The crystal structure described by Li4FeP2O9 crystallizes in the monoclinic C2/m space group. There are four inequivalent Li sites. In the first Li site, Li(1) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms to form distorted LiO6 octahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, edges with two equivalent Li(1)O6 octahedra, and edges with two equivalent P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 59°. In the second Li site, Li(2) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(4), and two equivalent O(6) atoms. In the third Li site, Li(3) is bonded in a 5-coordinate geometry to one O(1), one O(5), one O(7), and two equivalent O(2) atoms. In the fourth Li site, Li(4) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(7) atoms to form distorted LiO6 octahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent P(2)O4 tetrahedra, edges with two equivalent Li(4)O6 octahedra, and edges with two equivalent P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 63°. Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(6) atoms to form FeO6 octahedra that share corners with two equivalent Li(1)O6 octahedra, corners with two equivalent Li(4)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, and corners with two equivalent P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-63°. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(3), one O(4), and two equivalent O(2) atoms to form PO4 tetrahedra that share corners with two equivalent Li(1)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Li(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-61°. In the second P site, P(2) is bonded to one O(5), one O(7), and two equivalent O(6) atoms to form PO4 tetrahedra that share corners with two equivalent Li(4)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Li(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-62°. There are seven inequivalent O sites. In the first O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Li(2), two equivalent Li(4), and one P(1) atom. In the second O site, O(5) is bonded in a rectangular see-saw-like geometry to one Li(3), two equivalent Li(1), and one P(2) atom. In the third O site, O(6) is bonded in a 4-coordinate geometry to one Li(1), one Li(2), one Fe(1), and one P(2) atom. In the fourth O site, O(7) is bonded in a distorted rectangular see-saw-like geometry to one Li(3), two equivalent Li(4), and one P(2) atom. In the fifth O site, O(1) is bonded to one Li(2), one Li(3), and two equivalent Fe(1) atoms to form distorted OLi2Fe2 tetrahedra that share corners with two equivalent O(1)Li2Fe2 tetrahedra and  a cornercorner with one O(3)Li3P trigonal pyramid. In the sixth O site, O(2) is bonded in a 4-coordinate geometry to one Li(3), one Li(4), one Fe(1), and one P(1) atom. In the seventh O site, O(3) is bonded to one Li(2), two equivalent Li(1), and one P(1) atom to form distorted OLi3P trigonal pyramids that share  a cornercorner with one O(1)Li2Fe2 tetrahedra and  an edgeedge with one O(3)Li3P trigonal pyramid. is represented by the CIF file [CIF]
data_Li4FeP2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.973
_cell_length_b   7.973
_cell_length_c   7.110
_cell_angle_alpha   89.316
_cell_angle_beta   89.316
_cell_angle_gamma   50.391
_symmetry_Int_Tables_number   1
_cell_volume   348.148
_cell_formula_units_Z   2
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
  Li  Li0  1  0.754  0.246  0.000  1.0
  Li  Li1  1  0.896  0.896  0.236  1.0
  Li  Li2  1  0.629  0.629  0.296  1.0
  Li  Li3  1  0.246  0.754  0.000  1.0
  Li  Li4  1  0.104  0.104  0.764  1.0
  Li  Li5  1  0.371  0.371  0.704  1.0
  Li  Li6  1  0.000  0.500  0.500  1.0
  Li  Li7  1  0.500  0.000  0.500  1.0
  Fe  Fe8  1  0.500  0.000  0.000  1.0
  Fe  Fe9  1  0.000  0.500  0.000  1.0
  P  P10  1  0.876  0.876  0.706  1.0
  P  P11  1  0.398  0.398  0.246  1.0
  P  P12  1  0.124  0.124  0.294  1.0
  P  P13  1  0.602  0.602  0.754  1.0
  O  O14  1  0.237  0.237  0.897  1.0
  O  O15  1  0.988  0.371  0.237  1.0
  O  O16  1  0.031  0.031  0.191  1.0
  O  O17  1  0.012  0.629  0.763  1.0
  O  O18  1  0.873  0.873  0.492  1.0
  O  O19  1  0.496  0.496  0.762  1.0
  O  O20  1  0.969  0.969  0.809  1.0
  O  O21  1  0.763  0.763  0.103  1.0
  O  O22  1  0.561  0.181  0.130  1.0
  O  O23  1  0.439  0.819  0.870  1.0
  O  O24  1  0.347  0.347  0.436  1.0
  O  O25  1  0.653  0.653  0.564  1.0
  O  O26  1  0.127  0.127  0.508  1.0
  O  O27  1  0.371  0.988  0.237  1.0
  O  O28  1  0.629  0.012  0.763  1.0
  O  O29  1  0.819  0.439  0.870  1.0
  O  O30  1  0.504  0.504  0.238  1.0
  O  O31  1  0.181  0.561  0.130  1.0
[/CIF]
.
The crystal structure described by Li4FeP2O9 crystallizes in the monoclinic C2/m space group. There are four inequivalent Li sites. In the first Li site, Li(1) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms to form distorted LiO6 octahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, edges with two equivalent Li(1)O6 octahedra, and edges with two equivalent P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 59°. In the second Li site, Li(2) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(4), and two equivalent O(6) atoms. In the third Li site, Li(3) is bonded in a 5-coordinate geometry to one O(1), one O(5), one O(7), and two equivalent O(2) atoms. In the fourth Li site, Li(4) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(7) atoms to form distorted LiO6 octahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent P(2)O4 tetrahedra, edges with two equivalent Li(4)O6 octahedra, and edges with two equivalent P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 63°. Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(6) atoms to form FeO6 octahedra that share corners with two equivalent Li(1)O6 octahedra, corners with two equivalent Li(4)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, and corners with two equivalent P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-63°. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(3), one O(4), and two equivalent O(2) atoms to form PO4 tetrahedra that share corners with two equivalent Li(1)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Li(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-61°. In the second P site, P(2) is bonded to one O(5), one O(7), and two equivalent O(6) atoms to form PO4 tetrahedra that share corners with two equivalent Li(4)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Li(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-62°. There are seven inequivalent O sites. In the first O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Li(2), two equivalent Li(4), and one P(1) atom. In the second O site, O(5) is bonded in a rectangular see-saw-like geometry to one Li(3), two equivalent Li(1), and one P(2) atom. In the third O site, O(6) is bonded in a 4-coordinate geometry to one Li(1), one Li(2), one Fe(1), and one P(2) atom. In the fourth O site, O(7) is bonded in a distorted rectangular see-saw-like geometry to one Li(3), two equivalent Li(4), and one P(2) atom. In the fifth O site, O(1) is bonded to one Li(2), one Li(3), and two equivalent Fe(1) atoms to form distorted OLi2Fe2 tetrahedra that share corners with two equivalent O(1)Li2Fe2 tetrahedra and  a cornercorner with one O(3)Li3P trigonal pyramid. In the sixth O site, O(2) is bonded in a 4-coordinate geometry to one Li(3), one Li(4), one Fe(1), and one P(1) atom. In the seventh O site, O(3) is bonded to one Li(2), two equivalent Li(1), and one P(1) atom to form distorted OLi3P trigonal pyramids that share  a cornercorner with one O(1)Li2Fe2 tetrahedra and  an edgeedge with one O(3)Li3P trigonal pyramid. is represented by the CIF file [CIF]
data_Li4FeP2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.973
_cell_length_b   7.973
_cell_length_c   7.110
_cell_angle_alpha   89.316
_cell_angle_beta   89.316
_cell_angle_gamma   50.391
_symmetry_Int_Tables_number   1
_cell_volume   348.148
_cell_formula_units_Z   2
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
  Li  Li0  1  0.754  0.246  0.000  1.0
  Li  Li1  1  0.896  0.896  0.236  1.0
  Li  Li2  1  0.629  0.629  0.296  1.0
  Li  Li3  1  0.246  0.754  0.000  1.0
  Li  Li4  1  0.104  0.104  0.764  1.0
  Li  Li5  1  0.371  0.371  0.704  1.0
  Li  Li6  1  0.000  0.500  0.500  1.0
  Li  Li7  1  0.500  0.000  0.500  1.0
  Fe  Fe8  1  0.500  0.000  0.000  1.0
  Fe  Fe9  1  0.000  0.500  0.000  1.0
  P  P10  1  0.876  0.876  0.706  1.0
  P  P11  1  0.398  0.398  0.246  1.0
  P  P12  1  0.124  0.124  0.294  1.0
  P  P13  1  0.602  0.602  0.754  1.0
  O  O14  1  0.237  0.237  0.897  1.0
  O  O15  1  0.988  0.371  0.237  1.0
  O  O16  1  0.031  0.031  0.191  1.0
  O  O17  1  0.012  0.629  0.763  1.0
  O  O18  1  0.873  0.873  0.492  1.0
  O  O19  1  0.496  0.496  0.762  1.0
  O  O20  1  0.969  0.969  0.809  1.0
  O  O21  1  0.763  0.763  0.103  1.0
  O  O22  1  0.561  0.181  0.130  1.0
  O  O23  1  0.439  0.819  0.870  1.0
  O  O24  1  0.347  0.347  0.436  1.0
  O  O25  1  0.653  0.653  0.564  1.0
  O  O26  1  0.127  0.127  0.508  1.0
  O  O27  1  0.371  0.988  0.237  1.0
  O  O28  1  0.629  0.012  0.763  1.0
  O  O29  1  0.819  0.439  0.870  1.0
  O  O30  1  0.504  0.504  0.238  1.0
  O  O31  1  0.181  0.561  0.130  1.0
[/CIF]
.