| Research Abstract |
The phenomenon of spin crossover between the low-spin (LS) and high-spin (HS) states, which is induced by external perturbation such as temperature, pressure, and light irradiation, is one of the most spectacular examples of molecular bistability. The bistability of the spin crossover behavior is governed by the cooperative interaction between the spin crossover sites. Therefore, a novel ligand system, which can provide not only spin crossover but also can produce interaction between spin crossover sites, is now required. We synthesized here a new family of spin crossover complexes with the various oxidation states and the various degree of the deprotonation at the imidazole moiety, [Fe^<II>H_3L^<Me>](NO_3)_2・1.5H_2O (1), [Fe^<III>L^<Me>]・3.5H_2O (2), [Fe^<II>H_3L^<Me>][Fe^<II>L^<Me>]NO_3 (3), and [Fe^<II>H_3L^<Me>][Fe^<III>L^<Me>](NO_3)_2 (4). The crystal structural analysis of 3 showed an unprecedented 2D homochiral assembly structure constructed by the imidazole-imidazolate hydrogen bonds between [Fe^<II>H_3L]^<2+> and [Fe^<II>L]-components with the same chirality. Compounds 3 and 4 also present the LIESST (light induced excited spin state trapping) effect. More surprisingly, a series of compounds involving the multi-functional compound exhibiting such complicated electronic structures and bulk optical activity is obtained by the adjustment of pH and by a one-pot assembly reaction of a programmed single molecule.
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