The material structure described by NaMgCr3O8 crystallizes in the monoclinic Cm space group. Na(1) is bonded in a 5-coordinate geometry to one O(6), two equivalent O(2), and two equivalent O(5) atoms. Mg(1) is bonded to one O(4), one O(5), and two equivalent O(1) atoms to form distorted MgO4 trigonal pyramids that share corners with two equivalent Cr(1)O4 tetrahedra,  an edgeedge with one Cr(1)O4 tetrahedra, and  a faceface with one Cr(2)O6 octahedra. There are three inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(4), one O(5), and two equivalent O(1) atoms to form CrO4 tetrahedra that share corners with three equivalent Cr(2)O6 octahedra, corners with two equivalent Mg(1)O4 trigonal pyramids, and  an edgeedge with one Mg(1)O4 trigonal pyramid. The corner-sharing octahedral tilt angles range from 11-47°. In the second Cr site, Cr(2) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form CrO6 octahedra that share corners with three equivalent Cr(1)O4 tetrahedra, corners with three equivalent Cr(3)O4 tetrahedra, and  a faceface with one Mg(1)O4 trigonal pyramid. In the third Cr site, Cr(3) is bonded to one O(3), one O(6), and two equivalent O(2) atoms to form corner-sharing CrO4 tetrahedra. The corner-sharing octahedral tilt angles range from 17-38°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Mg(1), one Cr(1), and one Cr(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Na(1), one Cr(2), and one Cr(3) atom. In the third O site, O(3) is bonded in a distorted linear geometry to one Cr(2) and one Cr(3) atom. In the fourth O site, O(4) is bonded in a T-shaped geometry to one Mg(1), one Cr(1), and one Cr(2) atom. In the fifth O site, O(5) is bonded in a distorted L-shaped geometry to two equivalent Na(1), one Mg(1), and one Cr(1) atom. In the sixth O site, O(6) is bonded in a water-like geometry to one Na(1) and one Cr(3) atom. is represented by the CIF file [CIF]
data_NaMgCr3O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.495
_cell_length_b   5.495
_cell_length_c   7.370
_cell_angle_alpha   80.351
_cell_angle_beta   80.351
_cell_angle_gamma   59.539
_symmetry_Int_Tables_number   1
_cell_volume   188.202
_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
  Na  Na0  1  0.115  0.115  0.046  1.0
  Mg  Mg1  1  0.858  0.858  0.835  1.0
  Cr  Cr2  1  0.606  0.606  0.721  1.0
  Cr  Cr3  1  0.995  0.995  0.491  1.0
  Cr  Cr4  1  0.376  0.376  0.260  1.0
  O  O5  1  0.778  0.234  0.701  1.0
  O  O6  1  0.723  0.218  0.294  1.0
  O  O7  1  0.218  0.723  0.294  1.0
  O  O8  1  0.234  0.778  0.701  1.0
  O  O9  1  0.215  0.215  0.396  1.0
  O  O10  1  0.787  0.787  0.587  1.0
  O  O11  1  0.659  0.659  0.943  1.0
  O  O12  1  0.351  0.351  0.045  1.0
[/CIF]
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The material structure described by NaMgCr3O8 crystallizes in the monoclinic Cm space group. Na(1) is bonded in a 5-coordinate geometry to one O(6), two equivalent O(2), and two equivalent O(5) atoms. Mg(1) is bonded to one O(4), one O(5), and two equivalent O(1) atoms to form distorted MgO4 trigonal pyramids that share corners with two equivalent Cr(1)O4 tetrahedra,  an edgeedge with one Cr(1)O4 tetrahedra, and  a faceface with one Cr(2)O6 octahedra. There are three inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(4), one O(5), and two equivalent O(1) atoms to form CrO4 tetrahedra that share corners with three equivalent Cr(2)O6 octahedra, corners with two equivalent Mg(1)O4 trigonal pyramids, and  an edgeedge with one Mg(1)O4 trigonal pyramid. The corner-sharing octahedral tilt angles range from 11-47°. In the second Cr site, Cr(2) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form CrO6 octahedra that share corners with three equivalent Cr(1)O4 tetrahedra, corners with three equivalent Cr(3)O4 tetrahedra, and  a faceface with one Mg(1)O4 trigonal pyramid. In the third Cr site, Cr(3) is bonded to one O(3), one O(6), and two equivalent O(2) atoms to form corner-sharing CrO4 tetrahedra. The corner-sharing octahedral tilt angles range from 17-38°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Mg(1), one Cr(1), and one Cr(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Na(1), one Cr(2), and one Cr(3) atom. In the third O site, O(3) is bonded in a distorted linear geometry to one Cr(2) and one Cr(3) atom. In the fourth O site, O(4) is bonded in a T-shaped geometry to one Mg(1), one Cr(1), and one Cr(2) atom. In the fifth O site, O(5) is bonded in a distorted L-shaped geometry to two equivalent Na(1), one Mg(1), and one Cr(1) atom. In the sixth O site, O(6) is bonded in a water-like geometry to one Na(1) and one Cr(3) atom. is represented by the CIF file [CIF]
data_NaMgCr3O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.495
_cell_length_b   5.495
_cell_length_c   7.370
_cell_angle_alpha   80.351
_cell_angle_beta   80.351
_cell_angle_gamma   59.539
_symmetry_Int_Tables_number   1
_cell_volume   188.202
_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
  Na  Na0  1  0.115  0.115  0.046  1.0
  Mg  Mg1  1  0.858  0.858  0.835  1.0
  Cr  Cr2  1  0.606  0.606  0.721  1.0
  Cr  Cr3  1  0.995  0.995  0.491  1.0
  Cr  Cr4  1  0.376  0.376  0.260  1.0
  O  O5  1  0.778  0.234  0.701  1.0
  O  O6  1  0.723  0.218  0.294  1.0
  O  O7  1  0.218  0.723  0.294  1.0
  O  O8  1  0.234  0.778  0.701  1.0
  O  O9  1  0.215  0.215  0.396  1.0
  O  O10  1  0.787  0.787  0.587  1.0
  O  O11  1  0.659  0.659  0.943  1.0
  O  O12  1  0.351  0.351  0.045  1.0
[/CIF]
.