Single crystals of a new beta-octamolybdate salt containing protonated 1,4-diazabicyclo[2.2.2]octane cations were prepared under mild hydrothermal conditions. This compound, [C6H13N2](2)[C6H14N2][Mo8O26], was then used as a starting material in the synthesis of [C6H13N2](6)[Mo16O53F2]center dot 4H(2)O, which contains previously unreported [Mo16O53F2](12-) anions. The structure-directing properties of gamma-[Mo8O26](4-), a likely intermediate in this pH-dependent transformation, are responsible for the site selection of the fluoride incorporation. [Mo16O53F2](12-), the largest reported polyoxofluoromolybdate cluster, expands upon the limited number of such anions in the literature. The structures of both compounds were determined using single-crystal X-ray diffraction.