The crystal structure described by Zn2As2O9 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Zn sites. In the first Zn site, Zn(1) is bonded to one O(1), one O(2), one O(3), one O(6), one O(7), and one O(8) atom to form distorted ZnO6 octahedra that share corners with two equivalent As(2)O4 tetrahedra, corners with three equivalent As(1)O4 tetrahedra, and edges with two equivalent Zn(2)O6 octahedra. In the second Zn site, Zn(2) is bonded to one O(1), one O(3), one O(5), one O(6), one O(7), and one O(9) atom to form ZnO6 octahedra that share corners with two equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra, and edges with two equivalent Zn(1)O6 octahedra. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form AsO4 tetrahedra that share corners with two equivalent Zn(2)O6 octahedra, corners with three equivalent Zn(1)O6 octahedra, and  a cornercorner with one As(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 46-58°. In the second As site, As(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form AsO4 tetrahedra that share corners with two equivalent Zn(1)O6 octahedra, corners with three equivalent Zn(2)O6 octahedra, and  a cornercorner with one As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 47-58°. There are nine inequivalent O sites. In the first O site, O(5) is bonded in a bent 120 degrees geometry to one Zn(2) and one As(2) atom. In the second O site, O(6) is bonded in a distorted trigonal planar geometry to one Zn(1), one Zn(2), and one As(2) atom. In the third O site, O(7) is bonded in a distorted trigonal planar geometry to one Zn(1), one Zn(2), and one As(2) atom. In the fourth O site, O(8) is bonded in a single-bond geometry to one Zn(1) atom. In the fifth O site, O(1) is bonded in a distorted trigonal planar geometry to one Zn(1), one Zn(2), and one As(1) atom. In the sixth O site, O(9) is bonded in a single-bond geometry to one Zn(2) atom. In the seventh O site, O(2) is bonded in a bent 120 degrees geometry to one Zn(1) and one As(1) atom. In the eighth O site, O(3) is bonded in a distorted trigonal planar geometry to one Zn(1), one Zn(2), and one As(1) atom. In the ninth O site, O(4) is bonded in a bent 120 degrees geometry to one As(1) and one As(2) atom. is represented by the CIF file [CIF]
data_Zn2As2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   14.380
_cell_length_b   6.559
_cell_length_c   9.682
_cell_angle_alpha   53.457
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   733.635
_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
  Zn  Zn0  1  0.739  0.719  0.854  1.0
  Zn  Zn1  1  0.761  0.719  0.354  1.0
  Zn  Zn2  1  0.261  0.281  0.146  1.0
  Zn  Zn3  1  0.239  0.281  0.646  1.0
  Zn  Zn4  1  0.884  0.193  0.576  1.0
  Zn  Zn5  1  0.616  0.193  0.076  1.0
  Zn  Zn6  1  0.116  0.807  0.424  1.0
  Zn  Zn7  1  0.384  0.807  0.924  1.0
  As  As8  1  0.824  0.111  0.954  1.0
  As  As9  1  0.676  0.111  0.454  1.0
  As  As10  1  0.176  0.889  0.046  1.0
  As  As11  1  0.324  0.889  0.546  1.0
  As  As12  1  0.925  0.609  0.663  1.0
  As  As13  1  0.575  0.609  0.163  1.0
  As  As14  1  0.075  0.391  0.337  1.0
  As  As15  1  0.425  0.391  0.837  1.0
  O  O16  1  0.799  0.041  0.813  1.0
  O  O17  1  0.701  0.041  0.313  1.0
  O  O18  1  0.201  0.959  0.187  1.0
  O  O19  1  0.299  0.959  0.687  1.0
  O  O20  1  0.849  0.859  0.156  1.0
  O  O21  1  0.651  0.859  0.656  1.0
  O  O22  1  0.151  0.141  0.844  1.0
  O  O23  1  0.349  0.141  0.344  1.0
  O  O24  1  0.739  0.314  0.935  1.0
  O  O25  1  0.761  0.314  0.435  1.0
  O  O26  1  0.261  0.686  0.065  1.0
  O  O27  1  0.239  0.686  0.565  1.0
  O  O28  1  0.927  0.303  0.871  1.0
  O  O29  1  0.573  0.303  0.371  1.0
  O  O30  1  0.073  0.697  0.129  1.0
  O  O31  1  0.427  0.697  0.629  1.0
  O  O32  1  0.035  0.713  0.624  1.0
  O  O33  1  0.465  0.713  0.124  1.0
  O  O34  1  0.965  0.287  0.376  1.0
  O  O35  1  0.535  0.287  0.876  1.0
  O  O36  1  0.876  0.553  0.526  1.0
  O  O37  1  0.624  0.553  0.026  1.0
  O  O38  1  0.124  0.447  0.474  1.0
  O  O39  1  0.376  0.447  0.974  1.0
  O  O40  1  0.854  0.804  0.679  1.0
  O  O41  1  0.646  0.804  0.179  1.0
  O  O42  1  0.146  0.196  0.321  1.0
  O  O43  1  0.354  0.196  0.821  1.0
  O  O44  1  0.823  0.467  0.059  1.0
  O  O45  1  0.677  0.467  0.559  1.0
  O  O46  1  0.177  0.533  0.941  1.0
  O  O47  1  0.323  0.533  0.441  1.0
  O  O48  1  0.981  0.982  0.766  1.0
  O  O49  1  0.519  0.982  0.266  1.0
  O  O50  1  0.019  0.018  0.234  1.0
  O  O51  1  0.481  0.018  0.734  1.0
[/CIF]
.
The crystal structure described by Zn2As2O9 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Zn sites. In the first Zn site, Zn(1) is bonded to one O(1), one O(2), one O(3), one O(6), one O(7), and one O(8) atom to form distorted ZnO6 octahedra that share corners with two equivalent As(2)O4 tetrahedra, corners with three equivalent As(1)O4 tetrahedra, and edges with two equivalent Zn(2)O6 octahedra. In the second Zn site, Zn(2) is bonded to one O(1), one O(3), one O(5), one O(6), one O(7), and one O(9) atom to form ZnO6 octahedra that share corners with two equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra, and edges with two equivalent Zn(1)O6 octahedra. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form AsO4 tetrahedra that share corners with two equivalent Zn(2)O6 octahedra, corners with three equivalent Zn(1)O6 octahedra, and  a cornercorner with one As(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 46-58°. In the second As site, As(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form AsO4 tetrahedra that share corners with two equivalent Zn(1)O6 octahedra, corners with three equivalent Zn(2)O6 octahedra, and  a cornercorner with one As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 47-58°. There are nine inequivalent O sites. In the first O site, O(5) is bonded in a bent 120 degrees geometry to one Zn(2) and one As(2) atom. In the second O site, O(6) is bonded in a distorted trigonal planar geometry to one Zn(1), one Zn(2), and one As(2) atom. In the third O site, O(7) is bonded in a distorted trigonal planar geometry to one Zn(1), one Zn(2), and one As(2) atom. In the fourth O site, O(8) is bonded in a single-bond geometry to one Zn(1) atom. In the fifth O site, O(1) is bonded in a distorted trigonal planar geometry to one Zn(1), one Zn(2), and one As(1) atom. In the sixth O site, O(9) is bonded in a single-bond geometry to one Zn(2) atom. In the seventh O site, O(2) is bonded in a bent 120 degrees geometry to one Zn(1) and one As(1) atom. In the eighth O site, O(3) is bonded in a distorted trigonal planar geometry to one Zn(1), one Zn(2), and one As(1) atom. In the ninth O site, O(4) is bonded in a bent 120 degrees geometry to one As(1) and one As(2) atom. is represented by the CIF file [CIF]
data_Zn2As2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   14.380
_cell_length_b   6.559
_cell_length_c   9.682
_cell_angle_alpha   53.457
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   733.635
_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
  Zn  Zn0  1  0.739  0.719  0.854  1.0
  Zn  Zn1  1  0.761  0.719  0.354  1.0
  Zn  Zn2  1  0.261  0.281  0.146  1.0
  Zn  Zn3  1  0.239  0.281  0.646  1.0
  Zn  Zn4  1  0.884  0.193  0.576  1.0
  Zn  Zn5  1  0.616  0.193  0.076  1.0
  Zn  Zn6  1  0.116  0.807  0.424  1.0
  Zn  Zn7  1  0.384  0.807  0.924  1.0
  As  As8  1  0.824  0.111  0.954  1.0
  As  As9  1  0.676  0.111  0.454  1.0
  As  As10  1  0.176  0.889  0.046  1.0
  As  As11  1  0.324  0.889  0.546  1.0
  As  As12  1  0.925  0.609  0.663  1.0
  As  As13  1  0.575  0.609  0.163  1.0
  As  As14  1  0.075  0.391  0.337  1.0
  As  As15  1  0.425  0.391  0.837  1.0
  O  O16  1  0.799  0.041  0.813  1.0
  O  O17  1  0.701  0.041  0.313  1.0
  O  O18  1  0.201  0.959  0.187  1.0
  O  O19  1  0.299  0.959  0.687  1.0
  O  O20  1  0.849  0.859  0.156  1.0
  O  O21  1  0.651  0.859  0.656  1.0
  O  O22  1  0.151  0.141  0.844  1.0
  O  O23  1  0.349  0.141  0.344  1.0
  O  O24  1  0.739  0.314  0.935  1.0
  O  O25  1  0.761  0.314  0.435  1.0
  O  O26  1  0.261  0.686  0.065  1.0
  O  O27  1  0.239  0.686  0.565  1.0
  O  O28  1  0.927  0.303  0.871  1.0
  O  O29  1  0.573  0.303  0.371  1.0
  O  O30  1  0.073  0.697  0.129  1.0
  O  O31  1  0.427  0.697  0.629  1.0
  O  O32  1  0.035  0.713  0.624  1.0
  O  O33  1  0.465  0.713  0.124  1.0
  O  O34  1  0.965  0.287  0.376  1.0
  O  O35  1  0.535  0.287  0.876  1.0
  O  O36  1  0.876  0.553  0.526  1.0
  O  O37  1  0.624  0.553  0.026  1.0
  O  O38  1  0.124  0.447  0.474  1.0
  O  O39  1  0.376  0.447  0.974  1.0
  O  O40  1  0.854  0.804  0.679  1.0
  O  O41  1  0.646  0.804  0.179  1.0
  O  O42  1  0.146  0.196  0.321  1.0
  O  O43  1  0.354  0.196  0.821  1.0
  O  O44  1  0.823  0.467  0.059  1.0
  O  O45  1  0.677  0.467  0.559  1.0
  O  O46  1  0.177  0.533  0.941  1.0
  O  O47  1  0.323  0.533  0.441  1.0
  O  O48  1  0.981  0.982  0.766  1.0
  O  O49  1  0.519  0.982  0.266  1.0
  O  O50  1  0.019  0.018  0.234  1.0
  O  O51  1  0.481  0.018  0.734  1.0
[/CIF]
.