Chemical Bonds without Bonding Electron Density — Does the Difference Electron‐Density Analysis Suffice for a Description of the Chemical Bond?

Abstract

Formation of a covalent bond is not necessarily associated with an increase in electron density in the bonding region. This can be established by analysis of the single electron density distributions ρ(r) with the aid of the assigned Laplace field ▽2ρ(r). For “bonds without bonding electron density ρ(r)”, it is decisive that the density ρ(r) actually present in the region between the atoms results in a decrease in the local energy density and, hence, produces a stabilizing effect.

Organoselenium(ii) halides containing the pincer 2,6-(Me2NCH2)2C6H3ligand – an experimental and theoretical investigation

“…[38][39][40][41][42] The QTAIM properties at the BCPs of the Se-C bonds are very similar in 2a and 2-4 and in agreement with a covalent Se-C single bond picture as found for Se-C bonds in I-Se(C)-X hypervalent systems (X = I, Br, Cl). 33 As expected, the H 38 value is negative at the BCPs of the Se-N bonds; however, the positive values for the calculated ∇ 2 ρ 38 indicate an overall high polar covalent character for these bonds, in agreement with the very different NBO and QTAIM charges (Tables 2 and S6 ‡) calculated on the Se and N atoms.…”

Chemical Bonding in Molecules and Complexes Containing d-Elements Based on DFT

“…However, for F 2 we don't see any increase of L between the nuclei. As has been pointed out by Cremer and Kraka for F 2 [18], L is negative at the bond critical point r c (À2.908 e.Å À5 ), but still, the sum of G(r c ) þ V(r c )(¼2.247-4.292 ¼ À2.045 Hartree. Å À3 ) results in a negative value of the total energy density (…”

“…It might still lead to negative total energy densities at the bond critical points, however (see Section II and Ref. [18]). The situation changes if one considers the Laplacian of the density plot resolved into orbital contributions instead.…”

Electronic structure theory to decipher the chemical bonding in actinide systems

“…However, for weak or highly polar bonds, the analysis of the density and its Laplacian (close to zero) does not suffice to characterise the bonding. Additional information can be obtained from the eigenvalues (e.g., η = |λ 1 | λ 3 ) or the total electronic energy density H(r) (6) as the sum of the kinetic G(r) and the potential energy V (r) [78]:…”