data_MgNb4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.07
_cell_length_b   8.07
_cell_length_c   8.07
_cell_angle_alpha   109.47
_cell_angle_beta   109.47
_cell_angle_gamma   109.47
_symmetry_Int_Tables_number   1
_chemical_formula_structural   MgNb4
_chemical_formula_sum   'Mg4 Nb16'
_cell_volume   404.62
_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
  Mg  Mg0  1  0.9  0.9  0.9  1.0
  Mg  Mg1  1  0.24  0.76  0.76  1.0
  Mg  Mg2  1  0.76  0.24  0.76  1.0
  Mg  Mg3  1  0.76  0.76  0.24  1.0
  Nb  Nb4  1  0.59  0.59  0.59  1.0
  Nb  Nb5  1  0.93  0.07  0.07  1.0
  Nb  Nb6  1  0.07  0.93  0.07  1.0
  Nb  Nb7  1  0.07  0.07  0.93  1.0
  Nb  Nb8  1  0.0  0.0  0.11  1.0
  Nb  Nb9  1  0.0  0.0  0.21  1.0
  Nb  Nb10  1  0.0  0.11  0.0  1.0
  Nb  Nb11  1  0.0  0.21  0.0  1.0
  Nb  Nb12  1  0.11  0.0  0.0  1.0
  Nb  Nb13  1  0.21  0.0  0.0  1.0
  Nb  Nb14  1  0.66  0.0  0.33  1.0
  Nb  Nb15  1  0.0  0.66  0.33  1.0
  Nb  Nb16  1  0.0  0.33  0.66  1.0
  Nb  Nb17  1  0.66  0.33  0.0  1.0
  Nb  Nb18  1  0.33  0.66  0.0  1.0
  Nb  Nb19  1  0.33  0.0  0.66  1.0

data_MgNb4
_symmetry_space_group_name_H-M   R3m
_cell_length_a   13.18
_cell_length_b   13.18
_cell_length_c   8.07
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   MgNb4
_chemical_formula_sum   'Mg12 Nb48'
_cell_volume   1213.87
_cell_formula_units_Z   12
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
  2  '-y, x-y, z'
  3  '-x+y, -x, z'
  4  '-y, -x, z'
  5  '-x+y, y, z'
  6  'x, x-y, z'
  7  'x+2/3, y+1/3, z+1/3'
  8  '-y+2/3, x-y+1/3, z+1/3'
  9  '-x+y+2/3, -x+1/3, z+1/3'
  10  '-y+2/3, -x+1/3, z+1/3'
  11  '-x+y+2/3, y+1/3, z+1/3'
  12  'x+2/3, x-y+1/3, z+1/3'
  13  'x+1/3, y+2/3, z+2/3'
  14  '-y+1/3, x-y+2/3, z+2/3'
  15  '-x+y+1/3, -x+2/3, z+2/3'
  16  '-y+1/3, -x+2/3, z+2/3'
  17  '-x+y+1/3, y+2/3, z+2/3'
  18  'x+1/3, x-y+2/3, z+2/3'
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  9  0.17  0.35  0.59  1.0
  Mg  Mg1  3  0.0  0.0  0.9  1.0
  Nb  Nb2  18  0.0  0.33  0.33  1.0
  Nb  Nb3  9  0.05  0.09  0.02  1.0
  Nb  Nb4  9  0.07  0.04  0.04  1.0
  Nb  Nb5  9  0.14  0.07  0.07  1.0
  Nb  Nb6  3  0.0  0.0  0.59  1.0

Mg Mg Mg Mg Nb Nb Nb Nb Nb Nb Nb Nb Nb Nb Nb Nb Nb Nb Nb Nb
MgNb4 crystallizes in the trigonal R3m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 7-coordinate geometry to one Nb(1), three equivalent Nb(2), and three equivalent Nb(3) atoms. The Mg(1)-Nb(1) bond length is 2.49 Å. All Mg(1)-Nb(2) bond lengths are 1.46 Å. All Mg(1)-Nb(3) bond lengths are 1.41 Å. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Nb(4) and four equivalent Nb(5) atoms. The Mg(2)-Nb(4) bond length is 2.39 Å. There are two shorter (2.33 Å) and two longer (3.01 Å) Mg(2)-Nb(5) bond lengths. There are five inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a single-bond geometry to one Mg(1) atom. In the second Nb site, Nb(2) is bonded in a distorted water-like geometry to one Mg(1) and two equivalent Nb(3) atoms. Both Nb(2)-Nb(3) bond lengths are 0.98 Å. In the third Nb site, Nb(3) is bonded in a 4-coordinate geometry to one Mg(1), one Nb(4), and two equivalent Nb(2) atoms. The Nb(3)-Nb(4) bond length is 0.76 Å. In the fourth Nb site, Nb(4) is bonded in a distorted single-bond geometry to one Mg(2) and one Nb(3) atom. In the fifth Nb site, Nb(5) is bonded in a distorted single-bond geometry to two equivalent Mg(2) atoms.