Metal/ion systems

Note that the equation for metal-metal ion systems is a special case of this general equation since the reduced state is the metal itself and the concentration of a solid is a constant and omitted from the equation.)... 

Selected other metal ion systems. There have been a number of investigations of the reduction of iron macrocyclic ligand complexes. In one such study, the Fe(n) complex [FeL(CH3CN)2]2+ [where L = (292)] was shown to exhibit three reduction waves in acetonitrile (Rakowski Busch, 1973). Controlled-potential electrolysis at the first reduction plateau (—1.2 V) led to isolation of [FeL]+ for which the esr spectrum is typical of a low-spin Fe(i) system. The quasi-reversible Fe(i)/Fe(n) couple occurs at —0.69 V versus Ag/AgN03. 

Since then, chemists have attempted to synthesize model complexes that contain coordinated and uncoordinated phenoxyl radicals. This chapter reviews this literature from 1994 to early 2000. Earlier efforts describing the chemistry of extended radical-metal ion systems such as those derived from ligands shown in Fig. 1 and their metal complexes and oxidation products (3-13) have been reviewed recently by Goldberg and Lippard (14). The coordination chemistry of these interesting ligands remains to be firmly established as does its redox chemistry. 

The cooperative phenomenon of complexation was also observed for a heteronuclear polymer complex, e.g., the PVP-Cu,Mn mixed metal ion system (Tab. I). Although the complex forming ability of Mn ion itself is weak, the formation constant (K) for the Mn... 

In the last ten years several novel theories for the analysis of NMRD profiles have been proposed for different paramagnetic systems. These have resulted in novel equations and computer programs for numerical calculations. In this review we tried to summarize the classical theory as well as some recent theoretical treatments, and to show their applicability to different metal ion systems by selecting some experimental profiles which exhibit the most characteristic features. In the last few years, dedicated instruments, called field-cycling relaxometers, have appeared on the market... 

We think, however, that this certainly doesn t mean that there aren t any free radicals it means that the detection of these free radicals is going to be very difficult in these metal ion systems. We have to use flow techniques, oxygen-free solutions, and things of this sort in order to do it, and it s rather difficult. 

The theoretical model generally used for predicting the overvoltage-current function for metal/metal ion systems is based on the quasi-thermo-dynamic arguments of transition state theory. The anodic charge transfer process is considered to involve the rupture of the bond between an adatom - i.e. a metal atom in a favourable surface site - and the metal, followed by, or coincident with, the formation of electrostatic bonds between the newly formed ion and solvent or other complexing molecules. The cathodic charge transfer follows this mechanism in reverse ... 

The methanolyses of a series of <9,0-diethyl 0-aryl phosphates (101 X = O) and 0,0-diethyl 5-aryl phosphorothioates (101 X = S) promoted by methoxide and two metal ion systems, (La3+)2(MeO )2 and a complex of Zn2+ (MeO-) with 1,5,9-triazacyclododecane (79 M = Zn), has been studied in methanol at 25 °C. The kinetic data for the metal-catalysed reactions were analysed in terms of a common mechanism where there is extensive cleavage of the P-XAr bond in the transition state. The relevance of these findings to the mechanism of action of a phosphotriesterase enzyme present in a soil bacterium that hydrolyses paraoxon was discussed.100... 

Control of the particle valence/conduction band oxidation/reduction potential is not only achieved through a judicious choice of particle component material band edge redox thermodynamics of a single material are also affected by solution pH, semiconductor doping level and particle size. The relevant properties of the actinide metal are its range of available valence states and, for aqueous systems, the pH dependence of the thermodynamics of inter-valence conversion. Consequently, any study of semiconductor-particle-induced valence control has to be conducted in close consultation with the thermodynamic potential-pH speciation diagrams of both the targeted actinide metal ion system and the semiconductor material. 

Additional chelation in these systems proved to be helpful since the diastereoface discrimination, relative to benzyl bromide (Scheme 90), was greatly improved on going from the ether to a metal alcoholate, and this difference was associated to the chelation of the bulky metal ion system with the lone pair of the pyramidalized nitrogen atom437. 

From the example just discussed, it is clear that complexation can have a dramatic effect upon some of the redox and non-redox properties of a given metal ion system. Changing solution conditions and concentrations may shift the different equilibria from spontaneity to non-spontaneity, and vice versa. See Example 3.2. 

Recent discoveries include other metal ion systems capable of producing OH in a Fentonlike fashion [e.g., Co(II)/organic acid/H202, and Cu(II)/organic aci d/H2 O2 ]. 

A major focus in the study of mixed metal ion systems has been to examine metal ion discrimination. In particular, two specific mechanisms can be attributed to metal ion discrimination macrocyclic hole size and what Lindoy has termed as a dislocation mechaiusm. The key to this... 

Also in other transition metal ion systems, glycinate ligands tend to close the chelate ring rather slowly, e.g. with (Jordan 1994). A correlation with x yields... 

Attention may be called to the fact that if the equilibrium constant could be determined by chemical methods, and if one of the three standard potentials of a particular metal-ion system is known, the other two could be evaluated. This procedure was actually used for copper, the calculations given above being carried out in the reverse direction. ... 

It seems likely that in a system such as T1(I) — Tl(III), similar ideas may be applicable. The difference between these reagents and C1(V) — S(IV) is one of degree rather than kind. The arrangement of water molecules about T1 is undoubtedly strongly disturbed by the pair of s electrons that constitute the electronic difference between the two states of oxidation. However, there is no basis for a definite pronouncement about the mechanism in this or other of the metal ion systems which will be referred to. The treatment of these systems will feature mainly a review of the experimental observations. 

Spreadsheet Summary In the first exercise in Chapter 10 of Applications of Microsoft Excel in Analytical Chemistry, a spreadsheet is developed to calculate the electrode potentials as a function of the ratio of reductant-to-oxidant concentration ([R]/[0]) for the case of two soluble species. Plots of E versus [R]/[0] and E versus log([R]/[0]) are made, and the slopes and intercepts are determined. The spreadsheet is modified for metal/metal ion systems. 

An important aspect of photochemical effects in micelles is the formation and stabilization of charge transfer effects with a view to application in solar energy conversion. An example of this is a study of electron transfer in micellar-metal ion systems, where k and electron transfer yields from S. states of pyrene and N-ethylcarbazole, and the T state of N-methylphenothiazine by a... 

Palmqvist, U. et al.. In situ voltammetric determinations of metal ions in goethite suspensions Single metal ion systems, J. Colloid Interf. Sci. 196, 254, 1997. 

Fig. 9.1 Sketches of half-cells corresponding to (a) a metal metal ion system, (b) the hydrogen electrode, and (c) the silver silver chloride electrode.

In the same way one may define a type III electrode process. Such a system involves three equilibria, one involving the metal metal ion system and two equilibria in solution. Examples of type III electrodes are systems involving complex ions undergoing two complex formation steps. 

The transition metal ions, Cu , Ag and Au", all have a d ( 5) electronic state-configuration, with = 3,4 and 5, respectively. The RCEP used here were generated from Dirac-Fock (DF) all electron (AE) relativistic atomic orbitals, and therefore implicitly include the indirect relativistic effects of the core electron on the valence electrons, which in these metal ion systems are the major radial scaling effect. In these RCEP the s p subshells are included in the valence orbital space together with the d, ( + l)s and ( + l)p atomic orbitals and all must be adequately represented by basis functions. The need for such semi-core or semi-valence electrons to be treated explicitly together with the traditional valence orbitals for the heavier elements has been adequately documented The gaussian function basis set on each metal atom consists of the published 4 P3 distribution which is double-zeta each in the sp and n + l)sp orbital space, and triple-zeta for the nd electrons. 

In this review we discuss five techniques involving Fourier transform mass spectrometry (FTMS) for determining qualitative and quantitative metal ion-ligand bond energies. These include (i) exothermic ion-molecule reactions, (ii) equilibrium measurements, (iii) competitive collision-induced dissociation, (iv) endothermic ion-molecule reactions, and (v) photodissociation. A key advantage of the FTMS methodology is its ion and neutral manipulation capabilities which permit the formation and study of a limitless number of interesting metal-ion systems. 

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