The compound described by Al4B2O9 crystallizes in the monoclinic P2/m space group. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to two equivalent O(1) and four equivalent O(5) atoms to form AlO6 octahedra that share corners with four equivalent Al(3)O4 tetrahedra, edges with two equivalent Al(1)O6 octahedra, and edges with four equivalent B(1)O4 trigonal pyramids. In the second Al site, Al(2) is bonded to two equivalent O(2) and four equivalent O(4) atoms to form AlO6 octahedra that share corners with four equivalent Al(3)O4 tetrahedra, corners with four equivalent B(1)O4 trigonal pyramids, and edges with two equivalent Al(2)O6 octahedra. In the third Al site, Al(3) is bonded to one O(3), one O(5), and two equivalent O(2) atoms to form AlO4 tetrahedra that share corners with two equivalent Al(1)O6 octahedra, corners with two equivalent Al(2)O6 octahedra, corners with three equivalent Al(3)O4 tetrahedra, and  a cornercorner with one B(1)O4 trigonal pyramid. The corner-sharing octahedral tilt angles range from 55-68°. B(1) is bonded to one O(4), one O(5), and two equivalent O(1) atoms to form distorted BO4 trigonal pyramids that share corners with two equivalent Al(2)O6 octahedra,  a cornercorner with one Al(3)O4 tetrahedra, corners with two equivalent B(1)O4 trigonal pyramids, and edges with two equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Al(1) and two equivalent B(1) atoms. In the second O site, O(2) is bonded in a trigonal non-coplanar geometry to one Al(2) and two equivalent Al(3) atoms. In the third O site, O(3) is bonded in a linear geometry to two equivalent Al(3) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to two equivalent Al(2) and one B(1) atom. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to one Al(3), two equivalent Al(1), and one B(1) atom. is represented by the CIF card [CIF]
data_Al4B2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   2.884
_cell_length_b   7.876
_cell_length_c   6.812
_cell_angle_alpha   99.376
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   152.642
_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
  Al  Al0  1  0.000  0.000  0.000  1.0
  Al  Al1  1  0.000  0.500  0.500  1.0
  Al  Al2  1  0.500  0.334  0.818  1.0
  Al  Al3  1  0.500  0.666  0.182  1.0
  B  B4  1  0.500  0.220  0.235  1.0
  B  B5  1  0.500  0.780  0.765  1.0
  O  O6  1  0.000  0.133  0.250  1.0
  O  O7  1  0.000  0.676  0.330  1.0
  O  O8  1  0.000  0.324  0.670  1.0
  O  O9  1  0.500  0.500  0.000  1.0
  O  O10  1  0.500  0.381  0.351  1.0
  O  O11  1  0.500  0.160  0.982  1.0
  O  O12  1  0.500  0.619  0.649  1.0
  O  O13  1  0.500  0.840  0.018  1.0
  O  O14  1  0.000  0.867  0.750  1.0
[/CIF]
.
The compound described by Al4B2O9 crystallizes in the monoclinic P2/m space group. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to two equivalent O(1) and four equivalent O(5) atoms to form AlO6 octahedra that share corners with four equivalent Al(3)O4 tetrahedra, edges with two equivalent Al(1)O6 octahedra, and edges with four equivalent B(1)O4 trigonal pyramids. In the second Al site, Al(2) is bonded to two equivalent O(2) and four equivalent O(4) atoms to form AlO6 octahedra that share corners with four equivalent Al(3)O4 tetrahedra, corners with four equivalent B(1)O4 trigonal pyramids, and edges with two equivalent Al(2)O6 octahedra. In the third Al site, Al(3) is bonded to one O(3), one O(5), and two equivalent O(2) atoms to form AlO4 tetrahedra that share corners with two equivalent Al(1)O6 octahedra, corners with two equivalent Al(2)O6 octahedra, corners with three equivalent Al(3)O4 tetrahedra, and  a cornercorner with one B(1)O4 trigonal pyramid. The corner-sharing octahedral tilt angles range from 55-68°. B(1) is bonded to one O(4), one O(5), and two equivalent O(1) atoms to form distorted BO4 trigonal pyramids that share corners with two equivalent Al(2)O6 octahedra,  a cornercorner with one Al(3)O4 tetrahedra, corners with two equivalent B(1)O4 trigonal pyramids, and edges with two equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Al(1) and two equivalent B(1) atoms. In the second O site, O(2) is bonded in a trigonal non-coplanar geometry to one Al(2) and two equivalent Al(3) atoms. In the third O site, O(3) is bonded in a linear geometry to two equivalent Al(3) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to two equivalent Al(2) and one B(1) atom. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to one Al(3), two equivalent Al(1), and one B(1) atom. is represented by the CIF card [CIF]
data_Al4B2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   2.884
_cell_length_b   7.876
_cell_length_c   6.812
_cell_angle_alpha   99.376
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   152.642
_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
  Al  Al0  1  0.000  0.000  0.000  1.0
  Al  Al1  1  0.000  0.500  0.500  1.0
  Al  Al2  1  0.500  0.334  0.818  1.0
  Al  Al3  1  0.500  0.666  0.182  1.0
  B  B4  1  0.500  0.220  0.235  1.0
  B  B5  1  0.500  0.780  0.765  1.0
  O  O6  1  0.000  0.133  0.250  1.0
  O  O7  1  0.000  0.676  0.330  1.0
  O  O8  1  0.000  0.324  0.670  1.0
  O  O9  1  0.500  0.500  0.000  1.0
  O  O10  1  0.500  0.381  0.351  1.0
  O  O11  1  0.500  0.160  0.982  1.0
  O  O12  1  0.500  0.619  0.649  1.0
  O  O13  1  0.500  0.840  0.018  1.0
  O  O14  1  0.000  0.867  0.750  1.0
[/CIF]
.