The structure described by Ca(NiO2)2 crystallizes in the monoclinic C2/m space group. Ca(1) is bonded to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted CaO6 pentagonal pyramids that share corners with two equivalent Ni(2)O6 octahedra, corners with three equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(2)O6 octahedra, edges with three equivalent Ni(1)O6 octahedra, edges with two equivalent Ca(1)O6 pentagonal pyramids, and  a faceface with one Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 10-58°. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(2), two equivalent O(1), and three equivalent O(3) atoms to form NiO6 octahedra that share corners with four equivalent Ni(2)O6 octahedra, corners with three equivalent Ca(1)O6 pentagonal pyramids, edges with four equivalent Ni(1)O6 octahedra, and edges with three equivalent Ca(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 51-60°. In the second Ni site, Ni(2) is bonded to one O(1), two equivalent O(2), and three equivalent O(4) atoms to form distorted NiO6 octahedra that share corners with four equivalent Ni(1)O6 octahedra, corners with two equivalent Ca(1)O6 pentagonal pyramids, edges with four equivalent Ni(2)O6 octahedra, edges with two equivalent Ca(1)O6 pentagonal pyramids, and  a faceface with one Ca(1)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 51-60°. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), one Ni(2), and two equivalent Ni(1) atoms to form OCaNi3 trigonal pyramids that share  a cornercorner with one O(4)Ca2Ni3 square pyramid, corners with two equivalent O(3)Ca2Ni3 square pyramids, corners with two equivalent O(1)CaNi3 trigonal pyramids, corners with five equivalent O(2)CaNi3 trigonal pyramids, edges with two equivalent O(4)Ca2Ni3 square pyramids, and edges with three equivalent O(3)Ca2Ni3 square pyramids. In the second O site, O(2) is bonded to one Ca(1), one Ni(1), and two equivalent Ni(2) atoms to form distorted OCaNi3 trigonal pyramids that share corners with two equivalent O(4)Ca2Ni3 square pyramids, corners with five equivalent O(3)Ca2Ni3 square pyramids, corners with two equivalent O(2)CaNi3 trigonal pyramids, corners with five equivalent O(1)CaNi3 trigonal pyramids, and edges with three equivalent O(4)Ca2Ni3 square pyramids. In the third O site, O(3) is bonded to two equivalent Ca(1) and three equivalent Ni(1) atoms to form OCa2Ni3 square pyramids that share corners with two equivalent O(4)Ca2Ni3 square pyramids, corners with two equivalent O(1)CaNi3 trigonal pyramids, corners with five equivalent O(2)CaNi3 trigonal pyramids,  an edgeedge with one O(4)Ca2Ni3 square pyramid, edges with four equivalent O(3)Ca2Ni3 square pyramids, and edges with three equivalent O(1)CaNi3 trigonal pyramids. In the fourth O site, O(4) is bonded to two equivalent Ca(1) and three equivalent Ni(2) atoms to form OCa2Ni3 square pyramids that share corners with two equivalent O(3)Ca2Ni3 square pyramids,  a cornercorner with one O(1)CaNi3 trigonal pyramid, corners with two equivalent O(2)CaNi3 trigonal pyramids,  an edgeedge with one O(3)Ca2Ni3 square pyramid, edges with four equivalent O(4)Ca2Ni3 square pyramids, edges with two equivalent O(1)CaNi3 trigonal pyramids, and edges with three equivalent O(2)CaNi3 trigonal pyramids. is represented by the CIF file [CIF]
data_Ca(NiO2)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.074
_cell_length_b   7.899
_cell_length_c   6.770
_cell_angle_alpha   79.165
_cell_angle_beta   76.859
_cell_angle_gamma   78.780
_symmetry_Int_Tables_number   1
_cell_volume   155.242
_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  0.348  0.162  0.151  1.0
  Ca  Ca1  1  0.655  0.816  0.882  1.0
  Ni  Ni2  1  0.640  0.156  0.572  1.0
  Ni  Ni3  1  0.137  0.521  0.212  1.0
  Ni  Ni4  1  0.865  0.457  0.820  1.0
  Ni  Ni5  1  0.362  0.822  0.462  1.0
  O  O6  1  0.866  0.686  0.588  1.0
  O  O7  1  0.462  0.293  0.791  1.0
  O  O8  1  0.540  0.685  0.242  1.0
  O  O9  1  0.136  0.292  0.445  1.0
  O  O10  1  0.161  0.994  0.692  1.0
  O  O11  1  0.754  0.375  0.126  1.0
  O  O12  1  0.842  0.984  0.340  1.0
  O  O13  1  0.249  0.603  0.907  1.0
[/CIF]
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The structure described by Ca(NiO2)2 crystallizes in the monoclinic C2/m space group. Ca(1) is bonded to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted CaO6 pentagonal pyramids that share corners with two equivalent Ni(2)O6 octahedra, corners with three equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(2)O6 octahedra, edges with three equivalent Ni(1)O6 octahedra, edges with two equivalent Ca(1)O6 pentagonal pyramids, and  a faceface with one Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 10-58°. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(2), two equivalent O(1), and three equivalent O(3) atoms to form NiO6 octahedra that share corners with four equivalent Ni(2)O6 octahedra, corners with three equivalent Ca(1)O6 pentagonal pyramids, edges with four equivalent Ni(1)O6 octahedra, and edges with three equivalent Ca(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 51-60°. In the second Ni site, Ni(2) is bonded to one O(1), two equivalent O(2), and three equivalent O(4) atoms to form distorted NiO6 octahedra that share corners with four equivalent Ni(1)O6 octahedra, corners with two equivalent Ca(1)O6 pentagonal pyramids, edges with four equivalent Ni(2)O6 octahedra, edges with two equivalent Ca(1)O6 pentagonal pyramids, and  a faceface with one Ca(1)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 51-60°. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), one Ni(2), and two equivalent Ni(1) atoms to form OCaNi3 trigonal pyramids that share  a cornercorner with one O(4)Ca2Ni3 square pyramid, corners with two equivalent O(3)Ca2Ni3 square pyramids, corners with two equivalent O(1)CaNi3 trigonal pyramids, corners with five equivalent O(2)CaNi3 trigonal pyramids, edges with two equivalent O(4)Ca2Ni3 square pyramids, and edges with three equivalent O(3)Ca2Ni3 square pyramids. In the second O site, O(2) is bonded to one Ca(1), one Ni(1), and two equivalent Ni(2) atoms to form distorted OCaNi3 trigonal pyramids that share corners with two equivalent O(4)Ca2Ni3 square pyramids, corners with five equivalent O(3)Ca2Ni3 square pyramids, corners with two equivalent O(2)CaNi3 trigonal pyramids, corners with five equivalent O(1)CaNi3 trigonal pyramids, and edges with three equivalent O(4)Ca2Ni3 square pyramids. In the third O site, O(3) is bonded to two equivalent Ca(1) and three equivalent Ni(1) atoms to form OCa2Ni3 square pyramids that share corners with two equivalent O(4)Ca2Ni3 square pyramids, corners with two equivalent O(1)CaNi3 trigonal pyramids, corners with five equivalent O(2)CaNi3 trigonal pyramids,  an edgeedge with one O(4)Ca2Ni3 square pyramid, edges with four equivalent O(3)Ca2Ni3 square pyramids, and edges with three equivalent O(1)CaNi3 trigonal pyramids. In the fourth O site, O(4) is bonded to two equivalent Ca(1) and three equivalent Ni(2) atoms to form OCa2Ni3 square pyramids that share corners with two equivalent O(3)Ca2Ni3 square pyramids,  a cornercorner with one O(1)CaNi3 trigonal pyramid, corners with two equivalent O(2)CaNi3 trigonal pyramids,  an edgeedge with one O(3)Ca2Ni3 square pyramid, edges with four equivalent O(4)Ca2Ni3 square pyramids, edges with two equivalent O(1)CaNi3 trigonal pyramids, and edges with three equivalent O(2)CaNi3 trigonal pyramids. is represented by the CIF file [CIF]
data_Ca(NiO2)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.074
_cell_length_b   7.899
_cell_length_c   6.770
_cell_angle_alpha   79.165
_cell_angle_beta   76.859
_cell_angle_gamma   78.780
_symmetry_Int_Tables_number   1
_cell_volume   155.242
_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  0.348  0.162  0.151  1.0
  Ca  Ca1  1  0.655  0.816  0.882  1.0
  Ni  Ni2  1  0.640  0.156  0.572  1.0
  Ni  Ni3  1  0.137  0.521  0.212  1.0
  Ni  Ni4  1  0.865  0.457  0.820  1.0
  Ni  Ni5  1  0.362  0.822  0.462  1.0
  O  O6  1  0.866  0.686  0.588  1.0
  O  O7  1  0.462  0.293  0.791  1.0
  O  O8  1  0.540  0.685  0.242  1.0
  O  O9  1  0.136  0.292  0.445  1.0
  O  O10  1  0.161  0.994  0.692  1.0
  O  O11  1  0.754  0.375  0.126  1.0
  O  O12  1  0.842  0.984  0.340  1.0
  O  O13  1  0.249  0.603  0.907  1.0
[/CIF]
.