The material described by Ni2As2O9 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ni sites. In the first Ni site, Ni(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 NiO6 octahedra that share corners with two equivalent As(2)O4 tetrahedra, corners with three equivalent As(1)O4 tetrahedra, and edges with two equivalent Ni(2)O6 octahedra. In the second Ni site, Ni(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 NiO6 octahedra that share corners with two equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra, and edges with two equivalent Ni(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 Ni(2)O6 octahedra, corners with three equivalent Ni(1)O6 octahedra, and  a cornercorner with one As(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-62°. 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 Ni(1)O6 octahedra, corners with three equivalent Ni(2)O6 octahedra, and  a cornercorner with one As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 47-62°. There are nine inequivalent O sites. In the first O site, O(5) is bonded in a bent 120 degrees geometry to one Ni(2) and one As(2) atom. In the second O site, O(6) is bonded in a distorted trigonal planar geometry to one Ni(1), one Ni(2), and one As(2) atom. In the third O site, O(7) is bonded in a trigonal planar geometry to one Ni(1), one Ni(2), and one As(2) atom. In the fourth O site, O(8) is bonded in a single-bond geometry to one Ni(1) atom. In the fifth O site, O(1) is bonded in a distorted trigonal planar geometry to one Ni(1), one Ni(2), and one As(1) atom. In the sixth O site, O(9) is bonded in a single-bond geometry to one Ni(2) atom. In the seventh O site, O(2) is bonded in a bent 120 degrees geometry to one Ni(1) and one As(1) atom. In the eighth O site, O(3) is bonded in a distorted trigonal planar geometry to one Ni(1), one Ni(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 Crystallographic Information File (CIF) [CIF]
data_Ni2As2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   14.209
_cell_length_b   6.519
_cell_length_c   9.594
_cell_angle_alpha   51.803
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   698.443
_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
  Ni  Ni0  1  0.748  0.683  0.863  1.0
  Ni  Ni1  1  0.752  0.683  0.363  1.0
  Ni  Ni2  1  0.252  0.317  0.137  1.0
  Ni  Ni3  1  0.248  0.317  0.637  1.0
  Ni  Ni4  1  0.884  0.177  0.591  1.0
  Ni  Ni5  1  0.616  0.177  0.091  1.0
  Ni  Ni6  1  0.116  0.823  0.409  1.0
  Ni  Ni7  1  0.384  0.823  0.909  1.0
  As  As8  1  0.814  0.107  0.948  1.0
  As  As9  1  0.686  0.107  0.448  1.0
  As  As10  1  0.186  0.893  0.052  1.0
  As  As11  1  0.314  0.893  0.552  1.0
  As  As12  1  0.923  0.611  0.654  1.0
  As  As13  1  0.577  0.611  0.154  1.0
  As  As14  1  0.077  0.389  0.346  1.0
  As  As15  1  0.423  0.389  0.846  1.0
  O  O16  1  0.789  0.039  0.804  1.0
  O  O17  1  0.711  0.039  0.304  1.0
  O  O18  1  0.211  0.961  0.196  1.0
  O  O19  1  0.289  0.961  0.696  1.0
  O  O20  1  0.842  0.847  0.157  1.0
  O  O21  1  0.658  0.847  0.657  1.0
  O  O22  1  0.158  0.153  0.843  1.0
  O  O23  1  0.342  0.153  0.343  1.0
  O  O24  1  0.729  0.317  0.922  1.0
  O  O25  1  0.771  0.317  0.422  1.0
  O  O26  1  0.271  0.683  0.078  1.0
  O  O27  1  0.229  0.683  0.578  1.0
  O  O28  1  0.920  0.296  0.868  1.0
  O  O29  1  0.580  0.296  0.368  1.0
  O  O30  1  0.080  0.704  0.132  1.0
  O  O31  1  0.420  0.704  0.632  1.0
  O  O32  1  0.035  0.709  0.619  1.0
  O  O33  1  0.465  0.709  0.119  1.0
  O  O34  1  0.965  0.291  0.381  1.0
  O  O35  1  0.535  0.291  0.881  1.0
  O  O36  1  0.875  0.554  0.516  1.0
  O  O37  1  0.625  0.554  0.016  1.0
  O  O38  1  0.125  0.446  0.484  1.0
  O  O39  1  0.375  0.446  0.984  1.0
  O  O40  1  0.850  0.809  0.667  1.0
  O  O41  1  0.650  0.809  0.167  1.0
  O  O42  1  0.150  0.191  0.333  1.0
  O  O43  1  0.350  0.191  0.833  1.0
  O  O44  1  0.834  0.509  0.050  1.0
  O  O45  1  0.666  0.509  0.550  1.0
  O  O46  1  0.166  0.491  0.950  1.0
  O  O47  1  0.334  0.491  0.450  1.0
  O  O48  1  0.985  0.014  0.747  1.0
  O  O49  1  0.515  0.014  0.247  1.0
  O  O50  1  0.015  0.986  0.253  1.0
  O  O51  1  0.485  0.986  0.753  1.0
[/CIF]
.
The material described by Ni2As2O9 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ni sites. In the first Ni site, Ni(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 NiO6 octahedra that share corners with two equivalent As(2)O4 tetrahedra, corners with three equivalent As(1)O4 tetrahedra, and edges with two equivalent Ni(2)O6 octahedra. In the second Ni site, Ni(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 NiO6 octahedra that share corners with two equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra, and edges with two equivalent Ni(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 Ni(2)O6 octahedra, corners with three equivalent Ni(1)O6 octahedra, and  a cornercorner with one As(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-62°. 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 Ni(1)O6 octahedra, corners with three equivalent Ni(2)O6 octahedra, and  a cornercorner with one As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 47-62°. There are nine inequivalent O sites. In the first O site, O(5) is bonded in a bent 120 degrees geometry to one Ni(2) and one As(2) atom. In the second O site, O(6) is bonded in a distorted trigonal planar geometry to one Ni(1), one Ni(2), and one As(2) atom. In the third O site, O(7) is bonded in a trigonal planar geometry to one Ni(1), one Ni(2), and one As(2) atom. In the fourth O site, O(8) is bonded in a single-bond geometry to one Ni(1) atom. In the fifth O site, O(1) is bonded in a distorted trigonal planar geometry to one Ni(1), one Ni(2), and one As(1) atom. In the sixth O site, O(9) is bonded in a single-bond geometry to one Ni(2) atom. In the seventh O site, O(2) is bonded in a bent 120 degrees geometry to one Ni(1) and one As(1) atom. In the eighth O site, O(3) is bonded in a distorted trigonal planar geometry to one Ni(1), one Ni(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 Crystallographic Information File (CIF) [CIF]
data_Ni2As2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   14.209
_cell_length_b   6.519
_cell_length_c   9.594
_cell_angle_alpha   51.803
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   698.443
_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
  Ni  Ni0  1  0.748  0.683  0.863  1.0
  Ni  Ni1  1  0.752  0.683  0.363  1.0
  Ni  Ni2  1  0.252  0.317  0.137  1.0
  Ni  Ni3  1  0.248  0.317  0.637  1.0
  Ni  Ni4  1  0.884  0.177  0.591  1.0
  Ni  Ni5  1  0.616  0.177  0.091  1.0
  Ni  Ni6  1  0.116  0.823  0.409  1.0
  Ni  Ni7  1  0.384  0.823  0.909  1.0
  As  As8  1  0.814  0.107  0.948  1.0
  As  As9  1  0.686  0.107  0.448  1.0
  As  As10  1  0.186  0.893  0.052  1.0
  As  As11  1  0.314  0.893  0.552  1.0
  As  As12  1  0.923  0.611  0.654  1.0
  As  As13  1  0.577  0.611  0.154  1.0
  As  As14  1  0.077  0.389  0.346  1.0
  As  As15  1  0.423  0.389  0.846  1.0
  O  O16  1  0.789  0.039  0.804  1.0
  O  O17  1  0.711  0.039  0.304  1.0
  O  O18  1  0.211  0.961  0.196  1.0
  O  O19  1  0.289  0.961  0.696  1.0
  O  O20  1  0.842  0.847  0.157  1.0
  O  O21  1  0.658  0.847  0.657  1.0
  O  O22  1  0.158  0.153  0.843  1.0
  O  O23  1  0.342  0.153  0.343  1.0
  O  O24  1  0.729  0.317  0.922  1.0
  O  O25  1  0.771  0.317  0.422  1.0
  O  O26  1  0.271  0.683  0.078  1.0
  O  O27  1  0.229  0.683  0.578  1.0
  O  O28  1  0.920  0.296  0.868  1.0
  O  O29  1  0.580  0.296  0.368  1.0
  O  O30  1  0.080  0.704  0.132  1.0
  O  O31  1  0.420  0.704  0.632  1.0
  O  O32  1  0.035  0.709  0.619  1.0
  O  O33  1  0.465  0.709  0.119  1.0
  O  O34  1  0.965  0.291  0.381  1.0
  O  O35  1  0.535  0.291  0.881  1.0
  O  O36  1  0.875  0.554  0.516  1.0
  O  O37  1  0.625  0.554  0.016  1.0
  O  O38  1  0.125  0.446  0.484  1.0
  O  O39  1  0.375  0.446  0.984  1.0
  O  O40  1  0.850  0.809  0.667  1.0
  O  O41  1  0.650  0.809  0.167  1.0
  O  O42  1  0.150  0.191  0.333  1.0
  O  O43  1  0.350  0.191  0.833  1.0
  O  O44  1  0.834  0.509  0.050  1.0
  O  O45  1  0.666  0.509  0.550  1.0
  O  O46  1  0.166  0.491  0.950  1.0
  O  O47  1  0.334  0.491  0.450  1.0
  O  O48  1  0.985  0.014  0.747  1.0
  O  O49  1  0.515  0.014  0.247  1.0
  O  O50  1  0.015  0.986  0.253  1.0
  O  O51  1  0.485  0.986  0.753  1.0
[/CIF]
.