Design,Syntheses And Magnetic Properties Of Cobalt(?)Single-Ion Magnets

Single-molecule magnets(SMMs)have attracted continuous interests in the field of molecular magnetism since the discovery of magnetic bistability in Mn12 acetate clusters.These macroscopic compounds have opened a new window to the microscopic world of the quantum and are of great potential in high-density information storage and quantum computing.For a long time,metal clusters with high spin states have been highly pursued.However,the magnetization reversal barriers(Ueff)and blocking temperatures(TB)haven't been effectively enhanced.Recent researches on mononuclear lanthanide and transition metal based SMMs,also termed as single-ion magnets(SIMs)revealed that high magnetic anisotropy is vitally important for the performance of SMMs.As a result SIMs ha've aroused a growing interest in the field of molecular magnetism and numerous results have been reported.This thesis will reports our research results on the Cobalt(II)SIMs,and the innovative research on the collaborative SIM and spin crossover behaviors of Cobalt(?)complexes.(1)Co(?)Single-Ion Magnets(SIMs):We reported the synthetic,structural,computational,and magnetic studies of four air-stable PBP Co? SIMs,which represents a delicate modification of the magnetic anisotropy by tuning the chemical environment of the metal centers.Based on PBP Co? building blocks,we construct a series of one-dimensional(ID)and two-dimensional(2D)framework materials,including the first example of 1D and 2D PBP Co? SIMs,and observed field-induced slow magnetic relaxation in a coordination nanotube for the first time.From these results,we noticed that PBP mononuclear Co? complexes are roubst SIM system with easy-plane magnetic anisotropy,and negligible magnetic interactions can maintain the field-induced SIM behavior in these frameworks,while weak magnetic interactions suppress the slow magnetic relaxation.In addition,we also finely tuned the easy-plane magnetic anisotropy of four distorted octahedral Co? SIMs via organosulfonate anions for the first time.We also obtained a 1D and 2D SIMs with local Oh symmetry.Serendipitously,we prepeared a rare example of a two-component system with the coexistence of SIM and SCO behaviors and suggests a simple,yet very efficient strategy for the construction of multi-stable molecular materials.(2)Dynamic Co? molecular crystals with switchable magnetic properties.a)we present a mononuclear Co? complex to exhibit two step spin transition and field-induced SIM behavior accompanying with reversibly symmetry-breaking structural phase transition,which represents the first SIM with two-step SCO behaviors;b)we present the single-crystal-to-single-crystal(SC-SC)transformation triggered reversible on-off switching of hysteresis loop between a mononuclear Co? complex and its anhydrous analogue;c)we reported the first molecule,a mononuclear cobalt(?)complex,to exhibit on-off switching between SCO and SMM reversibly during crystal-to-crystal transformation.Subtle structural transformation triggered by a simple dehydration-rehydration process induces significant geometric changes of the Co? center and modification of the supramolecular interactions,and switches its colour and magnetic properties(dark red/SCO-on/SMM-off?orange/SCO-off/SMM-on).This work suggests that the modification of the weak supramolecular interactions could be very effective to achieve switchable materials involving both SCO and SMM properties.