data_HfMgB2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   2.82
_cell_length_b   2.82
_cell_length_c   6.65
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   HfMgB2
_chemical_formula_sum   'Hf1 Mg1 B2'
_cell_volume   53.02
_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
  Hf  Hf2  1  0.41  0.41  0.85  1.0
  Mg  Mg3  1  0.0  0.0  0.46  1.0
  B  B0  1  0.41  0.41  0.48  1.0
  B  B1  1  0.0  0.0  0.18  1.0

data_HfMgB2
_symmetry_space_group_name_H-M   Cm
_cell_length_a   3.99
_cell_length_b   3.99
_cell_length_c   6.65
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   8
_chemical_formula_structural   HfMgB2
_chemical_formula_sum   'Hf2 Mg2 B4'
_cell_volume   106.04
_cell_formula_units_Z   2
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
  2  'x, -y, z'
  3  'x+1/2, y+1/2, z'
  4  'x+1/2, -y+1/2, 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
  Hf  Hf0  2  0.41  0.0  0.85  1.0
  Mg  Mg1  2  0.0  0.0  0.46  1.0
  B  B2  2  0.0  0.0  0.18  1.0
  B  B3  2  0.41  0.0  0.48  1.0

Hf Mg B B
MgHfB2 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one B(2) and four equivalent B(1) atoms to form a mixture of distorted edge and corner-sharing MgB5 square pyramids. The Mg(1)-B(2) bond length is 1.90 Å. There are a spread of Mg(1)-B(1) bond distances ranging from 1.65-2.35 Å. Hf(1) is bonded in a 2-coordinate geometry to one B(1) and one B(2) atom. The Hf(1)-B(1) bond length is 2.45 Å. The Hf(1)-B(2) bond length is 2.72 Å. There are two inequivalent B sites. In the first B site, B(1) is bonded to four equivalent Mg(1) and one Hf(1) atom to form a mixture of distorted edge and corner-sharing BHfMg4 square pyramids. In the second B site, B(2) is bonded in a distorted single-bond geometry to one Mg(1) and one Hf(1) atom.