The crystal structure described by Ca3W2O9 crystallizes in the monoclinic P2_1/m space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(1), one O(3), one O(4), and two equivalent O(2) atoms to form CaO5 trigonal bipyramids that share  a cornercorner with one W(2)O4 tetrahedra, corners with three equivalent W(1)O4 tetrahedra,  a cornercorner with one Ca(3)O5 trigonal bipyramid, and edges with two equivalent Ca(2)O6 octahedra. In the second Ca site, Ca(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(6) atoms to form CaO6 octahedra that share corners with two equivalent Ca(2)O6 octahedra, corners with two equivalent W(1)O4 tetrahedra, corners with two equivalent W(2)O4 tetrahedra, edges with two equivalent Ca(1)O5 trigonal bipyramids, and edges with two equivalent Ca(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 57°. In the third Ca site, Ca(3) is bonded to one O(1), one O(5), one O(7), and two equivalent O(6) atoms to form distorted CaO5 trigonal bipyramids that share  a cornercorner with one W(1)O4 tetrahedra, corners with three equivalent W(2)O4 tetrahedra,  a cornercorner with one Ca(1)O5 trigonal bipyramid, and edges with two equivalent Ca(2)O6 octahedra. There are two inequivalent W sites. In the first W site, W(1) is bonded to one O(3), one O(5), and two equivalent O(2) atoms to form WO4 tetrahedra that share corners with two equivalent Ca(2)O6 octahedra,  a cornercorner with one Ca(3)O5 trigonal bipyramid, and corners with three equivalent Ca(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 49°. In the second W site, W(2) is bonded to one O(4), one O(7), and two equivalent O(6) atoms to form WO4 tetrahedra that share corners with two equivalent Ca(2)O6 octahedra,  a cornercorner with one Ca(1)O5 trigonal bipyramid, and corners with three equivalent Ca(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 44°. There are seven inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), one Ca(3), and two equivalent Ca(2) atoms to form corner-sharing OCa4 tetrahedra. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Ca(1), one Ca(2), and one W(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Ca(1) and one W(1) atom. In the fourth O site, O(4) is bonded in a linear geometry to one Ca(1) and one W(2) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Ca(3) and one W(1) atom. In the sixth O site, O(6) is bonded in a distorted T-shaped geometry to one Ca(2), one Ca(3), and one W(2) atom. In the seventh O site, O(7) is bonded in a linear geometry to one Ca(3) and one W(2) atom. is represented by the CIF card [CIF]
data_Ca3W2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.791
_cell_length_b   8.572
_cell_length_c   9.313
_cell_angle_alpha   62.285
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   550.627
_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  0.750  0.892  0.750  1.0
  Ca  Ca1  1  0.000  0.000  0.000  1.0
  Ca  Ca2  1  0.500  0.000  0.000  1.0
  Ca  Ca3  1  0.750  0.628  0.215  1.0
  Ca  Ca4  1  0.250  0.372  0.785  1.0
  Ca  Ca5  1  0.250  0.108  0.250  1.0
  W  W6  1  0.250  0.837  0.727  1.0
  W  W7  1  0.750  0.444  0.708  1.0
  W  W8  1  0.250  0.556  0.292  1.0
  W  W9  1  0.750  0.163  0.273  1.0
  O  O10  1  0.750  0.882  0.992  1.0
  O  O11  1  0.442  0.926  0.776  1.0
  O  O12  1  0.058  0.926  0.776  1.0
  O  O13  1  0.250  0.892  0.515  1.0
  O  O14  1  0.750  0.633  0.743  1.0
  O  O15  1  0.250  0.601  0.842  1.0
  O  O16  1  0.442  0.690  0.204  1.0
  O  O17  1  0.058  0.690  0.204  1.0
  O  O18  1  0.750  0.524  0.491  1.0
  O  O19  1  0.250  0.476  0.509  1.0
  O  O20  1  0.942  0.310  0.796  1.0
  O  O21  1  0.558  0.310  0.796  1.0
  O  O22  1  0.750  0.399  0.158  1.0
  O  O23  1  0.250  0.367  0.257  1.0
  O  O24  1  0.750  0.108  0.485  1.0
  O  O25  1  0.942  0.074  0.224  1.0
  O  O26  1  0.558  0.074  0.224  1.0
  O  O27  1  0.250  0.118  0.008  1.0
[/CIF]
.
The crystal structure described by Ca3W2O9 crystallizes in the monoclinic P2_1/m space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(1), one O(3), one O(4), and two equivalent O(2) atoms to form CaO5 trigonal bipyramids that share  a cornercorner with one W(2)O4 tetrahedra, corners with three equivalent W(1)O4 tetrahedra,  a cornercorner with one Ca(3)O5 trigonal bipyramid, and edges with two equivalent Ca(2)O6 octahedra. In the second Ca site, Ca(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(6) atoms to form CaO6 octahedra that share corners with two equivalent Ca(2)O6 octahedra, corners with two equivalent W(1)O4 tetrahedra, corners with two equivalent W(2)O4 tetrahedra, edges with two equivalent Ca(1)O5 trigonal bipyramids, and edges with two equivalent Ca(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 57°. In the third Ca site, Ca(3) is bonded to one O(1), one O(5), one O(7), and two equivalent O(6) atoms to form distorted CaO5 trigonal bipyramids that share  a cornercorner with one W(1)O4 tetrahedra, corners with three equivalent W(2)O4 tetrahedra,  a cornercorner with one Ca(1)O5 trigonal bipyramid, and edges with two equivalent Ca(2)O6 octahedra. There are two inequivalent W sites. In the first W site, W(1) is bonded to one O(3), one O(5), and two equivalent O(2) atoms to form WO4 tetrahedra that share corners with two equivalent Ca(2)O6 octahedra,  a cornercorner with one Ca(3)O5 trigonal bipyramid, and corners with three equivalent Ca(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 49°. In the second W site, W(2) is bonded to one O(4), one O(7), and two equivalent O(6) atoms to form WO4 tetrahedra that share corners with two equivalent Ca(2)O6 octahedra,  a cornercorner with one Ca(1)O5 trigonal bipyramid, and corners with three equivalent Ca(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 44°. There are seven inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), one Ca(3), and two equivalent Ca(2) atoms to form corner-sharing OCa4 tetrahedra. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Ca(1), one Ca(2), and one W(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Ca(1) and one W(1) atom. In the fourth O site, O(4) is bonded in a linear geometry to one Ca(1) and one W(2) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Ca(3) and one W(1) atom. In the sixth O site, O(6) is bonded in a distorted T-shaped geometry to one Ca(2), one Ca(3), and one W(2) atom. In the seventh O site, O(7) is bonded in a linear geometry to one Ca(3) and one W(2) atom. is represented by the CIF card [CIF]
data_Ca3W2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.791
_cell_length_b   8.572
_cell_length_c   9.313
_cell_angle_alpha   62.285
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   550.627
_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  0.750  0.892  0.750  1.0
  Ca  Ca1  1  0.000  0.000  0.000  1.0
  Ca  Ca2  1  0.500  0.000  0.000  1.0
  Ca  Ca3  1  0.750  0.628  0.215  1.0
  Ca  Ca4  1  0.250  0.372  0.785  1.0
  Ca  Ca5  1  0.250  0.108  0.250  1.0
  W  W6  1  0.250  0.837  0.727  1.0
  W  W7  1  0.750  0.444  0.708  1.0
  W  W8  1  0.250  0.556  0.292  1.0
  W  W9  1  0.750  0.163  0.273  1.0
  O  O10  1  0.750  0.882  0.992  1.0
  O  O11  1  0.442  0.926  0.776  1.0
  O  O12  1  0.058  0.926  0.776  1.0
  O  O13  1  0.250  0.892  0.515  1.0
  O  O14  1  0.750  0.633  0.743  1.0
  O  O15  1  0.250  0.601  0.842  1.0
  O  O16  1  0.442  0.690  0.204  1.0
  O  O17  1  0.058  0.690  0.204  1.0
  O  O18  1  0.750  0.524  0.491  1.0
  O  O19  1  0.250  0.476  0.509  1.0
  O  O20  1  0.942  0.310  0.796  1.0
  O  O21  1  0.558  0.310  0.796  1.0
  O  O22  1  0.750  0.399  0.158  1.0
  O  O23  1  0.250  0.367  0.257  1.0
  O  O24  1  0.750  0.108  0.485  1.0
  O  O25  1  0.942  0.074  0.224  1.0
  O  O26  1  0.558  0.074  0.224  1.0
  O  O27  1  0.250  0.118  0.008  1.0
[/CIF]
.