Fe离子识别--acs.inorgchem.6b00217 (2)

Uncommon Pyrazoyl-Carboxyl Bifunctional Ligand-Based Microporous Lanthanide Systems:Sorption and Luminescent Sensing Properties

Gao-Peng Li,?Ge Liu,?Yong-Zhi Li,?Lei Hou,*,?Yao-Yu Wang,?and Zhonghua Zhu?

?Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education,Shaanxi Key Laboratory of Physico-Inorganic Chemistry,College of Chemistry and Materials Science,Northwest University,Xi’an,Shaanxi710127,P.R.China ?School of Chemical Engineering,The University of Queensland,Brisbane,Queensland4072,Australia

*Supporting Information

INTRODUCTION

Fe3+and Cr2O72?ions are two well-known important ions,in

which Fe3+is an indispensable biological element and is also

widely used in industry production,while Cr2O72?is an

important oxidant in industry.1Accordingly,the massive

utilizations of these two ions have brought severe environ-

mental pollutants because Cr2O72?is very carcinogenic and

Fe3+causes health problems.2Therefore,a material with

selectivity and sensitivity for probing Fe3+and Cr2O72?ions is

urgently required.In the known detection methods,the ?uorometric determination has been intensively explored owing to high sensitivity,simplicity,short response time,and

so on.In this regard,?uorescent metal?organic framework

(MOF)as a new type of sensor has gained ever-increasing

attention of chemists due to not only regular and tunable

structures but also intense and visible luminescence to naked

eyes.3These MOFs displayed nice luminescent sensing for metal ions,such as K+,Mg2+,Co2+,Cu2+,Al3+,and organic molecules,3c?g however,fewer examples were engaged in probes for Fe3+and Cr2O72?ions.3i?l

Compared to transition metal-based MOFs,lanthanide

MOFs(Ln-MOFs),for example,Eu-and Tb-MOFs,due to

their unique optical advantages,such as large Stokes shift,

visible and very bright luminescent colors,high color purity,

relatively long decay lifetimes,and undisturbed emissive energy,

have been regarded as very promising luminescent sensing

materials.4For this goal,a variety of strategies,such as generation of exposed Ln3+sites and immobilization of open Lewis basic sites and carboxylic groups in MOFs,have been adopted,3l,4although Ln-MOFs are presently not as well developed as their competitors.In particular,very sporadic Ln-MOFs were observed to show luminescent sensing for Fe3+or Cr2O72?ions(Table S1),3l,5and meanwhile,only one example reveals sensing for these two ions.5

On the other hand,the rising content of CO2in the atmosphere has induced the most serious environmental issue as the result of rapidly increasing consumption of fossil fuels.6 In the context of clean energy,CH4,a primary component of natural gas and biogas,is a very ideal candidate to mitigate this problem for its lower sulfur and nitrogen content.7Therefore, developing a suitable material for CH4and CO2separation at room temperature is vital from economic and environmental considerations.Due to the high valence and?exible coordination number of Ln3+ions,great e?orts have been made by chemists on Ln-MOFs for CO2capture and separation.8

Notably,for either luminescent sensing or CO2capture in Ln-MOFs,the majority of Ln-MOFs were prepared by pure carboxylate or pyridyl-carboxylate ligands.3a,9It is known that pyrazole not only forms strong coordination with various metal ions but also can combine mixed carboxylate ligands to form stable MOFs.10The latest CCDC search(version 5.36) indicates that,although a large number of Ln-pyrazoyl

Received:January27,2016

complexes have been documented,only rare Ln-pyrazoyl-carboxyl coordination frameworks were recorded.11Moreover, the overwhelming majority in those systems was based on pyrazole-3,5-dicarboxylate ligand chelating with Ln3+cen-ters.11b?f Thus,the fabrication of Ln-MOFs through a pyrazoyl and carboxyl separated bifunctional ligand is an unprecedented and challenging project.Meanwhile,the incorporation of pyrazole with relatively high N contents in Ln-MOFs would strengthen the a?nity of the framework toward CO2.

We are interested in an unexplored ligand,3-(1H-pyrazol-3-yl)benzoic acid(H2pzbc),which contains one pyrazoyl and one carboxyl unit spaced by one phenyl ring and combines versatile coordination modes of carboxylic acid and pyrazole. Herein,seven isostructural3D Ln-MOFs,[Ln-(Hpzbc)2(NO3)]·H2O(1-Ln,Ln=Nd3+,Sm3+,Eu3+,Gd3+, Tb3+,Er3+,and Yb3+),have been constructed by H2pzbc,which represent the novel pyrazoyl-carboxyl ligand-incorporated3D microporous Ln-MOF systems.Strikingly,1-Eu displays excellent selective and sensitive?uorescent probes for Fe3+ and Cr2O72?ions and highly selective capture for CO2over N2 and CH4as well.

■EXPERIMENTAL SECTION

Materials and General Methods.All chemicals are commercially available and were used without further puri?cation.An infrared(IR) spectrum was obtained through an EQUINOX-55FT-IR spectrometer together with a KBr pellet from4000to400cm?1.Elemental analyses for C,H,and N were recorded on a PerkinElmer2400C Elemental Analyzer.Thermogravimetric analyses(TGA)were carried out in a N2 stream using a Netzsch TG209F3instrument at a heating rate of10°C min?1.Powder X-ray di?raction(PXRD)data were collected on a Bruker D8ADVANCE with Cu Kαradiation(λ=1.5418?).A luminescent spectrum was measured on an Edinburgh FLS55 luminescence spectrometer.UV?vis spectroscopic studies were measured on a Hitachi U-3310spectrometer.An Axis ultra spectrometer was used to measure X-ray photoelectron spectroscopy (XPS).All gas sorption isotherms were measured by ASAP2020M adsorption equipment.Grand Canonical Monte Carlo(GCMC) simulations were performed by the Sorption module of Material Studio(Supporting Information).

Synthesis of[Ln(Hpzbc)2(NO3)]·H2O(1-Ln).A mixture of Ln(NO3)3·6H2O(0.1mmol),H2pzbc(0.018g,0.1mmol),and CH3CN(9mL)was sealed in a25mL Te?on-lined stainless steel container.The container was heated at110°C for72h and then cooled to room temperature at a rate of5°C h?1to a?ord bulk crystals of1-Ln.

Synthesis of[Nd(Hpzbc)2(NO3)]·H2O(1-Nd).Yield:39%.Anal. Calcd for C20H16NdN5O8:C,40.13;H,2.69;N,11.70.Found:C, 40.03;H,2.82;N,11.61%.IR(KBr,cm?1):3344(s),1544(s),1430(s), 1297(m),1096(m),940(w),770(m),716(m),576(w).

Synthesis of[Sm(Hpzbc)2(NO3)]·H2O(1-Sm).Yield:43%.Anal. Calcd for C20H16SmN5O8:C,39.74;H,2.68;N,11.69.Found:C, 40.01;H,2.72;N,11.76%.IR(KBr,cm?1):3422(s),3147(s),1527(s), 1402(s),1279(m),1097(m),941(w),762(m),703(m),522(w). Synthesis of[Eu(Hpzbc)2(NO3)]·H2O(1-Eu).Yield:42%.Anal. Calcd for C20H16EuN5O8:C,39.60;H,2.64;N,11.55.Found:C, 39.73;H,2.59;N,11.49%.IR(KBr,cm?1):3263(s),1550(s),1432(s), 1305(m),1097(m),941(w),771(m),715(m),578(w). Synthesis of[Gd(Hpzbc)2(NO3)]·H2O(1-Gd).Yield:42%.Anal. Calcd for C20H16GdN5O8:C,39.28;H,2.62;N,11.46.Found:C, 39.35;H,2.72;N,11.53%.IR(KBr,cm?1):3372(s),1493(s),1280(s), 1063(m),932(w),761(m),702(m),572(w).

Synthesis of[Tb(Hpzbc)2(NO3)]·H2O(1-Tb).Yield:37%.Anal. Calcd for C20H16TbN5O8:C,39.15;H,2.61;N,11.42.Found:C, 39.22;H,2.48;N,11.51%.IR(KBr,cm?1):3291(s),1553(s),1401(s), 1307(m),1098(m),942(w),771(m),715(m),580(w).

Synthesis of[Er(Hpzbc)2(NO3)]·H2O(1-Er).Yield:46%.Anal. Calcd for C20H16ErN5O8:C,38.65;H,2.58;N,11.27.Found:C, 38.59;H,5.50;N,11.34%.IR(KBr,cm?1):3282(s),1547(s),1432(s), 1305(m),1053(w),762(m),715(m),580(w).

Synthesis of[Yb(Hpzbc)2(NO3)]·H2O(1-Yb).Yield:41%.Anal. Calcd for C20H16YbN5O8:C,38.28;H,2.55;N,11.16.Found:C, 38.38;H,2.41;N,11.23%.IR(KBr,cm?1):3379(s),3153(s),1532(s), 1403(s),1278(m),1095(m),941(w),762(m),705(m),462(w).

X-ray Crystallographic Measurements.A Bruker Smart CCD area-detector was utilized to get the crystal data of complexes1-Eu,1-Tb,and1-Er at296(2)K usingωrotation scans with widths of0.3°and Mo Kαradiation(λ=0.71073?).The structures were solved by the direct methods and re?ned by full-matrix least-squares re?nements based on F2with the SHELXTL program.12All non-hydrogen atoms were re?ned anisotropically.The hydrogen atoms were added to their geometrically ideal positions.Relevant crystallographic data were given in Table1,and the selected bond lengths and angles were listed in Table S2.

■RESULTS AND DISCUSSION

Crystal Structure.Single-crystal X-ray di?raction analysis reveals that complexes1-Eu,1-Tb,and1-Er show the isotypic structures with monoclinic C2/c space group(Figure S1).It failed to determine the structures of1-Nd,1-Yb,1-Gd,and1-Sm by X-ray single crystal di?raction due to very small sizes of crystals.However,PXRD con?rmed that they are isostructural with1-Eu(Figure S2).The structure of1-Eu is taken as an example.

In1-Eu,the asymmetry unit consists of half a Eu3+ion,one monodeprotonated Hpzbc,and half a coordinated NO3?anion (Figure1a).Eu3+ion with a distorted bicapped trigonal prism is eight-coordinated by six O atoms,from four carboxylate O atoms of four Hpzbc and two O atoms of one NO3?,and two pyrazole N atoms of two Hpzbc.The carboxylate group of Hpzbc with a syn-synμ2-fashion bridges Eu3+centers to form an in?nite chain-like secondary building unit(SBU)running along the c axis(Figure1b),which is characteristic of double helixes with opposite chirality but the same axis.The neighboring chains are interlinked by the coordination of pyrazole N

of Table1.Crystal Data and Structure Re?nement for1-Eu,1-Tb,and1-Er

201658201658201658 formula weight604.34613.30621.64 crystal system monoclinic monoclinic monoclinic

a(?)19.974(14)20.010(4)19.810(10)

b(?)13.135(10)13.193(3)13.153(7)

c(?)9.901(7)9.8950(19)9.806(5)

α(deg)909090

β(deg)113.308(11)113.142113.196(8)

γ(deg)909090

V(?3)2386(3)2402.1(8)2349(2)

Z444

D calc(g cm?3) 1.683 1.696 1.785

F(000)119212001212

R int0.05230.05080.0406

GOF on F2 1.014 1.024 1.036

R1a[I>2σ(I)]0.03500.03270.0290

wR2b(all data)0.08460.07510.0627

a R

1

=Σ∥F0|?|F c∥/Σ|F0|.b wR2=[Σw(F02?F c2)2/Σw(F02)2]1/2.

Hpzbc to a ?ord a 3D framework (Figure 1c),which contains one-dimensional (1D)channels with the window sizes of ca.4.5×3.5?2(excluding van der Waals radii of the atoms)along the c axis (Figure 1d).The uncoordinated O atoms of NO 3?

stand in the porous surface,which could behave as potential active sites for sensing and adsorption of guests.The ?NH group of pyrazolyl in Hpzbc is nondeprotonated and forms a N ?H ···O hydrogen bond with one coordinated O atom of

Figure 1.(a)Coordination environment of Eu 3+ion in 1-Eu (symmetry codes:#1=0.5?x ,0.5?y ,1?z ;#2=?0.5+x ,0.5?y ,?0.5+z ;#3=?x ,y ,0.5?z ;#4=x ,?y ,0.5+z ;#5=?x ,?y ,?z );(b)1D helical chain;(c)3D framework;(d)1D channel viewed along the c axis (green:inner surface of pores;yellow:outer surface of pores).

Figure 2.Luminescent intensity at 614nm of 1-Eu treated with 1.0×10?3M various cations (a)and anions (b)for 6h and the luminescent spectra of 1-Eu in the presence of Fe 3+(c)and Cr 2O 72?(d)ions with di ?erent concentrations (0?10?3M).Insets:the linear correlation for the plot of (I 0?I )/I 0vs concentration of Fe 3+and Cr 2O 72?ions,respectively,in low concentration range.

NO3?.Topologically,by regarding Eu3+center and Hpzbc as6-and3-connected nodes,respectively,the extended framework of1-Eu can be simpli?ed as a binodal(3,6)-connected ant net with the point symbol of(426)2(44628810)(Figure S3). Notably,although some Ln-pyrazolyl-carboxyl coordination polymers were observed in the past,11to the best of our knowledge,the corresponding porous framework was reported only in a La-MOF.11f However,di?ering from1-Eu,in that MOF,the coordination of La3+ions and pyrazole-3,5-dicarboxylates forms2D layers,which have to be connected by CO32?to produce a3D framework.Thereby,1-Ln represents the unprecedented microporous3D Ln-pyrazoyl-carboxyl systems.

PXRD and TGA.The experimental powder X-ray di?raction patterns of1-Ln agreed well with those simulated from the respective crystal structures,demonstrating phase purity of1-Ln(Figure S2a).1-Ln showed the similar weight loss processes under the N2environment,in accordance with their similar structures(Figure S4).TGA of1-Eu is representatively discussed.The?rst weight loss of3.5%in1-Eu below145°C corresponds to the release of all water molecules(calcd: 3.0%).The main framework is thermally stable up to305°C and then decomposes at a higher temperature. Luminescent Properties.The solid-state luminescent properties of1-Eu and free H2pzbc ligand were studied at room temperature(Figure S5).H2pzbc shows the strongest emission at350nm at an excitation of322nm.1-Eu has a maximum of excitation at394nm,and under this excitation,1-Eu displays the typical luminescence of Eu3+ion,wherein the four characteristic emission peaks at586,593,614,and698nm, originate from5D0?7F0,5D0?7F1,5D0?7F2,and5D0?7F3f?f transitions of Eu3+ion,respectively.The strongest5D0?7F2 transition at614nm resulted from the magnetic-dipole induced transitions leads to the strong red luminescence of1-Eu.1-Eu displays the double-exponential decays with the lifetimes of 4.96and612.81μs obtained by the decay lifetime curve(Figure S6).

In light of the nitrate O atom active sites exposed in pores and the bright red luminescence of1-Eu,the potential luminescent detection for cations and anions was further evaluated.In this experiment,5mg of1-Eu was dispersed in an 1×10?3M ethanol solution containing M(NO3)x(M=Cu2+, Zn2+,Na+,K+,Hg2+,Mn2+,Pb2+,Co2+,Cd2+,Ni2+,Mg2+,Ca2+, Al3+,and Fe3+).The emission spectra were shown in Figures2a and S7a.Interestingly,it was found that Cu2+,Zn2+,Na+,K+, and Hg2+ions slightly enhanced luminescent intensity of1-Eu, while other metal ions(Pb2+,Co2+,Cd2+,Ni2+,Mg2+,Ca2+,and Al3+)decreased luminescence to a di?erent extent.The most striking phenomenon is that Fe3+ion causes a very signi?cant quenching e?ect on luminescence of1-Eu.The obvious change of luminescent intensities a?ected by Fe3+relative to other metal ions implies the potential of1-Eu for recognizing and sensing Fe3+ion.The plot of I0/I vs concentration of Fe3+ion does not match with the Stern?Volmer equation,indicating the coexistence of the dynamic and static quenching processes,13 which can be well?tted by I0/I=1.029×exp(c/339.445)?0.266(I0and I are the luminescent intensity of1-Eu in the absence and presence of Fe3+,respectively,and c is the molar concentration of Fe3+)(Figure S8a).Thereby,the quenching process can be quantitatively controlled by the concentration of Fe3+ion.In addition,a good linear correlation is observed for the plot of(I0?I)/I0vs concentration of Fe3+ion in the range of0?220×10?6M(Figure2c,inset).By the calculated slope,the detection limit of2.6×10?5M is obtained by the ratio of 3δ/slope,in whichδis the standard deviation of luminescent intensity of blank solution for ten times.14Compared with the reported MOFs enumerated in Table S3,this detection limit is signi?cantly low,implying that1-Eu is very promising in the sensitive and selective detection for Fe3+ion.

Notably,although recyclability is one of the important indices of sensors,the related investigation on recyclable capacity of MOF sensors was scarcely explored.1-Eu was soaked in an ethanol solution of1×10?3M Fe3+ion for minutes to form Fe3+@1-Eu,which was washed several times to yield the recycled1-Eu,in which no Fe3+ion was remaining,as veri?ed by XPS(Figure S9a).Importantly,for three recycles, the luminescent intensity of each recycle is almost unchanged compared to that of1-Eu(Figure3a).Meanwhile,the PXRD

pattern of the recycled1-Eu shows structural integrity(Figure S10).The study of the quenching e?ect with di?erent immersion times illustrates that the emission of1-Eu is almost totally quenched after120s of the Fe3+ion(1×10?3M) addition(Figures4and S11a),which is greatly shorter than

those in[H2NMe2][Eu(C33H24O12)(H2O)]4h and[Tb(Hbtca)-(H2O)2](Table S3).4e The results indicate that1-Eu could be used for the fast and recycle?uorescent probe for Fe3+ion. In previous studies,the reasons for luminescent quenching caused by Fe3+ion were basically attributed to collapse of the framework,cationic exchange,competition absorption between Fe3+ion and Ln-MOFs,and strong framework-Fe3+inter-actions.3l,4h?j As re?ected by PXRD,the framework of1-Eu treated in metal ion solutions remains intact(Figure S12).It is also very di?cult for the neutral1-Eu to capture Fe3+by the Figure3.Luminescent intensity at614nm of1-Eu after three recycles (c1,c2,c3)in Fe3+(a)and Cr2O72?(b)solutions(10?3M). Figure4.Luminescent intensity of1-Eu at614nm at di?erent reaction times in Fe3+and Cr2O72?solutions.Inset:color changes of1-Eu induced by the addition of Fe3+and Cr2O72?ions.

cationic exchange.Meanwhile,the UV ?vis absorption spec-trum of Fe 3+ion solution shows little overlap with the excitation spectrum of 1-Eu ,so there is no clear evidence for competitive adsorption between Fe 3+ion and 1-Eu (Figure S13).We inferred that Fe 3+ion di ?used into the channels of 1-Eu and formed contacts with uncoordinated O atoms of NO 3?,leading to the luminescent quenching of 1-Eu .4i ,15

Simultaneously,ethanol (aq.90%)solutions containing various anions (F ?,Cl ?,I ?,ClO 4?,BrO 3?,IO 4?,PO 43?,H 2PO 4?,CO 32?,SO 42?,and Cr 2O 72?)at the same concen-tration (1.0×10?3M)were selected to evaluate their e ?ect on the luminescent intensity of 1-Eu .As shown in Figures 2b and S7b ,the luminescent intensities of the di ?erent suspensions are closely related to the types of anions.Uniquely,Cr 2O 72?completely quenches the luminescence of 1-Eu ,implying the great potential of 1-Eu for Cr 2O 72?ion sensing.Upon increasing the concentration of Cr 2O 72?,the luminescence of 1-Eu was gradually quenched,and the luminescent intensity obeys equation I 0/I =1.463×exp(c /345.886)?0.545(Figure S8b ),similar to the situation for Fe 3+ion.The luminescent quenching of 1-Eu induced by Cr 2O 72?ion can,on one hand,be attributed to the interactions between Cr 2O 72?ion and framework and,on the other hand,result from the competitive adsorption of excitation wavelength energy between 1-Eu and Cr 2O 72?ion because the UV ?vis adsorption spectra of K 2Cr 2O 7in ethanol shows the moderate overlap on the excitation spectra of 1-Eu (Figure S14).3j ,4h The detection limit (3δ/slope)for Cr 2O 72?reaches as low as 2.2×10?5M (Figure 2d,inset).Notably,there are rare Ln-MOFs that displayed luminescent quenching for Cr 2O 72?ion compared to other metal ions (Table S1).5PXRD patterns con ?rmed the samples of 1-Eu soaked in di ?erent anionic salts hold the structural integrity (Figure S15).In addition,the study of recyclability

(Figure 3b)and the quenching e ?ect with di ?erent immersion times in Cr 2O 72?solution (1×10?3M)indicates 1-Eu is very smart for Cr 2O 72?ion probe (Figures 4and S11b ).

Sorption Properties.H 2O solvent molecules in 1-Eu can be completely removed by heating sample at 160°C for 3h under vacuum,which was con ?rmed by TGA (Figure S16).Due to the existence of active sites in 1-Eu ,gas sorption capacities were assessed on the desolvated sample by gas adsorptions of N 2at 77K and of CO 2and CH 4at 195K,respectively (Figure 5a).At 1atm,1-Eu reveals a minimum N 2loading of 28.1cm 3(STP)g ?1but more CO 2and CH 4uptakes of 56.1and 36.5cm 3(STP)g ?1,respectively.This sorption isotherm of CO 2displays typical type-I microporous adsorption character,and the BET surface area of 158.2m 2g ?1(Langmuir surface area is 188.1m 2g ?1)and a mean pore width of 3.9?based on Horvath ?Kawazoe mode (Figure S17)are obtained,respectively.The adsorption capacities of 1-Eu for CO 2,CH 4,and N 2were also conducted at 298K (Figure 5b).It is found that 1-Eu at 1atm is nonadsorptive for N 2(the adsorption amount is too low to be detected by our instrument)and very low CH 4uptake (6.4cm 3(STP)g ?1),but a remarkable CO 2loading of 31.2cm 3(STP)g ?1,indicating the signi ?cant gas adsorption selectivities for CO 2over N 2and CH 4.To predict CO 2/CH 4selectivity in 1-Eu for a CO 2/CH 4binary mixture,the ideal adsorbed solution theory (IAST)16was employed on the basis of the adsorption curves of CO 2and CH 4at 298K (Figure S18).For CO 2/CH 4mixtures with general feed compositions of land ?ll gas (CO 2/CH 4=50:50)and natural gas (CO 2/CH 4=10:90and 5:95),the CO 2/CH 4selectivities calculated at 1atm were 12.8,10.3,and 10.4,respectively (Figure 6).Compared to most of the known MOFs which possessed good CO 2/CH 4selectivity at similar conditions (Table 2),the values of 1-Eu are even higher.The remarkable

Figure 5.Gas sorption isotherms of 1-Eu for (a)N 2at 77K,CO 2and CH 4at 195K;(b)CH 4at 298K,CO 2at 273.15,285,and 298K.Filled and open symbols represent adsorption and desorption curves,respectively.

Figure 6.IAST adsorption selectivities and isotherms of 1-Eu for CO 2over CH 4at di ?erent compositions.

selectivities for CO 2over CH 4and N 2render 1-Eu to be a promising material in postcombustion CO 2capture,natural gas upgrading,and land ?ll gas puri ?cation.

The signi ?cant sorption selectivity of 1-Eu for CO 2is closely related to the existence of NO 3?groups and rich-N pyrazole rings,which makes the framework very polar,as a result,to form speci ?c a ?nity for CO 2,which has a larger quadrupole moment and a higher polarizability value (CO 2,29.1×10?25cm ?3;CH 4,25.9×10?25cm ?3;N 2,17.4×10?25cm ?3)compared to CH 4and N 2.In particular,the uncoordinated O atoms in NO 3?can directly draw CO 2by dipole ?quadrupole interactions.The adsorption a ?nity of 1-Eu for CO 2can be evaluated by the isosteric heat (Q st )of adsorption calculated by the virial equation from the adsorption isotherms of CO 2at

273.15,285,and 298K (Figure S19).The initial Q st is 39.2kJ mol ?1,which is relatively high and compares with the MOFs containing open metal sites and other activity sites (Table S4).8b ,34Although Q st displays a gradual decrease with the increasing of CO 2coverage,Q st still reaches to 26.8kJ mol ?1at the maximum loading of 31.2cm 3(STP)g ?1,re ?ecting the strong framework ?CO 2interactions which lead to the signi ?cant selectivity for CO 2.

GCMC Simulation.For a better understanding of the interaction details of 1-Eu with CO 2,GCMC simulation has been employed at 298K and at di ?erent pressures (0.1and 100kPa,Figures S20and 7a).The obtained density contours revealed that,at both low and high pressures,the mostly populated sites are located in the vicinity of uncoordinated O atoms of NO 3?ions,pyrazoyl,and phenyl rings of Hpzbc linkers in channels.As revealed by the preferential locations derived from simulation (Figure 7b),one uncoordinated electronegative O atom of NO 3?attracts two electropositive C atoms of two CO 2molecules,in which the O ···C distances of 3.346and 3.589?approximate with the sum of van der Waals radii of carbon (1.70?)and oxygen (1.52?)atoms,indicating moderate contacts.Two CO 2molecules have similar environ-ments,and also form intermolecular interactions as one O atom of one CO 2interacts with the C atom of the other CO 2(O ···C =3.589?)by a T-shaped fashion.The O atoms of each CO 2also form O ···H (2.547?2.769?)hydrogen bonds with the ?CH groups of phenyl and pyrazoly rings of Hpzbc.Meanwhile,the C atom of each CO 2is also involved in C ···πinteractions with the pyrazoly rings (C ···πcentroid =3.775and 4.137?and 3.864and 4.088?,respectively).10g ,35However,no C ···πinteractions (C ···πcentroid =4.698?5.289?)between CO 2and phenyl rings in 1-Eu were observed,which is possibly due to less electronic density in phenyl relative to pyrazyl rings.These multipoint framework-CO 2contacts and CO 2?CO 2interactions are responsible for relatively high sorption heat and selectivity for CO 2.

■

CONCLUSIONS

In conclusion,a series of uncommon microporous Ln-pyrazoyl-carboxyl systems have been constructed by employing a pyrazoyl-carboxyl bifunctional ligand.The obtained frameworks feature 1D channels decorated by O atoms and pyrazoyl groups.As a result,1-Eu reveals excellent luminescent sensing

Table https://www.wendangku.net/doc/788475702.html,parison of CO 2/CH 4Selectivity Calculated by IAST Method for the Equimolar Mixture at 1atm and 298K of 1-Eu with the Selected MOFs

MOFs

selectivity ref UTSA-4933.717Cu-TDPDA 13.8

18MAF-X712.6,12.0a

19

1-Eu

12.8,10.3a ,10.4b this work [Cu(bpy)2(SiF 6)]

10.5

20[Mn 2(Hcbptz)2(Cl)(H 2O)]Cl 10.3,8.8a 21ZIF-979.1422ZIF-93

8.1922UiO-66-AD48.0423SNU-151′7.2024UiO-66

6.8723Zr-UiO-67AcOH 6.8a 25Co 9?INA

6.226[Zr 6O 4(OH)4(FDCA)6]

5.1b

27[CH 3NH 3][In 3(L1)2(H 2O)2.5] 4.6,4.3a 28[Cu(INIA)] 4.3

29dia-7i-1-Co 4.1,4.0a 30DMOF 3.231UiO-67 2.7b 23ZIF-25 2.5322MOF-205 2.232UMCM-1

1.82

33

a

CO 2/CH 4=5:95.b CO 2/CH 4=10:90.

Figure 7.(a)Density contours of CO 2adsorption in pores of 1-Eu obtained from GCMC simulation at 298K under pressure 100kPa and (b)view of CO 2molecules in pores of 1-Eu .

for Fe 3+and Cr 2O 72?ions with high sensitivity,selectivity,and simple and quick regeneration,as well as remarkably selective capture for CO 2over N 2and CH 4at ambient temperature.GCMC simulations con ?rmed the multiple CO 2-philic sites in 1-Eu .These facts indicate that 1-Eu can potentially be applied not only as an e ?cient luminescent sensor for Fe 3+and Cr 2O 72?detection but also as a promising material for CO 2capture and separation in some industry processes.This contribution also corroborates a less-investigated but feasible strategy by employing pyrazoyl-carboxyl bifunctional ligands to broaden functional Ln-MOFs.

■

ASSOCIATED CONTENT

*

Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI:10.1021/acs.inorg-chem.6b00217.

Additional structural ?gures,TGA,PXRD,excitation and emission spectra,the detailed calculations on sorption and bond length/angle,and GCMC simulation method-ology (PDF )

X-ray crystallographic data (CIF )

■AUTHOR INFORMATION

Corresponding Author *E-mail:lhou2009@https://www.wendangku.net/doc/788475702.html, (L.H.).

Notes

The authors declare no competing ?nancial interest.

■ACKNOWLEDGMENTS

This work is supported by NSFC (21471124,21531007,and 21371142),NSF of Shannxi province (2013KJXX-26,2014JQ2049,and 15JS113),the Australian Research Council Future Fellowship FT12010072,Open Foundation of Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education (338080060),and NFFTBS (J1210057).

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