data_MgSi4As
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.18
_cell_length_b   5.18
_cell_length_c   5.18
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   MgSi4As
_chemical_formula_sum   'Mg1 Si4 As1'
_cell_volume   98.28
_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
  Mg  Mg1  1  0.0  0.0  0.0  1.0
  Si  Si2  1  0.58  0.58  0.75  1.0
  Si  Si3  1  0.58  0.75  0.58  1.0
  Si  Si4  1  0.75  0.58  0.58  1.0
  Si  Si5  1  0.75  0.75  0.75  1.0
  As  As0  1  0.49  0.49  0.49  1.0

data_MgSi4As
_symmetry_space_group_name_H-M   R3m
_cell_length_a   5.18
_cell_length_b   5.18
_cell_length_c   12.69
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   MgSi4As
_chemical_formula_sum   'Mg3 Si12 As3'
_cell_volume   294.85
_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
  Mg  Mg0  3  0.0  0.0  0.0  1.0
  Si  Si1  9  0.06  0.11  0.37  1.0
  Si  Si2  3  0.0  0.0  0.25  1.0
  As  As3  3  0.0  0.0  0.51  1.0

Mg Si Si Si Si As
MgSi4As crystallizes in the trigonal R3m space group. Mg(1) is bonded in a 10-coordinate geometry to four equivalent Si(2) and six equivalent Si(1) atoms. There are three shorter (3.16 Å) and one longer (3.21 Å) Mg(1)-Si(2) bond length. All Mg(1)-Si(1) bond lengths are 2.80 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 2-coordinate geometry to two equivalent Mg(1), one Si(2), two equivalent Si(1), and one As(1) atom. The Si(1)-Si(2) bond length is 1.51 Å. Both Si(1)-Si(1) bond lengths are 0.87 Å. The Si(1)-As(1) bond length is 1.85 Å. In the second Si site, Si(2) is bonded in a 4-coordinate geometry to four equivalent Mg(1) and three equivalent Si(1) atoms. As(1) is bonded in a 3-coordinate geometry to three equivalent Si(1) atoms.