data_Ac3Tb
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.7
_cell_length_b   6.7
_cell_length_c   6.7
_cell_angle_alpha   131.5
_cell_angle_beta   131.5
_cell_angle_gamma   71.02
_symmetry_Int_Tables_number   1
_chemical_formula_structural   Ac3Tb
_chemical_formula_sum   'Ac3 Tb1'
_cell_volume   165.26
_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
  Ac  Ac0  1  0.0  0.0  0.45  1.0
  Ac  Ac1  1  0.0  0.75  0.73  1.0
  Ac  Ac2  1  0.75  0.0  0.73  1.0
  Tb  Tb3  1  0.0  0.0  0.0  1.0

data_Ac3Tb
_symmetry_space_group_name_H-M   Cm
_cell_length_a   7.78
_cell_length_b   7.78
_cell_length_c   6.7
_cell_angle_alpha   90.0
_cell_angle_beta   125.51
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   8
_chemical_formula_structural   Ac3Tb
_chemical_formula_sum   'Ac6 Tb2'
_cell_volume   330.52
_cell_formula_units_Z   2
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
  2  'x, -y, z'
  3  'x+1/2, y+1/2, z'
  4  'x+1/2, -y+1/2, 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
  Ac  Ac0  4  0.12  0.12  0.98  1.0
  Tb  Tb1  2  0.0  0.0  0.0  1.0
  Ac  Ac2  2  0.0  0.0  0.45  1.0

Ac Ac Ac Tb
Ac3Tb crystallizes in the monoclinic Cm space group. There are two inequivalent Ac sites. In the first Ac site, Ac(1) is bonded in a 5-coordinate geometry to four equivalent Ac(2) and one Tb(1) atom. There are two shorter (3.18 Å) and two longer (4.07 Å) Ac(1)-Ac(2) bond lengths. The Ac(1)-Tb(1) bond length is 3.05 Å. In the second Ac site, Ac(2) is bonded in a distorted single-bond geometry to two equivalent Ac(1) and one Tb(1) atom. The Ac(2)-Tb(1) bond length is 1.44 Å. Tb(1) is bonded in a distorted L-shaped geometry to one Ac(1) and two equivalent Ac(2) atoms.