The structure described by Hf8Ni21 crystallizes in the triclinic P-1 space group. There are four inequivalent Hf sites. In the first Hf site, Hf(1) is bonded in a 12-coordinate geometry to one Ni(11), one Ni(5), one Ni(6), one Ni(7), two equivalent Ni(2), two equivalent Ni(3), two equivalent Ni(8), and two equivalent Ni(9) atoms. In the second Hf site, Hf(2) is bonded in a 13-coordinate geometry to one Ni(1), one Ni(2), one Ni(3), one Ni(5), one Ni(7), one Ni(8), one Ni(9), two equivalent Ni(10), two equivalent Ni(11), and two equivalent Ni(4) atoms. In the third Hf site, Hf(3) is bonded in a 12-coordinate geometry to one Ni(1), one Ni(11), one Ni(3), one Ni(4), one Ni(6), one Ni(7), one Ni(8), one Ni(9), two equivalent Ni(10), and two equivalent Ni(5) atoms. In the fourth Hf site, Hf(4) is bonded in a 10-coordinate geometry to one Ni(10), one Ni(2), one Ni(3), one Ni(4), one Ni(5), one Ni(9), two equivalent Ni(6), and two equivalent Ni(7) atoms. There are eleven inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent Hf(2), two equivalent Hf(3), two equivalent Ni(11), two equivalent Ni(3), two equivalent Ni(8), and two equivalent Ni(9) atoms to form face-sharing NiHf4Ni8 cuboctahedra. In the second Ni site, Ni(2) is bonded in a 10-coordinate geometry to one Hf(2), one Hf(4), two equivalent Hf(1), one Ni(4), one Ni(5), one Ni(6), one Ni(7), one Ni(8), and one Ni(9) atom. In the third Ni site, Ni(3) is bonded to one Hf(2), one Hf(3), one Hf(4), two equivalent Hf(1), one Ni(1), one Ni(11), one Ni(4), one Ni(6), one Ni(7), one Ni(8), and one Ni(9) atom to form distorted NiHf5Ni7 cuboctahedra that share  a cornercorner with one Ni(3)Hf5Ni7 cuboctahedra,  an edgeedge with one Ni(3)Hf5Ni7 cuboctahedra,  a faceface with one Ni(1)Hf4Ni8 cuboctahedra, and faces with three equivalent Ni(9)Hf5Ni7 cuboctahedra. In the fourth Ni site, Ni(4) is bonded in a 3-coordinate geometry to one Hf(3), one Hf(4), two equivalent Hf(2), one Ni(2), one Ni(3), one Ni(5), one Ni(7), and two equivalent Ni(6) atoms. In the fifth Ni site, Ni(5) is bonded in a 12-coordinate geometry to one Hf(1), one Hf(2), one Hf(4), two equivalent Hf(3), one Ni(11), one Ni(2), one Ni(4), one Ni(6), one Ni(9), and two equivalent Ni(10) atoms. In the sixth Ni site, Ni(6) is bonded in a 12-coordinate geometry to one Hf(1), one Hf(3), two equivalent Hf(4), one Ni(2), one Ni(3), one Ni(5), one Ni(6), one Ni(7), one Ni(8), and two equivalent Ni(4) atoms. In the seventh Ni site, Ni(7) is bonded in a 12-coordinate geometry to one Hf(1), one Hf(2), one Hf(3), two equivalent Hf(4), one Ni(10), one Ni(11), one Ni(2), one Ni(3), one Ni(4), one Ni(6), and one Ni(8) atom. In the eighth Ni site, Ni(8) is bonded in a 4-coordinate geometry to one Hf(2), one Hf(3), two equivalent Hf(1), one Ni(1), one Ni(2), one Ni(3), one Ni(6), one Ni(7), one Ni(9), and two equivalent Ni(11) atoms. In the ninth Ni site, Ni(9) is bonded to one Hf(2), one Hf(3), one Hf(4), two equivalent Hf(1), one Ni(1), one Ni(10), one Ni(11), one Ni(2), one Ni(3), one Ni(5), and one Ni(8) atom to form distorted NiHf5Ni7 cuboctahedra that share  a cornercorner with one Ni(9)Hf5Ni7 cuboctahedra,  an edgeedge with one Ni(9)Hf5Ni7 cuboctahedra,  a faceface with one Ni(1)Hf4Ni8 cuboctahedra, and faces with three equivalent Ni(3)Hf5Ni7 cuboctahedra. In the tenth Ni site, Ni(10) is bonded in a 5-coordinate geometry to one Hf(4), two equivalent Hf(2), two equivalent Hf(3), one Ni(7), one Ni(9), and two equivalent Ni(5) atoms. In the eleventh Ni site, Ni(11) is bonded in a 12-coordinate geometry to one Hf(1), one Hf(3), two equivalent Hf(2), one Ni(1), one Ni(11), one Ni(3), one Ni(5), one Ni(7), one Ni(9), and two equivalent Ni(8) atoms. is represented by the CIF card [CIF]
data_Hf8Ni21
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.410
_cell_length_b   7.985
_cell_length_c   8.528
_cell_angle_alpha   75.130
_cell_angle_beta   68.126
_cell_angle_gamma   75.462
_symmetry_Int_Tables_number   1
_cell_volume   385.602
_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  Hf0  1  0.753  0.063  0.466  1.0
  Hf  Hf1  1  0.247  0.937  0.534  1.0
  Hf  Hf2  1  0.569  0.537  0.745  1.0
  Hf  Hf3  1  0.431  0.463  0.255  1.0
  Hf  Hf4  1  0.930  0.597  0.186  1.0
  Hf  Hf5  1  0.070  0.403  0.814  1.0
  Hf  Hf6  1  0.752  0.938  0.893  1.0
  Hf  Hf7  1  0.248  0.062  0.107  1.0
  Ni  Ni8  1  0.000  0.500  0.500  1.0
  Ni  Ni9  1  0.514  0.117  0.258  1.0
  Ni  Ni10  1  0.486  0.883  0.742  1.0
  Ni  Ni11  1  0.901  0.217  0.655  1.0
  Ni  Ni12  1  0.099  0.783  0.345  1.0
  Ni  Ni13  1  0.696  0.255  0.959  1.0
  Ni  Ni14  1  0.304  0.745  0.041  1.0
  Ni  Ni15  1  0.864  0.289  0.157  1.0
  Ni  Ni16  1  0.119  0.054  0.850  1.0
  Ni  Ni17  1  0.881  0.946  0.150  1.0
  Ni  Ni18  1  0.483  0.206  0.776  1.0
  Ni  Ni19  1  0.517  0.794  0.224  1.0
  Ni  Ni20  1  0.319  0.243  0.549  1.0
  Ni  Ni21  1  0.681  0.757  0.451  1.0
  Ni  Ni22  1  0.099  0.258  0.347  1.0
  Ni  Ni23  1  0.901  0.742  0.653  1.0
  Ni  Ni24  1  0.287  0.391  0.029  1.0
  Ni  Ni25  1  0.713  0.609  0.971  1.0
  Ni  Ni26  1  0.317  0.599  0.537  1.0
  Ni  Ni27  1  0.683  0.401  0.463  1.0
  Ni  Ni28  1  0.136  0.711  0.843  1.0
[/CIF]
.
The structure described by Hf8Ni21 crystallizes in the triclinic P-1 space group. There are four inequivalent Hf sites. In the first Hf site, Hf(1) is bonded in a 12-coordinate geometry to one Ni(11), one Ni(5), one Ni(6), one Ni(7), two equivalent Ni(2), two equivalent Ni(3), two equivalent Ni(8), and two equivalent Ni(9) atoms. In the second Hf site, Hf(2) is bonded in a 13-coordinate geometry to one Ni(1), one Ni(2), one Ni(3), one Ni(5), one Ni(7), one Ni(8), one Ni(9), two equivalent Ni(10), two equivalent Ni(11), and two equivalent Ni(4) atoms. In the third Hf site, Hf(3) is bonded in a 12-coordinate geometry to one Ni(1), one Ni(11), one Ni(3), one Ni(4), one Ni(6), one Ni(7), one Ni(8), one Ni(9), two equivalent Ni(10), and two equivalent Ni(5) atoms. In the fourth Hf site, Hf(4) is bonded in a 10-coordinate geometry to one Ni(10), one Ni(2), one Ni(3), one Ni(4), one Ni(5), one Ni(9), two equivalent Ni(6), and two equivalent Ni(7) atoms. There are eleven inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent Hf(2), two equivalent Hf(3), two equivalent Ni(11), two equivalent Ni(3), two equivalent Ni(8), and two equivalent Ni(9) atoms to form face-sharing NiHf4Ni8 cuboctahedra. In the second Ni site, Ni(2) is bonded in a 10-coordinate geometry to one Hf(2), one Hf(4), two equivalent Hf(1), one Ni(4), one Ni(5), one Ni(6), one Ni(7), one Ni(8), and one Ni(9) atom. In the third Ni site, Ni(3) is bonded to one Hf(2), one Hf(3), one Hf(4), two equivalent Hf(1), one Ni(1), one Ni(11), one Ni(4), one Ni(6), one Ni(7), one Ni(8), and one Ni(9) atom to form distorted NiHf5Ni7 cuboctahedra that share  a cornercorner with one Ni(3)Hf5Ni7 cuboctahedra,  an edgeedge with one Ni(3)Hf5Ni7 cuboctahedra,  a faceface with one Ni(1)Hf4Ni8 cuboctahedra, and faces with three equivalent Ni(9)Hf5Ni7 cuboctahedra. In the fourth Ni site, Ni(4) is bonded in a 3-coordinate geometry to one Hf(3), one Hf(4), two equivalent Hf(2), one Ni(2), one Ni(3), one Ni(5), one Ni(7), and two equivalent Ni(6) atoms. In the fifth Ni site, Ni(5) is bonded in a 12-coordinate geometry to one Hf(1), one Hf(2), one Hf(4), two equivalent Hf(3), one Ni(11), one Ni(2), one Ni(4), one Ni(6), one Ni(9), and two equivalent Ni(10) atoms. In the sixth Ni site, Ni(6) is bonded in a 12-coordinate geometry to one Hf(1), one Hf(3), two equivalent Hf(4), one Ni(2), one Ni(3), one Ni(5), one Ni(6), one Ni(7), one Ni(8), and two equivalent Ni(4) atoms. In the seventh Ni site, Ni(7) is bonded in a 12-coordinate geometry to one Hf(1), one Hf(2), one Hf(3), two equivalent Hf(4), one Ni(10), one Ni(11), one Ni(2), one Ni(3), one Ni(4), one Ni(6), and one Ni(8) atom. In the eighth Ni site, Ni(8) is bonded in a 4-coordinate geometry to one Hf(2), one Hf(3), two equivalent Hf(1), one Ni(1), one Ni(2), one Ni(3), one Ni(6), one Ni(7), one Ni(9), and two equivalent Ni(11) atoms. In the ninth Ni site, Ni(9) is bonded to one Hf(2), one Hf(3), one Hf(4), two equivalent Hf(1), one Ni(1), one Ni(10), one Ni(11), one Ni(2), one Ni(3), one Ni(5), and one Ni(8) atom to form distorted NiHf5Ni7 cuboctahedra that share  a cornercorner with one Ni(9)Hf5Ni7 cuboctahedra,  an edgeedge with one Ni(9)Hf5Ni7 cuboctahedra,  a faceface with one Ni(1)Hf4Ni8 cuboctahedra, and faces with three equivalent Ni(3)Hf5Ni7 cuboctahedra. In the tenth Ni site, Ni(10) is bonded in a 5-coordinate geometry to one Hf(4), two equivalent Hf(2), two equivalent Hf(3), one Ni(7), one Ni(9), and two equivalent Ni(5) atoms. In the eleventh Ni site, Ni(11) is bonded in a 12-coordinate geometry to one Hf(1), one Hf(3), two equivalent Hf(2), one Ni(1), one Ni(11), one Ni(3), one Ni(5), one Ni(7), one Ni(9), and two equivalent Ni(8) atoms. is represented by the CIF card [CIF]
data_Hf8Ni21
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.410
_cell_length_b   7.985
_cell_length_c   8.528
_cell_angle_alpha   75.130
_cell_angle_beta   68.126
_cell_angle_gamma   75.462
_symmetry_Int_Tables_number   1
_cell_volume   385.602
_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  Hf0  1  0.753  0.063  0.466  1.0
  Hf  Hf1  1  0.247  0.937  0.534  1.0
  Hf  Hf2  1  0.569  0.537  0.745  1.0
  Hf  Hf3  1  0.431  0.463  0.255  1.0
  Hf  Hf4  1  0.930  0.597  0.186  1.0
  Hf  Hf5  1  0.070  0.403  0.814  1.0
  Hf  Hf6  1  0.752  0.938  0.893  1.0
  Hf  Hf7  1  0.248  0.062  0.107  1.0
  Ni  Ni8  1  0.000  0.500  0.500  1.0
  Ni  Ni9  1  0.514  0.117  0.258  1.0
  Ni  Ni10  1  0.486  0.883  0.742  1.0
  Ni  Ni11  1  0.901  0.217  0.655  1.0
  Ni  Ni12  1  0.099  0.783  0.345  1.0
  Ni  Ni13  1  0.696  0.255  0.959  1.0
  Ni  Ni14  1  0.304  0.745  0.041  1.0
  Ni  Ni15  1  0.864  0.289  0.157  1.0
  Ni  Ni16  1  0.119  0.054  0.850  1.0
  Ni  Ni17  1  0.881  0.946  0.150  1.0
  Ni  Ni18  1  0.483  0.206  0.776  1.0
  Ni  Ni19  1  0.517  0.794  0.224  1.0
  Ni  Ni20  1  0.319  0.243  0.549  1.0
  Ni  Ni21  1  0.681  0.757  0.451  1.0
  Ni  Ni22  1  0.099  0.258  0.347  1.0
  Ni  Ni23  1  0.901  0.742  0.653  1.0
  Ni  Ni24  1  0.287  0.391  0.029  1.0
  Ni  Ni25  1  0.713  0.609  0.971  1.0
  Ni  Ni26  1  0.317  0.599  0.537  1.0
  Ni  Ni27  1  0.683  0.401  0.463  1.0
  Ni  Ni28  1  0.136  0.711  0.843  1.0
[/CIF]
.