Theoretical Prediction of Spin-Crossover Temperatures in Ligand-Driven Light-Induced Spin Change Systems

Spin-crossover compounds exhibit two alternative spin states with distinctive chemical and physical properties, a particular feature that makes them promising materials for nanotechnological applications as memory or display devices. A key parameter that characterizes these compounds is the spin-crossover temperature, T_1/2, defined as the temperature with equal populations of high and low-spin species. In this study, a theoretical/computational approach is described for the calculation of T_1/2 for the trans-[Fe­(styrylpyridine)₄(NCX)₂] (X = S, Se, and BH₃, styrylpyridine in the trans configuration) ligand driven light-induced spin change (LD-LISC) complexes. In all cases, the present calculations provide an accurate description of both structural and electronic properties of the LD-LISC complexes and, importantly, predict spin-crossover temperatures in good agreement with the corresponding experimental data. Fundamental insights into the dependence of T_1/2 on the nature of the axial ligands are obtained from the direct analysis of the underlying electronic structure in terms of the relevant molecular orbitals.