The structure described by CaCuAlSi2O9 crystallizes in the monoclinic C2/m space group. Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(6) atoms. Cu(1) is bonded to one O(6), two equivalent O(1), and two equivalent O(2) atoms to form distorted CuO5 trigonal bipyramids that share corners with two equivalent Si(1)O4 tetrahedra and edges with two equivalent Al(1)O6 octahedra. Al(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form AlO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra and edges with two equivalent Cu(1)O5 trigonal bipyramids. Si(1) is bonded to one O(1), one O(3), one O(4), and one O(5) atom to form SiO4 tetrahedra that share corners with two equivalent Al(1)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, and  a cornercorner with one Cu(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 37-49°. There are six inequivalent O sites. In the first O site, O(4) is bonded in a distorted bent 150 degrees geometry to two equivalent Ca(1) and two equivalent Si(1) atoms. In the second O site, O(5) is bonded in a bent 150 degrees geometry to two equivalent Si(1) atoms. In the third O site, O(6) is bonded in a trigonal non-coplanar geometry to two equivalent Ca(1) and one Cu(1) atom. In the fourth O site, O(1) is bonded in a distorted trigonal planar geometry to one Cu(1), one Al(1), and one Si(1) atom. In the fifth O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Ca(1), one Cu(1), and one Al(1) atom. In the sixth O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1), one Al(1), and one Si(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_CaAlCuSi2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.650
_cell_length_b   8.650
_cell_length_c   4.864
_cell_angle_alpha   81.744
_cell_angle_beta   81.744
_cell_angle_gamma   83.077
_symmetry_Int_Tables_number   1
_cell_volume   354.553
_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  0.834  0.166  0.500  1.0
  Ca  Ca1  1  0.166  0.834  0.500  1.0
  Al  Al2  1  0.000  0.500  0.500  1.0
  Al  Al3  1  0.500  0.000  0.500  1.0
  Cu  Cu4  1  0.226  0.226  0.437  1.0
  Cu  Cu5  1  0.774  0.774  0.563  1.0
  Si  Si6  1  0.745  0.480  0.063  1.0
  Si  Si7  1  0.480  0.745  0.063  1.0
  Si  Si8  1  0.255  0.520  0.937  1.0
  Si  Si9  1  0.520  0.255  0.937  1.0
  O  O10  1  0.824  0.569  0.764  1.0
  O  O11  1  0.569  0.824  0.764  1.0
  O  O12  1  0.176  0.431  0.236  1.0
  O  O13  1  0.431  0.176  0.236  1.0
  O  O14  1  0.045  0.284  0.666  1.0
  O  O15  1  0.284  0.045  0.666  1.0
  O  O16  1  0.955  0.716  0.334  1.0
  O  O17  1  0.716  0.955  0.334  1.0
  O  O18  1  0.861  0.427  0.296  1.0
  O  O19  1  0.427  0.861  0.296  1.0
  O  O20  1  0.139  0.573  0.704  1.0
  O  O21  1  0.573  0.139  0.704  1.0
  O  O22  1  0.688  0.312  0.000  1.0
  O  O23  1  0.312  0.688  0.000  1.0
  O  O24  1  0.591  0.591  0.187  1.0
  O  O25  1  0.409  0.409  0.813  1.0
  O  O26  1  0.082  0.082  0.299  1.0
  O  O27  1  0.918  0.918  0.701  1.0
[/CIF]
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The structure described by CaCuAlSi2O9 crystallizes in the monoclinic C2/m space group. Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(6) atoms. Cu(1) is bonded to one O(6), two equivalent O(1), and two equivalent O(2) atoms to form distorted CuO5 trigonal bipyramids that share corners with two equivalent Si(1)O4 tetrahedra and edges with two equivalent Al(1)O6 octahedra. Al(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form AlO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra and edges with two equivalent Cu(1)O5 trigonal bipyramids. Si(1) is bonded to one O(1), one O(3), one O(4), and one O(5) atom to form SiO4 tetrahedra that share corners with two equivalent Al(1)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, and  a cornercorner with one Cu(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 37-49°. There are six inequivalent O sites. In the first O site, O(4) is bonded in a distorted bent 150 degrees geometry to two equivalent Ca(1) and two equivalent Si(1) atoms. In the second O site, O(5) is bonded in a bent 150 degrees geometry to two equivalent Si(1) atoms. In the third O site, O(6) is bonded in a trigonal non-coplanar geometry to two equivalent Ca(1) and one Cu(1) atom. In the fourth O site, O(1) is bonded in a distorted trigonal planar geometry to one Cu(1), one Al(1), and one Si(1) atom. In the fifth O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Ca(1), one Cu(1), and one Al(1) atom. In the sixth O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1), one Al(1), and one Si(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_CaAlCuSi2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.650
_cell_length_b   8.650
_cell_length_c   4.864
_cell_angle_alpha   81.744
_cell_angle_beta   81.744
_cell_angle_gamma   83.077
_symmetry_Int_Tables_number   1
_cell_volume   354.553
_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  0.834  0.166  0.500  1.0
  Ca  Ca1  1  0.166  0.834  0.500  1.0
  Al  Al2  1  0.000  0.500  0.500  1.0
  Al  Al3  1  0.500  0.000  0.500  1.0
  Cu  Cu4  1  0.226  0.226  0.437  1.0
  Cu  Cu5  1  0.774  0.774  0.563  1.0
  Si  Si6  1  0.745  0.480  0.063  1.0
  Si  Si7  1  0.480  0.745  0.063  1.0
  Si  Si8  1  0.255  0.520  0.937  1.0
  Si  Si9  1  0.520  0.255  0.937  1.0
  O  O10  1  0.824  0.569  0.764  1.0
  O  O11  1  0.569  0.824  0.764  1.0
  O  O12  1  0.176  0.431  0.236  1.0
  O  O13  1  0.431  0.176  0.236  1.0
  O  O14  1  0.045  0.284  0.666  1.0
  O  O15  1  0.284  0.045  0.666  1.0
  O  O16  1  0.955  0.716  0.334  1.0
  O  O17  1  0.716  0.955  0.334  1.0
  O  O18  1  0.861  0.427  0.296  1.0
  O  O19  1  0.427  0.861  0.296  1.0
  O  O20  1  0.139  0.573  0.704  1.0
  O  O21  1  0.573  0.139  0.704  1.0
  O  O22  1  0.688  0.312  0.000  1.0
  O  O23  1  0.312  0.688  0.000  1.0
  O  O24  1  0.591  0.591  0.187  1.0
  O  O25  1  0.409  0.409  0.813  1.0
  O  O26  1  0.082  0.082  0.299  1.0
  O  O27  1  0.918  0.918  0.701  1.0
[/CIF]
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