The material described by Eu3Si6N4O9 crystallizes in the trigonal P3 space group. There are three inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 6-coordinate geometry to three equivalent O(2) and three equivalent O(3) atoms. In the second Eu site, Eu(2) is bonded in a 6-coordinate geometry to three equivalent O(2) and three equivalent O(3) atoms. In the third Eu site, Eu(3) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form distorted EuO6 octahedra that share corners with three equivalent Si(1)N2O2 tetrahedra and corners with three equivalent Si(2)N2O2 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to two equivalent N(2), one O(1), and one O(3) atom to form SiN2O2 tetrahedra that share  a cornercorner with one Eu(3)O6 octahedra, corners with two equivalent Si(1)N2O2 tetrahedra, and corners with three equivalent Si(2)N2O2 tetrahedra. The corner-sharing octahedral tilt angles are 72°. In the second Si site, Si(2) is bonded to one N(1), one N(2), one O(1), and one O(2) atom to form SiN2O2 tetrahedra that share  a cornercorner with one Eu(3)O6 octahedra, corners with two equivalent Si(2)N2O2 tetrahedra, and corners with three equivalent Si(1)N2O2 tetrahedra. The corner-sharing octahedral tilt angles are 64°. There are two inequivalent N sites. In the first N site, N(1) is bonded in a trigonal planar geometry to three equivalent Si(2) atoms. In the second N site, N(2) is bonded in a trigonal planar geometry to one Si(2) and two equivalent Si(1) atoms. There are three inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the second O site, O(2) is bonded to one Eu(1), one Eu(2), one Eu(3), and one Si(2) atom to form distorted corner-sharing OEu3Si tetrahedra. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Eu(1), one Eu(2), one Eu(3), and one Si(1) atom. is represented by the CIF card [CIF]
data_Eu3Si6N4O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.171
_cell_length_b   7.171
_cell_length_c   6.660
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   120.000
_symmetry_Int_Tables_number   1
_cell_volume   296.581
_cell_formula_units_Z   1
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  0.000  0.000  0.521  1.0
  Eu  Eu1  1  0.333  0.667  0.417  1.0
  Eu  Eu2  1  0.667  0.333  0.375  1.0
  Si  Si3  1  0.929  0.376  0.839  1.0
  Si  Si4  1  0.447  0.071  0.839  1.0
  Si  Si5  1  0.624  0.553  0.839  1.0
  Si  Si6  1  0.742  0.961  0.063  1.0
  Si  Si7  1  0.219  0.258  0.063  1.0
  Si  Si8  1  0.039  0.781  0.063  1.0
  N  N9  1  0.000  0.000  0.023  1.0
  N  N10  1  0.705  0.128  0.902  1.0
  N  N11  1  0.423  0.295  0.902  1.0
  N  N12  1  0.872  0.577  0.902  1.0
  O  O13  1  0.584  0.705  0.002  1.0
  O  O14  1  0.121  0.416  0.002  1.0
  O  O15  1  0.295  0.879  0.002  1.0
  O  O16  1  0.701  0.993  0.297  1.0
  O  O17  1  0.293  0.299  0.297  1.0
  O  O18  1  0.007  0.707  0.297  1.0
  O  O19  1  0.992  0.372  0.606  1.0
  O  O20  1  0.380  0.008  0.606  1.0
  O  O21  1  0.628  0.620  0.606  1.0
[/CIF]
.
The material described by Eu3Si6N4O9 crystallizes in the trigonal P3 space group. There are three inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 6-coordinate geometry to three equivalent O(2) and three equivalent O(3) atoms. In the second Eu site, Eu(2) is bonded in a 6-coordinate geometry to three equivalent O(2) and three equivalent O(3) atoms. In the third Eu site, Eu(3) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form distorted EuO6 octahedra that share corners with three equivalent Si(1)N2O2 tetrahedra and corners with three equivalent Si(2)N2O2 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to two equivalent N(2), one O(1), and one O(3) atom to form SiN2O2 tetrahedra that share  a cornercorner with one Eu(3)O6 octahedra, corners with two equivalent Si(1)N2O2 tetrahedra, and corners with three equivalent Si(2)N2O2 tetrahedra. The corner-sharing octahedral tilt angles are 72°. In the second Si site, Si(2) is bonded to one N(1), one N(2), one O(1), and one O(2) atom to form SiN2O2 tetrahedra that share  a cornercorner with one Eu(3)O6 octahedra, corners with two equivalent Si(2)N2O2 tetrahedra, and corners with three equivalent Si(1)N2O2 tetrahedra. The corner-sharing octahedral tilt angles are 64°. There are two inequivalent N sites. In the first N site, N(1) is bonded in a trigonal planar geometry to three equivalent Si(2) atoms. In the second N site, N(2) is bonded in a trigonal planar geometry to one Si(2) and two equivalent Si(1) atoms. There are three inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the second O site, O(2) is bonded to one Eu(1), one Eu(2), one Eu(3), and one Si(2) atom to form distorted corner-sharing OEu3Si tetrahedra. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Eu(1), one Eu(2), one Eu(3), and one Si(1) atom. is represented by the CIF card [CIF]
data_Eu3Si6N4O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.171
_cell_length_b   7.171
_cell_length_c   6.660
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   120.000
_symmetry_Int_Tables_number   1
_cell_volume   296.581
_cell_formula_units_Z   1
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  0.000  0.000  0.521  1.0
  Eu  Eu1  1  0.333  0.667  0.417  1.0
  Eu  Eu2  1  0.667  0.333  0.375  1.0
  Si  Si3  1  0.929  0.376  0.839  1.0
  Si  Si4  1  0.447  0.071  0.839  1.0
  Si  Si5  1  0.624  0.553  0.839  1.0
  Si  Si6  1  0.742  0.961  0.063  1.0
  Si  Si7  1  0.219  0.258  0.063  1.0
  Si  Si8  1  0.039  0.781  0.063  1.0
  N  N9  1  0.000  0.000  0.023  1.0
  N  N10  1  0.705  0.128  0.902  1.0
  N  N11  1  0.423  0.295  0.902  1.0
  N  N12  1  0.872  0.577  0.902  1.0
  O  O13  1  0.584  0.705  0.002  1.0
  O  O14  1  0.121  0.416  0.002  1.0
  O  O15  1  0.295  0.879  0.002  1.0
  O  O16  1  0.701  0.993  0.297  1.0
  O  O17  1  0.293  0.299  0.297  1.0
  O  O18  1  0.007  0.707  0.297  1.0
  O  O19  1  0.992  0.372  0.606  1.0
  O  O20  1  0.380  0.008  0.606  1.0
  O  O21  1  0.628  0.620  0.606  1.0
[/CIF]
.