Transition metals speciation

Doe BR (1994) Zinc, copper, and lead in mid-ocean ridge basalts and the source rock control on Zn/Pb in ocean-ridge hydrothermal deposits. Geochim Cosmochim Acta 58 2215-2223 Ehrlich S, Butler I, Halicz L, Rickard D, Oldroyd A, Matthews A (submitted) Experimental study of copper isotope fractionation between aqueous Cu(II) and covellite, CuS. Chem Geol Finney LA, O Halloran TV (2003) Transition metal speciation in the cell insights from the chemistry of metal ion receptors. Science 300 931-936... 

Miller, LA. and Bruland, K.W. (1997) Competitive equilibration techniques for determining transition metal speciation in natural waters evaluation using model data. Anal. Chim. Acta, 343, 161—181. 

Finney LA, O Halloran TV. Transition metal speciation in the cell insights from the chemistry of metal ion receptors. Science 2003 300 931-936. 

Rates of reductive dissolution of transition metal oxide/hydroxide minerals are controlled by rates of surface chemical reactions under most conditions of environmental and geochemical interest. This paper examines the mechanisms of reductive dissolution through a discussion of relevant elementary reaction processes. Reductive dissolution occurs via (i) surface precursor complex formation between reductant molecules and oxide surface sites, (ii) electron transfer within this surface complex, and (iii) breakdown of the successor complex and release of dissolved metal ions. Surface speciation is an important determinant of rates of individual surface chemical reactions and overall rates of reductive dissolution. 

As for all elements, the distribution of Mo in the environment depends critically on chemical speciation, including oxidation state (Bertine and Turekian 1973 Morford and Emerson 1999). However, Mo is somewhat unusual in both respects. In terms of ligand coordination. Mo is one of a small number of transition metals that commonly form oxy anions and coordinate only weakly with other environmentally common ligands such as Cl" or OH". Other such metals include Cr and W, which sit above and below Mo, respectively, in Group VI of the Periodic Table, as well as Tc, Re, Os and U. Hence, Mo chemistry has some analogies with these metals, as well as with nonmetals such as S, Se, P and As which also form oxyanions. 

Speciation of transition metals by natural organic substances that behave as complexing ligands may occur in the subsurface following waste and sludge disposal. As a result, metal solubility increases, favoring metal mobility with depth. 

Two classes of promoter have been identified for iridium catalysed carbonylation (i) transition metal carbonyls or halocarbonyls (ri) simple group 12 and 13 iodides. Increased rates of catalysis are achieved on addition of 1-10 mole equivalents (per Ir) of the promoter. An example from each class was chosen for spectroscopic study. An Inis promoter provides a relatively simple system since the main group metal does not tend to form carbonyl complexes which can interfere with the observation of iridium species by IR. In situ HP IR studies showed that an indium promoter (Inl3 Ir = 2 1) did not greatly affect the iridium speciation, with [MeIr(CO)2l3] being converted into [Ir(CO)2l4] as the batch reaction progressed, as in the absence of promoter. 

In the earlier volume of this book, the chapter dedicated to transition metal peroxides, written by Mimoun , gave a detailed description of the features of the identified peroxo species and a survey of their reactivity toward hydrocarbons. Here we begin from the point where Mimoun ended, thus we shall analyze the achievements made in the field in the last 20 years. In the first part of our chapter we shall review the newest species identified and characterized as an example we shall discuss in detail an important breakthrough, made more than ten years ago by Herrmann and coworkers who identified mono- and di-peroxo derivatives of methyl-trioxorhenium. With this catalyst, as we shall see in detail later on in the chapter, several remarkable oxidative processes have been developed. Attention will be paid to peroxy and hydroperoxide derivatives, very nnconunon species in 1982. Interesting aspects of the speciation of peroxo and peroxy complexes in solntion, made with the aid of spectroscopic and spectrometric techniqnes, will be also considered. The mechanistic aspects of the metal catalyzed oxidations with peroxides will be only shortly reviewed, with particular attention to some achievements obtained mainly with theoretical calculations. Indeed, for quite a long time there was an active debate in the literature regarding the possible mechanisms operating in particular with nucleophilic substrates. This central theme has been already very well described and discussed, so interested readers are referred to published reviews and book chapters . 

Carbonate has proved to be a versatile ligand. Its coordination mode expands from 1 to 6, the last one is visualized when each atom binds two metal ions simultaneously. In recent years, significant progress has been made in the synthesis, structure, and magnetic properties of polynuclear carbonato complexes of transition metal ions. Such studies have also been extended to lanthanides and actinides. The speciation studies of these metal ions in aquatic environments in the presence of carbonate have resulted in significant... 

Weschler, C.J., Mandich, M.L. and Graedel, T.E. (1986) Speciation, photosensitivity and reactions of transition metal ions in atmospheric droplets. /. Geophys. Res., 91, 5189-5204. 

A prototypical example of a molecular probe used extensively to study the mineral adsorbent-solution interface is the ESR spin-probe, Cu2+ (Sposito, 1993), whose spectroscopic properties are sensitive to changes in coordination environment. Since water does not interfere significantly with Cu11 ESR spectra, they may be recorded in situ for colloidal suspensions. Detailed, molecular-level information about coordination and orientation of both inner- and outer-sphere Cu2+ surface complexes has resulted from ESR studies of both phyllosilicates and metal oxyhydroxides. In addition, ESR techniques have been combined with closely related spectroscopic methods, like electron-spin-echo envelope modulation (ESEEM) and electron-nuclear double resonance (ENDOR), to provide complementary information about transition metal ion behaviour at mineral surfaces (Sposito, 1993). The level of sophistication and sensitivity of these kinds of surface speciation studies is increasing continually, such that the heterogeneous colloidal particles in soils can be investigated ever more accurately. 

The transition metals in Period 4 between Group 7 (Mn) and Group 12 (Zn) have remarkable and varied seawater speciation behaviours that are generally quite distinct from those of other elements in Groups 7-12. On this account, the speciation of these Period 4 metals (Mn, Fe, Co, Ni, Cu and Zn) will be discussed together, subsequent to the discussion of the other metals of Groups 7-18. 

Cobalt. The speciation of radiocobalt has been selected for discussion in this chapter because it exemplifies an element for which much information already exists regarding its stable chemical speciation, yet there are additional species which have become environmentally important as a result of the activities of the nuclear industry Cobalt, the middle member of the first triad of group VIII transition metals in the Periodic Table (iron, cobalt, nickel), is most stable in the divalent state when in simple compounds. Studies of radionuclide releases from nuclear power plants under tropical conditions in India seem to indicate that... 

Wilkins, R. G., Kinetics and Mechanism of Reactions of Transition Metal Complexes, VCH Publishers, New York, 1991. This classic textbook, by one of the key figures in the study of complexation reactions, offers a wealth of detail on the experimental aspects of aqueous speciation. 

Both GC and LC behavior of metal complexes of various ligand types including salicy-laldimines and Schiff bases and fluorinated /3-diketones was reported. Metal ions included the lanthanides, transition metals, Pt, Pd and Zn. Dissociation and thermal instabilities were found to be the main limitations in the chromatography of such derivatives. The data indicate that pre-column derivatization and GC is unlikely to provide a viable method for the ultratrace determination of metal ions except in rare circumstances. On the other hand, LC of complexed metal ions was found as a valuable technique that combines the advantages of versatility, specificity and sensitivity with the capacity for simultaneous determination and speciation. Diastereoisomers of oxovanadium(IV) complexes of tetradentate Schiff bases could be resolved by both GC and LC . ... 

The bioavailability of a given metal is influenced by its chemical speciation in the ambient environment. Although some metals occur predominantly in their free or aquo form (that is, the inner coordination sphere of the metal ion is occupied solely by water molecules), most bioactive metals occur as complexes in the natural environment. Hydroxide, carbonate, and chloride anions can all bind transition metals to a significant extent. For example, Fe + forms hydroxide... 

The predicted waste inventory for the repository indicates that potentially significant quantities of the organic ligands—acetate, citrate, oxalate, and EDTA—will be present (US DOE, 1996). Actinide interactions with these compounds were not considered in the speciation and solubility modeling, as calculations suggested that they would be mostly complexed by transition metal ions (Fe, Ni " ", Cr, and Mn " ") released by corrosion of the steel waste containers and waste components. A thermodynamic model of actinide-ligand interactions appropriate to brines will be included in solubility calculations for WIPP recertification. 

ESI-MS is becoming a detection method of choice, which readily identifies the molecular composition of species separated by flowing mobile phases. For space limitations, the reviews by Stewart for separation and speciation,24 by Szpunar for metallo-biopolymers,25 by Shepherd on transition metal complexes,1,75 by Colton, D Agostino, and Traeger,76 and Henderson, Nicholson, and McCaffery77 for organometallic complexes are highly recommended. The subject of ESI-MS is also presented in Chapter 2.28. 

G.J. De Menna, The Speciation and Structure Elucidation of Transition Metal Complexes by HPLC-DCP , Presentation Pittsburgh Conference 1986, Atlantic City, N.J., USA. 

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