The compound described by Er4LaSe7 crystallizes in the monoclinic Cm space group. There are four inequivalent Er sites. In the first Er site, Er(1) is bonded to one Se(2), one Se(6), two equivalent Se(5), and two equivalent Se(7) atoms to form ErSe6 octahedra that share  a cornercorner with one Er(2)Se6 octahedra, corners with two equivalent La(1)Se6 octahedra, corners with two equivalent Er(3)Se7 pentagonal bipyramids, corners with four equivalent Er(4)Se7 pentagonal bipyramids, edges with two equivalent Er(1)Se6 octahedra, edges with three equivalent La(1)Se6 octahedra, and  an edgeedge with one Er(4)Se7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 3-57°. In the second Er site, Er(2) is bonded to one Se(1), one Se(2), two equivalent Se(3), and two equivalent Se(4) atoms to form ErSe6 octahedra that share  a cornercorner with one Er(1)Se6 octahedra,  a cornercorner with one La(1)Se6 octahedra, corners with two equivalent Er(3)Se7 pentagonal bipyramids, corners with two equivalent Er(4)Se7 pentagonal bipyramids, edges with two equivalent Er(2)Se6 octahedra, edges with three equivalent Er(3)Se7 pentagonal bipyramids, and edges with three equivalent Er(4)Se7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 57°. In the third Er site, Er(3) is bonded to one Se(4), two equivalent Se(1), two equivalent Se(3), and two equivalent Se(6) atoms to form distorted ErSe7 pentagonal bipyramids that share corners with two equivalent Er(1)Se6 octahedra, corners with two equivalent Er(2)Se6 octahedra, corners with four equivalent La(1)Se6 octahedra,  an edgeedge with one La(1)Se6 octahedra, edges with three equivalent Er(2)Se6 octahedra, edges with two equivalent Er(4)Se7 pentagonal bipyramids, and faces with two equivalent Er(3)Se7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 22-64°. In the fourth Er site, Er(4) is bonded to one Se(3), two equivalent Se(2), two equivalent Se(4), and two equivalent Se(5) atoms to form distorted ErSe7 pentagonal bipyramids that share corners with two equivalent Er(2)Se6 octahedra, corners with two equivalent La(1)Se6 octahedra, corners with four equivalent Er(1)Se6 octahedra,  an edgeedge with one Er(1)Se6 octahedra, edges with three equivalent Er(2)Se6 octahedra, edges with two equivalent Er(3)Se7 pentagonal bipyramids, and faces with two equivalent Er(4)Se7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 22-69°. La(1) is bonded to one Se(1), one Se(5), two equivalent Se(6), and two equivalent Se(7) atoms to form LaSe6 octahedra that share  a cornercorner with one Er(2)Se6 octahedra, corners with two equivalent Er(1)Se6 octahedra, corners with two equivalent Er(4)Se7 pentagonal bipyramids, corners with four equivalent Er(3)Se7 pentagonal bipyramids, edges with two equivalent La(1)Se6 octahedra, edges with three equivalent Er(1)Se6 octahedra, and  an edgeedge with one Er(3)Se7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 3-57°. There are seven inequivalent Se sites. In the first Se site, Se(1) is bonded to one Er(2), two equivalent Er(3), and one La(1) atom to form SeLaEr3 tetrahedra that share  a cornercorner with one Se(2)Er4 tetrahedra, corners with two equivalent Se(1)LaEr3 tetrahedra,  a cornercorner with one Se(5)LaEr4 trigonal bipyramid, corners with four equivalent Se(3)Er5 trigonal bipyramids, corners with four equivalent Se(6)La2Er3 trigonal bipyramids,  an edgeedge with one Se(3)Er5 trigonal bipyramid,  an edgeedge with one Se(6)La2Er3 trigonal bipyramid, and edges with two equivalent Se(4)Er5 trigonal bipyramids. In the second Se site, Se(2) is bonded to one Er(1), one Er(2), and two equivalent Er(4) atoms to form distorted SeEr4 tetrahedra that share  a cornercorner with one Se(1)LaEr3 tetrahedra, corners with two equivalent Se(2)Er4 tetrahedra,  a cornercorner with one Se(6)La2Er3 trigonal bipyramid, corners with four equivalent Se(4)Er5 trigonal bipyramids, corners with four equivalent Se(5)LaEr4 trigonal bipyramids,  an edgeedge with one Se(4)Er5 trigonal bipyramid,  an edgeedge with one Se(5)LaEr4 trigonal bipyramid, and edges with two equivalent Se(3)Er5 trigonal bipyramids. In the third Se site, Se(3) is bonded to one Er(4), two equivalent Er(2), and two equivalent Er(3) atoms to form distorted SeEr5 trigonal bipyramids that share corners with four equivalent Se(1)LaEr3 tetrahedra, corners with two equivalent Se(4)Er5 trigonal bipyramids, corners with two equivalent Se(6)La2Er3 trigonal bipyramids, corners with two equivalent Se(5)LaEr4 trigonal bipyramids,  an edgeedge with one Se(1)LaEr3 tetrahedra, edges with two equivalent Se(2)Er4 tetrahedra,  an edgeedge with one Se(6)La2Er3 trigonal bipyramid, edges with two equivalent Se(3)Er5 trigonal bipyramids, and edges with three equivalent Se(4)Er5 trigonal bipyramids. In the fourth Se site, Se(4) is bonded to one Er(3), two equivalent Er(2), and two equivalent Er(4) atoms to form distorted SeEr5 trigonal bipyramids that share corners with four equivalent Se(2)Er4 tetrahedra, corners with two equivalent Se(3)Er5 trigonal bipyramids, corners with two equivalent Se(6)La2Er3 trigonal bipyramids, corners with two equivalent Se(5)LaEr4 trigonal bipyramids,  an edgeedge with one Se(2)Er4 tetrahedra, edges with two equivalent Se(1)LaEr3 tetrahedra,  an edgeedge with one Se(5)LaEr4 trigonal bipyramid, edges with two equivalent Se(4)Er5 trigonal bipyramids, and edges with three equivalent Se(3)Er5 trigonal bipyramids. In the fifth Se site, Se(5) is bonded to two equivalent Er(1), two equivalent Er(4), and one La(1) atom to form SeLaEr4 trigonal bipyramids that share  a cornercorner with one Se(1)LaEr3 tetrahedra, corners with four equivalent Se(2)Er4 tetrahedra, corners with two equivalent Se(3)Er5 trigonal bipyramids, corners with two equivalent Se(4)Er5 trigonal bipyramids,  an edgeedge with one Se(2)Er4 tetrahedra,  an edgeedge with one Se(4)Er5 trigonal bipyramid, edges with two equivalent Se(6)La2Er3 trigonal bipyramids, and edges with two equivalent Se(5)LaEr4 trigonal bipyramids. In the sixth Se site, Se(6) is bonded to one Er(1), two equivalent Er(3), and two equivalent La(1) atoms to form SeLa2Er3 trigonal bipyramids that share  a cornercorner with one Se(2)Er4 tetrahedra, corners with four equivalent Se(1)LaEr3 tetrahedra, corners with two equivalent Se(3)Er5 trigonal bipyramids, corners with two equivalent Se(4)Er5 trigonal bipyramids,  an edgeedge with one Se(1)LaEr3 tetrahedra,  an edgeedge with one Se(3)Er5 trigonal bipyramid, edges with two equivalent Se(6)La2Er3 trigonal bipyramids, and edges with two equivalent Se(5)LaEr4 trigonal bipyramids. In the seventh Se site, Se(7) is bonded in a rectangular see-saw-like geometry to two equivalent Er(1) and two equivalent La(1) atoms. is represented by the CIF file [CIF]
data_LaEr4Se7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.975
_cell_length_b   7.059
_cell_length_c   12.235
_cell_angle_alpha   103.862
_cell_angle_beta   90.000
_cell_angle_gamma   73.646
_symmetry_Int_Tables_number   1
_cell_volume   318.955
_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
  La  La0  1  0.888  0.225  0.422  1.0
  Er  Er1  1  0.113  0.774  0.582  1.0
  Er  Er2  1  0.000  0.999  0.998  1.0
  Er  Er3  1  0.700  0.600  0.186  1.0
  Er  Er4  1  0.300  0.399  0.814  1.0
  Se  Se5  1  0.046  0.907  0.207  1.0
  Se  Se6  1  0.958  0.085  0.785  1.0
  Se  Se7  1  0.342  0.316  0.049  1.0
  Se  Se8  1  0.660  0.680  0.950  1.0
  Se  Se9  1  0.736  0.529  0.655  1.0
  Se  Se10  1  0.250  0.500  0.348  1.0
  Se  Se11  1  0.507  0.985  0.505  1.0
[/CIF]
.
The compound described by Er4LaSe7 crystallizes in the monoclinic Cm space group. There are four inequivalent Er sites. In the first Er site, Er(1) is bonded to one Se(2), one Se(6), two equivalent Se(5), and two equivalent Se(7) atoms to form ErSe6 octahedra that share  a cornercorner with one Er(2)Se6 octahedra, corners with two equivalent La(1)Se6 octahedra, corners with two equivalent Er(3)Se7 pentagonal bipyramids, corners with four equivalent Er(4)Se7 pentagonal bipyramids, edges with two equivalent Er(1)Se6 octahedra, edges with three equivalent La(1)Se6 octahedra, and  an edgeedge with one Er(4)Se7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 3-57°. In the second Er site, Er(2) is bonded to one Se(1), one Se(2), two equivalent Se(3), and two equivalent Se(4) atoms to form ErSe6 octahedra that share  a cornercorner with one Er(1)Se6 octahedra,  a cornercorner with one La(1)Se6 octahedra, corners with two equivalent Er(3)Se7 pentagonal bipyramids, corners with two equivalent Er(4)Se7 pentagonal bipyramids, edges with two equivalent Er(2)Se6 octahedra, edges with three equivalent Er(3)Se7 pentagonal bipyramids, and edges with three equivalent Er(4)Se7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 57°. In the third Er site, Er(3) is bonded to one Se(4), two equivalent Se(1), two equivalent Se(3), and two equivalent Se(6) atoms to form distorted ErSe7 pentagonal bipyramids that share corners with two equivalent Er(1)Se6 octahedra, corners with two equivalent Er(2)Se6 octahedra, corners with four equivalent La(1)Se6 octahedra,  an edgeedge with one La(1)Se6 octahedra, edges with three equivalent Er(2)Se6 octahedra, edges with two equivalent Er(4)Se7 pentagonal bipyramids, and faces with two equivalent Er(3)Se7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 22-64°. In the fourth Er site, Er(4) is bonded to one Se(3), two equivalent Se(2), two equivalent Se(4), and two equivalent Se(5) atoms to form distorted ErSe7 pentagonal bipyramids that share corners with two equivalent Er(2)Se6 octahedra, corners with two equivalent La(1)Se6 octahedra, corners with four equivalent Er(1)Se6 octahedra,  an edgeedge with one Er(1)Se6 octahedra, edges with three equivalent Er(2)Se6 octahedra, edges with two equivalent Er(3)Se7 pentagonal bipyramids, and faces with two equivalent Er(4)Se7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 22-69°. La(1) is bonded to one Se(1), one Se(5), two equivalent Se(6), and two equivalent Se(7) atoms to form LaSe6 octahedra that share  a cornercorner with one Er(2)Se6 octahedra, corners with two equivalent Er(1)Se6 octahedra, corners with two equivalent Er(4)Se7 pentagonal bipyramids, corners with four equivalent Er(3)Se7 pentagonal bipyramids, edges with two equivalent La(1)Se6 octahedra, edges with three equivalent Er(1)Se6 octahedra, and  an edgeedge with one Er(3)Se7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 3-57°. There are seven inequivalent Se sites. In the first Se site, Se(1) is bonded to one Er(2), two equivalent Er(3), and one La(1) atom to form SeLaEr3 tetrahedra that share  a cornercorner with one Se(2)Er4 tetrahedra, corners with two equivalent Se(1)LaEr3 tetrahedra,  a cornercorner with one Se(5)LaEr4 trigonal bipyramid, corners with four equivalent Se(3)Er5 trigonal bipyramids, corners with four equivalent Se(6)La2Er3 trigonal bipyramids,  an edgeedge with one Se(3)Er5 trigonal bipyramid,  an edgeedge with one Se(6)La2Er3 trigonal bipyramid, and edges with two equivalent Se(4)Er5 trigonal bipyramids. In the second Se site, Se(2) is bonded to one Er(1), one Er(2), and two equivalent Er(4) atoms to form distorted SeEr4 tetrahedra that share  a cornercorner with one Se(1)LaEr3 tetrahedra, corners with two equivalent Se(2)Er4 tetrahedra,  a cornercorner with one Se(6)La2Er3 trigonal bipyramid, corners with four equivalent Se(4)Er5 trigonal bipyramids, corners with four equivalent Se(5)LaEr4 trigonal bipyramids,  an edgeedge with one Se(4)Er5 trigonal bipyramid,  an edgeedge with one Se(5)LaEr4 trigonal bipyramid, and edges with two equivalent Se(3)Er5 trigonal bipyramids. In the third Se site, Se(3) is bonded to one Er(4), two equivalent Er(2), and two equivalent Er(3) atoms to form distorted SeEr5 trigonal bipyramids that share corners with four equivalent Se(1)LaEr3 tetrahedra, corners with two equivalent Se(4)Er5 trigonal bipyramids, corners with two equivalent Se(6)La2Er3 trigonal bipyramids, corners with two equivalent Se(5)LaEr4 trigonal bipyramids,  an edgeedge with one Se(1)LaEr3 tetrahedra, edges with two equivalent Se(2)Er4 tetrahedra,  an edgeedge with one Se(6)La2Er3 trigonal bipyramid, edges with two equivalent Se(3)Er5 trigonal bipyramids, and edges with three equivalent Se(4)Er5 trigonal bipyramids. In the fourth Se site, Se(4) is bonded to one Er(3), two equivalent Er(2), and two equivalent Er(4) atoms to form distorted SeEr5 trigonal bipyramids that share corners with four equivalent Se(2)Er4 tetrahedra, corners with two equivalent Se(3)Er5 trigonal bipyramids, corners with two equivalent Se(6)La2Er3 trigonal bipyramids, corners with two equivalent Se(5)LaEr4 trigonal bipyramids,  an edgeedge with one Se(2)Er4 tetrahedra, edges with two equivalent Se(1)LaEr3 tetrahedra,  an edgeedge with one Se(5)LaEr4 trigonal bipyramid, edges with two equivalent Se(4)Er5 trigonal bipyramids, and edges with three equivalent Se(3)Er5 trigonal bipyramids. In the fifth Se site, Se(5) is bonded to two equivalent Er(1), two equivalent Er(4), and one La(1) atom to form SeLaEr4 trigonal bipyramids that share  a cornercorner with one Se(1)LaEr3 tetrahedra, corners with four equivalent Se(2)Er4 tetrahedra, corners with two equivalent Se(3)Er5 trigonal bipyramids, corners with two equivalent Se(4)Er5 trigonal bipyramids,  an edgeedge with one Se(2)Er4 tetrahedra,  an edgeedge with one Se(4)Er5 trigonal bipyramid, edges with two equivalent Se(6)La2Er3 trigonal bipyramids, and edges with two equivalent Se(5)LaEr4 trigonal bipyramids. In the sixth Se site, Se(6) is bonded to one Er(1), two equivalent Er(3), and two equivalent La(1) atoms to form SeLa2Er3 trigonal bipyramids that share  a cornercorner with one Se(2)Er4 tetrahedra, corners with four equivalent Se(1)LaEr3 tetrahedra, corners with two equivalent Se(3)Er5 trigonal bipyramids, corners with two equivalent Se(4)Er5 trigonal bipyramids,  an edgeedge with one Se(1)LaEr3 tetrahedra,  an edgeedge with one Se(3)Er5 trigonal bipyramid, edges with two equivalent Se(6)La2Er3 trigonal bipyramids, and edges with two equivalent Se(5)LaEr4 trigonal bipyramids. In the seventh Se site, Se(7) is bonded in a rectangular see-saw-like geometry to two equivalent Er(1) and two equivalent La(1) atoms. is represented by the CIF file [CIF]
data_LaEr4Se7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.975
_cell_length_b   7.059
_cell_length_c   12.235
_cell_angle_alpha   103.862
_cell_angle_beta   90.000
_cell_angle_gamma   73.646
_symmetry_Int_Tables_number   1
_cell_volume   318.955
_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
  La  La0  1  0.888  0.225  0.422  1.0
  Er  Er1  1  0.113  0.774  0.582  1.0
  Er  Er2  1  0.000  0.999  0.998  1.0
  Er  Er3  1  0.700  0.600  0.186  1.0
  Er  Er4  1  0.300  0.399  0.814  1.0
  Se  Se5  1  0.046  0.907  0.207  1.0
  Se  Se6  1  0.958  0.085  0.785  1.0
  Se  Se7  1  0.342  0.316  0.049  1.0
  Se  Se8  1  0.660  0.680  0.950  1.0
  Se  Se9  1  0.736  0.529  0.655  1.0
  Se  Se10  1  0.250  0.500  0.348  1.0
  Se  Se11  1  0.507  0.985  0.505  1.0
[/CIF]
.