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)

A new family of spin crossover complexes, [(FeH3LMe)-H-II](NO3)(2).1.5H(2)O (1), [(FeLMe)-L-III].3.5H(2)O (2), [(FeH3LMe)-H-II][(FeLMe)-L-II]-NO3 (3), and [(FeH3LMe)-H-II][(FeLMe)-L-III](NO3)(2) (4), has been synthesized and characterized, where H3LMe denotes a hexadentate N-6 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 Mossbauer 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 [(FeLMe)-L-II](-) with the deprotonated ligand participates in the spin transition process in the higher temperature range and the component [(FeH3LMe)-H-II](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 [(FeH3LMe)-H-II](2+) and [(FeLMe)-L-II](-) 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.