Investigations on the frontier orbitals of FeFn (n = 1–6) superhalogen complexes and prediction of novel salt series Li-(FeFn)

Abstract

First-principles calculations predict that atomic iron (Fe) combines with fluorine (F) to produce stable molecular complexes having the form FeFn (n=1–6) and the species with n≥3 exhibit superhalogen properties. Electron affinities of the complexes are found to increase successively upto 8.20eV for FeF6. The unusual properties of these complexes are due to the involvement of inner shell 3d-electrons, which allow FeFn complexes to belong to the class of superhalogens and also due to the tendency of Fe to have valency that can exceed the value of 3. Quantum chemical calculations were carried out using an all-electron linear combination of atomic orbitals scheme within the density functional theory (DFT) framework utilizing the popular B3LYP (Becke, three-parameter, Lee–Yang–Parr) exchange correlation functional. Analysis of HOMO-LUMO gaps, molecular orbitals and binding energies of these complexes indicate that the FeFn complexes are stable. Population analysis of molecular orbitals was also carried out to determine the percentage (%) contribution of Fe and F atoms to the frontier orbitals (LUMO and HOMO). The orbital overlap population (OOP) diagrams provide information related to bonding and anti-bonding nature of overlap in the molecular orbitals. The principle of maximum hardness was applied to determine the relative stability of the complexes. Also, the stability and viability of novel salt series Li-(FeFn) has been tested by analyzing the molecules Li-(FeF4), Li-(FeF5) and Li-(FeF6) in detail.