data_ErSn2As
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.19
_cell_length_b   5.19
_cell_length_c   5.19
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   ErSn2As
_chemical_formula_sum   'Er1 Sn2 As1'
_cell_volume   99.13
_cell_formula_units_Z   1
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
  Er  Er1  1  0.67  0.67  0.67  1.0
  Sn  Sn2  1  0.51  0.51  0.51  1.0
  Sn  Sn3  1  0.84  0.84  0.84  1.0
  As  As0  1  0.0  0.0  0.0  1.0

data_ErSn2As
_symmetry_space_group_name_H-M   R3m
_cell_length_a   5.19
_cell_length_b   5.19
_cell_length_c   12.72
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   ErSn2As
_chemical_formula_sum   'Er3 Sn6 As3'
_cell_volume   297.38
_cell_formula_units_Z   3
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
  2  '-y, x-y, z'
  3  '-x+y, -x, z'
  4  '-y, -x, z'
  5  '-x+y, y, z'
  6  'x, x-y, z'
  7  'x+1/3, y+2/3, z+2/3'
  8  '-y+1/3, x-y+2/3, z+2/3'
  9  '-x+y+1/3, -x+2/3, z+2/3'
  10  '-y+1/3, -x+2/3, z+2/3'
  11  '-x+y+1/3, y+2/3, z+2/3'
  12  'x+1/3, x-y+2/3, z+2/3'
  13  'x+2/3, y+1/3, z+1/3'
  14  '-y+2/3, x-y+1/3, z+1/3'
  15  '-x+y+2/3, -x+1/3, z+1/3'
  16  '-y+2/3, -x+1/3, z+1/3'
  17  '-x+y+2/3, y+1/3, z+1/3'
  18  'x+2/3, x-y+1/3, z+1/3'
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
  Er  Er0  3  0.0  0.0  0.33  1.0
  Sn  Sn1  3  0.0  0.0  0.16  1.0
  Sn  Sn2  3  0.0  0.0  0.49  1.0
  As  As3  3  0.0  0.0  0.0  1.0

Er Sn Sn As
ErSn2As crystallizes in the trigonal R3m space group. Er(1) is bonded to one Sn(1), one Sn(2), and three equivalent As(1) atoms to form distorted ErSn2As3 trigonal bipyramids that share corners with six equivalent Er(1)Sn2As3 trigonal bipyramids and  a cornercorner with one As(1)Er3Sn trigonal pyramid. The Er(1)-Sn(1) bond length is 2.08 Å. The Er(1)-Sn(2) bond length is 2.08 Å. All Er(1)-As(1) bond lengths are 3.00 Å. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded in a single-bond geometry to one Er(1) atom. In the second Sn site, Sn(2) is bonded in a distorted linear geometry to one Er(1) and one As(1) atom. The Sn(2)-As(1) bond length is 2.08 Å. As(1) is bonded to three equivalent Er(1) and one Sn(2) atom to form AsEr3Sn trigonal pyramids that share  a cornercorner with one Er(1)Sn2As3 trigonal bipyramid and corners with six equivalent As(1)Er3Sn trigonal pyramids.