The compound described by Eu2Si2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 8-coordinate geometry to one O(4), one O(5), one O(6), one O(7), two equivalent O(2), and two equivalent O(3) atoms. In the second Eu site, Eu(2) is bonded in a 9-coordinate geometry to one O(1), one O(2), one O(3), one O(5), one O(7), two equivalent O(4), and two equivalent O(6) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(5), and one O(6) atom to form corner-sharing SiO4 tetrahedra. In the second Si site, Si(2) is bonded to one O(1), one O(3), one O(4), and one O(7) atom to form corner-sharing SiO4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Eu(1), one Eu(2), and one Si(1) atom. In the second O site, O(6) is bonded in a 1-coordinate geometry to one Eu(1), two equivalent Eu(2), and one Si(1) atom. In the third O site, O(7) is bonded in a distorted trigonal planar geometry to one Eu(1), one Eu(2), and one Si(2) atom. In the fourth O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Eu(2), one Si(1), and one Si(2) atom. In the fifth O site, O(2) is bonded to one Eu(2), two equivalent Eu(1), and one Si(1) atom to form distorted edge-sharing OEu3Si tetrahedra. In the sixth O site, O(3) is bonded in a 4-coordinate geometry to one Eu(2), two equivalent Eu(1), and one Si(2) atom. In the seventh O site, O(4) is bonded in a distorted single-bond geometry to one Eu(1), two equivalent Eu(2), and one Si(2) atom. is represented by the CIF file [CIF]
data_Eu2Si2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.832
_cell_length_b   6.721
_cell_length_c   12.928
_cell_angle_alpha   71.401
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   562.559
_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
  Eu  Eu0  1  0.895  0.468  0.363  1.0
  Eu  Eu1  1  0.395  0.532  0.137  1.0
  Eu  Eu2  1  0.105  0.532  0.637  1.0
  Eu  Eu3  1  0.605  0.468  0.863  1.0
  Eu  Eu4  1  0.670  0.156  0.653  1.0
  Eu  Eu5  1  0.170  0.844  0.847  1.0
  Eu  Eu6  1  0.330  0.844  0.347  1.0
  Eu  Eu7  1  0.830  0.156  0.153  1.0
  Si  Si8  1  0.829  0.895  0.414  1.0
  Si  Si9  1  0.329  0.105  0.086  1.0
  Si  Si10  1  0.171  0.105  0.586  1.0
  Si  Si11  1  0.671  0.895  0.914  1.0
  Si  Si12  1  0.582  0.709  0.609  1.0
  Si  Si13  1  0.082  0.291  0.891  1.0
  Si  Si14  1  0.418  0.291  0.391  1.0
  Si  Si15  1  0.918  0.709  0.109  1.0
  O  O16  1  0.719  0.903  0.528  1.0
  O  O17  1  0.219  0.097  0.972  1.0
  O  O18  1  0.281  0.097  0.472  1.0
  O  O19  1  0.781  0.903  0.028  1.0
  O  O20  1  0.012  0.727  0.449  1.0
  O  O21  1  0.512  0.273  0.051  1.0
  O  O22  1  0.988  0.273  0.551  1.0
  O  O23  1  0.488  0.727  0.949  1.0
  O  O24  1  0.722  0.504  0.666  1.0
  O  O25  1  0.222  0.496  0.834  1.0
  O  O26  1  0.278  0.496  0.334  1.0
  O  O27  1  0.778  0.504  0.166  1.0
  O  O28  1  0.515  0.799  0.707  1.0
  O  O29  1  0.015  0.201  0.793  1.0
  O  O30  1  0.485  0.201  0.293  1.0
  O  O31  1  0.985  0.799  0.207  1.0
  O  O32  1  0.907  0.126  0.341  1.0
  O  O33  1  0.407  0.874  0.159  1.0
  O  O34  1  0.093  0.874  0.659  1.0
  O  O35  1  0.593  0.126  0.841  1.0
  O  O36  1  0.676  0.794  0.347  1.0
  O  O37  1  0.176  0.206  0.153  1.0
  O  O38  1  0.324  0.206  0.653  1.0
  O  O39  1  0.824  0.794  0.847  1.0
  O  O40  1  0.397  0.660  0.542  1.0
  O  O41  1  0.897  0.340  0.958  1.0
  O  O42  1  0.603  0.340  0.458  1.0
  O  O43  1  0.103  0.660  0.042  1.0
[/CIF]
.
The compound described by Eu2Si2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 8-coordinate geometry to one O(4), one O(5), one O(6), one O(7), two equivalent O(2), and two equivalent O(3) atoms. In the second Eu site, Eu(2) is bonded in a 9-coordinate geometry to one O(1), one O(2), one O(3), one O(5), one O(7), two equivalent O(4), and two equivalent O(6) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(5), and one O(6) atom to form corner-sharing SiO4 tetrahedra. In the second Si site, Si(2) is bonded to one O(1), one O(3), one O(4), and one O(7) atom to form corner-sharing SiO4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Eu(1), one Eu(2), and one Si(1) atom. In the second O site, O(6) is bonded in a 1-coordinate geometry to one Eu(1), two equivalent Eu(2), and one Si(1) atom. In the third O site, O(7) is bonded in a distorted trigonal planar geometry to one Eu(1), one Eu(2), and one Si(2) atom. In the fourth O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Eu(2), one Si(1), and one Si(2) atom. In the fifth O site, O(2) is bonded to one Eu(2), two equivalent Eu(1), and one Si(1) atom to form distorted edge-sharing OEu3Si tetrahedra. In the sixth O site, O(3) is bonded in a 4-coordinate geometry to one Eu(2), two equivalent Eu(1), and one Si(2) atom. In the seventh O site, O(4) is bonded in a distorted single-bond geometry to one Eu(1), two equivalent Eu(2), and one Si(2) atom. is represented by the CIF file [CIF]
data_Eu2Si2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.832
_cell_length_b   6.721
_cell_length_c   12.928
_cell_angle_alpha   71.401
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   562.559
_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
  Eu  Eu0  1  0.895  0.468  0.363  1.0
  Eu  Eu1  1  0.395  0.532  0.137  1.0
  Eu  Eu2  1  0.105  0.532  0.637  1.0
  Eu  Eu3  1  0.605  0.468  0.863  1.0
  Eu  Eu4  1  0.670  0.156  0.653  1.0
  Eu  Eu5  1  0.170  0.844  0.847  1.0
  Eu  Eu6  1  0.330  0.844  0.347  1.0
  Eu  Eu7  1  0.830  0.156  0.153  1.0
  Si  Si8  1  0.829  0.895  0.414  1.0
  Si  Si9  1  0.329  0.105  0.086  1.0
  Si  Si10  1  0.171  0.105  0.586  1.0
  Si  Si11  1  0.671  0.895  0.914  1.0
  Si  Si12  1  0.582  0.709  0.609  1.0
  Si  Si13  1  0.082  0.291  0.891  1.0
  Si  Si14  1  0.418  0.291  0.391  1.0
  Si  Si15  1  0.918  0.709  0.109  1.0
  O  O16  1  0.719  0.903  0.528  1.0
  O  O17  1  0.219  0.097  0.972  1.0
  O  O18  1  0.281  0.097  0.472  1.0
  O  O19  1  0.781  0.903  0.028  1.0
  O  O20  1  0.012  0.727  0.449  1.0
  O  O21  1  0.512  0.273  0.051  1.0
  O  O22  1  0.988  0.273  0.551  1.0
  O  O23  1  0.488  0.727  0.949  1.0
  O  O24  1  0.722  0.504  0.666  1.0
  O  O25  1  0.222  0.496  0.834  1.0
  O  O26  1  0.278  0.496  0.334  1.0
  O  O27  1  0.778  0.504  0.166  1.0
  O  O28  1  0.515  0.799  0.707  1.0
  O  O29  1  0.015  0.201  0.793  1.0
  O  O30  1  0.485  0.201  0.293  1.0
  O  O31  1  0.985  0.799  0.207  1.0
  O  O32  1  0.907  0.126  0.341  1.0
  O  O33  1  0.407  0.874  0.159  1.0
  O  O34  1  0.093  0.874  0.659  1.0
  O  O35  1  0.593  0.126  0.841  1.0
  O  O36  1  0.676  0.794  0.347  1.0
  O  O37  1  0.176  0.206  0.153  1.0
  O  O38  1  0.324  0.206  0.653  1.0
  O  O39  1  0.824  0.794  0.847  1.0
  O  O40  1  0.397  0.660  0.542  1.0
  O  O41  1  0.897  0.340  0.958  1.0
  O  O42  1  0.603  0.340  0.458  1.0
  O  O43  1  0.103  0.660  0.042  1.0
[/CIF]
.