Spin Crossover Behavior of Dinuclear FeII Complexes with Bis-Tetradentate Bridging-Type Ligands

The preparation and characterization of two new Fe-II dinuclear complexes with bis-tetradentate bridging-type ligands [{Fe(NCS)(2)}(2)(L)]center dot DMF center dot 2H(2)O (1: L = L-1{2,5-bis[N,N-bis(2-pyridylmethyl)aminomethyl]pyrazine}, 2: L = L2{2,3-bis[N,N-bis(2-pyridylmethyl)aminomethyl]pyrazine}) are reported. Magnetic measurements reveal that complexes 1 and 2 exhibit different thermal spin-crossover behavior. Complex 1 shows a crystalline solvent effect on spin crossover (SCO). After desorption of the crystalline solvent by heating, an abrupt one-step transition with a hysteresis loop was observed for the desolvated form 1'. Conversely, a gradual two-step SCO was obtained for 2. The photomagnetic effect was also investigated in 1' and 2, and both complexes clearly show light-induced excited spin state trapping. Interestingly, one-step and two-step thermal relaxation were observed for 1' and 2, respectively. Such different SCO properties occur because of the cooperative effects owing to the structure of the ligand.