The crystal structure described by Ba4Au2Si21 crystallizes in the orthorhombic Ama2 space group. There are four inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 20-coordinate geometry to one Si(10), one Si(11), one Si(12), one Si(7), two equivalent Si(1), two equivalent Si(2), two equivalent Si(3), two equivalent Si(4), two equivalent Si(5), two equivalent Si(6), two equivalent Si(8), and two equivalent Si(9) atoms. In the second Ba site, Ba(2) is bonded in a 11-coordinate geometry to one Au(2), two equivalent Au(1), two equivalent Si(5), two equivalent Si(6), two equivalent Si(8), and two equivalent Si(9) atoms. In the third Ba site, Ba(3) is bonded in a 10-coordinate geometry to two equivalent Au(2), two equivalent Si(10), two equivalent Si(11), two equivalent Si(12), two equivalent Si(2), and two equivalent Si(7) atoms. In the fourth Ba site, Ba(4) is bonded in a 11-coordinate geometry to one Au(2), two equivalent Au(1), two equivalent Si(5), two equivalent Si(6), two equivalent Si(8), two equivalent Si(9), and four equivalent Si(2) atoms. There are two inequivalent Au sites. In the first Au site, Au(1) is bonded to two equivalent Ba(2), two equivalent Ba(4), two equivalent Si(6), and two equivalent Si(9) atoms to form a mixture of corner and edge-sharing AuBa4Si4 tetrahedra. In the second Au site, Au(2) is bonded to one Ba(2), one Ba(4), two equivalent Ba(3), one Si(10), one Si(12), and two equivalent Si(8) atoms to form corner-sharing AuBa4Si4 tetrahedra. There are thirteen inequivalent Si sites. In the first Si site, Si(1) is bonded in a 5-coordinate geometry to one Ba(1), one Si(1), one Si(5), one Si(6), and one Si(7) atom. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Ba(1), one Ba(3), two equivalent Ba(4), one Si(10), one Si(2), one Si(8), and one Si(9) atom. In the third Si site, Si(3) is bonded in a 5-coordinate geometry to one Ba(1), one Si(11), one Si(4), one Si(6), and one Si(8) atom. In the fourth Si site, Si(4) is bonded in a 5-coordinate geometry to one Ba(1), one Si(12), one Si(3), one Si(5), and one Si(9) atom. In the fifth Si site, Si(5) is bonded in a 7-coordinate geometry to one Ba(1), one Ba(2), one Ba(4), one Si(1), one Si(13), one Si(4), and one Si(8) atom. In the sixth Si site, Si(6) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), one Ba(4), one Au(1), one Si(1), and one Si(3) atom. In the seventh Si site, Si(7) is bonded in a 7-coordinate geometry to one Ba(1), two equivalent Ba(3), one Si(12), one Si(13), and two equivalent Si(1) atoms. In the eighth Si site, Si(8) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), one Ba(4), one Au(2), one Si(2), one Si(3), and one Si(5) atom. In the ninth Si site, Si(9) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), one Ba(4), one Au(1), one Si(2), and one Si(4) atom. In the tenth Si site, Si(10) is bonded in a distorted single-bond geometry to one Ba(1), two equivalent Ba(3), one Au(2), one Si(11), and two equivalent Si(2) atoms. In the eleventh Si site, Si(11) is bonded in a 7-coordinate geometry to one Ba(1), two equivalent Ba(3), one Si(10), one Si(13), and two equivalent Si(3) atoms. In the twelfth Si site, Si(12) is bonded in a distorted single-bond geometry to one Ba(1), two equivalent Ba(3), one Au(2), one Si(7), and two equivalent Si(4) atoms. In the thirteenth Si site, Si(13) is bonded in a distorted tetrahedral geometry to one Si(11), one Si(7), and two equivalent Si(5) atoms. is represented by the CIF file [CIF]
data_Ba4Si21Au2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   10.498
_cell_length_b   10.498
_cell_length_c   10.438
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.036
_symmetry_Int_Tables_number   1
_cell_volume   1150.316
_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
  Ba  Ba0  1  0.499  0.001  0.250  1.0
  Ba  Ba1  1  0.001  0.499  0.750  1.0
  Ba  Ba2  1  0.759  0.011  0.750  1.0
  Ba  Ba3  1  0.011  0.759  0.250  1.0
  Ba  Ba4  1  0.489  0.489  0.500  1.0
  Ba  Ba5  1  0.240  0.012  0.750  1.0
  Ba  Ba6  1  0.012  0.240  0.250  1.0
  Ba  Ba7  1  0.489  0.489  0.000  1.0
  Si  Si8  1  0.685  0.814  0.434  1.0
  Si  Si9  1  0.317  0.184  0.065  1.0
  Si  Si10  1  0.317  0.184  0.435  1.0
  Si  Si11  1  0.685  0.814  0.066  1.0
  Si  Si12  1  0.685  0.183  0.065  1.0
  Si  Si13  1  0.318  0.814  0.435  1.0
  Si  Si14  1  0.318  0.814  0.065  1.0
  Si  Si15  1  0.685  0.183  0.435  1.0
  Si  Si16  1  0.814  0.685  0.934  1.0
  Si  Si17  1  0.184  0.317  0.565  1.0
  Si  Si18  1  0.184  0.317  0.935  1.0
  Si  Si19  1  0.814  0.685  0.566  1.0
  Si  Si20  1  0.183  0.685  0.565  1.0
  Si  Si21  1  0.814  0.318  0.935  1.0
  Si  Si22  1  0.814  0.318  0.565  1.0
  Si  Si23  1  0.183  0.685  0.935  1.0
  Si  Si24  1  0.501  0.881  0.556  1.0
  Si  Si25  1  0.803  0.999  0.367  1.0
  Si  Si26  1  0.617  0.693  0.250  1.0
  Si  Si27  1  0.501  0.118  0.944  1.0
  Si  Si28  1  0.199  0.999  0.132  1.0
  Si  Si29  1  0.382  0.305  0.250  1.0
  Si  Si30  1  0.501  0.118  0.556  1.0
  Si  Si31  1  0.199  0.999  0.368  1.0
  Si  Si32  1  0.501  0.881  0.944  1.0
  Si  Si33  1  0.803  0.999  0.133  1.0
  Si  Si34  1  0.619  0.305  0.250  1.0
  Si  Si35  1  0.384  0.694  0.250  1.0
  Si  Si36  1  0.881  0.501  0.056  1.0
  Si  Si37  1  0.999  0.803  0.867  1.0
  Si  Si38  1  0.693  0.617  0.750  1.0
  Si  Si39  1  0.118  0.501  0.444  1.0
  Si  Si40  1  0.999  0.199  0.632  1.0
  Si  Si41  1  0.305  0.382  0.750  1.0
  Si  Si42  1  0.118  0.501  0.056  1.0
  Si  Si43  1  0.999  0.199  0.868  1.0
  Si  Si44  1  0.881  0.501  0.444  1.0
  Si  Si45  1  0.999  0.803  0.633  1.0
  Si  Si46  1  0.305  0.619  0.750  1.0
  Si  Si47  1  0.694  0.384  0.750  1.0
  Si  Si48  1  0.750  0.499  0.250  1.0
  Si  Si49  1  0.499  0.750  0.750  1.0
  Au  Au50  1  0.000  0.000  0.500  1.0
  Au  Au51  1  0.251  0.500  0.250  1.0
  Au  Au52  1  0.500  0.251  0.750  1.0
  Au  Au53  1  0.000  0.000  0.000  1.0
[/CIF]
.
The crystal structure described by Ba4Au2Si21 crystallizes in the orthorhombic Ama2 space group. There are four inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 20-coordinate geometry to one Si(10), one Si(11), one Si(12), one Si(7), two equivalent Si(1), two equivalent Si(2), two equivalent Si(3), two equivalent Si(4), two equivalent Si(5), two equivalent Si(6), two equivalent Si(8), and two equivalent Si(9) atoms. In the second Ba site, Ba(2) is bonded in a 11-coordinate geometry to one Au(2), two equivalent Au(1), two equivalent Si(5), two equivalent Si(6), two equivalent Si(8), and two equivalent Si(9) atoms. In the third Ba site, Ba(3) is bonded in a 10-coordinate geometry to two equivalent Au(2), two equivalent Si(10), two equivalent Si(11), two equivalent Si(12), two equivalent Si(2), and two equivalent Si(7) atoms. In the fourth Ba site, Ba(4) is bonded in a 11-coordinate geometry to one Au(2), two equivalent Au(1), two equivalent Si(5), two equivalent Si(6), two equivalent Si(8), two equivalent Si(9), and four equivalent Si(2) atoms. There are two inequivalent Au sites. In the first Au site, Au(1) is bonded to two equivalent Ba(2), two equivalent Ba(4), two equivalent Si(6), and two equivalent Si(9) atoms to form a mixture of corner and edge-sharing AuBa4Si4 tetrahedra. In the second Au site, Au(2) is bonded to one Ba(2), one Ba(4), two equivalent Ba(3), one Si(10), one Si(12), and two equivalent Si(8) atoms to form corner-sharing AuBa4Si4 tetrahedra. There are thirteen inequivalent Si sites. In the first Si site, Si(1) is bonded in a 5-coordinate geometry to one Ba(1), one Si(1), one Si(5), one Si(6), and one Si(7) atom. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Ba(1), one Ba(3), two equivalent Ba(4), one Si(10), one Si(2), one Si(8), and one Si(9) atom. In the third Si site, Si(3) is bonded in a 5-coordinate geometry to one Ba(1), one Si(11), one Si(4), one Si(6), and one Si(8) atom. In the fourth Si site, Si(4) is bonded in a 5-coordinate geometry to one Ba(1), one Si(12), one Si(3), one Si(5), and one Si(9) atom. In the fifth Si site, Si(5) is bonded in a 7-coordinate geometry to one Ba(1), one Ba(2), one Ba(4), one Si(1), one Si(13), one Si(4), and one Si(8) atom. In the sixth Si site, Si(6) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), one Ba(4), one Au(1), one Si(1), and one Si(3) atom. In the seventh Si site, Si(7) is bonded in a 7-coordinate geometry to one Ba(1), two equivalent Ba(3), one Si(12), one Si(13), and two equivalent Si(1) atoms. In the eighth Si site, Si(8) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), one Ba(4), one Au(2), one Si(2), one Si(3), and one Si(5) atom. In the ninth Si site, Si(9) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), one Ba(4), one Au(1), one Si(2), and one Si(4) atom. In the tenth Si site, Si(10) is bonded in a distorted single-bond geometry to one Ba(1), two equivalent Ba(3), one Au(2), one Si(11), and two equivalent Si(2) atoms. In the eleventh Si site, Si(11) is bonded in a 7-coordinate geometry to one Ba(1), two equivalent Ba(3), one Si(10), one Si(13), and two equivalent Si(3) atoms. In the twelfth Si site, Si(12) is bonded in a distorted single-bond geometry to one Ba(1), two equivalent Ba(3), one Au(2), one Si(7), and two equivalent Si(4) atoms. In the thirteenth Si site, Si(13) is bonded in a distorted tetrahedral geometry to one Si(11), one Si(7), and two equivalent Si(5) atoms. is represented by the CIF file [CIF]
data_Ba4Si21Au2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   10.498
_cell_length_b   10.498
_cell_length_c   10.438
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.036
_symmetry_Int_Tables_number   1
_cell_volume   1150.316
_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
  Ba  Ba0  1  0.499  0.001  0.250  1.0
  Ba  Ba1  1  0.001  0.499  0.750  1.0
  Ba  Ba2  1  0.759  0.011  0.750  1.0
  Ba  Ba3  1  0.011  0.759  0.250  1.0
  Ba  Ba4  1  0.489  0.489  0.500  1.0
  Ba  Ba5  1  0.240  0.012  0.750  1.0
  Ba  Ba6  1  0.012  0.240  0.250  1.0
  Ba  Ba7  1  0.489  0.489  0.000  1.0
  Si  Si8  1  0.685  0.814  0.434  1.0
  Si  Si9  1  0.317  0.184  0.065  1.0
  Si  Si10  1  0.317  0.184  0.435  1.0
  Si  Si11  1  0.685  0.814  0.066  1.0
  Si  Si12  1  0.685  0.183  0.065  1.0
  Si  Si13  1  0.318  0.814  0.435  1.0
  Si  Si14  1  0.318  0.814  0.065  1.0
  Si  Si15  1  0.685  0.183  0.435  1.0
  Si  Si16  1  0.814  0.685  0.934  1.0
  Si  Si17  1  0.184  0.317  0.565  1.0
  Si  Si18  1  0.184  0.317  0.935  1.0
  Si  Si19  1  0.814  0.685  0.566  1.0
  Si  Si20  1  0.183  0.685  0.565  1.0
  Si  Si21  1  0.814  0.318  0.935  1.0
  Si  Si22  1  0.814  0.318  0.565  1.0
  Si  Si23  1  0.183  0.685  0.935  1.0
  Si  Si24  1  0.501  0.881  0.556  1.0
  Si  Si25  1  0.803  0.999  0.367  1.0
  Si  Si26  1  0.617  0.693  0.250  1.0
  Si  Si27  1  0.501  0.118  0.944  1.0
  Si  Si28  1  0.199  0.999  0.132  1.0
  Si  Si29  1  0.382  0.305  0.250  1.0
  Si  Si30  1  0.501  0.118  0.556  1.0
  Si  Si31  1  0.199  0.999  0.368  1.0
  Si  Si32  1  0.501  0.881  0.944  1.0
  Si  Si33  1  0.803  0.999  0.133  1.0
  Si  Si34  1  0.619  0.305  0.250  1.0
  Si  Si35  1  0.384  0.694  0.250  1.0
  Si  Si36  1  0.881  0.501  0.056  1.0
  Si  Si37  1  0.999  0.803  0.867  1.0
  Si  Si38  1  0.693  0.617  0.750  1.0
  Si  Si39  1  0.118  0.501  0.444  1.0
  Si  Si40  1  0.999  0.199  0.632  1.0
  Si  Si41  1  0.305  0.382  0.750  1.0
  Si  Si42  1  0.118  0.501  0.056  1.0
  Si  Si43  1  0.999  0.199  0.868  1.0
  Si  Si44  1  0.881  0.501  0.444  1.0
  Si  Si45  1  0.999  0.803  0.633  1.0
  Si  Si46  1  0.305  0.619  0.750  1.0
  Si  Si47  1  0.694  0.384  0.750  1.0
  Si  Si48  1  0.750  0.499  0.250  1.0
  Si  Si49  1  0.499  0.750  0.750  1.0
  Au  Au50  1  0.000  0.000  0.500  1.0
  Au  Au51  1  0.251  0.500  0.250  1.0
  Au  Au52  1  0.500  0.251  0.750  1.0
  Au  Au53  1  0.000  0.000  0.000  1.0
[/CIF]
.