The material described by Mg3Cu2(Si2O7)2 crystallizes in the monoclinic C2/c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(1), one O(2), one O(4), and two equivalent O(7) atoms to form MgO5 square pyramids that share  a cornercorner with one Cu(2)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with three equivalent Si(1)O4 tetrahedra,  a cornercorner with one Mg(2)O4 trigonal pyramid,  an edgeedge with one Cu(2)O6 octahedra, and  an edgeedge with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles are 45°. In the second Mg site, Mg(2) is bonded to two equivalent O(1) and two equivalent O(3) atoms to form distorted MgO4 trigonal pyramids that share corners with two equivalent Cu(2)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, and corners with four equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 59°. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a distorted rectangular see-saw-like geometry to two equivalent O(2) and two equivalent O(3) atoms. In the second Cu site, Cu(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form distorted CuO6 octahedra that share corners with two equivalent Mg(1)O5 square pyramids, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Mg(2)O4 trigonal pyramids, and edges with two equivalent Mg(1)O5 square pyramids. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Cu(2)O6 octahedra, corners with three equivalent Mg(1)O5 square pyramids, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 51°. In the second Si site, Si(2) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Cu(2)O6 octahedra,  a cornercorner with one Mg(1)O5 square pyramid, corners with two equivalent Si(1)O4 tetrahedra, and corners with two equivalent Mg(2)O4 trigonal pyramids. The corner-sharing octahedral tilt angles are 75°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Mg(1), one Mg(2), one Cu(2), and one Si(2) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cu(1), and one Cu(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(2), one Cu(1), and one Si(2) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Mg(1), one Cu(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Mg(1) and one Si(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Mg3Cu2(Si2O7)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.411
_cell_length_b   9.411
_cell_length_c   9.951
_cell_angle_alpha   58.143
_cell_angle_beta   58.143
_cell_angle_gamma   47.869
_symmetry_Int_Tables_number   1
_cell_volume   533.597
_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
  Mg  Mg0  1  0.260  0.070  0.548  1.0
  Mg  Mg1  1  0.930  0.740  0.952  1.0
  Mg  Mg2  1  0.070  0.260  0.048  1.0
  Mg  Mg3  1  0.608  0.392  0.250  1.0
  Mg  Mg4  1  0.740  0.930  0.452  1.0
  Mg  Mg5  1  0.392  0.608  0.750  1.0
  Cu  Cu6  1  0.220  0.780  0.250  1.0
  Cu  Cu7  1  0.780  0.220  0.750  1.0
  Cu  Cu8  1  0.000  0.000  0.000  1.0
  Cu  Cu9  1  0.000  0.000  0.500  1.0
  Si  Si10  1  0.072  0.558  0.671  1.0
  Si  Si11  1  0.558  0.072  0.171  1.0
  Si  Si12  1  0.253  0.512  0.130  1.0
  Si  Si13  1  0.512  0.253  0.630  1.0
  Si  Si14  1  0.442  0.928  0.829  1.0
  Si  Si15  1  0.747  0.488  0.870  1.0
  Si  Si16  1  0.488  0.747  0.370  1.0
  Si  Si17  1  0.928  0.442  0.329  1.0
  O  O18  1  0.327  0.818  0.538  1.0
  O  O19  1  0.887  0.985  0.722  1.0
  O  O20  1  0.636  0.452  0.820  1.0
  O  O21  1  0.985  0.887  0.222  1.0
  O  O22  1  0.022  0.214  0.455  1.0
  O  O23  1  0.506  0.072  0.797  1.0
  O  O24  1  0.452  0.636  0.320  1.0
  O  O25  1  0.786  0.978  0.045  1.0
  O  O26  1  0.494  0.928  0.203  1.0
  O  O27  1  0.701  0.602  0.417  1.0
  O  O28  1  0.113  0.015  0.278  1.0
  O  O29  1  0.978  0.786  0.545  1.0
  O  O30  1  0.928  0.494  0.703  1.0
  O  O31  1  0.818  0.327  0.038  1.0
  O  O32  1  0.602  0.701  0.917  1.0
  O  O33  1  0.214  0.022  0.955  1.0
  O  O34  1  0.468  0.925  0.657  1.0
  O  O35  1  0.299  0.398  0.583  1.0
  O  O36  1  0.075  0.532  0.843  1.0
  O  O37  1  0.398  0.299  0.083  1.0
  O  O38  1  0.072  0.506  0.297  1.0
  O  O39  1  0.015  0.113  0.778  1.0
  O  O40  1  0.925  0.468  0.157  1.0
  O  O41  1  0.364  0.548  0.180  1.0
  O  O42  1  0.532  0.075  0.343  1.0
  O  O43  1  0.548  0.364  0.680  1.0
  O  O44  1  0.182  0.673  0.962  1.0
  O  O45  1  0.673  0.182  0.462  1.0
[/CIF]
.
The material described by Mg3Cu2(Si2O7)2 crystallizes in the monoclinic C2/c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(1), one O(2), one O(4), and two equivalent O(7) atoms to form MgO5 square pyramids that share  a cornercorner with one Cu(2)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with three equivalent Si(1)O4 tetrahedra,  a cornercorner with one Mg(2)O4 trigonal pyramid,  an edgeedge with one Cu(2)O6 octahedra, and  an edgeedge with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles are 45°. In the second Mg site, Mg(2) is bonded to two equivalent O(1) and two equivalent O(3) atoms to form distorted MgO4 trigonal pyramids that share corners with two equivalent Cu(2)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, and corners with four equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 59°. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a distorted rectangular see-saw-like geometry to two equivalent O(2) and two equivalent O(3) atoms. In the second Cu site, Cu(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form distorted CuO6 octahedra that share corners with two equivalent Mg(1)O5 square pyramids, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Mg(2)O4 trigonal pyramids, and edges with two equivalent Mg(1)O5 square pyramids. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Cu(2)O6 octahedra, corners with three equivalent Mg(1)O5 square pyramids, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 51°. In the second Si site, Si(2) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Cu(2)O6 octahedra,  a cornercorner with one Mg(1)O5 square pyramid, corners with two equivalent Si(1)O4 tetrahedra, and corners with two equivalent Mg(2)O4 trigonal pyramids. The corner-sharing octahedral tilt angles are 75°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Mg(1), one Mg(2), one Cu(2), and one Si(2) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cu(1), and one Cu(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(2), one Cu(1), and one Si(2) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Mg(1), one Cu(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Mg(1) and one Si(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Mg3Cu2(Si2O7)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.411
_cell_length_b   9.411
_cell_length_c   9.951
_cell_angle_alpha   58.143
_cell_angle_beta   58.143
_cell_angle_gamma   47.869
_symmetry_Int_Tables_number   1
_cell_volume   533.597
_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
  Mg  Mg0  1  0.260  0.070  0.548  1.0
  Mg  Mg1  1  0.930  0.740  0.952  1.0
  Mg  Mg2  1  0.070  0.260  0.048  1.0
  Mg  Mg3  1  0.608  0.392  0.250  1.0
  Mg  Mg4  1  0.740  0.930  0.452  1.0
  Mg  Mg5  1  0.392  0.608  0.750  1.0
  Cu  Cu6  1  0.220  0.780  0.250  1.0
  Cu  Cu7  1  0.780  0.220  0.750  1.0
  Cu  Cu8  1  0.000  0.000  0.000  1.0
  Cu  Cu9  1  0.000  0.000  0.500  1.0
  Si  Si10  1  0.072  0.558  0.671  1.0
  Si  Si11  1  0.558  0.072  0.171  1.0
  Si  Si12  1  0.253  0.512  0.130  1.0
  Si  Si13  1  0.512  0.253  0.630  1.0
  Si  Si14  1  0.442  0.928  0.829  1.0
  Si  Si15  1  0.747  0.488  0.870  1.0
  Si  Si16  1  0.488  0.747  0.370  1.0
  Si  Si17  1  0.928  0.442  0.329  1.0
  O  O18  1  0.327  0.818  0.538  1.0
  O  O19  1  0.887  0.985  0.722  1.0
  O  O20  1  0.636  0.452  0.820  1.0
  O  O21  1  0.985  0.887  0.222  1.0
  O  O22  1  0.022  0.214  0.455  1.0
  O  O23  1  0.506  0.072  0.797  1.0
  O  O24  1  0.452  0.636  0.320  1.0
  O  O25  1  0.786  0.978  0.045  1.0
  O  O26  1  0.494  0.928  0.203  1.0
  O  O27  1  0.701  0.602  0.417  1.0
  O  O28  1  0.113  0.015  0.278  1.0
  O  O29  1  0.978  0.786  0.545  1.0
  O  O30  1  0.928  0.494  0.703  1.0
  O  O31  1  0.818  0.327  0.038  1.0
  O  O32  1  0.602  0.701  0.917  1.0
  O  O33  1  0.214  0.022  0.955  1.0
  O  O34  1  0.468  0.925  0.657  1.0
  O  O35  1  0.299  0.398  0.583  1.0
  O  O36  1  0.075  0.532  0.843  1.0
  O  O37  1  0.398  0.299  0.083  1.0
  O  O38  1  0.072  0.506  0.297  1.0
  O  O39  1  0.015  0.113  0.778  1.0
  O  O40  1  0.925  0.468  0.157  1.0
  O  O41  1  0.364  0.548  0.180  1.0
  O  O42  1  0.532  0.075  0.343  1.0
  O  O43  1  0.548  0.364  0.680  1.0
  O  O44  1  0.182  0.673  0.962  1.0
  O  O45  1  0.673  0.182  0.462  1.0
[/CIF]
.