The compound described by Sr2MgSi2O7 crystallizes in the monoclinic P2_1/c 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(4), one O(5), two equivalent O(6), and two equivalent O(7) atoms. In the second Sr site, Sr(2) is bonded in a 7-coordinate geometry to one O(1), one O(5), one O(7), two equivalent O(2), and two equivalent O(4) atoms. Mg(1) is bonded to one O(1), one O(2), one O(5), and one O(6) atom to form MgO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra and corners with two equivalent Si(2)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(3), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra and corners with two equivalent Mg(1)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with two equivalent Mg(1)O4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a 4-coordinate geometry to one Sr(2), two equivalent Sr(1), and one Si(1) atom. In the second O site, O(1) is bonded in a 3-coordinate geometry to one Sr(1), one Sr(2), one Mg(1), and one Si(2) atom. In the third O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Sr(2), one Mg(1), and one Si(2) atom. In the fourth O site, O(3) is bonded in a 3-coordinate geometry to one Sr(1), one Si(1), and one Si(2) atom. In the fifth O site, O(4) is bonded in a distorted single-bond geometry to one Sr(1), two equivalent Sr(2), and one Si(2) atom. In the sixth O site, O(5) is bonded in a distorted trigonal pyramidal geometry to one Sr(1), one Sr(2), one Mg(1), and one Si(1) atom. In the seventh O site, O(6) is bonded in a 4-coordinate geometry to two equivalent Sr(1), one Mg(1), and one Si(1) atom. is represented by the CIF card [CIF]
data_Sr2MgSi2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.970
_cell_length_b   9.494
_cell_length_c   9.627
_cell_angle_alpha   113.993
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   665.486
_cell_formula_units_Z   4
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  0.449  0.724  0.799  1.0
  Sr  Sr1  1  0.267  0.452  0.024  1.0
  Sr  Sr2  1  0.233  0.952  0.524  1.0
  Sr  Sr3  1  0.949  0.776  0.701  1.0
  Sr  Sr4  1  0.551  0.276  0.201  1.0
  Sr  Sr5  1  0.051  0.224  0.299  1.0
  Sr  Sr6  1  0.767  0.048  0.476  1.0
  Sr  Sr7  1  0.733  0.548  0.976  1.0
  Mg  Mg8  1  0.109  0.834  0.116  1.0
  Mg  Mg9  1  0.391  0.334  0.616  1.0
  Mg  Mg10  1  0.891  0.166  0.884  1.0
  Mg  Mg11  1  0.609  0.666  0.384  1.0
  Si  Si12  1  0.726  0.464  0.581  1.0
  Si  Si13  1  0.040  0.367  0.708  1.0
  Si  Si14  1  0.274  0.536  0.419  1.0
  Si  Si15  1  0.540  0.133  0.792  1.0
  Si  Si16  1  0.226  0.036  0.919  1.0
  Si  Si17  1  0.960  0.633  0.292  1.0
  Si  Si18  1  0.774  0.964  0.081  1.0
  Si  Si19  1  0.460  0.867  0.208  1.0
  O  O20  1  0.279  0.953  0.265  1.0
  O  O21  1  0.451  0.147  0.643  1.0
  O  O22  1  0.919  0.490  0.663  1.0
  O  O23  1  0.581  0.990  0.163  1.0
  O  O24  1  0.419  0.010  0.837  1.0
  O  O25  1  0.946  0.797  0.440  1.0
  O  O26  1  0.951  0.353  0.857  1.0
  O  O27  1  0.908  0.961  0.209  1.0
  O  O28  1  0.554  0.297  0.940  1.0
  O  O29  1  0.686  0.625  0.561  1.0
  O  O30  1  0.408  0.539  0.291  1.0
  O  O31  1  0.446  0.703  0.060  1.0
  O  O32  1  0.092  0.039  0.791  1.0
  O  O33  1  0.221  0.453  0.765  1.0
  O  O34  1  0.049  0.647  0.143  1.0
  O  O35  1  0.729  0.304  0.429  1.0
  O  O36  1  0.054  0.203  0.560  1.0
  O  O37  1  0.229  0.196  0.071  1.0
  O  O38  1  0.721  0.047  0.735  1.0
  O  O39  1  0.081  0.510  0.337  1.0
  O  O40  1  0.771  0.804  0.929  1.0
  O  O41  1  0.314  0.375  0.439  1.0
  O  O42  1  0.779  0.547  0.235  1.0
  O  O43  1  0.549  0.853  0.357  1.0
  O  O44  1  0.186  0.875  0.939  1.0
  O  O45  1  0.814  0.125  0.061  1.0
  O  O46  1  0.271  0.696  0.571  1.0
  O  O47  1  0.592  0.461  0.709  1.0
[/CIF]
.
The compound described by Sr2MgSi2O7 crystallizes in the monoclinic P2_1/c 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(4), one O(5), two equivalent O(6), and two equivalent O(7) atoms. In the second Sr site, Sr(2) is bonded in a 7-coordinate geometry to one O(1), one O(5), one O(7), two equivalent O(2), and two equivalent O(4) atoms. Mg(1) is bonded to one O(1), one O(2), one O(5), and one O(6) atom to form MgO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra and corners with two equivalent Si(2)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(3), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra and corners with two equivalent Mg(1)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with two equivalent Mg(1)O4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a 4-coordinate geometry to one Sr(2), two equivalent Sr(1), and one Si(1) atom. In the second O site, O(1) is bonded in a 3-coordinate geometry to one Sr(1), one Sr(2), one Mg(1), and one Si(2) atom. In the third O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Sr(2), one Mg(1), and one Si(2) atom. In the fourth O site, O(3) is bonded in a 3-coordinate geometry to one Sr(1), one Si(1), and one Si(2) atom. In the fifth O site, O(4) is bonded in a distorted single-bond geometry to one Sr(1), two equivalent Sr(2), and one Si(2) atom. In the sixth O site, O(5) is bonded in a distorted trigonal pyramidal geometry to one Sr(1), one Sr(2), one Mg(1), and one Si(1) atom. In the seventh O site, O(6) is bonded in a 4-coordinate geometry to two equivalent Sr(1), one Mg(1), and one Si(1) atom. is represented by the CIF card [CIF]
data_Sr2MgSi2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.970
_cell_length_b   9.494
_cell_length_c   9.627
_cell_angle_alpha   113.993
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   665.486
_cell_formula_units_Z   4
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  0.449  0.724  0.799  1.0
  Sr  Sr1  1  0.267  0.452  0.024  1.0
  Sr  Sr2  1  0.233  0.952  0.524  1.0
  Sr  Sr3  1  0.949  0.776  0.701  1.0
  Sr  Sr4  1  0.551  0.276  0.201  1.0
  Sr  Sr5  1  0.051  0.224  0.299  1.0
  Sr  Sr6  1  0.767  0.048  0.476  1.0
  Sr  Sr7  1  0.733  0.548  0.976  1.0
  Mg  Mg8  1  0.109  0.834  0.116  1.0
  Mg  Mg9  1  0.391  0.334  0.616  1.0
  Mg  Mg10  1  0.891  0.166  0.884  1.0
  Mg  Mg11  1  0.609  0.666  0.384  1.0
  Si  Si12  1  0.726  0.464  0.581  1.0
  Si  Si13  1  0.040  0.367  0.708  1.0
  Si  Si14  1  0.274  0.536  0.419  1.0
  Si  Si15  1  0.540  0.133  0.792  1.0
  Si  Si16  1  0.226  0.036  0.919  1.0
  Si  Si17  1  0.960  0.633  0.292  1.0
  Si  Si18  1  0.774  0.964  0.081  1.0
  Si  Si19  1  0.460  0.867  0.208  1.0
  O  O20  1  0.279  0.953  0.265  1.0
  O  O21  1  0.451  0.147  0.643  1.0
  O  O22  1  0.919  0.490  0.663  1.0
  O  O23  1  0.581  0.990  0.163  1.0
  O  O24  1  0.419  0.010  0.837  1.0
  O  O25  1  0.946  0.797  0.440  1.0
  O  O26  1  0.951  0.353  0.857  1.0
  O  O27  1  0.908  0.961  0.209  1.0
  O  O28  1  0.554  0.297  0.940  1.0
  O  O29  1  0.686  0.625  0.561  1.0
  O  O30  1  0.408  0.539  0.291  1.0
  O  O31  1  0.446  0.703  0.060  1.0
  O  O32  1  0.092  0.039  0.791  1.0
  O  O33  1  0.221  0.453  0.765  1.0
  O  O34  1  0.049  0.647  0.143  1.0
  O  O35  1  0.729  0.304  0.429  1.0
  O  O36  1  0.054  0.203  0.560  1.0
  O  O37  1  0.229  0.196  0.071  1.0
  O  O38  1  0.721  0.047  0.735  1.0
  O  O39  1  0.081  0.510  0.337  1.0
  O  O40  1  0.771  0.804  0.929  1.0
  O  O41  1  0.314  0.375  0.439  1.0
  O  O42  1  0.779  0.547  0.235  1.0
  O  O43  1  0.549  0.853  0.357  1.0
  O  O44  1  0.186  0.875  0.939  1.0
  O  O45  1  0.814  0.125  0.061  1.0
  O  O46  1  0.271  0.696  0.571  1.0
  O  O47  1  0.592  0.461  0.709  1.0
[/CIF]
.