BaAs2O9 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(10), one O(14), one O(16), one O(17), one O(3), one O(4), one O(5), one O(8), and one O(9) atom. In the second Ba site, Ba(2) is bonded in a 9-coordinate geometry to one O(11), one O(14), one O(15), one O(17), one O(2), one O(3), one O(6), one O(7), and one O(9) atom. There are four inequivalent As sites. In the first As site, As(1) is bonded in a trigonal planar geometry to one O(2), one O(3), and one O(4) atom. In the second As site, As(2) is bonded in a tetrahedral geometry to one O(5), one O(6), one O(7), and one O(8) atom. In the third As site, As(3) is bonded in a tetrahedral geometry to one O(10), one O(11), one O(12), and one O(9) atom. In the fourth As site, As(4) is bonded in a tetrahedral geometry to one O(13), one O(14), one O(15), and one O(16) atom. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a single-bond geometry to one O(18) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Ba(2) and one As(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), and one As(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Ba(1) and one As(1) atom. In the fifth O site, O(5) is bonded in a single-bond geometry to one Ba(1) and one As(2) atom. In the sixth O site, O(6) is bonded in a distorted single-bond geometry to one Ba(2) and one As(2) atom. In the seventh O site, O(7) is bonded in a distorted single-bond geometry to one Ba(2) and one As(2) atom. In the eighth O site, O(8) is bonded in a distorted bent 150 degrees geometry to one Ba(1) and one As(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 As(3) atom. In the tenth O site, O(10) is bonded in a 2-coordinate geometry to one Ba(1) and one As(3) atom. In the eleventh O site, O(11) is bonded in a distorted single-bond geometry to one Ba(2) and one As(3) atom. In the twelfth O site, O(12) is bonded in a distorted single-bond geometry to one As(3) and one O(18) atom. In the thirteenth O site, O(13) is bonded in a single-bond geometry to one As(4) atom. In the fourteenth O site, O(14) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), and one As(4) atom. In the fifteenth O site, O(15) is bonded in a 2-coordinate geometry to one Ba(2) and one As(4) atom. In the sixteenth O site, O(16) is bonded in a single-bond geometry to one Ba(1) and one As(4) atom. In the seventeenth O site, O(17) is bonded in a bent 150 degrees geometry to one Ba(1) and one Ba(2) atom. In the eighteenth O site, O(18) is bonded in a distorted bent 120 degrees geometry to one O(1) and one O(12) atom.
BaAs2O9 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(10), one O(14), one O(16), one O(17), one O(3), one O(4), one O(5), one O(8), and one O(9) atom. The Ba(1)-O(10) bond length is 2.64 Å. The Ba(1)-O(14) bond length is 2.93 Å. The Ba(1)-O(16) bond length is 3.10 Å. The Ba(1)-O(17) bond length is 2.78 Å. The Ba(1)-O(3) bond length is 2.92 Å. The Ba(1)-O(4) bond length is 2.70 Å. The Ba(1)-O(5) bond length is 3.31 Å. The Ba(1)-O(8) bond length is 2.75 Å. The Ba(1)-O(9) bond length is 2.76 Å. In the second Ba site, Ba(2) is bonded in a 9-coordinate geometry to one O(11), one O(14), one O(15), one O(17), one O(2), one O(3), one O(6), one O(7), and one O(9) atom. The Ba(2)-O(11) bond length is 3.06 Å. The Ba(2)-O(14) bond length is 2.79 Å. The Ba(2)-O(15) bond length is 2.69 Å. The Ba(2)-O(17) bond length is 2.77 Å. The Ba(2)-O(2) bond length is 2.88 Å. The Ba(2)-O(3) bond length is 2.95 Å. The Ba(2)-O(6) bond length is 2.79 Å. The Ba(2)-O(7) bond length is 2.79 Å. The Ba(2)-O(9) bond length is 3.07 Å. There are four inequivalent As sites. In the first As site, As(1) is bonded in a trigonal planar geometry to one O(2), one O(3), and one O(4) atom. The As(1)-O(2) bond length is 1.69 Å. The As(1)-O(3) bond length is 1.67 Å. The As(1)-O(4) bond length is 1.65 Å. In the second As site, As(2) is bonded in a tetrahedral geometry to one O(5), one O(6), one O(7), and one O(8) atom. The As(2)-O(5) bond length is 1.76 Å. The As(2)-O(6) bond length is 1.74 Å. The As(2)-O(7) bond length is 1.74 Å. The As(2)-O(8) bond length is 1.70 Å. In the third As site, As(3) is bonded in a tetrahedral geometry to one O(10), one O(11), one O(12), and one O(9) atom. The As(3)-O(10) bond length is 1.69 Å. The As(3)-O(11) bond length is 1.75 Å. The As(3)-O(12) bond length is 1.81 Å. The As(3)-O(9) bond length is 1.72 Å. In the fourth As site, As(4) is bonded in a tetrahedral geometry to one O(13), one O(14), one O(15), and one O(16) atom. The As(4)-O(13) bond length is 1.76 Å. The As(4)-O(14) bond length is 1.76 Å. The As(4)-O(15) bond length is 1.69 Å. The As(4)-O(16) bond length is 1.74 Å. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a single-bond geometry to one O(18) atom. The O(1)-O(18) bond length is 1.24 Å. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Ba(2) and one As(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), and one As(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Ba(1) and one As(1) atom. In the fifth O site, O(5) is bonded in a single-bond geometry to one Ba(1) and one As(2) atom. In the sixth O site, O(6) is bonded in a distorted single-bond geometry to one Ba(2) and one As(2) atom. In the seventh O site, O(7) is bonded in a distorted single-bond geometry to one Ba(2) and one As(2) atom. In the eighth O site, O(8) is bonded in a distorted bent 150 degrees geometry to one Ba(1) and one As(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 As(3) atom. In the tenth O site, O(10) is bonded in a 2-coordinate geometry to one Ba(1) and one As(3) atom. In the eleventh O site, O(11) is bonded in a distorted single-bond geometry to one Ba(2) and one As(3) atom. In the twelfth O site, O(12) is bonded in a distorted single-bond geometry to one As(3) and one O(18) atom. The O(12)-O(18) bond length is 1.68 Å. In the thirteenth O site, O(13) is bonded in a single-bond geometry to one As(4) atom. In the fourteenth O site, O(14) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), and one As(4) atom. In the fifteenth O site, O(15) is bonded in a 2-coordinate geometry to one Ba(2) and one As(4) atom. In the sixteenth O site, O(16) is bonded in a single-bond geometry to one Ba(1) and one As(4) atom. In the seventeenth O site, O(17) is bonded in a bent 150 degrees geometry to one Ba(1) and one Ba(2) atom. In the eighteenth O site, O(18) is bonded in a distorted bent 120 degrees geometry to one O(1) and one O(12) atom.