Solvent‐Regulated Lattice Elasticity and Pressure‐Induced Multi‐Stimuli Spin‐State Bistability in a Porous Hexagonal Framework

Spin-state switching in molecular materials becomes most effective when multiple external stimuli converge on a common structural pathway. Here we report a porous cyanide-bridged 4d-3d heterobimetallic framework formulated as Mo (CN) 8Fe (v-im) 42 (BF4). 2DMF. H2On (1·2DMF·H2O) (v-im = 1-vinylimidazole). Single-crystal x-ray diffraction reveals a flexible 3D hexagonal network where Mo (CN) 83 - units mediate magnetic communication through Fe (v-im) 4 nodes. Partial desolvation generates an elastic lattice (1·2DMF) that exhibits reversible thermally induced spin-state switching with T1/2 = 127 K and a pronounced light-induced excited spin-state trapping (LIESST) effect at TLIESST = 60 K. In contrast, the fully solvated framework (1·2DMF·H2O) remains HS at ambient conditions, but switches under hydrostatic pressure, demonstrating structural matrix-, stress- and squeeze-driven bistability. The cooperative response originates from dynamic coupling between solvent molecules, counter-ions, and the flexible framework, which collectively tune the spin-state energetics. This study establishes elastic-matrix squeezing as a unifying strategy for multi-stimuli bistability and highlights the convergence of porosity, elasticity, and spin-crossover behavior in adaptive molecular frameworks.