Substituent effects on spin-crossover Fe(<sc>ii</sc>)N4O2 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 HL1-4. Two deprotonated ligands are coordinated to the iron(ii) ions in an enolic form, leading to neutral complexes Fe-II(L-x)(2)<middle dot>xsol with a (FeN4O2)-N-II octahedral coordination environment. Magnetic measurements suggest that complex Fe(L-1)(2)<middle dot>2ACE (1<middle dot>2ACE, ACE = acetone) is mainly low spin below 300 K and complex Fe(L-3)(2)<middle dot>ACE (3<middle dot>ACE) is high spin, whereas complexes Fe(L-2)(2) (2) and Fe(L-4)(2)<middle dot>6H(2)O (4<middle dot>6H(2)O) 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<middle dot>6H(2)O.