The compound described by Mn2As2O9 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(7), and one O(9) atom to form MnO6 octahedra that share corners with two equivalent As(2)O4 tetrahedra, corners with three equivalent As(1)O4 tetrahedra, and edges with two equivalent Mn(2)O6 octahedra. In the second Mn site, Mn(2) is bonded to one O(1), one O(3), one O(5), one O(6), one O(7), and one O(8) atom to form distorted MnO6 octahedra that share corners with two equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra, and edges with two equivalent Mn(1)O6 octahedra. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form AsO4 tetrahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with three equivalent Mn(1)O6 octahedra, and  a cornercorner with one As(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-60°. In the second As site, As(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form AsO4 tetrahedra that share corners with two equivalent Mn(1)O6 octahedra, corners with three equivalent Mn(2)O6 octahedra, and  a cornercorner with one As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-59°. There are nine inequivalent O sites. In the first O site, O(5) is bonded in a distorted trigonal planar geometry to one Mn(1), one Mn(2), and one As(2) atom. In the second O site, O(6) is bonded in a bent 120 degrees geometry to one Mn(2) and one As(2) atom. In the third O site, O(7) is bonded in a distorted trigonal planar geometry to one Mn(1), one Mn(2), and one As(2) atom. In the fourth O site, O(8) is bonded in a single-bond geometry to one Mn(2) atom. In the fifth O site, O(1) is bonded in a trigonal planar geometry to one Mn(1), one Mn(2), and one As(1) atom. In the sixth O site, O(9) is bonded in a single-bond geometry to one Mn(1) atom. In the seventh O site, O(2) is bonded in a bent 120 degrees geometry to one Mn(1) and one As(1) atom. In the eighth O site, O(3) is bonded in a trigonal planar geometry to one Mn(1), one Mn(2), and one As(1) atom. In the ninth 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 card [CIF]
data_Mn2As2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   14.335
_cell_length_b   6.684
_cell_length_c   9.612
_cell_angle_alpha   51.986
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   725.582
_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
  Mn  Mn0  1  0.389  0.165  0.093  1.0
  Mn  Mn1  1  0.111  0.165  0.593  1.0
  Mn  Mn2  1  0.611  0.835  0.907  1.0
  Mn  Mn3  1  0.889  0.835  0.407  1.0
  Mn  Mn4  1  0.747  0.319  0.135  1.0
  Mn  Mn5  1  0.753  0.319  0.635  1.0
  Mn  Mn6  1  0.253  0.681  0.865  1.0
  Mn  Mn7  1  0.247  0.681  0.365  1.0
  As  As8  1  0.578  0.401  0.841  1.0
  As  As9  1  0.922  0.401  0.341  1.0
  As  As10  1  0.422  0.599  0.159  1.0
  As  As11  1  0.078  0.599  0.659  1.0
  As  As12  1  0.686  0.895  0.547  1.0
  As  As13  1  0.814  0.895  0.047  1.0
  As  As14  1  0.314  0.105  0.453  1.0
  As  As15  1  0.186  0.105  0.953  1.0
  O  O16  1  0.627  0.464  0.974  1.0
  O  O17  1  0.873  0.464  0.474  1.0
  O  O18  1  0.373  0.536  0.026  1.0
  O  O19  1  0.127  0.536  0.526  1.0
  O  O20  1  0.466  0.310  0.873  1.0
  O  O21  1  0.034  0.310  0.373  1.0
  O  O22  1  0.534  0.690  0.127  1.0
  O  O23  1  0.966  0.690  0.627  1.0
  O  O24  1  0.652  0.198  0.839  1.0
  O  O25  1  0.848  0.198  0.339  1.0
  O  O26  1  0.348  0.802  0.161  1.0
  O  O27  1  0.152  0.802  0.661  1.0
  O  O28  1  0.583  0.703  0.626  1.0
  O  O29  1  0.917  0.703  0.126  1.0
  O  O30  1  0.417  0.297  0.374  1.0
  O  O31  1  0.083  0.297  0.874  1.0
  O  O32  1  0.706  0.968  0.688  1.0
  O  O33  1  0.794  0.968  0.188  1.0
  O  O34  1  0.294  0.032  0.312  1.0
  O  O35  1  0.206  0.032  0.812  1.0
  O  O36  1  0.658  0.137  0.336  1.0
  O  O37  1  0.842  0.137  0.836  1.0
  O  O38  1  0.342  0.863  0.664  1.0
  O  O39  1  0.158  0.863  0.164  1.0
  O  O40  1  0.774  0.699  0.569  1.0
  O  O41  1  0.726  0.699  0.069  1.0
  O  O42  1  0.226  0.301  0.431  1.0
  O  O43  1  0.274  0.301  0.931  1.0
  O  O44  1  0.827  0.473  0.959  1.0
  O  O45  1  0.673  0.473  0.459  1.0
  O  O46  1  0.173  0.527  0.041  1.0
  O  O47  1  0.327  0.527  0.541  1.0
  O  O48  1  0.485  0.034  0.231  1.0
  O  O49  1  0.015  0.034  0.731  1.0
  O  O50  1  0.515  0.966  0.769  1.0
  O  O51  1  0.985  0.966  0.269  1.0
[/CIF]
.
The compound described by Mn2As2O9 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(7), and one O(9) atom to form MnO6 octahedra that share corners with two equivalent As(2)O4 tetrahedra, corners with three equivalent As(1)O4 tetrahedra, and edges with two equivalent Mn(2)O6 octahedra. In the second Mn site, Mn(2) is bonded to one O(1), one O(3), one O(5), one O(6), one O(7), and one O(8) atom to form distorted MnO6 octahedra that share corners with two equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra, and edges with two equivalent Mn(1)O6 octahedra. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form AsO4 tetrahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with three equivalent Mn(1)O6 octahedra, and  a cornercorner with one As(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-60°. In the second As site, As(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form AsO4 tetrahedra that share corners with two equivalent Mn(1)O6 octahedra, corners with three equivalent Mn(2)O6 octahedra, and  a cornercorner with one As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-59°. There are nine inequivalent O sites. In the first O site, O(5) is bonded in a distorted trigonal planar geometry to one Mn(1), one Mn(2), and one As(2) atom. In the second O site, O(6) is bonded in a bent 120 degrees geometry to one Mn(2) and one As(2) atom. In the third O site, O(7) is bonded in a distorted trigonal planar geometry to one Mn(1), one Mn(2), and one As(2) atom. In the fourth O site, O(8) is bonded in a single-bond geometry to one Mn(2) atom. In the fifth O site, O(1) is bonded in a trigonal planar geometry to one Mn(1), one Mn(2), and one As(1) atom. In the sixth O site, O(9) is bonded in a single-bond geometry to one Mn(1) atom. In the seventh O site, O(2) is bonded in a bent 120 degrees geometry to one Mn(1) and one As(1) atom. In the eighth O site, O(3) is bonded in a trigonal planar geometry to one Mn(1), one Mn(2), and one As(1) atom. In the ninth 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 card [CIF]
data_Mn2As2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   14.335
_cell_length_b   6.684
_cell_length_c   9.612
_cell_angle_alpha   51.986
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   725.582
_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
  Mn  Mn0  1  0.389  0.165  0.093  1.0
  Mn  Mn1  1  0.111  0.165  0.593  1.0
  Mn  Mn2  1  0.611  0.835  0.907  1.0
  Mn  Mn3  1  0.889  0.835  0.407  1.0
  Mn  Mn4  1  0.747  0.319  0.135  1.0
  Mn  Mn5  1  0.753  0.319  0.635  1.0
  Mn  Mn6  1  0.253  0.681  0.865  1.0
  Mn  Mn7  1  0.247  0.681  0.365  1.0
  As  As8  1  0.578  0.401  0.841  1.0
  As  As9  1  0.922  0.401  0.341  1.0
  As  As10  1  0.422  0.599  0.159  1.0
  As  As11  1  0.078  0.599  0.659  1.0
  As  As12  1  0.686  0.895  0.547  1.0
  As  As13  1  0.814  0.895  0.047  1.0
  As  As14  1  0.314  0.105  0.453  1.0
  As  As15  1  0.186  0.105  0.953  1.0
  O  O16  1  0.627  0.464  0.974  1.0
  O  O17  1  0.873  0.464  0.474  1.0
  O  O18  1  0.373  0.536  0.026  1.0
  O  O19  1  0.127  0.536  0.526  1.0
  O  O20  1  0.466  0.310  0.873  1.0
  O  O21  1  0.034  0.310  0.373  1.0
  O  O22  1  0.534  0.690  0.127  1.0
  O  O23  1  0.966  0.690  0.627  1.0
  O  O24  1  0.652  0.198  0.839  1.0
  O  O25  1  0.848  0.198  0.339  1.0
  O  O26  1  0.348  0.802  0.161  1.0
  O  O27  1  0.152  0.802  0.661  1.0
  O  O28  1  0.583  0.703  0.626  1.0
  O  O29  1  0.917  0.703  0.126  1.0
  O  O30  1  0.417  0.297  0.374  1.0
  O  O31  1  0.083  0.297  0.874  1.0
  O  O32  1  0.706  0.968  0.688  1.0
  O  O33  1  0.794  0.968  0.188  1.0
  O  O34  1  0.294  0.032  0.312  1.0
  O  O35  1  0.206  0.032  0.812  1.0
  O  O36  1  0.658  0.137  0.336  1.0
  O  O37  1  0.842  0.137  0.836  1.0
  O  O38  1  0.342  0.863  0.664  1.0
  O  O39  1  0.158  0.863  0.164  1.0
  O  O40  1  0.774  0.699  0.569  1.0
  O  O41  1  0.726  0.699  0.069  1.0
  O  O42  1  0.226  0.301  0.431  1.0
  O  O43  1  0.274  0.301  0.931  1.0
  O  O44  1  0.827  0.473  0.959  1.0
  O  O45  1  0.673  0.473  0.459  1.0
  O  O46  1  0.173  0.527  0.041  1.0
  O  O47  1  0.327  0.527  0.541  1.0
  O  O48  1  0.485  0.034  0.231  1.0
  O  O49  1  0.015  0.034  0.731  1.0
  O  O50  1  0.515  0.966  0.769  1.0
  O  O51  1  0.985  0.966  0.269  1.0
[/CIF]
.