1.Cyclometalated iridium(III) complexes containing hydroxide/chloride ligands: isolation of heterobridged dinuclear iridium(III) compounds containing μ-OH and μ-pyrazole ligands.
Chandrasekhar V1, Mahanti B, Bandipalli P, Bhanuprakash K. Inorg Chem. 2012 Oct 15;51(20):10536-47. doi: 10.1021/ic300694m. Epub 2012 Sep 26.
The reaction of the cyclometalated chloro-bridged iridium(III) dimers [(ppy)(2) Ir(μ-Cl)](2) (ppyH = 2-phenyl pyridine) and [(tpy)(2)Ir(μ-Cl)](2) (tpyH = 2-p-tolylpyridine) with 3,5-diphenylpyrazole (Ph(2)PzH) in the presence of sodium methoxide resulted in the formation of heterobridged dimers [(ppy)(2)Ir(μ-OH)(μ-Ph(2)Pz)Ir(ppy)(2)] (1) and [(tpy)(2)Ir(μ-OH)(μ-Ph(2)Pz)Ir(tpy)(2)] (2). Interestingly, the reaction of [(ppy)(2)Ir(μ-Cl)](2) with 3(5)-methyl-5(3)-phenylpyrazole (PhMePzH) afforded both a heterobridged dimer, [(ppy)(2)Ir(μ-OH)(μ-PhMePz)Ir(ppy)(2)] (3), and the monomer [(ppy)(2)Ir(PhMePz)Cl] (4). The compound [(ppy)(2)Ir(PhMePz)OH] (5) containing a terminal OH was obtained in a hydrolysis reaction involving 4, sodium methoxide, and PhMePzH. Complexes 1-5 were characterized by X-ray crystallography and electrospray ionization high-resolution mass spectrometry. All of the complexes are luminescent at room temperature in their dichloromethane solutions.
2.Boosting water oxidation layer-by-layer.
Hidalgo-Acosta JC1, Scanlon MD, Méndez MA, Amstutz V, Vrubel H, Opallo M, Girault HH. Phys Chem Chem Phys. 2016 Apr 7;18(13):9295-304. doi: 10.1039/c5cp06890h. Epub 2016 Mar 15.
Electrocatalysis of water oxidation was achieved using fluorinated tin oxide (FTO) electrodes modified with layer-by-layer deposited films consisting of bilayers of negatively charged citrate-stabilized IrO2 NPs and positively charged poly(diallyldimethylammonium chloride) (PDDA) polymer. The IrO2 NP surface coverage can be fine-tuned by controlling the number of bilayers. The IrO2 NP films were amorphous, with the NPs therein being well-dispersed and retaining their as-synthesized shape and sizes. UV/vis spectroscopic and spectro-electrochemical studies confirmed that the total surface coverage and electrochemically addressable surface coverage of IrO2 NPs increased linearly with the number of bilayers up to 10 bilayers. The voltammetry of the modified electrode was that of hydrous iridium oxide films (HIROFs) with an observed super-Nernstian pH response of the Ir(iii)/Ir(iv) and Ir(iv)-Ir(iv)/Ir(iv)-Ir(v) redox transitions and Nernstian shift of the oxygen evolution onset potential.
3.Oxidation of cysteinesulfinic acid by hexachloroiridate(IV).
Bhattarai N1, Stanbury DM. J Phys Chem B. 2014 Jan 30;118(4):1097-101. doi: 10.1021/jp4116723. Epub 2014 Jan 17.
We report the results of an experimental study of the oxidation of cysteinesulfinic acid (CysSO2H) by [IrCl6](2-) in aqueous media at 25 °C in order to gain insight into the mechanisms of oxidation of alkylsulfinic acids by simple one-electron oxidants. When the reaction is performed with exclusion of O2 between pH 3 and 5, it is complete in several seconds. The products are [IrCl6](3-) and CysSO3H. Kinetic data obtained by stopped-flow UV-vis methods with [CysSO2H] ≫ [Ir(IV)]0 reveal the rate law to be -d[Ir(IV)]/dt = k[Ir(IV)](2)[CysSO2H]/[Ir(III)] with a negligible pH dependence. The value of k is (6.8 ± 0.12) × 10(3) M(-1) s(-1) at μ = 0.1 M (NaClO4). A mechanism is inferred in which the first step is a rapid and reversible electron-transfer equilibrium between Ir(IV) and CysSO2(-) to form Ir(III) and CysSO2(•). The second step is the rate-limiting inner-sphere oxidation of CysSO2(•) by Ir(IV). Production of CysSO3H is proposed to occur through hydrolysis of an Ir(III)-bound sulfonyl chloride that is the immediate product of the inner-sphere second step.