多酸导向的间苯二酚杯4芳烃Co8配位笼的组装及电化学性质.pdf

基于多金属氧酸盐(POM)的超分子配位笼的设计和组装引起了广泛的研究兴趣，但在合成过程中仍然存在挑战。本文中，我们报道了一例基于POM杯芳烃的大型Co8配位笼Co8(MTR4A)6Cl8(SiW12O40)230DMF74EtOH(cage1)，该配位笼由6个碗状间苯二酚杯4芳烃(MTR4A)分子、8个Co阳离子、2个SiW12O404-抗衡阴离子和8个Cl-阴离子组装而成。值得注意的是，SiW12O404-阴离子通过氢键夹在层与层之间，形成一个三维超分子结构。此外，作为锂离子电池的负极材料，cage1表现出良好的锂离子存储能力。cage1也能够实现对亚硝酸盐(NO2-)的还原和抗坏血酸(AA)的氧化，是一种具有高活性的双功能催化剂。关键词：配位笼；间苯二酚杯4芳烃；多酸；电化学性质中图分类号：O614.81+2；O614.61+3文献标识码：A文章编号：10014861(2023)09179109DOI：10.11862/CJIC.2023.143Polyoxometalatedirecting calix4resorcinarenebased giant Co8 coordination cage:Selfassembly and electrochemical performanceGUO TingTingAN YanYanZHAO DanYAN JuanZhi(Department of Materials Science and Chemical Engineering,Taiyuan University,Taiyuan 030032,China)Abstract:Polyoxometalate(POM)based supramolecular coordination cages have aroused wide interest in terms oftheir design and fabrication,however,it still be challenging.Herein,we report a POMcalixarenebased giant Co8coordination cage,Co8(MTR4A)6Cl8(SiW12O40)230DMF74EtOH(cage1),assembled with six bowlshaped calix4resorcinarene(MTR4A)molecules,eight Co cations,two SiW12O404-counter anions,and eight Cl-anions.Remarkably,SiW12O404-anions were sandwiched between layers via hydrogenbonded to form a 3D supramolecular architecture.Moreover,cage1 showed a good lithiumion storage capacity as an anode material in lithiumionbatteries(LIBs).Furthermore,it was shown to be a highly active bifunctional electrocatalytic performance for reducing nitrite(NO2-)and oxidizing ascorbic acid(AA).CCDC:2248724.Keywords:coordination cages;calix4resorcinarene;polyoxometalate;electrocatalytic property0IntroductionSelfassembled supramolecular coordination cages have attracted considerable interest because of theirprominent applications in gas storage,catalysis,andelectrochemical sensing16.The coordination cagescould be rationally assembled with directional bridgingorganic ligands and different types of metal ions79.Fromthisperspective,calix4resorcinarenebasedderivatives,possessing large inner cavities and controllablecavityenvironments,havebeenextensivelyutilized as building blocks for supramolecular self无机化学学报第39卷assembly1013.For instance,Pei et al.synthesized agiant coordination cage that was formed by the selfassembly of calix4resorcinarene,Zn(NO3)26H2O and3,3,5,5azobenzene tetracarboxylic acid14.He et al.reported a huge cubic supramolecular nanocapsulebearing six calix4resorcinarene subunits15.The functionalized calix4resorcinarene cavitand is an essentialbuilding block for the controllable assembly of giantcoordination cages1619.Polyoxometalates(POMs),one fascinating class ofmetaloxo clusters,feature highvalent metal ions(e.g.,V,Mo,W)and abundant redox active sites,which havebeen proven to be candidate anode materials used inlithium ion batteries(LIBs)2023.Nonetheless,POMsare easily soluble in electrolytes,limiting their wideapplication24.Therefore,the selfassembly of supramolecular coordination cages and POMs is a syntheticapproach to take advantage of their structure features25.The POMs could act as inorganic buildingblocks and guest counter ions in the construction ofinorganicorganic hybrid complexes2634.Nevertheless,to our knowledge,POMcalixarenebased coordinationcages have been rarely reported,since giant coordination cage selfassembly and the strategy of introducingPOMs are still substantially challenging for crystalengineering in supramolecular chemistry35.Based on the above consideration,we designedanewPOMcalixarenebasedCo8coordinationcages,namely Co8(MTR4A)6Cl8(SiW12O40)230DMF74EtOH(cage1),synthesized with a methyl imidazolefunctionalized resorcin4arenebased ligand(MTR4A),H4SiO4(W3O9)4 and Co cations under solvothermalconditions(Scheme 1)36.Notably,cage1 is a uniqueexample of hexameric Co8 cationic coordination cagessurrounded by six MTR4A molecules with POMs counter anions.Importantly,cage 1 featured a satisfiedlithiumion storage capacity and stability.Moreover,cage1showedgoodelectrochemicalfunctionsinreducing nitrite(NO2-)and oxidizing ascorbic acid(AA).Scheme 1Synthetic procedure for cage11Experimental1.1Materials and physical measurementAll materials were provided by pharmaceuticalcompanies.FTIR spectroscopy was characterized usinga Nicolet Magna 560 Fourier transform IR spectrometer in 4 000400 cm-1.The VarioEL ElementalAnalyzer was employed to collect elemental results oncarbon,nitrogen,and hydrogen.The Rigaku SmartLabXray diffractometer was utilized to obtain powderXray diffraction(PXRD)patterns,under the graphitemonochromatized Cu K radiation(=0.154 nm,U=45kV,I=40 mA,2=230).An electrochemical workstation CHI660E was employed to record electrochemicalbehaviors.The LAND test system(LANHE CT2001A)was adopted for measuring the galvanostatic charge1792第9期discharge curves at 100 mAg-1and the potential of0.013 V(vs Li/Li+).1.2Synthesis of cage1Purple crystals of cage1(24 mg,80%based onMTR4A)were achieved from the solvothermal reactionof MTR4A(11 mg,10 mmol),CoCl26H2O(10 mg,40mmol)and H4SiO4(W3O9)4(14 mg,5 mmol)in DMF/EtOH(8 mL,1 1,V/V)at 80 for 3 d.Anal.Calcd.for Co8C574H990N78O232S24Cl8Si2W24(%):C,36.85;H,5.30;N,5.84.Found(%):C,37.22;H,5.12;N,5.78.IR data(KBr,cm-1):3 121(w),2 937(w),1 666(s),1 530(w),1 467(m),1 386(m),1 337(w),1 285(w),1 251(m),1 147(m),1 095(m),1 055(w),1 013(m),971(s),922(s),804(s),691(w),662(w),584(w),534(w).1.3Xray crystallographyThe Bruker D8 VENTURE Xray diffractometerwas used to record crystallographic data under theCu K radiation(=0.154 178 nm)for cage1 at 173K.The structure was improved onto F2using the fullmatrix leastsquares by adopting SHELXTL2018/3 inWINGX3739.All hydrogen atoms were placed geometrically.The highly disordered solvents were removed bythe SQUEEZE routine in PLATON40.Table S1 andTable S2(Supporting information)list structure refinement parameters and crystallographic results.CCDC:2248724.2Results and discussion2.1Crystal structure of cage1Thecalix4resorcinarenebasedCo8cationiccoordination cage was achieved by self assembly ofMTR4A,H4SiO4(W3O9)4 and CoCl26H2O under solvothermal conditions.Single crystal X ray diffractionreveals that cage1 crystallizes in space group P1 within a triclinic system.As shown in Fig.1a,cage1 iscomposed of six calix4resorciarene molecules,eightFig.1(a)Structure of cage1;(b)SiW12O404-cation with three cages from one direction by hydrogen bonding;(c)SiW12O404-cation with three cages from different directions by hydrogen bonding;(d)Hydrogenbondingsupramolecular structure of cage1郭婷婷等：多酸导向的间苯二酚杯4芳烃Co8配位笼的组装及电化学性质1793无机化学学报第39卷Co cations,two SiW12O404-counter anions,andeight Cl-anions.Each Co center adopts the fourcoordinated mode by three nitrogen atoms from thethree adjacent ligands,with CoN distances of 0.197 50.205 5 nm,and one chlorine atom,with CoCl distances of 0.205 5 0.22 51 nm,featuring an elegantnanosizedCo8coordinationcage.ThetwofreeSiW12O404-anions act as counter ions to balance thenegative charge.Noticeably,the SiW12O404-anionsreveal two different connected modes through weak CHOhydrogenbondinginteractions.Therelatedhydrogen bond data are listed in Table 1.They both aresurrounded by three MTR4A ligands,the difference isthat one SiW12O404-anion is surrounded by three cages from one direction,while the other from differentdirections to produce a 3D supramolecular structure(Fig.1b and 1c).As far as we know,cage1 representsthe initial instance where six calix4resorcinarene molecules are linked together via metal cations to form acharming Co8 cationic cage with two free SiW12O404-anions(Fig.1d).Table 1 Hydrogenbonding parameters for cage1DHAC49H49#3O61C105H105#1O37C114H114#2O66C115H11B#2O79C162H162#6O68C163H16C#6O47C214H21B#5O33C280H28C#4O39C336H33G#3O45d(DH)/nm0.0950.0950.0950.0980.0950.0980.0980.0980.098d(HA)/nm0.2590.2250.2510.2400.2300.2560.2510.2590.246d(DA)/nm0.330(2)0.310(3)0.326(3)0.322(2)0.317(2)0.330(17)0.323(3)0.321(3)0.301(3)DHA/()132.4149.7136.2141.6152.2132.2130.3121.2115.1Symmetry codes:#1:-x+1,-y+1,z;#2:-x+1,-y+1,-z+1;#3:-x+2,-y,-z+1;#4:x,y+1,z;#5:x+1,y+1,z;#6:x+1,y+1,z+2.2.2Electrochemical performanceGiven the potential application of POM basedmaterials,the electrochemical properties of cage1 asanode materials for LIBs were studied4143.The storageperformance of LIBs was analyzed through galvanostatic current charge discharge experiments and cyclicvoltammetry(CV).Fig.2a presents CV curves for cage1from 0.01 to 3 V at a scan rate of 0.1 mVs-1.One widereduction peak could be observed near 1.48 V duringthe first anodic scan,which disappeared in subsequentcycles and was associated with solid electrolyte interface(SEI)generation.And another peak at 0.8 V isattributed to the Li+ions insertion.In the first cathodicscan,the peak detected near 1.2 V could be caused byLi+ionsdeintercalation22,4446.Theelectrochemicalredox process mainly occurred on the W species inPOMs and the probable reaction mechanism may beexpressed as follows47:Co8(MTR4A)6Cl8(SiW12O40)2+24Li+24e-Co8Li24(MTR4A)6Cl8SiW12O402This similar reaction mechanism has been widelyobserved in the reported POMcalixarenebased complexes22,43.Insubsequentscans,theCVcurvesmatched well,indicating that cage1 has good electrochemical stability and reversibility.To explore the chargedischarge capability,galvanostatic current chargedischarge experiments with thecurrent density of 100 mAg-1were studied.Accordingto Fig.2b,cage1 had the original charge and dischargecapacities of 394 and 1 081 mAhg-1,respectively.Relative to commercial graphite,cage1 exhibited a highercapacity.Discharge capacity in the second cycle wasreduced to 428 mAhg-1,mainly attributed to the irreversible consumption of Li during SEI film generation.Obviously,the storage capacity of cage1 was higherthan that of commercial graphite,which may be thecontribution of the synergistic effect between POMsand the MTR4A ligand.Cycling stability is also a critical factor for evaluating the electrochemical performance of cage1 as the1794第9期LIBs anode material.Comprehensive longterm cyclingperformance at 100 mAg-1was further investigated.As shown in Fig.2c,the original discharge capacity canbe ignored due to SEI formation in the initial dischargeprocess.The anodes delivered a 428 mAhg-1capacityin the second cycle,which remained 83%(356 mAhg-1)following 100 cycles.Further,the cycling performance was detected under various current rates(Fig.S1),where the discharge capacity remained good.Therelatively stable electrochemical performance suggeststhat cage1 is an effective anode material for LIB.Normally,the rate performance of LIB is theimportantassessmentcriterionforcommercializedapplications.Theratecapabilityofcage1wasassessed under diverse current densities.According toFig.2d,the electrode showed capacities of 321,281,244,203,192,149,108,92,325,and 333 mAhg-1at0.1,0.2,0.4,0.8,1,2,4,5,and 0.1 Ag-1,respectively.The 333 mAhg-1reversible capacity was resumedwhen the current density was lowered back to 0.1 Ag-1,demonstrating that cage1 has good reversibility asthe LIBs anode material.Moreover,the electrochemical performance comparison of cage1 with thosereported complexesbased anodes for LIBs is given inTable S3.Notably,the discharge capacity was comparable to the reported complexes.The Li+ions storagemechanism of cage1 may attribute to the synergisticeffects of POMs and the MTR4A ligand.On the onehand,POMs in cage1 contain rich O sites,which canbind with Li+.In addition,the valence of metal W canbe changed from+6 to+5 to promote the storage ofLi+38.On the other hand,the MTR4A ligand possessesuncoordinated N and S atoms,which can capture Li+ions and participate in the insertion of Li,resulting inbetter electrochemical performance43,48.Additionally,POMs have been widely used in thefield of electrocatalysis due to their good electron transfer and storage ability4953.Some inorganic reagentsand small biological molecules,such as nitrite(NO2-),bromine ion(BrO3-),H2O2,and ascorbic acid(AA),canbe usually chosen to be the redox probes for electrocatalytic redox.Herein,NO2-and AA were selected toexplore the electrocatalytic behaviors of cage1 modified carbon paste electrode(cage1/CPE).Firstly,CVcurves for cage1/CPE were measured at 50 mVs-1inan H2SO4Na2SO4solution.As illustrated in Fig.3a,themidpoint potentials(Em)for,and redox couples have been calculated using the tangenFig.2Electrochemical performance of cage1:(a)CV curves at 0.1 mVs-1;(b)galvanostatic dischargecharge profiles;(c)cycling performance for 1 000 cycles;(d)rate performance under diverse current densities from 0.1 to 5 Ag-1郭婷婷等：多酸导向的间苯二酚杯4芳烃Co8配位笼的组装及电化学性质1795无机化学学报第39卷tial method for cage 1/CPE.The observed values of0.03,-0.35,and-0.63 V can be attributed to theelectron redox process involving central metal W in SiW12O404-54.Moreover,the Emof cage 1/CPE at0.44 V()suggests the occurrence of an electronredox process associated with the Co/Co centerswithin the cage1.Furthermore,the CV curves at different scan rates were determined in the same electrolyte.And with the increase of scan rates,the oxidationpeak gradually moved towards the direction of higherpotential,while the reduction peak moved in the opposite direction.Further,the scan rates were found toincrease proportionally upon increasing the redox peakcurrents,which proves that cage1/CPE adopts asurfaceconfined route(Fig.3b)55.The CV responses for cage1/CPE were analyzedwith NO2-and AA at a current density of 50 mAg-1within the H2SO4Na2SO4aqueous solutions.As shownin Fig.3c,oxidation peak currents for cage 1/CPEchanged as AA concentration elevated(from 0 to 20mmolL-1).The AA oxidation is catalyzed by electrontransfer via redox couple of Co/Co.Furthermore,asshown in Fig.3d,the reduction peak currents continuedto increase with adding NaNO2(from 0 to 20 mmolL-1),demonstrating the occurrence of the reduction ofNO2-.And the proposed redox mechanism is defined asshown in equations56:SiW12-nWnO40(4+n)-+NO2-+xH+SiW12O404-+productsSiW12-nWnO40(4+n)-+NO+yH+SiW12O404-+productsCo2+C6H8O6 Co+C6H6O6The electrocatalytic efficiency(CAT)of cage 1/CPE was calculated to be 77.68%,134.04%,209.70%,and 285.66%for AA,and CATof NO2-was calculatedto be 63.03%,110.33%,163.79%,and 187.58%(Fig.4and Table S4)5758.According to the results,cage1/CPE shows better performance for the oxidation of AAFig.3CV curves of cage1/CPE in H2SO4Na2SO4solutions:(a)at the 50 mVs-1scan rate;(b)at diverse scan rates of50500 mVs-1(Inset:linear relationships of the anode and the cathode peak current of vs scan rate);(c)with different AA concentrations(Scan rate:50 mVs-1;Inset:linear relationship of Ipvs cAA);(d)with differentNO2-concentrations(Scan rate:50 mVs-1;Inset:linear relationship of IpvscNO-2)1796第9期than the reduction of NO2-.3ConclusionsToconclude,wepresentapolyoxometalatedirecting calix4resorcinarenebased giant Co8 coordination cage(cage1).The cage is