The crystal structure described by Eu2Ta2O7 crystallizes in the orthorhombic Cmc2_1 space group. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 7-coordinate geometry to one O(3), three equivalent O(2), and three equivalent O(5) atoms. In the second Eu site, Eu(2) is bonded to one O(3), two equivalent O(1), two equivalent O(4), three equivalent O(7), and four equivalent O(6) atoms to form distorted EuO12 cuboctahedra that share corners with six equivalent Eu(2)O12 cuboctahedra, faces with four equivalent Eu(2)O12 cuboctahedra, faces with two equivalent Ta(1)O6 octahedra, and faces with six equivalent Ta(2)O6 octahedra. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(1), one O(2), one O(4), one O(5), and two equivalent O(3) atoms to form TaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with two equivalent Ta(2)O6 octahedra, and faces with two equivalent Eu(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 12-32°. In the second Ta site, Ta(2) is bonded to one O(1), one O(4), two equivalent O(6), and two equivalent O(7) atoms to form TaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with four equivalent Ta(2)O6 octahedra, and faces with six equivalent Eu(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 9-32°. There are seven inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Eu(2), one Ta(1), and one Ta(2) atom to form distorted OEu2Ta2 tetrahedra that share  a cornercorner with one O(5)Eu3Ta tetrahedra and corners with two equivalent O(1)Eu2Ta2 tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to three equivalent Eu(1) and one Ta(1) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to one Eu(1), one Eu(2), and two equivalent Ta(1) atoms. In the fourth O site, O(4) is bonded in a distorted linear geometry to two equivalent Eu(2), one Ta(1), and one Ta(2) atom. In the fifth O site, O(5) is bonded to three equivalent Eu(1) and one Ta(1) atom to form OEu3Ta tetrahedra that share  a cornercorner with one O(1)Eu2Ta2 tetrahedra and corners with six equivalent O(5)Eu3Ta tetrahedra. In the sixth O site, O(6) is bonded in a 6-coordinate geometry to four equivalent Eu(2) and two equivalent Ta(2) atoms. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to three equivalent Eu(2) and two equivalent Ta(2) atoms. is represented by the CIF file [CIF]
data_Eu2Ta2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   13.694
_cell_length_b   13.694
_cell_length_c   5.704
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   163.272
_symmetry_Int_Tables_number   1
_cell_volume   307.901
_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
  Eu  Eu0  1  0.711  0.289  0.353  1.0
  Eu  Eu1  1  0.289  0.711  0.853  1.0
  Eu  Eu2  1  0.447  0.553  0.294  1.0
  Eu  Eu3  1  0.553  0.447  0.794  1.0
  Ta  Ta4  1  0.840  0.160  0.317  1.0
  Ta  Ta5  1  0.160  0.840  0.817  1.0
  Ta  Ta6  1  0.944  0.056  0.794  1.0
  Ta  Ta7  1  0.056  0.944  0.294  1.0
  O  O8  1  0.907  0.093  0.490  1.0
  O  O9  1  0.093  0.907  0.990  1.0
  O  O10  1  0.800  0.200  0.587  1.0
  O  O11  1  0.200  0.800  0.087  1.0
  O  O12  1  0.349  0.651  0.288  1.0
  O  O13  1  0.651  0.349  0.788  1.0
  O  O14  1  0.890  0.110  0.006  1.0
  O  O15  1  0.110  0.890  0.506  1.0
  O  O16  1  0.784  0.216  0.106  1.0
  O  O17  1  0.216  0.784  0.606  1.0
  O  O18  1  0.994  0.006  0.054  1.0
  O  O19  1  0.006  0.994  0.554  1.0
  O  O20  1  0.548  0.452  0.274  1.0
  O  O21  1  0.452  0.548  0.774  1.0
[/CIF]
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The crystal structure described by Eu2Ta2O7 crystallizes in the orthorhombic Cmc2_1 space group. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 7-coordinate geometry to one O(3), three equivalent O(2), and three equivalent O(5) atoms. In the second Eu site, Eu(2) is bonded to one O(3), two equivalent O(1), two equivalent O(4), three equivalent O(7), and four equivalent O(6) atoms to form distorted EuO12 cuboctahedra that share corners with six equivalent Eu(2)O12 cuboctahedra, faces with four equivalent Eu(2)O12 cuboctahedra, faces with two equivalent Ta(1)O6 octahedra, and faces with six equivalent Ta(2)O6 octahedra. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(1), one O(2), one O(4), one O(5), and two equivalent O(3) atoms to form TaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with two equivalent Ta(2)O6 octahedra, and faces with two equivalent Eu(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 12-32°. In the second Ta site, Ta(2) is bonded to one O(1), one O(4), two equivalent O(6), and two equivalent O(7) atoms to form TaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with four equivalent Ta(2)O6 octahedra, and faces with six equivalent Eu(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 9-32°. There are seven inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Eu(2), one Ta(1), and one Ta(2) atom to form distorted OEu2Ta2 tetrahedra that share  a cornercorner with one O(5)Eu3Ta tetrahedra and corners with two equivalent O(1)Eu2Ta2 tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to three equivalent Eu(1) and one Ta(1) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to one Eu(1), one Eu(2), and two equivalent Ta(1) atoms. In the fourth O site, O(4) is bonded in a distorted linear geometry to two equivalent Eu(2), one Ta(1), and one Ta(2) atom. In the fifth O site, O(5) is bonded to three equivalent Eu(1) and one Ta(1) atom to form OEu3Ta tetrahedra that share  a cornercorner with one O(1)Eu2Ta2 tetrahedra and corners with six equivalent O(5)Eu3Ta tetrahedra. In the sixth O site, O(6) is bonded in a 6-coordinate geometry to four equivalent Eu(2) and two equivalent Ta(2) atoms. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to three equivalent Eu(2) and two equivalent Ta(2) atoms. is represented by the CIF file [CIF]
data_Eu2Ta2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   13.694
_cell_length_b   13.694
_cell_length_c   5.704
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   163.272
_symmetry_Int_Tables_number   1
_cell_volume   307.901
_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
  Eu  Eu0  1  0.711  0.289  0.353  1.0
  Eu  Eu1  1  0.289  0.711  0.853  1.0
  Eu  Eu2  1  0.447  0.553  0.294  1.0
  Eu  Eu3  1  0.553  0.447  0.794  1.0
  Ta  Ta4  1  0.840  0.160  0.317  1.0
  Ta  Ta5  1  0.160  0.840  0.817  1.0
  Ta  Ta6  1  0.944  0.056  0.794  1.0
  Ta  Ta7  1  0.056  0.944  0.294  1.0
  O  O8  1  0.907  0.093  0.490  1.0
  O  O9  1  0.093  0.907  0.990  1.0
  O  O10  1  0.800  0.200  0.587  1.0
  O  O11  1  0.200  0.800  0.087  1.0
  O  O12  1  0.349  0.651  0.288  1.0
  O  O13  1  0.651  0.349  0.788  1.0
  O  O14  1  0.890  0.110  0.006  1.0
  O  O15  1  0.110  0.890  0.506  1.0
  O  O16  1  0.784  0.216  0.106  1.0
  O  O17  1  0.216  0.784  0.606  1.0
  O  O18  1  0.994  0.006  0.054  1.0
  O  O19  1  0.006  0.994  0.554  1.0
  O  O20  1  0.548  0.452  0.274  1.0
  O  O21  1  0.452  0.548  0.774  1.0
[/CIF]
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