Ba2GaAsSe5 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(2), one Se(3), and two equivalent Se(1) atoms. As(1) is bonded in a distorted T-shaped geometry to one Se(4) and two 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 As(1) atom to form SeBa4As square pyramids that share corners with four equivalent Se(4)Ba4As square pyramids, corners with four equivalent Se(2)Ba4Ga square pyramids, corners with six equivalent Se(1)Ba2GaAs trigonal pyramids, edges with two equivalent Se(2)Ba4Ga square pyramids, edges with four equivalent Se(3)Ba4Ga square pyramids, and edges with two equivalent Se(1)Ba2GaAs trigonal pyramids. In the second Se site, Se(1) is bonded to two equivalent Ba(1), one Ga(1), and one As(1) atom to form distorted SeBa2GaAs trigonal pyramids that share corners with three equivalent Se(4)Ba4As square pyramids, corners with three equivalent Se(2)Ba4Ga square pyramids, corners with three equivalent Se(3)Ba4Ga square pyramids, corners with two equivalent Se(1)Ba2GaAs trigonal pyramids,  an edgeedge with one Se(4)Ba4As square pyramid,  an edgeedge with one Se(2)Ba4Ga square pyramid,  an edgeedge with one Se(3)Ba4Ga square pyramid, and  an edgeedge with one Se(1)Ba2GaAs trigonal pyramid. In the third Se site, Se(2) 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(4)Ba4As square pyramids, corners with four equivalent Se(3)Ba4Ga square pyramids, corners with six equivalent Se(1)Ba2GaAs trigonal pyramids,  an edgeedge with one Se(3)Ba4Ga square pyramid, edges with two equivalent Se(4)Ba4As square pyramids, edges with two equivalent Se(2)Ba4Ga square pyramids, edges with two equivalent Se(1)Ba2GaAs trigonal pyramids, and  a faceface with one Se(3)Ba4Ga square pyramid. In the fourth Se site, Se(3) 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)Ba4Ga square pyramids, corners with four equivalent Se(3)Ba4Ga square pyramids, corners with six equivalent Se(1)Ba2GaAs trigonal pyramids,  an edgeedge with one Se(2)Ba4Ga square pyramid, edges with four equivalent Se(4)Ba4As square pyramids, edges with two equivalent Se(1)Ba2GaAs trigonal pyramids, and  a faceface with one Se(2)Ba4Ga square pyramid.
Ba2GaAsSe5 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 (3.48 Å) and one longer (3.51 Å) Ba(1)-Se(1) bond length. There is one shorter (3.45 Å) and one longer (3.46 Å) Ba(1)-Se(2) bond length. There is one shorter (3.42 Å) and one longer (3.46 Å) Ba(1)-Se(3) bond length. There is one shorter (3.45 Å) and one longer (3.46 Å) Ba(1)-Se(4) bond length. Ga(1) is bonded in a tetrahedral geometry to one Se(2), one Se(3), and two equivalent Se(1) atoms. The Ga(1)-Se(2) bond length is 2.38 Å. The Ga(1)-Se(3) bond length is 2.40 Å. Both Ga(1)-Se(1) bond lengths are 2.47 Å. As(1) is bonded in a distorted T-shaped geometry to one Se(4) and two equivalent Se(1) atoms. The As(1)-Se(4) bond length is 2.44 Å. Both As(1)-Se(1) bond lengths are 2.50 Å. There are four inequivalent Se sites. In the first Se site, Se(4) is bonded to four equivalent Ba(1) and one As(1) atom to form SeBa4As square pyramids that share corners with four equivalent Se(4)Ba4As square pyramids, corners with four equivalent Se(2)Ba4Ga square pyramids, corners with six equivalent Se(1)Ba2GaAs trigonal pyramids, edges with two equivalent Se(2)Ba4Ga square pyramids, edges with four equivalent Se(3)Ba4Ga square pyramids, and edges with two equivalent Se(1)Ba2GaAs trigonal pyramids. In the second Se site, Se(1) is bonded to two equivalent Ba(1), one Ga(1), and one As(1) atom to form distorted SeBa2GaAs trigonal pyramids that share corners with three equivalent Se(4)Ba4As square pyramids, corners with three equivalent Se(2)Ba4Ga square pyramids, corners with three equivalent Se(3)Ba4Ga square pyramids, corners with two equivalent Se(1)Ba2GaAs trigonal pyramids,  an edgeedge with one Se(4)Ba4As square pyramid,  an edgeedge with one Se(2)Ba4Ga square pyramid,  an edgeedge with one Se(3)Ba4Ga square pyramid, and  an edgeedge with one Se(1)Ba2GaAs trigonal pyramid. In the third Se site, Se(2) 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(4)Ba4As square pyramids, corners with four equivalent Se(3)Ba4Ga square pyramids, corners with six equivalent Se(1)Ba2GaAs trigonal pyramids,  an edgeedge with one Se(3)Ba4Ga square pyramid, edges with two equivalent Se(4)Ba4As square pyramids, edges with two equivalent Se(2)Ba4Ga square pyramids, edges with two equivalent Se(1)Ba2GaAs trigonal pyramids, and  a faceface with one Se(3)Ba4Ga square pyramid. In the fourth Se site, Se(3) 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)Ba4Ga square pyramids, corners with four equivalent Se(3)Ba4Ga square pyramids, corners with six equivalent Se(1)Ba2GaAs trigonal pyramids,  an edgeedge with one Se(2)Ba4Ga square pyramid, edges with four equivalent Se(4)Ba4As square pyramids, edges with two equivalent Se(1)Ba2GaAs trigonal pyramids, and  a faceface with one Se(2)Ba4Ga square pyramid.