15-Crown-5-based metalides: computational insights into excess electrons and enhanced NLO response

This study explores a new category of excess electrons, a metalide complexes based on 15-crown-5, i.e., AM⁺(15-c-5)TM- (AM⁺ represents Li-K; TM^- is Zn-Hg), to assess their nonlinear optical (NLO) features. All designed complexes exhibit electronic and thermodynamic stability as confirmed by their vertical ionization potential ranging 2.18 to 2.95 eV and interaction energies ranging -129.89 to -214.89 kcal/mol. The metalide nature of complexes is validated through natural bond orbital, frontier molecular orbital, molecular electrostatic potential, and electron localization function mapping, showing negative charge, the position of HOMO, and excess electrons over TMs. The partial density of state spectra further validates the metalide nature. The UV-vis absorption spectra show that complexes are transparent in ultraviolet region. The polarizability (α_o) and hyperpolarizability (β_o) analysis indicates greater NLO response with highest β_o of 1.08 × 10⁶ a.u. and α_o of 1022 a.u. for Li⁺(15-c-5)Hg^- complex. Furthermore, application of an external electric field significantly enhances the NLO response. The largest enhancement is observed for Li⁺(15-c-5)Hg^-, where β₀ increases from 1.08 × 10⁶ to 2.56 × 10⁶ a.u under a positive external electric field ((+ 0.1 × 10⁻² a.u) applied along the AM to TM direction. These findings highlight the potential of metalides as a candidate for advanced NLO materials.

All the density functional theory calculations were performed at ωB97X-D functional with 6-31 + G (d,p) and LANL2DZ basis set in Gaussian 16. The GaussView 6.0 and Multiwfn software were used to analyze electronic properties and view geometries of complexes.