The material described by Ca(NiO2)2 crystallizes in the trigonal R3m space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(3) and three equivalent O(4) atoms to form CaO4 tetrahedra that share corners with nine equivalent Ni(2)O5 square pyramids. In the second Ca site, Ca(2) is bonded in a 6-coordinate geometry to three equivalent O(1) and three equivalent O(4) atoms. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(2) and three equivalent O(1) atoms to form corner-sharing NiO4 tetrahedra. In the second Ni site, Ni(2) is bonded to one O(3), two equivalent O(1), and two equivalent O(4) atoms to form distorted NiO5 square pyramids that share corners with two equivalent Ni(2)O5 square pyramids, corners with two equivalent Ni(1)O4 tetrahedra, corners with three equivalent Ca(1)O4 tetrahedra, and edges with two equivalent Ni(2)O5 square pyramids. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Ca(2), one Ni(1), and two equivalent Ni(2) atoms to form distorted OCaNi3 trigonal pyramids that share corners with seven equivalent O(4)Ca2Ni2 tetrahedra, corners with two equivalent O(1)CaNi3 trigonal pyramids, and edges with two equivalent O(1)CaNi3 trigonal pyramids. In the second O site, O(2) is bonded in a single-bond geometry to one Ni(1) atom. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Ca(1) and three equivalent Ni(2) atoms. In the fourth O site, O(4) is bonded to one Ca(1), one Ca(2), and two equivalent Ni(2) atoms to form distorted OCa2Ni2 tetrahedra that share corners with two equivalent O(4)Ca2Ni2 tetrahedra, corners with seven equivalent O(1)CaNi3 trigonal pyramids, and edges with two equivalent O(4)Ca2Ni2 tetrahedra. is represented by the CIF file [CIF]
data_Ca(NiO2)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.302
_cell_length_b   6.302
_cell_length_c   6.302
_cell_angle_alpha   57.315
_cell_angle_beta   57.315
_cell_angle_gamma   57.315
_symmetry_Int_Tables_number   1
_cell_volume   166.007
_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  0.014  0.014  0.014  1.0
  Ca  Ca1  1  0.625  0.625  0.625  1.0
  Ni  Ni2  1  0.233  0.233  0.233  1.0
  Ni  Ni3  1  0.639  0.639  0.114  1.0
  Ni  Ni4  1  0.114  0.639  0.639  1.0
  Ni  Ni5  1  0.639  0.114  0.639  1.0
  O  O6  1  0.363  0.836  0.363  1.0
  O  O7  1  0.836  0.363  0.363  1.0
  O  O8  1  0.363  0.363  0.836  1.0
  O  O9  1  0.347  0.347  0.347  1.0
  O  O10  1  0.874  0.874  0.874  1.0
  O  O11  1  0.877  0.877  0.449  1.0
  O  O12  1  0.449  0.877  0.877  1.0
  O  O13  1  0.877  0.449  0.877  1.0
[/CIF]
.
The material described by Ca(NiO2)2 crystallizes in the trigonal R3m space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(3) and three equivalent O(4) atoms to form CaO4 tetrahedra that share corners with nine equivalent Ni(2)O5 square pyramids. In the second Ca site, Ca(2) is bonded in a 6-coordinate geometry to three equivalent O(1) and three equivalent O(4) atoms. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(2) and three equivalent O(1) atoms to form corner-sharing NiO4 tetrahedra. In the second Ni site, Ni(2) is bonded to one O(3), two equivalent O(1), and two equivalent O(4) atoms to form distorted NiO5 square pyramids that share corners with two equivalent Ni(2)O5 square pyramids, corners with two equivalent Ni(1)O4 tetrahedra, corners with three equivalent Ca(1)O4 tetrahedra, and edges with two equivalent Ni(2)O5 square pyramids. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Ca(2), one Ni(1), and two equivalent Ni(2) atoms to form distorted OCaNi3 trigonal pyramids that share corners with seven equivalent O(4)Ca2Ni2 tetrahedra, corners with two equivalent O(1)CaNi3 trigonal pyramids, and edges with two equivalent O(1)CaNi3 trigonal pyramids. In the second O site, O(2) is bonded in a single-bond geometry to one Ni(1) atom. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Ca(1) and three equivalent Ni(2) atoms. In the fourth O site, O(4) is bonded to one Ca(1), one Ca(2), and two equivalent Ni(2) atoms to form distorted OCa2Ni2 tetrahedra that share corners with two equivalent O(4)Ca2Ni2 tetrahedra, corners with seven equivalent O(1)CaNi3 trigonal pyramids, and edges with two equivalent O(4)Ca2Ni2 tetrahedra. is represented by the CIF file [CIF]
data_Ca(NiO2)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.302
_cell_length_b   6.302
_cell_length_c   6.302
_cell_angle_alpha   57.315
_cell_angle_beta   57.315
_cell_angle_gamma   57.315
_symmetry_Int_Tables_number   1
_cell_volume   166.007
_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  0.014  0.014  0.014  1.0
  Ca  Ca1  1  0.625  0.625  0.625  1.0
  Ni  Ni2  1  0.233  0.233  0.233  1.0
  Ni  Ni3  1  0.639  0.639  0.114  1.0
  Ni  Ni4  1  0.114  0.639  0.639  1.0
  Ni  Ni5  1  0.639  0.114  0.639  1.0
  O  O6  1  0.363  0.836  0.363  1.0
  O  O7  1  0.836  0.363  0.363  1.0
  O  O8  1  0.363  0.363  0.836  1.0
  O  O9  1  0.347  0.347  0.347  1.0
  O  O10  1  0.874  0.874  0.874  1.0
  O  O11  1  0.877  0.877  0.449  1.0
  O  O12  1  0.449  0.877  0.877  1.0
  O  O13  1  0.877  0.449  0.877  1.0
[/CIF]
.