The crystal structure described by Ca2Ta2NiO8 crystallizes in the monoclinic C2/c space group. Ca(1) is bonded in a 4-coordinate geometry to three equivalent O(4) and four equivalent O(3) atoms. Ta(1) is bonded to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms to form distorted TaO6 octahedra that share corners with four equivalent Ni(1)O6 octahedra and edges with two equivalent Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-56°. Ni(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form NiO6 octahedra that share corners with eight equivalent Ta(1)O6 octahedra and edges with two equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-56°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Ta(1) and one Ni(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ta(1) and two equivalent Ni(1) atoms. In the third O site, O(3) is bonded in a 6-coordinate geometry to four equivalent Ca(1) and two equivalent Ta(1) atoms. In the fourth O site, O(4) is bonded to three equivalent Ca(1) and one Ta(1) atom to form a mixture of distorted corner and edge-sharing OCa3Ta tetrahedra. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ca2Ta2NiO8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.936
_cell_length_b   9.936
_cell_length_c   5.440
_cell_angle_alpha   88.568
_cell_angle_beta   88.568
_cell_angle_gamma   37.174
_symmetry_Int_Tables_number   1
_cell_volume   324.436
_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
  Ca  Ca0  1  0.881  0.535  0.258  1.0
  Ca  Ca1  1  0.465  0.119  0.242  1.0
  Ca  Ca2  1  0.119  0.465  0.742  1.0
  Ca  Ca3  1  0.535  0.881  0.758  1.0
  Ta  Ta4  1  0.040  0.740  0.250  1.0
  Ta  Ta5  1  0.260  0.960  0.250  1.0
  Ta  Ta6  1  0.960  0.260  0.750  1.0
  Ta  Ta7  1  0.740  0.040  0.750  1.0
  Ni  Ni8  1  0.633  0.367  0.250  1.0
  Ni  Ni9  1  0.367  0.633  0.750  1.0
  O  O10  1  0.058  0.806  0.587  1.0
  O  O11  1  0.194  0.942  0.913  1.0
  O  O12  1  0.942  0.194  0.413  1.0
  O  O13  1  0.806  0.058  0.087  1.0
  O  O14  1  0.302  0.585  0.082  1.0
  O  O15  1  0.415  0.698  0.418  1.0
  O  O16  1  0.698  0.415  0.918  1.0
  O  O17  1  0.585  0.302  0.582  1.0
  O  O18  1  0.883  0.759  0.990  1.0
  O  O19  1  0.241  0.117  0.510  1.0
  O  O20  1  0.471  0.159  0.839  1.0
  O  O21  1  0.841  0.529  0.661  1.0
  O  O22  1  0.529  0.841  0.161  1.0
  O  O23  1  0.159  0.471  0.339  1.0
  O  O24  1  0.759  0.883  0.490  1.0
  O  O25  1  0.117  0.241  0.010  1.0
[/CIF]
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The crystal structure described by Ca2Ta2NiO8 crystallizes in the monoclinic C2/c space group. Ca(1) is bonded in a 4-coordinate geometry to three equivalent O(4) and four equivalent O(3) atoms. Ta(1) is bonded to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms to form distorted TaO6 octahedra that share corners with four equivalent Ni(1)O6 octahedra and edges with two equivalent Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-56°. Ni(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form NiO6 octahedra that share corners with eight equivalent Ta(1)O6 octahedra and edges with two equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-56°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Ta(1) and one Ni(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ta(1) and two equivalent Ni(1) atoms. In the third O site, O(3) is bonded in a 6-coordinate geometry to four equivalent Ca(1) and two equivalent Ta(1) atoms. In the fourth O site, O(4) is bonded to three equivalent Ca(1) and one Ta(1) atom to form a mixture of distorted corner and edge-sharing OCa3Ta tetrahedra. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ca2Ta2NiO8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.936
_cell_length_b   9.936
_cell_length_c   5.440
_cell_angle_alpha   88.568
_cell_angle_beta   88.568
_cell_angle_gamma   37.174
_symmetry_Int_Tables_number   1
_cell_volume   324.436
_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
  Ca  Ca0  1  0.881  0.535  0.258  1.0
  Ca  Ca1  1  0.465  0.119  0.242  1.0
  Ca  Ca2  1  0.119  0.465  0.742  1.0
  Ca  Ca3  1  0.535  0.881  0.758  1.0
  Ta  Ta4  1  0.040  0.740  0.250  1.0
  Ta  Ta5  1  0.260  0.960  0.250  1.0
  Ta  Ta6  1  0.960  0.260  0.750  1.0
  Ta  Ta7  1  0.740  0.040  0.750  1.0
  Ni  Ni8  1  0.633  0.367  0.250  1.0
  Ni  Ni9  1  0.367  0.633  0.750  1.0
  O  O10  1  0.058  0.806  0.587  1.0
  O  O11  1  0.194  0.942  0.913  1.0
  O  O12  1  0.942  0.194  0.413  1.0
  O  O13  1  0.806  0.058  0.087  1.0
  O  O14  1  0.302  0.585  0.082  1.0
  O  O15  1  0.415  0.698  0.418  1.0
  O  O16  1  0.698  0.415  0.918  1.0
  O  O17  1  0.585  0.302  0.582  1.0
  O  O18  1  0.883  0.759  0.990  1.0
  O  O19  1  0.241  0.117  0.510  1.0
  O  O20  1  0.471  0.159  0.839  1.0
  O  O21  1  0.841  0.529  0.661  1.0
  O  O22  1  0.529  0.841  0.161  1.0
  O  O23  1  0.159  0.471  0.339  1.0
  O  O24  1  0.759  0.883  0.490  1.0
  O  O25  1  0.117  0.241  0.010  1.0
[/CIF]
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