The crystal structure described by NaCa6Ti(Si2O9)2 is Esseneite-derived structured and crystallizes in the triclinic P-1 space group. Na(1) is bonded to two equivalent O(1), two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms to form distorted NaO8 hexagonal bipyramids that share edges with two equivalent Ti(1)O6 octahedra, edges with two equivalent Si(1)O4 tetrahedra, and edges with two equivalent Si(2)O4 tetrahedra. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 6-coordinate geometry to one O(2), one O(6), one O(8), one O(9), and two equivalent O(4) atoms. In the second Ca site, Ca(2) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), two equivalent O(5), and two equivalent O(7) atoms. In the third Ca site, Ca(3) is bonded to one O(2), one O(4), one O(7), one O(8), and two equivalent O(9) atoms to form CaO6 octahedra that share  a cornercorner with one Ti(1)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Ca(3)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. Ti(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(7) atoms to form TiO6 octahedra that share corners with two equivalent Ca(3)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and edges with two equivalent Na(1)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 51°. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(3), one O(4), one O(6), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ti(1)O6 octahedra, corners with two equivalent Ca(3)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  an edgeedge with one Na(1)O8 hexagonal bipyramid. The corner-sharing octahedral tilt angles range from 32-53°. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(6), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Ti(1)O6 octahedra, corners with three equivalent Ca(3)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  an edgeedge with one Na(1)O8 hexagonal bipyramid. The corner-sharing octahedral tilt angles range from 33-56°. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Na(1), one Ca(2), one Ti(1), and one Si(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), one Ca(3), and one Si(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Na(1), one Ca(2), one Ti(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(3), two equivalent Ca(1), and one Si(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Na(1), two equivalent Ca(2), and one O(5) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Na(1), one Ca(1), one Si(1), and one Si(2) atom. In the seventh O site, O(7) is bonded to one Ca(3), two equivalent Ca(2), and one Ti(1) atom to form distorted OCa3Ti tetrahedra that share  a cornercorner with one O(7)Ca3Ti tetrahedra, corners with two equivalent O(9)Ca3Si trigonal pyramids, and  an edgeedge with one O(7)Ca3Ti tetrahedra. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Ca(1), one Ca(3), and one Si(1) atom. In the ninth O site, O(9) is bonded to one Ca(1), two equivalent Ca(3), and one Si(2) atom to form distorted OCa3Si trigonal pyramids that share corners with two equivalent O(7)Ca3Ti tetrahedra and  an edgeedge with one O(9)Ca3Si trigonal pyramid. is represented by the CIF file [CIF]
data_NaCa6Ti(Si2O9)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.708
_cell_length_b   7.602
_cell_length_c   9.814
_cell_angle_alpha   101.562
_cell_angle_beta   100.400
_cell_angle_gamma   89.726
_symmetry_Int_Tables_number   1
_cell_volume   410.144
_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
  Na  Na0  1  0.000  0.000  0.000  1.0
  Ca  Ca1  1  0.804  0.097  0.375  1.0
  Ca  Ca2  1  0.196  0.903  0.625  1.0
  Ca  Ca3  1  0.505  0.299  0.013  1.0
  Ca  Ca4  1  0.495  0.701  0.987  1.0
  Ca  Ca5  1  0.213  0.412  0.642  1.0
  Ca  Ca6  1  0.787  0.588  0.358  1.0
  Ti  Ti7  1  0.000  0.500  0.000  1.0
  Si  Si8  1  0.256  0.853  0.279  1.0
  Si  Si9  1  0.744  0.147  0.721  1.0
  Si  Si10  1  0.246  0.277  0.273  1.0
  Si  Si11  1  0.754  0.723  0.727  1.0
  O  O12  1  0.163  0.325  0.115  1.0
  O  O13  1  0.837  0.675  0.885  1.0
  O  O14  1  0.534  0.313  0.317  1.0
  O  O15  1  0.466  0.687  0.683  1.0
  O  O16  1  0.197  0.712  0.125  1.0
  O  O17  1  0.803  0.288  0.875  1.0
  O  O18  1  0.075  0.829  0.387  1.0
  O  O19  1  0.925  0.171  0.613  1.0
  O  O20  1  0.601  0.010  0.051  1.0
  O  O21  1  0.399  0.990  0.949  1.0
  O  O22  1  0.174  0.054  0.239  1.0
  O  O23  1  0.826  0.946  0.761  1.0
  O  O24  1  0.755  0.536  0.111  1.0
  O  O25  1  0.245  0.464  0.889  1.0
  O  O26  1  0.462  0.147  0.657  1.0
  O  O27  1  0.538  0.853  0.343  1.0
  O  O28  1  0.083  0.363  0.388  1.0
  O  O29  1  0.917  0.637  0.612  1.0
[/CIF]
.
The crystal structure described by NaCa6Ti(Si2O9)2 is Esseneite-derived structured and crystallizes in the triclinic P-1 space group. Na(1) is bonded to two equivalent O(1), two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms to form distorted NaO8 hexagonal bipyramids that share edges with two equivalent Ti(1)O6 octahedra, edges with two equivalent Si(1)O4 tetrahedra, and edges with two equivalent Si(2)O4 tetrahedra. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 6-coordinate geometry to one O(2), one O(6), one O(8), one O(9), and two equivalent O(4) atoms. In the second Ca site, Ca(2) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), two equivalent O(5), and two equivalent O(7) atoms. In the third Ca site, Ca(3) is bonded to one O(2), one O(4), one O(7), one O(8), and two equivalent O(9) atoms to form CaO6 octahedra that share  a cornercorner with one Ti(1)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Ca(3)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. Ti(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(7) atoms to form TiO6 octahedra that share corners with two equivalent Ca(3)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and edges with two equivalent Na(1)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 51°. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(3), one O(4), one O(6), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ti(1)O6 octahedra, corners with two equivalent Ca(3)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  an edgeedge with one Na(1)O8 hexagonal bipyramid. The corner-sharing octahedral tilt angles range from 32-53°. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(6), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Ti(1)O6 octahedra, corners with three equivalent Ca(3)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  an edgeedge with one Na(1)O8 hexagonal bipyramid. The corner-sharing octahedral tilt angles range from 33-56°. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Na(1), one Ca(2), one Ti(1), and one Si(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), one Ca(3), and one Si(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Na(1), one Ca(2), one Ti(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(3), two equivalent Ca(1), and one Si(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Na(1), two equivalent Ca(2), and one O(5) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Na(1), one Ca(1), one Si(1), and one Si(2) atom. In the seventh O site, O(7) is bonded to one Ca(3), two equivalent Ca(2), and one Ti(1) atom to form distorted OCa3Ti tetrahedra that share  a cornercorner with one O(7)Ca3Ti tetrahedra, corners with two equivalent O(9)Ca3Si trigonal pyramids, and  an edgeedge with one O(7)Ca3Ti tetrahedra. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Ca(1), one Ca(3), and one Si(1) atom. In the ninth O site, O(9) is bonded to one Ca(1), two equivalent Ca(3), and one Si(2) atom to form distorted OCa3Si trigonal pyramids that share corners with two equivalent O(7)Ca3Ti tetrahedra and  an edgeedge with one O(9)Ca3Si trigonal pyramid. is represented by the CIF file [CIF]
data_NaCa6Ti(Si2O9)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.708
_cell_length_b   7.602
_cell_length_c   9.814
_cell_angle_alpha   101.562
_cell_angle_beta   100.400
_cell_angle_gamma   89.726
_symmetry_Int_Tables_number   1
_cell_volume   410.144
_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
  Na  Na0  1  0.000  0.000  0.000  1.0
  Ca  Ca1  1  0.804  0.097  0.375  1.0
  Ca  Ca2  1  0.196  0.903  0.625  1.0
  Ca  Ca3  1  0.505  0.299  0.013  1.0
  Ca  Ca4  1  0.495  0.701  0.987  1.0
  Ca  Ca5  1  0.213  0.412  0.642  1.0
  Ca  Ca6  1  0.787  0.588  0.358  1.0
  Ti  Ti7  1  0.000  0.500  0.000  1.0
  Si  Si8  1  0.256  0.853  0.279  1.0
  Si  Si9  1  0.744  0.147  0.721  1.0
  Si  Si10  1  0.246  0.277  0.273  1.0
  Si  Si11  1  0.754  0.723  0.727  1.0
  O  O12  1  0.163  0.325  0.115  1.0
  O  O13  1  0.837  0.675  0.885  1.0
  O  O14  1  0.534  0.313  0.317  1.0
  O  O15  1  0.466  0.687  0.683  1.0
  O  O16  1  0.197  0.712  0.125  1.0
  O  O17  1  0.803  0.288  0.875  1.0
  O  O18  1  0.075  0.829  0.387  1.0
  O  O19  1  0.925  0.171  0.613  1.0
  O  O20  1  0.601  0.010  0.051  1.0
  O  O21  1  0.399  0.990  0.949  1.0
  O  O22  1  0.174  0.054  0.239  1.0
  O  O23  1  0.826  0.946  0.761  1.0
  O  O24  1  0.755  0.536  0.111  1.0
  O  O25  1  0.245  0.464  0.889  1.0
  O  O26  1  0.462  0.147  0.657  1.0
  O  O27  1  0.538  0.853  0.343  1.0
  O  O28  1  0.083  0.363  0.388  1.0
  O  O29  1  0.917  0.637  0.612  1.0
[/CIF]
.