Enhancing single-molecule magnet behavior of linear Co~Ⅱ-Dy~Ⅲ-Co~Ⅱ complex by introducing bulky diamagnetic moiety

Single-molecule magnets （SMMs） are regarded as promising candidates for ultrahigh-density storage, quantum information processing and molecular spintronics. It is a crucial challenge for chemists to modulate magnetic dynamics of SMMs. Here, we successfully synthesized two 3d-4f polynuclear compounds [Co2Dy（TTTTCl）2（MeOH）]NO3.3MeOH （1） and [Co2Dy（TTTTCl）2 （MeOH）][Co（HTTTTCl）]（NO3）z-2.5MeOH＇2H20 （2）, where H3TTTTCl=2,2＇,2＂-（（（nitrilotris（ethane-2,1-diyl）） tris（azanediyl）） tris（methylene））tris-（4-chlorophenol）. On applying the approach by co-crystallization of bulky diamagnetic moiety, the effective energy barrier enhances from 401 K （1） to 536 K （2）, which are both among the highest d-f heterometallic SMMs.

Reversible on-off switching of spin-crossover behavior via photochemical [2+2] cycloaddition reaction

Herein,we report the first example showing the reversible on-off switching of spin-crossover(SCO)property by solid state photochemical[2+2]reaction.The ultraviolet(UV)light-induced[2+2]cycloaddition reaction of 3-spy ligands in a twodimensional(2D)Hofmann-type framework[Fe(3-spy)_(2){Pd(CN)_(4)}](1,3-spy=3-styrylpyridine),which shows a hysteretic twostep SCO behavior,gives a 3D Hofmann-type framework[Fe(rctt-3-ppcb){Pd(CN)_(4)}](2,rctt-3-ppcb=rctt-1,3-bis(3-pyridyl)-2,4-bis(phenyl)cyclobutane,r=reference group,c=cis and t=trans)accompanied with the disappearing of SCO properties.Moreover,upon heating at 250℃ for 12 h,the rctt-3-ppcb ligand in 2 could be partially dedimerized to 3-spy with 68%completion through single-crystal-to-single-crystal(SCSC)transformation,giving the annealing complexes[Fe(3-spy)1.36(rctt-3-ppcb)0.32{Pd(CN)_(4)}](3)which display an incomplete SCO behavior.The 2■3 interconversion is successfully achieved via continuous UV irradiation and thermal annealing,demonstrating the effectiveness of photochemical[2+2]reaction on switching on-off SCO properties.

Seeking magneto-structural correlations in easily tailored pentagonal bipyramid Dy (Ⅲ) single-ion magnets

Controlling molecular magnetic anisotropy via structural engineering is delicate and fascinating,especially for single-molecule magnets(SMMs).Herein a family of dysprosium single-ion magnets(SIMs)sitting in pentagonal bipyramid geometry have been synthesized with the variable-size terminal ligands and counter anions,through which the subtle coordination geometry of Dy(Ⅲ)can be finely tuned based on the size effect.The effective energy barrier(Ueff)successfully increases from 439 to 632 K and the magnetic hysteresis temperature(under a 200 Oe/s sweep rate)raises from 11 to 24 K.Based on the crystal-field theory,a semi-quantitative magneto-structural correlation deduced experimentally for the first time is revealed that the Ueff is linearly proportional to the structural-related value S20 corresponding to the axial coordination bond lengths and the bond angles.Through the evaluation of the remanent magnetization from hysteresis,quantum tunneling of magnetization(QTM)is found to exhibit negative correlation with the structural-related value Stun corresponding to the axial coordination bond angles.

Multiresponsive Spin Crossover Driven by Rotation of Tetraphenylborate Anion in an Iron(Ⅲ)Complex

Dynamic molecular materials,which involvemechanical motions in crystals,usually exhibit tunable properties related to conformational polymorphs.Herein,we describe a solvent-free molecular crystal[{FeⅢ(salten)}2(TPB)](BPh_(4))_(2)(Ⅰ)developed by associating the rotatable tetraphenylborate anion with the spin crossover(SCO)binuclear iron(Ⅲ)cation.The solvent-free phaseⅠcan undergo a temperature-induced phase transformation to phaseⅡ,during which rotation of the BPh4−anion interplays with the SCO component,giving rise to fascinating variations in SCO(from gradual to abrupt)and dielectric properties.Most importantly,an unexpected polymorphic transformation fromⅡtoⅢorⅣ,with increasing magnetic hysteresis,is realized by exposingⅡto water or ethanol vapor;the transition is reversible by heating.This rare successive transformation is further rationalized by theoretical calculations.Hence,this multiresponse system provides a new way for modulating synergistic effects and designing dynamic SCO materials by integrating intramolecular motions in the crtystal lattice.