The crystal structure described by Ca2Mn3O8 crystallizes in the monoclinic C2/m space group. Ca(1) is bonded to one O(1), one O(2), and four equivalent O(3) atoms to form distorted CaO6 pentagonal pyramids that share corners with three equivalent Mn(1)O6 octahedra, corners with four equivalent Mn(2)O6 octahedra,  an edgeedge with one Mn(1)O6 octahedra, edges with two equivalent Mn(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 20-56°. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form MnO6 octahedra that share corners with six equivalent Ca(1)O6 pentagonal pyramids, edges with four equivalent Mn(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. In the second Mn site, Mn(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form MnO6 octahedra that share corners with four equivalent Ca(1)O6 pentagonal pyramids, edges with two equivalent Mn(1)O6 octahedra, edges with two equivalent Mn(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ca(1) and two equivalent Mn(2) atoms. In the second O site, O(2) is bonded to one Ca(1), one Mn(1), and two equivalent Mn(2) atoms to form distorted OCaMn3 trigonal pyramids that share  a cornercorner with one O(2)CaMn3 trigonal pyramid, corners with four equivalent O(3)Ca2Mn2 trigonal pyramids,  an edgeedge with one O(2)CaMn3 trigonal pyramid, and edges with four equivalent O(3)Ca2Mn2 trigonal pyramids. In the third O site, O(3) is bonded to two equivalent Ca(1), one Mn(1), and one Mn(2) atom to form distorted OCa2Mn2 trigonal pyramids that share corners with two equivalent O(2)CaMn3 trigonal pyramids, corners with six equivalent O(3)Ca2Mn2 trigonal pyramids, edges with two equivalent O(3)Ca2Mn2 trigonal pyramids, and edges with two equivalent O(2)CaMn3 trigonal pyramids. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ca2Mn3O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.940
_cell_length_b   5.831
_cell_length_c   6.241
_cell_angle_alpha   117.851
_cell_angle_beta   107.280
_cell_angle_gamma   89.997
_symmetry_Int_Tables_number   1
_cell_volume   149.703
_cell_formula_units_Z   1
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  0.725  0.450  1.0
  Ca  Ca1  1  0.333  0.275  0.550  1.0
  Mn  Mn2  1  0.500  1.000  0.000  1.0
  Mn  Mn3  1  1.000  0.741  0.000  1.0
  Mn  Mn4  1  0.000  0.259  1.000  1.0
  O  O5  1  0.042  0.397  0.795  1.0
  O  O6  1  0.958  0.603  0.205  1.0
  O  O7  1  0.098  0.904  0.807  1.0
  O  O8  1  0.902  0.096  0.193  1.0
  O  O9  1  0.391  0.322  0.200  1.0
  O  O10  1  0.391  0.878  0.200  1.0
  O  O11  1  0.609  0.122  0.800  1.0
  O  O12  1  0.609  0.678  0.800  1.0
[/CIF]
.
The crystal structure described by Ca2Mn3O8 crystallizes in the monoclinic C2/m space group. Ca(1) is bonded to one O(1), one O(2), and four equivalent O(3) atoms to form distorted CaO6 pentagonal pyramids that share corners with three equivalent Mn(1)O6 octahedra, corners with four equivalent Mn(2)O6 octahedra,  an edgeedge with one Mn(1)O6 octahedra, edges with two equivalent Mn(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 20-56°. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form MnO6 octahedra that share corners with six equivalent Ca(1)O6 pentagonal pyramids, edges with four equivalent Mn(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. In the second Mn site, Mn(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form MnO6 octahedra that share corners with four equivalent Ca(1)O6 pentagonal pyramids, edges with two equivalent Mn(1)O6 octahedra, edges with two equivalent Mn(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ca(1) and two equivalent Mn(2) atoms. In the second O site, O(2) is bonded to one Ca(1), one Mn(1), and two equivalent Mn(2) atoms to form distorted OCaMn3 trigonal pyramids that share  a cornercorner with one O(2)CaMn3 trigonal pyramid, corners with four equivalent O(3)Ca2Mn2 trigonal pyramids,  an edgeedge with one O(2)CaMn3 trigonal pyramid, and edges with four equivalent O(3)Ca2Mn2 trigonal pyramids. In the third O site, O(3) is bonded to two equivalent Ca(1), one Mn(1), and one Mn(2) atom to form distorted OCa2Mn2 trigonal pyramids that share corners with two equivalent O(2)CaMn3 trigonal pyramids, corners with six equivalent O(3)Ca2Mn2 trigonal pyramids, edges with two equivalent O(3)Ca2Mn2 trigonal pyramids, and edges with two equivalent O(2)CaMn3 trigonal pyramids. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ca2Mn3O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.940
_cell_length_b   5.831
_cell_length_c   6.241
_cell_angle_alpha   117.851
_cell_angle_beta   107.280
_cell_angle_gamma   89.997
_symmetry_Int_Tables_number   1
_cell_volume   149.703
_cell_formula_units_Z   1
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  0.725  0.450  1.0
  Ca  Ca1  1  0.333  0.275  0.550  1.0
  Mn  Mn2  1  0.500  1.000  0.000  1.0
  Mn  Mn3  1  1.000  0.741  0.000  1.0
  Mn  Mn4  1  0.000  0.259  1.000  1.0
  O  O5  1  0.042  0.397  0.795  1.0
  O  O6  1  0.958  0.603  0.205  1.0
  O  O7  1  0.098  0.904  0.807  1.0
  O  O8  1  0.902  0.096  0.193  1.0
  O  O9  1  0.391  0.322  0.200  1.0
  O  O10  1  0.391  0.878  0.200  1.0
  O  O11  1  0.609  0.122  0.800  1.0
  O  O12  1  0.609  0.678  0.800  1.0
[/CIF]
.