两例具有大磁滞的氰根桥联{FeⅢ2NiⅡ}单链磁体.pdf

我们利用具有不同对称性的同分异构体，通过改变分子间氢键网络，操控单链磁体行为，成功合成了 2例化合物：Ni(L1)Fe(Tp)(CN)323.5H2O(1)和Ni(L2)Fe(Tp)(CN)323H2O(2)，其中Tp=hydrotris(pyrazolyl)borate，L1=3，4bis(1Himidazol1yl)thiophen，L2=1，2bis(1Himidazol1yl)thiophen)。磁性研究表明，1和2表现为具有不同矫顽场的单链磁体行为。1的矫顽场为8.41 kOe，而2的矫顽场为3.84 kOe。关键词：单链磁体；氰基桥联；氢键；矫顽场中图分类号：O614.81+3；O614.81+1文献标识码：A文章编号：10014861(2023)09177507DOI：10.11862/CJIC.2023.136Two cyanobridged Fe2Ni singlechain magnets with huge magnetic hysteresisGUAN YaHuiZHAO LiangYAO NianTaoHiroki OshioLIU Tao(State Key Laboratory of Fine Chemicals,Dalian University of Technology,Dalian,Liaoning 116024,China)Abstract:Herein,two compounds Ni(L1)Fe(Tp)(CN)323.5H2O(1)and Ni(L2)Fe(Tp)(CN)323H2O(2),where Tp=hydrotris(pyrazolyl)borate,L1=3,4bis(1Himidazol1yl)thiophen,L2=1,2bis(1Himidazol1yl)thiophen,were successfully synthesized by using isomers with different symmetries to change the intermolecular hydrogen bonding network and manipulate the singlechain magnet behavior.The magnetic performance showed that 1and 2 displayed singlechain magnet behavior with huge coercive fields of 8.41 and 3.84 kOe,respectively.CCDC:2252145,1;2252151,2.Keywords:singlechain magnets;cyanobridged;hydrogen bonding;coercive fields0IntroductionThesinglechainmagnets(SCMs)withslowdynamic characteristics during magnetization and hysteresis relaxation12have attracted much attention fortheir potential applications in spintronics34,quantumcomputing56,and intelligent information storage7.Thefirst experimental evidence of SCMs was reported in2001 by Caneschi et al8.Since then,many new SCMshave been synthesized.However,achieving the SCMswith high blocking temperatures and energy barriersremains challenging912.The recent breakthrough hasbeen achieved in two CoWcyanide bridged SCMsreported by Yangs group,(Ph4P)Co(3Mepy)2.7(H2O)0.3W(CN)80.6H2O and(Ph4As)Co(3Mepy)3W(CN)8(3Mepy=3methylpyridine),which showed large relaxation barriers of 252 and 224 K,respectively13.Wanget al.also reported a MoMncyanide bridged SCMs,Mn(bida)(H2O)2Mo(CN)76H2O(bida=1,4bis(4imidazolyl)2,3diaza1,3butadiene),with ultralarge relaxation energy barriers of 178 K14.In general,to construct the SCMs,the large spin ground state,strong uni无机化学学报第39卷axial anisotropy,strong intramolecular coupling,andweakintermolecularinteractionsareindispensable1519.Up to now,it is still a big challenge to construct SCMs,especially with wide magnetic hysteresiswhich is crucial in information storage2021.The mainreason is that the lowdimension structure makes it difficult to maintain strong axial anisotropy and magneticcoupling within the chain.Recently,Sessolis grouphas successfully manipulated the coercivity field of theSCMsthroughacarefullyorchestratedinterplaybetween the dynamics of individual chains and the associated intermolecular interactions22.Long et al.havereported SCMs with the largest coercive field of 60 kOeand pointed out that the interaction of two orientationally distinct chains,and consequently magnetic sublattices in tandem with strong intrachain magnetic couplingis critical to the large coercivity23.Therefore,exquisitecontrol of interchain interactions is required to manipulate the coercivity of SCMs materials.On this basis,we chose Fe(Tp)(CN)3-(Tp=hydrotris(pyrazolyl)borate)as a building block to coordinatewith Nito construct SCMs,wherein the generallyferromagnetic Fe Ni coupling could provide strongintrachain interactions and uniaxial anisotropy2426.Moreover,two similar ditopic ligands,3,4bis(1Himidazol1yl)thiophen(L1)and 1,2bis(1Himidazol1yl)thiophen(L2),were selected to change the intermolecularhydrogenbondingnetworktomanipulatetheinterchaininteraction.Therefore,twoSCMs,Ni(L1)Fe(Tp)(CN)323.5H2O(1)and Ni(L2)Fe(Tp)(CN)323H2O(2),were successfully constructed,inwhich wide magnetic hysteresis with the coercive fieldof 8.41 and 3.84 kOe,respectively was observed.1Experimental1.1MaterialsL1 and L2 were prepared according to the literatures methods27.All other chemicals were obtainedfrom commercial vendors and used without further sublimation.1.2Synthesis of compounds 1 and 2The synthetic methods of compounds 1 and 2were similar.1 and 2 were synthesized by a diffusionmethod in a test tube.A 1.0 mL aqueous solution ofNi(ClO4)26H2O(0.005 mmol)was slowly added to thebottom of the test tube.Then a mixture of methanol/water(1 1,V/V,3 mL)was gently layered on the aqueous solution as an intermediate buffer.Last,1.0 mLmethanol solution of(Bu4N)Fe(Tp)(CN)32H2O(0.010mmol)and ligand L1 or L2(0.010 mmol)was carefullyadded as the third layer.After a few weeks,dark redcrystals of 1 and 2 were collected.Compound 1:Yield:18%based on the Ni(ClO4)26H2O.Elemental analysis calculated for C34H35B2Fe2N22NiO3.5S(%):C 39.54,H 3.39,N 29.85;Found(%):C40.12,H 3.23,N 29.56.IR data(KBr,cm-1):3 432(s),3 121(w),2 503(w),2 175(m),2 123(w),1 626(m),1 532(s),1 406(s),1 314(s),1 212(s),1 118(s),1 048(s),986(w),934(w),762(s),713(s),657(s)(Fig.S1,Supporting information).Compound 2:Yield:17%based on the Ni(ClO4)26H2O.Elemental analysis calculated for C33H31B2Fe2N22NiO3S(%):C 39.29,H 3.07,N 30.56;Found(%):C39.89,H 3.54,N 31.24.IR data(KBr,cm-1):3 435(s),2 490(w),2 176(w),2 121(w),1 633(s),1 501(w),1 401(s),1 314(w),1 210(w),1 159(w),1 116(m),1 047(m),756(w),711(w),660(w),614(w)(Fig.S1).1.3Physical measurementThe singlecrystal XRD data for 1 and 2 were collected on a Bruker D8 VENTURE CMOSbased diffractometer(Mo K radiation,=0.071 073 nm)using theSMART and SAINT programs.Final unit cell parameters were based on all observed reflections from theintegration of all frame data.The structures weresolved with the ShelXT structure solution programusing Intrinsic Phasing and refined with the ShelXLrefinement package using Least Squares minimizationthat was implanted in Olex2.The crystallographic datafor 1 and 2 are listed in Table S1.The powder Xraydiffraction(PXRD)patterns of 1 and 2 were obtainedon a Rigaku SmartLab 9kW X ray diffractometer(Cu K radiation,=0.154 178 nm,U=45 kV,I=200mA)in a range of 550 at 5()min-1.Variabletemperature infrared spectra were measured on KBrpellet samples using a Nicolet iS10 FTIR spectrometer equipped with a Bruker cryostat(Optistat CF2).1776第9期Magnetic measurement of the sample was performed ona Quantum Design PPMS9.Data were corrected forthe diamagnetic contribution calculated from Pascalconstants.The sample was measured under a DC fieldof 1 000 Oe.The variabletemperature magnetizationdata were collected within a temperature range of 2300 K at 2 Kmin-1.The Elemental analysis was performed by Elementar Vario EL (Germany).Thermogravimetric(TG)analysis was performed under an N2atmosphere at 10 K min-1using a TG/DTA STDQ600system(TA Instruments,the United States).CCDC:2252145,1;2252151,2.2Results and discussion2.1Crystal structureCompounds 1 and 2 were synthesized via the diffusion method by reacting Ni(ClO4)26H2O,the ligand(L1 for 1 and L2 for 2)and(Bu4N)Fe(Tp)(CN)32H2Oin a MeOH/H2O mixture28.The resulting materialswere characterized by IR and PXRD.PXRD analysisconfirmed the phase purity of 1 and 2 at room temperature(Fig.S2).Single crystal Xray diffraction analysisreveals that 1 and 2 crystallize in the orthorhombicspace group Pnma,with the Fe2Nibased chain alongthe crystallographic baxis(Fig.S3 and S4).The asymmetric unit of 1 and 2 consists of two crystallographically independent Fe(Tp)(CN)3-units,two Ni(L)2+moieties,and one(1)and two(2)uncoordinated watermolecules,respectively.In 1,the Ni ion is locatedon the inversion center,and a mirror plane exists onthe plane defined by the Fe1,Fe2,and sulfur atoms ofL1.Each Fe ion is located at a slightly distortedoctahedral coordination geometry,consisting of threecyanide carbon atoms and three nitrogen atoms fromthe Tp units.Each Ni ion is coordinated by fournitrogen atoms from the cyanide group in the equatorialplane and two nitrogen atoms from two L1 molecules inthe apical positions,providing an NiN6 octahedron geometry.Within the chain,each adjacent Ni ion islinked by two NCFeCN linkages and one L1ligand.The two Tp units and one L1 ligand form asmall shuttle shaped cage and connect the adjacentNi ions to form a wellisolated triply bridged chain(Fig.1).Compound 2 is isostructural to 1,and alsoexhibits a wellisolated triply bridged chain.The sulfuratoms of L2 in 2 cannot be distinguished due to thecentrosymmetric requirement.In 1,the NiN bond lengths are 0.202 6(5)0.210 7(4)nm,which is consistent with the previousobservations in the related high spin(HS)Ni compounds2930.The coordination bond lengths of theFeC are 0.189 8(6)0.191 5(9)nm and 0.190 5(11)0.191 4(6)nm for Fe1 and Fe2,respectively,and theFeN bond distances are 0.196 1(7)0.196 2(5)nmand 0.198 0(7)0.198 5(5)nm for Fe1 and Fe2,respectively,which is in good agreement with the previouslyreported in the related lowspin(LS)Fe compounds(Table S2)31.In 2,NiN bond lengths are 0.202 4(5)0.211 1(5)nm.The coordination bond lengths of theFeC are 0.188 8(6)0.192 2(10)nm and 0.190 1(6)0.191 0(11)nm for Fe1 and Fe2,respectively,and theFeN bond distances are 0.195 4(7)0.196 6(5)nmPartial H atoms are omitted for clarity;Fe,green;Ni,light blue;S,yellow;C,grey;N,dark blue;O,red;B,atrovirens;H,creamy white.Fig.1Hydrogen interactions in 1(a)and 2(b)管雅慧等：两例具有大磁滞的氰根桥联Fe2Ni单链磁体1777无机化学学报第39卷and 0.197 3(7)0.198 3(5)nm for Fe1 and Fe2,respectively(Table S3).According to the latest research,interchain interactions play a subtle role in constructing SCMs withhuge magnetic hysteresis32.The hydrogen bonding,acting as an elastic interaction,can be regulated based onthe distance between the hydrogen bonding donor andacceptor,thus it can be utilized to modulate the intermolecular interaction between single chains,resultingin the acquisition of high coercivity SCMs33.The interchain CH interactions between pyrazole andthiophene ring and intermolecular hydrogen bondinginteractions are observed in 1 and 2(Fig.S5S8).In 1,the intermolecular hydrogenbonding interactions areobserved between the nitrogen atoms of terminal cyanide,the sulfur and carbon atoms of L1,and the oxygen atoms of lattice water molecules,with CO distance of 0.343 2 nm,ON distances ranging from0.252 5 to 0.315 7 nm,an OO distance of 0.241 1 or0.235 2 nm and an OS distance of 0.354 4 nm(TableS4).Different from 1,the intermolecular hydrogen bonding interactions for 2 are formed between the nitrogen atoms of terminal cyanide and the oxygen atoms oflattice water molecules,with ON distances rangingfrom 0.248 6 to 0.297 8 nm(Table S5).2.2Magnetic propertyThe variable temperature magnetic susceptibilities for 1 and 2 were measured in a range of 2300 Kunder the direct current(dc)field of 1 000 Oe,whichshowed similar magnetic behaviors(Fig.2).At 300 K,the T value was 3.05 and 3.01 cm3mol-1K for 1 and2,respectively,which were higher than the spinonlyvalue of 2.482.79 cm3mol-1K expected for two isolated Fe(S=1/2,g=2.62.8)and one Ni(S=1,g=2.22.3).As cooling,the T value gradually increased to asharp maximum of 115.52 and 76.97 cm3mol-1K at 8and 9 K for 1 and 2,respectively,indicating the dominant ferromagnetic(FM)interaction between Fe andNi metal center34.Moreover,the CurieWeiss lawwas fit for the temperature range of 2300 K,whichgave Curie constant of 2.88 and 2.85 cm3mol-1K,andWeiss temperature of 13.71 and 5.66 K for 1 and 2,respectively.The positive Weiss constant confirms thedominant FM interactions in 1 and 2.Further lowingFig.2Temperaturedependent magnetic susceptibilities of 1(a)and 2(c)in a temperature range of 2300 Kunder an applied field of 1000 Oe;Hysteresis loops of 1(b)and 2(d)at 2 K1778第9期the temperature,the T value decreased rapidly and ultimately reached a value of 3.27 and 18.92 cm3mol-1K at 2 K for 1 and 2,probably due to the zerofieldsplitting and Zeeman splitting.At 2 K,the isothermalmagnetization increased sharply with the applied magnetic field rising and reached a value of 3.45N and3.30N at 50 kOe for 1 and 2,which was smaller thanthe saturation value of 4.54N expected for MS=g(SNi+2SFe),plausibly due to the zero field splitting of theNi ions and the orbital degeneration of LS Fe ions(Fig.S9).To further explore the switching or reversal of themagnetization with the applied field,the full hysteresisloops were recorded at 2 K.As shown in Fig.2b and 2d,1 and 2 exhibited an obvious hysteresis with a remnantmagnetization(Mr)of 3.05N and 1.73N and a coercive field(Hc)of 8.41 and 3.84 kOe,respectively.Todate,1 manifests the largest coercive field among thereported FeNiSCMs.The nearest interchain metalmetal distances are 1.144 1(6)and 1.143 9(14)nm for1 and 2,respectively.The significant interchain distance effectively isolates the interchain magnetic coupling,leading to the formation of SCMs with significanthysteresis.The positions of the thiophene sulfur atomsin the ligand result in water molecules being presentbetween the two thiophene groups in 1,which lengthens the interchain distance of 1.Consequently,theintermolecular interaction between the chains in 1 isweaker than that of 2,leading to a larger coercive fieldin 1.The magnetization curve of 2 changed strongly ata nearzero field,showing stepbystep magnetizationcharacteristics.The zerofieldcooled(ZFC)and fieldcooled(FC)magnetization measurements were performed for 1 and 2 in a range of 220 K,which showeda divergence at 4.9 and 3.8 K for 1 and 2,respectively.This indicates that 1 and 2 undergo spontaneous magnetization at low temperatures.To investigate the possibility of SCMs behavior,the alternating current(ac)magnetic susceptibility of 1and 2 was measured as a function of both temperatureand frequency,which shows similar magnetic behaviors(Fig.3).Both inphase()and outofphase()showed apparent frequency dependency from 4 to 8 Kfor 1 and 2,and the peak moved to a higher frequencywith temperature increasing,precluding a 3D ordering.For the relaxation process in low temperature(LT),theparameter=Tp/(Tplg f),a measure of the frequencydependence of the peak temperature shift(Tp)of,was estimated to be 0.15 and 0.14 for 1 and 2,respectively,which is out of the range for spinglass but liesin the expected range for a superparamagnet(0.1),and thus rules out the possibility of spinglass behavior.The relaxation rate can be simulated by the Arrhenius law of=0exp/(kBT),where,0,and/kBarerelaxation time,preexponential factor,and relaxationenergy barrier,respectively.Leastsquares fitting gavepreexponential factor 0=7.4710-11and 1.0610-10s,and/kB=87.48 and 83.35 K for 1 and 2,respectively,which were in good agreement with those values for other reported SCMs9.More importantly,the relaxationenergy barrier of 1 was significantly larger than that ofcompound 2.For an anisotropic Isinglike system,Tincreases exponentially with decreasing temperature,following the equation T/Ceff=exp/(