Soft character

Calculated Softness Character (E ) OF Selected Metal Cations... 

They indicated that the softness parameter may reasonably be considered as a quantitative measure of the softness of metal ions and is consistent with the HSAB principle by Pearson (1963, 1968). Wood et al. (1987) have shown experimentally that the relative solubilities of the metals in H20-NaCl-C02 solutions from 200°C to 350°C are consistent with the HSAB principle in chloride-poor solutions, the soft ions Au" " and Ag+ prefer to combine with the soft bisulfide ligand the borderline ions Fe +, Zn +, Pb +, Sb + and Bi- + prefer water, hydroxyl, carbonate or bicarbonate ligands, and the extremely hard Mo + bonds only to the hard anions OH and. Tables 1.23 and 1.24 show the classification of metals and ligands according to the HSAB principle of Ahrland et al. (1958), Pearson (1963, 1968) (Table 1.23) and softness parameter of Yamada and Tanaka (1975) (Table 1.24). Compari.son of Table 1.22 with Tables 1.23 and 1.24 makes it evident that the metals associated with the gold-silver deposits have a relatively soft character, whereas those associated with the base-metal deposits have a relatively hard (or borderline) character. For example, metals that tend to form hard acids (Mn +, Ga +, In- +, Fe +, Sn " ", MoO +, WO " ", CO2) and borderline acids (Fe +, Zn +, Pb +, Sb +) are enriched in the base-metal deposits, whereas metals that tend to form soft acids... 

As the concentration of Ge(IV) was increased in the electroless solution, the deposition rate decreased rapidly, while the Ge content in the deposits increased (Fig. 11(b)). In contrast to a Ni-Ge-P solution employing a complexant such a citrate, increasing the concentration of Ge(IV) in the aspartate solution does not significantly alter the concentration of uncomplexed Ni2+ species through consumption of aspartate by Ge(IY). Thus, the decrease in deposition rate is associated with the soft character of the latter, which manifests itself in terms of strong adsorption on the Ni-Ge-P surface thereby inhibiting the electroless deposition process. 

As was discussed in Chapter 6, the electronic polarizability, a, of species is very useful for correlating many chemical and physical properties. Values of a are usually expressed in cm3 per unit (atom, ion, or molecule). Because atomic dimensions are conveniently expressed in angstroms, the polarizability is also expressed as A3, so lCT24cm3 = 1 A3. The polarizability gives a measure of the ability of the electron cloud of a species to be distorted so it is also related to the hard-soft character of the species in a qualitative way. Table 9.6 gives the polarizabilities for ions and molecules. 

Because of the importance of being able to predict which complexes will be stable, it is necessary to know which ligands and metal species are soft and which are hard in terms of their electronic character. Table 16.2 gives a list of several species of each type grouped according to their hard-soft character. Some species are listed as borderline because they do not fit neatly into the hard or soft category. 

The most common method for the preparation of 1,2,3-benzothiadiazoles is the diazotization of 2-aminobenzenethiol. This method was discussed and exemplified in CHEC-II(1996). The method has been extended in recent years to include heterocyclic derivatives. The 2-aminothiophene 79 can be converted into the thienothiadiazole 82 on treatment with sodium nitrite in HC1 but in poor yield (16%). The bis(BOC)-protected derivative 80 or the mono(BOC)-protected derivative 81 when reacted under similar conditions afford product 82 in much higher yields (BOC = /-butoxycarbonyl Scheme 9). The increase in yield is explained in terms of hard and soft electrophilic character. The intermediate in the BOC-protected examples has a soft character allowing attack by sulfur to proceed more easily <1999JHC761>. 

Microbial resistance to established organic antibiotics is a potentially serious problem and provides an impetus for the development of novel antimicrobial metal compounds. The potency of Ag(I) ions is well known—but how does Ag(I) kill a bacterium Much current attention is focused on Bi(III) on account of its ability to kill Helicobacter pylori, an organism which prevents ulcers from healing. Bis-muth(III) chemistry has many unusual features a variable coordination number, strong bonds to alkoxide ligands, the stereochemical role of its 6s2 lone pair, facile formation of polymers, and dual hard and soft character. 

The property sets of raw PVCs as-polymerized are generally unsuitable for the range of intended applications. It is essential to upgrade and customize the raw polymers by compounding to satisfy the requirements of customers and applications. Numerous additives, fillers, plasticizers, stabilizers etc. are used, allowing the manufacture of a variety of parts and goods from a very rigid to a very soft character. 

Stabilized carbanions, such as malonyl ceubanions, which have a soft character, react with glycosyl halides affording the corresponding C-glycosyl malonates. Once more, the presence of a participating group at C-2 directs the attack of the nucleophile from the opposite side. An example of the application... 

When the metalation of 2-fluoropyridine (8) was carried out at lower temperatures (-60°C), aside from the product of addition 13, evidence for the DoM product 12 was obtained by a TMSC1 quench experiment (Scheme 4). Complete chemospecificity was achieved only with the more selective LDA base at -75°C. [81JOC4494,81JOM(215)139]. Whereas the soft character of n-BuLi favors nucleophilic reactivity, the hard LDA leads to preferential protophilic attack. The stronger kinetic basicity... 

Environmentally relevant nucleophiles (Lewis bases) may be classified according to Pearson s HSAB principle, as hard, soft, or borderline (possessing intermediate hard/soft character) as follows (Larson and Weber, 1994) ... 

The properties of dimethyl carbonate, (MeO)2CO, as an ambident electrophile have been investigated by analysis of the products of its reaction with various nucleophiles having different hard-soft character. Results were in good agreement with the Hard-Soft Acid-Base theory, hard nucleophiles attacking the hard C=0 group and soft nucleophiles the soft Me group (Scheme ll).37... 

Let us first define the external MEC in M, consisting of m atoms. Consider the global equilibrium of M in contact with a hypothetical electron reservoir (r) fi0 = fj1 where fi= fi, the chemical potential of r. Let z = N — N° = d/V denotes the vector of a hypothetical AIM electron-population displacements from their equilibrium values N°. Since d/V = - d/Vr, the assumed equilibrium removes the first-order contribution to the associated change due to z in the energy, = M + , of the combined (closed) system (Mir) moreover, taking into account the infinitely soft character of a macroscopic reservoir, the only contribution to the energy change in the quadratic approximation is ... 

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