[Article]物理化学学报(Wuli Huaxue Xuebao )Acta Phys.⁃Chim.Sin .2013,29(4),701-705April Received:January 10,2013;Revised:February 6,2013;Published on Web:February 21,2013.∗Corresponding authors.JIA Li-Hui,Email:jialihui715@;Tel:+86-10-62765703;Fax:+86-10-62765703.WANG Bing-Wu,Email:bwwang@;Tel:+86-10-62765703;Fax:+86-10-62765703.The project was supported by the National Natural Science Foundation of China (21101123,21071008).国家自然科学基金(21101123,21071008)资助项目ⒸEditorial office of Acta Physico ⁃Chimica Sinicadoi:10.3866/PKU.WHXB 201302212[Fe(N 2H 5)2(SO 4)2]n 的合成、结构和磁性质王艳君1贾丽慧1,*王炳武2,*(1武汉工程大学化工与制药学院,绿色化工过程省部共建教育部重点实验室,武汉430073;2北京大学化学与分子工程学院,北京分子科学国家实验室,稀土材料化学及应用国家重点实验室,北京100871)摘要:采用水热合成方法得到一例新的过渡金属铁(Fe)的含肼硫酸盐:[Fe(N 2H 5)2(SO 4)2]n (1).用单晶X 射线衍射的方法对其晶体结构进行了表征.结果表明,该化合物以硫酸根为桥连配体,质子化的肼分子为端基配体,形成一维(1D)链状结构.肼分子和硫酸根形成的链间氢键,将1D 链进一步扩展成三维(3D)结构.磁性测试表明化合物在低温下显示出反铁磁有序的磁行为.关键词:肼;硫酸根;亚铁离子;反铁磁交换作用;磁有序中图分类号:O641Synthesis,Structure and Magnetic Properties of Iron(II)SulfateContaining HydrazineWANG Yan-Jun 1JIA Li-Hui 1,*WANG Bing-Wu 2,*(1Key Laboratory for Green Chemical Process of Ministry of Education,School of Chemical Engineering and Pharmacy,Wuhan Institute of Technology,Wuhan 430073,P .R.China ;2Beijing National Laboratory of Molecular Science,State Key Laboratory of Rare Earth Materials Chemistry and Applications,College of Chemistry and Molecular Engineering,Peking University,Beijing 100871,P .R.China )Abstract:A novel transition metal iron(II)sulfate containing hydrazine (N 2H 4),[Fe(N 2H 5)2(SO 4)2]n (1),is prepared by a hydrothermal method.Single-crystal X-ray diffraction reveals that 1consists of one-dimensional (1D)sulfate-bridged homometallic chains with protonated hydrazine molecules as terminal ligands.Hydrogen bonds between protonated hydrazine and sulfate ions connect the chains into a three-dimensional (3D)extended framework.Magnetic measurements indicate that 1exhibits the antiferromagnetic ordering behavior at low temperature.Key Words:Hydrazine;Sulfate group;Ferrous ion;Antiferromagnetic interaction;Magnetic ordering1IntroductionIn molecule-based magnetic materials,short bridge ligands are expected to transmit strong magnetic coupling so shortbridges,such as O 2-,1CN -,2,3N 3-,4HCOO -,5and C 2O 42-,6,7are in-tensively employed in constructing transition-metal complex-es.A large number of studies on other two-atom bridged molec-ular magnetic systems,such as cyanide (CN -),and oximato(N ―O -)ligands,have been reported on the transition metal co-ordination polymers.8,9Here we focus our attention on a two-atom bridge ligand,which is also a rarely used,hydrazine (N 2H 4).As we all known,unsubstituted hydrazine (N 2H 4)can act as a monodentate,cis -bridging,trans -bridging or bidentate ligand when coordinating to transition metal ions.To the best of our knowledge,our previous work is the first time that the701Acta Phys.⁃Chim.Sin.2013V ol.29crystal structures of transition metal complexes containing un-substituted hydrazine ligand were reported.10As the ability ofhydrazine transmitting the magnetic coupling was scarcely in-vestigated,so we studied and reported the hydrothermal synthe-sis,structures and magnetism of transition metal(M=Mn2+,Co2+,Ni2+)sulfates with hydrazine in2011.As far as we know,it is the first time that transition metal sulfates containing hy-drazine were prepared by hydrothermal method and their mag-netic properties were systematically studied.On the otherhand,the spin-crossover(SCO)compounds and single mole-cule magnets(SMM)have attracted much attention in the fieldof current molecular magnetism due to potential applicationprospect in molecular switches,ultrahigh-density memory,in-formation storage,molecular spintronic devices,and quantumcomputing.For the unquenched orbital moment contribution,high spin Fe2+ion shows the obvious magnetic anisotropy andis the most suitable candidate to construct the above magneticmaterials with the interesting magnetic properties.It is wellknown that the first SCO is a mononuclear Fe2+triazole com-pound and most of the new SCO compounds are still focusedon the Fe2+compounds.Accordingly the observation of slowmagnetic relaxation for a high-spin complex,providing thefirst example of a mononuclear transition metal based sin-gle-molecule magnet.11-13Herein,based on our previous study,we designed and synthesized a transition metal iron(II)sulfatecontaining N2H4:[Fe(N2H5)2(SO4)2]n(1)and studied its structureand magnetic property.2ExperimentalAll starting materials were commercially available at analyti-cal grade and used as purchased without further purification. FeSO4·7H2O(≥99%),N2H4(85%),H2SO4(≥98%).2.1Preparations of[Fe(N2H5)2(SO4)2]n(1)FeSO4·7H2O(1mmol,0.27g),N2H40.8mL,diluted sulfu-ric acid(H2SO4)0.5mL and H2O5mL were mixed in a glass bottle,then the bottle was put in a25mL Teflon-lined stain-less-steel autoclave.The mixture was heated at130°C for3 days in a furnace and then naturally cooled.The colorless crys-tals were collected for measurement.Yields of1based on FeSO4:54%.Elemental analysis calcd. (%)for Fe(N2H5)2(SO4)2:N17.84,H3.21;found(%):N17.99, H3.17.IR(cm-1):988(m),1023(s),1079(vs),1127(vs), 1502(s),1573(m),1602(m),1630(m),2939(m),3072(m), 3239(s),3292(s).2.2X-ray crystallography and physical measurements The crystallographic data for the single crystal of compound 1was collected at293K on an Agilent Technology SuperNova Atlas Dual System with a Cu microfocus source and focusing multilayer optics.Empirical absorption corrections were ap-plied using the CrysAlisPro program.14,15The structure was solved by the direct method and refined by full matrix least-squares on F2using SHELXTL-97.16,17All the non-hydro-gen atoms were refined using anisotropic thermal parameters.The detailed crystallographic parameters of1were listed in Ta-ble1,selected bond lengths and angles in Table2,the data of hydrogen bonds in Table S1(Supporting Information). Powder X-ray diffraction(PXRD)data for compound1was collected in the range of5°-50°for2θon crystalline sample Table1Crystallographic data of compound1a R1=Σ||F o|-|F c||/Σ|F o|,b wR2={|Σw(F o2-F c2)2|/Σ[w(F o2)2]}1/2,c maximum and minimum residual densityParameterformulaFWT/Kcrystal systemspace groupa/nmb/nmc/nma/(°)β/(°)γ/(°)V/nm3ZD c/(g·cm-3)μ(Mo K a)/mm-1F(000)θmin,θmax/(°)index rangereflections collected/unique(R int)R1a,wR2b(I³2σ(I))R1a,wR2b(all data)GOFDρc/(e·nm-3)ValueFe(N2H5)2(SO4)2314.08293triclinicP10.53301(11)0.58264(12)0.73979(15)92.29(3)105.15(3)99.26(3)0.21806(8)11.8113.7371162.86,26.31-6≤h≤6-7≤k≤6-5≤l≤81394/834(0.0181)0.0542,0.11860.0599,0.13241.237683,-696Table2Selected bond lengths and bond angles of compound1symmetry transformations used to generate equivalent atoms:#1x+1,y,z;#2-x,-y+2,-z+1;#3x-1,y,z;#4-x+1,-y+2,-z+1 BondO(4)－S(2)O(4)－Fe(1)#1Fe(1)－O(2)#2Fe(1)－O(2)Fe(1)－O(4)#3Fe(1)－O(4)#4BondS(2)―O(4)―Fe(1)#1O(2)#2―Fe(1)―O(2)O(2)#2―Fe(1)―O(4)#3O(2)―Fe(1)―O(4)#3O(2)#2―Fe(1)―O(4)#4O(2)―Fe(1)―O(4)#4O(4)#3―Fe(1)―O(4)#4O(2)#2―Fe(1)―N(1)#2O(2)―Fe(1)―N(1)#2O(4)#3―Fe(1)―N(1)#2O(4)#4―Fe(1)―N(1)#2O(2)#2―Fe(1)―N(1)Bond length/nm0.1485(5)0.2157(4)0.2081(5)0.2081(5)0.2157(4)0.2157(4)Bond angle/(°)129.3(3)180.0(2)87.5(2)92.5(2)92.5(2)87.5(2)180.0(0)92.4(2)87.6(2)94.6(2)85.4(2)87.6(2)BondFe(1)―N(1)#2Fe(1)―N(1)S(2)―O(3)S(2)―O(1)S(2)―O(2)N(1)―N(2)BondO(2)―Fe(1)―N(1)O(4)#3―Fe(1)―N(1)O(4)#4―Fe(1)―N(1)N(1)#2―Fe(1)―N(1)O(3)―S(2)―O(1)O(3)―S(2)―O(4)O(1)―S(2)―O(4)O(3)―S(2)―O(2)O(1)―S(2)―O(2)O(4)―S(2)―O(2)S(2)―O(2)―Fe(1)N(2)―N(1)―Fe(1)Bond length/nm0.2182(5)0.2182(5)0.1466(4)0.1479(5)0.1486(5)0.1446(7)Bond angle/(°)92.4(2)85.4(2)94.6(2)180.0(0)109.4(3)110.5(3)108.7(3)110.5(3)108.8(3)109.0(3)142.4(3)117.1(4)702WANG Yan-Jun et al.:Synthesis,Structure and Magnetic Properties of Iron(II)Sulfate Containing Hydrazine No.4using a Rigaku Dmax2000diffracture with Cu Kαradiation in flat-plate geometry at room temperature.The experimental PXRD pattern was compared to the calculated one from the sin-gle-crystal structure to identify the phase of the sample in the Fig.S1(Supporting Information).Elemental analyses of nitrogen and hydrogen were per-formed using an Elementar Vario EL analyzer.The FTIR spectrum was recorded against pure sample in the range of4000to600cm-1using a Nicolet iN10MX Micro-in-frared Spectrometer.Magnetic measurement was performed on a MPMS XL-5 SQUID(Superconductivity Quantum Interference Device) magnetometer with crystalline sample fixed in a white capsule by eicosane.Diamagnetic corrections were estimated by using Pascal constants18and background connections by experimental measurements on sample holder.3Results and discussion3.1SynthesisHydrothermal reaction is a convenient and effective route to obtain high-quality single crystals.19,20It is really hard to synthe-size compound1because hydrazine is basic and Fe2+ions can be easily hydrolyzed to ferrous hydroxide in basic solution.In order to protect the Fe2+ions,diluted sulfuric acid(H2SO4) aqueous solution was used to adjust the pH of the reaction solu-tion.At the same time,the addition of sulfuric acid protonates hydrazine molecules,resulting the terminal hydrazine ligands in compound1.3.2IR spectroscopyThe IR spectrum of compound1reveals the presence of the hydrazine groups(N2H4)and the sulfate groups(SO42-)(Fig.S2 in the Supporting Information).The absorption peak at988 cm-1is theν(N―N)band of the protonated hydrazine mole-cule.Due to the existed terminal ligand of hydrazine,it has three consecutive bands and a strong band in the range of 1500-1650cm-1,which is the N―H deformation vibration re-gion.The strong absorption peak around1100cm-1is theν(S―O)band and it is broadened because of the coordination to Fe2+ ion.3.3X-ray crystal structureSingle-crystal X-ray diffraction analysis reveals that the title compound crystallized in the triclinic crystal system,P1space group.The structure of compound1is composed of homome-tallic chains of[Fe(N2H5)2(SO4)2]n,SO42-is the bridge ligand and protonated hydrazine is the terminal ligand.Fe2+ions lo-cate in the distorted octahedral and every Fe2+ion is surround-ed by four equatorial O atoms from four SO42-anions and two axial N atoms from two terminal hydrazine molecules(Fig.1 (a)).The cis angles of O―Fe―O and the N―Fe―O range from87.54°to92.46°,while all trans angles are180.0°(Table 2).Within the[Fe(N2H5)2(SO4)2]n chains,the adjacent Fe2+ions are bridged by two O―S―O bonds in an anti-anti bidentate mode and the intrachain Fe…Fe distance is0.5330nm.The in-finite chains run along a direction(Fig.1(b)).The chains are further connected into a3D extended framework by hydrogen bonds between the terminal ligands and SO42-anions(Fig.1(c)), and the interchain Fe…Fe distance is0.5826nm.The H-bonds (N―H…O)lengths range from0.2764to0.3085nm(Table S1).The strong hydrogen bonding interactions between the chains are the crucial magnetic super-exchange pathway in con-structing the3D magnetic order in the1D chain compound, which will be discussed later.The hydrazine N2H4is protonated to N2H5+and acts as mono-dentate terminal ligand,which is rare in the unsubstituted hy-drazine transition metal sulfates.The distance between the two nitrogen atoms(0.1446nm for1)is slightly shorter,compared with the uncoordinated hydrazine(N―N:0.1460nm)21be-cause of theprotonation.Fig.1Geometry structure of complex1(a)the coordination environment of Fe2+in1;(b)the1D chain of1;(c)the3D framework constructed through H-bonds in1703Acta Phys.⁃Chim.Sin.2013V ol.293.4Magnetic propertyMagnetic measurements were carried out on crystalline sam-ples.The temperature variable magnetic susceptibility drops on cooling,and theχM T(χM is the molar susceptibility)value at 300K is3.5cm3·mol-1·K,a little larger than the spin-only val-ue(3.0cm3·mol-1·K for S=2,S is the spin quantum number) for the orbital moment contribution.18The magnetic susceptibil-ity data in the range of30-300K obeys the Curie-Weiss law,χM=C/(T-q).The linear fitting of theχM-1versus T plots gives the Curie constant C=3.6cm3·mol-1·K and Weiss constant q=-13.8K(Fig.2(a)).The negative Weiss value indicates the overall AF ndéconstant g is2.19,estimated from the equation C=0.125g2S(S+1),indicating the small anisotropy of Fe2+ion in this coordination environment.The magnetic sus-ceptibilityχM for compound1in the direct current(dc)field of 1kOe shows a sharp peak upon cooling and the maximum val-ue is0.10cm3·mol-1at15.0K,suggesting the presence of pos-sible AF ordering in the title compound(Fig.2(b)).The Neel temperature,T N,determined from the sharp peak of d(χM T)/d T, is9.5K(inset of Fig.2(b)).22-24The ratio of T N/T(χM,max)=0.63for 1does show the low-dimensional AF ordering character.25The field dependence of the magnetization of compound1mea-sured at2K increases linearly with the increased dc field and the magnetization at50kOe is only0.43Nβ(the unit of magne-tization)(Fig.2c),far from the saturation value(4Nβfor S=2). This is another evidence that the AF ordering exists in com-pound1.The zero field cooled magnetization(ZFCM)and field cooled magnetization(FCM)at20Oe coincide,which confirms the AF magnetic coupling in1,and no long-range or-dering behavior(Fig.2d).Considering the1D equally spaced chain structure,theχM T value can be fitted by Fisherʹs1D Heisenberg chain model.26 With the spin Hamiltonian H=-2JS i S j,in which J is isotropic in-trachain magnetic interaction and S is spin vector of each mag-netic unit,the magnetic susceptibility could be expressed as:χchain=Ng2β2S(S+1)3kT1+u1-u(1) where u=cothéëêùûú2JS(S+1)kT-éëêùûúkT2JS(S+1),N is Avogadro num-ber,g is gyromagnetic factor,βis Bohr magneton,and k is Boltzmann constant.The interchain interaction term zjʹat the mean field approximation is added to describe the interchain spin-spin interaction.27Thus the expression for the magnetic susceptibility becomesχM=χchain1-(2zj′/Ng2β2)χchain(2) The best fitting parameters(above30K)are J=-1.78cm-1,zjʹ=-0.35cm-1,g=2.20,and R=4.22×10-4for1(R is defined as ∑[(χM T)obs-(χM T)calcd]2/∑[(χM T)obs]2).The value of J iscomparable to those of the previously reported three1D com-pounds,10so it is clear that AF coupling occurred not only be-tween intrachain metal ions but also among interchain metal centers.The interchain AF coupling is transmitted by hydrogen bonds,which should be held responsible for the occurrence of long range ordering.Obviously the AF coupling between intra-chain metal ions is transmitted by the sulfate bridge,whiletheFig.2Magnetic data of1(a)plots of temperature dependence ofχM T(□)andχM-1(○)under1kOe dc field of1.The solid lines are the fitted results;(b)the temperature dependence ofχM,,inset:d(χM T)/d T vs T;(c)field dependence of the magnetization at2K of1;(d)ZFCM and FCM of1at an external field of20Oe704WANG Yan-Jun et al.:Synthesis,Structure and Magnetic Properties of Iron(II)Sulfate Containing Hydrazine No.4interchain coupling is transmitted by hydrogen bonds between the terminal hydrazine ligands and the SO42-anions.4ConclusionsTo the best of our knowledge,it is the first time that iron sul-fate containing hydrazine has been synthesized and magnetical-ly characterized.The X-ray crystallography analysis shows that SO42-anions act as the bridge ligand forming the1D chains,which are further linked by the H-bonds between the protonated hydrazines and SO42-anions to form the3D frame-work.The magnetic data reveal the overall AF magnetic cou-pling.The negative fitted values of J and zjʹindicating both in-tra and interchain interactions are AF coupling.This work is al-so the complement of our previous work10and provides an un-precedented data for studying the coordination chemistry and magnetic properties of hydrazine complexes,and further en-riches the field of molecule-based magnetic material.For the magnetic anisotropy property of Fe2+,more synthetic work to separate the Fe2+chains is under way to study the spin dynam-ics of 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