Tripodal Podand Ligand with a Superhalogen Nature as an Effective Molecular Trap

Adrianna Cyraniak,Marcin Czapla

doi:10.3390/sym12091441

Abstract

Tris(2-methoxyethyl) fluoroborate anion (TMEFA), anovel tripodal ligand based on the BF4− superhalogen anion, is proposed and was investigated theoretically using ab initio MP2 (second-order Møller-Plesset perturbational method) and OVGF (outer valence Green function) methods. The studied molecule comprises three 2-methoxyethoxy groups (-O-CH2-CH2-O-CH3) connected to a central boron atom, which results in the C3-symmetry of the compound. The resulting anion was stable against fragmentation processes and its vertical electron detachment energy was found to be 5.72 eV. Due to its equilibrium structure resembling that of classical tripodal podands, the [F-B(O-CH2-CH2-O-CH3)3]− anion is capable of binding metal cations using its three arms, and thus may form strongly bound ionic complexes such as [F-B(O-CH2-CH2-O-CH3)3]−/Li+ and [F-B(O-CH2-CH2-O-CH3)3]−/Mg2+. The binding energies predicted for such compounds far exceed those of the similar neutral classical podand ligands, which likely makes the [F-B(O-CH2-CH2-O-CH3)3]− system a more effective molecular trap or steric shielding agent with respect to selected metal cations.

Highlights

40 years ago, Gutsev and Boldyrev postulated the possible existence of chemical compounds characterized by very high electron affinity (EA) values exceeding that of the chlorine atom (3.62 eV [1]).Due to their unique electron-accepting properties, such species were termed “superhalogens” [2].These unusual systems, initially described by a simple general formula MXk+1 [3], turned out to be capable of forming strongly bound and thermodynamically stable anions for which the vertical electron detachment energies (VDE) often exceeded 10 eV [4,5] and approached 14 eV in some cases [6,7]
As far as the binding energy values showing the strengths of the cation–ligand interactions are concerned, we found them to be large for the complexes formed by Tris(2-methoxyethyl) fluoroborate anion (TMEFA) ligand
The equilibrium structure of TMEFA resembles those adopted by many well-known tripodal podand ligands, with a negatively charged cavity created by three open-ended 2-methoxyethoxy groups which allows for binding of selected metal ions (Li+ and Mg2+ ) inside the molecular “arms”

Summary

Introduction

40 years ago, Gutsev and Boldyrev postulated the possible existence of chemical compounds characterized by very high electron affinity (EA) values exceeding that of the chlorine atom (3.62 eV [1]).Due to their unique electron-accepting properties, such species were termed “superhalogens” [2].These unusual systems, initially described by a simple general formula MXk+1 (where M is a central atom surrounded by k + 1 halogen ligands X, and k stands for the maximal formal valence of M) [3], turned out to be capable of forming strongly bound and thermodynamically stable anions for which the vertical electron detachment energies (VDE) often exceeded 10 eV [4,5] and approached 14 eV in some cases [6,7]. 40 years ago, Gutsev and Boldyrev postulated the possible existence of chemical compounds characterized by very high electron affinity (EA) values exceeding that of the chlorine atom (3.62 eV [1]). Due to their unique electron-accepting properties, such species were termed “superhalogens” [2]. Regarding the applications of neutral superhalogens and their daughter anions, it should be mentioned that these compounds can act as strong oxidizers (with respect to atoms and molecules characterized by high ionization potential (IP)

Methods

Results

Conclusion