ELECTROCHEMICALLY SWITCHED ANION TRANSLOCATION IN A MULTICOMPONENT COORDINATION COMPOUND

Complex [3a](2+) has been synthesized, which contains one Ni-II cyclam -like and one bipyridine fragment (cyclam = 1,4,8,11-tetraazacyclotetr adecane). Spectrophotometric and potentiometric titration experiments in aqueous solution demonstrated that in the examined pH range (2-10), the Ni-II cyclam-like subunit remains square planar, i.e., it does no t interact with the bipyridine unit, which is instead allowed to bind external metal centers. In particular, in the presence of 0.5 equiv of Cu-II the trinuclear multicomponent coordination compound [Cu-II(3a)( 2)-(H2O)](6+) is the only species existing in solution over a wide pH range. The water molecule bound to the Cu-II center can be substituted by inorganic anions, forming [Cu-II(3a)(2)(anion)](5+) species, and t he binding constants of a series of mononegative anions have been dete rmined, demonstrating the effectiveness of [Cu-II(3a)(2)(H2O)](6+) as an anion receptor. Voltammetric experiments have shown that the two Ni -II centers in [Cu-II(3a)(2)(H2O)](6+) can be reversibly oxidized to N i-III, a d(7) cation which needs further coordination in its axial pos itions. In the case of the [Cu-II(3a)(2)(anion)](5+) species, differen tial-pulse voltammetry experiments demonstrated that on oxidation of t he peripheral Ni-II centers, the anion bound to the central Cu-II cati on jumps onto one of the peripheral Ni-III centers. Thus, the transloc ation of an anion from the center to the periphery (and vice versa) ca n be electrochemically switched for the multicomponent coordination co mpound considered here.