The material described by PbAl2Si2O8 crystallizes in the monoclinic P2_1/c space group. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(13), one O(5), and one O(9) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Si(4)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(10), one O(14), one O(2), and one O(6) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, and corners with two equivalent Si(3)O4 tetrahedra. In the third Al site, Al(3) is bonded to one O(12), one O(16), one O(3), and one O(7) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. In the fourth Al site, Al(4) is bonded to one O(11), one O(15), one O(4), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, and corners with two equivalent Si(1)O4 tetrahedra. There are two inequivalent Pb sites. In the first Pb site, Pb(1) is bonded in a 5-coordinate geometry to one O(1), one O(13), one O(15), one O(2), and one O(3) atom. In the second Pb site, Pb(2) is bonded in a 6-coordinate geometry to one O(1), one O(14), one O(16), one O(2), one O(4), and one O(7) atom. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(11), one O(15), one O(2), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Al(3)O4 tetrahedra, and corners with two equivalent Al(4)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(1), one O(12), one O(16), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(4)O4 tetrahedra, and corners with two equivalent Al(3)O4 tetrahedra. In the third Si site, Si(3) is bonded to one O(10), one O(14), one O(3), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(3)O4 tetrahedra, and corners with two equivalent Al(2)O4 tetrahedra. In the fourth Si site, Si(4) is bonded to one O(13), one O(4), one O(6), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Al(4)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. There are sixteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Al(1), one Pb(1), one Pb(2), and one Si(2) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Al(2), one Pb(1), one Pb(2), and one Si(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Al(3), one Pb(1), and one Si(3) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Al(4), one Pb(2), and one Si(4) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(3) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(4) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Al(3), one Pb(2), and one Si(1) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Al(4) and one Si(2) atom. In the ninth O site, O(9) is bonded in a bent 120 degrees geometry to one Al(1) and one Si(4) atom. In the tenth O site, O(10) is bonded in a distorted bent 120 degrees geometry to one Al(2) and one Si(3) atom. In the eleventh O site, O(11) is bonded in a distorted bent 120 degrees geometry to one Al(4) and one Si(1) atom. In the twelfth O site, O(12) is bonded in a bent 120 degrees geometry to one Al(3) and one Si(2) atom. In the thirteenth O site, O(13) is bonded in a 2-coordinate geometry to one Al(1), one Pb(1), and one Si(4) atom. In the fourteenth O site, O(14) is bonded in a 2-coordinate geometry to one Al(2), one Pb(2), and one Si(3) atom. In the fifteenth O site, O(15) is bonded in a distorted bent 150 degrees geometry to one Al(4), one Pb(1), and one Si(1) atom. In the sixteenth O site, O(16) is bonded in a distorted bent 150 degrees geometry to one Al(3), one Pb(2), and one Si(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Al2Si2PbO8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.497
_cell_length_b   9.403
_cell_length_c   9.403
_cell_angle_alpha   89.614
_cell_angle_beta   82.874
_cell_angle_gamma   82.874
_symmetry_Int_Tables_number   1
_cell_volume   739.691
_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  0.114  0.062  0.204  1.0
  Al  Al1  1  0.386  0.796  0.938  1.0
  Al  Al2  1  0.886  0.938  0.796  1.0
  Al  Al3  1  0.614  0.204  0.062  1.0
  Al  Al4  1  0.975  0.449  0.709  1.0
  Al  Al5  1  0.525  0.291  0.551  1.0
  Al  Al6  1  0.025  0.551  0.291  1.0
  Al  Al7  1  0.475  0.709  0.449  1.0
  O  O8  1  0.006  0.134  0.367  1.0
  O  O9  1  0.494  0.633  0.866  1.0
  O  O10  1  0.994  0.866  0.633  1.0
  O  O11  1  0.506  0.367  0.134  1.0
  O  O12  1  0.552  0.855  0.353  1.0
  O  O13  1  0.948  0.647  0.145  1.0
  O  O14  1  0.448  0.145  0.647  1.0
  O  O15  1  0.052  0.353  0.855  1.0
  O  O16  1  0.304  0.009  0.251  1.0
  O  O17  1  0.196  0.749  0.991  1.0
  O  O18  1  0.696  0.991  0.749  1.0
  O  O19  1  0.804  0.251  0.009  1.0
  O  O20  1  0.777  0.522  0.765  1.0
  O  O21  1  0.723  0.235  0.478  1.0
  O  O22  1  0.223  0.478  0.235  1.0
  O  O23  1  0.277  0.765  0.522  1.0
  O  O24  1  0.112  0.177  0.057  1.0
  O  O25  1  0.388  0.943  0.823  1.0
  O  O26  1  0.888  0.823  0.943  1.0
  O  O27  1  0.612  0.057  0.177  1.0
  O  O28  1  0.601  0.673  0.582  1.0
  O  O29  1  0.899  0.418  0.327  1.0
  O  O30  1  0.399  0.327  0.418  1.0
  O  O31  1  0.101  0.582  0.673  1.0
  O  O32  1  1.000  0.919  0.180  1.0
  O  O33  1  0.500  0.820  0.081  1.0
  O  O34  1  0.000  0.081  0.820  1.0
  O  O35  1  0.500  0.180  0.919  1.0
  O  O36  1  0.511  0.425  0.684  1.0
  O  O37  1  0.989  0.316  0.575  1.0
  O  O38  1  0.489  0.575  0.316  1.0
  O  O39  1  0.011  0.684  0.425  1.0
  Pb  Pb40  1  0.306  0.416  0.936  1.0
  Pb  Pb41  1  0.194  0.064  0.584  1.0
  Pb  Pb42  1  0.694  0.584  0.064  1.0
  Pb  Pb43  1  0.806  0.936  0.416  1.0
  Si  Si44  1  0.600  0.565  0.716  1.0
  Si  Si45  1  0.900  0.284  0.435  1.0
  Si  Si46  1  0.400  0.435  0.284  1.0
  Si  Si47  1  0.100  0.716  0.565  1.0
  Si  Si48  1  0.488  0.939  0.212  1.0
  Si  Si49  1  0.012  0.788  0.061  1.0
  Si  Si50  1  0.512  0.061  0.788  1.0
  Si  Si51  1  0.988  0.212  0.939  1.0
[/CIF]
.
The material described by PbAl2Si2O8 crystallizes in the monoclinic P2_1/c space group. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(13), one O(5), and one O(9) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Si(4)O4 tetrahedra. In the second Al site, Al(2) is bonded to one O(10), one O(14), one O(2), and one O(6) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, and corners with two equivalent Si(3)O4 tetrahedra. In the third Al site, Al(3) is bonded to one O(12), one O(16), one O(3), and one O(7) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. In the fourth Al site, Al(4) is bonded to one O(11), one O(15), one O(4), and one O(8) atom to form AlO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(4)O4 tetrahedra, and corners with two equivalent Si(1)O4 tetrahedra. There are two inequivalent Pb sites. In the first Pb site, Pb(1) is bonded in a 5-coordinate geometry to one O(1), one O(13), one O(15), one O(2), and one O(3) atom. In the second Pb site, Pb(2) is bonded in a 6-coordinate geometry to one O(1), one O(14), one O(16), one O(2), one O(4), and one O(7) atom. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(11), one O(15), one O(2), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Al(3)O4 tetrahedra, and corners with two equivalent Al(4)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(1), one O(12), one O(16), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(4)O4 tetrahedra, and corners with two equivalent Al(3)O4 tetrahedra. In the third Si site, Si(3) is bonded to one O(10), one O(14), one O(3), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(1)O4 tetrahedra,  a cornercorner with one Al(3)O4 tetrahedra, and corners with two equivalent Al(2)O4 tetrahedra. In the fourth Si site, Si(4) is bonded to one O(13), one O(4), one O(6), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Al(2)O4 tetrahedra,  a cornercorner with one Al(4)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. There are sixteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Al(1), one Pb(1), one Pb(2), and one Si(2) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Al(2), one Pb(1), one Pb(2), and one Si(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Al(3), one Pb(1), and one Si(3) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Al(4), one Pb(2), and one Si(4) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(3) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Al(2) and one Si(4) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Al(3), one Pb(2), and one Si(1) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Al(4) and one Si(2) atom. In the ninth O site, O(9) is bonded in a bent 120 degrees geometry to one Al(1) and one Si(4) atom. In the tenth O site, O(10) is bonded in a distorted bent 120 degrees geometry to one Al(2) and one Si(3) atom. In the eleventh O site, O(11) is bonded in a distorted bent 120 degrees geometry to one Al(4) and one Si(1) atom. In the twelfth O site, O(12) is bonded in a bent 120 degrees geometry to one Al(3) and one Si(2) atom. In the thirteenth O site, O(13) is bonded in a 2-coordinate geometry to one Al(1), one Pb(1), and one Si(4) atom. In the fourteenth O site, O(14) is bonded in a 2-coordinate geometry to one Al(2), one Pb(2), and one Si(3) atom. In the fifteenth O site, O(15) is bonded in a distorted bent 150 degrees geometry to one Al(4), one Pb(1), and one Si(1) atom. In the sixteenth O site, O(16) is bonded in a distorted bent 150 degrees geometry to one Al(3), one Pb(2), and one Si(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Al2Si2PbO8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.497
_cell_length_b   9.403
_cell_length_c   9.403
_cell_angle_alpha   89.614
_cell_angle_beta   82.874
_cell_angle_gamma   82.874
_symmetry_Int_Tables_number   1
_cell_volume   739.691
_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  0.114  0.062  0.204  1.0
  Al  Al1  1  0.386  0.796  0.938  1.0
  Al  Al2  1  0.886  0.938  0.796  1.0
  Al  Al3  1  0.614  0.204  0.062  1.0
  Al  Al4  1  0.975  0.449  0.709  1.0
  Al  Al5  1  0.525  0.291  0.551  1.0
  Al  Al6  1  0.025  0.551  0.291  1.0
  Al  Al7  1  0.475  0.709  0.449  1.0
  O  O8  1  0.006  0.134  0.367  1.0
  O  O9  1  0.494  0.633  0.866  1.0
  O  O10  1  0.994  0.866  0.633  1.0
  O  O11  1  0.506  0.367  0.134  1.0
  O  O12  1  0.552  0.855  0.353  1.0
  O  O13  1  0.948  0.647  0.145  1.0
  O  O14  1  0.448  0.145  0.647  1.0
  O  O15  1  0.052  0.353  0.855  1.0
  O  O16  1  0.304  0.009  0.251  1.0
  O  O17  1  0.196  0.749  0.991  1.0
  O  O18  1  0.696  0.991  0.749  1.0
  O  O19  1  0.804  0.251  0.009  1.0
  O  O20  1  0.777  0.522  0.765  1.0
  O  O21  1  0.723  0.235  0.478  1.0
  O  O22  1  0.223  0.478  0.235  1.0
  O  O23  1  0.277  0.765  0.522  1.0
  O  O24  1  0.112  0.177  0.057  1.0
  O  O25  1  0.388  0.943  0.823  1.0
  O  O26  1  0.888  0.823  0.943  1.0
  O  O27  1  0.612  0.057  0.177  1.0
  O  O28  1  0.601  0.673  0.582  1.0
  O  O29  1  0.899  0.418  0.327  1.0
  O  O30  1  0.399  0.327  0.418  1.0
  O  O31  1  0.101  0.582  0.673  1.0
  O  O32  1  1.000  0.919  0.180  1.0
  O  O33  1  0.500  0.820  0.081  1.0
  O  O34  1  0.000  0.081  0.820  1.0
  O  O35  1  0.500  0.180  0.919  1.0
  O  O36  1  0.511  0.425  0.684  1.0
  O  O37  1  0.989  0.316  0.575  1.0
  O  O38  1  0.489  0.575  0.316  1.0
  O  O39  1  0.011  0.684  0.425  1.0
  Pb  Pb40  1  0.306  0.416  0.936  1.0
  Pb  Pb41  1  0.194  0.064  0.584  1.0
  Pb  Pb42  1  0.694  0.584  0.064  1.0
  Pb  Pb43  1  0.806  0.936  0.416  1.0
  Si  Si44  1  0.600  0.565  0.716  1.0
  Si  Si45  1  0.900  0.284  0.435  1.0
  Si  Si46  1  0.400  0.435  0.284  1.0
  Si  Si47  1  0.100  0.716  0.565  1.0
  Si  Si48  1  0.488  0.939  0.212  1.0
  Si  Si49  1  0.012  0.788  0.061  1.0
  Si  Si50  1  0.512  0.061  0.788  1.0
  Si  Si51  1  0.988  0.212  0.939  1.0
[/CIF]
.