The compound described by MgFeAs2O7 crystallizes in the monoclinic P2_1/c space group. Mg(1) is bonded to one O(1), one O(5), one O(6), one O(7), and two equivalent O(3) atoms to form MgO6 octahedra that share corners with three equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with two equivalent Fe(1)O5 trigonal bipyramids. Fe(1) is bonded to one O(1), one O(2), one O(5), one O(6), and one O(7) atom to form FeO5 trigonal bipyramids that share corners with two equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra, and edges with two equivalent Mg(1)O6 octahedra. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(2), one O(3), one O(4), and one O(6) atom to form AsO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra,  a cornercorner with one As(2)O4 tetrahedra, and corners with two equivalent Fe(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 50-53°. In the second As site, As(2) is bonded to one O(1), one O(4), one O(5), and one O(7) atom to form AsO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra,  a cornercorner with one As(1)O4 tetrahedra, and corners with three equivalent Fe(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 34-51°. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a trigonal planar geometry to one Mg(1), one Fe(1), and one As(2) atom. In the second O site, O(6) is bonded in a distorted trigonal planar geometry to one Mg(1), one Fe(1), and one As(1) atom. In the third O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Fe(1), and one As(2) atom. In the fourth O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(1), one Fe(1), and one As(2) atom. In the fifth O site, O(2) is bonded in a bent 150 degrees geometry to one Fe(1) and one As(1) atom. In the sixth O site, O(3) is bonded in a trigonal planar geometry to two equivalent Mg(1) and one As(1) atom. In the seventh O site, O(4) is bonded in a bent 120 degrees geometry to one As(1) and one As(2) atom. is represented by the CIF file [CIF]
data_MgFeAs2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.694
_cell_length_b   7.381
_cell_length_c   9.727
_cell_angle_alpha   66.032
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   570.366
_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  0.076  0.726  0.893  1.0
  Mg  Mg1  1  0.576  0.274  0.607  1.0
  Mg  Mg2  1  0.924  0.274  0.107  1.0
  Mg  Mg3  1  0.424  0.726  0.393  1.0
  Fe  Fe4  1  0.944  0.185  0.683  1.0
  Fe  Fe5  1  0.444  0.815  0.817  1.0
  Fe  Fe6  1  0.056  0.815  0.317  1.0
  Fe  Fe7  1  0.556  0.185  0.183  1.0
  As  As8  1  0.773  0.565  0.752  1.0
  As  As9  1  0.273  0.435  0.748  1.0
  As  As10  1  0.227  0.435  0.248  1.0
  As  As11  1  0.727  0.565  0.252  1.0
  As  As12  1  0.724  0.980  0.960  1.0
  As  As13  1  0.224  0.020  0.540  1.0
  As  As14  1  0.276  0.020  0.040  1.0
  As  As15  1  0.776  0.980  0.460  1.0
  O  O16  1  0.732  0.138  0.050  1.0
  O  O17  1  0.232  0.862  0.450  1.0
  O  O18  1  0.268  0.862  0.950  1.0
  O  O19  1  0.768  0.138  0.550  1.0
  O  O20  1  0.600  0.646  0.778  1.0
  O  O21  1  0.100  0.354  0.722  1.0
  O  O22  1  0.400  0.354  0.222  1.0
  O  O23  1  0.900  0.646  0.278  1.0
  O  O24  1  0.904  0.531  0.892  1.0
  O  O25  1  0.404  0.469  0.608  1.0
  O  O26  1  0.096  0.469  0.108  1.0
  O  O27  1  0.596  0.531  0.392  1.0
  O  O28  1  0.856  0.749  0.585  1.0
  O  O29  1  0.356  0.251  0.915  1.0
  O  O30  1  0.144  0.251  0.415  1.0
  O  O31  1  0.644  0.749  0.085  1.0
  O  O32  1  0.916  0.037  0.326  1.0
  O  O33  1  0.416  0.963  0.174  1.0
  O  O34  1  0.084  0.963  0.674  1.0
  O  O35  1  0.584  0.037  0.826  1.0
  O  O36  1  0.740  0.367  0.205  1.0
  O  O37  1  0.240  0.633  0.295  1.0
  O  O38  1  0.260  0.633  0.795  1.0
  O  O39  1  0.760  0.367  0.705  1.0
  O  O40  1  0.601  0.946  0.396  1.0
  O  O41  1  0.101  0.054  0.104  1.0
  O  O42  1  0.399  0.054  0.604  1.0
  O  O43  1  0.899  0.946  0.896  1.0
[/CIF]
.
The compound described by MgFeAs2O7 crystallizes in the monoclinic P2_1/c space group. Mg(1) is bonded to one O(1), one O(5), one O(6), one O(7), and two equivalent O(3) atoms to form MgO6 octahedra that share corners with three equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with two equivalent Fe(1)O5 trigonal bipyramids. Fe(1) is bonded to one O(1), one O(2), one O(5), one O(6), and one O(7) atom to form FeO5 trigonal bipyramids that share corners with two equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra, and edges with two equivalent Mg(1)O6 octahedra. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(2), one O(3), one O(4), and one O(6) atom to form AsO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra,  a cornercorner with one As(2)O4 tetrahedra, and corners with two equivalent Fe(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 50-53°. In the second As site, As(2) is bonded to one O(1), one O(4), one O(5), and one O(7) atom to form AsO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra,  a cornercorner with one As(1)O4 tetrahedra, and corners with three equivalent Fe(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 34-51°. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a trigonal planar geometry to one Mg(1), one Fe(1), and one As(2) atom. In the second O site, O(6) is bonded in a distorted trigonal planar geometry to one Mg(1), one Fe(1), and one As(1) atom. In the third O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Fe(1), and one As(2) atom. In the fourth O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(1), one Fe(1), and one As(2) atom. In the fifth O site, O(2) is bonded in a bent 150 degrees geometry to one Fe(1) and one As(1) atom. In the sixth O site, O(3) is bonded in a trigonal planar geometry to two equivalent Mg(1) and one As(1) atom. In the seventh O site, O(4) is bonded in a bent 120 degrees geometry to one As(1) and one As(2) atom. is represented by the CIF file [CIF]
data_MgFeAs2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.694
_cell_length_b   7.381
_cell_length_c   9.727
_cell_angle_alpha   66.032
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   570.366
_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  0.076  0.726  0.893  1.0
  Mg  Mg1  1  0.576  0.274  0.607  1.0
  Mg  Mg2  1  0.924  0.274  0.107  1.0
  Mg  Mg3  1  0.424  0.726  0.393  1.0
  Fe  Fe4  1  0.944  0.185  0.683  1.0
  Fe  Fe5  1  0.444  0.815  0.817  1.0
  Fe  Fe6  1  0.056  0.815  0.317  1.0
  Fe  Fe7  1  0.556  0.185  0.183  1.0
  As  As8  1  0.773  0.565  0.752  1.0
  As  As9  1  0.273  0.435  0.748  1.0
  As  As10  1  0.227  0.435  0.248  1.0
  As  As11  1  0.727  0.565  0.252  1.0
  As  As12  1  0.724  0.980  0.960  1.0
  As  As13  1  0.224  0.020  0.540  1.0
  As  As14  1  0.276  0.020  0.040  1.0
  As  As15  1  0.776  0.980  0.460  1.0
  O  O16  1  0.732  0.138  0.050  1.0
  O  O17  1  0.232  0.862  0.450  1.0
  O  O18  1  0.268  0.862  0.950  1.0
  O  O19  1  0.768  0.138  0.550  1.0
  O  O20  1  0.600  0.646  0.778  1.0
  O  O21  1  0.100  0.354  0.722  1.0
  O  O22  1  0.400  0.354  0.222  1.0
  O  O23  1  0.900  0.646  0.278  1.0
  O  O24  1  0.904  0.531  0.892  1.0
  O  O25  1  0.404  0.469  0.608  1.0
  O  O26  1  0.096  0.469  0.108  1.0
  O  O27  1  0.596  0.531  0.392  1.0
  O  O28  1  0.856  0.749  0.585  1.0
  O  O29  1  0.356  0.251  0.915  1.0
  O  O30  1  0.144  0.251  0.415  1.0
  O  O31  1  0.644  0.749  0.085  1.0
  O  O32  1  0.916  0.037  0.326  1.0
  O  O33  1  0.416  0.963  0.174  1.0
  O  O34  1  0.084  0.963  0.674  1.0
  O  O35  1  0.584  0.037  0.826  1.0
  O  O36  1  0.740  0.367  0.205  1.0
  O  O37  1  0.240  0.633  0.295  1.0
  O  O38  1  0.260  0.633  0.795  1.0
  O  O39  1  0.760  0.367  0.705  1.0
  O  O40  1  0.601  0.946  0.396  1.0
  O  O41  1  0.101  0.054  0.104  1.0
  O  O42  1  0.399  0.054  0.604  1.0
  O  O43  1  0.899  0.946  0.896  1.0
[/CIF]
.