FeII Complexes with Triple N1,N2-Triazole Bridge Schiff Base Ligand: Antiferromagnetic Dimer vs. Spin Conversion Trimer

Abstract

Based on the p-tolyl functionalized Schiff base 1,2,4-triazole ligand 4-(p-tolylidene-amino)-4H-1,2,4-triazole (toltrz), a series of three triazole-bridged FeII complexes have been prepared. The compounds represent a range of dinuclear and trinuclear species, with µ2-N1,N2-triazole bridges linking the FeII centers. Mössbauer spectroscopy and magnetic susceptibility measurements reveal a gradual single-step spin crossover (SCO) behavior for the trimeric compound 3 on the central FeII site. Single-crystal X-ray diffraction at 120 K confirms that the central FeII site undergoes a HS to LS transition while the peripheral FeII remain in HS state (HS = high spin; LS = low spin). Compounds 1 and 2 are isostructures with different terminal ligand XCN (X = S, Se), these two compounds stay in high spin state over the whole temperature range but display weak antiferromagnetic exchange coupling.