Approaching the uniaxiality of magnetic anisotropy in singlemolecule magnets

Single-molecule magnets(SMMs),which can exhibit slow magnetization relaxation and bulk-magnet-like hysteresis of purely molecular origin,are promising candidates for high-density information storage,molecular spintronics,and quantum computing.To realize their applications,it is crucial to improve the blocking temperature(TB)and the effective relaxation barrier(Ueff).Three decades of multidisciplinary research have yielded distinct SMMs with a state-of-the-art Ueff of up to 2,000 K and a TB of up to the liquid nitrogen region.Several strategies have been investigated and summarized,which revealed that enhancing the uniaxiality of magnetic anisotropy is critical for constructing high-performance SMMs.Therefore,magnetic anisotropy,a key property that connects the molecular structure symmetry and performance of SMMs,plays a fundamental role in dictating magneto-structural correlations.Understanding and employing magnetic anisotropy would be significantly beneficial for rationally designing high-performance SMMs.This review focuses on the magnetic anisotropy of SMMs.We illustrate the origin and manifestation of magnetic anisotropy in mononuclear 3d-and 4f-block metal complexes.We then introduce developed approaches to investigate magnetic anisotropy both theoretically and experimentally.Typical SMMs by optimizing uniaxial magnetic anisotropy through lanthanide metallocene,symmetry controlling,and low-coordination approaches are represented.Furthermore,the remaining challenges and opportunities in this field will be discussed.

Structures and magnetic relaxation properties of cyclopentadienyl/β-diketonate/trispyrazolylborate hybridized dysprosium single-molecule magnets

The combination of cyclopentadiene,β-diketonate and tripyrazoylborate ligands with dysprosium ion afforded five mononuclear compounds:[(Cp)2Dy(Tp∗)](1Dy),[(Cp)Dy(Tp∗)Cl(THF)](2Dy),[(Cp)Dy(Tp)Cl(THF)](3Dy),[(DBM)Dy(Tp)Cl(THF)](4Dy),[{(Tp)Dy(DBM)_(2)(H_(2)O)}·THF](5Dy)(Cp=cyclopentadiene;Tp∗=hydrotris(3,5-dimethyl-1-pyrazolyl)borate;Tp=hydrotris(1-pyrazolyl)borate;DBM=dibenzoylmethanoate).Magnetic study revealed that 1Dy and 3Dy exhibited typical butterfly-type hysteresis.AC susceptibility study combined with ab initio calculations indicated that the magnetic relaxation behaviors of 1Dy–4Dy were governed by the Orbach and Raman processes under applied DC field.Moreover,3Dy showed two-step magnetic relaxation,which was attributed to the static disordering of the coordinated THF molecule.Magnetic anisotropy analysis indicated that it was the relative strength of the interactions between DyIII and surrounding ligands that determined the orientation of the magnetic easy axis.

A Smart Molecule Showing Spin Crossover Responsive Aggregation-Induced Emission

The utilization of spin crossover(SCO)to modulate the luminescence properties in smart multifunctional materials and multichannel sensors is promising.However,it is challenging to build a strong coupling between SCO and luminescence in one system.Herein,we present a mononuclear compound[Fe(tpe-abpt)_(2)(SeCN)_(2)]·4DMF(1·4DMF,tpe-abpt:(4-(1,1,2,2-tetraphenylethene))-N-(3,5-bis(pyridin-2-yl)-4H-1,2,4-triazol-4yl)methanimine)showing aggregation-induced emission(AIE)and thermally induced SCO properties.Variable-temperature single-crystal structural analysis reveals that SCO changes the number of pathways and strength of intermolecular interactions,resulting in deactivation of nonradiative decay and significant enhancement of luminescence.The photoluminescence(PL)intensity of 1·4DMF exhibited a fivefold increase upon the spin transition from the low-spin to the high-spin states.In contrast with the current strategy of controlling the Förster resonance energy transfer(FRET)process by utilizing SCO to tune the overlap degree between the emission band of the luminophore and UV–vis absorption band of high-spin and low-spin states,we developed a new approach to tune the intermolecular interactions between AIE luminogens(AIEgens)by utilizing a subtle SCO-induced structural transformation,therefore leading to effective coupling between SCO and luminescence and a significant change in luminescence upon SCO.Our results provide a rational strategy to build smartmultifunctionalizedmaterials with remarkably synergetic SCO and luminescence.

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe_(2)Co} Coordination Polymers via Metal-to-Metal Charge Transfer

It is still a formidable challenge to simultaneously switch single-chain magnet(SCM)behavior via ligand modification and light irradiation in the field of molecular spintronics.Herein,we present a ligandbridged layer{[pzTpFe(CN)3]4Co2(Bib)4}·3H2O(1;pzTp,tetra-kis(1-pyrazolyl)borate;Bib,1,4-bis-(1Himidazol-1-yl)benzene)and a well-isolated double chain{[pzTpFe(CN)3]2Co(Bpi)2}·CH3CN·4H2O(2;Bpi,1-Biphenyl-4-yl-1H-imidazole)that display reversible metal-to-metal charge transfer(MMCT)between FeIII LS(μ-CN)CoII HS(μ-NC)FeIII LS(LS,low spin;HS,high spin)and FeIII LS(μ-CN)CoIII LS(μ-NC)FeII LS linkages under alternating irradiation with 808 and 532 nm lasers.The bidirectional light irradiations induces significant changes in anisotropy and intrachain magnetic interactions,resulting in the on/off switching of SCM behavior with observable hysteresis loops by 808 and 532 nm light irradiations for both compounds.Because of the ligand modification,the SCM property of 2 with the monodentate ligand is greatly improved with a correlation length increased to 83,which is the largest correlation length among all reported light actuated SCMs.Furthermore,the influence of ligand modification on their thermally induced MMCT is also discussed.This study provides a rational approach for the swift and reversible control of SCM behavior via ligand modified and light induced MMCT,which is crucial to the future technological demand for high-density data storage and processing.

Thermally Induced Reversible Metal-to-Metal Charge Transfer in Mixed-Valence{Fe^(Ⅲ)_(4)Fe^(Ⅱ)_(4)}Cubes

The engineering of switchable moleculeswith dramatic magnetic change is currently among themost active areas in chemical research.Here,two cyanide-bridged mixed-valence{Fe^(Ⅲ)_(4)Fe^(Ⅱ)_(4)}cubes were prepared,both of which,interestingly,exhibited reversible thermally inducedmetal-to-metal charge transfer(MMCT)behavior between{Fe^(Ⅲ,LS)_(4)Fe^(Ⅱ,HS)_(4)}and{Fe^(Ⅱ,LS)_(4)Fe^(Ⅲ,HS)_(4)}configurations with the transition temperature(T_(1/2))of 274 and 230 K,respectively.These cubes provided a rare example of discrete homometallic complexes exhibiting the reversible MMCT rather than spin crossover behavior.In stark contrast to the heterometallic Fe/Co system,in which the charge transfer(CT)and spin transition(ST)processes occur simultaneously,the detailed structural and Mössbauer spectroscopy analyses confirmed the CT property without involving ST.In addition,both of these cubes showed excellent redox flexibility in solutionwith seven quasi accessible electronic states.