Entanglement of Spin Transition and Elastic Interactions: Manipulating the Slow Spin Equilibrium by Guest-Mediated Fine-Tuning Elastic Frustration

A comprehensive analysis of the physical and chemical properties using the same family of complexes is crucial for understanding and designing structure-property relationships. However, finding the appropriate system remains challenging. Here, a series of guest-saturated states based on the 2D Hofmann-type framework [Fe ^II (prentrz) ₂ Pd ^II (CN) ₄ ]·guest (prentrz = (1 E ,2 E )-3-phenyl-N-(4H-1,2,4-triazol-4-yl)prop-2-en-1-imine, 1 ·guest) is reported, which exhibit a guest-manipulated slow dynamic effect of spin equilibrium in an incomplete two-step spin-crossover (SCO) process. Using a full-sealed method by modulating the mixing ratios and types of CH ₃ OH, H ₂ O, and D ₂ O, stable maintenance of guest-saturated states allows fine-tuning elastic frustration (ξ) of the framework to realize SCO behaviors in the unexplored region between one-step incomplete (HS _0.5 LS _0.5 ↔HS) and two-step complete (LS↔HS _0.5 LS _0.5 ↔HS) processes. A semi-sealed method enables continuous guest molecule loss until the guest-saturated state disappears, transitioning slow spin equilibrium from difficult to overcome to overcome fully. The study demonstrates that guest molecule modulation is more controllable than structural deformation effects on elastic frustration, offering a pathway to discover hidden types of SCO materials and develop new stimulus-responsive materials.