Recently, there has been renewed interest in the preparation and properties of compounds that contain one-dimensional chains of metal centers. The unusual properties of these materials make them very attractive for nanotechnology since they offer the possibility of developing electronic devices with very small dimensions. Dihalodicarbonyliridate(I) complexes show a tendency to form linear chains through metal-metal interaction in solid state. One-dimensional crystals of iridium complexes can be prepared by electrochemical oxidation of tetraphenylarsonium dihalodicarbonyliridate(I) in dichloromethane containing tetra(alkyl)ammonium salts as supporting electrolyte. The electrochemical properties of [Ir(CO)₂X₂]¯ (X = Cl, Br, and I) complexes have been studied using cyclic voltammetry, chronoamperometry, electrochemical quartz crystal microbalance (EQCM), and scanning electron microscopy (SEM). The cyclic voltammograms of [IrX₂(CO)₂]¯ (X=Cl, Br, I) oxidation is shown of Figure 1. The first oxidation step (peak O₁) of [IrCl₂(CO)₂]¯ and [IrBr₂(CO)₂]¯ is reversible, and responsible for the formation one-dimensional of the long and thin needles on the electrode surface. The needles are about 10 - 15 µm long and 0.2 - 0.4 µm thick. In the case of [IrI₂(CO)₂]¯, a broad and irreversible oxidation peak is observed. No reduction current was recorded during the negatively going potential sweep. Deposit formed during oxidation of this complex exhibit different morphology. This deposit exhibit three-dimensional structure.

Fig. 1. Cyclic voltammograms recorded in dichloromethane containing 0.05 mol dm^-3 tetra(ethyl)ammonium percghlorate and: (a) 1.7 mmol dm^-3 (Ph₄As)[Ir(CO)₂Cl₂], (b) 1.5 mmol dm^-3 (Ph₄As)[Ir(CO)₂Br₂], (c) 1.5 mmol dm^-3 (Ph₄As)[Ir(CO)₂I₂], at a gold electrode (1.5 mm diameter). The sweep rate was 50 mV s^-1.

The process of [Ir(CO)₂X₂]¯ (X is Br or Cl) oxidation can be described by the following reaction:

The stoichiometry of one-dimensional crystals depends on the electrode reactant (TAA)_0.6[IrCl₂(CO)₂] and (TAA)_0.7[IrBr₂(CO)₂] (TAA is tetra(alkyl)ammonium cation) salts are formed on the electrode surface. In solutions containing high concentration of iridium complexes or upon repeating potential cycling, the formation of electroactive thin film on the electrode surface is observed.

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