Water anionic clusters

The diffuse nature of the electron clouds of the anion and the involvement of the hydrogen of the water molecule in binding to the anion make them distinctly different from the corresponding cationic water clusters (Figure 2). In the context of the smaller anionic water clusters, there is a lot of debate on whether the anion is solvated within a shell of water molecules (internal state) or the anion is bound to a condensed phase network of water molecules (surface solvated ionic state) [30,47-51]. 

Thus, cation water clusters favour internal structures in contrast to the surface strucmres favoured by anionic water clusters. This critical difference in the structural preferences of hydrated cation and anion clusters provides important cues for the design of cation- and anion-specific ionophores and receptors. Indeed, we note that most cation receptors have spherical structures, while almost all anion receptors do not have compact spherical structures but have a vacant space around the anion binding site without full coordination (which might be exceptional for the F ion with strong electronegativity for which the excess electron is strongly bound to F due to its small ion radius). However, as the temperature increases, the hydration structure tends to be more spherical due to entropy effects. 

Static structural calculations for the water cluster anion have revealed the quantum mechanical origin of the binding force for the excess electron and various equilibrium structures. [87, 158, 195, 211, 339] It is now established that the excess electron is bound principally by the dipole field formed by the water molecules. In their elaborate studies on the potential landscape of anion water clusters, Choi and Jordan [87] explored a large number of local minima as well as the transition states on the potential... 

C. F. Williams and J. M. Herbert,/. Phys. Chem. A, 112, 6171-6178 (2008). Influence of Structure on Electron Correlation Effects and Electron-Water Dispersion Interactions in Anionic Water Clusters. 

The uptake and hydrolysis of N2Os on pure liquid water appears to be about the same as for sulfuric acid-water mixtures, ranging from about 0.01 to 0.06 over the temperature range from 262 to 293 K (e.g., Van Doren et al., 1990 Kirchner et al., 1990 George et al., 1994). It is also noteworthy that similar reactions of N205 occur with anionic and cationic water clusters (Wincel et al., 1994, 1995). 

Submitted by MICHAEL 1. BRUCE and MICHAEL L. WILLIAMS Checked by GUY LAVIGNE and TH RESE ARLIGUIEt This tetranuclear ruthenium carbonyl hydride was described on several occasions,5 but early preparations were usually contaminated with Ru3(CO)12, giving rise to suggestions of the existence of two isomeric forms. The situation was clarified by the work of Kaesz and coworkers,6 who discovered the direct route from Ru3(CO)12 and hydrogen, which is described below. The compound is often obtained from reactions between Ru3(CO)12 and substrates containing hydrogen (hydrocarbons, ethers, alcohols, water, etc.) and by acidification of anionic ruthenium cluster carbonyls.7... 

Byrne, P., Lloyd, G. 0., Clarke, N., Steed, J. W., A compartmental Borromeo sheet coordination polymer exhibiting saturated hydrogen bonding to anions and water cluster inclusion. Angew. Chem. 2008, 47, 5761-5764. 

The possible accumulation of negative ions at the air/ water interface was first predicted by Perera and Berkow-itz,8 who found out from molecular dynamics simulations, surprisingly, that the large anions (Cl , Br , and I ) are expelled from water clusters to their interface. Their predictions are supported by the recent large-scale molecular dynamics simulations for the air/water interface of various electrolyte solutions, which reveal that, when the polarization of ions and water molecules is explicitly taken into account, the large anions are accumulated near the interface.9... 

Jalbout A, Adamowicz L (2001). Dipole-bound anions of adenine-water clusters. Ab initio study. 

Schiedt J, Weinkauf R, Neumark DN, Schlag E (1998). Anion spectroscopy of uracil, thymine and the amino-oxo and amino-hydroxy tautomers of cytosine and their water clusters. Chem Phys 239 511-524. 

Figure 5. Schematic energy diagram for photoexcitation into CTTS precursor states in I (water) clusters. Abs and VDE represent CTTS-type absorption and vertical detachment energy from the anion ground state, respectively.

J.E. Combariza, N.R. Kestner and J. Jortner, Energy-structure relationships for microscopic solvation of anions in water clusters, J. 

Another interesting application is the selective reduction of aldehyde functions under water-gas shift reaction conditions [21]. Starting from Rh6(CO)i6 in the presence of an amine in aqueous media, the anionic cluster anion [Rh6(CO)i5H] forms via nucleophilic attack of hydroxide, followed by elimination of carbon dioxide. The anionic hydride cluster is thought to be the active species in the reduction of a number of aldehydes according to eq. (10). 

Water can be used as the hydrogen source in reduction of p-benzoqui-none to p-dihydroxybenzene in the presence of the anionic platinum cluster [Pt12(CO)24]2... 

G. Jacoby, U. Kaldor, and P. Jungwirth, Relaxation of chlorine anions solvated in small water clusters upon electron photodetachment the three lowest potential energy surfaces of the neutral CI H2O complex, Chem. Phys. Lett. 293, 309-316 (1998). (d) J. Baik, J. Kim,... 

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