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具有荧光响应功能的分子四边形的组装

2022-03-21 来源:我们爱旅游
第26卷第12期 2010年12月 无 机 化 学 学 报 Vo1.26 No.12 2l38—2142 CHINESE JOURNAl OF INORGANIC CHEMISTRY 具有荧光响应功能的分子四边形的组装 朱翔黄薇何 成 段春迎 (大连理工大学化工学院,精细化工国 家重点实验室,大连 1160121 摘要:由缩氨基脲和2-喹啉醛合成了席夫碱配体H L, 与过渡金属离子Cd 组装得到了四边形配合物CQ。用X射线衍射对 配合物的晶体结构进行了测定,发现其具有,4。/n空间群 通过荧光测试发现该配合物在CH CN溶液中具有较强的荧光,加人 间苯二甲酸、对苯二甲酸阴离子后荧光发生淬灭,而加入邻苯二甲酸阴离子荧光无变化.可以将邻苯二甲酸阴离子从其他2种 二酸阴离子f{l隧分出来。 关键词:镉离子;荧光;席大碱配体:二酸阴离子 中图分类号:0614.24+2 文献标识码:A 文章编号:1001—4861(2010)12—2138—05 Self-assembly of Fluorescent Molecular Squares ZHU Xiang HUANG Wei HE Cheng DUAN Chun—Ying (State Key Labortaory of Fine Chemicals,Dalian University f oTechnology,Dalian,Liaoning 1 16012) Abstract:A novel Cd—based tetranuclear complex CQ([Cd4H2L4](NO3)2・14H20,where H2L=bis[2一Quinoline methy1] carbohydrazone1 has been synthesized via self-assembly.Single—crystal X—ray diffraction analysis shows that CQ is a molecular square,which crystallizes in an 141/a space group.CQ shows a strong lfuorescent emission band in CH3CN solution.The fluorescent titration experiment shows the CQ has a lfuorescent quenching effect toward P—phthalate and m—phthalate dicarboxylates,while silent for the 0一phthalate one,suggesting it can be used as a fluorescent chemosensor for distinguishing o.phthalate from two other isomers of dicarboxylates.CCDC:791 184. Key word:Cd ions;luminescence;Schif base ligand;dicarboxylates 0 Introduction includes detecting and amplifying guest—bonding events to produce a measurable output闱.Thus.a proper comm- Supramolecular assembly of predesigned organic and inorganic building blocks is an excellent tool for constructing well—defined nanosize molecular cavities…. Synthetic strategies for constructing functional coor— unication system that is able to transduce the recogni- tion information into an easy・・to--measure signal must be included in the overall molecular design[4 ̄. Recently,the development of synthetic receptors dination cages with various structures and novel inclu— able to bind anions selectively in a detectable fashion to an observer via changes in electrochemical response or in fluorescence intensity constitutes an important yet sion properties have been well established these years【2『| As the development of supramolecular chemistry,the major challenge goes beyond achieving a size—or a shape—selective dynamic molecular recognition and 收稿日期:2010.05.20收修改稿}』期:2Ol0.O6 30 日家自然科学基金(No 2080l008)资助项目 通讯联系人 E-mai/:}le( heng@dlut edu l dificult task facing supramolecular chemistsI5J.since these species are not only strongly solvated in protonic 第 作者:朱翔, .25岁.硕十研究生:研究,J向:配位化学 第l2期 朱 翔等:具有荧光响应功能的分子四边形的组装 2139 media but also characterized by multiple charges and complex shapes.Differentiation of geometric isomers (such as ortho/meta/para dicarboxylates)is,in general, a dififcult task,because of their similar chemical and physical properties e.g.charge density and structural complexity . In this paper,we report the synthesis and structure of a tetranuclear cadmium square via self-assembly. The ligand combining two quinoline groups into a semicarbazone group as an edge of a quadrilateral is used to design the well—programmed molecular square and addressed the problem of discriminating o- phthalate from m・・phthalate and P・-phthalate isomers by the molecular square.Each quinoline group acts as both fluorophore and binding site.On the other hand, urea and thiourea derivatives are well known as attractive building block in the construction of neutral hydrogen bonding receptors_8J_Hence.each ligand can provide two—armed N2O tridentate coordinating site for the metal ion,which are simultaneously introduced as trigger sites to achieve efifcient host-guest interactions.consequently yielding signal response .In the presence of a specific anion as the eonformational template,the hydrogen bonding interaction between the urea groups and the anion is expected and the lfuorescent signal changes results ”. 1 Experimental 1.1 Materials and instrumentation A11 the chemicals and solvents were of reagent grade quality obtained from eommereial sources and used without further puriifcation.The salts solutions of metal ions was Cd(NO )1・4H,0.The elemental analyses 0f C.H and N were performed on a vario EL m elemental analyzer. H NMR spectra were measured on a BRUKER 400M spectrometer.ESI mass spectra were ca ̄ied out on a HPLC--Q・-Tof MS spectrometer using aeetonitrile as mobile phase.UV—Vis spectra were measured on a HP 8453 spectrometer.The fluorescent spectra were measured on EDINBURGH FS920. 1.2 Synthesis of the ligand H2L l 0 drops of acetic acid were added to a methanol f50 mL)solution of 2.quinoline carboxaldehyde(0.690 g,4.4 mmo1)with semicarbazone(0.1 80 g,2 mmo1). After refluxed for 6 h,a white floccule was collected by ifltration washed with methanol,and dried in vacuo. Yield:0.56g,76%. H NMR(400 MHz,DMSO—d6,ppm) 6:1 1.34(s,2H),8.45(d,4H),8.32(s,2H),8.03(d,4H), 7.82 fm,2H)。7.65 fm,2H).Element analysis Calcd.for C21Hl6N6O(%):C 68.45;H,4.38;N,22.8 1.Found ): C,68.81;H,4.83;N,22.36(Scheme 1). Scheme 1 Chemical structure of H2L 1.3 Preparation of compound CQ The solution of Cd(NO3)2・4H20(0.03 1 g,0.1 mmol1 in 1 0 mL methanol was added to a suspension of H2L(0.038 g,0.1 mmo1)in 10 mL methano1.Red block single crystals of CQ suitable ofr X-ray crystallographic analyses were carried out from evaporating the mixture for one week and collected by filtration,washed with methano1.and dried in vacuum.Yield:30%.Element analysis Calcd.for C84H86Cd4N26024(%):c,43.99;H, 3.78;N,15.88.Found(%):C,44.35;H,3.56 N,16.21. ESI of CQ in a CH CN solution exhibits the intense peak at m/z=638.72 and m/z=644.72 with the isotopic distirbution patterns separated by 0.33+0.01.which could be assigned to the species of[Cd4H3Id¨and 【Cd4H3L4・H20 respectively,indicating the stability of Cd—based molecular square in solution. 1.4 Structure determination Suitable crystals were selected for single—crystal X—ray diffraction structural analysis and the data were collected on a Bruker SMART APEX CCD diffraeto. meter with graphite—monochromatized Mo Ka radiation (A=0.07 1 073 nm),using the SMART and SAINT prog- rams[ 1.The structures were solved by direct method and refined on F by fu11.matirx least.squares methods with SHELXTL version 5.1 Crytsal data of CQ:Cs4H86 Cd4N26024, =2 293.39,Tetragonal,space group,41/n, red block,a=2.912 67(9)nm,c=1.226 80(7)nm, = 10.407 7(71 nm .Z=4 =180 K.4 004 unique reflec— 2l40 无机化学学报 第26卷 tions(R, =0.067 5).Final R l(with,>2 60)=0.068 6, wR2 fall data)=0.1 77 9,for 20=48.5。.Except the slovent molecules and the counter aion。anisotropic thermal parameters were refined for lion—hydrogen atoms,hydro— gen atoms were localized in their calculation positions square suggests the four ligands lost six protons in virtue of coordination to metal ionsl I.As a result.all the bond distances within two arms are intermediate between the normal single bond and double bond, further indicating extensive delocalization over the entire molecular skeleton.Neighboring Cd“ions are and refined by using the riding mode1.The solvent water oxygen atoms were added with hydrogen atoms which were found from the difference Fourier maps and then fixed with the O…H distances of 0.096 nm and H …bridged by the single oxygen atoms of the ligand “edges”with M・・・M separations of approximately 0.425 nm and M一0-M angles of about 1 30。.There are four H distances of 1.52.isotropic parameters of these urea groups in the tetranuclear complex CQ which located within the square,providing static,geometric, coordinative,and functional properties to the square— like complex,which are important for the recognition of hydrogen atoms were fixed as 1.5 times the isotropic parameters of the oxygen atom it was attached. C DC:791 184 2 Results and discussion 2.1 Structure feature carboxylate derivatives,such as dicarboxylatesl ‘81. The structure analysis SHOWS that CQ is a centro. symmetry neutral tetranuclear Cd(1I)square,which is crystallized in centrosymmetric/4l/a space group of tetragonal crystal system.In this square four Cd(U)ions occupy the corners of the molecular square,and each ligand acts as the bridge between two metal ions to form an edge(Fig.1).Each Cd(Ⅱ)ion is therefore oetahedrally coordinated by the carbonyl oxygen atoms,the quinoline and imine nitrogen atoms from two ligands in the mer—configuration,and the dihedral angle between the two chelating planes around each Cd(11)center ranges from 85。to 92。.With the two chelating units at the para positions of the urea spacer,the ligand displays a nearly linear configuration leading to a relatively large and planar molecular square.The Displacement ellipsoild aI'e drawn at the 30%probability leve1. hydrogen atoms,solvent molecules and counter anion are omitted for clarity presence of two counteranions for each CQ molecule Fig.1 Molecular structure of the mo]ecular square CQ Table 1 Selected bond distance(nm)and angle(。) Cd( )一N(2) Cd( )一o(1A) 0.227 4(6) 0.234 6(51 0.128 7(8) Cd(1)一N(5A) Cd(1)-N(1) C(1 1)一N(3) O.228 7(61 0.235 1(6) 0.134 4(9) Cd(1)一O(1) Cd0)一N(6A) C(1 1)-N(4) 0.234 6(5) 0.238 0(6) C(1 O.135 4(9) (2)一Cd(D—N(SA) N(2)一Cd(1)一O(1) N(2)-Cd(1)一N(1) O(1)一Cd(1)-N(1) 171.2(2) 68.2(2) 71.5(2) N(2)一Ca(1)一O(1A) N(5A)一Ca(1)一o(1) N(5A)-Cd(1)一N(1) N(2)一Ca(1)一N(6A) O(1) Ca(1)一N(6A) 1O8 8(2) 103.3(2) 1 16.5(21 1 10.6(2), 3f2) N(5A)一Ca(1)一O(1A) 68‘O(1)-Ca(1)一O(1 A) O(1A1一Cd(1)-N(11 90.4(2) 93.9(2) 138.6(2) N(5A)一Cd(1)一N(6A) 71.1(2) .O(1A)・Ca(1)一N(6A) 139.1(2) Symmetry(:ode凡:一v+sf4.x+l/4 一z一7/4 94.1(2) N(1)一Ca(1)一N(6A) 108.6(2) ;.时~^】ls lu— ^I苗一 第12期 2.2 Fluorescence feature 朱 翔等:具有荧光响应功能的分子四边形的组装 2l41 the emission intensity decreases slightly(Fig.2). Although we don t have any further proof to confirm the Fluorescence spectrum of CQ in the CH3CN solution shows a strong emission band at 620 nm interaction of hydrogen bond between anion and the attirbuting to the Cd—quinoline group(excitation at 468 nm)(Fig.2).Upon addition of an o-phthalate ion in the form of tetrabutylamm0nium(TBA)saIt ,the emission intensity decreases slightly,and no signiifcant shitf of the wavelength is found when excited at 468 nm.But upon the addition of,,lj—or P—phthalate ions.the intensity of the emission band at 620 nm decreases drastically.The observed fluorescent quenching could square,the receptor CQ has high selectivity toward the o—phthalate anion over the other two isomers of dicarbo— xylates.Based on the luminescent titrations,it is suggested that there are two square bind one m— phthalate or P—phthalate anion.the two CO0一in the m— or P—phthalate anion combine the urea groups of two squares tightly and cause the decrease of the fluores— cence drastically (Scheme 2),but the fluorescence decreases slightly with the addition of o—phthalate anion because the angle of two CO0一is too narrow to form be attirbuted to the typical guest—induced PET process .Upon coordination of the anion with the sensor,the hydrogen bonds between the anion and urea cause a decrease in the oxidation potential of the urea tightly hydrogen bond with both squares. .j时\暑 嚣 lu— AI甚I。 2 2 1 日\receptor,which tirggers the PET from urea to coordinate to the relatively electron deficient Cd— quinoline fluorophore,leading to the enhancement of a PET effect,thus causing the fluorescence to be “switched-off”. 2 5×lO 2 O×1O Wavelength/tim l 5×1O Fig.3 Fluorescent response of CQ(50 Ixmol・L )upon addition of p—phthalate dicarboxylate in CHsCN, the insert picture shows the fluorescence titration profile around 620 nm with the 1 O×l0 5 O×l0 excitation wavelength of 468 nm 0 O Wavelength/nm 2 Fig.2 Selectivity experiment of CQ(50 txmol・L )toward OH—and the three forms of diearboxylate(1 equiv) in CH3CN,A =468 nm…A =620 nm 2 Upon the addition of,n—or P—phthalate ions to the CH3CN solution of CQ,the intensity of the emission band at 620 nm decreases similarly(Fig.3,4).The luminescent titrations with the two isomeric phthalates Wavelength/tim suggest the formation of 2:1 stoichiometry host—guest interacted as the titration curve shows a steady and smooth decrease until a plateau is reached with 0.5 equiv of the P一.and m—phthalate anions,respectively. 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