以均苯四甲酸根为桥联配体的双核钴_II_配合物的合成与磁性_英文_

文章编号:0490-6756(2001)06-0856-07SYNTHESIS AND MAGNETIC PROPERTIES OF BINUCLEARC OBALT (Ⅱ)C OMPLEXES WITH TETRACARBOXYLATOGR OUPS AS BRIDGING LIGANDL I Y an -tuan 1,Y AN Cui -wei 2,CHEN Yong 1,ZENG X ian -cheng1,＊(1.The Faculty of Chemistry ,Sichuan University ,Chengdu 610064,China ;2.Qufu Normal University ,Shan -dong Qufu 273165,China )Abstract :Three new (μ-tetracarboxylato binuclear cobalt (II )com plexes described by theoverall formula [Co 2(PM TA )(L )4],w here PM TA represents the tetraanio n of py romellitic acid ;and L deno tes o -benzenediamine (obda ),2-dimethylaminoethylamine (Me2en )o r 3-dimethy -laminopropylamine (Me 2pn ),respectively ,have been synthesized and characterized by elementalanalyses ,molar conductivity measurements ,I R and electronic spectra .It is proposed that thesecomplexes have PM TA -bridged structures and consist of two cobalt (II )ions ,each in a distortedoctahedral environment .The [Co 2(PM TA )(M e 2pn )4]complex w as further characterized byvariable temperature mag netic susceptibility measurements (4～300K )and the observed datawere successfully simulated by the equation based on the spin Hamiltonian operator , H =2J S 1·S 2,giving the exchange integ ral J =-0.28cm -1.The result revealed the operatio n of antifer -rom agnetic spin -ex change interaction betw een the tw o Co (II )ions within the molecule .Key words :μ-tetracarbo xylato ;binuclear cobalt (II )complex ,mag netic property ;sy nthesis ;characterizationCLC number :Q67 Document Code :A 1　IntroductionThe syntheses and long -range magnetic exchange interactions of binuclear transition -metal complexes ,in w hich spin coupling betw een paramagnetic metals is propagated by multiatom bridges ,have been an active field of research in recent years ,not only for gaining some insight into the pathw ays of electron transfers in biological systems ,but also for obtaining information about designing and synthesizing molecule -based magnets ,and for investigating the spin -exchange mech -anism betw een paramagnetic metal ions [1～10].In view of the bridging functaion the tetraanion of pyromellitic acid (abbreviated as PM TA ),Chaudhuri et al [6].first utilized the PM TA as a multiatom bridge to synthesize the binuclear cop -per (II )complex [LCu (μ-tetracarboxylato )CuL ]·4H 2O (L =1,4,7-trimethyl -1,4,7-triazacy -clononane ).It has been revealed by the single crystal X -ray and magnetic analyses [6]that the long -range antiferro -magnetic coupling could occur betw een the copper (II )ions bridged by the PM TA ligand although the Cu …Cu separation is 7.8 .In order to provide more examples of PM TAReceived :1999-12-29Foundation team :T he National N atural Science Foundation of China (29873031)＊Corresponding autho r 2001年12月第38卷第6期四川大学学报(自然科学版)Journal of Sichuan University (Natural Science Edition )Dec .2001Vol .38　No .6-bridged binuclear complexes and to understand better the factors affecting the superexchange in -teractions propagated by PM TA ,it w as necessary to synthesize a series of binuclear complexes of essentially the same structure except for the metal ion .In this paper ,we describe the synthesis and magnetic property of three new cobalt (II )binuclear complexes using the PM TA as a bridging ligand :[Co 2(PM TA )(M e 2pn )4](1)and [Co 2(PM TA )(Me 2en )4](2)and [Co 2(PM TA )(obda )4](3),w here PM TA represents the tetraanion of py romellitic acid ,and ob -da ,M e 2en and M e 2pn denote o -benzenediamine ,2-dimethylaminoethylamine or 3-dimethy -laminopropylamine ,respectively .2　Experimental2.1　MaterialsThe hydrated cobalt (II )perchlorate w as prepared and purified by the literature method [9].Py romellitic acid (H 4PM TA )(Beiging Chem .Co .),LiOH (H 2O (Shanghai Chem .Co .)and the terminal ligands o -benzenediamine (obda )(Shanghai Chem .Co .),2-dimethylaminoethylamine (M e 2en )or 3-dimethyl -aminopropylamine (Me 2pn )(analytical grade ,Aldrich Co .)w ere used as commercially obtained .2.2　Synthesis of binuclear complexes2.2.1　Synthesis of [Co 2(PM TA )(Me 2pn )4](1)　To a solution of 254.3mg (1mmol )of py -romellitic acid in methanol (15mL )was added dropw ise a methanol solution (20mL )of 167.8mg (4mmol )of LiOH ·H 2O under stirring at room temperature .The stirring w as continued until the mixture became clear .This solution w as then filtered .To the filtrate w as added a methanol solution (15mL )of 731.8mg (2mmol )of Co (ClO 4)2·6H 2O and 408.7mg (4mmol )of M e 2pn in 20mL methanol solution under N 2.The color of the solution changed immediately from orange to red and a small amount of precipitate formed .Stirring w as continued for 8h ,the precipitate formed w as filtered ,w ashed w ith methanol ,w ater and diethyl ether for several times and dried w ith P 2O 5under reduced pressure .Recrystallization w as carried out from acetonitrile /ethanol (4∶1)mixture .Yield ,582.5(80%);mp ,197.5℃.Found :C ,46.17;H ,7.42;N ,14.20;Co ,15.03%.Anal .calc .for C 30H 58N 8O 8Co 2(M .W .776.70):C ,46.39;H ,7.53;N ,14.43;Co ,15.18%.2.2.2　Synthesis of [Co 2(PM TA )(M e 2en )4](2)　This complex w as obtained as orange -red mi -crocrystals by the same procedure using M e 2en instead of M e 2pn .Yield ,540.4mg (75%);mp ,213℃.Found :C ,43.18;H ,6.73;N ,15.21;Co ,16.04%.Anal .calc .for C 26H 50N 8O 8Co 2(M .W .720.60):C ,43.34;H ,6.99;N ,15.55;Co ,16.36%.2.2.3　Synthesis of [Co 2(PM TA )(obda )4](3)　This complex w as obtained as reddish micro -crystals by the same procedure as above ,using obad instead of M e 2pn .It was recrystallized from a hot DM F solution .yield ,680.5mg (85%);mp ,257℃.Found :C ,50.89;H ,4.19;N ,13.81;Co ,14.50%.Anal .calc .for C 34H 34N 8O 8Co 2(M .W .800.56):C ,51.01;H ,4.28;N ,14.00;Co ,14.72%.857第6期李延团等:以均苯四甲酸根为桥联配体的双核钴(II )配合物的合成与磁性2.3　Physical measurementsC ,H and N analyses were performed w ith a M odel 240Perkin -Elmer elemental analyzer .The metal contents w ere determined by EDTA titration .The IR spectra w ere measured on a Shi -madzu infrared spectrometer Model 810in KBr pellets .Reflectance spect ra were measured on a Hitachi -340spect rophotometer .The melting points of the complexes were determined by a M odel XT 7-1micro -melting point meter .Molar conductances were measured (DM F solution )w ith a Shanghai DDS -11A conductometer .Variable temperature magnetic susceptibilities (4～300K )w ere measured using a M odel M PMS -5magnetometer .Diamagnetic corrections w ere made w ith Pascal 's constants [11]for all the constituent atoms and the effective magnetic moments w ere calcu -lated by the equation μeff =2.828(χM T )1/2,w here χM is the magnetic susceptibility per molecule corrected for diamagnetism of the constituting atoms .3　Results and Discussion3.1　Preparation and coordination environment of the binuclear complexesThe PM TA -bridged binuclear complexes w ere obtained by the reaction of H 2PM TA w ith Co (ClO 4)2·6H 2O and L (L =Me 2en ,M e 2pn ,obda )in methanol solution in the presence of a base .The use of LiOH ·H 2O as the base gave good results because it and its salt (LiClO 4)formed in the reaction are fairly soluble in methanol and the products are little contaminated with these in -organic materials .Indeed ,elemental analytic data for the new ly prepared complexes indicate that the reaction of PM TA w ith Co (ClO 4)2·6H 2O and L (L =M e 2en ,M e 2pn ,obda )yielded the bin -uclear complexes of the general formula [Co 2(PM TA )L 4].Based on the conductivity measure -ments ,spectroscopic characterization and magnetic studies (vide infra )these complexes are pre -sumed to have the coordination environment as show n in Fig 1.Fig 1.　Suggested coo rdination environment of the complexes (N N =Me 2en ,M e 2pn ,obda )3.2　Solu bility and molar condu ctanceAll the binuclear complexes are sparingly soluble in w ater ,ethanol ,carbon tetrachloride ,chloroform and benzene ,but soluble in acetone ,acetonitrile ,DMF and DM SO to give stable solu -tion at room temperature .For the three complexes ,the molar conductance values in DMF solution (see Table 1)show that all the complexes are non -elect rolytes [12].This is consistent w ith the mea -sured IR data .858四川大学学报(自然科学版)第38卷3.3　Infrared spectraThe IR spectra taken in the region 4000～400cm -1provide some information regarding the mode of coordination in the complexes and w ere analysed in comparison with that of the free ligand (H 4PM TA ).The most relevant IR absorption bands due to the complexes together with their as -signments are show n in Table 1.The IR spectrum of pyromellitic acid shows a broad band at near1700cm -1w hich is attributed to ν(C =O )of the carboxylic g roup .However ,in the IR spectra of all complexes ,this band disappeared ,accompanied by the appearance of two characteristic strongand broad bands at ca .1600cm -1and 1370cm -1attributed to νas (CO -2)(1630～1610cm -1and νs (CO -2)(1380～1370cm -1)stretching vibrations of the coordinated carboxylate groups .The absence of any splitting of the νas (CO -2)and νs (CO -2)bands strongly suggests the end -to -end lik -ing of the PM TA ligand in an equivalent way at both sites [5].M oreover ,the coordination modes ofcarboxylate g roups have often been diagnosed by the separation betw een νas (CO -2)and νs (CO -2).That is ,bidentate carboxylate g roups show a separation smaller than 200cm -1w hereas unidentatecarboxylate groups show a separation larger than 200cm -1Thus ,for the present complexes ,thesetwo bands w ere separated by ca .240cm -1(see Table 1),suggesting an unidentate coordinationmode for the four carboxylato groups of the PM TA ligand [13].The unidentate coordination modes of the carboxylates in PM TA w ere supported by the crystal st ructure of the analogous complex[LCu (μ-tet racar -boxylato )CuL ]·4H 2O (L =1,4,7-trimethyl -1,4,7-triazacyclononane )[6].Theappearance of a new band at 540～545cm -1due to ν(Co -O )further confirms the coordinated na -ture of the PM TA groups in these complexes .In addition ,the -NH 2vibrations for the terminal ligands (M es 2en ,M es 2pn ,obda )are observed in corresponding binuclear complexes (see Table1),suggesting that the N atoms of the terminal ligands coordinated w ith the metal ion .This view is further supported by the appearance of the band corresponding to the metal -nitrogen stretching vibration at 480～485cm -1in the complexes .Furthermore ,the band centered at 1100cm -1typi -cal for the ν(Cl -O )stretching of the perchlorate group [14],w as not found for the complexes .This is consistent with the conductance measurements and elemental analyses of the complexes .Table 1　Physical data for the binuclear complexesComplexΛM (S ·cm 2·mo l -1)I R (cm -1)νas (CO -2)νs (CO -2)ν(NH 2)ν(Co -N )ν(Co -O )U V (cm -1)CT (1)4.81630138032454855453820041000(2)4.01625138032104805303800040100(3)5.716101370332048254039950415003.4　Electronic spectraIn order to obtain further information on the mode of bonding of the Co (II )ion to the free ligand ,the reflectance spectra of the three complexes are measured at room temperature .For all three binuclear complexes ,tw o strong absorptions in the UV range w ere observed (see Table 1),859第6期李延团等:以均苯四甲酸根为桥联配体的双核钴(II )配合物的合成与磁性w hich may be assigned to the charge-transfer absorption bands[15],and three w eaker bands(Table 2)appearing in the9020～9310,18980～19400and20240～21770cm-1regions w hich may rea-sonably correspond to the4T1g(F)※4T2g(F)(ν1),4T1g(F)※4A2g(F)(ν2)and 4T1g(F)※4T1g(P)(ν3)transitions,respectively,consistent with the presence of an octahedral coordination geometry[16]around the cobalt(II)ion.According to Lever's method[16],some coor-dination field parameters of the complexes can be obtained by using the tw o observed bands(ν1and ν3)and the calculated results are summarized in Table2.Thus,it can be seen that the observed ν2values are in agreement with the calculated ones(see Table2).This show s that the assign-ments are reasonable and are additional evidence for the octahedral structure.In addition,the val-ues ofβ<1show strongly covalent bonding for cobalt(II)in these complexes.Ta ble2　Electronic spectral data and some coordination field parameters of the complexesComplexAssignmentsν1ν2ν3D q(cm-1)B(cm-1)β(1)915019250(19500)＊2090010378640.891(2)902018980(19290)2177010279340.963(3)931019400(19810)2024010508080.833 ＊T he val ues in parentheses are the calculated valuesAll our efforts to grow large crystals of these binuclear cobalt(II)complexes suitable for X-ray structure determination have so far been unsuccessful.How ever,based on the composition of these complexes,IR and electronic spectra as w ell as conductivity measurements,the results of variable-temperature susceptibilities,w hich we w ill discuss later,and crystal structure of the anal-ogous complex[6],it is reasonable to suppose that these complexes to have an extended PM TA-bridged st ructure,in w hich each carboxylic g roup is bound to cobalt(II)ion in a monodentate fashion through only one oxygen atom,yielding tw o seven-membered rings,each cobalt(II)ion is in a distorted octahedral environment(Fig1).3.5　Magnetic Property of complex[Co2(PMTA)(Me2pn)4]In order to obtain further information on the st ructure of the complexes,the magnetic data have been used to deduce the indicated binuclear structure.Thus,variable-temperature susceptibil-ity(4～300K)data were collected for the[Co2(PM TA)(Me2pn)4](1)complex,as an example,and were show n in Figure2in the form of theχM ,μeffversus T plot,χMbeing the molar mag-netic susceptibility,μeff the effective moment and T the absolute temperature.The cobalt(II)ion under O h-symmet ry possesses the4T1g ground state w hose magnetic moment is temperature-depen-dent.Therefore,the magnetic susceptibility for a binuclear cobalt(II)-cobalt(II)(S1=S2=3/ 2)complex w ith cobalt(II)under O h-symmetry is difficult to explain.However,the configuration around the cobalt(II)ion for the present case is somewhat distorted f rom O h-symmetry.There-fore,according to Sinn[17],the magnetic susceptibilities for the present cobalt(II)-cobalt(II)com-plexes can be interpreted by the Heisenberg model,because the symmetry around the metal is low-860四川大学学报(自然科学版)第38卷Fig 2　T emperature varia tio n of χM (lower curve )and μeff (upper curve )for the co mplex [Co 2(PM TA )(M e 2pn )4]The curves are based on equation (1)using the magnetic parameters given in the text ;(·)ex -perimental data ;(-),calculated curves as described in the texter than for a regular octahedron .From Figure 2it is evident that the effective magnetic moments (μeff )are virtually constant in the 30～300K region ,but sharply decrease below 30K .This be -havior is characteristic of weak antiferromagnetic spin -exchange interaction betw een cobalt (II )ions through the PM TA -bridge w ithin the molecule . In order to understand quantitatively the magnitudes of the spin -exchange interaction between cobalt (II )and cobalt (II )ions ,a magnetic analysis w as performed with the susceptibility equation derived from the Heisenberg spin opeator H =-2J S 1· S 2,where the exchange integral J is nega -tive for antiferromagnetic interaction and positive for ferromagnetic interaction .For the Co (II )-Co (II )(S 1=S 2=3/2)system ,the molar magnetic susceptibility is given by the expression [18]of e -quation (1):χM =2N β2g 2K T 14+5exp (-6J /K T )+exp (-10J /K T )7+5exp (-6J /K T )+exp (-10J /K T )+exp (-12J /K T )(1)w here χM denotes the susceptibility per dinuclear complex and the remaining symbols have their usual meanings .As show n in Figure 2,good least -squares fitting of the experimental data to equa -tion (1)gave J =-0.28cm -1,g =2.40.The agreement factor F ,defined here asF =[΢(χM )obs .-΢(χM )calc .]2/΢(χM)obs ,is then equal to 3.9×10-4.The results (negative and small J values )indicate that the complex exhibits weak antiferromagnetic spin -exchange interac -tion betw een binuclear cobalt (II )centre in the complex .The small J value of the complex may be brought out[15]mainly by the geometry st ructures of the complex and the property of the bridged -ligand .861第6期李延团等:以均苯四甲酸根为桥联配体的双核钴(II )配合物的合成与磁性862四川大学学报(自然科学版)第38卷References:[1]Willett R D,G atteschi D,K ahn O,Eds.M ag neto-Structural Correlations in Ex change Coupled Systems,D.Reidel,Dor-drecht,Holland,1985.523.[2]Gatteschi D,Kahn O,M iller J S,Eds.M olecular M agnetic M aterials,NA TO A WT Series,K luw er,Dordrecht,1991.[3]Kahn O.Struct.Bond,1986,68:89.[4]Baron V,Gillon B,Plantevin O,et al.J.Am.Chem.Soc,1996,118:11822.[5]Verdaguer M,G outeron J,Jeannins,et al.I norg.Chem,1984,23:4291.[6]Chaudhuri P,Oder K,Wieg hardt K,et al.J.Am.Chem.Soc,1988,110:3657.[7]Deng Z L,Shi J,Jiang Z H,et al.Polyhedron,1992,11:885.[8]Jiang Z H,M a S L,Liao D Z,et al.J.Chem.Soc,mun,1993.745.[9]Li Y T,Liao D Z,Jiang Z H,et al.Synth.React.Ino rg.M et.-O rg.Chem,1994:24,769.[10]Li Y T,Cheng P,Liao D Z,et al.Sy nth.React.Inorg.M et.-Org.Chem,1996,26:409.[11]Selwood P W.M ag netochemistry[M].I nterscience,New York,1956.78.[12]Geary W J.Coo rd.Chem.Rev,1971,7:81.[13]Deaco n G B,Philips R.Coord.Chem.Rev,1980,88:227.[14]Radecka-P ary zek W.Ino rg.Chim.Acta,1979,34:5.[15]K ahn O.A ngew.Chem.I nt.Ed.Eng l,1985,24:384.[16]Lever A B P.I norg anic Electronic Spectroscopy[M].Elsevier Science Publishers B.V,Amster-dam,O xford,New Yor k:T oky o,1984.[17]Sinn E.Coord.Chem.Rev,1970,5:384.[18]Ball P W,Blka A B.J.Chem.Soc.Dalton T rans,1974.852.以均苯四甲酸根为桥联配体的双核钴(II)配合物的合成与磁性李延团1,焉翠蔚2,陈勇1,曾宪诚1(1.四川大学化学学院,成都610064;2.曲阜师范大学,山东曲阜273165)摘要:作者合成和表征了3个通式为[Co2(PM T A)L4]的新双核钴(II)配合物,其中,PM T A代表均苯四甲酸根四价阴离子,L分别为邻苯二胺(obda)、2-二甲氨基乙胺(M e2en)和3-二甲氨基丙胺(M e2pn).根据元素分析、摩尔电导测定、红外和电子光谱等手段,已推定这些配合物具有均苯四甲酸根桥联的双核钴(I I)结构,其中,两个钴(II)离子均处于畸变的八面体配位环境.作者还测定并解析了配合物[Co2(PM TA)(Me2pn)4]的变温(4～300K)磁化率,求得交换积分J=-0.28cm-1.根据实验结果作者认为,在双核钴(II)配合物中的钴(II)离子间存在极弱的反铁磁自旋超交换作用.关键词:μ-均苯四甲酸根桥;双核钴(II)配合物;合成;磁性中图分类号:Q67 文献标识码:A。