Tuning the spin-crossover properties of [Fe2] metal–organic cages

Abstract

A computational study on the interplay between ligand functionalization and guest effects on the transition temperature (T_1/2) in the [Fe₂(L₁^R)₃]@X (L₁ = 1,3-bis-(3-(pyridin-2-yl)-1H-pyrazol-5-yl)benzene, X = H⁻, F⁻, Cl⁻, Br⁻, I⁻ and [BF₄]⁻, R = H, F, or CH₃) family of metal–organic cages (MOCs) is presented. Our results indicate that ligand functionalization with electron-donating or electron-withdrawing groups can significantly impact the T_1/2 as expected, while the guest effect in lowering the T_1/2 has a linear correlation with the increasing guest size. More importantly, small guests can move away from the center of the cavity, thus enhancing the two-step characteristic of the transition. All the data can be understood by analyzing the underlying electronic structure of the studied systems in terms of the relevant d-based molecular orbitals. These results can help in the rational design of new MOCs that can operate as sensors at specific temperatures, thus accelerating the discovery of new SCO devices with tailored properties.