The structure described by Ca2Mn3O8 is Marcasite-derived structured and 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 Mn(1)O6 octahedra, corners with three equivalent Ca(2)O4 tetrahedra, and edges with three equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. 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 Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 59-76°. Mn(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form MnO6 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 Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. 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 Mn(1) atoms. In the second O site, O(2) is bonded to one Ca(1), one Ca(2), and two equivalent Mn(1) atoms to form OCa2Mn2 tetrahedra that share  a cornercorner with one O(4)CaMn3 tetrahedra, corners with two equivalent O(2)Ca2Mn2 tetrahedra,  an edgeedge with one O(4)CaMn3 tetrahedra, and edges with two equivalent O(2)Ca2Mn2 tetrahedra. In the third O site, O(3) is bonded in a distorted T-shaped geometry to three equivalent Mn(1) atoms. In the fourth O site, O(4) is bonded to one Ca(2) and three equivalent Mn(1) atoms to form a mixture of distorted corner and edge-sharing OCaMn3 tetrahedra. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ca2Mn3O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.983
_cell_length_b   5.983
_cell_length_c   10.542
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   120.000
_symmetry_Int_Tables_number   1
_cell_volume   326.796
_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  0.027  1.0
  Ca  Ca1  1  0.333  0.667  0.527  1.0
  Ca  Ca2  1  0.667  0.333  0.431  1.0
  Ca  Ca3  1  0.333  0.667  0.931  1.0
  Mn  Mn4  1  0.671  0.836  0.246  1.0
  Mn  Mn5  1  0.836  0.164  0.746  1.0
  Mn  Mn6  1  0.164  0.329  0.246  1.0
  Mn  Mn7  1  0.836  0.671  0.746  1.0
  Mn  Mn8  1  0.329  0.164  0.746  1.0
  Mn  Mn9  1  0.164  0.836  0.246  1.0
  O  O10  1  0.846  0.154  0.155  1.0
  O  O11  1  0.691  0.846  0.655  1.0
  O  O12  1  0.154  0.309  0.655  1.0
  O  O13  1  0.846  0.691  0.155  1.0
  O  O14  1  0.309  0.154  0.155  1.0
  O  O15  1  0.154  0.846  0.655  1.0
  O  O16  1  0.522  0.478  0.848  1.0
  O  O17  1  0.044  0.522  0.348  1.0
  O  O18  1  0.478  0.956  0.348  1.0
  O  O19  1  0.522  0.044  0.848  1.0
  O  O20  1  0.000  0.000  0.341  1.0
  O  O21  1  0.000  0.000  0.841  1.0
  O  O22  1  0.333  0.667  0.149  1.0
  O  O23  1  0.956  0.478  0.848  1.0
  O  O24  1  0.478  0.522  0.348  1.0
  O  O25  1  0.667  0.333  0.649  1.0
[/CIF]
.
The structure described by Ca2Mn3O8 is Marcasite-derived structured and 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 Mn(1)O6 octahedra, corners with three equivalent Ca(2)O4 tetrahedra, and edges with three equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. 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 Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 59-76°. Mn(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form MnO6 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 Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. 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 Mn(1) atoms. In the second O site, O(2) is bonded to one Ca(1), one Ca(2), and two equivalent Mn(1) atoms to form OCa2Mn2 tetrahedra that share  a cornercorner with one O(4)CaMn3 tetrahedra, corners with two equivalent O(2)Ca2Mn2 tetrahedra,  an edgeedge with one O(4)CaMn3 tetrahedra, and edges with two equivalent O(2)Ca2Mn2 tetrahedra. In the third O site, O(3) is bonded in a distorted T-shaped geometry to three equivalent Mn(1) atoms. In the fourth O site, O(4) is bonded to one Ca(2) and three equivalent Mn(1) atoms to form a mixture of distorted corner and edge-sharing OCaMn3 tetrahedra. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ca2Mn3O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.983
_cell_length_b   5.983
_cell_length_c   10.542
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   120.000
_symmetry_Int_Tables_number   1
_cell_volume   326.796
_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  0.027  1.0
  Ca  Ca1  1  0.333  0.667  0.527  1.0
  Ca  Ca2  1  0.667  0.333  0.431  1.0
  Ca  Ca3  1  0.333  0.667  0.931  1.0
  Mn  Mn4  1  0.671  0.836  0.246  1.0
  Mn  Mn5  1  0.836  0.164  0.746  1.0
  Mn  Mn6  1  0.164  0.329  0.246  1.0
  Mn  Mn7  1  0.836  0.671  0.746  1.0
  Mn  Mn8  1  0.329  0.164  0.746  1.0
  Mn  Mn9  1  0.164  0.836  0.246  1.0
  O  O10  1  0.846  0.154  0.155  1.0
  O  O11  1  0.691  0.846  0.655  1.0
  O  O12  1  0.154  0.309  0.655  1.0
  O  O13  1  0.846  0.691  0.155  1.0
  O  O14  1  0.309  0.154  0.155  1.0
  O  O15  1  0.154  0.846  0.655  1.0
  O  O16  1  0.522  0.478  0.848  1.0
  O  O17  1  0.044  0.522  0.348  1.0
  O  O18  1  0.478  0.956  0.348  1.0
  O  O19  1  0.522  0.044  0.848  1.0
  O  O20  1  0.000  0.000  0.341  1.0
  O  O21  1  0.000  0.000  0.841  1.0
  O  O22  1  0.333  0.667  0.149  1.0
  O  O23  1  0.956  0.478  0.848  1.0
  O  O24  1  0.478  0.522  0.348  1.0
  O  O25  1  0.667  0.333  0.649  1.0
[/CIF]
.