Polynuclear Li12F13 − anion as a steric shielding agent with respect to selected metal ions

Abstract

Boldyrev [1]. In general, the superhalogens were defined as a group of compounds matching the MX k+1 formula (where M is a metal atom having the maximal formal valence k, while X corresponds to the halogen atom) and characterized by the electron affinity (EA) higher than that of the chlorine atom (EA = 3.62 eV) [2]. It implies that superhalogens form very strongly bound and thermodynamically stable molecular anions [3][4][5] which are characterized by the enormous values of vertical electron detachment energies (VDEs) approaching 14 eV in certain cases [6,7]. The very first experimental evidence of the superhalogen existence was provided in 1999 by the Wang's group who reported the photoelectron spectra of the selected triatomic MX 2 − superhalogen anions (M = Li, Na; X = Cl, Br, I) [8]. Since then, many other superhalogen anions [e.g., Na k Cl − k+1 (k = 1-4) and MX 3 − (where M = Be, Mg, Ca; X = Cl, Br)] have also been identified experimentally [9,10]. As indicated by both theoretical predictions and experimental measurements, the original superhalogen formula (MX k+1 ) can be extended to include the polynuclear M n X nk+1 neutral superhalogen compounds (containing n central atoms) whose corresponding polynuclear M n X − nk+1 anions exhibit even larger electron binding energies than their mononuclear counterparts [11][12][13][14][15][16][17]. In addition to numerous applications of superhalogens, we have recently pointed out their possible usage as strong oxidizing agents [18][19][20][21] and Lewis-Brønsted superacid precursors [7,22, 23]. It should also be mentioned that some recent works revealed novel superhalogen applications in Li-ion batteries, solar cells, and hydrogen storage materials [24][25][26][27].It was also established that one of the important features characterizing superhalogen anions is their tendency to adopt high-symmetry compact structures [10]. Recent report concerning the properties of the Li n F − n+1 (n = 2-5) superhalogen anions confirmed that observation, as the Abstract Polynuclear superhalogen anion Li 12 F 13 − and its ionic complexes formed by the interaction with selected metal ions (i.e., Li 12 F 13 − Na + , Li 12 F 13 − K + , Li 12 F 13 − Mg 2+ , and Li 12 F 13 − Zn 2+ ) are proposed and investigated on the basis of ab initio calculations. The thermodynamic stability, vertical excess electron detachment energy, and binding energies between ionic components were examined and discussed. The Li 12 F 13 − anion has been proved stable against fragmentation and its vertical electronic stability was found to approach 10 eV. Due to its specific equilibrium structure that resembles a molecular basket, the Li 12 F 13 − anion was found capable of trapping positively charged metal ions inside to form strongly bound ionic complexes. The large values of binding energies predicted for the Li 12 F 13 − Na + , Li 12 F 13 − K + , Li 12 F 13 − Mg 2+ , and Li 12 F 13 − Zn 2+ systems and their specific equilibrium structures indicate that the Li 12 F 13 − anion can be useful as a steric shielding...