13  1  0.242  0.838  0.105  1.0
  O  O14  1  0.242  0.338  0.395  1.0
  O  O15  1  0.758  0.338  0.605  1.0
  O  O16  1  0.242  0.162  0.105  1.0
  O  O17  1  0.758  0.162  0.895  1.0
  O  O18  1  0.652  0.500  0.821  1.0
  O  O19  1  0.348  0.500  0.179  1.0
  O  O20  1  0.652  0.000  0.679  1.0
  O  O21  1  0.348  0.000  0.321  1.0
  O  O22  1  0.056  0.500  0.754  1.0
  O  O23  1  0.944  0.500  0.246  1.0
  O  O24  1  0.056  0.000  0.746  1.0
  O  O25  1  0.944  0.000  0.254  1.0
  O  O26  1  0.378  0.500  0.587  1.0
  O  O27  1  0.622  0.500  0.413  1.0
  O  O28  1  0.378  0.000  0.913  1.0
  O  O29  1  0.622  0.000  0.087  1.0
  O  O30  1  0.366  0.687  0.927  1.0
  O  O31  1  0.634  0.687  0.073  1.0
  O  O32  1  0.366  0.813  0.573  1.0
  O  O33  1  0.634  0.813  0.427  1.0
  O  O34  1  0.634  0.313  0.073  1.0
  O  O35  1  0.366  0.313  0.927  1.0
  O  O36  1  0.634  0.187  0.427  1.0
  O  O37  1  0.366  0.187  0.573  1.0
[/CIF]
.