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

Abstract

ABSTRACT 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 (BF 4 ).2DMF.H 2 O} n ( 1 ·2DMF·H 2 O ) (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 T 1/2  = 127 K and a pronounced light‐induced excited spin‐state trapping (LIESST) effect at T LIESST  = 60 K. In contrast, the fully solvated framework ( 1 ·2DMF·H 2 O) 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.