The structure described by Cu4As2O9 crystallizes in the triclinic P-1 space group. There are four inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(2), one O(4), one O(5), one O(7), and one O(9) atom to form distorted CuO5 trigonal bipyramids that share corners with two equivalent As(1)O4 tetrahedra, corners with two equivalent As(2)O4 tetrahedra,  a cornercorner with one Cu(4)O5 trigonal bipyramid,  an edgeedge with one Cu(2)O6 octahedra, and  an edgeedge with one Cu(4)O5 trigonal bipyramid. In the second Cu site, Cu(2) is bonded to one O(1), one O(3), one O(5), one O(7), and two equivalent O(6) atoms to form distorted CuO6 octahedra that share corners with two equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra,  an edgeedge with one Cu(2)O6 octahedra,  an edgeedge with one Cu(1)O5 trigonal bipyramid, and  an edgeedge with one Cu(4)O5 trigonal bipyramid. In the third Cu site, Cu(3) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(7), one O(8), and two equivalent O(2) atoms. In the fourth Cu site, Cu(4) is bonded to one O(3), one O(4), one O(7), one O(8), and one O(9) atom to form distorted CuO5 trigonal bipyramids that share corners with two equivalent As(1)O4 tetrahedra, corners with two equivalent As(2)O4 tetrahedra,  a cornercorner with one Cu(1)O5 trigonal bipyramid,  an edgeedge with one Cu(2)O6 octahedra, and  an edgeedge with one Cu(1)O5 trigonal bipyramid. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(2), one O(6), one O(8), and one O(9) atom to form AsO4 tetrahedra that share corners with two equivalent Cu(2)O6 octahedra, corners with two equivalent Cu(1)O5 trigonal bipyramids, and corners with two equivalent Cu(4)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 56-58°. In the second As site, As(2) is bonded to one O(1), one O(3), one O(4), and one O(5) atom to form AsO4 tetrahedra that share corners with three equivalent Cu(2)O6 octahedra, corners with two equivalent Cu(1)O5 trigonal bipyramids, and corners with two equivalent Cu(4)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 44-60°. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Cu(2), one Cu(3), and one As(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Cu(1), two equivalent Cu(3), and one As(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Cu(2), one Cu(4), and one As(2) atom. In the fourth O site, O(4) is bonded in a trigonal non-coplanar geometry to one Cu(1), one Cu(4), and one As(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Cu(1), one Cu(2), and one As(2) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to two equivalent Cu(2) and one As(1) atom. In the seventh O site, O(7) is bonded in a tetrahedral geometry to one Cu(1), one Cu(2), one Cu(3), and one Cu(4) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Cu(3), one Cu(4), and one As(1) atom. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Cu(1), one Cu(4), and one As(1) atom. is represented by the CIF file [CIF]
data_Cu4As2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.407
_cell_length_b   7.670
_cell_length_c   8.253
_cell_angle_alpha   98.744
_cell_angle_beta   112.436
_cell_angle_gamma   97.881
_symmetry_Int_Tables_number   1
_cell_volume   361.980
_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
  Cu  Cu0  1  0.619  0.386  0.743  1.0
  Cu  Cu1  1  0.146  0.881  0.086  1.0
  Cu  Cu2  1  0.347  0.842  0.550  1.0
  Cu  Cu3  1  0.095  0.356  0.733  1.0
  Cu  Cu4  1  0.854  0.119  0.914  1.0
  Cu  Cu5  1  0.381  0.614  0.257  1.0
  Cu  Cu6  1  0.905  0.644  0.267  1.0
  Cu  Cu7  1  0.653  0.158  0.450  1.0
  As  As8  1  0.131  0.231  0.352  1.0
  As  As9  1  0.502  0.289  0.088  1.0
  As  As10  1  0.869  0.769  0.648  1.0
  As  As11  1  0.498  0.711  0.912  1.0
  O  O12  1  0.502  0.886  0.809  1.0
  O  O13  1  0.374  0.172  0.490  1.0
  O  O14  1  0.230  0.310  0.971  1.0
  O  O15  1  0.770  0.690  0.029  1.0
  O  O16  1  0.626  0.489  0.253  1.0
  O  O17  1  0.661  0.280  0.964  1.0
  O  O18  1  0.008  0.932  0.844  1.0
  O  O19  1  0.374  0.511  0.747  1.0
  O  O20  1  0.805  0.224  0.709  1.0
  O  O21  1  0.992  0.068  0.156  1.0
  O  O22  1  0.035  0.769  0.529  1.0
  O  O23  1  0.195  0.776  0.291  1.0
  O  O24  1  0.339  0.720  0.036  1.0
  O  O25  1  0.498  0.114  0.191  1.0
  O  O26  1  0.173  0.440  0.314  1.0
  O  O27  1  0.827  0.560  0.686  1.0
  O  O28  1  0.965  0.231  0.471  1.0
  O  O29  1  0.626  0.828  0.510  1.0
[/CIF]
.
The structure described by Cu4As2O9 crystallizes in the triclinic P-1 space group. There are four inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(2), one O(4), one O(5), one O(7), and one O(9) atom to form distorted CuO5 trigonal bipyramids that share corners with two equivalent As(1)O4 tetrahedra, corners with two equivalent As(2)O4 tetrahedra,  a cornercorner with one Cu(4)O5 trigonal bipyramid,  an edgeedge with one Cu(2)O6 octahedra, and  an edgeedge with one Cu(4)O5 trigonal bipyramid. In the second Cu site, Cu(2) is bonded to one O(1), one O(3), one O(5), one O(7), and two equivalent O(6) atoms to form distorted CuO6 octahedra that share corners with two equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra,  an edgeedge with one Cu(2)O6 octahedra,  an edgeedge with one Cu(1)O5 trigonal bipyramid, and  an edgeedge with one Cu(4)O5 trigonal bipyramid. In the third Cu site, Cu(3) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(7), one O(8), and two equivalent O(2) atoms. In the fourth Cu site, Cu(4) is bonded to one O(3), one O(4), one O(7), one O(8), and one O(9) atom to form distorted CuO5 trigonal bipyramids that share corners with two equivalent As(1)O4 tetrahedra, corners with two equivalent As(2)O4 tetrahedra,  a cornercorner with one Cu(1)O5 trigonal bipyramid,  an edgeedge with one Cu(2)O6 octahedra, and  an edgeedge with one Cu(1)O5 trigonal bipyramid. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(2), one O(6), one O(8), and one O(9) atom to form AsO4 tetrahedra that share corners with two equivalent Cu(2)O6 octahedra, corners with two equivalent Cu(1)O5 trigonal bipyramids, and corners with two equivalent Cu(4)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 56-58°. In the second As site, As(2) is bonded to one O(1), one O(3), one O(4), and one O(5) atom to form AsO4 tetrahedra that share corners with three equivalent Cu(2)O6 octahedra, corners with two equivalent Cu(1)O5 trigonal bipyramids, and corners with two equivalent Cu(4)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 44-60°. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Cu(2), one Cu(3), and one As(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Cu(1), two equivalent Cu(3), and one As(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Cu(2), one Cu(4), and one As(2) atom. In the fourth O site, O(4) is bonded in a trigonal non-coplanar geometry to one Cu(1), one Cu(4), and one As(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Cu(1), one Cu(2), and one As(2) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to two equivalent Cu(2) and one As(1) atom. In the seventh O site, O(7) is bonded in a tetrahedral geometry to one Cu(1), one Cu(2), one Cu(3), and one Cu(4) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Cu(3), one Cu(4), and one As(1) atom. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Cu(1), one Cu(4), and one As(1) atom. is represented by the CIF file [CIF]
data_Cu4As2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.407
_cell_length_b   7.670
_cell_length_c   8.253
_cell_angle_alpha   98.744
_cell_angle_beta   112.436
_cell_angle_gamma   97.881
_symmetry_Int_Tables_number   1
_cell_volume   361.980
_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
  Cu  Cu0  1  0.619  0.386  0.743  1.0
  Cu  Cu1  1  0.146  0.881  0.086  1.0
  Cu  Cu2  1  0.347  0.842  0.550  1.0
  Cu  Cu3  1  0.095  0.356  0.733  1.0
  Cu  Cu4  1  0.854  0.119  0.914  1.0
  Cu  Cu5  1  0.381  0.614  0.257  1.0
  Cu  Cu6  1  0.905  0.644  0.267  1.0
  Cu  Cu7  1  0.653  0.158  0.450  1.0
  As  As8  1  0.131  0.231  0.352  1.0
  As  As9  1  0.502  0.289  0.088  1.0
  As  As10  1  0.869  0.769  0.648  1.0
  As  As11  1  0.498  0.711  0.912  1.0
  O  O12  1  0.502  0.886  0.809  1.0
  O  O13  1  0.374  0.172  0.490  1.0
  O  O14  1  0.230  0.310  0.971  1.0
  O  O15  1  0.770  0.690  0.029  1.0
  O  O16  1  0.626  0.489  0.253  1.0
  O  O17  1  0.661  0.280  0.964  1.0
  O  O18  1  0.008  0.932  0.844  1.0
  O  O19  1  0.374  0.511  0.747  1.0
  O  O20  1  0.805  0.224  0.709  1.0
  O  O21  1  0.992  0.068  0.156  1.0
  O  O22  1  0.035  0.769  0.529  1.0
  O  O23  1  0.195  0.776  0.291  1.0
  O  O24  1  0.339  0.720  0.036  1.0
  O  O25  1  0.498  0.114  0.191  1.0
  O  O26  1  0.173  0.440  0.314  1.0
  O  O27  1  0.827  0.560  0.686  1.0
  O  O28  1  0.965  0.231  0.471  1.0
  O  O29  1  0.626  0.828  0.510  1.0
[/CIF]
.