Single crystals of CsGa7O11, RbGa7O11, and RbGa(4)In(5)O(14)were grown from alkali halide melts and their structures were characterized by single crystal and powder X-ray diffraction. CsGa(7)O(11)and RbGa(7)O(11)adopt the same structure type, reminiscent of the hollandite structure type, as it contains nearly rectangular channels made up of two dimers of edge-sharing GaO(6)octahedra, and two corner-sharing octahedron/tetrahedron pairs. The structure of RbGa(4)In(5)O(14)is more complex and is comprised of indium octahedra, gallium trigonal bipyramids, and gallium tetrahedra, and contains similar sized tunnels as CsGa(7)O(11)and RbGa7O11. CsGa(7)O(11)and RbGa(4)In(5)O(14)were further characterized by TGA, ion exchange experiments, and DFT studies revealing that both structures are thermodynamically stable up to 850 degrees C; however, CsGa(7)O(11)decomposes to GaO(OH) xH(2)O when heated in warm aqueous solutions. CsGa(7)O(11)undergoes ion exchange in both an aqueous solution of RbCl and a RbNO(3)melt, as predicted by DFT studies, where the ion exchange is more extensive in the RbNO(3)melt.