The structure described by CaAl2(Si2O7)2 crystallizes in the monoclinic C2 space group. Ca(1) is bonded to one O(13), one O(14), one O(2), one O(3), one O(4), and one O(5) atom to form distorted CaO6 pentagonal pyramids that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra,  an edgeedge with one Al(1)O4 tetrahedra, and  an edgeedge with one Al(2)O4 tetrahedra. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(12), one O(2), one O(4), and one O(7) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Ca(1)O6 pentagonal pyramid. In the second Al site, Al(2) is bonded to one O(11), one O(3), one O(5), and one O(6) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, and  an edgeedge with one Ca(1)O6 pentagonal pyramid. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(4), one O(6), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(1)O6 pentagonal pyramid,  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(4)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(10), one O(12), one O(2), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(1)O6 pentagonal pyramid,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. In the third Si site, Si(3) is bonded to one O(10), one O(11), one O(3), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(1)O6 pentagonal pyramid,  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, and corners with two equivalent Al(2)O4 tetrahedra. In the fourth Si site, Si(4) is bonded to one O(1), one O(5), one O(7), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(1)O6 pentagonal pyramid,  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(4) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Si(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(2), and one Si(3) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Ca(1), one Al(1), and one Si(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Al(2), and one Si(4) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(1) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(4) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Si(3) and one Si(4) atom. In the tenth O site, O(10) is bonded in a bent 150 degrees geometry to one Si(2) and one Si(3) atom. In the eleventh O site, O(11) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(3) atom. In the twelfth O site, O(12) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(2) atom. In the thirteenth O site, O(13) is bonded in a single-bond geometry to one Ca(1) atom. In the fourteenth O site, O(14) is bonded in a single-bond geometry to one Ca(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_CaAl2(Si2O7)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   10.038
_cell_length_b   10.038
_cell_length_c   7.563
_cell_angle_alpha   74.396
_cell_angle_beta   74.396
_cell_angle_gamma   82.980
_symmetry_Int_Tables_number   1
_cell_volume   705.883
_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  0.988  0.518  0.763  1.0
  Ca  Ca1  1  0.482  0.012  0.237  1.0
  Al  Al2  1  0.053  0.202  0.762  1.0
  Al  Al3  1  0.798  0.947  0.238  1.0
  Al  Al4  1  0.670  0.589  0.767  1.0
  Al  Al5  1  0.411  0.330  0.233  1.0
  Si  Si6  1  0.090  0.391  0.341  1.0
  Si  Si7  1  0.609  0.910  0.659  1.0
  Si  Si8  1  0.935  0.231  0.176  1.0
  Si  Si9  1  0.769  0.065  0.824  1.0
  Si  Si10  1  0.699  0.466  0.177  1.0
  Si  Si11  1  0.534  0.301  0.823  1.0
  Si  Si12  1  0.856  0.624  0.346  1.0
  Si  Si13  1  0.376  0.144  0.654  1.0
  O  O14  1  0.997  0.532  0.270  1.0
  O  O15  1  0.468  0.003  0.730  1.0
  O  O16  1  0.999  0.293  0.947  1.0
  O  O17  1  0.707  0.001  0.053  1.0
  O  O18  1  0.762  0.536  0.950  1.0
  O  O19  1  0.464  0.238  0.050  1.0
  O  O20  1  0.062  0.357  0.573  1.0
  O  O21  1  0.643  0.938  0.427  1.0
  O  O22  1  0.824  0.599  0.577  1.0
  O  O23  1  0.401  0.176  0.423  1.0
  O  O24  1  0.251  0.416  0.235  1.0
  O  O25  1  0.584  0.749  0.765  1.0
  O  O26  1  0.881  0.784  0.242  1.0
  O  O27  1  0.216  0.119  0.758  1.0
  O  O28  1  0.041  0.259  0.290  1.0
  O  O29  1  0.741  0.959  0.710  1.0
  O  O30  1  0.723  0.571  0.298  1.0
  O  O31  1  0.429  0.277  0.702  1.0
  O  O32  1  0.789  0.320  0.236  1.0
  O  O33  1  0.680  0.211  0.764  1.0
  O  O34  1  0.563  0.462  0.780  1.0
  O  O35  1  0.538  0.437  0.220  1.0
  O  O36  1  0.932  0.090  0.774  1.0
  O  O37  1  0.910  0.068  0.226  1.0
  O  O38  1  0.236  0.526  0.750  1.0
  O  O39  1  0.474  0.764  0.250  1.0
  O  O40  1  0.005  0.740  0.846  1.0
  O  O41  1  0.260  0.995  0.154  1.0
[/CIF]
.
The structure described by CaAl2(Si2O7)2 crystallizes in the monoclinic C2 space group. Ca(1) is bonded to one O(13), one O(14), one O(2), one O(3), one O(4), and one O(5) atom to form distorted CaO6 pentagonal pyramids that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra,  an edgeedge with one Al(1)O4 tetrahedra, and  an edgeedge with one Al(2)O4 tetrahedra. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(12), one O(2), one O(4), and one O(7) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Ca(1)O6 pentagonal pyramid. In the second Al site, Al(2) is bonded to one O(11), one O(3), one O(5), and one O(6) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, and  an edgeedge with one Ca(1)O6 pentagonal pyramid. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(4), one O(6), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(1)O6 pentagonal pyramid,  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(4)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(10), one O(12), one O(2), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(1)O6 pentagonal pyramid,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. In the third Si site, Si(3) is bonded to one O(10), one O(11), one O(3), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(1)O6 pentagonal pyramid,  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, and corners with two equivalent Al(2)O4 tetrahedra. In the fourth Si site, Si(4) is bonded to one O(1), one O(5), one O(7), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Ca(1)O6 pentagonal pyramid,  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(4) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Si(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(2), and one Si(3) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Ca(1), one Al(1), and one Si(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Al(2), and one Si(4) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(1) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(4) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Si(3) and one Si(4) atom. In the tenth O site, O(10) is bonded in a bent 150 degrees geometry to one Si(2) and one Si(3) atom. In the eleventh O site, O(11) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(3) atom. In the twelfth O site, O(12) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(2) atom. In the thirteenth O site, O(13) is bonded in a single-bond geometry to one Ca(1) atom. In the fourteenth O site, O(14) is bonded in a single-bond geometry to one Ca(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_CaAl2(Si2O7)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   10.038
_cell_length_b   10.038
_cell_length_c   7.563
_cell_angle_alpha   74.396
_cell_angle_beta   74.396
_cell_angle_gamma   82.980
_symmetry_Int_Tables_number   1
_cell_volume   705.883
_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  0.988  0.518  0.763  1.0
  Ca  Ca1  1  0.482  0.012  0.237  1.0
  Al  Al2  1  0.053  0.202  0.762  1.0
  Al  Al3  1  0.798  0.947  0.238  1.0
  Al  Al4  1  0.670  0.589  0.767  1.0
  Al  Al5  1  0.411  0.330  0.233  1.0
  Si  Si6  1  0.090  0.391  0.341  1.0
  Si  Si7  1  0.609  0.910  0.659  1.0
  Si  Si8  1  0.935  0.231  0.176  1.0
  Si  Si9  1  0.769  0.065  0.824  1.0
  Si  Si10  1  0.699  0.466  0.177  1.0
  Si  Si11  1  0.534  0.301  0.823  1.0
  Si  Si12  1  0.856  0.624  0.346  1.0
  Si  Si13  1  0.376  0.144  0.654  1.0
  O  O14  1  0.997  0.532  0.270  1.0
  O  O15  1  0.468  0.003  0.730  1.0
  O  O16  1  0.999  0.293  0.947  1.0
  O  O17  1  0.707  0.001  0.053  1.0
  O  O18  1  0.762  0.536  0.950  1.0
  O  O19  1  0.464  0.238  0.050  1.0
  O  O20  1  0.062  0.357  0.573  1.0
  O  O21  1  0.643  0.938  0.427  1.0
  O  O22  1  0.824  0.599  0.577  1.0
  O  O23  1  0.401  0.176  0.423  1.0
  O  O24  1  0.251  0.416  0.235  1.0
  O  O25  1  0.584  0.749  0.765  1.0
  O  O26  1  0.881  0.784  0.242  1.0
  O  O27  1  0.216  0.119  0.758  1.0
  O  O28  1  0.041  0.259  0.290  1.0
  O  O29  1  0.741  0.959  0.710  1.0
  O  O30  1  0.723  0.571  0.298  1.0
  O  O31  1  0.429  0.277  0.702  1.0
  O  O32  1  0.789  0.320  0.236  1.0
  O  O33  1  0.680  0.211  0.764  1.0
  O  O34  1  0.563  0.462  0.780  1.0
  O  O35  1  0.538  0.437  0.220  1.0
  O  O36  1  0.932  0.090  0.774  1.0
  O  O37  1  0.910  0.068  0.226  1.0
  O  O38  1  0.236  0.526  0.750  1.0
  O  O39  1  0.474  0.764  0.250  1.0
  O  O40  1  0.005  0.740  0.846  1.0
  O  O41  1  0.260  0.995  0.154  1.0
[/CIF]
.