Ba2YGaSe5 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. Y(1) is bonded to one Se(1), one Se(2), two equivalent Se(3), and two equivalent Se(4) atoms to form YSe6 octahedra that share edges with two equivalent Y(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 Y(1)Se6 octahedra. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded in a 5-coordinate geometry to one Ba(1), two equivalent Ba(2), one Y(1), and one Ga(1) atom. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to one Ba(2), two equivalent Ba(1), one Y(1), and one Ga(1) atom. In the third Se site, Se(3) is bonded to one Ba(2), two equivalent Ba(1), two equivalent Y(1), and one Ga(1) atom to form distorted SeBa3Y2Ga octahedra that share corners with four equivalent Se(5)Ba4Ga square pyramids, corners with two equivalent Se(4)Ba3Y2 trigonal bipyramids, edges with two equivalent Se(3)Ba3Y2Ga octahedra, edges with three equivalent Se(4)Ba3Y2 trigonal bipyramids, and  a faceface with one Se(5)Ba4Ga square pyramid. In the fourth Se site, Se(4) is bonded to one Ba(1), two equivalent Ba(2), and two equivalent Y(1) atoms to form distorted SeBa3Y2 trigonal bipyramids that share corners with two equivalent Se(3)Ba3Y2Ga octahedra, corners with four equivalent Se(5)Ba4Ga square pyramids, edges with three equivalent Se(3)Ba3Y2Ga octahedra,  an edgeedge with one Se(5)Ba4Ga square pyramid, and edges with two equivalent Se(4)Ba3Y2 trigonal bipyramids. The corner-sharing octahedral tilt angles are 6°. 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 four equivalent Se(3)Ba3Y2Ga octahedra, corners with four equivalent Se(4)Ba3Y2 trigonal bipyramids, edges with two equivalent Se(5)Ba4Ga square pyramids,  an edgeedge with one Se(4)Ba3Y2 trigonal bipyramid, and  a faceface with one Se(3)Ba3Y2Ga octahedra. The corner-sharing octahedral tilt angles range from 44-67°.
Ba2YGaSe5 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 3.34 Å. The Ba(1)-Se(4) bond length is 3.43 Å. There is one shorter (3.35 Å) and one longer (3.74 Å) Ba(1)-Se(2) bond length. There is one shorter (3.45 Å) and one longer (3.57 Å) Ba(1)-Se(3) bond length. There is one shorter (3.27 Å) and one longer (3.32 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 3.39 Å. The Ba(2)-Se(3) bond length is 3.52 Å. There is one shorter (3.39 Å) and one longer (3.65 Å) Ba(2)-Se(1) bond length. There is one shorter (3.35 Å) and one longer (3.56 Å) Ba(2)-Se(4) bond length. There is one shorter (3.29 Å) and one longer (3.33 Å) Ba(2)-Se(5) bond length. Y(1) is bonded to one Se(1), one Se(2), two equivalent Se(3), and two equivalent Se(4) atoms to form YSe6 octahedra that share edges with two equivalent Y(1)Se6 octahedra and edges with two equivalent Ga(1)Se4 tetrahedra. The Y(1)-Se(1) bond length is 2.90 Å. The Y(1)-Se(2) bond length is 2.89 Å. There is one shorter (3.03 Å) and one longer (3.06 Å) Y(1)-Se(3) bond length. There is one shorter (2.83 Å) and one longer (2.84 Å) Y(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 Y(1)Se6 octahedra. The Ga(1)-Se(1) bond length is 2.43 Å. The Ga(1)-Se(2) bond length is 2.43 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 in a 5-coordinate geometry to one Ba(1), two equivalent Ba(2), one Y(1), and one Ga(1) atom. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to one Ba(2), two equivalent Ba(1), one Y(1), and one Ga(1) atom. In the third Se site, Se(3) is bonded to one Ba(2), two equivalent Ba(1), two equivalent Y(1), and one Ga(1) atom to form distorted SeBa3Y2Ga octahedra that share corners with four equivalent Se(5)Ba4Ga square pyramids, corners with two equivalent Se(4)Ba3Y2 trigonal bipyramids, edges with two equivalent Se(3)Ba3Y2Ga octahedra, edges with three equivalent Se(4)Ba3Y2 trigonal bipyramids, and  a faceface with one Se(5)Ba4Ga square pyramid. In the fourth Se site, Se(4) is bonded to one Ba(1), two equivalent Ba(2), and two equivalent Y(1) atoms to form distorted SeBa3Y2 trigonal bipyramids that share corners with two equivalent Se(3)Ba3Y2Ga octahedra, corners with four equivalent Se(5)Ba4Ga square pyramids, edges with three equivalent Se(3)Ba3Y2Ga octahedra,  an edgeedge with one Se(5)Ba4Ga square pyramid, and edges with two equivalent Se(4)Ba3Y2 trigonal bipyramids. The corner-sharing octahedral tilt angles are 6°. 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 four equivalent Se(3)Ba3Y2Ga octahedra, corners with four equivalent Se(4)Ba3Y2 trigonal bipyramids, edges with two equivalent Se(5)Ba4Ga square pyramids,  an edgeedge with one Se(4)Ba3Y2 trigonal bipyramid, and  a faceface with one Se(3)Ba3Y2Ga octahedra. The corner-sharing octahedral tilt angles range from 44-67°.