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.
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. The Ba(1)-O(12) bond length is 2.84 Å. The Ba(1)-O(14) bond length is 2.84 Å. The Ba(1)-O(25) bond length is 2.67 Å. The Ba(1)-O(27) bond length is 2.70 Å. The Ba(1)-O(29) bond length is 2.71 Å. The Ba(1)-O(31) bond length is 2.67 Å. The Ba(1)-O(34) bond length is 2.83 Å. There is one shorter (2.72 Å) and one longer (2.76 Å) Ba(1)-O(22) bond length. 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. The Ba(2)-O(11) bond length is 2.83 Å. The Ba(2)-O(13) bond length is 2.84 Å. The Ba(2)-O(26) bond length is 2.66 Å. The Ba(2)-O(28) bond length is 2.71 Å. The Ba(2)-O(30) bond length is 2.71 Å. The Ba(2)-O(32) bond length is 2.66 Å. The Ba(2)-O(33) bond length is 2.83 Å. There is one shorter (2.72 Å) and one longer (2.76 Å) Ba(2)-O(21) bond length. 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. The Ba(3)-O(10) bond length is 2.84 Å. The Ba(3)-O(16) bond length is 2.84 Å. The Ba(3)-O(25) bond length is 2.71 Å. The Ba(3)-O(27) bond length is 2.67 Å. The Ba(3)-O(29) bond length is 2.68 Å. The Ba(3)-O(31) bond length is 2.70 Å. The Ba(3)-O(36) bond length is 2.84 Å. There is one shorter (2.72 Å) and one longer (2.76 Å) Ba(3)-O(24) bond length. 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. The Ba(4)-O(15) bond length is 2.84 Å. The Ba(4)-O(26) bond length is 2.71 Å. The Ba(4)-O(28) bond length is 2.66 Å. The Ba(4)-O(30) bond length is 2.66 Å. The Ba(4)-O(32) bond length is 2.71 Å. The Ba(4)-O(35) bond length is 2.83 Å. The Ba(4)-O(9) bond length is 2.84 Å. There is one shorter (2.72 Å) and one longer (2.76 Å) Ba(4)-O(23) bond length. 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. The Si(1,5)-O(1) bond length is 1.64 Å. The Si(1,5)-O(17) bond length is 1.62 Å. The Si(1,5)-O(8) bond length is 1.64 Å. The Si(1,5)-O(9) bond length is 1.67 Å. 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. The Si(2,6)-O(10) bond length is 1.67 Å. The Si(2,6)-O(18) bond length is 1.62 Å. The Si(2,6)-O(2) bond length is 1.64 Å. The Si(2,6)-O(7) bond length is 1.64 Å. 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. The Si(3)-O(11) bond length is 1.67 Å. The Si(3)-O(19) bond length is 1.62 Å. The Si(3)-O(3) bond length is 1.64 Å. The Si(3)-O(6) bond length is 1.64 Å. 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. The Si(4,8)-O(12) bond length is 1.67 Å. The Si(4,8)-O(20) bond length is 1.62 Å. The Si(4,8)-O(4) bond length is 1.64 Å. The Si(4,8)-O(5) bond length is 1.64 Å. 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. The Si(7)-O(15) bond length is 1.67 Å. The Si(7)-O(17) bond length is 1.62 Å. The Si(7)-O(2) bond length is 1.64 Å. The Si(7)-O(7) bond length is 1.64 Å. 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. The O(1)-Si(4,8) bond length is 1.64 Å. 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. The O(3)-Si(2,6) bond length is 1.64 Å. 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. The O(4)-Si(1,5) bond length is 1.64 Å. 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. The O(5)-Si(1,5) bond length is 1.64 Å. 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. The O(6)-Si(2,6) bond length is 1.64 Å. 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. The O(8)-Si(4,8) bond length is 1.64 Å. 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. The O(9)-O(32) bond length is 1.48 Å. 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. The O(10)-O(31) bond length is 1.48 Å. 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. The O(11)-O(30) bond length is 1.48 Å. 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. The O(12)-O(29) bond length is 1.48 Å. 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. The O(13)-Si(1,5) bond length is 1.67 Å. The O(13)-O(28) bond length is 1.48 Å. 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. The O(14)-Si(2,6) bond length is 1.67 Å. The O(14)-O(27) bond length is 1.48 Å. 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. The O(15)-O(26) bond length is 1.48 Å. 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. The O(16)-Si(4,8) bond length is 1.67 Å. The O(16)-O(25) bond length is 1.48 Å. 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. The O(18)-Si(4,8) bond length is 1.62 Å. In the nineteenth O site, O(19) is bonded in a linear geometry to one Si(1,5) and one Si(3) atom. The O(19)-Si(1,5) bond length is 1.62 Å. In the twentieth O site, O(20) is bonded in a linear geometry to one Si(2,6) and one Si(4,8) atom. The O(20)-Si(2,6) bond length is 1.62 Å. 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. The O(21)-O(33) bond length is 1.28 Å. 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. The O(22)-O(34) bond length is 1.28 Å. 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. The O(23)-O(35) bond length is 1.28 Å. 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. The O(24)-O(36) bond length is 1.28 Å. 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.