The compound described by Ba2Mg(NiO3)2 crystallizes in the monoclinic Cm space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 7-coordinate geometry to one O(4), two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. In the second Ba site, Ba(2) is bonded in a 9-coordinate geometry to one O(3), two equivalent O(2), two equivalent O(4), and four equivalent O(1) atoms. Mg(1) is bonded to one O(4), two equivalent O(1), and two equivalent O(2) atoms to form distorted MgO5 square pyramids that share corners with three equivalent Ni(2)O6 octahedra and  an edgeedge with one Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 12-26°. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a 6-coordinate geometry to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms. In the second Ni site, Ni(2) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form NiO6 octahedra that share corners with three equivalent Mg(1)O5 square pyramids and  an edgeedge with one Mg(1)O5 square pyramid. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ba(1), two equivalent Ba(2), one Mg(1), one Ni(1), and one Ni(2) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Ba(1), one Ba(2), one Mg(1), one Ni(1), and one Ni(2) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Ba(2), two equivalent Ba(1), one Ni(1), and one Ni(2) atom. In the fourth O site, O(4) is bonded to one Ba(1), two equivalent Ba(2), one Mg(1), one Ni(1), and one Ni(2) atom to form distorted corner-sharing OBa3MgNi2 octahedra. The corner-sharing octahedral tilt angles are 11°. is represented by the CIF card [CIF]
data_Ba2Mg(NiO3)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.710
_cell_length_b   5.819
_cell_length_c   5.475
_cell_angle_alpha   104.676
_cell_angle_beta   90.000
_cell_angle_gamma   119.381
_symmetry_Int_Tables_number   1
_cell_volume   151.668
_cell_formula_units_Z   1
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  0.620  0.240  0.850  1.0
  Ba  Ba1  1  0.358  0.716  0.222  1.0
  Mg  Mg2  1  0.766  0.531  0.439  1.0
  Ni  Ni3  1  0.042  0.085  0.481  1.0
  Ni  Ni4  1  0.001  0.002  0.986  1.0
  O  O5  1  0.861  0.225  0.283  1.0
  O  O6  1  0.683  0.797  0.706  1.0
  O  O7  1  0.146  0.291  0.839  1.0
  O  O8  1  0.868  0.736  0.179  1.0
  O  O9  1  0.114  0.797  0.706  1.0
  O  O10  1  0.364  0.225  0.283  1.0
[/CIF]
.
The compound described by Ba2Mg(NiO3)2 crystallizes in the monoclinic Cm space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 7-coordinate geometry to one O(4), two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. In the second Ba site, Ba(2) is bonded in a 9-coordinate geometry to one O(3), two equivalent O(2), two equivalent O(4), and four equivalent O(1) atoms. Mg(1) is bonded to one O(4), two equivalent O(1), and two equivalent O(2) atoms to form distorted MgO5 square pyramids that share corners with three equivalent Ni(2)O6 octahedra and  an edgeedge with one Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 12-26°. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a 6-coordinate geometry to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms. In the second Ni site, Ni(2) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form NiO6 octahedra that share corners with three equivalent Mg(1)O5 square pyramids and  an edgeedge with one Mg(1)O5 square pyramid. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ba(1), two equivalent Ba(2), one Mg(1), one Ni(1), and one Ni(2) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Ba(1), one Ba(2), one Mg(1), one Ni(1), and one Ni(2) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Ba(2), two equivalent Ba(1), one Ni(1), and one Ni(2) atom. In the fourth O site, O(4) is bonded to one Ba(1), two equivalent Ba(2), one Mg(1), one Ni(1), and one Ni(2) atom to form distorted corner-sharing OBa3MgNi2 octahedra. The corner-sharing octahedral tilt angles are 11°. is represented by the CIF card [CIF]
data_Ba2Mg(NiO3)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.710
_cell_length_b   5.819
_cell_length_c   5.475
_cell_angle_alpha   104.676
_cell_angle_beta   90.000
_cell_angle_gamma   119.381
_symmetry_Int_Tables_number   1
_cell_volume   151.668
_cell_formula_units_Z   1
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  0.620  0.240  0.850  1.0
  Ba  Ba1  1  0.358  0.716  0.222  1.0
  Mg  Mg2  1  0.766  0.531  0.439  1.0
  Ni  Ni3  1  0.042  0.085  0.481  1.0
  Ni  Ni4  1  0.001  0.002  0.986  1.0
  O  O5  1  0.861  0.225  0.283  1.0
  O  O6  1  0.683  0.797  0.706  1.0
  O  O7  1  0.146  0.291  0.839  1.0
  O  O8  1  0.868  0.736  0.179  1.0
  O  O9  1  0.114  0.797  0.706  1.0
  O  O10  1  0.364  0.225  0.283  1.0
[/CIF]
.