Electrochemical Oxidation of (Ph4As)[IrCl2(CO)2] in the Presence of Tetra(alkyl)ammonium Salts. Electrocrystallization of Different Forms of IridiumBased Linear Chain Complexes

The conducting iridium complexes (TAA)x[IrCl2(CO)2] (where TAA is tetra(n-hexyl)ammonium, tetra(n-butyl) ammonium, and tetra(ethyl)ammonium cation, and x = 0.55, 0.62, and 0.55, respectively) were electrochemically synthesized on a gold electrode through electro-oxidation of [IrCl2(CO)2]- in various organic solvents (dichloromethane, 1,2-dichloroethane, acetonitrile, and 4:1 toluene\acetonitrile) using cyclic voltammetry. In dichloromethane and 1,2dichloroethane electrocrystallization results in formation of long, randomly distributed crystalline needles on the electrode surface. The solid phase grows by a progressive nucleation mechanism followed by one-dimensional growth of microcrystals. These crystals are reversibly reduced in a subsequent anodic voltammetric potential scan. They can also be oxidized at more positive potentials. This second oxidation process results in structural changes of the solid phase and its slow dissolution. In a solution containing tetra(n-butyl)ammonium cations, the deposit forms two distinct structures that can be observed visually. The initially produced film forms an irregular porous structure on the electrode surface. Subsequently, needlelike crystals are deposited on the electrode surface. In a toluene\acetone mixture the process of [IrCl2(CO)2]- oxidation under multicyclic voltammetry conditions results in the formation of a stable electroactive species on the electrode surface. In polar solvents, such as N,N-dimethylformamide or dimethyl sulfoxide, the irreversible oxidation of [IrCl2(CO)2]- occurs without precipitation of any deposit at the electrode surface