The material structure described by Ca3Si2O7 crystallizes in the monoclinic P2_1/c space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(7), and two equivalent O(5) atoms. In the second Ca site, Ca(2) is bonded to one O(1), one O(2), one O(5), one O(6), one O(7), and two equivalent O(3) atoms to form distorted CaO7 pentagonal bipyramids that share  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra,  an edgeedge with one Ca(2)O7 pentagonal bipyramid,  an edgeedge with one Si(1)O4 tetrahedra, and  an edgeedge with one Si(2)O4 tetrahedra. In the third Ca site, Ca(3) is bonded in a 7-coordinate geometry to one O(2), one O(4), one O(7), two equivalent O(1), and two equivalent O(6) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share corners with two equivalent Ca(2)O7 pentagonal bipyramids,  a cornercorner with one Si(2)O4 tetrahedra, and  an edgeedge with one Ca(2)O7 pentagonal bipyramid. In the second Si site, Si(2) 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 Ca(2)O7 pentagonal bipyramid,  a cornercorner with one Si(1)O4 tetrahedra, and  an edgeedge with one Ca(2)O7 pentagonal bipyramid. There are seven inequivalent O sites. In the first O site, O(4) is bonded to one Ca(1), one Ca(3), one Si(1), and one Si(2) atom to form a mixture of distorted corner and edge-sharing OCa2Si2 trigonal pyramids. In the second O site, O(5) is bonded in a 4-coordinate geometry to one Ca(2), two equivalent Ca(1), and one Si(2) atom. In the third O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to one Ca(2), two equivalent Ca(3), and one Si(2) atom. In the fourth O site, O(7) is bonded to one Ca(1), one Ca(2), one Ca(3), and one Si(2) atom to form a mixture of distorted corner and edge-sharing OCa3Si trigonal pyramids. In the fifth O site, O(1) is bonded in a distorted single-bond geometry to one Ca(1), one Ca(2), two equivalent Ca(3), and one Si(1) atom. In the sixth O site, O(2) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Ca(3), and one Si(1) atom. In the seventh O site, O(3) is bonded in a 4-coordinate geometry to one Ca(1), two equivalent Ca(2), and one Si(1) atom. is represented by the CIF file [CIF]
data_Ca3Si2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.994
_cell_length_b   7.927
_cell_length_c   10.680
_cell_angle_alpha   60.672
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   663.827
_cell_formula_units_Z   4
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
  Ca  Ca0  1  0.594  0.286  0.157  1.0
  Ca  Ca1  1  0.094  0.714  0.343  1.0
  Ca  Ca2  1  0.406  0.714  0.843  1.0
  Ca  Ca3  1  0.906  0.286  0.657  1.0
  Ca  Ca4  1  0.925  0.208  0.331  1.0
  Ca  Ca5  1  0.425  0.792  0.169  1.0
  Ca  Ca6  1  0.075  0.792  0.669  1.0
  Ca  Ca7  1  0.575  0.208  0.831  1.0
  Ca  Ca8  1  0.440  0.290  0.492  1.0
  Ca  Ca9  1  0.940  0.710  0.008  1.0
  Ca  Ca10  1  0.560  0.710  0.508  1.0
  Ca  Ca11  1  0.060  0.290  0.992  1.0
  Si  Si12  1  0.284  0.985  0.411  1.0
  Si  Si13  1  0.784  0.015  0.089  1.0
  Si  Si14  1  0.716  0.015  0.589  1.0
  Si  Si15  1  0.216  0.985  0.911  1.0
  Si  Si16  1  0.267  0.433  0.204  1.0
  Si  Si17  1  0.767  0.567  0.296  1.0
  Si  Si18  1  0.733  0.567  0.796  1.0
  Si  Si19  1  0.233  0.433  0.704  1.0
  O  O20  1  0.335  0.938  0.573  1.0
  O  O21  1  0.835  0.062  0.927  1.0
  O  O22  1  0.665  0.062  0.427  1.0
  O  O23  1  0.165  0.938  0.073  1.0
  O  O24  1  0.360  0.843  0.359  1.0
  O  O25  1  0.860  0.157  0.141  1.0
  O  O26  1  0.640  0.157  0.641  1.0
  O  O27  1  0.140  0.843  0.859  1.0
  O  O28  1  0.104  0.973  0.401  1.0
  O  O29  1  0.604  0.027  0.099  1.0
  O  O30  1  0.896  0.027  0.599  1.0
  O  O31  1  0.396  0.973  0.901  1.0
  O  O32  1  0.346  0.210  0.297  1.0
  O  O33  1  0.846  0.790  0.203  1.0
  O  O34  1  0.654  0.790  0.703  1.0
  O  O35  1  0.154  0.210  0.797  1.0
  O  O36  1  0.398  0.548  0.089  1.0
  O  O37  1  0.898  0.452  0.411  1.0
  O  O38  1  0.602  0.452  0.911  1.0
  O  O39  1  0.102  0.548  0.589  1.0
  O  O40  1  0.397  0.420  0.643  1.0
  O  O41  1  0.897  0.580  0.857  1.0
  O  O42  1  0.603  0.580  0.357  1.0
  O  O43  1  0.103  0.420  0.143  1.0
  O  O44  1  0.239  0.509  0.821  1.0
  O  O45  1  0.739  0.491  0.679  1.0
  O  O46  1  0.761  0.491  0.179  1.0
  O  O47  1  0.261  0.509  0.321  1.0
[/CIF]
.
The material structure described by Ca3Si2O7 crystallizes in the monoclinic P2_1/c space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(7), and two equivalent O(5) atoms. In the second Ca site, Ca(2) is bonded to one O(1), one O(2), one O(5), one O(6), one O(7), and two equivalent O(3) atoms to form distorted CaO7 pentagonal bipyramids that share  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra,  an edgeedge with one Ca(2)O7 pentagonal bipyramid,  an edgeedge with one Si(1)O4 tetrahedra, and  an edgeedge with one Si(2)O4 tetrahedra. In the third Ca site, Ca(3) is bonded in a 7-coordinate geometry to one O(2), one O(4), one O(7), two equivalent O(1), and two equivalent O(6) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share corners with two equivalent Ca(2)O7 pentagonal bipyramids,  a cornercorner with one Si(2)O4 tetrahedra, and  an edgeedge with one Ca(2)O7 pentagonal bipyramid. In the second Si site, Si(2) 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 Ca(2)O7 pentagonal bipyramid,  a cornercorner with one Si(1)O4 tetrahedra, and  an edgeedge with one Ca(2)O7 pentagonal bipyramid. There are seven inequivalent O sites. In the first O site, O(4) is bonded to one Ca(1), one Ca(3), one Si(1), and one Si(2) atom to form a mixture of distorted corner and edge-sharing OCa2Si2 trigonal pyramids. In the second O site, O(5) is bonded in a 4-coordinate geometry to one Ca(2), two equivalent Ca(1), and one Si(2) atom. In the third O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to one Ca(2), two equivalent Ca(3), and one Si(2) atom. In the fourth O site, O(7) is bonded to one Ca(1), one Ca(2), one Ca(3), and one Si(2) atom to form a mixture of distorted corner and edge-sharing OCa3Si trigonal pyramids. In the fifth O site, O(1) is bonded in a distorted single-bond geometry to one Ca(1), one Ca(2), two equivalent Ca(3), and one Si(1) atom. In the sixth O site, O(2) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Ca(3), and one Si(1) atom. In the seventh O site, O(3) is bonded in a 4-coordinate geometry to one Ca(1), two equivalent Ca(2), and one Si(1) atom. is represented by the CIF file [CIF]
data_Ca3Si2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.994
_cell_length_b   7.927
_cell_length_c   10.680
_cell_angle_alpha   60.672
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   663.827
_cell_formula_units_Z   4
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
  Ca  Ca0  1  0.594  0.286  0.157  1.0
  Ca  Ca1  1  0.094  0.714  0.343  1.0
  Ca  Ca2  1  0.406  0.714  0.843  1.0
  Ca  Ca3  1  0.906  0.286  0.657  1.0
  Ca  Ca4  1  0.925  0.208  0.331  1.0
  Ca  Ca5  1  0.425  0.792  0.169  1.0
  Ca  Ca6  1  0.075  0.792  0.669  1.0
  Ca  Ca7  1  0.575  0.208  0.831  1.0
  Ca  Ca8  1  0.440  0.290  0.492  1.0
  Ca  Ca9  1  0.940  0.710  0.008  1.0
  Ca  Ca10  1  0.560  0.710  0.508  1.0
  Ca  Ca11  1  0.060  0.290  0.992  1.0
  Si  Si12  1  0.284  0.985  0.411  1.0
  Si  Si13  1  0.784  0.015  0.089  1.0
  Si  Si14  1  0.716  0.015  0.589  1.0
  Si  Si15  1  0.216  0.985  0.911  1.0
  Si  Si16  1  0.267  0.433  0.204  1.0
  Si  Si17  1  0.767  0.567  0.296  1.0
  Si  Si18  1  0.733  0.567  0.796  1.0
  Si  Si19  1  0.233  0.433  0.704  1.0
  O  O20  1  0.335  0.938  0.573  1.0
  O  O21  1  0.835  0.062  0.927  1.0
  O  O22  1  0.665  0.062  0.427  1.0
  O  O23  1  0.165  0.938  0.073  1.0
  O  O24  1  0.360  0.843  0.359  1.0
  O  O25  1  0.860  0.157  0.141  1.0
  O  O26  1  0.640  0.157  0.641  1.0
  O  O27  1  0.140  0.843  0.859  1.0
  O  O28  1  0.104  0.973  0.401  1.0
  O  O29  1  0.604  0.027  0.099  1.0
  O  O30  1  0.896  0.027  0.599  1.0
  O  O31  1  0.396  0.973  0.901  1.0
  O  O32  1  0.346  0.210  0.297  1.0
  O  O33  1  0.846  0.790  0.203  1.0
  O  O34  1  0.654  0.790  0.703  1.0
  O  O35  1  0.154  0.210  0.797  1.0
  O  O36  1  0.398  0.548  0.089  1.0
  O  O37  1  0.898  0.452  0.411  1.0
  O  O38  1  0.602  0.452  0.911  1.0
  O  O39  1  0.102  0.548  0.589  1.0
  O  O40  1  0.397  0.420  0.643  1.0
  O  O41  1  0.897  0.580  0.857  1.0
  O  O42  1  0.603  0.580  0.357  1.0
  O  O43  1  0.103  0.420  0.143  1.0
  O  O44  1  0.239  0.509  0.821  1.0
  O  O45  1  0.739  0.491  0.679  1.0
  O  O46  1  0.761  0.491  0.179  1.0
  O  O47  1  0.261  0.509  0.321  1.0
[/CIF]
.