A topological analysis of electron density and chemical bonding in cyclophosphazenes PnNnX2n (X = H, F, Cl; n = 2, 3, 4)

Probing the nature of the Co(III) ion in cobalamins: The reactions of aquacobalamin (vitamin B12a), aqua-10-chlorocobalamin and aqua-10-bromocobalamin with anionic and neutral ligands

“…As a consequence, the Co-OH 2 becomes weaker (q at bond critical point decreases). Counter-intuitively, however, the covalency of the Co-OH 2 bond increases on substituting C-10 H by Cl and Br (the Laplacian r 2 q decreases and the ratio of the potential energy density V and the kinetic density G, |V|/G, increases [62][63][64][65][66]). It is therefore difficult to rationalise the difference in the pK a s of the complexes based on the crystallographic data (which, as we pointed out above, have to be treated with some caution) and the DFT modelling.…”

DFT RX3LYP and RPBEPBE studies on the structural, electronic, and vibrational properties of some amino-alcohol ligands

“…Values of q BCP < 0.10 au are indicative of a closed-shell (i.e., predominantly non-covalent) interaction [90]; it is usually accompanied by a relatively small and positive value of r 2 q BCP [91]. By contrast, for a shared (i.e., predominantly covalent) interaction, q BCP is usually >0.1 au [90] (or >0.15 au [92]) and r 2 q BCP , which may be positive or negative [90] (but usually negative [92]), is typically of the same order as q BCP . As seen in Table 5, the values for the covalent framework are consistent with the covalent character of these bonds (q(r) > 0.2 au and r 2 q(r) < 0).…”

Physical Nature of Interactions in ZnIIComplexes with 2,2′-Bipyridyl: Quantum Theory of Atoms in Molecules (QTAIM), Interacting Quantum Atoms (IQA), Noncovalent Interactions (NCI), and Extended Transition State Coupled with Natural Orbitals for Chemical Valence (ETS-NOCV) Comparative Studies

“…88 The local electron potential energy density V(r) dominates the local electron kinetic energy density, G(r), in these two coordination bonds and results in the overall negative (although small) value of the total energy density, H(r) = G(r) + V(r). This strongly points out at a significant covalent contribution, [88][89][90][91][92][93] Figure S3 of the SI; relationships obtained for bonds involving water molecules are shown in Figure S4 of the SI). We observe that  BCP decreases while V BCP becomes more positive when d(Zn--L) increases; this (and relationships shown in Figure S4 of the SI) indicates weakening of coordination bonds from ZnL to ZnL 3 , the latter being most crowded.…”