The compound described by Rb4Mg(Se2O7)2 crystallizes in the triclinic P1 space group. There are four inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 9-coordinate geometry to one O(1), one O(10), one O(11), one O(13), one O(4), one O(5), one O(6), one O(8), and one O(9) atom. In the second Rb site, Rb(2) is bonded to one O(10), one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form distorted RbO6 octahedra that share  a cornercorner with one Rb(3)O7 pentagonal bipyramid,  a cornercorner with one Se(1)O4 tetrahedra,  a cornercorner with one Se(4)O4 tetrahedra, corners with two equivalent Se(3)O4 tetrahedra,  a cornercorner with one Mg(1)O5 trigonal bipyramid, and  an edgeedge with one Rb(3)O7 pentagonal bipyramid. In the third Rb site, Rb(3) is bonded to one O(1), one O(11), one O(2), one O(3), one O(6), one O(7), and one O(9) atom to form distorted RbO7 pentagonal bipyramids that share  a cornercorner with one Rb(2)O6 octahedra,  a cornercorner with one Se(3)O4 tetrahedra, corners with two equivalent Se(1)O4 tetrahedra,  an edgeedge with one Rb(2)O6 octahedra,  an edgeedge with one Se(3)O4 tetrahedra, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 67°. In the fourth Rb site, Rb(4) is bonded in a 7-coordinate geometry to one O(1), one O(12), one O(14), one O(5), one O(7), one O(8), and one O(9) atom. Mg(1) is bonded to one O(10), one O(11), one O(12), one O(2), and one O(8) atom to form MgO5 trigonal bipyramids that share  a cornercorner with one Rb(2)O6 octahedra,  a cornercorner with one Se(3)O4 tetrahedra,  an edgeedge with one Rb(3)O7 pentagonal bipyramid, and  an edgeedge with one Se(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 56°. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded to one O(1), one O(13), one O(5), and one O(9) atom to form SeO4 tetrahedra that share  a cornercorner with one Rb(2)O6 octahedra and corners with two equivalent Rb(3)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 57°. In the second Se site, Se(2) is bonded in a distorted trigonal non-coplanar geometry to one O(10), one O(13), one O(2), and one O(6) atom. In the third Se site, Se(3) is bonded to one O(11), one O(14), one O(3), and one O(7) atom to form SeO4 tetrahedra that share corners with two equivalent Rb(2)O6 octahedra,  a cornercorner with one Rb(3)O7 pentagonal bipyramid,  a cornercorner with one Se(4)O4 tetrahedra,  a cornercorner with one Mg(1)O5 trigonal bipyramid, and  an edgeedge with one Rb(3)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 26-43°. In the fourth Se site, Se(4) is bonded to one O(12), one O(14), one O(4), and one O(8) atom to form distorted SeO4 tetrahedra that share  a cornercorner with one Rb(2)O6 octahedra,  a cornercorner with one Se(3)O4 tetrahedra, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 57°. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Rb(1), one Rb(3), one Rb(4), and one Se(1) atom. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Rb(3), one Mg(1), and one Se(2) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Rb(2), one Rb(3), and one Se(3) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Rb(1), one Rb(2), and one Se(4) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Rb(1), one Rb(2), one Rb(4), and one Se(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Rb(1), one Rb(2), one Rb(3), and one Se(2) atom. In the seventh O site, O(7) is bonded in a distorted single-bond geometry to one Rb(2), one Rb(3), one Rb(4), and one Se(3) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Rb(1), one Rb(4), one Mg(1), and one Se(4) atom. In the ninth O site, O(9) is bonded in a distorted single-bond geometry to one Rb(1), one Rb(3), one Rb(4), and one Se(1) atom. In the tenth O site, O(10) is bonded in a 3-coordinate geometry to one Rb(1), one Rb(2), one Mg(1), and one Se(2) atom. In the eleventh O site, O(11) is bonded in a distorted bent 120 degrees geometry to one Rb(1), one Rb(3), one Mg(1), and one Se(3) atom. In the twelfth O site, O(12) is bonded in a 3-coordinate geometry to one Rb(4), one Mg(1), and one Se(4) atom. In the thirteenth O site, O(13) is bonded in a distorted single-bond geometry to one Rb(1), one Se(1), and one Se(2) atom. In the fourteenth O site, O(14) is bonded in a distorted single-bond geometry to one Rb(4), one Se(3), and one Se(4) atom. is represented by the CIF file [CIF]
data_Rb4Mg(Se2O7)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.638
_cell_length_b   7.994
_cell_length_c   8.178
_cell_angle_alpha   87.914
_cell_angle_beta   87.546
_cell_angle_gamma   56.993
_symmetry_Int_Tables_number   1
_cell_volume   473.088
_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  0.181  0.499  0.371  1.0
  Rb  Rb1  1  0.441  0.845  0.144  1.0
  Rb  Rb2  1  0.679  0.544  0.577  1.0
  Rb  Rb3  1  0.660  0.076  0.824  1.0
  Mg  Mg4  1  0.067  0.381  0.854  1.0
  Se  Se5  1  0.706  0.060  0.359  1.0
  Se  Se6  1  0.888  0.310  0.112  1.0
  Se  Se7  1  0.219  0.996  0.653  1.0
  Se  Se8  1  0.178  0.646  0.893  1.0
  O  O9  1  0.604  0.251  0.488  1.0
  O  O10  1  0.807  0.419  0.921  1.0
  O  O11  1  0.297  0.883  0.475  1.0
  O  O12  1  0.272  0.628  0.073  1.0
  O  O13  1  0.563  0.105  0.209  1.0
  O  O14  1  0.797  0.491  0.250  1.0
  O  O15  1  0.391  0.914  0.782  1.0
  O  O16  1  0.289  0.416  0.802  1.0
  O  O17  1  0.777  0.846  0.462  1.0
  O  O18  1  0.116  0.236  0.077  1.0
  O  O19  1  0.106  0.249  0.635  1.0
  O  O20  1  0.966  0.676  0.918  1.0
  O  O21  1  0.907  0.027  0.275  1.0
  O  O22  1  0.055  0.959  0.737  1.0
[/CIF]
.
The compound described by Rb4Mg(Se2O7)2 crystallizes in the triclinic P1 space group. There are four inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 9-coordinate geometry to one O(1), one O(10), one O(11), one O(13), one O(4), one O(5), one O(6), one O(8), and one O(9) atom. In the second Rb site, Rb(2) is bonded to one O(10), one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form distorted RbO6 octahedra that share  a cornercorner with one Rb(3)O7 pentagonal bipyramid,  a cornercorner with one Se(1)O4 tetrahedra,  a cornercorner with one Se(4)O4 tetrahedra, corners with two equivalent Se(3)O4 tetrahedra,  a cornercorner with one Mg(1)O5 trigonal bipyramid, and  an edgeedge with one Rb(3)O7 pentagonal bipyramid. In the third Rb site, Rb(3) is bonded to one O(1), one O(11), one O(2), one O(3), one O(6), one O(7), and one O(9) atom to form distorted RbO7 pentagonal bipyramids that share  a cornercorner with one Rb(2)O6 octahedra,  a cornercorner with one Se(3)O4 tetrahedra, corners with two equivalent Se(1)O4 tetrahedra,  an edgeedge with one Rb(2)O6 octahedra,  an edgeedge with one Se(3)O4 tetrahedra, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 67°. In the fourth Rb site, Rb(4) is bonded in a 7-coordinate geometry to one O(1), one O(12), one O(14), one O(5), one O(7), one O(8), and one O(9) atom. Mg(1) is bonded to one O(10), one O(11), one O(12), one O(2), and one O(8) atom to form MgO5 trigonal bipyramids that share  a cornercorner with one Rb(2)O6 octahedra,  a cornercorner with one Se(3)O4 tetrahedra,  an edgeedge with one Rb(3)O7 pentagonal bipyramid, and  an edgeedge with one Se(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 56°. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded to one O(1), one O(13), one O(5), and one O(9) atom to form SeO4 tetrahedra that share  a cornercorner with one Rb(2)O6 octahedra and corners with two equivalent Rb(3)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 57°. In the second Se site, Se(2) is bonded in a distorted trigonal non-coplanar geometry to one O(10), one O(13), one O(2), and one O(6) atom. In the third Se site, Se(3) is bonded to one O(11), one O(14), one O(3), and one O(7) atom to form SeO4 tetrahedra that share corners with two equivalent Rb(2)O6 octahedra,  a cornercorner with one Rb(3)O7 pentagonal bipyramid,  a cornercorner with one Se(4)O4 tetrahedra,  a cornercorner with one Mg(1)O5 trigonal bipyramid, and  an edgeedge with one Rb(3)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 26-43°. In the fourth Se site, Se(4) is bonded to one O(12), one O(14), one O(4), and one O(8) atom to form distorted SeO4 tetrahedra that share  a cornercorner with one Rb(2)O6 octahedra,  a cornercorner with one Se(3)O4 tetrahedra, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 57°. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Rb(1), one Rb(3), one Rb(4), and one Se(1) atom. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Rb(3), one Mg(1), and one Se(2) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Rb(2), one Rb(3), and one Se(3) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Rb(1), one Rb(2), and one Se(4) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Rb(1), one Rb(2), one Rb(4), and one Se(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Rb(1), one Rb(2), one Rb(3), and one Se(2) atom. In the seventh O site, O(7) is bonded in a distorted single-bond geometry to one Rb(2), one Rb(3), one Rb(4), and one Se(3) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Rb(1), one Rb(4), one Mg(1), and one Se(4) atom. In the ninth O site, O(9) is bonded in a distorted single-bond geometry to one Rb(1), one Rb(3), one Rb(4), and one Se(1) atom. In the tenth O site, O(10) is bonded in a 3-coordinate geometry to one Rb(1), one Rb(2), one Mg(1), and one Se(2) atom. In the eleventh O site, O(11) is bonded in a distorted bent 120 degrees geometry to one Rb(1), one Rb(3), one Mg(1), and one Se(3) atom. In the twelfth O site, O(12) is bonded in a 3-coordinate geometry to one Rb(4), one Mg(1), and one Se(4) atom. In the thirteenth O site, O(13) is bonded in a distorted single-bond geometry to one Rb(1), one Se(1), and one Se(2) atom. In the fourteenth O site, O(14) is bonded in a distorted single-bond geometry to one Rb(4), one Se(3), and one Se(4) atom. is represented by the CIF file [CIF]
data_Rb4Mg(Se2O7)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.638
_cell_length_b   7.994
_cell_length_c   8.178
_cell_angle_alpha   87.914
_cell_angle_beta   87.546
_cell_angle_gamma   56.993
_symmetry_Int_Tables_number   1
_cell_volume   473.088
_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  0.181  0.499  0.371  1.0
  Rb  Rb1  1  0.441  0.845  0.144  1.0
  Rb  Rb2  1  0.679  0.544  0.577  1.0
  Rb  Rb3  1  0.660  0.076  0.824  1.0
  Mg  Mg4  1  0.067  0.381  0.854  1.0
  Se  Se5  1  0.706  0.060  0.359  1.0
  Se  Se6  1  0.888  0.310  0.112  1.0
  Se  Se7  1  0.219  0.996  0.653  1.0
  Se  Se8  1  0.178  0.646  0.893  1.0
  O  O9  1  0.604  0.251  0.488  1.0
  O  O10  1  0.807  0.419  0.921  1.0
  O  O11  1  0.297  0.883  0.475  1.0
  O  O12  1  0.272  0.628  0.073  1.0
  O  O13  1  0.563  0.105  0.209  1.0
  O  O14  1  0.797  0.491  0.250  1.0
  O  O15  1  0.391  0.914  0.782  1.0
  O  O16  1  0.289  0.416  0.802  1.0
  O  O17  1  0.777  0.846  0.462  1.0
  O  O18  1  0.116  0.236  0.077  1.0
  O  O19  1  0.106  0.249  0.635  1.0
  O  O20  1  0.966  0.676  0.918  1.0
  O  O21  1  0.907  0.027  0.275  1.0
  O  O22  1  0.055  0.959  0.737  1.0
[/CIF]
.