The compound described by Mg3Cu2(AsO4)3 crystallizes in the monoclinic C2/c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form distorted MgO6 pentagonal pyramids that share corners with two equivalent As(2)O4 tetrahedra, corners with four equivalent As(1)O4 tetrahedra, and edges with two equivalent Mg(2)O6 octahedra. In the second Mg site, Mg(2) is bonded to one O(1), one O(3), one O(4), one O(6), and two equivalent O(5) atoms to form MgO6 octahedra that share corners with two equivalent As(2)O4 tetrahedra, corners with four equivalent As(1)O4 tetrahedra,  an edgeedge with one Mg(2)O6 octahedra, and  an edgeedge with one Mg(1)O6 pentagonal pyramid. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a linear geometry to two equivalent O(3) atoms. In the second Cu site, Cu(2) is bonded in a square co-planar geometry to two equivalent O(2) and two equivalent O(6) atoms. 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(5) atom to form AsO4 tetrahedra that share corners with four equivalent Mg(2)O6 octahedra and corners with two equivalent Mg(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 39-61°. In the second As site, As(2) is bonded to two equivalent O(1) and two equivalent O(6) atoms to form AsO4 tetrahedra that share corners with four equivalent Mg(2)O6 octahedra and corners with two equivalent Mg(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 61-63°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mg(2), and one As(2) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cu(2), and one As(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(2), one Cu(1), and one As(1) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Mg(1), one Mg(2), and one As(1) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to two equivalent Mg(2) and one As(1) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Mg(2), one Cu(2), and one As(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Mg3Cu2(AsO4)3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.885
_cell_length_b   8.885
_cell_length_c   6.823
_cell_angle_alpha   74.620
_cell_angle_beta   74.620
_cell_angle_gamma   94.500
_symmetry_Int_Tables_number   1
_cell_volume   494.297
_cell_formula_units_Z   2
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  0.743  0.257  0.250  1.0
  Mg  Mg1  1  0.257  0.743  0.750  1.0
  Mg  Mg2  1  0.629  0.944  0.121  1.0
  Mg  Mg3  1  0.371  0.056  0.879  1.0
  Mg  Mg4  1  0.056  0.371  0.379  1.0
  Mg  Mg5  1  0.944  0.629  0.621  1.0
  Cu  Cu6  1  0.000  0.000  0.000  1.0
  Cu  Cu7  1  0.000  0.000  0.500  1.0
  Cu  Cu8  1  0.497  0.503  0.250  1.0
  Cu  Cu9  1  0.503  0.497  0.750  1.0
  As  As10  1  0.350  0.114  0.377  1.0
  As  As11  1  0.650  0.886  0.623  1.0
  As  As12  1  0.886  0.650  0.123  1.0
  As  As13  1  0.114  0.350  0.877  1.0
  As  As14  1  0.287  0.713  0.250  1.0
  As  As15  1  0.713  0.287  0.750  1.0
  O  O16  1  0.251  0.819  0.022  1.0
  O  O17  1  0.749  0.181  0.978  1.0
  O  O18  1  0.181  0.749  0.478  1.0
  O  O19  1  0.819  0.251  0.522  1.0
  O  O20  1  0.495  0.276  0.315  1.0
  O  O21  1  0.505  0.724  0.685  1.0
  O  O22  1  0.724  0.505  0.185  1.0
  O  O23  1  0.276  0.495  0.815  1.0
  O  O24  1  0.828  0.834  0.111  1.0
  O  O25  1  0.172  0.166  0.889  1.0
  O  O26  1  0.166  0.172  0.389  1.0
  O  O27  1  0.834  0.828  0.611  1.0
  O  O28  1  0.666  0.011  0.377  1.0
  O  O29  1  0.334  0.989  0.623  1.0
  O  O30  1  0.989  0.334  0.123  1.0
  O  O31  1  0.011  0.666  0.877  1.0
  O  O32  1  0.404  0.025  0.179  1.0
  O  O33  1  0.596  0.975  0.821  1.0
  O  O34  1  0.975  0.596  0.321  1.0
  O  O35  1  0.025  0.404  0.679  1.0
  O  O36  1  0.488  0.726  0.235  1.0
  O  O37  1  0.512  0.274  0.765  1.0
  O  O38  1  0.274  0.512  0.265  1.0
  O  O39  1  0.726  0.488  0.735  1.0
[/CIF]
.
The compound described by Mg3Cu2(AsO4)3 crystallizes in the monoclinic C2/c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form distorted MgO6 pentagonal pyramids that share corners with two equivalent As(2)O4 tetrahedra, corners with four equivalent As(1)O4 tetrahedra, and edges with two equivalent Mg(2)O6 octahedra. In the second Mg site, Mg(2) is bonded to one O(1), one O(3), one O(4), one O(6), and two equivalent O(5) atoms to form MgO6 octahedra that share corners with two equivalent As(2)O4 tetrahedra, corners with four equivalent As(1)O4 tetrahedra,  an edgeedge with one Mg(2)O6 octahedra, and  an edgeedge with one Mg(1)O6 pentagonal pyramid. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a linear geometry to two equivalent O(3) atoms. In the second Cu site, Cu(2) is bonded in a square co-planar geometry to two equivalent O(2) and two equivalent O(6) atoms. 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(5) atom to form AsO4 tetrahedra that share corners with four equivalent Mg(2)O6 octahedra and corners with two equivalent Mg(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 39-61°. In the second As site, As(2) is bonded to two equivalent O(1) and two equivalent O(6) atoms to form AsO4 tetrahedra that share corners with four equivalent Mg(2)O6 octahedra and corners with two equivalent Mg(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 61-63°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mg(2), and one As(2) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cu(2), and one As(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(2), one Cu(1), and one As(1) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Mg(1), one Mg(2), and one As(1) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to two equivalent Mg(2) and one As(1) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Mg(2), one Cu(2), and one As(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Mg3Cu2(AsO4)3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.885
_cell_length_b   8.885
_cell_length_c   6.823
_cell_angle_alpha   74.620
_cell_angle_beta   74.620
_cell_angle_gamma   94.500
_symmetry_Int_Tables_number   1
_cell_volume   494.297
_cell_formula_units_Z   2
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  0.743  0.257  0.250  1.0
  Mg  Mg1  1  0.257  0.743  0.750  1.0
  Mg  Mg2  1  0.629  0.944  0.121  1.0
  Mg  Mg3  1  0.371  0.056  0.879  1.0
  Mg  Mg4  1  0.056  0.371  0.379  1.0
  Mg  Mg5  1  0.944  0.629  0.621  1.0
  Cu  Cu6  1  0.000  0.000  0.000  1.0
  Cu  Cu7  1  0.000  0.000  0.500  1.0
  Cu  Cu8  1  0.497  0.503  0.250  1.0
  Cu  Cu9  1  0.503  0.497  0.750  1.0
  As  As10  1  0.350  0.114  0.377  1.0
  As  As11  1  0.650  0.886  0.623  1.0
  As  As12  1  0.886  0.650  0.123  1.0
  As  As13  1  0.114  0.350  0.877  1.0
  As  As14  1  0.287  0.713  0.250  1.0
  As  As15  1  0.713  0.287  0.750  1.0
  O  O16  1  0.251  0.819  0.022  1.0
  O  O17  1  0.749  0.181  0.978  1.0
  O  O18  1  0.181  0.749  0.478  1.0
  O  O19  1  0.819  0.251  0.522  1.0
  O  O20  1  0.495  0.276  0.315  1.0
  O  O21  1  0.505  0.724  0.685  1.0
  O  O22  1  0.724  0.505  0.185  1.0
  O  O23  1  0.276  0.495  0.815  1.0
  O  O24  1  0.828  0.834  0.111  1.0
  O  O25  1  0.172  0.166  0.889  1.0
  O  O26  1  0.166  0.172  0.389  1.0
  O  O27  1  0.834  0.828  0.611  1.0
  O  O28  1  0.666  0.011  0.377  1.0
  O  O29  1  0.334  0.989  0.623  1.0
  O  O30  1  0.989  0.334  0.123  1.0
  O  O31  1  0.011  0.666  0.877  1.0
  O  O32  1  0.404  0.025  0.179  1.0
  O  O33  1  0.596  0.975  0.821  1.0
  O  O34  1  0.975  0.596  0.321  1.0
  O  O35  1  0.025  0.404  0.679  1.0
  O  O36  1  0.488  0.726  0.235  1.0
  O  O37  1  0.512  0.274  0.765  1.0
  O  O38  1  0.274  0.512  0.265  1.0
  O  O39  1  0.726  0.488  0.735  1.0
[/CIF]
.