The compound described by K3Mg4(Si2O7)2 crystallizes in the monoclinic Pm space group. There are three inequivalent K sites. In the first K site, K(1) is bonded in a 9-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and three equivalent O(7) atoms. In the second K site, K(2) is bonded in a 9-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and three equivalent O(7) atoms. In the third K site, K(3) is bonded in a 9-coordinate geometry to two equivalent O(4), two equivalent O(5), two equivalent O(6), and three equivalent O(8) atoms. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form MgO6 octahedra that share corners with three equivalent Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, and edges with three equivalent Mg(2)O6 octahedra. In the second Mg site, Mg(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form MgO6 octahedra that share corners with three equivalent Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, and edges with three equivalent Mg(1)O6 octahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(7) atom to form SiO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with three equivalent Mg(2)O6 octahedra, and  a cornercorner with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-55°. In the second Si site, Si(2) is bonded to one O(4), one O(5), one O(6), and one O(8) atom to form SiO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with three equivalent Mg(2)O6 octahedra, and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-54°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Mg(1), one Mg(2), and one Si(1) atom. In the second O site, O(2) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Mg(1), one Mg(2), and one Si(1) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Mg(1), one Mg(2), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one K(3), one Mg(1), one Mg(2), and one Si(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one K(3), one Mg(1), one Mg(2), and one Si(2) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one K(3), one Mg(1), one Mg(2), and one Si(2) atom. In the seventh O site, O(7) is bonded in a linear geometry to three equivalent K(1), three equivalent K(2), and two equivalent Si(1) atoms. In the eighth O site, O(8) is bonded in a linear geometry to three equivalent K(3) and two equivalent Si(2) atoms. is represented by the CIF file [CIF]
data_K3Mg4(Si2O7)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.124
_cell_length_b   5.126
_cell_length_c   13.280
_cell_angle_alpha   89.995
_cell_angle_beta   90.009
_cell_angle_gamma   119.999
_symmetry_Int_Tables_number   1
_cell_volume   302.066
_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  0.331  0.656  0.750  1.0
  K  K1  1  0.669  0.325  0.750  1.0
  K  K2  1  0.680  0.339  0.250  1.0
  Mg  Mg3  1  0.335  0.666  0.493  1.0
  Mg  Mg4  1  0.667  0.333  0.501  1.0
  Mg  Mg5  1  0.667  0.333  0.999  1.0
  Mg  Mg6  1  0.335  0.666  0.007  1.0
  Si  Si7  1  1.000  0.996  0.621  1.0
  Si  Si8  1  0.004  0.001  0.376  1.0
  Si  Si9  1  0.004  0.001  0.124  1.0
  Si  Si10  1  1.000  0.996  0.879  1.0
  O  O11  1  0.311  0.996  0.909  1.0
  O  O12  1  0.688  0.685  0.909  1.0
  O  O13  1  0.000  0.307  0.909  1.0
  O  O14  1  0.699  0.006  0.088  1.0
  O  O15  1  0.313  0.305  0.088  1.0
  O  O16  1  0.997  0.691  0.088  1.0
  O  O17  1  0.699  0.006  0.412  1.0
  O  O18  1  0.313  0.305  0.412  1.0
  O  O19  1  0.997  0.691  0.412  1.0
  O  O20  1  0.311  0.996  0.591  1.0
  O  O21  1  0.688  0.685  0.591  1.0
  O  O22  1  0.000  0.307  0.590  1.0
  O  O23  1  0.001  0.997  0.750  1.0
  O  O24  1  0.001  0.001  0.250  1.0
[/CIF]
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The compound described by K3Mg4(Si2O7)2 crystallizes in the monoclinic Pm space group. There are three inequivalent K sites. In the first K site, K(1) is bonded in a 9-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and three equivalent O(7) atoms. In the second K site, K(2) is bonded in a 9-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and three equivalent O(7) atoms. In the third K site, K(3) is bonded in a 9-coordinate geometry to two equivalent O(4), two equivalent O(5), two equivalent O(6), and three equivalent O(8) atoms. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form MgO6 octahedra that share corners with three equivalent Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, and edges with three equivalent Mg(2)O6 octahedra. In the second Mg site, Mg(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form MgO6 octahedra that share corners with three equivalent Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, and edges with three equivalent Mg(1)O6 octahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(7) atom to form SiO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with three equivalent Mg(2)O6 octahedra, and  a cornercorner with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-55°. In the second Si site, Si(2) is bonded to one O(4), one O(5), one O(6), and one O(8) atom to form SiO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with three equivalent Mg(2)O6 octahedra, and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-54°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Mg(1), one Mg(2), and one Si(1) atom. In the second O site, O(2) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Mg(1), one Mg(2), and one Si(1) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Mg(1), one Mg(2), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one K(3), one Mg(1), one Mg(2), and one Si(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one K(3), one Mg(1), one Mg(2), and one Si(2) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one K(3), one Mg(1), one Mg(2), and one Si(2) atom. In the seventh O site, O(7) is bonded in a linear geometry to three equivalent K(1), three equivalent K(2), and two equivalent Si(1) atoms. In the eighth O site, O(8) is bonded in a linear geometry to three equivalent K(3) and two equivalent Si(2) atoms. is represented by the CIF file [CIF]
data_K3Mg4(Si2O7)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.124
_cell_length_b   5.126
_cell_length_c   13.280
_cell_angle_alpha   89.995
_cell_angle_beta   90.009
_cell_angle_gamma   119.999
_symmetry_Int_Tables_number   1
_cell_volume   302.066
_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  0.331  0.656  0.750  1.0
  K  K1  1  0.669  0.325  0.750  1.0
  K  K2  1  0.680  0.339  0.250  1.0
  Mg  Mg3  1  0.335  0.666  0.493  1.0
  Mg  Mg4  1  0.667  0.333  0.501  1.0
  Mg  Mg5  1  0.667  0.333  0.999  1.0
  Mg  Mg6  1  0.335  0.666  0.007  1.0
  Si  Si7  1  1.000  0.996  0.621  1.0
  Si  Si8  1  0.004  0.001  0.376  1.0
  Si  Si9  1  0.004  0.001  0.124  1.0
  Si  Si10  1  1.000  0.996  0.879  1.0
  O  O11  1  0.311  0.996  0.909  1.0
  O  O12  1  0.688  0.685  0.909  1.0
  O  O13  1  0.000  0.307  0.909  1.0
  O  O14  1  0.699  0.006  0.088  1.0
  O  O15  1  0.313  0.305  0.088  1.0
  O  O16  1  0.997  0.691  0.088  1.0
  O  O17  1  0.699  0.006  0.412  1.0
  O  O18  1  0.313  0.305  0.412  1.0
  O  O19  1  0.997  0.691  0.412  1.0
  O  O20  1  0.311  0.996  0.591  1.0
  O  O21  1  0.688  0.685  0.591  1.0
  O  O22  1  0.000  0.307  0.590  1.0
  O  O23  1  0.001  0.997  0.750  1.0
  O  O24  1  0.001  0.001  0.250  1.0
[/CIF]
.