Precise Control and Consecutive Modulation of Spin Transition Temperature Using Chemical Migration in Porous Coordination Polymers

摘要

Precise control of spin transition temperature (T_c) is one of the most important challenges in molecular magnetism. A Hofmann-type porous coordination polymer {Fe(pz)[Pt~Ⅱ (CN)_4]} (1; pz = pyrazine) exhibited cooperative spin transition near room temperature (T_c~(up) = 304 K and T_c~(down) = 284 K) and its iodine adduct {Fe(pz)[Pt~(Ⅱ/Ⅳ)(CN)_4(I)]} (1-I), prepared by oxidative addition of iodine to the open metal sites of Pt~Ⅱ , raised the T_c by 100 K. DSC and microscopic Raman spectra of a solid mixture of 1-1 and 1 revealed that iodine migrated from 1-I to 1 through the grain boundary after heating above 398 K. We have succeeded in precisely controlling the iodine content of {Fe(pz)[Pt(CN)_4(I)_n]} (1-In; n = 0.0-1.0), which resulted in consecutive modulation of T_c in the range 300-400 Kwhile maintaining the hysteresis width. Furthermore, it was demonstrated that iodine migration in the solid mixture was triggered by the spin transition of 1-I. The magnetically bistable porous framework decorating guest interactive open-metal-site in the pore surface makes it possible to modulate T_c ad arbitrium through unique postsynthetic method using iodine migration.