Guest‐Dependent Pressure‐Induced Spin Crossover in Fe<sup>II</sup><sub>4</sub>[M<sup>IV</sup>(CN)<sub>8</sub>]<sub>2</sub> (M=Mo, W) Cluster‐Based Material Showing Persistent Solvent‐Driven Structural Transformations
Robert Jankowski, Mateusz Reczyński, Szymon Chorąży, Mikołaj Żychowicz, Mirosław Arczyński, Marcin Kozieł, Karolina Ogorzały, Wacław Makowski, Dawid Pinkowicz, Barbara Sieklucka
Abstract
Abstract Discrete molecular species that can perform certain functions in response to multiple external stimuli constitute a special class of multifunctional molecular materials called smart molecules. Herein, cyanido‐bridged coordination clusters {[Fe II (2‐pyrpy) 2 ] 4 [M IV (CN) 8 ] 2 } ⋅ 4 MeOH ⋅ 6 H 2 O (M=Mo ( 1 solv ), M=W ( 2 solv ) and 2‐pyrpy=2‐(1‐pyrazolyl)pyridine are presented, which show persistent solvent driven single‐crystal‐to‐single‐crystal transformations upon sorption/desorption of water and methanol molecules. Three full desolvation–resolvation cycles with the concomitant change of the host molecules do not damage the single crystals. More importantly, the Fe 4 M 2 molecules constitute a unique example where the presence of the guests directly affects the pressure‐induced thermal spin crossover (SCO) phenomenon occurring at the Fe II centres. The hydrated phases show a partial SCO with approximately two out‐of‐four Fe II centres undergoing a gradual thermal SCO at 1 GPa, while in the anhydrous form the pressure‐induced SCO effect is almost quenched with only 15 % of the Fe II centres undergoing high‐spin to low‐spin transition at 1 GPa.