Ba2CuAlF9 crystallizes in the monoclinic P2_1 space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 10-coordinate geometry to one F(2), one F(4), two equivalent F(1), two equivalent F(3), two equivalent F(5), and two equivalent F(8) atoms. In the second Ba site, Ba(2) is bonded in a 11-coordinate geometry to one F(1), one F(2), one F(3), two equivalent F(4), two equivalent F(6), two equivalent F(7), and two equivalent F(9) atoms. Cu(1) is bonded to one F(1), one F(3), one F(5), one F(7), and one F(9) atom to form distorted CuF5 trigonal bipyramids that share corners with two equivalent Al(1)F6 octahedra. The corner-sharing octahedral tilt angles range from 38-46°. Al(1) is bonded to one F(2), one F(4), one F(6), one F(7), one F(8), and one F(9) atom to form AlF6 octahedra that share corners with two equivalent Cu(1)F5 trigonal bipyramids. There are nine inequivalent F sites. In the first F site, F(1) is bonded in a distorted single-bond geometry to one Ba(2), two equivalent Ba(1), and one Cu(1) atom. In the second F site, F(2) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), and one Al(1) atom. In the third F site, F(3) is bonded in a 1-coordinate geometry to one Ba(2), two equivalent Ba(1), and one Cu(1) atom. In the fourth F site, F(4) is bonded in a distorted single-bond geometry to one Ba(1), two equivalent Ba(2), and one Al(1) atom. In the fifth F site, F(5) is bonded in a 3-coordinate geometry to two equivalent Ba(1) and one Cu(1) atom. In the sixth F site, F(6) is bonded in a distorted single-bond geometry to two equivalent Ba(2) and one Al(1) atom. In the seventh F site, F(7) is bonded in a distorted bent 150 degrees geometry to two equivalent Ba(2), one Cu(1), and one Al(1) atom. In the eighth F site, F(8) is bonded in a distorted single-bond geometry to two equivalent Ba(1) and one Al(1) atom. In the ninth F site, F(9) is bonded in a 2-coordinate geometry to two equivalent Ba(2), one Cu(1), and one Al(1) atom.
Ba2CuAlF9 crystallizes in the monoclinic P2_1 space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 10-coordinate geometry to one F(2), one F(4), two equivalent F(1), two equivalent F(3), two equivalent F(5), and two equivalent F(8) atoms. The Ba(1)-F(2) bond length is 2.83 Å. The Ba(1)-F(4) bond length is 2.94 Å. There is one shorter (2.88 Å) and one longer (2.89 Å) Ba(1)-F(1) bond length. There is one shorter (2.86 Å) and one longer (3.09 Å) Ba(1)-F(3) bond length. There is one shorter (2.66 Å) and one longer (2.77 Å) Ba(1)-F(5) bond length. There is one shorter (2.72 Å) and one longer (3.13 Å) Ba(1)-F(8) bond length. In the second Ba site, Ba(2) is bonded in a 11-coordinate geometry to one F(1), one F(2), one F(3), two equivalent F(4), two equivalent F(6), two equivalent F(7), and two equivalent F(9) atoms. The Ba(2)-F(1) bond length is 2.71 Å. The Ba(2)-F(2) bond length is 2.77 Å. The Ba(2)-F(3) bond length is 2.66 Å. There is one shorter (2.79 Å) and one longer (3.15 Å) Ba(2)-F(4) bond length. There is one shorter (2.78 Å) and one longer (2.90 Å) Ba(2)-F(6) bond length. There is one shorter (2.89 Å) and one longer (3.01 Å) Ba(2)-F(7) bond length. There is one shorter (2.82 Å) and one longer (2.99 Å) Ba(2)-F(9) bond length. Cu(1) is bonded to one F(1), one F(3), one F(5), one F(7), and one F(9) atom to form distorted CuF5 trigonal bipyramids that share corners with two equivalent Al(1)F6 octahedra. The corner-sharing octahedral tilt angles range from 38-46°. The Cu(1)-F(1) bond length is 1.89 Å. The Cu(1)-F(3) bond length is 1.92 Å. The Cu(1)-F(5) bond length is 2.06 Å. The Cu(1)-F(7) bond length is 2.07 Å. The Cu(1)-F(9) bond length is 2.01 Å. Al(1) is bonded to one F(2), one F(4), one F(6), one F(7), one F(8), and one F(9) atom to form AlF6 octahedra that share corners with two equivalent Cu(1)F5 trigonal bipyramids. The Al(1)-F(2) bond length is 1.80 Å. The Al(1)-F(4) bond length is 1.82 Å. The Al(1)-F(6) bond length is 1.84 Å. The Al(1)-F(7) bond length is 1.89 Å. The Al(1)-F(8) bond length is 1.77 Å. The Al(1)-F(9) bond length is 1.89 Å. There are nine inequivalent F sites. In the first F site, F(1) is bonded in a distorted single-bond geometry to one Ba(2), two equivalent Ba(1), and one Cu(1) atom. In the second F site, F(2) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), and one Al(1) atom. In the third F site, F(3) is bonded in a 1-coordinate geometry to one Ba(2), two equivalent Ba(1), and one Cu(1) atom. In the fourth F site, F(4) is bonded in a distorted single-bond geometry to one Ba(1), two equivalent Ba(2), and one Al(1) atom. In the fifth F site, F(5) is bonded in a 3-coordinate geometry to two equivalent Ba(1) and one Cu(1) atom. In the sixth F site, F(6) is bonded in a distorted single-bond geometry to two equivalent Ba(2) and one Al(1) atom. In the seventh F site, F(7) is bonded in a distorted bent 150 degrees geometry to two equivalent Ba(2), one Cu(1), and one Al(1) atom. In the eighth F site, F(8) is bonded in a distorted single-bond geometry to two equivalent Ba(1) and one Al(1) atom. In the ninth F site, F(9) is bonded in a 2-coordinate geometry to two equivalent Ba(2), one Cu(1), and one Al(1) atom.