نمونه متن انگلیسی مقاله
In this work we investigate the nature of the Cl···N interactions in complexes formed between substituted ammonium [NHn(X3-n) (with n00, 1, 2, 3 and X0−CH3, −F] as Lewis bases and F−Cl molecule as Lewis acid. They have been chosen as a study case due to the wide range of variation of their binding energies, BEs. Møller-Plesset [MP2/6-311+ +G(2d,2p)] calculations show that the BEs for this set of complexes lie in the range from 1.27 kcal/mol (in F −Cl···NF3) to 27.62 kcal/mol [in F−Cl···N(CH3)3]. The intermolecular distribution of the electronic charge density and their L(r)0−¼∇2 ρ(r) function have been investigated within the framework of the atoms in molecules (AIM) theory. The intermolecular interaction energy decomposition has also been analyzed using the reduced variational space (RVS) method. The topological analysis of the L(r) function reveals that the local topological properties measured at the (3,+1) critical point [in L(r) topology] are good descriptors of the strength of the halogen bonding interactions. The results obtained from energy decomposition analysis indicate that electrostatic interactions play a key role in these halogen bonding interactions. These results allow us to establish that, when the halogen atom is bonded to a group with high electron-withdrawing capacity, the electrostatic interaction between the electron cloud of the Lewis base and the halogen atom unprotected nucleus of the Lewis acid produces the formation and determines the geometry of the halogen bonded complexes. In addition, a good linear relationship has been established between: the natural logarithm of the BEs and the electrostatic interaction energy between electron charge distribution of N atom and nucleus of Cl atom, denoted as Ve-n(N, Cl) within the AIM theory.
There has recently been an increasing interest in halogen bonds, XBs, because of their unique properties and their tremendous potential in the fields of molecular recognition, crystal engineering, supramolecular chemistry and the development of new pharmaceutical compounds. The study of the nature of halogen bonding interactions has turned out to be an important aspect of this topic. Studies of the electrostatic potentials of halogen-containing molecules show that the atoms of a halogen covalently bound often have a region of positive electrostatic potential on the outermost portion of the halogen atom, centered on the extension of the D−X bond [1–4]. Politzer et al. have attributed the formation of halogen bonds to the attractive electrostatic interaction between this positive potential and a lone pair of the acceptor. The presence of a region with positive electrostatic potential on a halogen indicates that noncovalent interactions between that halogen and a Lewis base should be highly electrostatic in nature. However, there are several studies showing that other components of the interaction energy can be decisive. Recently, Tomura  has studied the H4–nCClnIIIπC2H2 (with n01, 2, 3, 4) systems by RVS method , finding that these complexes are mainly stabilized by the dispersion interaction while the electrostatic interaction also plays an important role in the attraction between acetylene and chloromethane molecules. Moreover, Riley et al.  have investigated the nature of the XBs using high-level computational methods, including the symmetry-adapted perturbation theory (SAPT) . These authors have found that, the interactions between fluorinated and nonfluorinated halomethanes with formaldehyde (as well as with methanol) depend strongly on the electrostatic contributions as well as on the dispersion. However, in the interactions of substituted bromobenzenes and bromopyrimidines with acetone, only the electrostatic forces play the key role.