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)₈][Fe(v-im)₄]₂(BF₄).2DMF.H₂O}n (1·2DMF·H₂O) (v-im = 1-vinylimidazole). Single-crystal x-ray diffraction reveals a flexible 3D hexagonal network where [Mo(CN)₈]³ ⁻ 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.