Tb3GaO6 crystallizes in the orthorhombic Cmc2_1 space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to one O(1), two equivalent O(4), and four equivalent O(3) atoms to form distorted TbO7 pentagonal bipyramids that share  a cornercorner with one Ga(1)O4 tetrahedra, edges with two equivalent Tb(1)O7 pentagonal bipyramids, and  an edgeedge with one Ga(1)O4 tetrahedra. In the second Tb site, Tb(2) is bonded in a 7-coordinate geometry to one O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. Ga(1) is bonded to one O(1), one O(2), and two equivalent O(4) atoms to form GaO4 tetrahedra that share  a cornercorner with one Tb(1)O7 pentagonal bipyramid and  an edgeedge with one Tb(1)O7 pentagonal bipyramid. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Tb(1), two equivalent Tb(2), and one Ga(1) atom to form distorted OTb3Ga tetrahedra that share corners with eight equivalent O(3)Tb4 tetrahedra,  a cornercorner with one O(2)Tb4Ga trigonal bipyramid, corners with four equivalent O(4)Tb3Ga trigonal pyramids, edges with two equivalent O(2)Tb4Ga trigonal bipyramids, and edges with two equivalent O(4)Tb3Ga trigonal pyramids. In the second O site, O(2) is bonded to four equivalent Tb(2) and one Ga(1) atom to form distorted OTb4Ga trigonal bipyramids that share  a cornercorner with one O(1)Tb3Ga tetrahedra, corners with four equivalent O(3)Tb4 tetrahedra, corners with six equivalent O(4)Tb3Ga trigonal pyramids, edges with two equivalent O(1)Tb3Ga tetrahedra, edges with two equivalent O(3)Tb4 tetrahedra, edges with two equivalent O(2)Tb4Ga trigonal bipyramids, and edges with two equivalent O(4)Tb3Ga trigonal pyramids. In the third O site, O(3) is bonded to two equivalent Tb(1) and two equivalent Tb(2) atoms to form OTb4 tetrahedra that share corners with two equivalent O(3)Tb4 tetrahedra, corners with four equivalent O(1)Tb3Ga tetrahedra, corners with two equivalent O(2)Tb4Ga trigonal bipyramids, corners with six equivalent O(4)Tb3Ga trigonal pyramids, edges with three equivalent O(3)Tb4 tetrahedra,  an edgeedge with one O(2)Tb4Ga trigonal bipyramid, and  an edgeedge with one O(4)Tb3Ga trigonal pyramid. In the fourth O site, O(4) is bonded to one Tb(1), two equivalent Tb(2), and one Ga(1) atom to form distorted OTb3Ga trigonal pyramids that share corners with two equivalent O(1)Tb3Ga tetrahedra, corners with six equivalent O(3)Tb4 tetrahedra, corners with three equivalent O(2)Tb4Ga trigonal bipyramids, corners with two equivalent O(4)Tb3Ga trigonal pyramids,  an edgeedge with one O(1)Tb3Ga tetrahedra,  an edgeedge with one O(3)Tb4 tetrahedra,  an edgeedge with one O(2)Tb4Ga trigonal bipyramid, and  an edgeedge with one O(4)Tb3Ga trigonal pyramid.
Tb3GaO6 crystallizes in the orthorhombic Cmc2_1 space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to one O(1), two equivalent O(4), and four equivalent O(3) atoms to form distorted TbO7 pentagonal bipyramids that share  a cornercorner with one Ga(1)O4 tetrahedra, edges with two equivalent Tb(1)O7 pentagonal bipyramids, and  an edgeedge with one Ga(1)O4 tetrahedra. The Tb(1)-O(1) bond length is 2.41 Å. Both Tb(1)-O(4) bond lengths are 2.44 Å. There are two shorter (2.27 Å) and two longer (2.29 Å) Tb(1)-O(3) bond lengths. In the second Tb site, Tb(2) is bonded in a 7-coordinate geometry to one O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. The Tb(2)-O(1) bond length is 2.36 Å. There is one shorter (2.53 Å) and one longer (2.58 Å) Tb(2)-O(2) bond length. There is one shorter (2.21 Å) and one longer (2.25 Å) Tb(2)-O(3) bond length. There is one shorter (2.27 Å) and one longer (2.39 Å) Tb(2)-O(4) bond length. Ga(1) is bonded to one O(1), one O(2), and two equivalent O(4) atoms to form GaO4 tetrahedra that share  a cornercorner with one Tb(1)O7 pentagonal bipyramid and  an edgeedge with one Tb(1)O7 pentagonal bipyramid. The Ga(1)-O(1) bond length is 1.84 Å. The Ga(1)-O(2) bond length is 1.88 Å. Both Ga(1)-O(4) bond lengths are 1.87 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Tb(1), two equivalent Tb(2), and one Ga(1) atom to form distorted OTb3Ga tetrahedra that share corners with eight equivalent O(3)Tb4 tetrahedra,  a cornercorner with one O(2)Tb4Ga trigonal bipyramid, corners with four equivalent O(4)Tb3Ga trigonal pyramids, edges with two equivalent O(2)Tb4Ga trigonal bipyramids, and edges with two equivalent O(4)Tb3Ga trigonal pyramids. In the second O site, O(2) is bonded to four equivalent Tb(2) and one Ga(1) atom to form distorted OTb4Ga trigonal bipyramids that share  a cornercorner with one O(1)Tb3Ga tetrahedra, corners with four equivalent O(3)Tb4 tetrahedra, corners with six equivalent O(4)Tb3Ga trigonal pyramids, edges with two equivalent O(1)Tb3Ga tetrahedra, edges with two equivalent O(3)Tb4 tetrahedra, edges with two equivalent O(2)Tb4Ga trigonal bipyramids, and edges with two equivalent O(4)Tb3Ga trigonal pyramids. In the third O site, O(3) is bonded to two equivalent Tb(1) and two equivalent Tb(2) atoms to form OTb4 tetrahedra that share corners with two equivalent O(3)Tb4 tetrahedra, corners with four equivalent O(1)Tb3Ga tetrahedra, corners with two equivalent O(2)Tb4Ga trigonal bipyramids, corners with six equivalent O(4)Tb3Ga trigonal pyramids, edges with three equivalent O(3)Tb4 tetrahedra,  an edgeedge with one O(2)Tb4Ga trigonal bipyramid, and  an edgeedge with one O(4)Tb3Ga trigonal pyramid. In the fourth O site, O(4) is bonded to one Tb(1), two equivalent Tb(2), and one Ga(1) atom to form distorted OTb3Ga trigonal pyramids that share corners with two equivalent O(1)Tb3Ga tetrahedra, corners with six equivalent O(3)Tb4 tetrahedra, corners with three equivalent O(2)Tb4Ga trigonal bipyramids, corners with two equivalent O(4)Tb3Ga trigonal pyramids,  an edgeedge with one O(1)Tb3Ga tetrahedra,  an edgeedge with one O(3)Tb4 tetrahedra,  an edgeedge with one O(2)Tb4Ga trigonal bipyramid, and  an edgeedge with one O(4)Tb3Ga trigonal pyramid.