Ba2GaBiSe5 crystallizes in the orthorhombic Pnma space group. Ba(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent Se(2), two equivalent Se(3), and two equivalent Se(4) atoms. Ga(1) is bonded in a tetrahedral geometry to one Se(3), one Se(4), and two equivalent Se(1) atoms. Bi(1) is bonded in a 6-coordinate geometry to one Se(2), one Se(3), and four equivalent Se(1) atoms. There are four inequivalent Se sites. In the first Se site, Se(4) is bonded to four equivalent Ba(1) and one Ga(1) atom to form distorted SeBa4Ga square pyramids that share corners with four equivalent Se(2)Ba4Bi square pyramids, corners with six equivalent Se(1)Ba2GaBi2 trigonal bipyramids, edges with two equivalent Se(2)Ba4Bi square pyramids, edges with two equivalent Se(4)Ba4Ga square pyramids, and edges with two equivalent Se(1)Ba2GaBi2 trigonal bipyramids. In the second Se site, Se(1) is bonded to two equivalent Ba(1), one Ga(1), and two equivalent Bi(1) atoms to form distorted SeBa2GaBi2 trigonal bipyramids that share corners with two equivalent Se(2)Ba4Bi square pyramids, corners with three equivalent Se(4)Ba4Ga square pyramids, corners with five equivalent Se(1)Ba2GaBi2 trigonal bipyramids,  an edgeedge with one Se(4)Ba4Ga square pyramid, edges with two equivalent Se(2)Ba4Bi square pyramids, and edges with two equivalent Se(1)Ba2GaBi2 trigonal bipyramids. In the third Se site, Se(2) is bonded to four equivalent Ba(1) and one Bi(1) atom to form SeBa4Bi square pyramids that share corners with four equivalent Se(2)Ba4Bi square pyramids, corners with four equivalent Se(4)Ba4Ga square pyramids, corners with four equivalent Se(1)Ba2GaBi2 trigonal bipyramids, edges with two equivalent Se(4)Ba4Ga square pyramids, and edges with four equivalent Se(1)Ba2GaBi2 trigonal bipyramids. In the fourth Se site, Se(3) is bonded in a 6-coordinate geometry to four equivalent Ba(1), one Ga(1), and one Bi(1) atom.
Ba2GaBiSe5 crystallizes in the orthorhombic Pnma space group. Ba(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent Se(2), two equivalent Se(3), and two equivalent Se(4) atoms. There is one shorter (3.46 Å) and one longer (3.59 Å) Ba(1)-Se(1) bond length. There is one shorter (3.46 Å) and one longer (3.48 Å) Ba(1)-Se(2) bond length. There is one shorter (3.46 Å) and one longer (3.50 Å) Ba(1)-Se(3) bond length. There is one shorter (3.44 Å) and one longer (3.45 Å) Ba(1)-Se(4) bond length. Ga(1) is bonded in a tetrahedral geometry to one Se(3), one Se(4), and two equivalent Se(1) atoms. The Ga(1)-Se(3) bond length is 2.43 Å. The Ga(1)-Se(4) bond length is 2.37 Å. Both Ga(1)-Se(1) bond lengths are 2.47 Å. Bi(1) is bonded in a 6-coordinate geometry to one Se(2), one Se(3), and four equivalent Se(1) atoms. The Bi(1)-Se(2) bond length is 2.72 Å. The Bi(1)-Se(3) bond length is 3.36 Å. There are two shorter (2.79 Å) and two longer (3.23 Å) Bi(1)-Se(1) bond lengths. There are four inequivalent Se sites. In the first Se site, Se(4) is bonded to four equivalent Ba(1) and one Ga(1) atom to form distorted SeBa4Ga square pyramids that share corners with four equivalent Se(2)Ba4Bi square pyramids, corners with six equivalent Se(1)Ba2GaBi2 trigonal bipyramids, edges with two equivalent Se(2)Ba4Bi square pyramids, edges with two equivalent Se(4)Ba4Ga square pyramids, and edges with two equivalent Se(1)Ba2GaBi2 trigonal bipyramids. In the second Se site, Se(1) is bonded to two equivalent Ba(1), one Ga(1), and two equivalent Bi(1) atoms to form distorted SeBa2GaBi2 trigonal bipyramids that share corners with two equivalent Se(2)Ba4Bi square pyramids, corners with three equivalent Se(4)Ba4Ga square pyramids, corners with five equivalent Se(1)Ba2GaBi2 trigonal bipyramids,  an edgeedge with one Se(4)Ba4Ga square pyramid, edges with two equivalent Se(2)Ba4Bi square pyramids, and edges with two equivalent Se(1)Ba2GaBi2 trigonal bipyramids. In the third Se site, Se(2) is bonded to four equivalent Ba(1) and one Bi(1) atom to form SeBa4Bi square pyramids that share corners with four equivalent Se(2)Ba4Bi square pyramids, corners with four equivalent Se(4)Ba4Ga square pyramids, corners with four equivalent Se(1)Ba2GaBi2 trigonal bipyramids, edges with two equivalent Se(4)Ba4Ga square pyramids, and edges with four equivalent Se(1)Ba2GaBi2 trigonal bipyramids. In the fourth Se site, Se(3) is bonded in a 6-coordinate geometry to four equivalent Ba(1), one Ga(1), and one Bi(1) atom.