Iron(ii) complexes of tris(2-pyridylmethyl)amine (TPMA) and neutral bidentate ligands showing thermal- and photo-induced spin crossover

Abstract

Three new mononuclear Fe(II) complexes have been prepared and characterized by the combination of tetradentate tris(2-pyridylmethyl)amine (TPMA) with three neutral bidentate ligands, such as ethylenediamine (en), 1,2-diaminopropane (pn) and 2-picolylamine (2-pic), in compounds [Fe^II(TPMA)(en)](ClO₄)₂ (1), [Fe^II(TPMA)(2-pic)](ClO₄)₂ (2) and [Fe^II(TPMA)(pn)](ClO₄)₂ (3). Structural and magnetic characterization demonstrates that the three compounds present a complete SCO behavior. The absence of strong intermolecular interactions and solvent molecules leads to reversible and gradual spin transitions. The different ligands allow tuning T_1/2 from 130 K (2) to 325 K (3). The compound with the lowest T_1/2 (2) shows the LIESST effect with a T_LIESST of 43 K. Interestingly, the use of these relatively small bidentate ligands leads to the crystallization in non-centrosymmetric space groups in contrast with previous studies using other bidentate ligands.