Monolayer shells of polyoxotungstate cluster anions on gold nanoparticles in water were electrostatically stabilized by structurally integrated countercations, with formation constants, K, increasing in the order: Li+ < Na+ < K+ < TMA(+) < Cs+ (TMA(+) = tetramethylammonium). We now report that for hexaniobate cluster anions, K values increase in the same order, with the notable exception of TMA(+), which is effectively unable to induce monolayer formation. These findings point to a new structural model in which hexaniobate anions form a spherical coordination polymer at the gold surface with alkali metal countercations serving as single-atom structural building units between hexaniobate linkers.