Crucial role of anions on the deprotonation of the cationic dihydrogen complex trans-[FeH(eta2-H2)(dppe)2]+

The kinetics of reaction of the dihydrogen complex trans-[FeH(eta2-H2)(dppe)2]+ with an excess of NEt3 to form cis-[FeH2(dppe)2] shows a first-order dependence with respect to both the metal complex and the base. The corresponding second-order rate constant only shows minor changes when the solvent is changed from THF to acetone. However, the presence of salts containing the BF4-, PF6-, and BPh4- anions causes larger kinetic changes, the reaction being accelerated by BF4- and PF6- and decelerated in the presence of BPh4-. These results can be interpreted considering that the ion pairs formed by the complex and the anion provide a reaction pathway more efficient than that going through the unpaired metal complex. From the kinetic results in acetone solution, the stability of the ion pairs and the rate constant for their conversion to the reaction products have been derived. Theoretical calculations provide additional information about the reaction mechanism both in the absence and in the presence of anions. In all cases, the reaction occurs with proton transfer from the trans-dihydride to the base through intermediate structures showing Fe-H2...N and Fe-H...H...N dihydrogen bonds, isomerization to the cis product occurring once the proton transfer step has been completed. Optimized geometries for the ion pairs show that the anions are placed close to the H2 ligand. In the case of BPh4-, the bulky phenyls hinder the approach of the base and make the ion pairs unproductive for proton transfer. However, ion pairs with BF4- and PF6- can interact with the base and evolve to the final products, the anion accompanying the proton through the whole proton transfer process, which occurs with an activation barrier lower than for the unpaired metal complex.     

Interaction of copper and NO2: Effect of joint presence of SO2, relative humidity and temperature

This paper reports laboratory tests involving the dry deposition on copper surfaces of NO₂, alone and in combination with SO₂, at different concentrations (200 and 800 μg m⁻³), temperatures (15, 25 and 35 °C) and relative humidities (50%, 70% and 90%). Gravimetric results and characterisation of the corrosion products by optical microscopy, scanning electron microscopy (SEM/EDX), grazing incidence X-ray diffraction (GIXD) and X-ray photoelectron spectroscopy (XPS) show that the corrosive effect of NO₂ acting alone depends greatly on the RH. At 90% RH copper behaves in the same way as in unpolluted atmospheres, while at lower RH localised attack is detected. Analysis reveals the presence of basic copper nitrate (gerhardtite, Cu₂(OH)₃NO₃). However, in SO₂-polluted atmospheres no differential behaviour with RH or temperature is observed. In these atmospheres copper corrosion is similar to that obtained in unpolluted or in NO₂-polluted atmospheres at high RH, although GIXD detects basic copper sulphate (posnjakite, Cu₄(OH)₆SO₄·2H₂O). In the case of mixed atmospheres (SO₂+NO₂) a significant accelerating effect is observed when [NO₂]>[SO₂]. Otherwise an inhibitive effect is detected. At high RH in the presence of SO₂, NO₂ favours SO₂ oxidation and finally sulphuric acid formation, which attacks the cuprite layer. S-containing compounds, especially basic copper sulphate, are easily detected by GIXD and XPS in the outermost corrosion product layer. However, at low RH, NO₂ reacts preferentially with adsorbed water to produce nitrous and nitric acids that attack the cuprite layer. In this case, an outer corrosion product layer containing copper nitrite (soluble) and basic copper nitrate is formed over an intermediate layer that contains significant amounts of basic copper sulphate from the previous interaction of sulphuric acid and cuprite.     

Study of the charge displacement at constant potential during CO adsorption on Pt(110) and Pt(111) electrodes in contact with a perchloric acid solution

A new electrochemical approach has been made, employing the current—time transient responses when a CO adlayer is formed at a platinum electrode at various controlled potentials where CO oxidation does not take place. The case of Pt(110) is compared with those of Pt(111) and Pt(111) disordered after ten cycles of oxygen adsorption—desorption. In order to avoid interference with anion-specific adsorption, the study was carried out in a perchloric acid solution. There is good agreement between the charge measured by voltammetry in the absence of CO and the charges measured during the current—time transients. This is indicative that the latter charges are produced by the displacement of the species at the interface as a result of CO adlayer formations. The sign of the current transient has been found to depend on the potential at which CO adsorption is carried out. This dependence may be related to the nature of species which are present in the interfacial region, providing new complementary information that voltammetry cannot yield.     

Mild, Reversible Reaction of Iridium(III) Amido Complexes with Carbon Dioxide

Unlike some other Ir(III) hydrides, the aminopyridine complex [(2-NH(2)-C(5)NH(4))IrH(3)(PPh(3))(2)] (1-PPh(3)) does not insert CO(2) into the Ir-H bond. Instead 1-PPh(3) loses H(2) to form the cyclometalated species [(κ(2)-N,N-2-NH-C(5)NH(4))IrH(2)(PPh(3))(2)] (2-PPh(3)), which subsequently reacts with CO(2) to form the carbamato species [(κ(2)-O,N-2-OC(O)NH-C(5)NH(4))IrH(2)(PPh(3))(2)] (10-PPh(3)). To study the insertion of CO(2) into the Ir-N bond of the cyclometalated species, a family of compounds of the type [(κ(2)-N,N-2-NR-C(5)NH(4))IrH(2)(PR'(3))(2)] (R = H, R' = Ph (2-PPh(3)); R = H, R' = Cy (2-PCy(3)); R = Me, R' = Ph (4-PPh(3)); R = Ph, R' = Ph (5-PPh(3)); R = Ph, R' = Cy (5-PCy(3))) and the pyrimidine complex [(κ(2)-N,N-2-NH-C(4)N(2)H(3))IrH(2)(PPh(3))(2)] (6-PPh(3)) were prepared. The rate of CO(2) insertion is faster for the more nucleophilic amides. DFT studies suggest that the mechanism of insertion involves initial nucleophilic attack of the nitrogen lone pair of the amide on CO(2) to form an N-bound carbamato complex, followed by rearrangement to the O-bound species. CO(2) insertion into 1-PPh(3) is reversible in the presence of H(2) and treatment of 10-PPh(3) with H(2) regenerates 1-PPh(3), along with Ir(PPh(3))(2)H(5).     

Determination of the entropy of formation of the Pt(111)∣ perchloric acid solution interface. Estimation of the entropy of adsorbed hydrogen and OH species

The entropy of formation of the interface between a Pt(111) electrode and a 0.1-M HClO₄ solution is calculated here for the first time from the temperature dependence of total charge vs potential curves following a thermodynamic analysis based on the electrocapillary equation. From this quantity, the absolute entropies of specifically adsorbed species (hydrogen and OH) can be estimated. The present method is an alternative treatment of data that overcomes some of the limitations involved in the approach that uses a generalized isotherm. However, it requires additional experimental data: the temperature coefficient of the potential of zero total charge of the working electrode and the temperature coefficient of the reference electrode. Comparison of the results obtained by both approaches shows that, for hydrogen adsorption, the agreement is reasonable, but the differences are larger for OH adsorption, thus showing the limitations inherent in the treatment based on the generalized isotherm. Dedicated to Professor Oleg Petrii on the occasion of his 70th birthday on August 24, 2007.     

An oscillating C2(2-) unit inside a copper rectangle

[Cu4(mu-dppm)4(mu4-eta1,eta2-C[triple bond]C-)]2+ has been shown by 31P and 1H NMR studies to undergo two fluxional processes in solution, the oscillation of the C[triple bond]C2- unit inside the copper rectangle and the flipping of the diphosphines, and this has been supported by DFT(B3LYP) calculations.