Oxyanions metal complexes

Brintzinger, H. Hester, R. E. (1966). Vibrational Analysis of Some Oxyanion-Metal Complexes. Inorganic Chemistry, Vol.5, No.6, pp. 980-985. 

Fig. 15-5 Comparative adsorption of several metals onto amorphous iron oxyhydroxide systems containing 10 M Fej and 0.1 m NaNOs. (a) Effect of solution pH on sorption of uncomplexed metals, (b) Comparison of binding constants for formation of soluble Me-OH complexes and formation of surface Me-O-Si complexes i.e. sorption onto Si02 particles, (c) Effect of solution pH on sorption of oxyanionic metals. (Figures (a), (c) reprinted with permission from Manzione, M. A. and Merrill, D. T. (1989). "Trace Metal Removal by Iron Coprecipitation Field Evaluation," EPRI report GS-6438, Electric Power Research Institute, California. Figure (b) reprinted with permission from Balistrieri, L. et al. (1981). Scavenging residence times of trace metals and surface chemistry of sinking particles in the deep ocean, Deep-Sea Res. 28A 101-121, Pergamon Press.)...

The (5)-tryptophan-derived oxazaborolidenes utilized in this aldol study have been previously examined by Corey as effective catalysts for enantioselective Diels-Alder cycloaddition reactions [6]. Corey has documented unique physical properties of the complex and has proposed that the electron-rich indole participates in stabilizing a donor-acceptor interaction with the metal-bound polarized aldehyde. More recently, Corey has formulated a model exemplified by 7 in which binding by the aldehyde to the metal is rigidified through the formation of a hydrogen-bond between the polarized formyl C-H and an oxyanionic ligand [7], The model illustrates the sophisticated design elements that can be incorporated into the preparation of transition-metal complexes that lead to exquisite control in aldehyde enantiofacial differentiation. 

Electroraffination — (see also electrorefining) Purification of metals by means of dissolution and subsequent electrodeposition. Common method in - electrometallurgy for the removal of impurities from raw metals. Upon anodic dissolution the metallic constituents of the anode are dissolved as cations, oxyanions, or complex ions. All impurities - whether metallic or not - are also dissolved or will fall to the bottom of the cell. At the cathode set to a suitable potential (in most cases only fractions of one volt are needed) the desired metal is deposited. Less noble metals stay in solution, they can be recovered by processing the electrode solution. Metals more noble than the metal under consideration are in most cases not dissolved anodically, instead they settle in the solid deposit at the cell bottom. From this residue they can be recovered. 

The perchlorate ion CIO 3 is a recognized contaminant in groundwater as well as soil with more than a hundred contamination sites in 35 states.67 Perchlorate toxicity arises from its interference with thyroid function. CIO i is unique among the inorganic oxyanions in that it is weakly coordinating and when used as a counteranion with metal complexes, the salts yield high-quality single crystals. Nevertheless, the... 

There are three major ways by which elementally different metal ions can be incorporated into the same compound. First, a metal cation can coordinate directly to an anionic metal complex. This is especially conmum among metals which form stable oxyanions, and such compounds form the basis of many minerals such as aluminates, chromates, molybdates, etc. [62]. Next, two or more metal ions may be... 

Alcohols react with boric acid with elimination of water to form borate esters, B(OR)3. A wide variety of borate salts and complexes have been prepared by the reaction of boric acid and inorganic bases, amines, and heavy-metal cations or oxyanions (44,45). Fusion with metal oxides yields... 

Fe(III)(hydr)oxides introduced into the lake and formed within the lake - Strong affinity (surface complex formation) for heavy metals, phosphates, silicates and oxyanions of As, Se Fe(III) oxides even if present in small proportions can exert significant removal of trace elements. - At the oxic-anoxic boundary of a lake (see Chapter 9.6) Fe(III) oxides may represent a large part of settling particles. Internal cycling of Fe by reductive dissolution and by oxidation-precipitation is coupled to the cycling of metal ions as discussed in Chapter 9. 

The principle of hard and soft Lewis acids and bases, proposed by Pearson (1963), is useful to describe these reactions. A Lewis acid is any chemical species that employs an empty electronic orbital available for reaction, while a Lewis base is any chemical species that employs a doubly occupied electronic orbital in a reaction. Lewis acids and bases can be neutral molecules, simple or complex ions, or neutral or charged macromolecules. The proton and all metal cations of interest in subsurface aqueous solutions are Lewis acids. Lewis bases include H, O, oxyanions, and organic N, S, and P electron donors. A list of selected hard and soft Lewis acids and bases found in soil solutions is presented in Table 6.1. 

Oxyanions also affect the coordination chemistry of the metal center (84). Molybdate and tungstate are tightly bound noncompetitive inhibitors (Ki s of ca. 4 (iM) (85). These anions bind to the reduced form of the enzyme, changing the rhombic EPR spectrum of the native enzyme to axial (Figure 1) and affecting the NMR shifts observed (84,85). Comparisons of the ENDOR spectra of reduced uterofenin and its molybdate complex show that molybdate binding causes the loss of iH features which are also lost when the reduced enzyme is placed in deuterated solvent (86). These observations suggest that molybdate displaces a bound water upon complexation. 

Be is implied The proven validity of the differences method for this kind of system will enable more complex systems to be studied, like those composed of particular metal-IDA complexes with some resin and oxyanions such as selenite and tellurite. 

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