The crystal structure described by Mg2TaNb2O8 crystallizes in the triclinic P-1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 6-coordinate geometry to one O(6), one O(7), two equivalent O(5), and two equivalent O(8) atoms. In the second Mg site, Mg(2) is bonded to one O(5), one O(8), two equivalent O(6), and two equivalent O(7) atoms to form distorted MgO6 octahedra that share corners with two equivalent Nb(2)O6 octahedra, corners with four equivalent Nb(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, and  a faceface with one Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 38-63°. Ta(1) is bonded to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms to form TaO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra, corners with four equivalent Nb(2)O6 octahedra, and edges with two equivalent Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-64°. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(6), and one O(8) atom to form NbO6 octahedra that share corners with four equivalent Mg(2)O6 octahedra, corners with four equivalent Ta(1)O6 octahedra, and edges with two equivalent Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 38-64°. In the second Nb site, Nb(2) is bonded to one O(1), one O(2), one O(4), one O(5), one O(6), and one O(7) atom to form distorted NbO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra, corners with four equivalent Ta(1)O6 octahedra, edges with two equivalent Nb(1)O6 octahedra, and  a faceface with one Mg(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-64°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ta(1), one Nb(1), and one Nb(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ta(1), one Nb(1), and one Nb(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Ta(1) and one Nb(1) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to two equivalent Ta(1) and one Nb(2) atom. In the fifth O site, O(5) is bonded to one Mg(2), two equivalent Mg(1), one Nb(1), and one Nb(2) atom to form distorted OMg3Nb2 trigonal bipyramids that share  a cornercorner with one O(7)Mg3Nb trigonal pyramid, corners with two equivalent O(8)Mg3Nb trigonal pyramids,  an edgeedge with one O(5)Mg3Nb2 trigonal bipyramid, edges with two equivalent O(7)Mg3Nb trigonal pyramids, and edges with two equivalent O(8)Mg3Nb trigonal pyramids. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to one Mg(1), two equivalent Mg(2), one Nb(1), and one Nb(2) atom. In the seventh O site, O(7) is bonded to one Mg(1), two equivalent Mg(2), and one Nb(2) atom to form OMg3Nb trigonal pyramids that share  a cornercorner with one O(5)Mg3Nb2 trigonal bipyramid, corners with four equivalent O(8)Mg3Nb trigonal pyramids, edges with two equivalent O(5)Mg3Nb2 trigonal bipyramids, and  an edgeedge with one O(7)Mg3Nb trigonal pyramid. In the eighth O site, O(8) is bonded to one Mg(2), two equivalent Mg(1), and one Nb(1) atom to form OMg3Nb trigonal pyramids that share corners with two equivalent O(5)Mg3Nb2 trigonal bipyramids, corners with four equivalent O(7)Mg3Nb trigonal pyramids, edges with two equivalent O(5)Mg3Nb2 trigonal bipyramids, and  an edgeedge with one O(8)Mg3Nb trigonal pyramid. is represented by the CIF file [CIF]
data_Mg2TaNb2O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.230
_cell_length_b   5.982
_cell_length_c   10.005
_cell_angle_alpha   103.858
_cell_angle_beta   93.274
_cell_angle_gamma   91.720
_symmetry_Int_Tables_number   1
_cell_volume   303.116
_cell_formula_units_Z   2
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
  Mg  Mg0  1  0.767  0.419  0.553  1.0
  Mg  Mg1  1  0.745  0.861  0.460  1.0
  Mg  Mg2  1  0.233  0.581  0.447  1.0
  Mg  Mg3  1  0.255  0.139  0.540  1.0
  Ta  Ta4  1  0.755  0.656  0.994  1.0
  Ta  Ta5  1  0.245  0.344  0.006  1.0
  Nb  Nb6  1  0.719  0.247  0.248  1.0
  Nb  Nb7  1  0.716  0.008  0.768  1.0
  Nb  Nb8  1  0.281  0.753  0.752  1.0
  Nb  Nb9  1  0.284  0.992  0.232  1.0
  O  O10  1  0.067  0.205  0.136  1.0
  O  O11  1  0.390  0.091  0.885  1.0
  O  O12  1  0.933  0.795  0.864  1.0
  O  O13  1  0.610  0.909  0.115  1.0
  O  O14  1  0.587  0.448  0.113  1.0
  O  O15  1  0.904  0.329  0.898  1.0
  O  O16  1  0.413  0.552  0.887  1.0
  O  O17  1  0.096  0.671  0.102  1.0
  O  O18  1  0.427  0.299  0.380  1.0
  O  O19  1  0.066  0.920  0.632  1.0
  O  O20  1  0.376  0.846  0.383  1.0
  O  O21  1  0.134  0.457  0.617  1.0
  O  O22  1  0.624  0.154  0.617  1.0
  O  O23  1  0.866  0.543  0.383  1.0
  O  O24  1  0.934  0.080  0.368  1.0
  O  O25  1  0.573  0.701  0.620  1.0
[/CIF]
.
The crystal structure described by Mg2TaNb2O8 crystallizes in the triclinic P-1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 6-coordinate geometry to one O(6), one O(7), two equivalent O(5), and two equivalent O(8) atoms. In the second Mg site, Mg(2) is bonded to one O(5), one O(8), two equivalent O(6), and two equivalent O(7) atoms to form distorted MgO6 octahedra that share corners with two equivalent Nb(2)O6 octahedra, corners with four equivalent Nb(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, and  a faceface with one Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 38-63°. Ta(1) is bonded to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms to form TaO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra, corners with four equivalent Nb(2)O6 octahedra, and edges with two equivalent Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-64°. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(6), and one O(8) atom to form NbO6 octahedra that share corners with four equivalent Mg(2)O6 octahedra, corners with four equivalent Ta(1)O6 octahedra, and edges with two equivalent Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 38-64°. In the second Nb site, Nb(2) is bonded to one O(1), one O(2), one O(4), one O(5), one O(6), and one O(7) atom to form distorted NbO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra, corners with four equivalent Ta(1)O6 octahedra, edges with two equivalent Nb(1)O6 octahedra, and  a faceface with one Mg(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-64°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ta(1), one Nb(1), and one Nb(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ta(1), one Nb(1), and one Nb(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Ta(1) and one Nb(1) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to two equivalent Ta(1) and one Nb(2) atom. In the fifth O site, O(5) is bonded to one Mg(2), two equivalent Mg(1), one Nb(1), and one Nb(2) atom to form distorted OMg3Nb2 trigonal bipyramids that share  a cornercorner with one O(7)Mg3Nb trigonal pyramid, corners with two equivalent O(8)Mg3Nb trigonal pyramids,  an edgeedge with one O(5)Mg3Nb2 trigonal bipyramid, edges with two equivalent O(7)Mg3Nb trigonal pyramids, and edges with two equivalent O(8)Mg3Nb trigonal pyramids. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to one Mg(1), two equivalent Mg(2), one Nb(1), and one Nb(2) atom. In the seventh O site, O(7) is bonded to one Mg(1), two equivalent Mg(2), and one Nb(2) atom to form OMg3Nb trigonal pyramids that share  a cornercorner with one O(5)Mg3Nb2 trigonal bipyramid, corners with four equivalent O(8)Mg3Nb trigonal pyramids, edges with two equivalent O(5)Mg3Nb2 trigonal bipyramids, and  an edgeedge with one O(7)Mg3Nb trigonal pyramid. In the eighth O site, O(8) is bonded to one Mg(2), two equivalent Mg(1), and one Nb(1) atom to form OMg3Nb trigonal pyramids that share corners with two equivalent O(5)Mg3Nb2 trigonal bipyramids, corners with four equivalent O(7)Mg3Nb trigonal pyramids, edges with two equivalent O(5)Mg3Nb2 trigonal bipyramids, and  an edgeedge with one O(8)Mg3Nb trigonal pyramid. is represented by the CIF file [CIF]
data_Mg2TaNb2O8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.230
_cell_length_b   5.982
_cell_length_c   10.005
_cell_angle_alpha   103.858
_cell_angle_beta   93.274
_cell_angle_gamma   91.720
_symmetry_Int_Tables_number   1
_cell_volume   303.116
_cell_formula_units_Z   2
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
  Mg  Mg0  1  0.767  0.419  0.553  1.0
  Mg  Mg1  1  0.745  0.861  0.460  1.0
  Mg  Mg2  1  0.233  0.581  0.447  1.0
  Mg  Mg3  1  0.255  0.139  0.540  1.0
  Ta  Ta4  1  0.755  0.656  0.994  1.0
  Ta  Ta5  1  0.245  0.344  0.006  1.0
  Nb  Nb6  1  0.719  0.247  0.248  1.0
  Nb  Nb7  1  0.716  0.008  0.768  1.0
  Nb  Nb8  1  0.281  0.753  0.752  1.0
  Nb  Nb9  1  0.284  0.992  0.232  1.0
  O  O10  1  0.067  0.205  0.136  1.0
  O  O11  1  0.390  0.091  0.885  1.0
  O  O12  1  0.933  0.795  0.864  1.0
  O  O13  1  0.610  0.909  0.115  1.0
  O  O14  1  0.587  0.448  0.113  1.0
  O  O15  1  0.904  0.329  0.898  1.0
  O  O16  1  0.413  0.552  0.887  1.0
  O  O17  1  0.096  0.671  0.102  1.0
  O  O18  1  0.427  0.299  0.380  1.0
  O  O19  1  0.066  0.920  0.632  1.0
  O  O20  1  0.376  0.846  0.383  1.0
  O  O21  1  0.134  0.457  0.617  1.0
  O  O22  1  0.624  0.154  0.617  1.0
  O  O23  1  0.866  0.543  0.383  1.0
  O  O24  1  0.934  0.080  0.368  1.0
  O  O25  1  0.573  0.701  0.620  1.0
[/CIF]
.