The structure described by MgEr2Cr2O8 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(2), one O(5), and one O(6) atom to form MgO4 tetrahedra that share corners with two equivalent Cr(1)O6 octahedra, corners with two equivalent Er(1)O6 pentagonal pyramids, and  an edgeedge with one Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-54°. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(7), and one O(8) atom to form distorted ErO6 pentagonal pyramids that share corners with two equivalent Cr(1)O6 octahedra, corners with two equivalent Mg(1)O4 tetrahedra, edges with two equivalent Cr(1)O6 octahedra, and edges with two equivalent Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles are 37°. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to one O(3), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(7), and one O(8) atom to form distorted CrO6 octahedra that share corners with two equivalent Er(1)O6 pentagonal pyramids, corners with two equivalent Mg(1)O4 tetrahedra, edges with two equivalent Cr(2)O6 octahedra, and edges with two equivalent Er(1)O6 pentagonal pyramids. In the second Cr site, Cr(2) is bonded to one O(3), one O(4), one O(5), one O(6), one O(7), and one O(8) atom to form CrO6 octahedra that share edges with two equivalent Cr(1)O6 octahedra, edges with two equivalent Er(1)O6 pentagonal pyramids, and  an edgeedge with one Mg(1)O4 tetrahedra. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal non-coplanar geometry to one Mg(1), one Er(1), and one Cr(1) atom. In the second O site, O(2) is bonded in a trigonal non-coplanar geometry to one Mg(1), one Er(1), and one Cr(1) atom. In the third O site, O(3) is bonded to one Er(1), one Er(2), one Cr(1), and one Cr(2) atom to form a mixture of distorted corner and edge-sharing OEr2Cr2 trigonal pyramids. In the fourth O site, O(4) is bonded to one Er(1), one Er(2), one Cr(1), and one Cr(2) atom to form a mixture of distorted corner and edge-sharing OEr2Cr2 trigonal pyramids. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Mg(1), one Er(2), and one Cr(2) atom. In the sixth O site, O(6) is bonded in a distorted T-shaped geometry to one Mg(1), one Er(2), and one Cr(2) atom. In the seventh O site, O(7) is bonded to one Er(1), one Er(2), one Cr(1), and one Cr(2) atom to form a mixture of distorted corner and edge-sharing OEr2Cr2 trigonal pyramids. In the eighth O site, O(8) is bonded to one Er(1), one Er(2), one Cr(1), and one Cr(2) atom to form a mixture of distorted corner and edge-sharing OEr2Cr2 trigonal pyramids. is represented by the CIF file [CIF]
data_Er2MgCr2O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.008
_cell_length_b   5.113
_cell_length_c   8.186
_cell_angle_alpha   111.906
_cell_angle_beta   111.433
_cell_angle_gamma   79.364
_symmetry_Int_Tables_number   1
_cell_volume   180.756
_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
  Er  Er0  1  0.578  0.828  0.155  1.0
  Er  Er1  1  0.404  0.154  0.809  1.0
  Mg  Mg2  1  0.735  0.484  0.465  1.0
  Cr  Cr3  1  0.067  0.317  0.132  1.0
  Cr  Cr4  1  0.929  0.679  0.858  1.0
  O  O5  1  0.407  0.235  0.308  1.0
  O  O6  1  0.905  0.579  0.309  1.0
  O  O7  1  0.725  0.478  0.929  1.0
  O  O8  1  0.204  0.950  0.929  1.0
  O  O9  1  0.638  0.792  0.670  1.0
  O  O10  1  0.032  0.376  0.670  1.0
  O  O11  1  0.251  0.517  0.052  1.0
  O  O12  1  0.801  0.036  0.052  1.0
[/CIF]
.
The structure described by MgEr2Cr2O8 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(2), one O(5), and one O(6) atom to form MgO4 tetrahedra that share corners with two equivalent Cr(1)O6 octahedra, corners with two equivalent Er(1)O6 pentagonal pyramids, and  an edgeedge with one Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-54°. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(7), and one O(8) atom to form distorted ErO6 pentagonal pyramids that share corners with two equivalent Cr(1)O6 octahedra, corners with two equivalent Mg(1)O4 tetrahedra, edges with two equivalent Cr(1)O6 octahedra, and edges with two equivalent Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles are 37°. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to one O(3), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(7), and one O(8) atom to form distorted CrO6 octahedra that share corners with two equivalent Er(1)O6 pentagonal pyramids, corners with two equivalent Mg(1)O4 tetrahedra, edges with two equivalent Cr(2)O6 octahedra, and edges with two equivalent Er(1)O6 pentagonal pyramids. In the second Cr site, Cr(2) is bonded to one O(3), one O(4), one O(5), one O(6), one O(7), and one O(8) atom to form CrO6 octahedra that share edges with two equivalent Cr(1)O6 octahedra, edges with two equivalent Er(1)O6 pentagonal pyramids, and  an edgeedge with one Mg(1)O4 tetrahedra. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal non-coplanar geometry to one Mg(1), one Er(1), and one Cr(1) atom. In the second O site, O(2) is bonded in a trigonal non-coplanar geometry to one Mg(1), one Er(1), and one Cr(1) atom. In the third O site, O(3) is bonded to one Er(1), one Er(2), one Cr(1), and one Cr(2) atom to form a mixture of distorted corner and edge-sharing OEr2Cr2 trigonal pyramids. In the fourth O site, O(4) is bonded to one Er(1), one Er(2), one Cr(1), and one Cr(2) atom to form a mixture of distorted corner and edge-sharing OEr2Cr2 trigonal pyramids. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Mg(1), one Er(2), and one Cr(2) atom. In the sixth O site, O(6) is bonded in a distorted T-shaped geometry to one Mg(1), one Er(2), and one Cr(2) atom. In the seventh O site, O(7) is bonded to one Er(1), one Er(2), one Cr(1), and one Cr(2) atom to form a mixture of distorted corner and edge-sharing OEr2Cr2 trigonal pyramids. In the eighth O site, O(8) is bonded to one Er(1), one Er(2), one Cr(1), and one Cr(2) atom to form a mixture of distorted corner and edge-sharing OEr2Cr2 trigonal pyramids. is represented by the CIF file [CIF]
data_Er2MgCr2O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.008
_cell_length_b   5.113
_cell_length_c   8.186
_cell_angle_alpha   111.906
_cell_angle_beta   111.433
_cell_angle_gamma   79.364
_symmetry_Int_Tables_number   1
_cell_volume   180.756
_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
  Er  Er0  1  0.578  0.828  0.155  1.0
  Er  Er1  1  0.404  0.154  0.809  1.0
  Mg  Mg2  1  0.735  0.484  0.465  1.0
  Cr  Cr3  1  0.067  0.317  0.132  1.0
  Cr  Cr4  1  0.929  0.679  0.858  1.0
  O  O5  1  0.407  0.235  0.308  1.0
  O  O6  1  0.905  0.579  0.309  1.0
  O  O7  1  0.725  0.478  0.929  1.0
  O  O8  1  0.204  0.950  0.929  1.0
  O  O9  1  0.638  0.792  0.670  1.0
  O  O10  1  0.032  0.376  0.670  1.0
  O  O11  1  0.251  0.517  0.052  1.0
  O  O12  1  0.801  0.036  0.052  1.0
[/CIF]
.