The structure described by Ca2Ni3O8 crystallizes in the hexagonal P6_3mc space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted CaO6 octahedra that share corners with six equivalent Ni(1)O6 octahedra, corners with three equivalent Ca(2)O4 tetrahedra, and edges with three equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 53°. In the second Ca site, Ca(2) is bonded to one O(4) and three equivalent O(2) atoms to form CaO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra and corners with nine equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 58-78°. Ni(1) 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 two equivalent Ca(1)O6 octahedra, corners with three equivalent Ca(2)O4 tetrahedra,  an edgeedge with one Ca(1)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 53°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Ca(1) and two equivalent Ni(1) atoms. In the second O site, O(2) is bonded to one Ca(1), one Ca(2), and two equivalent Ni(1) atoms to form distorted OCa2Ni2 tetrahedra that share  a cornercorner with one O(4)CaNi3 tetrahedra, corners with two equivalent O(2)Ca2Ni2 tetrahedra,  an edgeedge with one O(4)CaNi3 tetrahedra, and edges with two equivalent O(2)Ca2Ni2 tetrahedra. In the third O site, O(3) is bonded in a distorted T-shaped geometry to three equivalent Ni(1) atoms. In the fourth O site, O(4) is bonded to one Ca(2) and three equivalent Ni(1) atoms to form a mixture of distorted corner and edge-sharing OCaNi3 tetrahedra. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ca2Ni3O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.829
_cell_length_b   5.829
_cell_length_c   10.399
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   120.000
_symmetry_Int_Tables_number   1
_cell_volume   306.009
_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  0.667  0.333  0.028  1.0
  Ca  Ca1  1  0.333  0.667  0.528  1.0
  Ca  Ca2  1  0.667  0.333  0.434  1.0
  Ca  Ca3  1  0.333  0.667  0.934  1.0
  Ni  Ni4  1  0.670  0.835  0.247  1.0
  Ni  Ni5  1  0.835  0.165  0.747  1.0
  Ni  Ni6  1  0.165  0.330  0.247  1.0
  Ni  Ni7  1  0.835  0.670  0.747  1.0
  Ni  Ni8  1  0.330  0.165  0.747  1.0
  Ni  Ni9  1  0.165  0.835  0.247  1.0
  O  O10  1  0.848  0.152  0.155  1.0
  O  O11  1  0.696  0.848  0.655  1.0
  O  O12  1  0.152  0.304  0.655  1.0
  O  O13  1  0.848  0.696  0.155  1.0
  O  O14  1  0.304  0.152  0.155  1.0
  O  O15  1  0.152  0.848  0.655  1.0
  O  O16  1  0.522  0.478  0.845  1.0
  O  O17  1  0.044  0.522  0.345  1.0
  O  O18  1  0.478  0.956  0.345  1.0
  O  O19  1  0.522  0.044  0.845  1.0
  O  O20  1  0.000  0.000  0.338  1.0
  O  O21  1  0.000  0.000  0.838  1.0
  O  O22  1  0.333  0.667  0.154  1.0
  O  O23  1  0.956  0.478  0.845  1.0
  O  O24  1  0.478  0.522  0.345  1.0
  O  O25  1  0.667  0.333  0.654  1.0
[/CIF]
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The structure described by Ca2Ni3O8 crystallizes in the hexagonal P6_3mc space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted CaO6 octahedra that share corners with six equivalent Ni(1)O6 octahedra, corners with three equivalent Ca(2)O4 tetrahedra, and edges with three equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 53°. In the second Ca site, Ca(2) is bonded to one O(4) and three equivalent O(2) atoms to form CaO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra and corners with nine equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 58-78°. Ni(1) 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 two equivalent Ca(1)O6 octahedra, corners with three equivalent Ca(2)O4 tetrahedra,  an edgeedge with one Ca(1)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 53°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Ca(1) and two equivalent Ni(1) atoms. In the second O site, O(2) is bonded to one Ca(1), one Ca(2), and two equivalent Ni(1) atoms to form distorted OCa2Ni2 tetrahedra that share  a cornercorner with one O(4)CaNi3 tetrahedra, corners with two equivalent O(2)Ca2Ni2 tetrahedra,  an edgeedge with one O(4)CaNi3 tetrahedra, and edges with two equivalent O(2)Ca2Ni2 tetrahedra. In the third O site, O(3) is bonded in a distorted T-shaped geometry to three equivalent Ni(1) atoms. In the fourth O site, O(4) is bonded to one Ca(2) and three equivalent Ni(1) atoms to form a mixture of distorted corner and edge-sharing OCaNi3 tetrahedra. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ca2Ni3O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.829
_cell_length_b   5.829
_cell_length_c   10.399
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   120.000
_symmetry_Int_Tables_number   1
_cell_volume   306.009
_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  0.667  0.333  0.028  1.0
  Ca  Ca1  1  0.333  0.667  0.528  1.0
  Ca  Ca2  1  0.667  0.333  0.434  1.0
  Ca  Ca3  1  0.333  0.667  0.934  1.0
  Ni  Ni4  1  0.670  0.835  0.247  1.0
  Ni  Ni5  1  0.835  0.165  0.747  1.0
  Ni  Ni6  1  0.165  0.330  0.247  1.0
  Ni  Ni7  1  0.835  0.670  0.747  1.0
  Ni  Ni8  1  0.330  0.165  0.747  1.0
  Ni  Ni9  1  0.165  0.835  0.247  1.0
  O  O10  1  0.848  0.152  0.155  1.0
  O  O11  1  0.696  0.848  0.655  1.0
  O  O12  1  0.152  0.304  0.655  1.0
  O  O13  1  0.848  0.696  0.155  1.0
  O  O14  1  0.304  0.152  0.155  1.0
  O  O15  1  0.152  0.848  0.655  1.0
  O  O16  1  0.522  0.478  0.845  1.0
  O  O17  1  0.044  0.522  0.345  1.0
  O  O18  1  0.478  0.956  0.345  1.0
  O  O19  1  0.522  0.044  0.845  1.0
  O  O20  1  0.000  0.000  0.338  1.0
  O  O21  1  0.000  0.000  0.838  1.0
  O  O22  1  0.333  0.667  0.154  1.0
  O  O23  1  0.956  0.478  0.845  1.0
  O  O24  1  0.478  0.522  0.345  1.0
  O  O25  1  0.667  0.333  0.654  1.0
[/CIF]
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