The crystal structure described by MgNi6Si6 crystallizes in the orthorhombic Cmmm space group. Mg(1) is bonded to four equivalent Ni(1), eight equivalent Ni(2), two equivalent Si(1), and six equivalent Si(2) atoms to form distorted MgSi8Ni12 hexagonal bipyramids that share faces with eight equivalent Ni(1)Mg2Si6Ni4 cuboctahedra, faces with sixteen equivalent Ni(2)Mg2Si6Ni4 cuboctahedra, and faces with six equivalent Mg(1)Si8Ni12 hexagonal bipyramids. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent Mg(1), four equivalent Ni(2), two equivalent Si(1), two equivalent Si(2), and two equivalent Si(3) atoms to form distorted NiMg2Si6Ni4 cuboctahedra that share corners with six equivalent Ni(1)Mg2Si6Ni4 cuboctahedra, corners with eight equivalent Ni(2)Mg2Si6Ni4 cuboctahedra, edges with three equivalent Ni(1)Mg2Si6Ni4 cuboctahedra, edges with four equivalent Ni(2)Mg2Si6Ni4 cuboctahedra,  a faceface with one Ni(1)Mg2Si6Ni4 cuboctahedra, faces with eight equivalent Ni(2)Mg2Si6Ni4 cuboctahedra, and faces with four equivalent Mg(1)Si8Ni12 hexagonal bipyramids. In the second Ni site, Ni(2) is bonded to two equivalent Mg(1), two equivalent Ni(1), two equivalent Ni(2), two equivalent Si(1), two equivalent Si(2), and two equivalent Si(3) atoms to form distorted NiMg2Si6Ni4 cuboctahedra that share corners with four equivalent Ni(1)Mg2Si6Ni4 cuboctahedra, corners with ten equivalent Ni(2)Mg2Si6Ni4 cuboctahedra, edges with two equivalent Ni(1)Mg2Si6Ni4 cuboctahedra, edges with five equivalent Ni(2)Mg2Si6Ni4 cuboctahedra, faces with four equivalent Ni(1)Mg2Si6Ni4 cuboctahedra, faces with five equivalent Ni(2)Mg2Si6Ni4 cuboctahedra, and faces with four equivalent Mg(1)Si8Ni12 hexagonal bipyramids. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to one Mg(1), two equivalent Ni(1), four equivalent Ni(2), and one Si(1) atom. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to three equivalent Mg(1), two equivalent Ni(1), and four equivalent Ni(2) atoms. In the third Si site, Si(3) is bonded in a 6-coordinate geometry to two equivalent Ni(1) and four equivalent Ni(2) atoms. In the fourth Si site, Si(1) is bonded in a 8-coordinate geometry to one Mg(1), two equivalent Ni(1), four equivalent Ni(2), and one Si(1) atom. is represented by the CIF card [CIF]
data_Mg(SiNi)6
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.894
_cell_length_b   4.909
_cell_length_c   7.613
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   119.903
_symmetry_Int_Tables_number   1
_cell_volume   158.552
_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
  Mg  Mg0  1  1.000  0.000  0.000  1.0
  Si  Si1  1  1.000  0.000  0.346  1.0
  Si  Si2  1  1.000  0.000  0.654  1.0
  Si  Si3  1  0.333  0.666  0.000  1.0
  Si  Si4  1  0.667  0.334  0.000  1.0
  Si  Si5  1  0.333  0.666  0.500  1.0
  Si  Si6  1  0.667  0.334  0.500  1.0
  Ni  Ni7  1  0.500  0.000  0.250  1.0
  Ni  Ni8  1  0.500  0.500  0.250  1.0
  Ni  Ni9  1  1.000  0.500  0.250  1.0
  Ni  Ni10  1  0.500  0.000  0.750  1.0
  Ni  Ni11  1  0.500  0.500  0.750  1.0
  Ni  Ni12  1  1.000  0.500  0.750  1.0
[/CIF]
.
The crystal structure described by MgNi6Si6 crystallizes in the orthorhombic Cmmm space group. Mg(1) is bonded to four equivalent Ni(1), eight equivalent Ni(2), two equivalent Si(1), and six equivalent Si(2) atoms to form distorted MgSi8Ni12 hexagonal bipyramids that share faces with eight equivalent Ni(1)Mg2Si6Ni4 cuboctahedra, faces with sixteen equivalent Ni(2)Mg2Si6Ni4 cuboctahedra, and faces with six equivalent Mg(1)Si8Ni12 hexagonal bipyramids. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent Mg(1), four equivalent Ni(2), two equivalent Si(1), two equivalent Si(2), and two equivalent Si(3) atoms to form distorted NiMg2Si6Ni4 cuboctahedra that share corners with six equivalent Ni(1)Mg2Si6Ni4 cuboctahedra, corners with eight equivalent Ni(2)Mg2Si6Ni4 cuboctahedra, edges with three equivalent Ni(1)Mg2Si6Ni4 cuboctahedra, edges with four equivalent Ni(2)Mg2Si6Ni4 cuboctahedra,  a faceface with one Ni(1)Mg2Si6Ni4 cuboctahedra, faces with eight equivalent Ni(2)Mg2Si6Ni4 cuboctahedra, and faces with four equivalent Mg(1)Si8Ni12 hexagonal bipyramids. In the second Ni site, Ni(2) is bonded to two equivalent Mg(1), two equivalent Ni(1), two equivalent Ni(2), two equivalent Si(1), two equivalent Si(2), and two equivalent Si(3) atoms to form distorted NiMg2Si6Ni4 cuboctahedra that share corners with four equivalent Ni(1)Mg2Si6Ni4 cuboctahedra, corners with ten equivalent Ni(2)Mg2Si6Ni4 cuboctahedra, edges with two equivalent Ni(1)Mg2Si6Ni4 cuboctahedra, edges with five equivalent Ni(2)Mg2Si6Ni4 cuboctahedra, faces with four equivalent Ni(1)Mg2Si6Ni4 cuboctahedra, faces with five equivalent Ni(2)Mg2Si6Ni4 cuboctahedra, and faces with four equivalent Mg(1)Si8Ni12 hexagonal bipyramids. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to one Mg(1), two equivalent Ni(1), four equivalent Ni(2), and one Si(1) atom. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to three equivalent Mg(1), two equivalent Ni(1), and four equivalent Ni(2) atoms. In the third Si site, Si(3) is bonded in a 6-coordinate geometry to two equivalent Ni(1) and four equivalent Ni(2) atoms. In the fourth Si site, Si(1) is bonded in a 8-coordinate geometry to one Mg(1), two equivalent Ni(1), four equivalent Ni(2), and one Si(1) atom. is represented by the CIF card [CIF]
data_Mg(SiNi)6
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.894
_cell_length_b   4.909
_cell_length_c   7.613
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   119.903
_symmetry_Int_Tables_number   1
_cell_volume   158.552
_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
  Mg  Mg0  1  1.000  0.000  0.000  1.0
  Si  Si1  1  1.000  0.000  0.346  1.0
  Si  Si2  1  1.000  0.000  0.654  1.0
  Si  Si3  1  0.333  0.666  0.000  1.0
  Si  Si4  1  0.667  0.334  0.000  1.0
  Si  Si5  1  0.333  0.666  0.500  1.0
  Si  Si6  1  0.667  0.334  0.500  1.0
  Ni  Ni7  1  0.500  0.000  0.250  1.0
  Ni  Ni8  1  0.500  0.500  0.250  1.0
  Ni  Ni9  1  1.000  0.500  0.250  1.0
  Ni  Ni10  1  0.500  0.000  0.750  1.0
  Ni  Ni11  1  0.500  0.500  0.750  1.0
  Ni  Ni12  1  1.000  0.500  0.750  1.0
[/CIF]
.