The material described by K4MgNb4(Si2O7)4 crystallizes in the monoclinic Cm space group. There are three inequivalent K sites. In the first K site, K(1) is bonded in a 11-coordinate geometry to one O(1), one O(10), one O(13), one O(16), one O(17), one O(2), one O(3), one O(4), one O(5), one O(7), and one O(9) atom. In the second K site, K(2) is bonded in a 7-coordinate geometry to one Mg(1), one O(11), one O(14), two equivalent O(1), and two equivalent O(7) atoms. In the third K site, K(3) is bonded in a 12-coordinate geometry to one O(11), one O(14), two equivalent O(16), two equivalent O(17), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. Mg(1) is bonded in a 4-coordinate geometry to one K(2), two equivalent O(13), and two equivalent O(2) atoms. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(13), one O(15), one O(16), one O(17), and one O(3) atom to form NbO6 octahedra that share corners with two equivalent Nb(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(5)O4 tetrahedra, and corners with two equivalent Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 4-6°. In the second Nb site, Nb(2) is bonded to one O(15), one O(16), one O(2), one O(4), one O(5), and one O(7) atom to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(6)O4 tetrahedra, and corners with two equivalent Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 4-6°. There are six inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(8), one O(9), and two equivalent O(3) atoms to form SiO4 tetrahedra that share corners with two equivalent Nb(1)O6 octahedra,  a cornercorner with one Si(5)O4 tetrahedra, and  a cornercorner with one Si(6)O4 tetrahedra. The corner-sharing octahedral tilt angles are 22°. In the second Si site, Si(2) is bonded to one O(10), one O(12), and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with two equivalent Nb(2)O6 octahedra,  a cornercorner with one Si(5)O4 tetrahedra, and  a cornercorner with one Si(6)O4 tetrahedra. The corner-sharing octahedral tilt angles are 39°. In the third Si site, Si(3) is bonded to one O(14), one O(4), one O(6), and one O(7) atom to form SiO4 tetrahedra that share corners with two equivalent Nb(2)O6 octahedra,  a cornercorner with one Si(3)O4 tetrahedra, and  a cornercorner with one Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 23-26°. In the fourth Si site, Si(4) is bonded to one O(1), one O(11), one O(17), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Nb(1)O6 octahedra,  a cornercorner with one Si(3)O4 tetrahedra, and  a cornercorner with one Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 24-28°. In the fifth Si site, Si(5) is bonded to one O(12), one O(9), and two equivalent O(13) atoms to form SiO4 tetrahedra that share corners with two equivalent Nb(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 39°. In the sixth Si site, Si(6) is bonded to one O(10), one O(8), and two equivalent O(5) atoms to form SiO4 tetrahedra that share corners with two equivalent Nb(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 21°. There are seventeen inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Nb(1), and one Si(4) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one K(1), one Mg(1), one Nb(2), and one Si(2) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to one K(1), one K(3), one Nb(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one K(1), one K(3), one Nb(2), and one Si(3) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one K(1), one K(3), one Nb(2), and one Si(6) atom. In the sixth O site, O(6) is bonded in a linear geometry to one Si(3) and one Si(4) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Nb(2), and one Si(3) atom. In the eighth O site, O(8) is bonded in a linear geometry to one Si(1) and one Si(6) atom. In the ninth O site, O(9) is bonded in a distorted bent 150 degrees geometry to two equivalent K(1), one Si(1), and one Si(5) atom. In the tenth O site, O(10) is bonded in a distorted bent 150 degrees geometry to two equivalent K(1), one Si(2), and one Si(6) atom. In the eleventh O site, O(11) is bonded in a 4-coordinate geometry to one K(2), one K(3), and two equivalent Si(4) atoms. In the twelfth O site, O(12) is bonded in a linear geometry to one Si(2) and one Si(5) atom. In the thirteenth O site, O(13) is bonded in a 3-coordinate geometry to one K(1), one Mg(1), one Nb(1), and one Si(5) atom. In the fourteenth O site, O(14) is bonded in a 4-coordinate geometry to one K(2), one K(3), and two equivalent Si(3) atoms. In the fifteenth O site, O(15) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the sixteenth O site, O(16) is bonded in a distorted linear geometry to one K(1), one K(3), one Nb(1), and one Nb(2) atom. In the seventeenth O site, O(17) is bonded in a distorted bent 150 degrees geometry to one K(1), one K(3), one Nb(1), and one Si(4) atom. is represented by the CIF card [CIF]
data_K4MgNb4(Si2O7)4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.047
_cell_length_b   8.989
_cell_length_c   8.989
_cell_angle_alpha   90.406
_cell_angle_beta   89.977
_cell_angle_gamma   90.023
_symmetry_Int_Tables_number   1
_cell_volume   650.245
_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
  K  K0  1  0.995  0.669  0.217  1.0
  K  K1  1  0.997  0.872  0.628  1.0
  K  K2  1  0.995  0.283  0.831  1.0
  K  K3  1  0.995  0.184  0.316  1.0
  Mg  Mg4  1  0.993  0.662  0.838  1.0
  Nb  Nb5  1  0.745  0.499  0.502  1.0
  Nb  Nb6  1  0.242  0.499  0.503  1.0
  Nb  Nb7  1  0.745  0.998  0.001  1.0
  Nb  Nb8  1  0.242  0.997  0.001  1.0
  Si  Si9  1  0.692  0.374  0.126  1.0
  Si  Si10  1  0.295  0.616  0.884  1.0
  Si  Si11  1  0.298  0.879  0.375  1.0
  Si  Si12  1  0.298  0.125  0.621  1.0
  Si  Si13  1  0.695  0.125  0.621  1.0
  Si  Si14  1  0.695  0.879  0.375  1.0
  Si  Si15  1  0.691  0.616  0.884  1.0
  Si  Si16  1  0.298  0.373  0.127  1.0
  O  O17  1  0.762  0.721  0.437  1.0
  O  O18  1  0.197  0.769  0.927  1.0
  O  O19  1  0.757  0.211  0.077  1.0
  O  O20  1  0.757  0.423  0.289  1.0
  O  O21  1  0.226  0.290  0.587  1.0
  O  O22  1  0.762  0.063  0.779  1.0
  O  O23  1  0.233  0.422  0.290  1.0
  O  O24  1  0.496  0.121  0.612  1.0
  O  O25  1  0.230  0.062  0.779  1.0
  O  O26  1  0.495  0.392  0.108  1.0
  O  O27  1  0.769  0.496  0.004  1.0
  O  O28  1  0.220  0.495  0.005  1.0
  O  O29  1  0.496  0.888  0.379  1.0
  O  O30  1  0.768  0.012  0.488  1.0
  O  O31  1  0.493  0.624  0.876  1.0
  O  O32  1  0.790  0.770  0.926  1.0
  O  O33  1  0.233  0.210  0.078  1.0
  O  O34  1  0.230  0.721  0.438  1.0
  O  O35  1  0.226  0.913  0.210  1.0
  O  O36  1  0.225  0.013  0.487  1.0
  O  O37  1  0.496  0.503  0.513  1.0
  O  O38  1  0.996  0.503  0.495  1.0
  O  O39  1  0.197  0.573  0.731  1.0
  O  O40  1  0.767  0.914  0.210  1.0
  O  O41  1  0.496  0.987  0.997  1.0
  O  O42  1  0.790  0.574  0.730  1.0
  O  O43  1  0.996  0.005  0.997  1.0
  O  O44  1  0.767  0.290  0.586  1.0
[/CIF]
.
The material described by K4MgNb4(Si2O7)4 crystallizes in the monoclinic Cm space group. There are three inequivalent K sites. In the first K site, K(1) is bonded in a 11-coordinate geometry to one O(1), one O(10), one O(13), one O(16), one O(17), one O(2), one O(3), one O(4), one O(5), one O(7), and one O(9) atom. In the second K site, K(2) is bonded in a 7-coordinate geometry to one Mg(1), one O(11), one O(14), two equivalent O(1), and two equivalent O(7) atoms. In the third K site, K(3) is bonded in a 12-coordinate geometry to one O(11), one O(14), two equivalent O(16), two equivalent O(17), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. Mg(1) is bonded in a 4-coordinate geometry to one K(2), two equivalent O(13), and two equivalent O(2) atoms. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(13), one O(15), one O(16), one O(17), and one O(3) atom to form NbO6 octahedra that share corners with two equivalent Nb(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(5)O4 tetrahedra, and corners with two equivalent Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 4-6°. In the second Nb site, Nb(2) is bonded to one O(15), one O(16), one O(2), one O(4), one O(5), and one O(7) atom to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(6)O4 tetrahedra, and corners with two equivalent Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 4-6°. There are six inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(8), one O(9), and two equivalent O(3) atoms to form SiO4 tetrahedra that share corners with two equivalent Nb(1)O6 octahedra,  a cornercorner with one Si(5)O4 tetrahedra, and  a cornercorner with one Si(6)O4 tetrahedra. The corner-sharing octahedral tilt angles are 22°. In the second Si site, Si(2) is bonded to one O(10), one O(12), and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with two equivalent Nb(2)O6 octahedra,  a cornercorner with one Si(5)O4 tetrahedra, and  a cornercorner with one Si(6)O4 tetrahedra. The corner-sharing octahedral tilt angles are 39°. In the third Si site, Si(3) is bonded to one O(14), one O(4), one O(6), and one O(7) atom to form SiO4 tetrahedra that share corners with two equivalent Nb(2)O6 octahedra,  a cornercorner with one Si(3)O4 tetrahedra, and  a cornercorner with one Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 23-26°. In the fourth Si site, Si(4) is bonded to one O(1), one O(11), one O(17), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Nb(1)O6 octahedra,  a cornercorner with one Si(3)O4 tetrahedra, and  a cornercorner with one Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 24-28°. In the fifth Si site, Si(5) is bonded to one O(12), one O(9), and two equivalent O(13) atoms to form SiO4 tetrahedra that share corners with two equivalent Nb(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 39°. In the sixth Si site, Si(6) is bonded to one O(10), one O(8), and two equivalent O(5) atoms to form SiO4 tetrahedra that share corners with two equivalent Nb(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 21°. There are seventeen inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Nb(1), and one Si(4) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one K(1), one Mg(1), one Nb(2), and one Si(2) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to one K(1), one K(3), one Nb(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one K(1), one K(3), one Nb(2), and one Si(3) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one K(1), one K(3), one Nb(2), and one Si(6) atom. In the sixth O site, O(6) is bonded in a linear geometry to one Si(3) and one Si(4) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Nb(2), and one Si(3) atom. In the eighth O site, O(8) is bonded in a linear geometry to one Si(1) and one Si(6) atom. In the ninth O site, O(9) is bonded in a distorted bent 150 degrees geometry to two equivalent K(1), one Si(1), and one Si(5) atom. In the tenth O site, O(10) is bonded in a distorted bent 150 degrees geometry to two equivalent K(1), one Si(2), and one Si(6) atom. In the eleventh O site, O(11) is bonded in a 4-coordinate geometry to one K(2), one K(3), and two equivalent Si(4) atoms. In the twelfth O site, O(12) is bonded in a linear geometry to one Si(2) and one Si(5) atom. In the thirteenth O site, O(13) is bonded in a 3-coordinate geometry to one K(1), one Mg(1), one Nb(1), and one Si(5) atom. In the fourteenth O site, O(14) is bonded in a 4-coordinate geometry to one K(2), one K(3), and two equivalent Si(3) atoms. In the fifteenth O site, O(15) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the sixteenth O site, O(16) is bonded in a distorted linear geometry to one K(1), one K(3), one Nb(1), and one Nb(2) atom. In the seventeenth O site, O(17) is bonded in a distorted bent 150 degrees geometry to one K(1), one K(3), one Nb(1), and one Si(4) atom. is represented by the CIF card [CIF]
data_K4MgNb4(Si2O7)4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.047
_cell_length_b   8.989
_cell_length_c   8.989
_cell_angle_alpha   90.406
_cell_angle_beta   89.977
_cell_angle_gamma   90.023
_symmetry_Int_Tables_number   1
_cell_volume   650.245
_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
  K  K0  1  0.995  0.669  0.217  1.0
  K  K1  1  0.997  0.872  0.628  1.0
  K  K2  1  0.995  0.283  0.831  1.0
  K  K3  1  0.995  0.184  0.316  1.0
  Mg  Mg4  1  0.993  0.662  0.838  1.0
  Nb  Nb5  1  0.745  0.499  0.502  1.0
  Nb  Nb6  1  0.242  0.499  0.503  1.0
  Nb  Nb7  1  0.745  0.998  0.001  1.0
  Nb  Nb8  1  0.242  0.997  0.001  1.0
  Si  Si9  1  0.692  0.374  0.126  1.0
  Si  Si10  1  0.295  0.616  0.884  1.0
  Si  Si11  1  0.298  0.879  0.375  1.0
  Si  Si12  1  0.298  0.125  0.621  1.0
  Si  Si13  1  0.695  0.125  0.621  1.0
  Si  Si14  1  0.695  0.879  0.375  1.0
  Si  Si15  1  0.691  0.616  0.884  1.0
  Si  Si16  1  0.298  0.373  0.127  1.0
  O  O17  1  0.762  0.721  0.437  1.0
  O  O18  1  0.197  0.769  0.927  1.0
  O  O19  1  0.757  0.211  0.077  1.0
  O  O20  1  0.757  0.423  0.289  1.0
  O  O21  1  0.226  0.290  0.587  1.0
  O  O22  1  0.762  0.063  0.779  1.0
  O  O23  1  0.233  0.422  0.290  1.0
  O  O24  1  0.496  0.121  0.612  1.0
  O  O25  1  0.230  0.062  0.779  1.0
  O  O26  1  0.495  0.392  0.108  1.0
  O  O27  1  0.769  0.496  0.004  1.0
  O  O28  1  0.220  0.495  0.005  1.0
  O  O29  1  0.496  0.888  0.379  1.0
  O  O30  1  0.768  0.012  0.488  1.0
  O  O31  1  0.493  0.624  0.876  1.0
  O  O32  1  0.790  0.770  0.926  1.0
  O  O33  1  0.233  0.210  0.078  1.0
  O  O34  1  0.230  0.721  0.438  1.0
  O  O35  1  0.226  0.913  0.210  1.0
  O  O36  1  0.225  0.013  0.487  1.0
  O  O37  1  0.496  0.503  0.513  1.0
  O  O38  1  0.996  0.503  0.495  1.0
  O  O39  1  0.197  0.573  0.731  1.0
  O  O40  1  0.767  0.914  0.210  1.0
  O  O41  1  0.496  0.987  0.997  1.0
  O  O42  1  0.790  0.574  0.730  1.0
  O  O43  1  0.996  0.005  0.997  1.0
  O  O44  1  0.767  0.290  0.586  1.0
[/CIF]
.