a Energies in kcal mol-1. Selected bond lengths and bond angles in Å and degrees, respectively.
The total energy density, Hb , is sum of the “gradient” kinetic energy density, Gb , and the potential energy density, Vb , (Hb = Gb + Vb ). From Table S1, it is clear that Hb is negative for several complexes, implying that they conceive medium-to-strongly bound interactions. For instance, it is most negative for the S···O bond (Hb = –0.166 a.u.) in Br2O···SCN. Both this and the ∇2ρ b of –0.258 a.u. at the S···O bcp signify the formation of a covalent bond between the S and O atoms in the complex. This conclusion is consistent with the recommendation of Cremer and Kraka,78 who have suggested that if Vb is dominant overGb at the bcps (hence, Hb< 0), this indicates that the region has a “charge density concentration”. On the other hand, and for the weakly bound interactions in the complexes shown in 5-6, 11, 13-14, 22, 25, 29-30 and 33-34 of Fig. 1, the Hb values are all positive. This is not unexpected since the intermolecular distances in these complexes are relatively longer (Table 1) and the nature of these interactions are closed-shell type. This occurs when there is an appreciable depletion in the charge density at the bcps of bonded atomic basins. A similar insight into the ionic and covalent nature of the aforesaid interactions can be gained from the ratio –Vb /Gb (values not shown).79,80