Metallopolymeric films featuring widely varying metal-to-metal linkage lengths have been prepared via a combination of oxidative and reductive electropolymerization schemes. Each of the film materials exhibits strong size selective permeability behavior towards molecular reactants, therefore providing a primitive physical basis for selectivity with respect to reactivity at an underlying electrode. Surprisingly, the observed molecular size cut-offs are essentially independent of film composition, implying that a uniform molecular cavity or pore size exists. Attempts to modify effective pore sizes by introducing large ligand substituents (phenyl groups) at the monomer synthesis stage have failed to alter the pattern of size selectivity. We speculate that (a) potential pore size expansion effects expected from linkage length extension are offset by enhanced cross-linking, and/or (b) electrolyte anion templating effects during film synthesis may be defining the effective minimum pore size, thereby yielding uniform permeation size cut-offs.