Sm2As4O9 crystallizes in the triclinic P-1 space group. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 9-coordinate geometry to one O(1), one O(2), one O(4), one O(6), one O(8), two equivalent O(5), and two equivalent O(9) atoms. In the second Sm site, Sm(2) is bonded in a 8-coordinate geometry to one O(1), one O(4), one O(5), one O(6), two equivalent O(7), and two equivalent O(8) atoms. There are four inequivalent As sites. In the first As site, As(1) is bonded in a distorted T-shaped geometry to one O(1), one O(2), and one O(3) atom. In the second As site, As(2) is bonded in a distorted trigonal non-coplanar geometry to one O(2), one O(3), and one O(4) atom. In the third As site, As(3) is bonded in a distorted trigonal non-coplanar geometry to one O(5), one O(6), and one O(9) atom. In the fourth As site, As(4) is bonded in a distorted T-shaped geometry to one O(7), one O(8), and one O(9) atom. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Sm(1), one Sm(2), and one As(1) atom. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Sm(1), one As(1), and one As(2) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one As(1) and one As(2) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Sm(1), one Sm(2), and one As(2) atom. In the fifth O site, O(5) is bonded to one Sm(2), two equivalent Sm(1), and one As(3) atom to form a mixture of distorted corner and edge-sharing OSm3As tetrahedra. In the sixth O site, O(6) is bonded in a distorted trigonal non-coplanar geometry to one Sm(1), one Sm(2), and one As(3) atom. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Sm(2) and one As(4) atom. In the eighth O site, O(8) is bonded to one Sm(1), two equivalent Sm(2), and one As(4) atom to form a mixture of distorted corner and edge-sharing OSm3As tetrahedra. In the ninth O site, O(9) is bonded in a 4-coordinate geometry to two equivalent Sm(1), one As(3), and one As(4) atom.
Sm2As4O9 crystallizes in the triclinic P-1 space group. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 9-coordinate geometry to one O(1), one O(2), one O(4), one O(6), one O(8), two equivalent O(5), and two equivalent O(9) atoms. The Sm(1)-O(1) bond length is 2.49 Å. The Sm(1)-O(2) bond length is 2.44 Å. The Sm(1)-O(4) bond length is 2.57 Å. The Sm(1)-O(6) bond length is 2.35 Å. The Sm(1)-O(8) bond length is 2.34 Å. There is one shorter (2.42 Å) and one longer (2.59 Å) Sm(1)-O(5) bond length. There is one shorter (2.55 Å) and one longer (2.86 Å) Sm(1)-O(9) bond length. In the second Sm site, Sm(2) is bonded in a 8-coordinate geometry to one O(1), one O(4), one O(5), one O(6), two equivalent O(7), and two equivalent O(8) atoms. The Sm(2)-O(1) bond length is 2.38 Å. The Sm(2)-O(4) bond length is 2.47 Å. The Sm(2)-O(5) bond length is 2.64 Å. The Sm(2)-O(6) bond length is 2.35 Å. There is one shorter (2.34 Å) and one longer (2.43 Å) Sm(2)-O(7) bond length. There is one shorter (2.39 Å) and one longer (2.54 Å) Sm(2)-O(8) bond length. There are four inequivalent As sites. In the first As site, As(1) is bonded in a distorted T-shaped geometry to one O(1), one O(2), and one O(3) atom. The As(1)-O(1) bond length is 1.74 Å. The As(1)-O(2) bond length is 1.85 Å. The As(1)-O(3) bond length is 1.80 Å. In the second As site, As(2) is bonded in a distorted trigonal non-coplanar geometry to one O(2), one O(3), and one O(4) atom. The As(2)-O(2) bond length is 1.85 Å. The As(2)-O(3) bond length is 1.81 Å. The As(2)-O(4) bond length is 1.73 Å. In the third As site, As(3) is bonded in a distorted trigonal non-coplanar geometry to one O(5), one O(6), and one O(9) atom. The As(3)-O(5) bond length is 1.78 Å. The As(3)-O(6) bond length is 1.73 Å. The As(3)-O(9) bond length is 1.87 Å. In the fourth As site, As(4) is bonded in a distorted T-shaped geometry to one O(7), one O(8), and one O(9) atom. The As(4)-O(7) bond length is 1.73 Å. The As(4)-O(8) bond length is 1.79 Å. The As(4)-O(9) bond length is 1.90 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Sm(1), one Sm(2), and one As(1) atom. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Sm(1), one As(1), and one As(2) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one As(1) and one As(2) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Sm(1), one Sm(2), and one As(2) atom. In the fifth O site, O(5) is bonded to one Sm(2), two equivalent Sm(1), and one As(3) atom to form a mixture of distorted corner and edge-sharing OSm3As tetrahedra. In the sixth O site, O(6) is bonded in a distorted trigonal non-coplanar geometry to one Sm(1), one Sm(2), and one As(3) atom. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Sm(2) and one As(4) atom. In the eighth O site, O(8) is bonded to one Sm(1), two equivalent Sm(2), and one As(4) atom to form a mixture of distorted corner and edge-sharing OSm3As tetrahedra. In the ninth O site, O(9) is bonded in a 4-coordinate geometry to two equivalent Sm(1), one As(3), and one As(4) atom.