The crystal structure described by Mg2Nb2CuO8 crystallizes in the monoclinic C2/c space group. Mg(1) is bonded in a 6-coordinate geometry to three equivalent O(3) and three equivalent O(4) atoms. Nb(1) is bonded in a 6-coordinate geometry to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms. Cu(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form edge-sharing CuO6 octahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to two equivalent Nb(1) and one Cu(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Nb(1) and two equivalent Cu(1) atoms. In the third O site, O(3) is bonded to three equivalent Mg(1) and two equivalent Nb(1) atoms to form distorted OMg3Nb2 trigonal bipyramids that share corners with two equivalent O(3)Mg3Nb2 trigonal bipyramids, corners with three equivalent O(4)Mg3Nb trigonal pyramids, edges with three equivalent O(3)Mg3Nb2 trigonal bipyramids, and edges with four equivalent O(4)Mg3Nb trigonal pyramids. In the fourth O site, O(4) is bonded to three equivalent Mg(1) and one Nb(1) atom to form OMg3Nb trigonal pyramids that share corners with three equivalent O(3)Mg3Nb2 trigonal bipyramids, corners with four equivalent O(4)Mg3Nb trigonal pyramids, edges with four equivalent O(3)Mg3Nb2 trigonal bipyramids, and  an edgeedge with one O(4)Mg3Nb trigonal pyramid. is represented by the CIF card [CIF]
data_Mg2Nb2CuO8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   10.027
_cell_length_b   10.027
_cell_length_c   5.165
_cell_angle_alpha   88.357
_cell_angle_beta   88.357
_cell_angle_gamma   35.262
_symmetry_Int_Tables_number   1
_cell_volume   299.647
_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
  Mg  Mg0  1  0.870  0.587  0.752  1.0
  Mg  Mg1  1  0.413  0.130  0.748  1.0
  Mg  Mg2  1  0.130  0.413  0.248  1.0
  Mg  Mg3  1  0.587  0.870  0.252  1.0
  Nb  Nb4  1  0.049  0.720  0.736  1.0
  Nb  Nb5  1  0.280  0.951  0.764  1.0
  Nb  Nb6  1  0.951  0.280  0.264  1.0
  Nb  Nb7  1  0.720  0.049  0.236  1.0
  Cu  Cu8  1  0.651  0.349  0.750  1.0
  Cu  Cu9  1  0.349  0.651  0.250  1.0
  O  O10  1  0.039  0.816  0.069  1.0
  O  O11  1  0.184  0.961  0.431  1.0
  O  O12  1  0.961  0.184  0.931  1.0
  O  O13  1  0.816  0.039  0.569  1.0
  O  O14  1  0.306  0.581  0.561  1.0
  O  O15  1  0.419  0.694  0.939  1.0
  O  O16  1  0.694  0.419  0.439  1.0
  O  O17  1  0.581  0.306  0.061  1.0
  O  O18  1  0.915  0.710  0.453  1.0
  O  O19  1  0.290  0.085  0.047  1.0
  O  O20  1  0.452  0.165  0.378  1.0
  O  O21  1  0.835  0.548  0.122  1.0
  O  O22  1  0.548  0.835  0.622  1.0
  O  O23  1  0.165  0.452  0.878  1.0
  O  O24  1  0.710  0.915  0.953  1.0
  O  O25  1  0.085  0.290  0.547  1.0
[/CIF]
.
The crystal structure described by Mg2Nb2CuO8 crystallizes in the monoclinic C2/c space group. Mg(1) is bonded in a 6-coordinate geometry to three equivalent O(3) and three equivalent O(4) atoms. Nb(1) is bonded in a 6-coordinate geometry to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms. Cu(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form edge-sharing CuO6 octahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to two equivalent Nb(1) and one Cu(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Nb(1) and two equivalent Cu(1) atoms. In the third O site, O(3) is bonded to three equivalent Mg(1) and two equivalent Nb(1) atoms to form distorted OMg3Nb2 trigonal bipyramids that share corners with two equivalent O(3)Mg3Nb2 trigonal bipyramids, corners with three equivalent O(4)Mg3Nb trigonal pyramids, edges with three equivalent O(3)Mg3Nb2 trigonal bipyramids, and edges with four equivalent O(4)Mg3Nb trigonal pyramids. In the fourth O site, O(4) is bonded to three equivalent Mg(1) and one Nb(1) atom to form OMg3Nb trigonal pyramids that share corners with three equivalent O(3)Mg3Nb2 trigonal bipyramids, corners with four equivalent O(4)Mg3Nb trigonal pyramids, edges with four equivalent O(3)Mg3Nb2 trigonal bipyramids, and  an edgeedge with one O(4)Mg3Nb trigonal pyramid. is represented by the CIF card [CIF]
data_Mg2Nb2CuO8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   10.027
_cell_length_b   10.027
_cell_length_c   5.165
_cell_angle_alpha   88.357
_cell_angle_beta   88.357
_cell_angle_gamma   35.262
_symmetry_Int_Tables_number   1
_cell_volume   299.647
_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
  Mg  Mg0  1  0.870  0.587  0.752  1.0
  Mg  Mg1  1  0.413  0.130  0.748  1.0
  Mg  Mg2  1  0.130  0.413  0.248  1.0
  Mg  Mg3  1  0.587  0.870  0.252  1.0
  Nb  Nb4  1  0.049  0.720  0.736  1.0
  Nb  Nb5  1  0.280  0.951  0.764  1.0
  Nb  Nb6  1  0.951  0.280  0.264  1.0
  Nb  Nb7  1  0.720  0.049  0.236  1.0
  Cu  Cu8  1  0.651  0.349  0.750  1.0
  Cu  Cu9  1  0.349  0.651  0.250  1.0
  O  O10  1  0.039  0.816  0.069  1.0
  O  O11  1  0.184  0.961  0.431  1.0
  O  O12  1  0.961  0.184  0.931  1.0
  O  O13  1  0.816  0.039  0.569  1.0
  O  O14  1  0.306  0.581  0.561  1.0
  O  O15  1  0.419  0.694  0.939  1.0
  O  O16  1  0.694  0.419  0.439  1.0
  O  O17  1  0.581  0.306  0.061  1.0
  O  O18  1  0.915  0.710  0.453  1.0
  O  O19  1  0.290  0.085  0.047  1.0
  O  O20  1  0.452  0.165  0.378  1.0
  O  O21  1  0.835  0.548  0.122  1.0
  O  O22  1  0.548  0.835  0.622  1.0
  O  O23  1  0.165  0.452  0.878  1.0
  O  O24  1  0.710  0.915  0.953  1.0
  O  O25  1  0.085  0.290  0.547  1.0
[/CIF]
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