The structure described by PbAl2Si2O8 crystallizes in the monoclinic C2/c space group. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(3), one O(5), and one O(7) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with three equivalent Si(2)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(2), one O(4), one O(6), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra and corners with three equivalent Si(1)O4 tetrahedra. Pb(1) is bonded in a 5-coordinate geometry to one O(2), one O(7), one O(8), and two equivalent O(1) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(4), one O(6), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra and corners with three equivalent Al(2)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(2), one O(3), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra and corners with three equivalent Al(1)O4 tetrahedra. There are eight inequivalent O sites. In the first O site, O(7) is bonded in a 2-coordinate geometry to one Al(1), one Pb(1), and one Si(2) atom. In the second O site, O(8) is bonded in a distorted bent 150 degrees geometry to one Al(2), one Pb(1), and one Si(1) atom. In the third O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Al(1), two equivalent Pb(1), and one Si(1) atom. In the fourth O site, O(2) is bonded in a distorted trigonal planar geometry to one Al(2), one Pb(1), and one Si(2) atom. In the fifth O site, O(3) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(2) atom. In the sixth O site, O(4) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(1) atom. In the seventh O site, O(5) is bonded in a bent 120 degrees geometry to one Al(1) and one Si(2) atom. In the eighth O site, O(6) is bonded in a bent 120 degrees geometry to one Al(2) and one Si(1) atom. is represented by the CIF file [CIF]
data_Al2Si2PbO8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.375
_cell_length_b   9.375
_cell_length_c   8.490
_cell_angle_alpha   82.944
_cell_angle_beta   82.944
_cell_angle_gamma   89.637
_symmetry_Int_Tables_number   1
_cell_volume   734.881
_cell_formula_units_Z   4
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
  Al  Al0  1  0.937  0.796  0.887  1.0
  Al  Al1  1  0.796  0.937  0.387  1.0
  Al  Al2  1  0.063  0.204  0.113  1.0
  Al  Al3  1  0.204  0.063  0.613  1.0
  Al  Al4  1  0.552  0.293  0.023  1.0
  Al  Al5  1  0.293  0.552  0.523  1.0
  Al  Al6  1  0.448  0.707  0.977  1.0
  Al  Al7  1  0.707  0.448  0.477  1.0
  Si  Si8  1  0.433  0.286  0.397  1.0
  Si  Si9  1  0.286  0.433  0.897  1.0
  Si  Si10  1  0.567  0.714  0.603  1.0
  Si  Si11  1  0.714  0.567  0.103  1.0
  Si  Si12  1  0.060  0.787  0.514  1.0
  Si  Si13  1  0.787  0.060  0.014  1.0
  Si  Si14  1  0.940  0.213  0.486  1.0
  Si  Si15  1  0.213  0.940  0.986  1.0
  Pb  Pb16  1  0.579  0.068  0.696  1.0
  Pb  Pb17  1  0.068  0.579  0.196  1.0
  Pb  Pb18  1  0.421  0.932  0.304  1.0
  Pb  Pb19  1  0.932  0.421  0.804  1.0
  O  O20  1  0.366  0.134  0.501  1.0
  O  O21  1  0.134  0.366  0.001  1.0
  O  O22  1  0.634  0.866  0.499  1.0
  O  O23  1  0.866  0.634  0.999  1.0
  O  O24  1  0.646  0.145  0.950  1.0
  O  O25  1  0.145  0.646  0.450  1.0
  O  O26  1  0.354  0.855  0.050  1.0
  O  O27  1  0.855  0.354  0.550  1.0
  O  O28  1  0.987  0.745  0.698  1.0
  O  O29  1  0.745  0.987  0.198  1.0
  O  O30  1  0.013  0.255  0.302  1.0
  O  O31  1  0.255  0.013  0.802  1.0
  O  O32  1  0.479  0.239  0.220  1.0
  O  O33  1  0.239  0.479  0.720  1.0
  O  O34  1  0.521  0.761  0.780  1.0
  O  O35  1  0.761  0.521  0.280  1.0
  O  O36  1  0.823  0.943  0.889  1.0
  O  O37  1  0.943  0.823  0.389  1.0
  O  O38  1  0.177  0.057  0.111  1.0
  O  O39  1  0.057  0.177  0.611  1.0
  O  O40  1  0.324  0.420  0.394  1.0
  O  O41  1  0.420  0.324  0.894  1.0
  O  O42  1  0.676  0.580  0.606  1.0
  O  O43  1  0.580  0.676  0.106  1.0
  O  O44  1  0.084  0.821  0.996  1.0
  O  O45  1  0.821  0.084  0.496  1.0
  O  O46  1  0.916  0.179  0.004  1.0
  O  O47  1  0.179  0.916  0.504  1.0
  O  O48  1  0.570  0.318  0.492  1.0
  O  O49  1  0.318  0.570  0.992  1.0
  O  O50  1  0.430  0.682  0.508  1.0
  O  O51  1  0.682  0.430  0.008  1.0
[/CIF]
.
The structure described by PbAl2Si2O8 crystallizes in the monoclinic C2/c space group. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(3), one O(5), and one O(7) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with three equivalent Si(2)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(2), one O(4), one O(6), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra and corners with three equivalent Si(1)O4 tetrahedra. Pb(1) is bonded in a 5-coordinate geometry to one O(2), one O(7), one O(8), and two equivalent O(1) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(4), one O(6), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra and corners with three equivalent Al(2)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(2), one O(3), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra and corners with three equivalent Al(1)O4 tetrahedra. There are eight inequivalent O sites. In the first O site, O(7) is bonded in a 2-coordinate geometry to one Al(1), one Pb(1), and one Si(2) atom. In the second O site, O(8) is bonded in a distorted bent 150 degrees geometry to one Al(2), one Pb(1), and one Si(1) atom. In the third O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Al(1), two equivalent Pb(1), and one Si(1) atom. In the fourth O site, O(2) is bonded in a distorted trigonal planar geometry to one Al(2), one Pb(1), and one Si(2) atom. In the fifth O site, O(3) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(2) atom. In the sixth O site, O(4) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(1) atom. In the seventh O site, O(5) is bonded in a bent 120 degrees geometry to one Al(1) and one Si(2) atom. In the eighth O site, O(6) is bonded in a bent 120 degrees geometry to one Al(2) and one Si(1) atom. is represented by the CIF file [CIF]
data_Al2Si2PbO8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.375
_cell_length_b   9.375
_cell_length_c   8.490
_cell_angle_alpha   82.944
_cell_angle_beta   82.944
_cell_angle_gamma   89.637
_symmetry_Int_Tables_number   1
_cell_volume   734.881
_cell_formula_units_Z   4
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
  Al  Al0  1  0.937  0.796  0.887  1.0
  Al  Al1  1  0.796  0.937  0.387  1.0
  Al  Al2  1  0.063  0.204  0.113  1.0
  Al  Al3  1  0.204  0.063  0.613  1.0
  Al  Al4  1  0.552  0.293  0.023  1.0
  Al  Al5  1  0.293  0.552  0.523  1.0
  Al  Al6  1  0.448  0.707  0.977  1.0
  Al  Al7  1  0.707  0.448  0.477  1.0
  Si  Si8  1  0.433  0.286  0.397  1.0
  Si  Si9  1  0.286  0.433  0.897  1.0
  Si  Si10  1  0.567  0.714  0.603  1.0
  Si  Si11  1  0.714  0.567  0.103  1.0
  Si  Si12  1  0.060  0.787  0.514  1.0
  Si  Si13  1  0.787  0.060  0.014  1.0
  Si  Si14  1  0.940  0.213  0.486  1.0
  Si  Si15  1  0.213  0.940  0.986  1.0
  Pb  Pb16  1  0.579  0.068  0.696  1.0
  Pb  Pb17  1  0.068  0.579  0.196  1.0
  Pb  Pb18  1  0.421  0.932  0.304  1.0
  Pb  Pb19  1  0.932  0.421  0.804  1.0
  O  O20  1  0.366  0.134  0.501  1.0
  O  O21  1  0.134  0.366  0.001  1.0
  O  O22  1  0.634  0.866  0.499  1.0
  O  O23  1  0.866  0.634  0.999  1.0
  O  O24  1  0.646  0.145  0.950  1.0
  O  O25  1  0.145  0.646  0.450  1.0
  O  O26  1  0.354  0.855  0.050  1.0
  O  O27  1  0.855  0.354  0.550  1.0
  O  O28  1  0.987  0.745  0.698  1.0
  O  O29  1  0.745  0.987  0.198  1.0
  O  O30  1  0.013  0.255  0.302  1.0
  O  O31  1  0.255  0.013  0.802  1.0
  O  O32  1  0.479  0.239  0.220  1.0
  O  O33  1  0.239  0.479  0.720  1.0
  O  O34  1  0.521  0.761  0.780  1.0
  O  O35  1  0.761  0.521  0.280  1.0
  O  O36  1  0.823  0.943  0.889  1.0
  O  O37  1  0.943  0.823  0.389  1.0
  O  O38  1  0.177  0.057  0.111  1.0
  O  O39  1  0.057  0.177  0.611  1.0
  O  O40  1  0.324  0.420  0.394  1.0
  O  O41  1  0.420  0.324  0.894  1.0
  O  O42  1  0.676  0.580  0.606  1.0
  O  O43  1  0.580  0.676  0.106  1.0
  O  O44  1  0.084  0.821  0.996  1.0
  O  O45  1  0.821  0.084  0.496  1.0
  O  O46  1  0.916  0.179  0.004  1.0
  O  O47  1  0.179  0.916  0.504  1.0
  O  O48  1  0.570  0.318  0.492  1.0
  O  O49  1  0.318  0.570  0.992  1.0
  O  O50  1  0.430  0.682  0.508  1.0
  O  O51  1  0.682  0.430  0.008  1.0
[/CIF]
.