FORMATION OF 2-DIMENSIONAL PHASES OF 4,4'-BIPYRIDINE CATION-RADICAL OVER MERCURY IN THE PRESENCE OF IODIDE-IONS

The behavior of 4,4'-bipyridine cation radical (bpyH-2.+) over mercury in the presence of iodide ions at pH 1.5 was studied by cyclic voltam metry, chronoamperometry, and capacity measurements. The results show the occurrence of three nucleation or phase-change processes below 15- degrees-C, all of which can be ascribed to the formation of the cation radical at the electrode. The surface concentration of the cation rad ical obtained is consistent with the occurrence over a given potential range of a mixed bpyH-2.+-I- phase over the electrode at low temperat ures. At more negative potentials than those of the above-mentioned ra nge, a new phase consisting solely of bpyH2.+ is formed that covers th e electrode throughout. The molecular area obtained is intermediate be tween those of molecules lying parallel and normal to the electrode su rface.