Ba2NdGaSe5 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 8-coordinate geometry to one Se(1), one Se(4), two equivalent Se(2), two equivalent Se(3), and two equivalent Se(5) atoms. In the second Ba site, Ba(2) is bonded in a 8-coordinate geometry to one Se(2), one Se(3), two equivalent Se(1), two equivalent Se(4), and two equivalent Se(5) atoms. Nd(1) is bonded to one Se(1), one Se(2), two equivalent Se(3), and two equivalent Se(4) atoms to form NdSe6 octahedra that share edges with two equivalent Nd(1)Se6 octahedra and edges with two equivalent Ga(1)Se4 tetrahedra. Ga(1) is bonded to one Se(1), one Se(2), one Se(3), and one Se(5) atom to form GaSe4 tetrahedra that share edges with two equivalent Nd(1)Se6 octahedra. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded to one Ba(1), two equivalent Ba(2), one Nd(1), and one Ga(1) atom to form distorted SeBa3NdGa trigonal bipyramids that share corners with three equivalent Se(5)Ba4Ga square pyramids, corners with five equivalent Se(4)Ba3Nd2 trigonal bipyramids, edges with two equivalent Se(5)Ba4Ga square pyramids,  an edgeedge with one Se(4)Ba3Nd2 trigonal bipyramid, and  an edgeedge with one Se(1)Ba3NdGa trigonal bipyramid. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to one Ba(2), two equivalent Ba(1), one Nd(1), and one Ga(1) atom. In the third Se site, Se(3) is bonded in a 6-coordinate geometry to one Ba(2), two equivalent Ba(1), two equivalent Nd(1), and one Ga(1) atom. In the fourth Se site, Se(4) is bonded to one Ba(1), two equivalent Ba(2), and two equivalent Nd(1) atoms to form distorted SeBa3Nd2 trigonal bipyramids that share corners with four equivalent Se(5)Ba4Ga square pyramids, corners with five equivalent Se(1)Ba3NdGa trigonal bipyramids,  an edgeedge with one Se(5)Ba4Ga square pyramid,  an edgeedge with one Se(1)Ba3NdGa trigonal bipyramid, and edges with two equivalent Se(4)Ba3Nd2 trigonal bipyramids. In the fifth Se site, Se(5) is bonded to two equivalent Ba(1), two equivalent Ba(2), and one Ga(1) atom to form SeBa4Ga square pyramids that share corners with three equivalent Se(1)Ba3NdGa trigonal bipyramids, corners with four equivalent Se(4)Ba3Nd2 trigonal bipyramids, edges with two equivalent Se(5)Ba4Ga square pyramids,  an edgeedge with one Se(4)Ba3Nd2 trigonal bipyramid, and edges with two equivalent Se(1)Ba3NdGa trigonal bipyramids.
Ba2NdGaSe5 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 8-coordinate geometry to one Se(1), one Se(4), two equivalent Se(2), two equivalent Se(3), and two equivalent Se(5) atoms. The Ba(1)-Se(1) bond length is 3.33 Å. The Ba(1)-Se(4) bond length is 3.45 Å. There is one shorter (3.35 Å) and one longer (3.69 Å) Ba(1)-Se(2) bond length. There is one shorter (3.47 Å) and one longer (3.70 Å) Ba(1)-Se(3) bond length. There is one shorter (3.29 Å) and one longer (3.35 Å) Ba(1)-Se(5) bond length. In the second Ba site, Ba(2) is bonded in a 8-coordinate geometry to one Se(2), one Se(3), two equivalent Se(1), two equivalent Se(4), and two equivalent Se(5) atoms. The Ba(2)-Se(2) bond length is 3.43 Å. The Ba(2)-Se(3) bond length is 3.52 Å. There is one shorter (3.44 Å) and one longer (3.60 Å) Ba(2)-Se(1) bond length. There is one shorter (3.38 Å) and one longer (3.61 Å) Ba(2)-Se(4) bond length. There is one shorter (3.31 Å) and one longer (3.37 Å) Ba(2)-Se(5) bond length. Nd(1) is bonded to one Se(1), one Se(2), two equivalent Se(3), and two equivalent Se(4) atoms to form NdSe6 octahedra that share edges with two equivalent Nd(1)Se6 octahedra and edges with two equivalent Ga(1)Se4 tetrahedra. The Nd(1)-Se(1) bond length is 2.99 Å. The Nd(1)-Se(2) bond length is 2.97 Å. There is one shorter (3.09 Å) and one longer (3.12 Å) Nd(1)-Se(3) bond length. There is one shorter (2.91 Å) and one longer (2.92 Å) Nd(1)-Se(4) bond length. Ga(1) is bonded to one Se(1), one Se(2), one Se(3), and one Se(5) atom to form GaSe4 tetrahedra that share edges with two equivalent Nd(1)Se6 octahedra. The Ga(1)-Se(1) bond length is 2.44 Å. The Ga(1)-Se(2) bond length is 2.44 Å. The Ga(1)-Se(3) bond length is 2.51 Å. The Ga(1)-Se(5) bond length is 2.39 Å. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded to one Ba(1), two equivalent Ba(2), one Nd(1), and one Ga(1) atom to form distorted SeBa3NdGa trigonal bipyramids that share corners with three equivalent Se(5)Ba4Ga square pyramids, corners with five equivalent Se(4)Ba3Nd2 trigonal bipyramids, edges with two equivalent Se(5)Ba4Ga square pyramids,  an edgeedge with one Se(4)Ba3Nd2 trigonal bipyramid, and  an edgeedge with one Se(1)Ba3NdGa trigonal bipyramid. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to one Ba(2), two equivalent Ba(1), one Nd(1), and one Ga(1) atom. In the third Se site, Se(3) is bonded in a 6-coordinate geometry to one Ba(2), two equivalent Ba(1), two equivalent Nd(1), and one Ga(1) atom. In the fourth Se site, Se(4) is bonded to one Ba(1), two equivalent Ba(2), and two equivalent Nd(1) atoms to form distorted SeBa3Nd2 trigonal bipyramids that share corners with four equivalent Se(5)Ba4Ga square pyramids, corners with five equivalent Se(1)Ba3NdGa trigonal bipyramids,  an edgeedge with one Se(5)Ba4Ga square pyramid,  an edgeedge with one Se(1)Ba3NdGa trigonal bipyramid, and edges with two equivalent Se(4)Ba3Nd2 trigonal bipyramids. In the fifth Se site, Se(5) is bonded to two equivalent Ba(1), two equivalent Ba(2), and one Ga(1) atom to form SeBa4Ga square pyramids that share corners with three equivalent Se(1)Ba3NdGa trigonal bipyramids, corners with four equivalent Se(4)Ba3Nd2 trigonal bipyramids, edges with two equivalent Se(5)Ba4Ga square pyramids,  an edgeedge with one Se(4)Ba3Nd2 trigonal bipyramid, and edges with two equivalent Se(1)Ba3NdGa trigonal bipyramids.