Lewis acid-bases mercury based

Complex [(CXI )Ir(/j,-pz)(/i,-SBu )(/j,-Ph2PCH2PPh2)Ir(CO)] reacts with iodine to form 202 (X = I) as the typical iridium(II)-iridium(II) symmetrical species [90ICA(178)179]. The terminal iodide ligands can be readily displaced in reactions with silversalts. Thus, 202 (X = I), upon reaction with silver nitrate, produces 202 (X = ONO2). Complex [(OC)Ir(/i,-pz )(/z-SBu )(/i-Ph2PCH2PPh2)Ir(CO)] reacts with mercury dichloride to form 203, traditionally interpreted as the product of oxidative addition to one iridium atom and simultaneous Lewis acid-base interaction with the other. The rhodium /i-pyrazolato derivative is prepared in a similar way. Unexpectedly, the iridium /z-pyrazolato analog in similar conditions produces mercury(I) chloride and forms the dinuclear complex 204. 

Many years ago, geochemists recognized that whereas some metallic elements are found as sulfides in the Earth s crust, others are usually encountered as oxides, chlorides, or carbonates. Copper, lead, and mercury are most often found as sulfide ores Na and K are found as their chloride salts Mg and Ca exist as carbonates and Al, Ti, and Fe are all found as oxides. Today chemists understand the causes of this differentiation among metal compounds. The underlying principle is how tightly an atom binds its valence electrons. The strength with which an atom holds its valence electrons also determines the ability of that atom to act as a Lewis base, so we can use the Lewis acid-base model to describe many affinities that exist among elements. This notion not only explains the natural distribution of minerals, but also can be used to predict patterns of chemical reactivity. 

Lewis acids based on boronic acid derivatives or main group elements such as mercury, tin and silicon form strong bonds to anions with considerable covalency, exemplified by hydride sponge and the anticrowns. 

One of the first anion-directed assemblies is the [12]mer-curacarborand-4 (1) reported by Hawthorne in 1991. which can be prepared in high yields by reacting 1,2-dilithio-carborane with mercuric chloride (see Fig. 1). " This compound consists of four bivalent 1 2-carborane cages linked by four mercury atoms forming a macrocycle with a chloride ion located at its center. The anion displays strong Lewis-acid-base interactions with the four mercury atoms of the macrocycle. Such interactions play an important role in directing the formation of the cyclic... 

Upon addition of about 1.5 equivalents of TBAF, the absorption maximum of PSS (generated by irradiation with 365 run) was blue-shifted from 560 to 490 nm. When about 6 equivalents of Hg(C104)2 was added, the absorption maximum of PSS was blue-shifted from 560 to 440 nm. Moreover, the absorption intensity decreased. The modulation mechanism is attributed to the Lewis acid-base interaction between a trivalent boron atom and a fluoride irai, and the complexation interaction between mercury and the sulfur atom (Fig. 2). 

The most spectacular effects of salts on reaction rates are observed in micellar solutions. For instance the presence of anionic surfactants such as dodecyl or tetradecyl sulphate accelerates rates of mercury(n)-catalysed aquation of [CoCNHalsCl] by several orders of magnitude, and polyethylene or polystyrene sulphonates have a similar effect on mercury(n), thallium(m), and silver(i) catalyses of the aquation of the [CoCNHalsBr] cation. Cationic surfactants such as the octylammonium or dodecyl-ammonium ions have a dramatic effect on rates of aquation of the [Cr(ox)3] " anion. Both anionic and cationic surfactants catalyse the (associative) hydrolysis of the Lewis acid-base adduct EtgN.SOs. ... 

Metals that are soft Lewis acids, for example cadmium, mercury, and lead, are extremely hazardous to living organisms. Tin, in contrast, is not. One reason is that tin oxide is highly insoluble, so tin seldom is found at measurable levels in aqueous solution. Perhaps more important, the toxic metals generally act by binding to sulfur in essential enz Tnes. Tin is a harder Lewis acid than the other heavy metals, so it has a lower affinity for sulfur, a relatively soft Lewis base. 

Figure 2 Examples of mercury-based polydentate Lewis acids ...

Perhaps the most eye catching of the receptors utilizing Lewis acidic centers are those based on mercury. Mercury is sp (linear) hybridized which has two consequences. 

Mercury(II), Hg , is a soft Lewis acid, and so is found in nature only combined with soft Lewis bases, the most common of which is S ". Sulfide can readily and permanently abstract Hg from its complexes with harder bases in ore-forming geological reaction mixtures. Zinc(II), which exhibits borderline behaviour, is harder and forms... 

Mercury(II) is a very soft Lewis acid, which forms stable complexes preferentially with soft Lewis bases such as sulfur ligands. You should remember here that the major natural form of mercury is sulfides. Increasing the pH of the aqueous solution due to... 

Mercury(ll) is a very soft Lewis acid, which forms stable complexes preferentially with soft Lewis bases such as sulfur ligands. You should remember here that the major natural form of mercury is sulfides. Increasing the pH of the aqueous solution due to pollution or river water discharge to marine water leads to precipitation of HgO. We know that HgO has finite solubility in water, and the solution may be described in terms of mercury(II) hydroxide as the following reactions (2)-(4)... 

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