Microsolvation of the Potassium Ion with Aromatic Rings: Comparison between Hexafluorobenzene and Benzene

Abstract

We employ a recently developed methodology to study structural and energetic properties of the first solvation shells of the potassium ion in nonpolar environments due to aromatic rings, which is important to understand the selectivity of several biochemical phenomena. Our evolutionary algorithm is used in the global optimization study of clusters formed of K(+) solvated with hexafluorobenzene (HFBz) molecules. The global intermolecular interaction for these clusters has been decomposed in HFBz-HFBz and in K(+)-HFBz contributions, using a potential model based on different decompositions of the molecular polarizability of hexafluorobenzene. Putative global minimum structures of microsolvation clusters up to 21 hexafluorobenzene molecules were obtained and compared with the analogous K(+)-benzene clusters reported in our previous work (J. Phys. Chem. A 2012, 116, 4947-4956). We have found that both K(+)-(Bz)n and K(+)-(HFBz)n clusters show a strong magic number around the closure of the first solvation shell. Nonetheless, all K(+)-benzene clusters have essentially the same first solvation shell geometry with four solvent molecules around the ion, whereas the corresponding one for K(+)-(HFBz)n is completed with nine HFBz species, and its structural motif varies as n increases. This is attributed to the ion-solvent interaction that has a larger magnitude for K(+)-Bz than in the case of K(+)-HFBz. In addition, the ability of having more HFBz than Bz molecules around K(+) in the first solvation shell is intimately related to the inversion in the sign of the quadrupole moment of the two solvent species, which leads to a distinct ion-solvent geometry of approach.

A global optimization perspective on molecular clusters

“…In contrast with some similarity between the structures of Bz n and HFBz n (see above), we have shown [30] that the scenario changes completely for the clusters resulting from the microsolvation of K + with Bz and HFBz. While the ion approaches Bz preferentially along the C 6 axis, the lowest minimum for K + -HFBz is a planar structure with K + equidistant from two fluorine atoms.…”

“…Recently, an improved Lennard-Jones (ILJ) function [28] spectroscopic data and it has been demonstrated that it removes most of the inadequacies of the traditional LJ model due to an excessive repulsion at short range and a too strong attraction at long range, which can modify the interaction behaviour especially for large clusters. Some examples of applications of this method are given in [29,30] (see also references therein). In addition, the basic potential parameters of V nel and V el can be properly optimized by comparing the method predictions with the results of the experimental investigation, when available, and/or with highlevel ab initio calculations, performed at defined structures of the simplest aggregates (see for instance [31]).…”

“…While the ion approaches Bz preferentially along the C 6 axis, the lowest minimum for K + -HFBz is a planar structure with K + equidistant from two fluorine atoms. Such a difference was attributed [30] to the inversion in the sign of the quadrupole moment of Bz and HFBz [68][69][70], which is well described by the potential model employed in our global optimization studies. Although we have obtained global minimum structures up to n = 21 for both solvents [29,30], special attention has been devoted to the formation of the first solvation shell.…”

Low‐energy structures of benzene clusters with a novel accurate potential surface

“…More recently, good results have been also obtained for and (with ) clusters, as modeled with semi‐empirical potentials; in fact, new lowest‐energy structures were discovered for , and . In addition, the EA has been also used by two of the present authors to study the microsolvation of the alkali‐ions , and with either benzene or hexafluorobenzene; global minimum structures of the alkali‐ions microsolvation clusters formed by up to 21 benzene molecules were achieved. It is worth noting that the EA was able to distinguish between the global minimum of such microsolvation clusters and several low‐energy structures separated by no more than .…”

Thermodynamic, structural and dynamic properties of ionic liquids [C4mim][CF3COO], [C4mim][Br] in the condensed phase, using molecular simulations

“…In the case of [C 4 mim][Br] IL a weak hydrogen bond for every [Br] À anion labeled as A is displayed, followed by a series of slightly weaker hydrogen bonds labeled as B, for the same [Br] À anion, continuing with weaker hydrogen bonds labeled as C and D. The number of interactions in the [C 4 mim][Br] IL anion is related with the RDF coordination numbers presented in Table 3. The larger the number of interaction for a single anion, the weaker the interaction strength, 114 as observed in Fig. 8d and N coord in Table 3.…”