The crystal structure described by MgNi4O9 crystallizes in the triclinic P1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 8-coordinate geometry to one O(10), one O(11), one O(12), one O(13), one O(14), one O(7), one O(8), and one O(9) atom. In the second Mg site, Mg(2) is bonded in a 8-coordinate geometry to one O(15), one O(16), one O(17), one O(18), one O(3), one O(4), one O(5), and one O(6) atom. There are eight inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(1), one O(13), one O(14), one O(17), and one O(8) atom to form a mixture of distorted corner and edge-sharing NiO5 trigonal bipyramids. In the second Ni site, Ni(2) is bonded to one O(1), one O(11), one O(17), one O(18), and one O(6) atom to form a mixture of distorted corner and edge-sharing NiO5 trigonal bipyramids. In the third Ni site, Ni(3) is bonded to one O(12), one O(14), one O(15), one O(2), and one O(7) atom to form a mixture of distorted corner and edge-sharing NiO5 square pyramids. In the fourth Ni site, Ni(4) is bonded to one O(12), one O(16), one O(18), one O(2), and one O(5) atom to form a mixture of distorted corner and edge-sharing NiO5 trigonal bipyramids. In the fifth Ni site, Ni(5) is bonded to one O(1), one O(11), one O(12), one O(16), and one O(9) atom to form a mixture of corner and edge-sharing NiO5 trigonal bipyramids. In the sixth Ni site, Ni(6) is bonded to one O(10), one O(11), one O(13), one O(18), and one O(2) atom to form a mixture of corner and edge-sharing NiO5 trigonal bipyramids. In the seventh Ni site, Ni(7) is bonded to one O(13), one O(15), one O(17), one O(2), and one O(4) atom to form a mixture of corner and edge-sharing NiO5 trigonal bipyramids. In the eighth Ni site, Ni(8) is bonded to one O(1), one O(14), one O(15), one O(16), and one O(3) atom to form a mixture of corner and edge-sharing NiO5 trigonal bipyramids. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Ni(1), one Ni(2), one Ni(5), and one Ni(8) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Ni(3), one Ni(4), one Ni(6), and one Ni(7) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(2), one Ni(8), and one O(4) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Mg(2), one Ni(7), and one O(3) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(2), one Ni(4), and one O(6) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Mg(2), one Ni(2), and one O(5) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Mg(1), one Ni(3), and one O(8) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Mg(1), one Ni(1), and one O(7) atom. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Mg(1), one Ni(5), and one O(10) atom. In the tenth O site, O(10) is bonded in a 3-coordinate geometry to one Mg(1), one Ni(6), and one O(9) atom. In the eleventh O site, O(11) is bonded in a see-saw-like geometry to one Mg(1), one Ni(2), one Ni(5), and one Ni(6) atom. In the twelfth O site, O(12) is bonded in a distorted see-saw-like geometry to one Mg(1), one Ni(3), one Ni(4), and one Ni(5) atom. In the thirteenth O site, O(13) is bonded in a see-saw-like geometry to one Mg(1), one Ni(1), one Ni(6), and one Ni(7) atom. In the fourteenth O site, O(14) is bonded in a see-saw-like geometry to one Mg(1), one Ni(1), one Ni(3), and one Ni(8) atom. In the fifteenth O site, O(15) is bonded in a see-saw-like geometry to one Mg(2), one Ni(3), one Ni(7), and one Ni(8) atom. In the sixteenth O site, O(16) is bonded in a see-saw-like geometry to one Mg(2), one Ni(4), one Ni(5), and one Ni(8) atom. In the seventeenth O site, O(17) is bonded in a distorted see-saw-like geometry to one Mg(2), one Ni(1), one Ni(2), and one Ni(7) atom. In the eighteenth O site, O(18) is bonded in a see-saw-like geometry to one Mg(2), one Ni(2), one Ni(4), and one Ni(6) atom. is represented by the CIF file [CIF]
data_MgNi4O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.351
_cell_length_b   8.139
_cell_length_c   8.301
_cell_angle_alpha   92.187
_cell_angle_beta   90.263
_cell_angle_gamma   90.114
_symmetry_Int_Tables_number   1
_cell_volume   361.275
_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  0.765  0.754  0.739  1.0
  Mg  Mg1  1  0.236  0.257  0.237  1.0
  Ni  Ni2  1  0.411  0.666  0.465  1.0
  Ni  Ni3  1  0.600  0.530  0.164  1.0
  Ni  Ni4  1  0.404  0.031  0.663  1.0
  Ni  Ni5  1  0.584  0.163  0.969  1.0
  Ni  Ni6  1  0.465  0.836  0.033  1.0
  Ni  Ni7  1  0.449  0.469  0.842  1.0
  Ni  Ni8  1  0.546  0.337  0.531  1.0
  Ni  Ni9  1  0.545  0.970  0.340  1.0
  O  O10  1  0.495  0.753  0.242  1.0
  O  O11  1  0.520  0.254  0.746  1.0
  O  O12  1  0.871  0.110  0.338  1.0
  O  O13  1  0.875  0.253  0.420  1.0
  O  O14  1  0.898  0.233  0.096  1.0
  O  O15  1  0.905  0.384  0.172  1.0
  O  O16  1  0.094  0.889  0.664  1.0
  O  O17  1  0.095  0.741  0.583  1.0
  O  O18  1  0.131  0.754  0.928  1.0
  O  O19  1  0.123  0.608  0.851  1.0
  O  O20  1  0.625  0.649  0.954  1.0
  O  O21  1  0.581  0.946  0.856  1.0
  O  O22  1  0.570  0.548  0.644  1.0
  O  O23  1  0.588  0.863  0.539  1.0
  O  O24  1  0.377  0.147  0.451  1.0
  O  O25  1  0.413  0.042  0.140  1.0
  O  O26  1  0.421  0.449  0.353  1.0
  O  O27  1  0.414  0.362  0.040  1.0
[/CIF]
.
The crystal structure described by MgNi4O9 crystallizes in the triclinic P1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 8-coordinate geometry to one O(10), one O(11), one O(12), one O(13), one O(14), one O(7), one O(8), and one O(9) atom. In the second Mg site, Mg(2) is bonded in a 8-coordinate geometry to one O(15), one O(16), one O(17), one O(18), one O(3), one O(4), one O(5), and one O(6) atom. There are eight inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(1), one O(13), one O(14), one O(17), and one O(8) atom to form a mixture of distorted corner and edge-sharing NiO5 trigonal bipyramids. In the second Ni site, Ni(2) is bonded to one O(1), one O(11), one O(17), one O(18), and one O(6) atom to form a mixture of distorted corner and edge-sharing NiO5 trigonal bipyramids. In the third Ni site, Ni(3) is bonded to one O(12), one O(14), one O(15), one O(2), and one O(7) atom to form a mixture of distorted corner and edge-sharing NiO5 square pyramids. In the fourth Ni site, Ni(4) is bonded to one O(12), one O(16), one O(18), one O(2), and one O(5) atom to form a mixture of distorted corner and edge-sharing NiO5 trigonal bipyramids. In the fifth Ni site, Ni(5) is bonded to one O(1), one O(11), one O(12), one O(16), and one O(9) atom to form a mixture of corner and edge-sharing NiO5 trigonal bipyramids. In the sixth Ni site, Ni(6) is bonded to one O(10), one O(11), one O(13), one O(18), and one O(2) atom to form a mixture of corner and edge-sharing NiO5 trigonal bipyramids. In the seventh Ni site, Ni(7) is bonded to one O(13), one O(15), one O(17), one O(2), and one O(4) atom to form a mixture of corner and edge-sharing NiO5 trigonal bipyramids. In the eighth Ni site, Ni(8) is bonded to one O(1), one O(14), one O(15), one O(16), and one O(3) atom to form a mixture of corner and edge-sharing NiO5 trigonal bipyramids. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Ni(1), one Ni(2), one Ni(5), and one Ni(8) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Ni(3), one Ni(4), one Ni(6), and one Ni(7) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(2), one Ni(8), and one O(4) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Mg(2), one Ni(7), and one O(3) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(2), one Ni(4), and one O(6) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Mg(2), one Ni(2), and one O(5) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Mg(1), one Ni(3), and one O(8) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Mg(1), one Ni(1), and one O(7) atom. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Mg(1), one Ni(5), and one O(10) atom. In the tenth O site, O(10) is bonded in a 3-coordinate geometry to one Mg(1), one Ni(6), and one O(9) atom. In the eleventh O site, O(11) is bonded in a see-saw-like geometry to one Mg(1), one Ni(2), one Ni(5), and one Ni(6) atom. In the twelfth O site, O(12) is bonded in a distorted see-saw-like geometry to one Mg(1), one Ni(3), one Ni(4), and one Ni(5) atom. In the thirteenth O site, O(13) is bonded in a see-saw-like geometry to one Mg(1), one Ni(1), one Ni(6), and one Ni(7) atom. In the fourteenth O site, O(14) is bonded in a see-saw-like geometry to one Mg(1), one Ni(1), one Ni(3), and one Ni(8) atom. In the fifteenth O site, O(15) is bonded in a see-saw-like geometry to one Mg(2), one Ni(3), one Ni(7), and one Ni(8) atom. In the sixteenth O site, O(16) is bonded in a see-saw-like geometry to one Mg(2), one Ni(4), one Ni(5), and one Ni(8) atom. In the seventeenth O site, O(17) is bonded in a distorted see-saw-like geometry to one Mg(2), one Ni(1), one Ni(2), and one Ni(7) atom. In the eighteenth O site, O(18) is bonded in a see-saw-like geometry to one Mg(2), one Ni(2), one Ni(4), and one Ni(6) atom. is represented by the CIF file [CIF]
data_MgNi4O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.351
_cell_length_b   8.139
_cell_length_c   8.301
_cell_angle_alpha   92.187
_cell_angle_beta   90.263
_cell_angle_gamma   90.114
_symmetry_Int_Tables_number   1
_cell_volume   361.275
_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  0.765  0.754  0.739  1.0
  Mg  Mg1  1  0.236  0.257  0.237  1.0
  Ni  Ni2  1  0.411  0.666  0.465  1.0
  Ni  Ni3  1  0.600  0.530  0.164  1.0
  Ni  Ni4  1  0.404  0.031  0.663  1.0
  Ni  Ni5  1  0.584  0.163  0.969  1.0
  Ni  Ni6  1  0.465  0.836  0.033  1.0
  Ni  Ni7  1  0.449  0.469  0.842  1.0
  Ni  Ni8  1  0.546  0.337  0.531  1.0
  Ni  Ni9  1  0.545  0.970  0.340  1.0
  O  O10  1  0.495  0.753  0.242  1.0
  O  O11  1  0.520  0.254  0.746  1.0
  O  O12  1  0.871  0.110  0.338  1.0
  O  O13  1  0.875  0.253  0.420  1.0
  O  O14  1  0.898  0.233  0.096  1.0
  O  O15  1  0.905  0.384  0.172  1.0
  O  O16  1  0.094  0.889  0.664  1.0
  O  O17  1  0.095  0.741  0.583  1.0
  O  O18  1  0.131  0.754  0.928  1.0
  O  O19  1  0.123  0.608  0.851  1.0
  O  O20  1  0.625  0.649  0.954  1.0
  O  O21  1  0.581  0.946  0.856  1.0
  O  O22  1  0.570  0.548  0.644  1.0
  O  O23  1  0.588  0.863  0.539  1.0
  O  O24  1  0.377  0.147  0.451  1.0
  O  O25  1  0.413  0.042  0.140  1.0
  O  O26  1  0.421  0.449  0.353  1.0
  O  O27  1  0.414  0.362  0.040  1.0
[/CIF]
.