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, FeIIH3LMeFeIILMeNO3, and FeIIH3LMeFeIIILMe(NO3)2(H3LMe= Tris2-(((2-methylimidazol-4-yl)methylidene)amino)ethylamine)

A new family of spin crossover complexes, Fe(II)H(3)L(Me)(NO(3))(2).1.5H(2)O (1), Fe(III)L(Me).3.5H(2)O (2), Fe(II)H(3)L(Me)Fe(II)L(Me)NO(3) (3), and Fe(II)H(3)L(Me)Fe(III)L(Me)(NO(3))(2) (4), has been synthesized and characterized, where H(3)L(Me) denotes a hexadentate N(6) tripod ligand containing three imidazole groups, tris2-(((2-methylimidazol-4-yl)methylidene)amino)ethylamine. 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-Fe(II) complex, 2 exhibits a spin equilibrium between HS and LS-Fe(III), 3 exhibits a two-step spin transition, where the component Fe(II)L(Me)(-) with the deprotonated ligand participates in the spin transition process in the higher temperature range and the component Fe(II)H(3)L(Me)(2+) with the neutral ligand participates in the spin transition process in the lower temperature range, and 4 exhibits spin transition of both the Fe(II) and Fe(III) sites. The crystal structure of 3 consists of homochiral extended 2D puckered sheets, in which the capped tripodlike components Fe(II)H(3)L(Me)(2+) and Fe(II)L(Me)(-) 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.