The material structure described by Sr2Al2SiO7 crystallizes in the monoclinic P2_1 space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 8-coordinate geometry to one O(1), one O(3), one O(6), one O(7), two equivalent O(2), and two equivalent O(4) atoms. In the second Sr site, Sr(2) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(6), one O(7), two equivalent O(3), and two equivalent O(5) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form AlO4 tetrahedra that share corners with two equivalent Al(2)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(1), 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 and corners with two equivalent Al(1)O4 tetrahedra. Si(1) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra and corners with two equivalent Al(1)O4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Sr(1), one Sr(2), one Al(2), and one Si(1) atom. In the second O site, O(2) is bonded to one Sr(2), two equivalent Sr(1), and one Al(2) atom to form distorted corner-sharing OSr3Al tetrahedra. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Sr(1), two equivalent Sr(2), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent Sr(1), one Al(1), and one Al(2) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to two equivalent Sr(2), one Al(1), and one Si(1) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Sr(1), one Sr(2), one Al(1), and one Si(1) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Sr(1), one Sr(2), one Al(1), and one Al(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Sr2Al2SiO7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.913
_cell_length_b   5.328
_cell_length_c   7.927
_cell_angle_alpha   89.935
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   334.188
_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
  Sr  Sr0  1  0.840  0.513  0.078  1.0
  Sr  Sr1  1  0.340  0.487  0.922  1.0
  Sr  Sr2  1  0.165  0.510  0.402  1.0
  Sr  Sr3  1  0.665  0.490  0.598  1.0
  Al  Al4  1  0.500  1.000  0.250  1.0
  Al  Al5  1  1.000  0.000  0.750  1.0
  Al  Al6  1  0.642  0.966  0.892  1.0
  Al  Al7  1  0.142  0.034  0.108  1.0
  Si  Si8  1  0.358  0.960  0.608  1.0
  Si  Si9  1  0.858  0.040  0.392  1.0
  O  O10  1  0.993  0.162  0.255  1.0
  O  O11  1  0.493  0.838  0.745  1.0
  O  O12  1  0.641  0.291  0.887  1.0
  O  O13  1  0.141  0.709  0.113  1.0
  O  O14  1  0.358  0.263  0.604  1.0
  O  O15  1  0.858  0.737  0.396  1.0
  O  O16  1  0.583  0.815  0.085  1.0
  O  O17  1  0.083  0.185  0.915  1.0
  O  O18  1  0.414  0.826  0.426  1.0
  O  O19  1  0.914  0.174  0.574  1.0
  O  O20  1  0.674  0.171  0.342  1.0
  O  O21  1  0.174  0.829  0.658  1.0
  O  O22  1  0.333  0.188  0.173  1.0
  O  O23  1  0.833  0.812  0.827  1.0
[/CIF]
.
The material structure described by Sr2Al2SiO7 crystallizes in the monoclinic P2_1 space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 8-coordinate geometry to one O(1), one O(3), one O(6), one O(7), two equivalent O(2), and two equivalent O(4) atoms. In the second Sr site, Sr(2) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(6), one O(7), two equivalent O(3), and two equivalent O(5) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form AlO4 tetrahedra that share corners with two equivalent Al(2)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(1), 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 and corners with two equivalent Al(1)O4 tetrahedra. Si(1) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra and corners with two equivalent Al(1)O4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Sr(1), one Sr(2), one Al(2), and one Si(1) atom. In the second O site, O(2) is bonded to one Sr(2), two equivalent Sr(1), and one Al(2) atom to form distorted corner-sharing OSr3Al tetrahedra. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Sr(1), two equivalent Sr(2), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent Sr(1), one Al(1), and one Al(2) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to two equivalent Sr(2), one Al(1), and one Si(1) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Sr(1), one Sr(2), one Al(1), and one Si(1) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Sr(1), one Sr(2), one Al(1), and one Al(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Sr2Al2SiO7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.913
_cell_length_b   5.328
_cell_length_c   7.927
_cell_angle_alpha   89.935
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   334.188
_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
  Sr  Sr0  1  0.840  0.513  0.078  1.0
  Sr  Sr1  1  0.340  0.487  0.922  1.0
  Sr  Sr2  1  0.165  0.510  0.402  1.0
  Sr  Sr3  1  0.665  0.490  0.598  1.0
  Al  Al4  1  0.500  1.000  0.250  1.0
  Al  Al5  1  1.000  0.000  0.750  1.0
  Al  Al6  1  0.642  0.966  0.892  1.0
  Al  Al7  1  0.142  0.034  0.108  1.0
  Si  Si8  1  0.358  0.960  0.608  1.0
  Si  Si9  1  0.858  0.040  0.392  1.0
  O  O10  1  0.993  0.162  0.255  1.0
  O  O11  1  0.493  0.838  0.745  1.0
  O  O12  1  0.641  0.291  0.887  1.0
  O  O13  1  0.141  0.709  0.113  1.0
  O  O14  1  0.358  0.263  0.604  1.0
  O  O15  1  0.858  0.737  0.396  1.0
  O  O16  1  0.583  0.815  0.085  1.0
  O  O17  1  0.083  0.185  0.915  1.0
  O  O18  1  0.414  0.826  0.426  1.0
  O  O19  1  0.914  0.174  0.574  1.0
  O  O20  1  0.674  0.171  0.342  1.0
  O  O21  1  0.174  0.829  0.658  1.0
  O  O22  1  0.333  0.188  0.173  1.0
  O  O23  1  0.833  0.812  0.827  1.0
[/CIF]
.