The crystal structure described by Ca3SiBr2 is Caswellsilverite-like structured and crystallizes in the trigonal R3m space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to three equivalent Br(1) and three equivalent Br(2) atoms to form distorted CaBr6 pentagonal pyramids that share corners with three equivalent Ca(3)Si3Br3 octahedra, corners with six equivalent Ca(2)Si3Br3 octahedra, edges with three equivalent Ca(3)Si3Br3 octahedra, edges with six equivalent Ca(1)Br6 pentagonal pyramids, and  a faceface with one Ca(2)Si3Br3 octahedra. The corner-sharing octahedral tilt angles range from 4-44°. In the second Ca site, Ca(2) is bonded to three equivalent Si(1) and three equivalent Br(1) atoms to form CaSi3Br3 octahedra that share corners with three equivalent Ca(3)Si3Br3 octahedra, corners with six equivalent Ca(1)Br6 pentagonal pyramids, edges with three equivalent Ca(3)Si3Br3 octahedra, edges with six equivalent Ca(2)Si3Br3 octahedra, and  a faceface with one Ca(1)Br6 pentagonal pyramid. The corner-sharing octahedra are not tilted. In the third Ca site, Ca(3) is bonded to three equivalent Si(1) and three equivalent Br(2) atoms to form CaSi3Br3 octahedra that share corners with three equivalent Ca(2)Si3Br3 octahedra, corners with three equivalent Ca(1)Br6 pentagonal pyramids, edges with three equivalent Ca(2)Si3Br3 octahedra, edges with six equivalent Ca(3)Si3Br3 octahedra, and edges with three equivalent Ca(1)Br6 pentagonal pyramids. The corner-sharing octahedra are not tilted. Si(1) is bonded to three equivalent Ca(2) and three equivalent Ca(3) atoms to form SiCa6 octahedra that share corners with three equivalent Br(2)Ca6 octahedra, corners with three equivalent Br(1)Ca6 pentagonal pyramids, edges with three equivalent Br(2)Ca6 octahedra, edges with six equivalent Si(1)Ca6 octahedra, and edges with three equivalent Br(1)Ca6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 9°. There are two inequivalent Br sites. In the first Br site, Br(1) is bonded to three equivalent Ca(1) and three equivalent Ca(2) atoms to form distorted BrCa6 pentagonal pyramids that share corners with three equivalent Si(1)Ca6 octahedra, corners with six equivalent Br(2)Ca6 octahedra, edges with three equivalent Si(1)Ca6 octahedra, edges with six equivalent Br(1)Ca6 pentagonal pyramids, and  a faceface with one Br(2)Ca6 octahedra. The corner-sharing octahedral tilt angles range from 10-46°. In the second Br site, Br(2) is bonded to three equivalent Ca(1) and three equivalent Ca(3) atoms to form BrCa6 octahedra that share corners with three equivalent Si(1)Ca6 octahedra, corners with six equivalent Br(1)Ca6 pentagonal pyramids, edges with three equivalent Si(1)Ca6 octahedra, edges with six equivalent Br(2)Ca6 octahedra, and  a faceface with one Br(1)Ca6 pentagonal pyramid. The corner-sharing octahedral tilt angles are 9°. is represented by the CIF file [CIF]
data_Ca3SiBr2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   11.954
_cell_length_b   11.954
_cell_length_c   11.954
_cell_angle_alpha   20.125
_cell_angle_beta   20.125
_cell_angle_gamma   20.125
_symmetry_Int_Tables_number   1
_cell_volume   176.912
_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  0.451  0.451  0.451  1.0
  Ca  Ca1  1  0.573  0.573  0.573  1.0
  Ca  Ca2  1  0.999  0.999  0.999  1.0
  Si  Si3  1  0.286  0.286  0.286  1.0
  Br  Br4  1  0.841  0.841  0.841  1.0
  Br  Br5  1  0.729  0.729  0.729  1.0
[/CIF]
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The crystal structure described by Ca3SiBr2 is Caswellsilverite-like structured and crystallizes in the trigonal R3m space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to three equivalent Br(1) and three equivalent Br(2) atoms to form distorted CaBr6 pentagonal pyramids that share corners with three equivalent Ca(3)Si3Br3 octahedra, corners with six equivalent Ca(2)Si3Br3 octahedra, edges with three equivalent Ca(3)Si3Br3 octahedra, edges with six equivalent Ca(1)Br6 pentagonal pyramids, and  a faceface with one Ca(2)Si3Br3 octahedra. The corner-sharing octahedral tilt angles range from 4-44°. In the second Ca site, Ca(2) is bonded to three equivalent Si(1) and three equivalent Br(1) atoms to form CaSi3Br3 octahedra that share corners with three equivalent Ca(3)Si3Br3 octahedra, corners with six equivalent Ca(1)Br6 pentagonal pyramids, edges with three equivalent Ca(3)Si3Br3 octahedra, edges with six equivalent Ca(2)Si3Br3 octahedra, and  a faceface with one Ca(1)Br6 pentagonal pyramid. The corner-sharing octahedra are not tilted. In the third Ca site, Ca(3) is bonded to three equivalent Si(1) and three equivalent Br(2) atoms to form CaSi3Br3 octahedra that share corners with three equivalent Ca(2)Si3Br3 octahedra, corners with three equivalent Ca(1)Br6 pentagonal pyramids, edges with three equivalent Ca(2)Si3Br3 octahedra, edges with six equivalent Ca(3)Si3Br3 octahedra, and edges with three equivalent Ca(1)Br6 pentagonal pyramids. The corner-sharing octahedra are not tilted. Si(1) is bonded to three equivalent Ca(2) and three equivalent Ca(3) atoms to form SiCa6 octahedra that share corners with three equivalent Br(2)Ca6 octahedra, corners with three equivalent Br(1)Ca6 pentagonal pyramids, edges with three equivalent Br(2)Ca6 octahedra, edges with six equivalent Si(1)Ca6 octahedra, and edges with three equivalent Br(1)Ca6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 9°. There are two inequivalent Br sites. In the first Br site, Br(1) is bonded to three equivalent Ca(1) and three equivalent Ca(2) atoms to form distorted BrCa6 pentagonal pyramids that share corners with three equivalent Si(1)Ca6 octahedra, corners with six equivalent Br(2)Ca6 octahedra, edges with three equivalent Si(1)Ca6 octahedra, edges with six equivalent Br(1)Ca6 pentagonal pyramids, and  a faceface with one Br(2)Ca6 octahedra. The corner-sharing octahedral tilt angles range from 10-46°. In the second Br site, Br(2) is bonded to three equivalent Ca(1) and three equivalent Ca(3) atoms to form BrCa6 octahedra that share corners with three equivalent Si(1)Ca6 octahedra, corners with six equivalent Br(1)Ca6 pentagonal pyramids, edges with three equivalent Si(1)Ca6 octahedra, edges with six equivalent Br(2)Ca6 octahedra, and  a faceface with one Br(1)Ca6 pentagonal pyramid. The corner-sharing octahedral tilt angles are 9°. is represented by the CIF file [CIF]
data_Ca3SiBr2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   11.954
_cell_length_b   11.954
_cell_length_c   11.954
_cell_angle_alpha   20.125
_cell_angle_beta   20.125
_cell_angle_gamma   20.125
_symmetry_Int_Tables_number   1
_cell_volume   176.912
_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  0.451  0.451  0.451  1.0
  Ca  Ca1  1  0.573  0.573  0.573  1.0
  Ca  Ca2  1  0.999  0.999  0.999  1.0
  Si  Si3  1  0.286  0.286  0.286  1.0
  Br  Br4  1  0.841  0.841  0.841  1.0
  Br  Br5  1  0.729  0.729  0.729  1.0
[/CIF]
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