Preliminary electrochemical studies of the permeation of mesoporous films of the "molecular square" compound, [Re(Co)3(Cl)(μ-pyrazine)]4, by redox-silent cations:: Redox-active counter anions as reporters on the cation size dependence of the permeation process

The permeation-controlled transport (or lack of transport) of cations of various size through thin films of the "molecular square" compound, [Re(CO)(3)(Cl)(mu-pyrazine)](4), was studied using cyclic voltammetry. Cations smaller than the available cavity in the square molecules were found to permeate the film, while cations larger than the cavity showed no appreciable permeation. The permeation by the redox-silent cations was indirectly observed by monitoring the oxidation of iodide or chloride counter ions. These results indicate that the available cavity size in the title compound is between 4.1 and 6.1 Angstrom, which, as expected, is smaller than the ca. 7.2 Angstrom, Re Re distance observed by X-ray crystallography.