Multicenter (FX)n/NH3 Halogen Bonds (X = Cl, Br and n = 1-5). QTAIM Descriptors of the Strength of the X∙∙∙N Interaction.

In the present work an in depth deep electronic study of multicenter XBs (FX)n/NH3 (X = Cl, Br and n = 1-5) is conducted. The ways in which X∙∙∙X lateral contacts affect the electrostatic or covalent nature of the X∙∙∙N interactions are explored at the CCSD(T)/aug-cc-pVTZ level and in the framework of the quantum theory of atoms in molecules (QTAIM). Calculations show that relatively strong XBs have been found with interaction energies lying between -41 and -90 kJ mol-1 for chlorine complexes, and between -56 and -113 kJ mol-1 for bromine complexes. QTAIM parameters reveal that in these complexes: (i) local (kinetics and potential) energy densities measure the ability that the system has to concentrate electron charge density at the intermolecular X∙∙∙N region; (ii) the delocalization indices [δ(A,B)] and the exchange contribution [VEX(X,N)] of the interacting quantum atoms (IQA) scheme, could constitute a quantitative measure of the covalence of these molecular interactions; (iii) both classical electrostatic and quantum exchange show high values, indicating that strong ionic and covalent contributions are not mutually exclusive.

Simultaneous Occurrence of Quadruple Lewis Acid-Base Interactions between Selenium Atoms in Selenocarbonyl Dimers.

High-level quantum chemical calculations are performed to investigate C=Se⋅⋅⋅Se=C interactions. Bounded structures are found with binding energies between -4 and -7 kJ mol-1 . An energy decomposition analysis shows that dispersion is the more attractive term, and in all cases save one, the electrostatic interaction is attractive despite each selenium atom having a positive σ-hole at the extension of the C=Se bond. The topological analysis of the molecular electrostatic potential and L(r)=-∇2 ρ(r) function, and natural bond orbital analysis reveal that these particular Se⋅⋅⋅Se contacts can be considered to be quadruple Lewis acid-base interactions.