The material structure described by BaSi2O9 crystallizes in the triclinic P1 space group. There are four inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 9-coordinate geometry to one O(12), one O(14), one O(25), one O(27), one O(29), one O(31), one O(34), and two equivalent O(22) atoms. In the second Ba site, Ba(2) is bonded in a 9-coordinate geometry to one O(11), one O(13), one O(26), one O(28), one O(30), one O(32), one O(33), and two equivalent O(21) atoms. In the third Ba site, Ba(3) is bonded in a 9-coordinate geometry to one O(10), one O(16), one O(25), one O(27), one O(29), one O(31), one O(36), and two equivalent O(24) atoms. In the fourth Ba site, Ba(4) is bonded in a 9-coordinate geometry to one O(15), one O(26), one O(28), one O(30), one O(32), one O(35), one O(9), and two equivalent O(23) atoms. There are five inequivalent Si sites. In the first Si site, Si(1,5) is bonded to one O(1), one O(17), one O(8), and one O(9) atom to form corner-sharing SiO4 tetrahedra. In the second Si site, Si(2,6) is bonded to one O(10), one O(18), one O(2), and one O(7) atom to form corner-sharing SiO4 tetrahedra. In the third Si site, Si(3) is bonded to one O(11), one O(19), one O(3), and one O(6) atom to form corner-sharing SiO4 tetrahedra. In the fourth Si site, Si(4,8) is bonded to one O(12), one O(20), one O(4), and one O(5) atom to form corner-sharing SiO4 tetrahedra. In the fifth Si site, Si(7) is bonded to one O(15), one O(17), one O(2), and one O(7) atom to form corner-sharing SiO4 tetrahedra. There are thirty-six inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Si(1,5) and one Si(4,8) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Si(2,6) and one Si(7) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Si(2,6) and one Si(3) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Si(1,5) and one Si(4,8) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Si(1,5) and one Si(4,8) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Si(2,6) and one Si(3) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Si(2,6) and one Si(7) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Si(1,5) and one Si(4,8) atom. In the ninth O site, O(9) is bonded in a distorted single-bond geometry to one Ba(4); one Si(1,5); and one O(32) atom. In the tenth O site, O(10) is bonded in a distorted single-bond geometry to one Ba(3); one Si(2,6); and one O(31) atom. In the eleventh O site, O(11) is bonded in a distorted single-bond geometry to one Ba(2), one Si(3), and one O(30) atom. In the twelfth O site, O(12) is bonded in a distorted single-bond geometry to one Ba(1); one Si(4,8); and one O(29) atom. In the thirteenth O site, O(13) is bonded in a distorted single-bond geometry to one Ba(2); one Si(1,5); and one O(28) atom. In the fourteenth O site, O(14) is bonded in a distorted single-bond geometry to one Ba(1); one Si(2,6); and one O(27) atom. In the fifteenth O site, O(15) is bonded in a distorted single-bond geometry to one Ba(4), one Si(7), and one O(26) atom. In the sixteenth O site, O(16) is bonded in a distorted single-bond geometry to one Ba(3); one Si(4,8); and one O(25) atom. In the seventeenth O site, O(17) is bonded in a linear geometry to one Si(1,5) and one Si(7) atom. In the eighteenth O site, O(18) is bonded in a linear geometry to one Si(2,6) and one Si(4,8) atom. In the nineteenth O site, O(19) is bonded in a linear geometry to one Si(1,5) and one Si(3) atom. In the twentieth O site, O(20) is bonded in a linear geometry to one Si(2,6) and one Si(4,8) atom. In the twenty-first O site, O(21) is bonded in a distorted T-shaped geometry to two equivalent Ba(2) and one O(33) atom. In the twenty-second O site, O(22) is bonded in a distorted T-shaped geometry to two equivalent Ba(1) and one O(34) atom. In the twenty-third O site, O(23) is bonded in a distorted T-shaped geometry to two equivalent Ba(4) and one O(35) atom. In the twenty-fourth O site, O(24) is bonded in a distorted T-shaped geometry to two equivalent Ba(3) and one O(36) atom. In the twenty-fifth O site, O(25) is bonded in a 3-coordinate geometry to one Ba(1), one Ba(3), and one O(16) atom. In the twenty-sixth O site, O(26) is bonded in a 3-coordinate geometry to one Ba(2), one Ba(4), and one O(15) atom. In the twenty-seventh O site, O(27) is bonded in a 3-coordinate geometry to one Ba(1), one Ba(3), and one O(14) atom. In the twenty-eighth O site, O(28) is bonded in a 3-coordinate geometry to one Ba(2), one Ba(4), and one O(13) atom. In the twenty-ninth O site, O(29) is bonded in a 3-coordinate geometry to one Ba(1), one Ba(3), and one O(12) atom. In the thirtieth O site, O(30) is bonded in a 3-coordinate geometry to one Ba(2), one Ba(4), and one O(11) atom. In the thirty-first O site, O(31) is bonded in a 3-coordinate geometry to one Ba(1), one Ba(3), and one O(10) atom. In the thirty-second O site, O(32) is bonded in a 3-coordinate geometry to one Ba(2), one Ba(4), and one O(9) atom. In the thirty-third O site, O(33) is bonded in a 2-coordinate geometry to one Ba(2) and one O(21) atom. In the thirty-fourth O site, O(34) is bonded in a 2-coordinate geometry to one Ba(1) and one O(22) atom. In the thirty-fifth O site, O(35) is bonded in a 2-coordinate geometry to one Ba(4) and one O(23) atom. In the thirty-sixth O site, O(36) is bonded in a 2-coordinate geometry to one Ba(3) and one O(24) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_BaSi2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.475
_cell_length_b   8.285
_cell_length_c   17.213
_cell_angle_alpha   90.014
_cell_angle_beta   89.875
_cell_angle_gamma   90.047
_symmetry_Int_Tables_number   1
_cell_volume   780.775
_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
  Ba  Ba0  1  0.634  0.251  0.999  1.0
  Ba  Ba1  1  0.135  0.250  0.501  1.0
  Ba  Ba2  1  0.366  0.749  0.001  1.0
  Ba  Ba3  1  0.864  0.750  0.499  1.0
  Si  Si4  1  0.712  0.055  0.294  1.0
  Si  Si5  1  0.213  0.444  0.206  1.0
  Si  Si6  1  0.288  0.556  0.706  1.0
  Si  Si7  1  0.787  0.945  0.794  1.0
  Si  Si8  1  0.288  0.945  0.706  1.0
  Si  Si9  1  0.787  0.555  0.794  1.0
  Si  Si10  1  0.712  0.444  0.294  1.0
  Si  Si11  1  0.213  0.055  0.206  1.0
  O  O12  1  0.948  0.999  0.242  1.0
  O  O13  1  0.448  0.500  0.258  1.0
  O  O14  1  0.052  0.500  0.758  1.0
  O  O15  1  0.552  0.001  0.742  1.0
  O  O16  1  0.052  0.001  0.758  1.0
  O  O17  1  0.552  0.499  0.742  1.0
  O  O18  1  0.949  0.500  0.242  1.0
  O  O19  1  0.448  0.999  0.258  1.0
  O  O20  1  0.717  0.967  0.381  1.0
  O  O21  1  0.218  0.532  0.119  1.0
  O  O22  1  0.283  0.467  0.619  1.0
  O  O23  1  0.782  0.033  0.881  1.0
  O  O24  1  0.283  0.033  0.619  1.0
  O  O25  1  0.783  0.468  0.881  1.0
  O  O26  1  0.717  0.533  0.381  1.0
  O  O27  1  0.218  0.967  0.119  1.0
  O  O28  1  0.713  0.250  0.304  1.0
  O  O29  1  0.215  0.250  0.196  1.0
  O  O30  1  0.287  0.750  0.696  1.0
  O  O31  1  0.785  0.750  0.804  1.0
  O  O32  1  0.632  0.251  0.501  1.0
  O  O33  1  0.131  0.250  0.997  1.0
  O  O34  1  0.368  0.750  0.498  1.0
  O  O35  1  0.870  0.751  0.003  1.0
  O  O36  1  0.462  0.012  0.089  1.0
  O  O37  1  0.957  0.485  0.412  1.0
  O  O38  1  0.538  0.512  0.911  1.0
  O  O39  1  0.043  0.985  0.588  1.0
  O  O40  1  0.538  0.988  0.911  1.0
  O  O41  1  0.043  0.515  0.588  1.0
  O  O42  1  0.462  0.488  0.089  1.0
  O  O43  1  0.957  0.015  0.412  1.0
  O  O44  1  0.673  0.250  0.575  1.0
  O  O45  1  0.175  0.250  0.924  1.0
  O  O46  1  0.326  0.750  0.425  1.0
  O  O47  1  0.826  0.750  0.076  1.0
[/CIF]
.
The material structure described by BaSi2O9 crystallizes in the triclinic P1 space group. There are four inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 9-coordinate geometry to one O(12), one O(14), one O(25), one O(27), one O(29), one O(31), one O(34), and two equivalent O(22) atoms. In the second Ba site, Ba(2) is bonded in a 9-coordinate geometry to one O(11), one O(13), one O(26), one O(28), one O(30), one O(32), one O(33), and two equivalent O(21) atoms. In the third Ba site, Ba(3) is bonded in a 9-coordinate geometry to one O(10), one O(16), one O(25), one O(27), one O(29), one O(31), one O(36), and two equivalent O(24) atoms. In the fourth Ba site, Ba(4) is bonded in a 9-coordinate geometry to one O(15), one O(26), one O(28), one O(30), one O(32), one O(35), one O(9), and two equivalent O(23) atoms. There are five inequivalent Si sites. In the first Si site, Si(1,5) is bonded to one O(1), one O(17), one O(8), and one O(9) atom to form corner-sharing SiO4 tetrahedra. In the second Si site, Si(2,6) is bonded to one O(10), one O(18), one O(2), and one O(7) atom to form corner-sharing SiO4 tetrahedra. In the third Si site, Si(3) is bonded to one O(11), one O(19), one O(3), and one O(6) atom to form corner-sharing SiO4 tetrahedra. In the fourth Si site, Si(4,8) is bonded to one O(12), one O(20), one O(4), and one O(5) atom to form corner-sharing SiO4 tetrahedra. In the fifth Si site, Si(7) is bonded to one O(15), one O(17), one O(2), and one O(7) atom to form corner-sharing SiO4 tetrahedra. There are thirty-six inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Si(1,5) and one Si(4,8) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Si(2,6) and one Si(7) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Si(2,6) and one Si(3) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Si(1,5) and one Si(4,8) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Si(1,5) and one Si(4,8) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Si(2,6) and one Si(3) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Si(2,6) and one Si(7) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Si(1,5) and one Si(4,8) atom. In the ninth O site, O(9) is bonded in a distorted single-bond geometry to one Ba(4); one Si(1,5); and one O(32) atom. In the tenth O site, O(10) is bonded in a distorted single-bond geometry to one Ba(3); one Si(2,6); and one O(31) atom. In the eleventh O site, O(11) is bonded in a distorted single-bond geometry to one Ba(2), one Si(3), and one O(30) atom. In the twelfth O site, O(12) is bonded in a distorted single-bond geometry to one Ba(1); one Si(4,8); and one O(29) atom. In the thirteenth O site, O(13) is bonded in a distorted single-bond geometry to one Ba(2); one Si(1,5); and one O(28) atom. In the fourteenth O site, O(14) is bonded in a distorted single-bond geometry to one Ba(1); one Si(2,6); and one O(27) atom. In the fifteenth O site, O(15) is bonded in a distorted single-bond geometry to one Ba(4), one Si(7), and one O(26) atom. In the sixteenth O site, O(16) is bonded in a distorted single-bond geometry to one Ba(3); one Si(4,8); and one O(25) atom. In the seventeenth O site, O(17) is bonded in a linear geometry to one Si(1,5) and one Si(7) atom. In the eighteenth O site, O(18) is bonded in a linear geometry to one Si(2,6) and one Si(4,8) atom. In the nineteenth O site, O(19) is bonded in a linear geometry to one Si(1,5) and one Si(3) atom. In the twentieth O site, O(20) is bonded in a linear geometry to one Si(2,6) and one Si(4,8) atom. In the twenty-first O site, O(21) is bonded in a distorted T-shaped geometry to two equivalent Ba(2) and one O(33) atom. In the twenty-second O site, O(22) is bonded in a distorted T-shaped geometry to two equivalent Ba(1) and one O(34) atom. In the twenty-third O site, O(23) is bonded in a distorted T-shaped geometry to two equivalent Ba(4) and one O(35) atom. In the twenty-fourth O site, O(24) is bonded in a distorted T-shaped geometry to two equivalent Ba(3) and one O(36) atom. In the twenty-fifth O site, O(25) is bonded in a 3-coordinate geometry to one Ba(1), one Ba(3), and one O(16) atom. In the twenty-sixth O site, O(26) is bonded in a 3-coordinate geometry to one Ba(2), one Ba(4), and one O(15) atom. In the twenty-seventh O site, O(27) is bonded in a 3-coordinate geometry to one Ba(1), one Ba(3), and one O(14) atom. In the twenty-eighth O site, O(28) is bonded in a 3-coordinate geometry to one Ba(2), one Ba(4), and one O(13) atom. In the twenty-ninth O site, O(29) is bonded in a 3-coordinate geometry to one Ba(1), one Ba(3), and one O(12) atom. In the thirtieth O site, O(30) is bonded in a 3-coordinate geometry to one Ba(2), one Ba(4), and one O(11) atom. In the thirty-first O site, O(31) is bonded in a 3-coordinate geometry to one Ba(1), one Ba(3), and one O(10) atom. In the thirty-second O site, O(32) is bonded in a 3-coordinate geometry to one Ba(2), one Ba(4), and one O(9) atom. In the thirty-third O site, O(33) is bonded in a 2-coordinate geometry to one Ba(2) and one O(21) atom. In the thirty-fourth O site, O(34) is bonded in a 2-coordinate geometry to one Ba(1) and one O(22) atom. In the thirty-fifth O site, O(35) is bonded in a 2-coordinate geometry to one Ba(4) and one O(23) atom. In the thirty-sixth O site, O(36) is bonded in a 2-coordinate geometry to one Ba(3) and one O(24) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_BaSi2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.475
_cell_length_b   8.285
_cell_length_c   17.213
_cell_angle_alpha   90.014
_cell_angle_beta   89.875
_cell_angle_gamma   90.047
_symmetry_Int_Tables_number   1
_cell_volume   780.775
_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
  Ba  Ba0  1  0.634  0.251  0.999  1.0
  Ba  Ba1  1  0.135  0.250  0.501  1.0
  Ba  Ba2  1  0.366  0.749  0.001  1.0
  Ba  Ba3  1  0.864  0.750  0.499  1.0
  Si  Si4  1  0.712  0.055  0.294  1.0
  Si  Si5  1  0.213  0.444  0.206  1.0
  Si  Si6  1  0.288  0.556  0.706  1.0
  Si  Si7  1  0.787  0.945  0.794  1.0
  Si  Si8  1  0.288  0.945  0.706  1.0
  Si  Si9  1  0.787  0.555  0.794  1.0
  Si  Si10  1  0.712  0.444  0.294  1.0
  Si  Si11  1  0.213  0.055  0.206  1.0
  O  O12  1  0.948  0.999  0.242  1.0
  O  O13  1  0.448  0.500  0.258  1.0
  O  O14  1  0.052  0.500  0.758  1.0
  O  O15  1  0.552  0.001  0.742  1.0
  O  O16  1  0.052  0.001  0.758  1.0
  O  O17  1  0.552  0.499  0.742  1.0
  O  O18  1  0.949  0.500  0.242  1.0
  O  O19  1  0.448  0.999  0.258  1.0
  O  O20  1  0.717  0.967  0.381  1.0
  O  O21  1  0.218  0.532  0.119  1.0
  O  O22  1  0.283  0.467  0.619  1.0
  O  O23  1  0.782  0.033  0.881  1.0
  O  O24  1  0.283  0.033  0.619  1.0
  O  O25  1  0.783  0.468  0.881  1.0
  O  O26  1  0.717  0.533  0.381  1.0
  O  O27  1  0.218  0.967  0.119  1.0
  O  O28  1  0.713  0.250  0.304  1.0
  O  O29  1  0.215  0.250  0.196  1.0
  O  O30  1  0.287  0.750  0.696  1.0
  O  O31  1  0.785  0.750  0.804  1.0
  O  O32  1  0.632  0.251  0.501  1.0
  O  O33  1  0.131  0.250  0.997  1.0
  O  O34  1  0.368  0.750  0.498  1.0
  O  O35  1  0.870  0.751  0.003  1.0
  O  O36  1  0.462  0.012  0.089  1.0
  O  O37  1  0.957  0.485  0.412  1.0
  O  O38  1  0.538  0.512  0.911  1.0
  O  O39  1  0.043  0.985  0.588  1.0
  O  O40  1  0.538  0.988  0.911  1.0
  O  O41  1  0.043  0.515  0.588  1.0
  O  O42  1  0.462  0.488  0.089  1.0
  O  O43  1  0.957  0.015  0.412  1.0
  O  O44  1  0.673  0.250  0.575  1.0
  O  O45  1  0.175  0.250  0.924  1.0
  O  O46  1  0.326  0.750  0.425  1.0
  O  O47  1  0.826  0.750  0.076  1.0
[/CIF]
.