Classification of bonding interactions

Bianchi et al. present a concise pictorial summary of the QTAIM characterisation and classification of bonding interactions in the conclusion of their paper about the electron density of Mn2(CO)io [114]. Figure 2 is an adaptation (with modifications) of their scheme. The classification is to be taken as a general guide since exceptions and special cases do arise as one attempts to draw a correspondence between classical bonding descriptors (ionic, covalent, etc.) and quantum mechanical quantities. 

Table 4 Classification of bonding interaction accrading to ELF criteria core valence bifurcation index bond dissociation variations of the number of basins, A, and of the basin synaptie orders A

The bonds formed between germanium and elements of Group VA can be divided into two categories those in which the element is bonded via a covalent bond and others in which a Lewis acid-Lewis base interaction between the two elements results in coordinate bond formation. The same classification of bond types is also appropriate when discussing organogermanium derivatives of Groups VIA and VII A. 

Table I. Classification of atomic interactions on the basis of local topological and energetic properties at the bond critical point...

We see that solids can be classified according to the types of bonding interactions that hold the atoms together. This classification helps us make general predictions about the properties of solids. 

The classification of bonds proposed previously remains valid with this new nomenclature. The shared electron interaction (a more consistent name is shared valence basin interaction) is characterized by a di or polysynaptic basin. The lone pairs give rise to monosynaptic basins. It is important to note that this picture of the chemical bond implies a somehow different point of view than that currently adopted in Chemistry. In the standard pictures a bond is considered as a link joining an atom to another one. 

Figure 2.1 (Plate 2.1) shows a classification of the processes that we consider they aU involve interaction of the reactants both with the solvent and with the metal electrode. In simple outer sphere electron transfer, the reactant is separated from the electrode by at least one layer of solvent hence, the interaction with the metal is comparatively weak. This is the realm of the classical theories of Marcus [1956], Hush [1958], Levich [1970], and German and Dogonadze [1974]. Outer sphere transfer can also involve the breaking of a bond (Fig. 2. lb), although the reactant is not in direct contact with the metal. In inner sphere processes (Fig. 2. Ic, d) the reactant is in contact with the electrode depending on the electronic structure of the system, the electronic interaction can be weak or strong. Naturally, catalysis involves a strong...

Thus, as of today, there is no reliable classification of various types of adsorption. Presumably, it would be most correct to consider various types of adsorption interactions consistent with classification of chemical bonds [19]. 

Another type of classification of hydrogen bonds is based upon the relative strength of the interaction ... 

Many observations concerning these trends had been made over the years, and in the 1950s S. Ahrland, J. J. Chatt, and M. Davies presented a classification of metals based on their preferred interaction with donor atoms. Class A metals are those that interact preferentially when the donor atom is in the first row of the periodic table. For example, they prefer to bond to N rather than P donor atoms. Class B metals are those which interact better when the donor atom is in the second row of the periodic table. For example, a class B metal would bond better to P than to N. The following table summarizes the behavior of metal atoms according to this classification. 

Following our general classification of hydrogen bonds, a negatively polarized hydrogen atom in H-Y, where Y is a less electronegative element than H (e.g., B, Al, Re, K, Mg, etc.), could be considered an unusual or nonconventional proton acceptor. Then the interaction... 

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