Borate anions

The ways in which inhibitive anions affect the corrosion of zinc are mainly similar to those described above for iron. In inhibition by chromate, localised uptake of chromium has been shown to occur at low chromate concentrations and in the presence of chloride ions Thus under conditions unfavourable for inhibition, pore plugging occurs on zinc. Inhibitive anions also promote the passivation of zinc, e.g. passivation is much easier in solutions of the inhibitive anion, borate , than in solutions of the non-inhibitive anions, carbonate and bicarbonate , A critical... 

Other studies have supported the reports of considerable stabilisation of carbohydrates by borates the thermal stability of ribose increases under acidic conditions, while glucose is favoured under basic conditions. Thus, the pre-RNA world chemistry of furanosyl borate diesters of ribose could have taken place at high temperatures and low pH. A pre-metabolism world at high temperatures and in the basic pH range would have involved glucose borates and anion borates (Scorei and Cimpoia u, 2006). 

The thallium salts 153 are stable to moisture and oxygen both in solution and in the solid state. X-ray crystallography of 153a (R = Ph) revealed a significant separation between the thallium ion and the anionic borate counteranion (B-Tl distance is equal to 425.3 pm) <2001CC2152>. 

Tricoordinated boron compounds (boranes) are coordinatively unsaturated and their chemistry is dominated by reactions in which complexes are formed. These complexes are either neutral molecules (borane complexes), anions (borates) or boron cations. Space limitations mean that little or no attention will be paid to complexes containing several boron atoms and to species of the type L-BH3, [BH,]- and [L2BH2]+ (L = neutral ligand), discussed in detail in several books and reviews. Similarly, little attention will be paid to the plethora of metal borates and the cyclic and polymeric amino- and phosphino-boranes. 

With these assumptions, the distribution of boron species (among boric acid, borate anion, borate esters, and borate diesters) reduces to a function of boron concentration, polymer concentration, radius of gyration and solvated volume fraction of a polymer unit, solution pH, and the association constants for the borate esters of the functional groups employed. 

The success of polypyrazolylborates prompted the development of the coordination chemistry of polyazolylmethanes, the neutral counterpart of anionic borates <86JCS(D)645>. This interest resulted in the preparation of a large family of ligands whose principal representatives are shown below... 

Eluting anions Borate Silicate Formate Sulfide Chloride Cyanide... 

Figure 25 Examples of monoanionic phosphorus and nitrogen donor ligands that incorporate an anionic borate unit.

The reaction of benzoxaborole with alizarin red S, a catechol fluorescent dye, was studied kineticaUy over a range of pH values, reveahng that condensation to form adduct 2 takes place with both the neutral boronic acid and anionic borate forms (Scheme 1) (2012JOC11200). 

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