Celina Sikorska

BX4- and AlX4- superhalogen anions (X = F, Cl, Br): an ab initio study.

The vertical electron detachment energies (VDEs) of 30 MX 4 (-) (M = B, Al; X = F, Cl, Br) anions were calculated at the OVGF level with the 6-311+G(3df) basis sets. The largest vertical electron binding energy was found for the AlF 4 (-) system (9.789 eV). The strong VDE dependence on the symmetry of the species, ligand type, ligand-central atom distance, and bonding/nonbonding/antibonding character of the highest occupied molecular orbital was observed and discussed.

Moderately Reactive Molecules Forming Stable Ionic Compounds with Superhalogens

An explanation of the ability of selected moderately reactive molecules to form stable systems with superhalogens (AlF(4) and AlCl(4)) is provided on the basis of theoretical considerations supported by ab initio calculations. It is demonstrated that even the molecules possessing high ionization potentials (such as SiO(2), NH(3), CHCl(3), CCl(2)F(2)) should form stable and strongly bound ionic compounds when combined with a properly chosen superhalogen system (acting as an oxidizing agent). The conclusion is supported by providing the structural parameters and interaction energies for the SiO(2)AlF(4), NH(3)AlF(4), CHCl(3)AlF(4), CCl(2)F(2)AlF(4), SiO(2)AlCl(4), and NH(3)AlCl(4) compounds obtained at the CCSD(T)/6-311++G(d,p)//MP2/6-311++G(d,p) level. On the other hand, the AlF(4) and AlCl(4) superhalogens were found to be incapable of reacting with molecules whose ionization potentials (IP) exceed 13 eV (e.g., CO(2), CH(4)). Finally, it is demonstrated that the competition between the electron binding energy of the superhalogen system and the IP of the molecule the superhalogen is combined with is a key factor for predicting the stability of certain species.

Theoretical Search for Alternative Nine-Electron Ligands Suitable for Superhalogen Anions

The calculations performed at the OVGF/6-311++G(3df,3pd)//MP2/6-311++G(d,p) level for the representative NaX(2)(-) and AlX(4)(-) anions matching the MX(k+1)(-) superhalogen formula and utilizing 9-electron systems (i.e., consisting of various possible combinations of atoms containing nine electrons when brought together) revealed that the OH, Li(2)H(3), and NH(2) groups might be considered as alternative ligands X due to their thermodynamic stability and large values of electron binding energy (approaching or even exceeding 6 eV in some cases). All aluminum-containing AlX(4)(-) anions (excluding Al(HBLi)(4)(-)) were predicted to be thermodynamically stable, whereas the NaX(2)(-) anions for X = CH(3), HBLi, CLi, BeB, and H(2)BeLi were found to be susceptible to the fragmentations leading to Na(-) loss. Among the MX(k+1)(-) (M = Na, Al; X = Li(2)H(3), OH, H(2)BeLi, BeB, NH(2), HBLi, CH(3), Be(2)H, CLi) anions utilizing systems containing 9 electrons (and thus isoelectronic with the F atom) the largest vertical electron detachment energy of 6.38 eV was obtained for Al(OH)(4)(-).

The Reason Why HAlCl4 Acid Does Not Exist

The explanation of the hypothetical HAlCl(4) acid instability is provided on the basis of theoretical considerations supported by ab initio calculations. The equilibrium structures of LiAlCl(4), NaAlCl(4), and KAlCl(4) salts were examined and compared to that of their corresponding parent acid. The process of formation of the representative NaAlCl(4) salt was analyzed, and the interaction energy between NaCl and AlCl(3) was estimated to be ca. 55 kcal/mol while that between HCl and AlCl(3) (when the HAlCl(4) species is formed) was calculated to be smaller by an order of magnitude (ca. 8 kcal/mol). The hypothetical HAlCl(4) acid was identified as an HCl...AlCl(3) adduct (with the hydrogen chloride tethered weakly to the quasi-planar aluminum chloride molecule). The electron affinity of the neutral AlCl(4) superhalogen molecule was found to be the factor determining the ability to form a stable compound of MAlCl(4) type.

THE PERFORMANCE OF SELECTED AB INITIO METHODS IN ESTIMATING ELECTRON BINDING ENERGIES OF SUPERHALOGEN ANIONS

The capability of reproducing the vertical electron detachment energies (VDE) of four representative superhalogen anions was tested using the selected ab initio (Hartree-Fock (HF), second, third, and fourth-order Moller-Plesset perturbational scheme (MP2, MP3, MP4), coupled-cluster CCSD(T), and outer valence Green function (OVGF)) methods together with the variety of one-electron basis sets. Certain theoretical treatments (e.g. MP2/aug–cc–pVTZ and MP2/6-311+G(3df)) were found to be satisfactory for preliminary estimates of electron binding energies of superhalogen anions, whereas the use of the OVGF/6-311+G(3df) approach has been proven to assure a very high accuracy of the results.

Towards an understanding of the nature of superhalogen anions: an ab initio study of the system

The calculations performed at the OVGF/6-311+G//HF/6-311+G(d) level for the anion matching the superhalogen formula and utilizing very strong electron acceptors (C6F5 groups) as ligands revealed that the resulting vertical electron binding energy of (7.15 eV) is smaller than the analogous value predicted for (9.92 eV). This finding seems surprising taking into account that the electron affinity of the C6F5 radical (4.5 eV) significantly exceeds that of the fluorine atom (3.4 eV). As a consequence, it is postulated that the simple and useful concept of the ‘collective effects’ introduced in the past to explain the large electronic stability of superhalogen anions needs to be further re-examined.

The performance of selected semi-empirical and DFT methods in studying C60 fullerene derivatives

The capability of reproducing the open circuit voltages (V(oc)) of 15 representative C60 fullerene derivatives was tested using the selected quantum mechanical methods (B3LYP, PM6, and PM7) together with the two one-electron basis sets. Certain theoretical treatments (e.g. PM6) were found to be satisfactory for preliminary estimates of the open circuit voltages (V(oc)), whereas the use of the B3LYP/6-31G(d) approach has been proven to assure highly accurate results. We also examined the structural similarity of 19 fullerene derivatives by employing principle component analysis (PCA). In order to express the structural features of the studied compounds we used molecular descriptors calculated with semi-empirical (PM6 and PM7) and density functional (B3LYP/6-31G(d)) methods separately. In performing PCA, we noticed that semi-empirical methods (i.e. PM6 and PM7) seem satisfactory for molecules, in which one can distinguish the aromatic and the aliphatic parts in the cyclopropane ring of PCBM (phenyl-C61-buteric acid methyl ester) and they significantly overestimate the energy of the highest occupied molecular orbital (E(HOMO)). The use of the B3LYP functional, however, is recommended for studying methanofullerenes, which closely resemble the structure of PCBM, and for their modifications.

Development of a novel in silico model of zeta potential for metal oxide nanoparticles: a nano-QSPR approach

Once released into the aquatic environment, nanoparticles (NPs) are expected to interact (e.g. dissolve, agglomerate/aggregate, settle), with important consequences for NP fate and toxicity. A clear understanding of how internal and environmental factors influence the NP toxicity and fate in the environment is still in its infancy. In this study, a quantitative structure-property relationship (QSPR) approach was employed to systematically explore factors that affect surface charge (zeta potential) under environmentally realistic conditions. The nano-QSPR model developed with multiple linear regression (MLR) was characterized by high robustness [Formula: see text] and external predictivity [Formula: see text] The results clearly showed that zeta potential values varied markedly as functions of the ionic radius of the metal atom in the metal oxides, confirming that agglomeration and the extent of release of free MexOy largely depend on their intrinsic properties. A developed nano-QSPR model was successfully applied to predict zeta potential in an ionized solution of NPs for which experimentally determined values of response have been unavailable. Hence, the application of our model is possible when the values of zeta potential in the ionized solution for metal oxide nanoparticles are undetermined, without the necessity of performing more time consuming and expensive experiments. We believe that our studies will be helpful in predicting the conditions under which MexOy is likely to become problematic for the environment and human health.

Are noble gas molecules able to exhibit a superhalogen nature

Superhalogens are a class of highly electronegative molecules whose electron affinities even exceed those of the halogen elements. Since such species can serve as new oxidizing agents, biocatalysts, and building blocks of unusual salts, they are important to the chemical industry. The ability of noble gas (Ng) atoms to form stable mononuclear (NgF7−) and dinuclear (Ng2F13−) superhalogen anions has been reported. Theoretical considerations supported by ab initio calculations revealed that Ng atoms (i.e. Kr, Xe, Rn) should form strongly bound anionic systems when combined with fluorine atoms (acting as ligands). Particularly, those anionic molecules exhibit larger vertical electron detachment energies (6.97–9.56 eV) than that of the chlorine atom (3.62 eV), confirming their superhalogen nature. We believe that the results provided in this contribution will not only provide evidence of a new type of superhalogen molecule but also stimulate more research interest and efforts in the amazing superatom realm.

Modeling adsorption of brominated, chlorinated and mixed bromo/chloro-dibenzo-p-dioxins on C60 fullerene using Nano-QSPR

Many technological implementations in the field of nanotechnology have involved carbon nanomaterials, including fullerenes such as the buckminsterfullerene, C60. The unprecedented properties of such organic nanomaterials (in particular their large surface area) gained extensive attention for their potential use as organic pollutant sorbents. Sorption interactions can be very hazardous and useful at the same time. This work investigates the influence of halogenation by bromine and/or chlorine in dibenzo-p-dioxins on their sorption ability on the C60 fullerene surface. Halogenated dibenzo-p-dioxins (PXDDs, where X = Br or Cl) are ever-present in the environment and accidently produced in many technological processes in only approximately known quantities. If all combinatorial Br and/or Cl dioxin substitution possibilities are present in the environment, the experimental characterization and investigation of sorbent effectiveness is more than difficult. In this work, we have developed a quantitative structure–property relationship (QSPR) model (R2 = 0.998), predicting the adsorption energy [kcal/mol] for 1,701 PXDDs adsorbed on C60 (PXDD@C60). Based on the QSPR model reported herein, we concluded that the lowest energy PXDD@C60 complexes are those that the World Health Organization (WHO) considers to be less dangerous with respect to the aryl hydrocarbon receptor (AhR) toxicity mechanism. Therefore, the effectiveness of fullerenes as sorbent agents may be underestimated as sorption could be less effective for toxic congeners than previously believed.