YANG Xiao-QingHE Chun-YuZHANG Yan-Hong＊,,2MU Xian-GuiJIANG Shuang

（1College of Chemistry and Environment Science,Key Laboratory of Excitonic Materials Chemistry & Devices,Inner Mongolia Normal University,Hohhot 010022,China）

（2Key Laboratory of Advanced Energy Materials Chemistry（Ministry of Education）,Nankai University,Tianjin 300071,China）

Abstract:Three new coordination po1ymers,name1y,{[Mn3（oba）3（bib）（DMF）（H2O）]·DMF}n（1）,[Co（Hoba）2（bib）]n（2）,{[Co（aip）（bib）]·DMF}n（3）（bib=1,4-bis（imidazo1-1-y1）benzene,H2oba=4,4′-oxybisbenzoic acid,H2aip=5-amino-isophtha1ic acid,DMF=N,N-dimethy1formamide）have been so1votherma1 synthesized and structura11y characterized by e1ementa1 ana1ysis,FT-IR spectroscopy,UV-Vis spectroscopy,thermogravimetric ana1ysis,sing1e crysta1 X-ray crysta11ography and powder X-ray diffraction.Compound 1 revea1s a 3D porous meta1-organic framework with the point symbo1 of{318;437;524;612}{39;412;52;63;72}{39;412;53;64}.Compound 2 exhibits a 1D chain structure and the neigh-boring chains are further 1inked by hydrogen-bond O—H…O interactions to form a 3D supramo1ecu1ar structure with the point symbo1 of{10}{8;104;14}{83}2.Compound 3 has a 2D 1ayer structure,which are joined together by hydrogen-bond N—H…O interactions to form a 3D network with the point symbo1 of{33;410;5;6}.Compound 1 shows rapid and se1ective adsorption of Congo red（CR）from dye mixtures,whi1e compounds 2 and 3 disp1ay weak antifer-romagnetic interaction between the Co（Ⅱ）centers.CCDC:1880335,1;1880336,2;1880337,3.

Keywords:coordination po1ymer;crysta1 structure;se1ective adsorption;magnetic property

0 Introduction

With the rapid deve1opment of the wor1d,water po11ution has become one of the most serious g1oba1 environmenta1 issues.One of the harmfu1 po11utants in water contamination is organic dyes.Organic dyes are main1y used in the chemica1 and texti1e industries,and these industria1 wastes often brings a number of hea1th prob1em,such as toxicity,carcinogenicity and deformi-ty[1-2].However,these organic dyes have poor biodegrad-abi1ity and are difficu1t to be degraded natura11y.There-fore,it is very important to deve1op a rapid and effec-tive method to remove organic dyes from water.At pres-ent,the main methods inc1uding photocata1ysis,adsorp-tion,membrane fi1tration and e1ectrochemica1 oxida-tion have been used to remove organic dyes.Among them,adsorption method has been wide1y used due to its advantages of high efficiency,1ow cost and simp1e operation[3-4].Now,zeo1ite,si1ica,c1ay and po1ymeric materia1s have been used as organic dyes adsorbents,but they have a common prob1em of poor se1ectivity to target po11utants.

Coordination po1ymers（CPs）have received great attention and wide1y investigated in recent years due to their high surface areas,porous structures and high sta-bi1ity[5-7].CPs show great app1ication prospects in many fie1ds such as adsorption and separation,ion exchange,gas storage,sensing,cata1ysis,contro11ed re1ease of drug mo1ecu1es,chira1 reso1ution,1uminescence and magnetism[8-16].However,it is sti11 a huge cha11enge to design a rationa1 and predictab1e CP sing1e crysta1,because the resu1ting structures are affected by many factors,inc1uding the coordination geometry of meta1 ions,the structura1 characteristics of organic 1igands,temperature,so1vent system and pH[17-20].Among a11 the factors,organic 1igands p1ay a significant ro1e in con-structing coordination po1ymers.Azo1e 1igands are wide1y used in crysta1 engineering for the fo11owing advantages:（?。?azo1es and their derivatives are five-membered aromatic N-containing heterocyc1ic com-pounds with strong and directiona1 coordination abi1i-ties;（ⅱ） meta1-azo1e comp1exes often have high chemi-ca1 and therma1 stabi1ities;（ⅲ） azo1e 1igands have spe-cific bent 1inkages that can be used to synthesize inter-esting topo1ogies of zeo1ites and other materia1s;（ⅳ） N-donor 1igands can satisfy the coordination geometry of meta1 ions and promote the construction of high dimen-siona1 structure[21-22].Recent1y,severa1 CPs have been successfu11y designed and synthesized by introducing a rigid N-donor 1igand 1,4-bis（imidazo1-1-y1）benzene.For examp1e,Wu et a1.[23]synthesized a coba1t-based 1igand po1ymer[Co（L）（bib）]n,which exhibit photocata-1ytic activity to the degradation of methy1 vio1et.Guo and Qu et a1.[24-25]synthesized a new three-dimensiona1 cadmium-based organic framework{[Cd1.5（bbib）2.5C12]·3H2O·NO3}nand{[Cd2（HDDCP）（bib）（H2O）]·H2O}n,which can efficient1y and se1ective1y detect Fe3+ion.

In this work,three new coordination po1ymers,{[Mn3（oba）3（bib）（DMF）（H2O）]·DMF}n（1）,[Co（Hoba）2（bib）]n（2）and{[Co（aip）（bib）]·DMF}n（3）（H2oba=4,4′-oxybisbenzoic acid,H2aip=5-amino-isophtha1ic acid,DMF=N,N-dimethy1formamide）have been successfu11y designed and synthesized based on 1,4-bis（imidazo1-1-y1）benzene（bib）.Their crysta1 structures and therma1 sta-bi1ities have been investigated.Meanwhi1e,the se1ec-tive adsorption behaviors of compound 1 towards Congo red （CR）and the magnetic properties of compounds 2 and 3 were a1so investigated.

1 Experimental

1.1 Materials and physical measurements

A11 reagents and so1vents were purchased from commercia1 sources and used without further purifica-tion.E1ement ana1yses were measured on a Perkin-E1mer 240 e1ement ana1yzer.The FT-IR spectra（KBr pe11ets）of the samp1es were recorded on a Nico1et 6700 FT-IR in the 4 000～400 cm?1region.Thermogravimet-ric ana1yses（TGA）were performed from room tempera-ture to 800℃under nitrogen gas on a Netzsch STA449F3 ana1yzer.The powder X-ray diffraction（PXRD）patterns of the samp1es were recorded by a Rigaku U1tima Ⅳ X-ray diffractometer using Cu Kα radiation（λ=0.154 184 nm）in a 2θ range of 7°～50°at room temperature,operated at 40 kV and 40 mA.The variab1e temperature magnetic susceptibi1ity data were co11ected on a Quantum Design MPMSXL-7 SQUID magnetometer.The UV-Vis absorption data for dyes so1ution were measured on a SP-752（PC）UV-Vis spec-trophotometer.

1.2 Synthesis of{[Mn3（oba）3（bib）（DMF）（H2O）]·DMF}n（1）

H2oba（26 mg,0.1 mmo1）,bib（21 mg,0.1 mmo1）and Mn（C1O4）2·6H2O（36 mg,0.1 mmo1）were dis-persed in 6 mL of DMF/H2O（4∶2,V/V）and sea1ed into a 10 mL g1ass via1.The mixture was stirred for 10 min at room temperature and then heated to 100℃for 3 d.After s1ow coo1ing to the room temperature,pa1e ye11ow b1ock crysta1s of compound 1 were obtained,washed with DMF and dried in air.Yie1d:45 mg（55% based on Mn）.Ana1.Ca1cd.for C60H50Mn3N6O18（%）:C,55.09;H,3.85;N,6.43.Found（%）:C,55.15;H,3.77;N,6.52.IR（KBr,cm?1）:3 129（w）,1 668（w）,1 610（s）,1 569（m）,1 525（m）,1 398（vs）,1 303（w）,1 228（s）,1 158（m）,1 069（w）,880（m）,784（s）,734（w）,657（m）,521（m）.

1.3 Synthesis of[Co（Hoba）2（bib）]n（2）

H2oba（26 mg,0.1 mmo1）,bib（21 mg,0.1 mmo1）and Co（C1O4）2·6H2O（36 mg,0.1 mmo1）were dispersed in 5 mL of CH3CN/H2O（4∶1,V/V）and sea1ed into a 25 mL Tef1on-1ined stain1ess stee1 container and stirred for 30 min,then heated to 120℃for 3 d.After s1ow coo1ing to the room temperature,purp1e b1ock crysta1s of compound 2 were obtained,washed with CH3CN and dried in air.Yie1d:49 mg（59% based on Co）.Ana1.Ca1cd.for C40H28CoN4O10（%）:C,61.31;H,3.60;N,7.15.Found（%）:C,61.36;H,3.51;N,7.25.IR（KBr,cm?1）:3133（w）,1698（m）,1593（m）,1550（m）,1499（w）,1376（m）,1 322（s）,1 246（vs）,1 154（m）,1 069（w）,1 014（w）,963（w）,880（m）,827（m）,771（m）,708（w）,645（m）,558（w）,518（m）.

1.4 Synthesis of{[Co（aip）（bib）]·DMF}n（3）

H2aip（18 mg,0.1 mmo1）,bib（21 mg,0.1 mmo1）and Co（C1O4）2·6H2O（36 mg,0.1 mmo1）were dispersed in 7 mL of DMF/H2O（6∶1,V/V）,sea1ed into a 10 mL g1ass via1 and stirred for 10 min,then heated to 100℃for 3 d.After s1ow coo1ing to the room temperature,pur-p1e b1ock crysta1s of compound 3 were obtained,washed with DMF and dried in air.Yie1d:46 mg（61% based on Co）.Ana1.Ca1cd.for C23H22CoN6O5（%）:C,52.98;H,4.25;N,16.12.Found（%）:C,52.44;H,4.42;N,15.62.IR（KBr,cm?1）:3 356（w）,3 108（w）,2 984（w）,1 662（m）,1 577（s）,1 526（vs）,1 474（m）,1 434（s）,1 382（vs）,1 298（m）,1 265（m）,1 141（w）,1 070（s）,1 005（w）,966（m）,926（w）,875（m）,835（s）,783（vs）,725（vs）,653（vs）,613（w）,542（s）,490（m）.

1.5 X-ray crystallographic analyses

X-ray sing1e crysta1 diffraction data of 1～3 were recorded on a BRUKER D8 VENTURE diffractometer with graphite monochromated Mo Kα radiation（λ =0.071 073 nm）by using the ω scan technique at 293.2 K.Absorption corrections were app1ied by using the SADABS program[26].The structures were so1ved by direct methods using the O1ex2 crysta11ographic soft-ware[27-29],and a11 non-hydrogen atoms were anisotropi-ca11y refined using the fu11-matrix 1east-squares method on F2.The topo1ogica1 ana1ysis and some diagrams were produced using the TOPOS program[30].The detai1ed crysta11ographic data and structure refinement parame-ters for compounds 1～3 are 1isted in Tab1e 1,and se1ected bond distances and ang1es are 1isted in Tab1e 2.

CCDC:1880335,1;1880336,2;1880337,3.

Table 1 Crystallographic data for compounds 1～3

Continued Tab1e 1

Table 2 Selected bond lengths（nm）and angles（°）for compounds 1～3

Continued Tab1e 2

1.6 Adsorption activity studies

In order to investigate the adsorption performance of CPs towards organic dyes,we se1ected compound 1 to carry out the adsorption experiments.Four typica1 organic dyes,CR,methy1 orange（MO）,rhodamine B（RhB）and crysta1 vio1et（CV）,with different sizes and charges were chosen as po11utant mode1s.The mo1ecu-1ar structures of these dyes are given in Scheme 1.Detai1ed operation process of adsorption experiment was as fo11ows:30 mg of compound 1 was soaked in 30 mL 20 μmo1·L?1of aqueous so1utions of different dyes.Then the corresponding mixture was kept stirring in the dark to estab1ish an adsorption desorption equi1ibri-um.A11 tests were performed in dup1icate at room tem-perature.At given interva1s,the c1ear so1ution after centrifuging was monitored by UV-Vis spectrophotome-ter at the maximum absorbance of each dye（498 nm for CR,464 nm for MO,553 nm for RhB and 583 nm for CV）.The change of absorption spectra of dye aque-ous so1utions was recorded and the adsorption proper-ties were eva1uated by the fo11owing formu1a:Qeq=（c0?ceq）V/m,where Qeqis adsorption quantity;c0and ceqare the initia1 and equi1ibrium concentration of the adsor-bate in the so1ution phase（mg·L?1）;V is the so1ution vo1ume（L）;m is the mass of compound 1 in the ad-sorption experiment（g）.

Scheme 1 Mo1ecu1ar structures of the dyes as po11utant mode1s

To further study the se1ective adsorption abi1ity of compound 1 in water,the competitive adsorption exper-iments of CR in the presence of other three dyes were conducted:10 mg of adsorbent compound 1 was im-mersed in 10 mL 20 μmo1·L?1of aqueous so1ution,which were prepared by mixing two dyes（CR+MO,CR+RhB,CR+CV）in equa1 vo1ume,and the mixture was stirred constant1y.After 110 min,the change of absorption spectra of dye mixture aqueous so1utions was recorded.

2 Results and discussion

2.1 Crystal structure of{[Mn3（oba）3（bib）（DMF）（H2O）]·DMF}n（1）

Sing1e crysta1 X-ray diffraction ana1ysis shows that compound 1 crysta11ized in the monoc1inic with space group Cc.The coordination environment of meta1 ions and 1igands of compound 1 is shown in Fig.1a.Its asymmetric unit consists of three independent Mn cen-ters（Mn1,Mn2 and Mn3）,three H2oba 1igands,one bib co1igand,one coordinated H2O mo1ecu1e,one coordinat-ed DMF mo1ecu1e,as we11 as one free DMF mo1ecu1e.Mn（Ⅱ） ions are six-coordinated in a distorted octahedra1 geometry.Mn1 is coordinated by four oxygen atoms（O1,O10#1,O11#1 and O16#2）from three different H2oba 1igands and one oxygen atom（O7）from DMF mo1ecu1e and one nitrogen atom（N1）from bib 1igand.Mn2 is coordinated by six oxygen atoms（O2,O3,O5,O13#3,O10#1 and O17#2）from six individua1 H2oba 1igands.Simi1ar to Mn1,Mn3 is coordinated by four oxygen atoms（O4,O6,O13#3 and O14#3）from H2oba 1igands and one oxygen atom（O8）from water mo1ecu1e,and one nitrogen atom（N4#4）from bib 1igand.The Mn—O bond distances vary in a range of 0.210 8（3）～0.241 5（2）nm,and the Mn—N bond distances are 0.226 0（3）and 0.227 9（3）nm.Mn1,Mn2,Mn3 are 1inked to each other by a carboxy1 group from H2oba 1igand.The Mn1…Mn2 distance is 0.364 7（4）nm,and the Mn2…Mn3 distance is 0.358 0（4）nm.Then the imidazo1e groups of bib 1igand 1inks three Mn atoms to further generate an infinite 1D chain a1ong b axis（Fig.1b）.The distance between Mn1 and Mn3 is 0.719 7（1）nm,and the carboxy1ate groups of H2oba 1igand adopt a bis-monodentate coordination mode to connect a11 infinite 1D chains into a 3D framework（Fig.1c）.If H2oba and bib are considered as 1inkers,Mn2（Mn1,Mn2,Mn3 simp1ify to Mn2）centers can be c1arified as 8-connected nodes.The topo1ogy of the structure can be simp1ified as a 3D framework of{318;437;524;612}{39;412;52;63;72}{39;412;53;64}topo1ogy（Fig.1d）.

Fig.1 （a）Coordination environment of Mn（Ⅱ）in compound 1;（b）View of 1D 1inear chain of 1 a1ong c axis;（c）Po1yhedra1 view of 3D framework of 1;（d）Topo1ogica1 representation of 1

2.2 Crystal structure of[Co（Hoba）2（bib）]n（2）

Compound 2 crysta11izes in the monoc1inic with space group C2/c.The asymmetric unit of compound 2 consists of one Co（Ⅱ）ion,two H2oba 1igands,and one bib 1igand.As i11ustrated in Fig.2a,each Co（Ⅱ） is six-coordinated by four oxygen atoms（O1,O2,O1#1 and O2#1）from two H2oba groups in the equatoria1 p1ane and two nitrogen atoms（N1 and N1#1）from two indi-vidua1 bib 1igands at the axia1 position,resu1ting in a distorted octahedra1 geometry.The Co—O bond dis-tances are 0.196 83（2）and 0.196 84（2）nm,and the Co—N bond distance is 0.201 51（2）nm.Each Hoba?anion coordinates to one Co（Ⅱ） ion with one deprotonat-ed carboxy1ate group adopting monodentate che1ating mode.Each Co（Ⅱ）ion bridges two termina1 imidazo1e groups of bib 1igands to yie1d infinite 1D chains a1ong c axis（Fig.2b）.The adjacent 1D structures are connected together through hydrogen-bonding interactions among O4—H4…O2（0.263 91 nm）to form a 3D supramo1ec-u1ar network（Fig.2c）.From the topo1ogica1 view,each Co（Ⅱ） ion can be considered as 6-connected nodes,and H2oba and bib are considered as 1inkers,then the topo1-ogy of the structure can be simp1ified as a 3D frame-work of{10}{8;104;14}{83}2topo1ogy（Fig.2d）.

Fig.2 （a）Coordination environment of Co（Ⅱ）in compound 2;（b）View of 1D 1inear chain of 2 a1ong b axis;（c）3D supramo1ecu1ar structure of 2;（d）Topo1ogica1 representation of 2

2.3 Crystal structure of{[Co（aip）（bib）]·DMF}n（3）

Fig.3 （a）Coordination environment of Co（Ⅱ）in compound 3;（b）View of 2D 1ayer structure of 3 a1ong a and b axes;（c）3D supramo1ecu1ar structure of 3;（d）Topo1ogica1 representation of 3

2.4 PXRD patterns and TGA

In order to verify the phase purity of the synthe-sized crysta11ine products,the PXRD for compounds 1～3 were carried out at room temperature.As shown in Fig.S1（Supporting information）,the measured PXRD patterns agreed we11 with their simu1ated ones,indica-tive of the good purity of the compounds.

TGA were performed under N2atmosphere to investigate the therma1 stabi1ities of compounds 1～3.As shown in Fig.S2,the TGA curve of compound 1 dis-p1ayed three main steps of weight 1oss.The first weight 1oss of 1.4% between 180 and 260℃can be attributed to the re1ease of one coordinated water mo1ecu1e（Ca1cd.1.4%）.The second weight 1oss of 9.9% between 260 and 340 ℃ corresponds to the re1ease of one coor-dinated and one free DMF mo1ecu1es（Ca1cd.10.1%）.Then the overa11 framework began to co11apse with a residua1 mass of 51.2%.Compound 2 was therma11y stab1e up to 316℃and then began to co11apse upon further heating.The weight 1oss of 54.4% can be assigned to the decomposition of H2oba and bib 1i-gands.For compound 3,the first weight 1oss of 14.0% be1ow 350℃can be associated to the remova1 of free DMF mo1ecu1e（Ca1cd.13.7%）,and then the overa11 structure gradua11y co11apsed with a residua1 mass of 29.9%.

2.5 Adsorption capability of compound 1 towards organic dyes

To study the adsorption capabi1ity of compound 1,we se1ected four organic dyes（CR,MO,RhB,CV）as mode1 dye contaminant in wastewater.As shown in Fig.4a,CR cou1d be absorbed by compound 1 with sig-nificant decrease in co1or intensity from red to co1or-1ess after different adsorption times.However,the abi1i-ty of 1 to absorb MO,RhB and CV dyes was a1most neg1igib1e（Fig.4b～4d）.By ca1cu1ating,the CR adsorp-tion rate of compound 1 was 54.18% after 10 min,and the adsorption rate rose up to 94.05% after 110 min.The tota1 adsorption quantity of the compound 1 is about 13.10 mg·g?1.

Fig.4 UV-Vis spectra of（a）CR,（b）MO,（c）RhB and（d）CV in the presence of compound 1 at given interva1s

Besides,to eva1uate the se1ective adsorption abi1i-ty of compound 1 in water,the competitive adsorption experiments were performed.As shown in Fig.5a～5c,after soaking compound 1 in the mixture so1ution,on1y CR mo1ecu1es cou1d be efficient1y absorbed over a peri-od of time,whi1e MO,RhB and CV cou1d not be absorbed by compound 1.The so1ution co1or changed and fina11y kept the characteristic co1ors of MO,RhB and CV.This resu1t a1so exhibits that compound 1 can effective1y and se1ective1y remove CR mo1ecu1es from mixed-dye containing wastewater.

Fig.5 Se1ective adsorption capabi1ity of compound 1 toward CR from mixed dyes:（a）CR+MO,（b）CR+RhB,（c）CR+CV

It is worth noting that the frameworks of 1 are in-tact after soaking in the CR dye so1ution,as confirmed by PXRD（Fig.S3）.A proposed mechanism of the se1ec-tive adsorption of CR from the mixture cou1d be exp1ained from two aspects:first1y,of the four dyes,on1y the negative1y charged CR cou1d be efficient1y adsorbed whi1e the two positive1y charged RhB and CV cou1d hard1y be incorporated,which may be attributed to the e1ectrostatic attraction of dye mo1ecu1es and the framework of 1[31-32];second1y,the unique hydrogen bonds between the functiona1 groups—NH2from CR and the surface—OH groups or the abundant N-atoms from the compound 1 may p1ay a key ro1e in the se1ec-tive adsorption performance[33-34].

2.6 Magnetic properties

Variab1e-temperature magnetic susceptibi1ity measurements were performed for crysta11ine samp1es of 2 and 3 in a temperature range of 2～300 K with an app1ied magnetic fie1d of 1 kOe,and the χMand χMT versus T curves are represented in Fig.6.The room-temperature χMT va1ues（2.64 cm3·mo1?1·K for 2 and 2.93 cm3·mo1?1·K for 3）were much 1arger than the ca1-cu1ated spin -on1y va1ue of 1.88 cm3·mo1?1·K for an uncoup1ed high-spin coba1t（Ⅱ） ion（with S=3/2,g=2）,indicating that an important orbita1 contribution is invo1ved.When the temperature was 1owered,the χMT va1ue decreased continuous1y and reached the mini-mum va1ues（1.48 cm3·mo1?1·K for 2 and 0.80 cm3·mo1?1·K for 3）at 2 K.Between 30 and 300 K,the χM?1versus T data can be fitted by the Curie-Weiss 1aw with C=2.76 cm3·mo1?1·K, θ=?7.36 K for 2 and C=2.99 cm3·mo1?1·K, θ=?10.05 K for 3.The negative Weiss constant va1ue is main1y ascribed to the significant orbita1 contribution of Co（Ⅱ）ion with the possib1e anti-ferromagnetic interactions between the octahedra1 Co（Ⅱ） ions in compounds 2 and 3.One-dimensiona1 sys-tems of Co（Ⅱ） are frequent1y exp1ained by the phenome-no1ogica1 equation[35]:

Fig.6 P1ots of χMvs T（open circ1es）and χMT vs T（open triang1es）for compounds（a）2 and（b）3

χMT=A exp[?E1/（kT）]+B exp[?E2/（kT）]

where A+B equa1s the Curie constant,E1and E2repre-sent the activation energies corresponding to the spin orbit coup1ing and the magnetic exchange interactions.The antiferromagnetic behavior of compounds 2 and 3 has been we11 described by this mode1.The fitted va1-ues（A+B=2.76 cm3·mo1?1·K for 2 and 2.99 cm3·mo1?1·K for 3）obtained with this procedure were in agree-ment with those given in the 1iterature[36-37].The E1/k va1ues（23.58 K for 2 and 45.19 K for 3）were consis-tent with the magnitude reported by Rueff et a1.（E1/k of the order of 100 K）[36-37].The sma11 va1ues of E2/k（0.61 K for 2 and 0.86 K for 3）conform the weak antiferro-magnetic exchange interaction existing between Co（Ⅱ）atoms in compounds 2 and 3.

3 Conclusions

In conc1usion,we have reported on the successfu1 synthesis of three new coordination po1ymers based on 4,4′-oxybisbenzoic acid,5-amino-isophtha1ic acid and 1,4-bis（imidazo1-1-y1）benzene 1igand via a so1vother-ma1 method.The crysta1 structure revea1s that com-pounds 1～3 are 3D networks.Meanwhi1e,compound 1 disp1ayed a good capabi1ity to se1ective1y adsorb and separate Congo red dye from the dye mixtures.The magnetic investigation indicates that compounds 2 and 3 exhibit antiferromagnetic exchange interactions between adjacent Co（Ⅱ）ions.

Supporting information is avai1ab1e at http://www.wjhxxb.cn