Covalent/shared interaction

Forty six years ago, on the basis mainly of empirical arguments, I formulated a description of the interatomic forces in metals (2) that had some novel features. I pointed out that according to this view the metallic bond is very closely related to the ordinary covalent (shared-electron-pair) bond some of the electrons in each atom in a metal are involved with those of neighboring atoms in an interaction described as covalent-bond... 

The outer shell of each atom in CI2 possesses a full octet of electrons seven electrons of its own (which explains why it belongs to Group VII(b) of the periodic table) and an extra electron from covalent sharing with the other atom in the CI2 molecule. The only other simple interactions in molecular chlorine are the inevitable induced dipolar forces, which are too weak at room temperature to allow for the liquefying of Cl2(g). 

Relief maps of the charge density and L(r) in the plane of the water molecule are shown in Fig. 6.9. The L(r) at the bond critical point shows an accumulation in the internuclear surface. This is due to the shared electrostatic attraction of the electrons by both nuclei. Such a shared interaction is typical for covalent bonds. 

The % bonding system arises from the interaction of one of the occupied oxygen sp orbitals with the unoccupied 2pz orbital of the nitrogen. Notice that this, again, is a coordinate covalent sharing, except that in this instance, it is the oxygen atom that... 

The results of such studies appear to be more conclusive for covalent than for hydrogen bonds. The topology of non-polar shared interactions is found to be... 

The ligand nuclear moments (Ij) interact with the electronic spin which is covalently shared to some extent between 57Fe and the ligands. The proper term to add to the Hamiltonian [Eq. (3)] is ]>// -Bj-S where Bj is a coupling tensor for the jth ligand nucleus. ... 

The major conclusion of their paper is the experimental proof of the presence of a genuine, covalent Co-Co bond. However, their conclusion is not reached in a straightforward manner because based on the Laplacian (Figure 14) one might conclude that the Co-Co interaction is not shared. Also, the electron density at the BCP between the two cobalt atoms is small. Based on the observations made in F2 and invoking the functions ( )159 [ ( ) = F(r) + G(r)] and G(r)/p(r) Macchi et al. conclude that the Co-Co is far from the closed-shell limit and we do not find any reason for not considering it a shared interaction as suggested by common chemical sense. ... 

These observations emphasize what we feel is a key difference between the roles of Vs,min (or Vmin) and Is,min- The former reflects electrostatic factors, whereas the latter is related to charge transfer and polarization. Thus hydrogen bonding, a non-covalent interaction, is described well in terms of the electrostatic potential [19,27,46], while pKa, which involves charge transfer, requires Is,min- The two properties complement each other Vs,min determines the initial approach of the electrophile and Is,min its subsequent charge-sharing interaction, if any. 

Chemisorption represents the formation of a surface chemical bond, which is either covalent (sharing of electrons) or ionic (electron transfer). The understanding of chemisorption phenomena is rather complex and requires knowledge on the geometrical structure of the system, adsorbate binding and charge transfer, the electronic structure of adsorbate and substrate, as well as vibrational frequencies [63]. Three dominant types of interactions may occur between chemisorbed species dipole-dipole (direct and screened by the electrolyte), electron-electron (indirectvia substrate electrons or direct at short distances), and elastic (via substrate ions) [31, 32, 65, 66]. 

Chemical bonds to a neutral main group atom E are usually considered covalent bonds that come from the electron-sharing interactions of unpaired electrons of atom E. In the following section, we discuss compounds EL2> which are better described in terms of donor-acceptor interactions L->E<-L... 

Sarasa et carried out DFT calculations on the organometaUic clusters [( 7-C5H5)TiN]4 and [Cl3MoN]4 with the aim of comparing the energies and the electronic structures of the cubane and planar forms for these two clusters. For [( 7-C5H5)V(p3-P)]4P2 they computed V p at a P-P BCP and found a shared interaction, indicating covalency. 

Noteworthy, BCPs properties usually provide valuable information about the bond itself. For instance, covalent bonds are characterized by high electron density values (pc) at BCPs, while pc is typically very low for non-covalent bonds like hydrogen, agostic, halogen, and van der Waals ones [94—97]. Another important descriptor is the BCP density laplacian value that quantifies the electron accumulation (negative values) or depletion (positive values) at the BCP. Thus, very negative values are observed for covalent bonds ( shared interactions in Bader s vocabulary), while ionic ( closed-shell interactions) ones feature positive values. Many relationships between interaction energies and (p, have been reported in the literature. 

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