The compound described by Mg2PO8 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(3), one O(4), one O(6), one O(7), and two equivalent O(5) atoms to form distorted MgO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with two 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(5), one O(6), and one O(8) atom to form distorted MgO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and edges with two equivalent Mg(1)O6 octahedra. P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with two equivalent Mg(1)O6 octahedra and corners with three equivalent Mg(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-61°. There are eight inequivalent O sites. In the first O site, O(6) is bonded in a bent 120 degrees geometry to one Mg(1) and one Mg(2) atom. In the second O site, O(7) is bonded in a single-bond geometry to one Mg(1) atom. In the third O site, O(8) is bonded in a single-bond geometry to one Mg(2) atom. In the fourth O site, O(1) is bonded in a bent 120 degrees geometry to one Mg(2) and one P(1) atom. In the fifth O site, O(2) is bonded in a bent 120 degrees geometry to one Mg(2) and one P(1) atom. In the sixth O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mg(2), and one P(1) atom. In the seventh O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Mg(1) and one P(1) atom. In the eighth O site, O(5) is bonded in a trigonal non-coplanar geometry to one Mg(2) and two equivalent Mg(1) atoms. is represented by the CIF card [CIF]
data_Mg2PO8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.644
_cell_length_b   10.084
_cell_length_c   12.068
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   100.850
_symmetry_Int_Tables_number   1
_cell_volume   555.088
_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
  Mg  Mg0  1  0.095  0.683  0.010  1.0
  Mg  Mg1  1  0.905  0.817  0.510  1.0
  Mg  Mg2  1  0.905  0.317  0.990  1.0
  Mg  Mg3  1  0.095  0.183  0.490  1.0
  Mg  Mg4  1  0.978  0.517  0.234  1.0
  Mg  Mg5  1  0.022  0.983  0.734  1.0
  Mg  Mg6  1  0.022  0.483  0.766  1.0
  Mg  Mg7  1  0.978  0.017  0.266  1.0
  P  P8  1  0.599  0.745  0.186  1.0
  P  P9  1  0.401  0.755  0.686  1.0
  P  P10  1  0.401  0.255  0.814  1.0
  P  P11  1  0.599  0.245  0.314  1.0
  O  O12  1  0.588  0.890  0.229  1.0
  O  O13  1  0.412  0.610  0.729  1.0
  O  O14  1  0.412  0.110  0.771  1.0
  O  O15  1  0.588  0.390  0.271  1.0
  O  O16  1  0.759  0.671  0.272  1.0
  O  O17  1  0.241  0.829  0.772  1.0
  O  O18  1  0.241  0.329  0.728  1.0
  O  O19  1  0.759  0.171  0.228  1.0
  O  O20  1  0.292  0.662  0.163  1.0
  O  O21  1  0.708  0.838  0.663  1.0
  O  O22  1  0.708  0.338  0.837  1.0
  O  O23  1  0.292  0.162  0.337  1.0
  O  O24  1  0.772  0.764  0.075  1.0
  O  O25  1  0.228  0.736  0.575  1.0
  O  O26  1  0.228  0.236  0.925  1.0
  O  O27  1  0.772  0.264  0.425  1.0
  O  O28  1  0.827  0.489  0.064  1.0
  O  O29  1  0.173  0.011  0.564  1.0
  O  O30  1  0.173  0.511  0.936  1.0
  O  O31  1  0.827  0.989  0.436  1.0
  O  O32  1  0.918  0.648  0.851  1.0
  O  O33  1  0.082  0.852  0.351  1.0
  O  O34  1  0.082  0.352  0.149  1.0
  O  O35  1  0.918  0.148  0.649  1.0
  O  O36  1  0.432  0.859  0.974  1.0
  O  O37  1  0.568  0.641  0.474  1.0
  O  O38  1  0.568  0.141  0.026  1.0
  O  O39  1  0.432  0.359  0.526  1.0
  O  O40  1  0.264  0.468  0.387  1.0
  O  O41  1  0.736  0.032  0.887  1.0
  O  O42  1  0.736  0.532  0.613  1.0
  O  O43  1  0.264  0.968  0.113  1.0
[/CIF]
.
The compound described by Mg2PO8 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(3), one O(4), one O(6), one O(7), and two equivalent O(5) atoms to form distorted MgO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with two 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(5), one O(6), and one O(8) atom to form distorted MgO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and edges with two equivalent Mg(1)O6 octahedra. P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with two equivalent Mg(1)O6 octahedra and corners with three equivalent Mg(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-61°. There are eight inequivalent O sites. In the first O site, O(6) is bonded in a bent 120 degrees geometry to one Mg(1) and one Mg(2) atom. In the second O site, O(7) is bonded in a single-bond geometry to one Mg(1) atom. In the third O site, O(8) is bonded in a single-bond geometry to one Mg(2) atom. In the fourth O site, O(1) is bonded in a bent 120 degrees geometry to one Mg(2) and one P(1) atom. In the fifth O site, O(2) is bonded in a bent 120 degrees geometry to one Mg(2) and one P(1) atom. In the sixth O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mg(2), and one P(1) atom. In the seventh O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Mg(1) and one P(1) atom. In the eighth O site, O(5) is bonded in a trigonal non-coplanar geometry to one Mg(2) and two equivalent Mg(1) atoms. is represented by the CIF card [CIF]
data_Mg2PO8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.644
_cell_length_b   10.084
_cell_length_c   12.068
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   100.850
_symmetry_Int_Tables_number   1
_cell_volume   555.088
_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
  Mg  Mg0  1  0.095  0.683  0.010  1.0
  Mg  Mg1  1  0.905  0.817  0.510  1.0
  Mg  Mg2  1  0.905  0.317  0.990  1.0
  Mg  Mg3  1  0.095  0.183  0.490  1.0
  Mg  Mg4  1  0.978  0.517  0.234  1.0
  Mg  Mg5  1  0.022  0.983  0.734  1.0
  Mg  Mg6  1  0.022  0.483  0.766  1.0
  Mg  Mg7  1  0.978  0.017  0.266  1.0
  P  P8  1  0.599  0.745  0.186  1.0
  P  P9  1  0.401  0.755  0.686  1.0
  P  P10  1  0.401  0.255  0.814  1.0
  P  P11  1  0.599  0.245  0.314  1.0
  O  O12  1  0.588  0.890  0.229  1.0
  O  O13  1  0.412  0.610  0.729  1.0
  O  O14  1  0.412  0.110  0.771  1.0
  O  O15  1  0.588  0.390  0.271  1.0
  O  O16  1  0.759  0.671  0.272  1.0
  O  O17  1  0.241  0.829  0.772  1.0
  O  O18  1  0.241  0.329  0.728  1.0
  O  O19  1  0.759  0.171  0.228  1.0
  O  O20  1  0.292  0.662  0.163  1.0
  O  O21  1  0.708  0.838  0.663  1.0
  O  O22  1  0.708  0.338  0.837  1.0
  O  O23  1  0.292  0.162  0.337  1.0
  O  O24  1  0.772  0.764  0.075  1.0
  O  O25  1  0.228  0.736  0.575  1.0
  O  O26  1  0.228  0.236  0.925  1.0
  O  O27  1  0.772  0.264  0.425  1.0
  O  O28  1  0.827  0.489  0.064  1.0
  O  O29  1  0.173  0.011  0.564  1.0
  O  O30  1  0.173  0.511  0.936  1.0
  O  O31  1  0.827  0.989  0.436  1.0
  O  O32  1  0.918  0.648  0.851  1.0
  O  O33  1  0.082  0.852  0.351  1.0
  O  O34  1  0.082  0.352  0.149  1.0
  O  O35  1  0.918  0.148  0.649  1.0
  O  O36  1  0.432  0.859  0.974  1.0
  O  O37  1  0.568  0.641  0.474  1.0
  O  O38  1  0.568  0.141  0.026  1.0
  O  O39  1  0.432  0.359  0.526  1.0
  O  O40  1  0.264  0.468  0.387  1.0
  O  O41  1  0.736  0.032  0.887  1.0
  O  O42  1  0.736  0.532  0.613  1.0
  O  O43  1  0.264  0.968  0.113  1.0
[/CIF]
.