The compound described by RbMgCr3O8 crystallizes in the monoclinic Cm space group. Rb(1) is bonded in a 6-coordinate geometry to one O(5), one O(6), two equivalent O(1), and two equivalent O(2) atoms. Mg(1) is bonded to one O(3), one O(6), and two equivalent O(1) atoms to form distorted MgO4 trigonal pyramids that share corners with three equivalent Cr(3)O6 octahedra, corners with two equivalent Cr(1)O4 tetrahedra, and  an edgeedge with one Cr(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-64°. There are three inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(3), one O(6), and two equivalent O(2) atoms to form CrO4 tetrahedra that share corners with three equivalent Cr(3)O6 octahedra and corners with two equivalent Mg(1)O4 trigonal pyramids. The corner-sharing octahedral tilt angles range from 39-47°. In the second Cr site, Cr(2) 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(3)O6 octahedra and  an edgeedge with one Mg(1)O4 trigonal pyramid. The corner-sharing octahedral tilt angles range from 44-53°. In the third Cr site, Cr(3) 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(2)O4 tetrahedra, and corners with three equivalent Mg(1)O4 trigonal pyramids. There are six inequivalent O sites. In the first O site, O(1) is bonded to one Rb(1), one Mg(1), one Cr(2), and one Cr(3) atom to form distorted edge-sharing ORbMgCr2 tetrahedra. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Rb(1), one Cr(1), and one Cr(3) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to one Mg(1), one Cr(1), and one Cr(3) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Cr(2) and one Cr(3) atom. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to one Rb(1) and one Cr(2) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one Rb(1), one Mg(1), and one Cr(1) atom. is represented by the CIF card [CIF]
data_RbMgCr3O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.332
_cell_length_b   5.332
_cell_length_c   7.100
_cell_angle_alpha   87.165
_cell_angle_beta   87.165
_cell_angle_gamma   65.071
_symmetry_Int_Tables_number   1
_cell_volume   182.764
_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
  Rb  Rb0  1  0.989  0.989  0.017  1.0
  Mg  Mg1  1  0.332  0.332  0.744  1.0
  Cr  Cr2  1  0.366  0.366  0.286  1.0
  Cr  Cr3  1  0.639  0.639  0.704  1.0
  Cr  Cr4  1  0.997  0.997  0.509  1.0
  O  O5  1  0.732  0.268  0.698  1.0
  O  O6  1  0.714  0.236  0.323  1.0
  O  O7  1  0.236  0.714  0.323  1.0
  O  O8  1  0.268  0.732  0.698  1.0
  O  O9  1  0.226  0.226  0.489  1.0
  O  O10  1  0.772  0.772  0.528  1.0
  O  O11  1  0.698  0.698  0.917  1.0
  O  O12  1  0.306  0.306  0.061  1.0
[/CIF]
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The compound described by RbMgCr3O8 crystallizes in the monoclinic Cm space group. Rb(1) is bonded in a 6-coordinate geometry to one O(5), one O(6), two equivalent O(1), and two equivalent O(2) atoms. Mg(1) is bonded to one O(3), one O(6), and two equivalent O(1) atoms to form distorted MgO4 trigonal pyramids that share corners with three equivalent Cr(3)O6 octahedra, corners with two equivalent Cr(1)O4 tetrahedra, and  an edgeedge with one Cr(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-64°. There are three inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(3), one O(6), and two equivalent O(2) atoms to form CrO4 tetrahedra that share corners with three equivalent Cr(3)O6 octahedra and corners with two equivalent Mg(1)O4 trigonal pyramids. The corner-sharing octahedral tilt angles range from 39-47°. In the second Cr site, Cr(2) 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(3)O6 octahedra and  an edgeedge with one Mg(1)O4 trigonal pyramid. The corner-sharing octahedral tilt angles range from 44-53°. In the third Cr site, Cr(3) 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(2)O4 tetrahedra, and corners with three equivalent Mg(1)O4 trigonal pyramids. There are six inequivalent O sites. In the first O site, O(1) is bonded to one Rb(1), one Mg(1), one Cr(2), and one Cr(3) atom to form distorted edge-sharing ORbMgCr2 tetrahedra. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Rb(1), one Cr(1), and one Cr(3) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to one Mg(1), one Cr(1), and one Cr(3) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Cr(2) and one Cr(3) atom. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to one Rb(1) and one Cr(2) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one Rb(1), one Mg(1), and one Cr(1) atom. is represented by the CIF card [CIF]
data_RbMgCr3O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.332
_cell_length_b   5.332
_cell_length_c   7.100
_cell_angle_alpha   87.165
_cell_angle_beta   87.165
_cell_angle_gamma   65.071
_symmetry_Int_Tables_number   1
_cell_volume   182.764
_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
  Rb  Rb0  1  0.989  0.989  0.017  1.0
  Mg  Mg1  1  0.332  0.332  0.744  1.0
  Cr  Cr2  1  0.366  0.366  0.286  1.0
  Cr  Cr3  1  0.639  0.639  0.704  1.0
  Cr  Cr4  1  0.997  0.997  0.509  1.0
  O  O5  1  0.732  0.268  0.698  1.0
  O  O6  1  0.714  0.236  0.323  1.0
  O  O7  1  0.236  0.714  0.323  1.0
  O  O8  1  0.268  0.732  0.698  1.0
  O  O9  1  0.226  0.226  0.489  1.0
  O  O10  1  0.772  0.772  0.528  1.0
  O  O11  1  0.698  0.698  0.917  1.0
  O  O12  1  0.306  0.306  0.061  1.0
[/CIF]
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