Ba2C4O9 crystallizes in the triclinic P-1 space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 9-coordinate geometry to one O(2), one O(4), one O(5), one O(7), one O(9), two equivalent O(1), and two equivalent O(8) atoms. In the second Ba site, Ba(2) is bonded in a 7-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(9), and two equivalent O(6) atoms. There are four inequivalent C sites. In the first C site, C(1) is bonded in a distorted bent 120 degrees geometry to one O(5) and one O(9) atom. In the second C site, C(2) is bonded in a trigonal planar geometry to one O(6), one O(7), and one O(8) atom. In the third C site, C(3) is bonded in a distorted bent 120 degrees geometry to one O(2) and one O(4) atom. In the fourth C site, C(4) is bonded in a linear geometry to one O(1) and one O(3) atom. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a single-bond geometry to two equivalent Ba(1) and one C(4) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), and one C(3) atom. In the third O site, O(3) is bonded in a single-bond geometry to one Ba(2) and one C(4) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), and one C(3) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Ba(1), one Ba(2), and one C(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to two equivalent Ba(2) and one C(2) atom. In the seventh O site, O(7) is bonded in a distorted single-bond geometry to one Ba(1) and one C(2) atom. In the eighth O site, O(8) is bonded in a distorted single-bond geometry to two equivalent Ba(1) and one C(2) atom. In the ninth O site, O(9) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), and one C(1) atom.
Ba2C4O9 crystallizes in the triclinic P-1 space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 9-coordinate geometry to one O(2), one O(4), one O(5), one O(7), one O(9), two equivalent O(1), and two equivalent O(8) atoms. The Ba(1)-O(2) bond length is 2.90 Å. The Ba(1)-O(4) bond length is 2.84 Å. The Ba(1)-O(5) bond length is 2.79 Å. The Ba(1)-O(7) bond length is 2.71 Å. The Ba(1)-O(9) bond length is 3.01 Å. There is one shorter (3.07 Å) and one longer (3.21 Å) Ba(1)-O(1) bond length. Both Ba(1)-O(8) bond lengths are 2.73 Å. In the second Ba site, Ba(2) is bonded in a 7-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(9), and two equivalent O(6) atoms. The Ba(2)-O(2) bond length is 2.79 Å. The Ba(2)-O(3) bond length is 3.27 Å. The Ba(2)-O(4) bond length is 2.86 Å. The Ba(2)-O(5) bond length is 2.69 Å. The Ba(2)-O(9) bond length is 2.92 Å. There is one shorter (2.60 Å) and one longer (2.72 Å) Ba(2)-O(6) bond length. There are four inequivalent C sites. In the first C site, C(1) is bonded in a distorted bent 120 degrees geometry to one O(5) and one O(9) atom. The C(1)-O(5) bond length is 1.27 Å. The C(1)-O(9) bond length is 1.27 Å. In the second C site, C(2) is bonded in a trigonal planar geometry to one O(6), one O(7), and one O(8) atom. The C(2)-O(6) bond length is 1.32 Å. The C(2)-O(7) bond length is 1.28 Å. The C(2)-O(8) bond length is 1.31 Å. In the third C site, C(3) is bonded in a distorted bent 120 degrees geometry to one O(2) and one O(4) atom. The C(3)-O(2) bond length is 1.27 Å. The C(3)-O(4) bond length is 1.27 Å. In the fourth C site, C(4) is bonded in a linear geometry to one O(1) and one O(3) atom. The C(4)-O(1) bond length is 1.18 Å. The C(4)-O(3) bond length is 1.18 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a single-bond geometry to two equivalent Ba(1) and one C(4) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), and one C(3) atom. In the third O site, O(3) is bonded in a single-bond geometry to one Ba(2) and one C(4) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), and one C(3) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Ba(1), one Ba(2), and one C(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to two equivalent Ba(2) and one C(2) atom. In the seventh O site, O(7) is bonded in a distorted single-bond geometry to one Ba(1) and one C(2) atom. In the eighth O site, O(8) is bonded in a distorted single-bond geometry to two equivalent Ba(1) and one C(2) atom. In the ninth O site, O(9) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), and one C(1) atom.