The crystal structure described by BaMg2Si2O7 crystallizes in the monoclinic C2/c space group. Ba(1) is bonded in a 9-coordinate geometry to one O(1), one O(3), one O(4), one O(5), one O(6), two equivalent O(2), and two equivalent O(7) atoms. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(4) and two equivalent O(6) atoms to form MgO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and corners with two equivalent Mg(3)O5 trigonal bipyramids. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(6) atoms. In the third Mg site, Mg(3) is bonded to one O(1), one O(4), one O(7), and two equivalent O(3) atoms to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra,  an edgeedge with one Si(2)O4 tetrahedra, and  an edgeedge with one Mg(3)O5 trigonal bipyramid. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Mg(3)O5 trigonal bipyramids. In the second Si site, Si(2) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Mg(3)O5 trigonal bipyramid, and  an edgeedge with one Mg(3)O5 trigonal bipyramid. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Mg(3), and one Si(1) atom. In the second O site, O(1) is bonded in a distorted trigonal planar geometry to one Ba(1), one Mg(2), one Mg(3), and one Si(1) atom. In the third O site, O(2) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Mg(2), and one Si(2) atom. In the fourth O site, O(6) is bonded in a 4-coordinate geometry to one Ba(1), one Mg(1), one Mg(2), and one Si(1) atom. In the fifth O site, O(3) is bonded in a 4-coordinate geometry to one Ba(1), two equivalent Mg(3), and one Si(2) atom. In the sixth O site, O(4) is bonded in a 3-coordinate geometry to one Ba(1), one Mg(1), one Mg(3), and one Si(2) atom. In the seventh O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Si(1), and one Si(2) atom. is represented by the CIF card [CIF]
data_BaMg2Si2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.306
_cell_length_b   7.306
_cell_length_c   13.797
_cell_angle_alpha   89.908
_cell_angle_beta   89.908
_cell_angle_gamma   120.626
_symmetry_Int_Tables_number   1
_cell_volume   633.775
_cell_formula_units_Z   4
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
  Ba  Ba0  1  0.820  0.783  0.120  1.0
  Ba  Ba1  1  0.217  0.180  0.380  1.0
  Ba  Ba2  1  0.180  0.217  0.880  1.0
  Ba  Ba3  1  0.783  0.820  0.620  1.0
  Mg  Mg4  1  0.769  0.231  0.250  1.0
  Mg  Mg5  1  0.231  0.769  0.750  1.0
  Mg  Mg6  1  0.230  0.770  0.250  1.0
  Mg  Mg7  1  0.770  0.230  0.750  1.0
  Mg  Mg8  1  0.195  0.726  0.509  1.0
  Mg  Mg9  1  0.274  0.805  0.991  1.0
  Mg  Mg10  1  0.805  0.274  0.491  1.0
  Mg  Mg11  1  0.726  0.195  0.009  1.0
  Si  Si12  1  0.587  0.841  0.367  1.0
  Si  Si13  1  0.159  0.413  0.133  1.0
  Si  Si14  1  0.413  0.159  0.633  1.0
  Si  Si15  1  0.841  0.587  0.867  1.0
  Si  Si16  1  0.780  0.571  0.379  1.0
  Si  Si17  1  0.429  0.220  0.121  1.0
  Si  Si18  1  0.220  0.429  0.621  1.0
  Si  Si19  1  0.571  0.780  0.879  1.0
  O  O20  1  0.350  0.802  0.386  1.0
  O  O21  1  0.198  0.650  0.114  1.0
  O  O22  1  0.650  0.198  0.614  1.0
  O  O23  1  0.802  0.350  0.886  1.0
  O  O24  1  0.946  0.714  0.296  1.0
  O  O25  1  0.286  0.054  0.204  1.0
  O  O26  1  0.054  0.286  0.704  1.0
  O  O27  1  0.714  0.946  0.796  1.0
  O  O28  1  0.887  0.608  0.486  1.0
  O  O29  1  0.392  0.113  0.014  1.0
  O  O30  1  0.113  0.392  0.514  1.0
  O  O31  1  0.608  0.887  0.986  1.0
  O  O32  1  0.674  0.315  0.365  1.0
  O  O33  1  0.685  0.326  0.135  1.0
  O  O34  1  0.326  0.685  0.635  1.0
  O  O35  1  0.315  0.674  0.865  1.0
  O  O36  1  0.574  0.608  0.380  1.0
  O  O37  1  0.392  0.426  0.120  1.0
  O  O38  1  0.426  0.392  0.620  1.0
  O  O39  1  0.608  0.574  0.880  1.0
  O  O40  1  0.636  0.920  0.254  1.0
  O  O41  1  0.080  0.364  0.246  1.0
  O  O42  1  0.364  0.080  0.746  1.0
  O  O43  1  0.920  0.636  0.754  1.0
  O  O44  1  0.769  0.001  0.441  1.0
  O  O45  1  0.999  0.231  0.059  1.0
  O  O46  1  0.231  0.999  0.559  1.0
  O  O47  1  0.001  0.769  0.941  1.0
[/CIF]
.
The crystal structure described by BaMg2Si2O7 crystallizes in the monoclinic C2/c space group. Ba(1) is bonded in a 9-coordinate geometry to one O(1), one O(3), one O(4), one O(5), one O(6), two equivalent O(2), and two equivalent O(7) atoms. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(4) and two equivalent O(6) atoms to form MgO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and corners with two equivalent Mg(3)O5 trigonal bipyramids. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(6) atoms. In the third Mg site, Mg(3) is bonded to one O(1), one O(4), one O(7), and two equivalent O(3) atoms to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra,  an edgeedge with one Si(2)O4 tetrahedra, and  an edgeedge with one Mg(3)O5 trigonal bipyramid. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Mg(3)O5 trigonal bipyramids. In the second Si site, Si(2) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Mg(3)O5 trigonal bipyramid, and  an edgeedge with one Mg(3)O5 trigonal bipyramid. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Mg(3), and one Si(1) atom. In the second O site, O(1) is bonded in a distorted trigonal planar geometry to one Ba(1), one Mg(2), one Mg(3), and one Si(1) atom. In the third O site, O(2) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Mg(2), and one Si(2) atom. In the fourth O site, O(6) is bonded in a 4-coordinate geometry to one Ba(1), one Mg(1), one Mg(2), and one Si(1) atom. In the fifth O site, O(3) is bonded in a 4-coordinate geometry to one Ba(1), two equivalent Mg(3), and one Si(2) atom. In the sixth O site, O(4) is bonded in a 3-coordinate geometry to one Ba(1), one Mg(1), one Mg(3), and one Si(2) atom. In the seventh O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Si(1), and one Si(2) atom. is represented by the CIF card [CIF]
data_BaMg2Si2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.306
_cell_length_b   7.306
_cell_length_c   13.797
_cell_angle_alpha   89.908
_cell_angle_beta   89.908
_cell_angle_gamma   120.626
_symmetry_Int_Tables_number   1
_cell_volume   633.775
_cell_formula_units_Z   4
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
  Ba  Ba0  1  0.820  0.783  0.120  1.0
  Ba  Ba1  1  0.217  0.180  0.380  1.0
  Ba  Ba2  1  0.180  0.217  0.880  1.0
  Ba  Ba3  1  0.783  0.820  0.620  1.0
  Mg  Mg4  1  0.769  0.231  0.250  1.0
  Mg  Mg5  1  0.231  0.769  0.750  1.0
  Mg  Mg6  1  0.230  0.770  0.250  1.0
  Mg  Mg7  1  0.770  0.230  0.750  1.0
  Mg  Mg8  1  0.195  0.726  0.509  1.0
  Mg  Mg9  1  0.274  0.805  0.991  1.0
  Mg  Mg10  1  0.805  0.274  0.491  1.0
  Mg  Mg11  1  0.726  0.195  0.009  1.0
  Si  Si12  1  0.587  0.841  0.367  1.0
  Si  Si13  1  0.159  0.413  0.133  1.0
  Si  Si14  1  0.413  0.159  0.633  1.0
  Si  Si15  1  0.841  0.587  0.867  1.0
  Si  Si16  1  0.780  0.571  0.379  1.0
  Si  Si17  1  0.429  0.220  0.121  1.0
  Si  Si18  1  0.220  0.429  0.621  1.0
  Si  Si19  1  0.571  0.780  0.879  1.0
  O  O20  1  0.350  0.802  0.386  1.0
  O  O21  1  0.198  0.650  0.114  1.0
  O  O22  1  0.650  0.198  0.614  1.0
  O  O23  1  0.802  0.350  0.886  1.0
  O  O24  1  0.946  0.714  0.296  1.0
  O  O25  1  0.286  0.054  0.204  1.0
  O  O26  1  0.054  0.286  0.704  1.0
  O  O27  1  0.714  0.946  0.796  1.0
  O  O28  1  0.887  0.608  0.486  1.0
  O  O29  1  0.392  0.113  0.014  1.0
  O  O30  1  0.113  0.392  0.514  1.0
  O  O31  1  0.608  0.887  0.986  1.0
  O  O32  1  0.674  0.315  0.365  1.0
  O  O33  1  0.685  0.326  0.135  1.0
  O  O34  1  0.326  0.685  0.635  1.0
  O  O35  1  0.315  0.674  0.865  1.0
  O  O36  1  0.574  0.608  0.380  1.0
  O  O37  1  0.392  0.426  0.120  1.0
  O  O38  1  0.426  0.392  0.620  1.0
  O  O39  1  0.608  0.574  0.880  1.0
  O  O40  1  0.636  0.920  0.254  1.0
  O  O41  1  0.080  0.364  0.246  1.0
  O  O42  1  0.364  0.080  0.746  1.0
  O  O43  1  0.920  0.636  0.754  1.0
  O  O44  1  0.769  0.001  0.441  1.0
  O  O45  1  0.999  0.231  0.059  1.0
  O  O46  1  0.231  0.999  0.559  1.0
  O  O47  1  0.001  0.769  0.941  1.0
[/CIF]
.