Solvent Effects on the Structural and Magnetic Properties of FeIII Spin-Crossover Complexes

Molecular devices based on spin-crossover (SCO) compounds are important targets for molecular electronics. In this study, six air-stable FeIII complexes have been prepared: [Fe­(naphBzen)2]Cl (1), [Fe­(naphBzen)2]­Cl·0.5hexane (1·0.5hexane); [Fe­(naphBzen)2]­Cl·2CHCl3·1.15hexane (1·2CHCl3·1.15hexane), [Fe­(naphBzen)2]Br (2), [Fe­(naphBzen)2]­Br·0.5hexane (2·0.5hexane), and [Fe­(naphBzen)2]­Br·2CHCl3 (2·2CHCl3). The hexane solvates are isostructural, crystallizing in the tetragonal space group I41/a. Weak van der Waals interactions between the cations result in the Fe1 and Fe2 centers packing into chiral chains and exhibiting two-step SCO. In contrast, the nonisostructural CHCl3 solvates have a single Fe center and crystallize in the triclinic space group P1̅ and are LS up to 350 K. The solvent-free systems are also not isostructural with [Fe­(naphBzen)2]­Cl, crystallizing in the triclinic space group P1̅, while [Fe­(naphBzen)2]Br undergoes a phase transition from tetragonal P43 to P43212 upon heating from 150 to 280 K. In both cases the compounds are trapped in the LS state. Magnetic data reveals that SCO occurs only in the hexane solvates, indicating that even very weak interactions can be critical in observing spin-crossover behavior.