HSIP

In other words, OH is a much stronger base than SH . The orbital holding the unshared pair of electrons on the oxygen atom is smaller than the one holding the electron pair on the sulfur atom. Therefore, H+ interacts more strongly with OH- than it does with SH . The HSIP does not say that hard acids will not bond to soft bases. Rather, it says that bonding between hard acids and hard bases is more effective than between hard acids and soft bases. A similar statement can also be made for bonding as a result of the interaction between soft acids and soft bases. 

Although the approach just shown ratifies our conclusion that was reached on the basis of HSIP, it would be convenient if a general method could be developed. The energies involved are determined... 

Applications of the Hard-Soft Interaction Principle (HSIP)... 

Linkage isomers. Ions such as SCN- have two potential electron donor atoms. When bonding to metal ions, the bonding mode may be predicted by means of the HSIP. 

The HSIP also applies to precipitation of solids from solution. Ionic solids precipitate best from aqueous solutions when the ions are of similar size, preferably with the two ions having charges of the same magnitude. For the reaction... 

The application of the HSIP is of considerable importance in preparative coordination chemistry because some solid complexes are stable only when they are precipitated using a counter ion conforming to the preceding rule. For example, [CuCl5]3- is not stable in aqueous solution but can be isolated as [Cr(NH3)6][CuCl5]. Attempts to isolate solid compounds containing the complex ion [Ni(CN)5]3- as K3[Ni(CN)5] yield KCN and K2[Ni(CN)4] instead. It has been found, however, that when counter ions such as [Cr(NH3)6]3+ or [Cr(en)3]3+ are used, solids containing the [Ni(CN)5]3- ion are obtained. 

Reactive site preference. We have already used the HSIP principle as it applies to... 

Another reaction that illustrates the HSIP is the reaction of PC13 with AsF3 ... 

However, K+ is hard and Cl- is hard, and the CH3 and SiH3 groups are considerably softer. Thus, Eq. (5.46) represents the actual reaction between KSiH3 and CH3C1. Using the HSIP, we can predict that the following reactions would occur as written ... 

From these examples, we see that the HSIP is useful in many areas of chemistry. 

There is a series of analogous cyclic thiophosphoric acids with the formula (HSiP), that may be prepared by the oxidation of red or white phosphorus with polysulfides under a variety of conditions. For example, the reaction of white phosphorus with a mixture of sulfur and hydrogen sulfide dissolved in triethylamine (which acts as a base) and chloroform opens the phosphorus cage to form the tetrameric cyclic anion ... 

We have already alluded to one of the most useful and pervasive principles in aU of chemistry, that being the hard-soft interaction principle (HSIP). This principle relates to many areas, but it is most directly applicable to interactions in which there is electron pair donation and acceptance (Lewis acid-base interactions). The terms hard and soft relate essentially to the polarizability of the interacting species. For example, 1 has a large size, so its electron cloud is much more distortable than that of F . Likewise, Hg2+ is a large metal ion having a low charge, while Be " " is a very small ion. The result is that Hg is considered to be a soft Lewis acid while Be is considered to be a hard Lewis acid. As a result of these characteristics, Hg + interacts preferentially with 1 rather than F , while Be " " interacts preferentially with F . The hard-soft interaction principle indicates that species of similar electronic character (hard or soft) interact best. It does not say that hard Lewis acids will not interact with soft Lewis bases, but the interaction is more favorable when the acid and base are similar in hard-soft character. 

The primary reason for discussing the hard-soft interaction principle at this time is because of its usefulness in dealing with solubility and solvation. Certainly, the principle like dissolves like has been known for a very long time. We wiU mention here only a few aspects of the HSIP and its relationship to solubihty. As an example, we can consider that NaCl is essentially insoluble in nitrobenzene (/t = 4.27D). Even though nitrobenzene is quite polar, it can not solvate ions hke Na or Cl because of the size of the molecules. It is polar, but depends on both the quantity of charge separated and the distance of separation. Since nitrobenzene is a large molecule, its size causes the dipole moment to be large, but it also limits the ability of the molecules to solvate small ions. 

While we have barely introduced the appHcations of the HSIP (often referred to as HSAB when acid-base chemistry is the focus), the suggested readings at the end of this chapter can be consulted for additional details. A great deal of what will be discussed later about the solvation of reactants and transition states can be reduced to applications of this very important and versatile principle, which was first systematized by Ralph G. Pearson in the 1960s. 

Chang, M.R., Lee, D.J., Lai, J.Y., 2006. Coagulation and filtration of nanoparticles in waste-water from Hsinchu Science-Based Industrial Park (HSIP). Sep. Sci. Technol. 41, 1303-1311. 

With the discrete pressure equation written for each fluid column, and by Including the pressure boundary conditions, the (imax jmax) unknown discrete pressures can be expressed In terms of (loiax jBiax) equations. This work solved the system of equations by using a modified strongly Implicit solution procedure (HSIP) [23], and established a technique Whereby the cavitation boundary could be located at any position between adjacent pressure grid points. 

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