Substituent effects on spin-crossover Fe(II)N 4 O 2 pyrenylhydrazone complexes.

Multifunctional magnetic materials have broad application prospects in molecular switches and information storage. In this study, four mononuclear Fe(II) complexes are synthesized using a series of pyrenylhydrazone ligands HL 1-4 . Two deprotonated ligands are coordinated to the iron(II) ions in an enolic form, leading to neutral complexes Fe II (L x ) 2 · xsol with a Fe II N 4 O 2 octahedral coordination environment. Magnetic measurements suggest that complex Fe(L 1 ) 2 ·2ACE (1·2ACE, ACE = acetone) is mainly low spin below 300 K and complex Fe(L 3 ) 2 ·ACE (3·ACE) is high spin, whereas complexes Fe(L 2 ) 2 (2) and Fe(L 4 ) 2 ·6H 2 O (4·6H2O) exhibit gradual spin crossover behavior. The spin states of complexes 1-4 are confirmed by single-crystal X-ray diffraction analysis. The substituent effect on the magnetic properties of the complexes is significant in this system. Temperature-dependent fluorescence emission spectra show the coexistence but no coupling effect of spin crossover and fluorescence for complexes 2 and 4·6H2O.