Some Isoperimetric Inequalities in Electrochemistry and Hele Shaw Flows

Isoperimetric inequalities are applied to a moving-boundaryproblem for doubly-connected domains. This problem occurs forexample in electrochemistry, in which case the domains in questionare the electrolyte of an electrolytic cell. The two electrodessurrounding the electrolyte are assumed to grow or dissolve,at different rates in general, by electrochemical reaction.We obtain optimal estimates showing, for example, that the leastchange in volume of each electrode always occurs in sphericalsymmetry.     

Probing the self-assembly of inorganic cluster architectures in solution with cryospray mass spectrometry: growth of polyoxomolybdate clusters and polymers mediated by silver(I) ions

Cryospray mass spectrometry (CSI-MS) has been used to probe the mechanism of self-assembly of polyoxometalate clusters in solution. By using CSI-MS and electronic absorbance spectroscopy it was possible to monitor in real-time the self-assembly of polymeric chains based on [Ag 2Mo 8O 26] (2-) n building blocks. The role of the Ag (I) ion in the solution state rearrangement of molybdenum Lindqvist ({Mo 6}) into the silver-linked beta-octamolybdate ({Mo 8}) structure (( n-C 4H 9) 4N) 2 n [Ag 2Mo 8O 26] n ( 1) is revealed in unprecedented detail. A monoanionic series, in particular [AgMo m O 3 m+1 ] (-) where m = 2 to 4, and series involving mixed oxidation state polyoxomolybdate species, which illustrate the in-solution formation of the (Ag{Mo 8}Ag) building blocks, have been observed. CSI-MS detection of species with increasing metal nuclearity concomitant with increasing organic cation contribution supports the hypothesis that the organic cations used in the synthesis play an important structure-directing role in polyoxometalate (POM) growth in solution. A real-time decrease in [{Mo 6}] and associated increase in [{Mo 8}] have been observed using CSI-MS and electronic absorbance spectroscopy, and the rate of {Mo 6} interconversion to {Mo 8} was found to decrease on increasing the size of the countercation. This result can be attributed to the steric bulk of larger organic groups hindering {Mo 6} to {Mo 8} rearrangement and hindering the contact between silver cations and molybdenum anions.     

Gas-phase study of the chemistry and coordination of lead(II) in the presence of oxygen-, nitrogen-, sulfur-, and phosphorus-donating ligands

Using a pickup technique in association with high-energy electron impact ionization, complexes have been formed in the gas phase between Pb(2+) and a wide range of ligands. The coordinating atoms are oxygen, nitrogen, sulfur, and phosphorus, together with complexes consisting of benzene and argon in association with Pb(2+). Certain ligands are unable to stabilze the metal dication, the most obvious group being water and the lower alcohols, but CS(2) is also unable to form [Pb(CS(2))(N)](2+) complexes. Unlike many other metal dication complexes, those associated with lead appear to exhibit very little chemical reactivity following collisional activation. Such reactions are normally promoted via charge transfer and are initiated using the energy difference between M(2+) + e(-) --> M(+) and L --> L(+) + e(-), which is typically approximately 5 eV. In the case of Pb(2+), this energy difference usually leads to the appearance of L(+) and the loss of a significant fraction of the remaining ligands as neutral species. In many instances, Pb(+) appears as a charge-transfer product. The only group of ligands to consistently exhibit chemical reactivity are those containing sulfur, where a typical product might be PbS(+)(L)(M) or PbSCH(3)(+)(L)(M).     

Fragmentation pathways of [Mg(NH3)n]2+ complexes: electron capture versus charge separation

New experimental results are presented from a detailed study of gas-phase [Mg(NH(3))(n)](2+) complexes and their fragmentation pathways. The reactions examined range from those observed as metastable (unimolecular) decompositions through to collision-induced processes, which have been accessed using a variety of collision gases. Measurements of ion intensity distributions coupled with unimolecular decay studies show that [Mg(NH(3))(4)](2+) not only is the most intense species detected but also sits at a critical boundary between complexes that are unstable with respect to charge separation and those that are sufficiently solvated to be deemed stable on the time scale of the experiment. Metastable fragmentation patterns have been used to provide information on the evolution of solvent structure around the central dication. In addition to highlighting the particular significance of [Mg(NH(3))(4)](2+), these measurements show some evidence to suggest the buildup of structures via a hydrogen-bonded network to give conformers of the form (4+1) and (4+2), respectively. Collision-induced dissociation studies show the ions to exhibit several fragmentation pathways, including the loss of NH(3) and NH(3) + H, which are promoted primarily through electron capture dissociation (ECD). This picture contrasts with the conclusion from a number of earlier studies that collisional activation mainly promotes charge separation. From the results presented it is suggested that electron capture may play a more dominant role in the charge reduction of multiply charged metal-ligand species than had previously been appreciated.     

What is required to stabilize Al3+? A gas-phase perspective

With a combination of experiment and theory (ab initio and DFT), we demonstrate that the Al(3+) cation can be stabilized in the gas phase using ligands, which have the ability to act as powerful sigma electron donors and electron acceptors. The latter property, which implies that electron density from the aluminum cation moves into ligand antibonding orbitals, has not previously been considered significant when accounting for the behavior of Al(3+). Of the three ligands identified as falling into the above category, acetonitrile appears to form the most stable complexes in the gas phase, which is in accord with the long established fact that solid-state complexes with Al(3+) are readily isolated. From the results, it is suggested that chain or ring compounds containing the -C triple bond N group might act as successful sequestering agents for Al(3+) from aqueous solutions.