The crystal structure described by MgSm2Nb2O8 crystallizes in the monoclinic C2 space group. Mg(1) is bonded to two equivalent O(3) and two equivalent O(4) atoms to form MgO4 tetrahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with two equivalent Sm(1)O6 pentagonal pyramids, and  an edgeedge with one Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles are 54°. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted SmO6 pentagonal pyramids that share corners with two equivalent Nb(1)O6 octahedra, corners with two equivalent Mg(1)O4 tetrahedra, edges with two equivalent Nb(1)O6 octahedra, and edges with two equivalent Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles are 36°. In the second Sm site, Sm(2) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted NbO6 octahedra that share corners with two equivalent Sm(1)O6 pentagonal pyramids, corners with two equivalent Mg(1)O4 tetrahedra, edges with two equivalent Nb(2)O6 octahedra, and edges with two equivalent Sm(1)O6 pentagonal pyramids. In the second Nb site, Nb(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form NbO6 octahedra that share edges with two equivalent Nb(1)O6 octahedra, edges with two equivalent Sm(1)O6 pentagonal pyramids, and  an edgeedge with one Mg(1)O4 tetrahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Sm(1), one Sm(2), one Nb(1), and one Nb(2) atom to form a mixture of distorted edge and corner-sharing OSm2Nb2 trigonal pyramids. In the second O site, O(2) is bonded to one Sm(1), one Sm(2), one Nb(1), and one Nb(2) atom to form a mixture of distorted edge and corner-sharing OSm2Nb2 trigonal pyramids. In the third O site, O(3) is bonded in a trigonal non-coplanar geometry to one Mg(1), one Sm(1), and one Nb(1) atom. In the fourth O site, O(4) is bonded in a T-shaped geometry to one Mg(1), one Sm(2), and one Nb(2) atom. is represented by the CIF card [CIF]
data_Sm2MgNb2O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.416
_cell_length_b   5.313
_cell_length_c   7.973
_cell_angle_alpha   105.520
_cell_angle_beta   105.978
_cell_angle_gamma   101.136
_symmetry_Int_Tables_number   1
_cell_volume   203.507
_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
  Sm  Sm0  1  0.330  0.580  0.660  1.0
  Sm  Sm1  1  0.649  0.399  0.298  1.0
  Mg  Mg2  1  0.980  0.730  0.959  1.0
  Nb  Nb3  1  0.820  0.070  0.640  1.0
  Nb  Nb4  1  0.176  0.926  0.351  1.0
  O  O5  1  0.018  0.793  0.557  1.0
  O  O6  1  0.539  0.263  0.557  1.0
  O  O7  1  0.971  0.197  0.422  1.0
  O  O8  1  0.451  0.725  0.422  1.0
  O  O9  1  0.075  0.424  0.817  1.0
  O  O10  1  0.742  0.893  0.817  1.0
  O  O11  1  0.857  0.627  0.150  1.0
  O  O12  1  0.292  0.023  0.150  1.0
[/CIF]
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The crystal structure described by MgSm2Nb2O8 crystallizes in the monoclinic C2 space group. Mg(1) is bonded to two equivalent O(3) and two equivalent O(4) atoms to form MgO4 tetrahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with two equivalent Sm(1)O6 pentagonal pyramids, and  an edgeedge with one Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles are 54°. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted SmO6 pentagonal pyramids that share corners with two equivalent Nb(1)O6 octahedra, corners with two equivalent Mg(1)O4 tetrahedra, edges with two equivalent Nb(1)O6 octahedra, and edges with two equivalent Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles are 36°. In the second Sm site, Sm(2) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted NbO6 octahedra that share corners with two equivalent Sm(1)O6 pentagonal pyramids, corners with two equivalent Mg(1)O4 tetrahedra, edges with two equivalent Nb(2)O6 octahedra, and edges with two equivalent Sm(1)O6 pentagonal pyramids. In the second Nb site, Nb(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form NbO6 octahedra that share edges with two equivalent Nb(1)O6 octahedra, edges with two equivalent Sm(1)O6 pentagonal pyramids, and  an edgeedge with one Mg(1)O4 tetrahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Sm(1), one Sm(2), one Nb(1), and one Nb(2) atom to form a mixture of distorted edge and corner-sharing OSm2Nb2 trigonal pyramids. In the second O site, O(2) is bonded to one Sm(1), one Sm(2), one Nb(1), and one Nb(2) atom to form a mixture of distorted edge and corner-sharing OSm2Nb2 trigonal pyramids. In the third O site, O(3) is bonded in a trigonal non-coplanar geometry to one Mg(1), one Sm(1), and one Nb(1) atom. In the fourth O site, O(4) is bonded in a T-shaped geometry to one Mg(1), one Sm(2), and one Nb(2) atom. is represented by the CIF card [CIF]
data_Sm2MgNb2O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.416
_cell_length_b   5.313
_cell_length_c   7.973
_cell_angle_alpha   105.520
_cell_angle_beta   105.978
_cell_angle_gamma   101.136
_symmetry_Int_Tables_number   1
_cell_volume   203.507
_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
  Sm  Sm0  1  0.330  0.580  0.660  1.0
  Sm  Sm1  1  0.649  0.399  0.298  1.0
  Mg  Mg2  1  0.980  0.730  0.959  1.0
  Nb  Nb3  1  0.820  0.070  0.640  1.0
  Nb  Nb4  1  0.176  0.926  0.351  1.0
  O  O5  1  0.018  0.793  0.557  1.0
  O  O6  1  0.539  0.263  0.557  1.0
  O  O7  1  0.971  0.197  0.422  1.0
  O  O8  1  0.451  0.725  0.422  1.0
  O  O9  1  0.075  0.424  0.817  1.0
  O  O10  1  0.742  0.893  0.817  1.0
  O  O11  1  0.857  0.627  0.150  1.0
  O  O12  1  0.292  0.023  0.150  1.0
[/CIF]
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