The compound described by Ni2Si(P2O7)2 crystallizes in the monoclinic C2/c space group. Ni(1) is bonded to one O(3), one O(6), two equivalent O(5), and two equivalent O(7) atoms to form NiO6 octahedra that share corners with two equivalent Ni(1)O6 octahedra, corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and  an edgeedge with one Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 59°. Si(1) is bonded to two equivalent O(1) and two equivalent O(4) atoms to form SiO4 tetrahedra that share corners with two equivalent P(1)O4 tetrahedra and corners with two equivalent P(2)O4 tetrahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(3), and one O(5) atom to form PO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-63°. In the second P site, P(2) is bonded to one O(2), one O(4), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 43-57°. There are seven inequivalent O sites. In the first O site, O(4) is bonded in a linear geometry to one Si(1) and one P(2) atom. In the second O site, O(5) is bonded in a trigonal planar geometry to two equivalent Ni(1) and one P(1) atom. In the third O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Ni(1) and one P(2) atom. In the fourth O site, O(7) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one P(2) atom. In the fifth O site, O(1) is bonded in a bent 150 degrees geometry to one Si(1) and one P(1) atom. In the sixth O site, O(2) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the seventh O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Ni(1) and one P(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_SiNi2(P2O7)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.886
_cell_length_b   8.886
_cell_length_c   12.340
_cell_angle_alpha   76.956
_cell_angle_beta   76.956
_cell_angle_gamma   32.508
_symmetry_Int_Tables_number   1
_cell_volume   508.971
_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
  Si  Si0  1  0.659  0.341  0.750  1.0
  Si  Si1  1  0.341  0.659  0.250  1.0
  Ni  Ni2  1  0.898  0.597  0.371  1.0
  Ni  Ni3  1  0.403  0.102  0.129  1.0
  Ni  Ni4  1  0.597  0.898  0.871  1.0
  Ni  Ni5  1  0.102  0.403  0.629  1.0
  P  P6  1  0.994  0.259  0.864  1.0
  P  P7  1  0.198  0.529  0.916  1.0
  P  P8  1  0.006  0.741  0.136  1.0
  P  P9  1  0.471  0.802  0.584  1.0
  P  P10  1  0.259  0.994  0.364  1.0
  P  P11  1  0.529  0.198  0.416  1.0
  P  P12  1  0.741  0.006  0.636  1.0
  P  P13  1  0.802  0.471  0.084  1.0
  O  O14  1  0.806  0.103  0.678  1.0
  O  O15  1  0.623  0.187  0.518  1.0
  O  O16  1  0.103  0.806  0.178  1.0
  O  O17  1  0.698  0.014  0.121  1.0
  O  O18  1  0.302  0.986  0.879  1.0
  O  O19  1  0.468  0.405  0.332  1.0
  O  O20  1  0.194  0.897  0.322  1.0
  O  O21  1  0.498  0.891  0.293  1.0
  O  O22  1  0.405  0.468  0.832  1.0
  O  O23  1  0.891  0.498  0.793  1.0
  O  O24  1  0.813  0.377  0.982  1.0
  O  O25  1  0.918  0.772  0.868  1.0
  O  O26  1  0.772  0.918  0.368  1.0
  O  O27  1  0.014  0.698  0.621  1.0
  O  O28  1  0.261  0.330  0.456  1.0
  O  O29  1  0.228  0.082  0.632  1.0
  O  O30  1  0.986  0.302  0.379  1.0
  O  O31  1  0.330  0.261  0.956  1.0
  O  O32  1  0.377  0.813  0.482  1.0
  O  O33  1  0.082  0.228  0.132  1.0
  O  O34  1  0.109  0.502  0.207  1.0
  O  O35  1  0.739  0.670  0.544  1.0
  O  O36  1  0.502  0.109  0.707  1.0
  O  O37  1  0.595  0.532  0.168  1.0
  O  O38  1  0.897  0.194  0.822  1.0
  O  O39  1  0.187  0.623  0.018  1.0
  O  O40  1  0.532  0.595  0.668  1.0
  O  O41  1  0.670  0.739  0.044  1.0
[/CIF]
.
The compound described by Ni2Si(P2O7)2 crystallizes in the monoclinic C2/c space group. Ni(1) is bonded to one O(3), one O(6), two equivalent O(5), and two equivalent O(7) atoms to form NiO6 octahedra that share corners with two equivalent Ni(1)O6 octahedra, corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and  an edgeedge with one Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 59°. Si(1) is bonded to two equivalent O(1) and two equivalent O(4) atoms to form SiO4 tetrahedra that share corners with two equivalent P(1)O4 tetrahedra and corners with two equivalent P(2)O4 tetrahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(3), and one O(5) atom to form PO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-63°. In the second P site, P(2) is bonded to one O(2), one O(4), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 43-57°. There are seven inequivalent O sites. In the first O site, O(4) is bonded in a linear geometry to one Si(1) and one P(2) atom. In the second O site, O(5) is bonded in a trigonal planar geometry to two equivalent Ni(1) and one P(1) atom. In the third O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Ni(1) and one P(2) atom. In the fourth O site, O(7) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one P(2) atom. In the fifth O site, O(1) is bonded in a bent 150 degrees geometry to one Si(1) and one P(1) atom. In the sixth O site, O(2) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the seventh O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Ni(1) and one P(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_SiNi2(P2O7)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.886
_cell_length_b   8.886
_cell_length_c   12.340
_cell_angle_alpha   76.956
_cell_angle_beta   76.956
_cell_angle_gamma   32.508
_symmetry_Int_Tables_number   1
_cell_volume   508.971
_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
  Si  Si0  1  0.659  0.341  0.750  1.0
  Si  Si1  1  0.341  0.659  0.250  1.0
  Ni  Ni2  1  0.898  0.597  0.371  1.0
  Ni  Ni3  1  0.403  0.102  0.129  1.0
  Ni  Ni4  1  0.597  0.898  0.871  1.0
  Ni  Ni5  1  0.102  0.403  0.629  1.0
  P  P6  1  0.994  0.259  0.864  1.0
  P  P7  1  0.198  0.529  0.916  1.0
  P  P8  1  0.006  0.741  0.136  1.0
  P  P9  1  0.471  0.802  0.584  1.0
  P  P10  1  0.259  0.994  0.364  1.0
  P  P11  1  0.529  0.198  0.416  1.0
  P  P12  1  0.741  0.006  0.636  1.0
  P  P13  1  0.802  0.471  0.084  1.0
  O  O14  1  0.806  0.103  0.678  1.0
  O  O15  1  0.623  0.187  0.518  1.0
  O  O16  1  0.103  0.806  0.178  1.0
  O  O17  1  0.698  0.014  0.121  1.0
  O  O18  1  0.302  0.986  0.879  1.0
  O  O19  1  0.468  0.405  0.332  1.0
  O  O20  1  0.194  0.897  0.322  1.0
  O  O21  1  0.498  0.891  0.293  1.0
  O  O22  1  0.405  0.468  0.832  1.0
  O  O23  1  0.891  0.498  0.793  1.0
  O  O24  1  0.813  0.377  0.982  1.0
  O  O25  1  0.918  0.772  0.868  1.0
  O  O26  1  0.772  0.918  0.368  1.0
  O  O27  1  0.014  0.698  0.621  1.0
  O  O28  1  0.261  0.330  0.456  1.0
  O  O29  1  0.228  0.082  0.632  1.0
  O  O30  1  0.986  0.302  0.379  1.0
  O  O31  1  0.330  0.261  0.956  1.0
  O  O32  1  0.377  0.813  0.482  1.0
  O  O33  1  0.082  0.228  0.132  1.0
  O  O34  1  0.109  0.502  0.207  1.0
  O  O35  1  0.739  0.670  0.544  1.0
  O  O36  1  0.502  0.109  0.707  1.0
  O  O37  1  0.595  0.532  0.168  1.0
  O  O38  1  0.897  0.194  0.822  1.0
  O  O39  1  0.187  0.623  0.018  1.0
  O  O40  1  0.532  0.595  0.668  1.0
  O  O41  1  0.670  0.739  0.044  1.0
[/CIF]
.