Silicate complex

The category of builders consists predominantly of several types of materials -specific precipitating alkaline materials such as sodium carbonate and sodium silicate complexing agents like sodium triphosphate or nitrilotriacetic acid (NTA) and ion exchangers, such as water-soluble polycarboxylic acids and zeolites (e.g., zeolite A). 

Several ion-exchange methods are also known that offer efficient recovery of lithium from its ores. In such processes, ore is heated with an acid, or its sodium or potassium salt, at moderate temperatures between 100 to 350°C. Often an aqueous solution of sodium or potassium salt such as sodium carbonate is employed which is heated with the ground ore in a steam autoclave. Lithium ions are liberated into aqueous solution from the silicate complex, exchanging hydrogen, sodium or potassium ions. 

Mowery and DeShong used the commercially available hypervalent silicate complex TBAT as a phenylating agent for the cross-coupling reaction with allylic esters. They later reported on the use of the same organosilane for the coupling with aryl iodides and triflates and electron-deficient aryl bromides. The reactions were catalyzed by either Pd(dba)2 or [Pd(allyl)Cl]2 without the need of added phosphine ligands. 

It is also worth mentioning that the constants for the metal silicate complexes tit very well into the relative order of ligand stability, even though they have been classified as uncertain data (see discussion below) because of... 

To some extent, the aqueous metal silicate complexes constitute an entire class of placeholders. There is ample evidence that silica forms strong complexes with several metals, but the stoichiometry of such complexes has not yet been established. Different speciation schemes have been proposed to interpret experimental data, for example, 1 2 complexes, chelates, or mixed hydroxide silicate complexes. Despite these ambiguities we decided to include several metal silicate complexes in the data base as guidelines for modellers. Should such complexes turn out to be of crucial importance in particular systems, additional experimental studies would be called for. 

The most obvious future data needs concern the missing, uncertain, and conflicting data identified above. Additional experimental investigations are needed in the case of Fe(III) and Zr(IV) carbonate complexation, and in the case of the Sn(IV)/Sn(II) and the Se(0)/Se(-II) redox couples. The molecular structure of metal silicate complexes needs clarification in order to remove ambiguities in the speciation scheme of these complexes. A rather challenging topic concerns the supposed transformation of crystalline tetra-valent actinide oxides, AnOz(cr), to solids with an amorphous surface layer as soon as the An4+ ion hydrolyses. The consequences of such... 

Jeffrey, L. M., Hood, D. W., "Chemistry of Organo-Silicate Complexes... 

This enolate is more stable than the isomeric 1,3-enolate in which the O substituent is in the 2-position three resonance forms can be written for the former enolate while only two can be written for the latter. Me3SiCl then reacts with the dienolate A at the oxygen atom. The dienol silyl ether C is obtained in this way. Silyl ether C reacts with MeLi—in analogy to the reaction B — A shown in Figure 13.19—via the silicate complex B to give the desired enolate. Note that the product enolate is not accessible by treatment of cyclohexanone with LDA (Figure 13.14). 

Fig. 13.22. O-Silylation of an ester enolate to give a silyl ketene acetal. (The formation of the silicate complex in step 1 of the reaction is plausible but has not yet been proven.)...

Sahai, N. and Tossell, J.A., Formation energies and NMR chemical shifts calculated for putative serine-silicate complexes in silica biomineralization, Geochim. Cosmo-chim. Acta, 65, 2043, 2001. 

In nature, dissolution caused by carbonic and sihcic acids is a slow process. Because formation of carbonate and silicate complexes is very slow and mostly occurs on a geological time scale, it is difficult to reproduce the necessary reactions in the laboratory. On the other hand, acid-base cements may be produced within hours, and controlling the rate of reaction in these materials is easier than accelerating reactions in carbonate and sihcate minerals. Acid-base cements have considerable potential for commercial applications by exploiting the solubility of cation donors of oxides in acidic solutions. For this reason, we next explore the dissolution steps involved in formation of these cements in more detail. 

Borate, B(OH)4 and silicate, H3Si04, form weak complexes with major cations. Because the concentration of major cations is much larger than that of silicate, complexing of cations by silicate is negligible, but complexing of silicate by metal ions may be significant. For the complex formation M -1- A MA, the ratio of complex bound to unbound anion A is... 

Taking into account the different possible orientations of the two oxolane rings, relative to the apical ligand, for the three compounds 82, 83 and 84, the existence of syn/syn isomers in addition to syn/anti and anti/anti isomers must be considered. Although there is some confusion in the literature [92,93,94,95,96,97] about the correct interpretation of the NMR data of silicate complexes, there is no doubt that the three above-mentioned compounds exist in solution. In O Fig. 19, Si and (DEPT-135) NMR spectra of 82 and 83 are shown. 

A phyllosilicate-rich clay was studied by 29Si MAS-NMR spectroscopy.520 13C CP/MAS-NMR and 29Si MAS-NMR spectra were used to characterise silylated montmorillonites, and to estimate the extent of the silylation reaction.521 Ab initio calculations have been made of 29Si NMR chemical shifts for silicate complexes with carboxylates, amino acids and multicarboxylic acids.522 Structural changes on thermal treatment of kaolinite were followed using 29Si MAS-NMR spectra.523... 

Molster, F.J. Waters, L.B.F.M. Tielens, A.G.G.M. Crystalline silicate dust around evolved stars. II. The crystalline silicate complexes. Astron. Astrophys. 2002, 382, 222-240. 

An important and often overlooked aspect of complicated solution chemistry of salts other than inert electrolytes is fomiation of water soluble complex species involving products of dissolution of sparingly soluble materials (adsorbents). For instance, indirect spectroscopic evidence has been presented [1] that a silicate complex is the dominating soluble species of Eu (total Eu concentration of 10 mol dm ) in the presence of silicates (2.7x 10 mol Si dm ) over the pH range 6-8. The solubility of silica is about 10 mol dm, thus, water soluble silicate complexes can play an important role in the partition of Eu (and other trivalent lanthanides) between aqueous solution and silica. 

Siderite, lEP of, 208 Silica (see also Quartz Stober silica) effect on lEP of metal oxides, 75 kinetics of dissolution, 2 Silicate complexes, of Eu, 312 Silicates... 

Compounds 30-32 represent tris[hydroximato(2-)]silicate complexes. They were prepared by using the same preparative approach (synthesis of 30 Scheme 24.2) and isolated as the fac- (30, 31MeOH) or mer-isomer... 

Titration of hydrochloric acid, containing the same amount of aluminum chloride as in 2, with sodium silicate (alumino-silicate complex formed)... 

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