Metal ions preparation

In this context, much attention is currently devoted to the preparation of highly branched tree-like species, variously called cascade molecules, arborols, or dendrimers. The reasons why such compounds are interesting from a fundamental viewpoint and promising for a variety of applications have been reviewed and highlighted by several authors. Many of the dendrimers obtained so far are organic in nature. This review describes a novel family of dendrimers containing metal ions, prepared in our laboratories over the last few years. 

Groppi and co-workers23,24 investigated the thermal evolution of Mn- and Fe-substituted hexaaluminates with different amounts of transition metal ions prepared via the co-precipation route. The dried precursors of BaMnxAl 2.xOJ9... 

Figure 20 DE-MALDI-TOF spectrum of a mixture of Sanger dideoxy DNA sequencing reactions containing about 0.1 pmol of each termination fragment generated by primer extension on a 50-base-pair template. The matrix used was a mixture of of 3-hydroxypicolinic acid and picolinic acid including diammonium citrate to complex metal ions (prepared according to Wu et al. [98]). The four panels correspond to termination with (A) ddA. (B) ddC, (C) ddG, and (D) DDT. (From Ref. 82.)...

Simplest examples are prepared by the cyclic oligomerization of ethylene oxide. They act as complexing agents which solubilize alkali metal ions in non-polar solvents, complex alkaline earth cations, transition metal cations and ammonium cations, e.g. 12—crown —4 is specific for the lithium cation. Used in phase-transfer chemistry. ... 

Consequently they cannot be prepared by the addition of sulphide ions to a solution of the metal salt, the hydrated metal ions being so strongly acidic that the following reaction occurs, for example... 

Perhaps the most extensively studied catalytic reaction in acpreous solutions is the metal-ion catalysed hydrolysis of carboxylate esters, phosphate esters , phosphate diesters, amides and nittiles". Inspired by hydrolytic metalloenzymes, a multitude of different metal-ion complexes have been prepared and analysed with respect to their hydrolytic activity. Unfortunately, the exact mechanism by which these complexes operate is not completely clarified. The most important role of the catalyst is coordination of a hydroxide ion that is acting as a nucleophile. The extent of activation of tire substrate througji coordination to the Lewis-acidic metal centre is still unclear and probably varies from one substrate to another. For monodentate substrates this interaction is not very efficient. Only a few quantitative studies have been published. Chan et al. reported an equilibrium constant for coordination of the amide carbonyl group of... 

The strength of this bonding depends on the kind of ether Simple ethers form relatively weak complexes with metal ions but Charles J Pedersen of Du Pont discovered that cer tain polyethers form much more stable complexes with metal ions than do simple ethers Pedersen prepared a series of macrocyclic polyethers cyclic compounds contain mg four or more oxygens m a ring of 12 or more atoms He called these compounds crown ethers, because their molecular models resemble crowns Systematic nomencla ture of crown ethers is somewhat cumbersome and so Pedersen devised a shorthand description whereby the word crown is preceded by the total number of atoms m the ring and is followed by the number of oxygen atoms... 

In a back titration, a slight excess of the metal salt solution must sometimes be added to yield the color of the metal-indicator complex. Where metal ions are easily hydrolyzed, the complexing agent is best added at a suitable, low pH and only when the metal is fully complexed is the pH adjusted upward to the value required for the back titration. In back titrations, solutions of the following metal ions are commonly employed Cu(II), Mg, Mn(II), Pb(II), Th(IV), and Zn. These solutions are usually prepared in the approximate strength desired from their nitrate salts (or the solution of the metal or its oxide or carbonate in nitric acid), and a minimum amount of acid is added to repress hydrolysis of the metal ion. The solutions are then standardized against an EDTA solution (or other chelon solution) of known strength. 

Small amounts of specially functionalized monomers are often copolymerized with acryUc monomers in order to modify or improve the properties of the polymer. These functional monomers can bring about improvements either directiy or by providing sites for further reaction with metal ions, cross-linkers, or other compounds and resins. Table 9 Hsts some of the more common functional monomers used in the preparation of acryUc copolymers. 

In electroless deposition, the substrate, prepared in the same manner as in electroplating (qv), is immersed in a solution containing the desired film components (see Electroless plating). The solutions generally used contain soluble nickel salts, hypophosphite, and organic compounds, and plating occurs by a spontaneous reduction of the metal ions by the hypophosphite at the substrate surface, which is presumed to catalyze the oxidation—reduction reaction. 

The red tetrathiomolybdate ion appears to be a principal participant in the biological Cu—Mo antagonism and is reactive toward other transition-metal ions to produce a wide variety of heteronuclear transition-metal sulfide complexes and clusters (13,14). For example, tetrathiomolybdate serves as a bidentate ligand for Co, forming Co(MoSTetrathiomolybdates and their mixed metal complexes are of interest as catalyst precursors for the hydrotreating of petroleum (qv) (15) and the hydroHquefaction of coal (see Coal conversion processes) (16). The intermediate forms MoOS Mo02S 2> MoO S have also been prepared (17). 

The superoxides are ionic soHds containing the superoxide, O - A comprehensive review of the superoxides was pubHshed ia 1963 (109) they are described ia Reference 1. Superoxides of all of the alkaU metals have been prepared. Alkaline-earth metals, cadmium, and 2iac all form superoxides, but these have been observed only ia mixtures with the corresponding peroxides (110). The tendency to form superoxides ia the alkaU metal series iacreases with increasing size of the metal ion. 

Thiosulfates. The ammonium, alkaU metal, and aLkaline-earth thiosulfates are soluble in water. Neutral or slightly alkaline solutions containing excess base or the corresponding sulfite are more stable than acid solutions. Thiosulfate solutions of other metal ions can be prepared, but their stabiUty depends on the presence of excess thiosulfate, the formation of complexes, and the prevention of insoluble sulfide precipitates. 

Ferrous orthotitanate [12160-20-2] Fe2Ti04, is orthorhombic and opaque. It has been prepared by heating a mixture of ferrous oxide and titanium dioxide. Ferrous dititanate [12160-10-0] FeTi20, is orthorhombic and has been prepared by reducing ilmenite with carbon at 1000°C. The metallic ion formed in the reaction is removed, leaving a composition that is essentially the dititanate. Ferric titanate [1310-39-0] (pseudobrookite), Fe2TiO, is orthorhombic and occurs to a limited state in nature. It has been prepared by heating a mixture of ferric oxide and titanium dioxide in a sealed quartz tube at 1000°C. 

Three features of chelation chemistry are fundamental to most of the appHcations of the chelating agents. The first and probably the most extensively used feature is the control of free metal ion concentration by means of the binding—dissociation equiUbria. The second, often called the preparative feature, is that in which the special properties of the chelate itself provide the basis of the appHcation. The third feature comprises displacement reactions metal by other metal ions, chelant by chelant, and chelant by other ligands or ions. An appHcation may be termed defensive if an undesirable property in a process or product is mitigated, or aggressive if a new and beneficial property is induced. 

---