A New Family of Spin Crossover Complexes with a Tripod Ligand Containing Three Imidazoles: Synthesis, Characterization, and Magnetic Properties of [FeIIH3LMe](NO3)2·1.5H2O, [FeIIILMe]·3.5H2O, [FeIIH3LMe][FeIILMe]NO3, and [FeIIH3LMe][FeIIILMe](NO3)2 (H3LMe = Tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine)

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Abstract
A new family of spin crossover complexes, [FeIIH3LMe](NO3)2·1.5H2O (1), [FeIIILMe]·3.5H2O (2), [FeIIH3LMe][FeIILMe]NO3 (3), and [FeIIH3LMe][FeIIILMe](NO3)2 (4), has been synthesized and characterized, where H3LMe denotes a hexadentate N6 tripod ligand containing three imidazole groups, tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine. It was found that the spin and oxidation states of the iron complexes with this tripod ligand are tuned by the degree of deprotonation of the imidazole groups and by the 2-methyl imidazole substituent. Magnetic susceptibility and Mössbauer studies revealed that 1 is an HS-FeII complex, 2 exhibits a spin equilibrium between HS and LS-FeIII, 3 exhibits a two-step spin transition, where the component [FeIILMe]- with the deprotonated ligand participates in the spin transition process in the higher temperature range and the component [FeIIH3LMe]2+ with the neutral ligand participates in the spin transition process in the lower temperature range, and 4 exhibits spin transition of both the FeII and FeIII sites. The crystal structure of 3 consists of homochiral extended 2D puckered sheets, in which the capped tripodlike components [FeIIH3LMe]2+ and [FeIILMe]- are alternately arrayed in an up-and-down mode and are linked by the imidazole−imidazolate hydrogen bonds. Furthermore, the adjacent 2D homochiral sheets are stacked in the crystal lattice yielding a conglomerate as confirmed by the enantiomeric circular dichorism spectra. Compounds 3 and 4 showed the LIESST (light induced excited spin state trapping) and reverse-LIESST effects upon irradiation with green and red light, respectively.