The compound described by Na2Er2B2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to one O(1), one O(3), two equivalent O(2), and two equivalent O(5) atoms. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(4), two equivalent O(6), and two equivalent O(7) atoms. In the second Er site, Er(2) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), one O(6), and two equivalent O(7) atoms. There are two inequivalent B sites. In the first B site, B(1) is bonded in a trigonal planar geometry to one O(1), one O(3), and one O(6) atom. In the second B site, B(2) is bonded in a trigonal planar geometry to one O(2), one O(4), and one O(5) atom. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a distorted single-bond geometry to two equivalent Na(1), two equivalent Na(2), one Er(2), and one B(2) atom. In the second O site, O(6) is bonded in a distorted single-bond geometry to one Er(2), two equivalent Er(1), and one B(1) atom. In the third O site, O(7) is bonded to two equivalent Er(1) and two equivalent Er(2) atoms to form a mixture of edge and corner-sharing OEr4 tetrahedra. In the fourth O site, O(1) is bonded in a distorted single-bond geometry to one Na(2), one Er(2), two equivalent Er(1), and one B(1) atom. In the fifth O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Na(1), two equivalent Na(2), one Er(2), and one B(2) atom. In the sixth O site, O(3) is bonded in a distorted single-bond geometry to one Na(2), two equivalent Na(1), one Er(2), and one B(1) atom. In the seventh O site, O(4) is bonded in a 4-coordinate geometry to one Er(2), two equivalent Er(1), and one B(2) atom. is represented by the CIF file [CIF]
data_Na2Er2B2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.225
_cell_length_b   10.270
_cell_length_c   10.622
_cell_angle_alpha   62.267
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   601.114
_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
  Na  Na0  1  0.557  0.764  0.476  1.0
  Na  Na1  1  0.943  0.264  0.476  1.0
  Na  Na2  1  0.241  0.548  0.388  1.0
  Na  Na3  1  0.759  0.452  0.612  1.0
  Na  Na4  1  0.443  0.236  0.524  1.0
  Na  Na5  1  0.741  0.952  0.612  1.0
  Na  Na6  1  0.057  0.736  0.524  1.0
  Na  Na7  1  0.259  0.048  0.388  1.0
  Er  Er8  1  0.459  0.184  0.015  1.0
  Er  Er9  1  0.959  0.316  0.985  1.0
  Er  Er10  1  0.418  0.585  0.819  1.0
  Er  Er11  1  0.918  0.915  0.181  1.0
  Er  Er12  1  0.541  0.816  0.985  1.0
  Er  Er13  1  0.041  0.684  0.015  1.0
  Er  Er14  1  0.582  0.415  0.181  1.0
  Er  Er15  1  0.082  0.085  0.819  1.0
  B  B16  1  0.153  0.352  0.206  1.0
  B  B17  1  0.252  0.917  0.687  1.0
  B  B18  1  0.248  0.417  0.687  1.0
  B  B19  1  0.752  0.583  0.313  1.0
  B  B20  1  0.653  0.148  0.794  1.0
  B  B21  1  0.847  0.648  0.794  1.0
  B  B22  1  0.347  0.852  0.206  1.0
  B  B23  1  0.748  0.083  0.313  1.0
  O  O24  1  0.257  0.271  0.147  1.0
  O  O25  1  0.663  0.446  0.396  1.0
  O  O26  1  0.252  0.866  0.314  1.0
  O  O27  1  0.757  0.229  0.853  1.0
  O  O28  1  0.752  0.634  0.686  1.0
  O  O29  1  0.837  0.946  0.396  1.0
  O  O30  1  0.763  0.133  0.164  1.0
  O  O31  1  0.748  0.134  0.686  1.0
  O  O32  1  0.352  0.833  0.635  1.0
  O  O33  1  0.737  0.633  0.164  1.0
  O  O34  1  0.544  0.914  0.147  1.0
  O  O35  1  0.956  0.414  0.147  1.0
  O  O36  1  0.852  0.667  0.365  1.0
  O  O37  1  0.148  0.333  0.635  1.0
  O  O38  1  0.375  0.597  0.026  1.0
  O  O39  1  0.248  0.366  0.314  1.0
  O  O40  1  0.163  0.054  0.604  1.0
  O  O41  1  0.263  0.367  0.836  1.0
  O  O42  1  0.125  0.097  0.026  1.0
  O  O43  1  0.456  0.086  0.853  1.0
  O  O44  1  0.743  0.729  0.853  1.0
  O  O45  1  0.237  0.867  0.836  1.0
  O  O46  1  0.044  0.586  0.853  1.0
  O  O47  1  0.648  0.167  0.365  1.0
  O  O48  1  0.337  0.554  0.604  1.0
  O  O49  1  0.875  0.903  0.974  1.0
  O  O50  1  0.625  0.403  0.974  1.0
  O  O51  1  0.243  0.771  0.147  1.0
[/CIF]
.
The compound described by Na2Er2B2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to one O(1), one O(3), two equivalent O(2), and two equivalent O(5) atoms. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(4), two equivalent O(6), and two equivalent O(7) atoms. In the second Er site, Er(2) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), one O(6), and two equivalent O(7) atoms. There are two inequivalent B sites. In the first B site, B(1) is bonded in a trigonal planar geometry to one O(1), one O(3), and one O(6) atom. In the second B site, B(2) is bonded in a trigonal planar geometry to one O(2), one O(4), and one O(5) atom. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a distorted single-bond geometry to two equivalent Na(1), two equivalent Na(2), one Er(2), and one B(2) atom. In the second O site, O(6) is bonded in a distorted single-bond geometry to one Er(2), two equivalent Er(1), and one B(1) atom. In the third O site, O(7) is bonded to two equivalent Er(1) and two equivalent Er(2) atoms to form a mixture of edge and corner-sharing OEr4 tetrahedra. In the fourth O site, O(1) is bonded in a distorted single-bond geometry to one Na(2), one Er(2), two equivalent Er(1), and one B(1) atom. In the fifth O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Na(1), two equivalent Na(2), one Er(2), and one B(2) atom. In the sixth O site, O(3) is bonded in a distorted single-bond geometry to one Na(2), two equivalent Na(1), one Er(2), and one B(1) atom. In the seventh O site, O(4) is bonded in a 4-coordinate geometry to one Er(2), two equivalent Er(1), and one B(2) atom. is represented by the CIF file [CIF]
data_Na2Er2B2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.225
_cell_length_b   10.270
_cell_length_c   10.622
_cell_angle_alpha   62.267
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   601.114
_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
  Na  Na0  1  0.557  0.764  0.476  1.0
  Na  Na1  1  0.943  0.264  0.476  1.0
  Na  Na2  1  0.241  0.548  0.388  1.0
  Na  Na3  1  0.759  0.452  0.612  1.0
  Na  Na4  1  0.443  0.236  0.524  1.0
  Na  Na5  1  0.741  0.952  0.612  1.0
  Na  Na6  1  0.057  0.736  0.524  1.0
  Na  Na7  1  0.259  0.048  0.388  1.0
  Er  Er8  1  0.459  0.184  0.015  1.0
  Er  Er9  1  0.959  0.316  0.985  1.0
  Er  Er10  1  0.418  0.585  0.819  1.0
  Er  Er11  1  0.918  0.915  0.181  1.0
  Er  Er12  1  0.541  0.816  0.985  1.0
  Er  Er13  1  0.041  0.684  0.015  1.0
  Er  Er14  1  0.582  0.415  0.181  1.0
  Er  Er15  1  0.082  0.085  0.819  1.0
  B  B16  1  0.153  0.352  0.206  1.0
  B  B17  1  0.252  0.917  0.687  1.0
  B  B18  1  0.248  0.417  0.687  1.0
  B  B19  1  0.752  0.583  0.313  1.0
  B  B20  1  0.653  0.148  0.794  1.0
  B  B21  1  0.847  0.648  0.794  1.0
  B  B22  1  0.347  0.852  0.206  1.0
  B  B23  1  0.748  0.083  0.313  1.0
  O  O24  1  0.257  0.271  0.147  1.0
  O  O25  1  0.663  0.446  0.396  1.0
  O  O26  1  0.252  0.866  0.314  1.0
  O  O27  1  0.757  0.229  0.853  1.0
  O  O28  1  0.752  0.634  0.686  1.0
  O  O29  1  0.837  0.946  0.396  1.0
  O  O30  1  0.763  0.133  0.164  1.0
  O  O31  1  0.748  0.134  0.686  1.0
  O  O32  1  0.352  0.833  0.635  1.0
  O  O33  1  0.737  0.633  0.164  1.0
  O  O34  1  0.544  0.914  0.147  1.0
  O  O35  1  0.956  0.414  0.147  1.0
  O  O36  1  0.852  0.667  0.365  1.0
  O  O37  1  0.148  0.333  0.635  1.0
  O  O38  1  0.375  0.597  0.026  1.0
  O  O39  1  0.248  0.366  0.314  1.0
  O  O40  1  0.163  0.054  0.604  1.0
  O  O41  1  0.263  0.367  0.836  1.0
  O  O42  1  0.125  0.097  0.026  1.0
  O  O43  1  0.456  0.086  0.853  1.0
  O  O44  1  0.743  0.729  0.853  1.0
  O  O45  1  0.237  0.867  0.836  1.0
  O  O46  1  0.044  0.586  0.853  1.0
  O  O47  1  0.648  0.167  0.365  1.0
  O  O48  1  0.337  0.554  0.604  1.0
  O  O49  1  0.875  0.903  0.974  1.0
  O  O50  1  0.625  0.403  0.974  1.0
  O  O51  1  0.243  0.771  0.147  1.0
[/CIF]
.