Aquation

About: Aquation is a research topic. Over the lifetime, 1443 publications have been published within this topic receiving 17507 citations.

Ligand Exchange in Pd(II)-NaCl-H2O and Pd(II)-HCl-H2O Systems: Quantum-Chemical Consideration

Abstract: The behavior of potassium tetrachloropalladate(II) in media simulating biological liquids is studied. The rate of aquation in aqueous NaCl solutions is shown to be higher than the rate at which the Cl− ligand enters the inner coordination sphere of the Pd atom. In HCl solutions, the formation of the Pd chloro complexes predominates due to protonation of water molecules in the composition of aqua complexes. The reactions of replacement of the ligands (H2O molecules and H3O+ ion) in the planar Pd(II) complexes by the chloride ion are studied by the ZINDO/1 method. All the complexes containing H2O and H3O+ ligands, except for [Pd(H2O)4]2+, contain intramolecular hydrogen bonds. The ZINDO/1 and RHF/STO-6G(d) calculations revealed “nonclassic” symmetrical O⋯ H⋯O hydrogen bond in the [[Pd(H2O)3(H3O)]3+ and trans-[Pd(H2O)2(H3O)Cl]2+ complexes. The replacement of the H3O+ ion by the Cl− ion at the first three steps is thermodynamically more advantageous than the displacement of water molecules from the metal coordination sphere. The logarithms of stepwise stability constants of Pd(II) chloro complexes are found to correlate linearly with the enthalpies (ZINDO/1, PM3) of reactions of H2O replacement by Cl−.

A study of some redox reactions of the chromium(II)–ethylenediamine-tetra-acetate complex. Evidence for outer-sphere mechanisms

Abstract: Reactions of the chromium(II)–EDTA complex with CrF2+, CrCl2+, CrBr2+, Co(NH3)5Cl2+, Cl2, Br2, I2, and IrCl62– have been studied in perchlorate reaction media pH 2·7–5·0, and at temperatures in the range 0–20°. The reactions are all rapid and final spectra were recorded within 3 min. of mixing. The products are [CrIIIYH(H2O)] and the related conjugate-base form [CrIIIY(H2O)]–(ethylenediaminetetra-acetate, EDTA = Y4–). Complexes of the type [CrIIIYH(X)]–, where X– is a halide ion, have not as yet been prepared. If it is assumed that the aquation of such complexes is slow then the chromium(II)–EDTA reactions are probably of the outer-sphere type. Other possible mechanisms are considered. Reactions with H2O2, O2, and (H2O)4Cr(OH)2Cr(H2O)44+ are also rapid, the same products are obtained, and there is no evidence for the formation of binuclear chromium(III)–EDTA complexes. Again outer-sphere mechanisms are a strong possibility.

Mechanism of the nitrous acid-catalysed aquation of aquochromium(III) complexes

Abstract: Nitrous acid, in perchloric acid, dramatically increases the rate of aquation of Cr(H2O)5X2+(X = Cl or Br), cis- and trans-Cr(H2O)4Cl2+, and cis-Cr(NH3)4(OH2)Cl2+, but has little effect upon the rate of hydrolysis of Cr(NH3)5Br2+ and trans-Cr(NH3)4(OH2)Cl2+. The mechanism is believed to involve the formation of traces of nitrito-intermediates by O-nitrosation, with H2NO2+ or NO+ as the nitrosating agent. These preliminary results indicate that the catalysis may be stereospecifically restricted to complexes containing an aquo-ligand in a cis-position relative to the leaving group. Some new nitrito-chromium(III) compounds are reported.

Substitution reactions of trans-[Ru(NH3)4{P(OEt)3}(H2O)]2+ revisited. Mechanistic elucidation from a volume-profile analysis

Abstract: The complex-formation reactions of trans-[Ru(NH3)4{P(OEt)3}(H2O)]2+ with L = imidazole (Him), isonicotinamide (isn) and pyrazine (pyz) were studied in aqueous solution (I= 0.10 mol dm–3, CF3CO2Na) as a function of entering ligand concentration and pressure up to 100 MPa, at 25.0 ± 0.1 °C. The volumes of activation for the complex-formation reactions were +4.2 ± 0.2 (pH 8.6), +1.9 ± 0.3 (pH 5.3) and +2.0 ± 0.3 cm3 mol–1(pH 5.0), for L = Him, isn and pyz, respectively. In the case of isn and pyz as entering ligands the volumes of activation for the reverse aquation reactions were found to be +7.5 ± 0.4 and +10.4 ± 0.3 cm3 mol–1, respectively. Based on the volume of activation data and the constructed volume profiles a dissociative interchange mechanism is proposed.