Hydration metal ions

Structural investigations of metal-ion hydration have been carried out by spectroscopic, scadering and diffraction teclmiques, but these teclmiques do not always give identical results since they measure in different timescales. There are tliree distinct types of measurement ... 

Pratt, L. R., Rempe, S. B., Topol, I. A., and Burt, S. K. (2000). Alkali metal ion hydration and energetics of selectivity by ion-channels. Biophys.J. 78, P2057-P2057. 

An interesting combined use of discrete molecular and continuum techniques was demonstrated by Floris et al.181,182 They used the PCM to develop effective pair potentials and then applied these to molecular dynamics simulations of metal ion hydration. Another approach to such systems is to do an ab initio cluster calculation for the first hydration shell, which would typically involve four to eight water molecules, and then to depict the remainder of the solvent as a continuum. This was done by Sanchez Marcos et al. for a group of five cations 183 the continuum model was that developed by Rivail, Rinaldi et al.14,108-112 (Section III.2.ii). Their results are compared in Table 14 with those of Floris et al.,139 who used a similar procedure but PCM-based. In... 

There are only few main group metal ion hydrates open to detailed mechanistic study of water exchange by NMR Be , Mg , Al" , Ga" and to a less extent, In" . They provide the opportunity to study the influence of size and charge on exchange rate constant and mechanism without the complicating effects of the variation of the electronic occupancy of the d-orbitals. All of the alkali ions as well as Ca , Sr, and Ba are very labile as a consequence of their relatively low surface charge density. However, indications on water exchange on Sr " can be obtained from... 

Table 12.1. Colours of Transition Metal Ion Hydrates in Solution j (Together with those of certain preceding and following ions)...

Robinson RA, Stokes RH (1959) Electrolyte Solutions, 2nd edn. Butterworths, London Rode BM, Lim LHV (2010) The influence of the lone electron pair on structure and dynamics of divalent group IV metal ion hydrates. J Mol Liq 157 79-82 Sacco A, Weingartner H, Braun BM, Holz M (1994) Study of the stiucture-breaking effect on aqueous CsCl solutions based on H20/D20 isotope effects on transpoit coefficients and microdynamical properties. J Chem Soc Faraday Trans 90 849-854 Samoilov OYa (1957) A new approach to the study of hydration of ions in aqueous solutions. Disc Faraday Soc 24 141-146... 

The most common procedure involves the reduction of solution phase metal ions - hydrated or complexed -to elemental metal on the cathode. In the case of anodic deposition of metal as an oxide or halide, the stoichiometry must include any water present. 

The method of direct visual observation can be used in conjunction with in-situ Raman spectra. X-ray absorption fine structure (XAFS) and X-ray diffraction measurements (Zotov and Keppler, 2000 Fulton et al., 2000 Schmidt and Rickers, 2003 Bassett etal., 2000 Mayanovic etal., 2003) to study salt solubility, metal ion hydration, complexation and oxidation state in aqueous solution in a wide range of temperatures and pressures, and with the hydrothermal scanning force microscopy technique (Higgins etal., 1998) for observation of the advance or retreat of atomic layers (steps) on a crystal surface during the processes of dissolution or crystal growth. 

Kebarle cites calculations using a model involving Lennard-Jones (6,12) potential energy terms, plus ion-dipole, ion-induced-dipole, and dipole-dipole terms that agreed weU with most of the experimental findings for the alkah-metal ion hydrates. It was found necessary to allow explicitly for some covalent interaction between sodium or (especially) lithium and the first two or three water molecnles. 

Model calculations have been employed in elucidating the mechanism of electron transfer reactions in aqueous solution. The contribution of inner shell OH bonds to activation barriers has been estimated from calculation for metal ion hydrates. Calculated electron transfer matrix elements (Hjf) for redox processes of the type, MLe + MLe =... 

A very complicated quantum mechanical model for computation of the energies of metal ion hydration has been used which, in addition to the coordination sphere, included two hydration shells, with limited success. There were attempts to apply molecular modeling for a better understanding of the ligand exchange processes. Success has been achieved in applying the ab ini-... 

Brittain HG, Choppin GR, Barthelemy P.P. pH-dependence of the metal ion hydration state in lanthanide complexes of polyaminopolycarboxylate ligands. J Coord Chem. 1992 26 143-153. 

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