"Perfect" electrochemical molecular sieving by thin and ultrathin metallopolymeric films

Oxidative electropolymerization at glassy carbon and indium-tin-oxide elect rodes from unbuffered aqueous solutions of Fe(5-NH2-phen)(3)(2+) and Ru(5-N H2-phen)(3)(2+) yields electrode-supported films that self-limit at thickne sses of ca. 50 and 2 nm, respectively. Electrodeposition is characterized b y formation of nonelectroactive films, which are electronically insulating at least over the electrochemical potential range of 0 to +1 V. Electrochem ical measurements of redox-active probe molecules demonstrate that these fi lms exhibit highly selective molecular sieving. Neutral permeants and hydro phobic permeants are observed to penetrate the polymeric coating more rapid ly than charged or hydrophilic forms. Atomic force microscopy, UV-vis spect roscopy, and X-ray photoelectron spectroscopy were used to correlate the po lymeric molecular structure with the observed electrochemical reactivity. M olecular sieving behavior is discussed in terms of a membrane transport mod el implying that the films are comprised of metallopolymeric molecular cavi ties of uniform size and distribution.