劉秀秀 程美令 任艷秋 夏慶洪 韓 偉 劉 琦＊,,2

(1常州大學(xué)石油化工學(xué)院，江蘇省綠色催化材料和技術(shù)重點實驗室，常州213164)

(2南京大學(xué)配位化學(xué)國家重點實驗室，南京210093)

以3，5-二甲基-1-羧甲基-4-吡唑甲酸為配體的兩個鋅的配合物的合成、晶體結(jié)構(gòu)和熒光性能

劉秀秀1程美令1任艷秋1夏慶洪1韓 偉1劉 琦＊,1,2

(1常州大學(xué)石油化工學(xué)院，江蘇省綠色催化材料和技術(shù)重點實驗室，常州213164)

(2南京大學(xué)配位化學(xué)國家重點實驗室，南京210093)

以3，5-二甲基-1-羧甲基-4-吡唑甲酸和4，4′-聯(lián)吡啶為配體，合成了1個單核鋅配合物[Zn(4,4′-bpy)(Hcmdpca)2(H2O)3]· 2H2O(1)和1個鋅的一維配位聚合物[Zn(4，4′-bpy)(Hcmdpca)2(H2O)]·3H2O(2)(H2cmdpca=3，5-二甲基-1-羧甲基-4-吡唑甲酸；4，4′-bpy=4，4′-聯(lián)吡啶)，并用元素分析、紅外光譜、X-射線單晶衍射結(jié)構(gòu)分析、熱重分析等對其進行了表征。配合物1和2都屬于單斜晶系，空間群為P21/c。配合物1的鋅離子都位于一個畸變的八面體構(gòu)型中。配合物1中的獨立結(jié)構(gòu)單元間通過分子間氫鍵作用構(gòu)成一個三維的超分子結(jié)構(gòu)。而在2中，鋅離子位于一個畸變的四方錐構(gòu)型中，每個4，4′-聯(lián)吡啶分子橋聯(lián)2個相鄰的鋅離子，形成一個一維鏈；這些一維鏈和水分子通過分子間氫鍵進一步形成一個三維的結(jié)構(gòu)。此外還考察了1和2的熱穩(wěn)定性和固體熒光性質(zhì)。

鋅；3，5-二甲基-1-羧甲基-4-吡唑甲酸；4，4′-聯(lián)吡啶；晶體結(jié)構(gòu)；熒光

Supramolecular frameworks/coordination polymers assembled by coordinate bond and hydrogen bond have attracted increasing research interest not only because of their appealing structural and topological novelty but also owing to their tremendous potential applications in gas storage[1-3],separation[4-5],magnetic and optical materials[6-8],catalysis[9-11]and lithium-ion batteries[12-14].Generally speaking,the structural diversity of such crystalline materials is dependent on many factors,such as the metal ion,the templating agents,the metal-ligand ratio,the pH value,the counteranion and the number of coordination sites provided by organic ligands[15-16].Among the strategies, the rational selection of organic ligands or coligands according to their length,rigidity and functional groups is important for the assembly of structural controllable supramolecular frameworks,and a great deal of significant works have been done by using this strategy[17].Pyrazole carboxylic acid type ligand,as a multidentate ligand,not only can provide multicoordination sites involving nitrogen atoms on pyrazole ring and carboxylate oxygen atoms[18-24],but also act as a donor and/or acceptor in hydrogen bond interactions.They have proven to be considerable advantageous ligands for the self-assembly of supramolecular frameworks[25-26].Recently,we have synthesized some luminescent complexes containing pyrazole carboxylic acids,such as 3,4-pyrazoledicarboxylic acid[18-19],and 5-methyl-1H-pyrazole-3-carboxylicacid[20-24]etc.In order to expand the study in this field,we designed and synthesized a new ligand 1-carboxymethyl-3,5-dimethyl-1H-pyrazole-4-carboxylicacid(H2cmdpca) (Scheme 1),Compared to 3,5-dimethyl-1H-pyrazole-4-carboxylic acid with rigid structure,due to the flexible carboxymethyl group addition,H2cmdpca has become a semi-rigid ligand and has more potential coordination sites.Besides,two carboxyl groups of H2cmdpca can be partially or fully deprotonated to generate Hcmdpca-and cmdpca2-at different pH values,which is useful to synthesize new functional complexes.On the other hand,4,4′-bipyridine(4,4′-bpy)is a good candidateformolecularbuildingblocks.Many coordination polymers based on 4,4′-bpy have been reported[12,27].As the continuation of our research,and motivatedbyourinterestinfunctionalmetal complexes,we carried out the reactions of H2cmdpca, 4,4′-bpy and Zn(NO3)2·6H2O,and obtained two new complexeswithuncoordinatedcarbonylgroups, namely,[Zn(4,4′-bpy)(Hcmdpca)2(H2O)3]·2H2O(1), and[Zn(4,4′-bpy)(Hcmdpca)2(H2O)]·3H2O(2).Moreover,thermal stability and fluorescence properties of the complexes have also been studied.To the best of our knowledge,this is the first report on the metal complexes based on H2cmdpca.

Scheme 1Molecular structure of H2cmdpca

1 Experimental

1.1 Materials and instruments

All reagents and solvents were used as received from the commercial source without further purification.Theligand1-carboxymethyl-3,5-dimethyl-1H-pyrazole-4-carboxylic acid(H2cmdpca)was prepared according to similar method reported in literature[28]. The single-crystal X-ray determination measurement of 1 and 2 was performed on a Bruker SMART CCD diffractometer at 293(2)K.The elemental analysis(C, H and N)was performed with a Perkin-Elmer 2400 Series II element analyzer.FIIR spectra were recorded on a Nicolet 460 spectrometer using KBr pellets in the range of 4 000～400 cm-1.The luminescent spectra of the solid samples were recorded with a Varian Cary Eclipsespectrometer.Thermogravimetricanalysis(TGA) experiments were carried out on a DuPont thermal analyzer from room temperature to 800℃under N2atmosphere at a heating rate of 10℃·min-1.

1.2 Synthesis

1.2.1 Synthesis of complex[Zn(4,4′-bpy)(Hcmdpca)2(H2O)3]·2H2O(1)

A solution of Zn(NO3)2·6H2O(0.1 mmol,0.029 7 g)in distilled water(2 mL)was slowly added to a solution of H2cmdpca(0.2 mmol,0.039 6 g)and 4,4′-bpy(0.05 mmol,0.009 9 g)in DMF(4 mL)to obtain a colorless solution.The resulting solution was allowed to stand at ambient temperature for some days,giving colorless crystals in 33.8%yield based on Zn.Anal. Calcd.For C26H36N6O13Zn(%):C,44.23;H,5.14;N, 11.88.Found(%):C,44.21;H,5.13;N,11.85.IR(KBr pellet,cm-1):3 395(s),3 156(m),2 674(m),2 592(m), 1957(w),1637(vs),1597(w),1547(w),1497(s),1430 (w),1 388(vs),1 310(s),1 289(s),1 127(vs),1 102(w), 1070(s),943(m),924(w),877(m),853(w).

1.2.2 Synthesis of complex[Zn(4,4′-bpy)(Hcmdpca)2(H2O)]·3H2O(2)

Synthesis of 2 was similar to that of 1,but the molar ratio of nZn2+∶nH2cmdpca∶n4,4′-bpyis 1∶2∶1.The resulting solution was allowed to stand at ambient temperature for some days,yielding colorless crystals in 24.67% yield based on Zn.Anal.Calcd.For C26H34ZnN6O12(%): C,45.35;H,4.94;N,12.21.Found(%):C,45.38;H, 4.99;N,12.20.IR(KBr pellet,cm-1):3 450(m),2 993 (s),2 782(s),2 423(m),1 667(m),1 571(s),1 386(vs), 1 290(w),1 201(m),1 141(m),1 043(m),885(w),807 (s),762(w).

1.3 X-ray analysis

Single-crystalX-raydiffractionmeasurements were carried out with a Bruker Smart Apex CCD area detector at 293(2)K.Intensity reflections were measured adopting graphite-monochromatized Mo Kα radiation (λ=0.071 073 nm)with the φ-ω scan mode.The structure were solved by direct methods and refined by full-matrix least-squares methods on F2employing the SHELXTL-97program[29].Anisotropic thermal factors were assigned to all the non-hydrogen atoms, H atoms attached to C were placed geometrically and allowed to ride during subsequent refinement with an isotropic displacement parameter fixed at 1.2 times Ueqof the parent atoms.H atoms attached to O atoms fromthewatermoleculeswerefirstlocatedin difference Fourier maps and then placed in the calculated sites and included in the refinement. Structurecrystallographicdataandexperimental details for the two compounds are summarized in Table 1.The selected bond lengths and bond angles are given in Table 2,and the hydrogen bond distances and angles are presented in Table 3.

CCDC:963357,1;979480,2.

Table1 Crystal data and structure refinement parameters for 1 and 2

Continued Table 1

Table2 Selected bond lengths(nm)and angles(°)for complexes 1 and 2

Table3 Hydrogen bond distances(nm)and angles(°)for compounds 1 and 2

Continued Table 1

2 Results and discussion

2.1 Syntheses and infrared spectra

Complex 1 can be obtained by slow evaporation of a mixed solution of DMF and deionized water of Znand ligands with molar ratio of 1∶2∶0.5().When the molar ratio changed into 1∶2∶1, complex 2 was obtained.This fact shows that the outcome is molar-ratio-dependent.For complexes 1 and 2,they have similar IR spectra(see supporting information,Fig.S1).The strong and broad peaks around 3 000～3 500 cm-1are assigned to ν(OH)of the water molecules.The strong peaks at 1 637 cm-1(1), 1 667 cm-1(2),and 1 388 cm-1(1),1 386 cm-1(2),are assigned to the νas(OCO)and νs(OCO)stretching vibration ofHcmdpca-[30].Those assignments are supported by the X-ray crystal structure analysis.

2.2 Crystal structures of complexes 1 and 2

Complex 1 possesses mononuclear structure and crystallizes in the monoclinic space group P21/c.As shown in Fig.1 ,in 1,the coordination sphere is defined by two oxygen atoms(O1,O5)from two carboxyl groups of two Hcmdpca-anions ligands, three oxygen atoms(O9,O10,O11)from three coordinated water molecules respectively,and a nitrogen atom(N5)from one 4,4′-bpy,leading to a distorted octahedron geometry.Four oxygen atoms(O1,O5,O9, O10)form the equatorial plane of the octahedron,one nitrogen atom(N5)and one oxygen(O11)occupy the apical position.The bond distances of Zn1-O are in the range of 0.205 2～0.214 8 nm and Zn1-N bond length is 0.215 2 nm(Table 2),which are close to those observed in zinc complexes based pyrazole derivative ligands[28].The degree of distortion from the idealoctahedralgeometryisreflectedincisoid (87.08(18)°～93.09(18)°)and transoid angles(175.6(18)°～179.8(2)°).

Fig.1 Molecular structure of the complex 1 with thermal ellipsoid at 30%probability level

In addition,independent components[Zn(4,4′-bpy)(Hcmdpca)2(H2O)3]and H2O are linked by three kinds of hydrogen bonds(N-H…O,O-H…O,C-H…O)(Table 3),as shown in Fig.2 ,resulting in the formationofathreedimensionalsupramolecular architecture;while the intermolecular π-π interactions betweenpyrazolylringsandbetween4,4′-bpy molecules(centroid-centroid distances are in the range of 0.359 6～0.365 5 nm)further increase the stability of the structure.

Fig.2 3D network of complex 1

Fig.3 A view of the coordination environment around the Znions in 2 with thermal ellipsoid at 30% probability level

Complex 2 also crystallizes in monoclinic system and space group P21/c.The asymmetric unit of 2 contains one Znion,two Hcmdpca-anion ligands, one 4,4′-bpy molecule,and one coordinated water molecule.As shown in Fig.3 ,the Znion is fivecoordinated and surrounded by two oxygen atoms(O1, O5)from two carboxylate groups of two Hcmdpcaanionligands,oneoxygenatoms(O9)froma coordinated water molecule,and two nitrogen atoms (N5,N6ii)from two 4,4′-bpy,leading to a distorted square-pyramidal coordination geometry.Two nitrogen atoms and two oxygen atoms(N6ii,N5,O1,and O5) form the base plane of the square-pyramidal structure, one oxygen atom(O9)occupy the apical position.N6ii, N5,O1 and O5,and Zndeviate 0.033 1 and 0.004 84 nm from the the base plane,respectively.The bond distances of Zn1-O and Zn1-N are in the range of 0.230 1～0.230 0 nm and 0.228 6～0.230 0 nm respectively(Table 2),which are slight larger than the values observed in the complex 1.The bond angles of N5AZn1-N6,N6-Zn1-O9,N5A-Zn1-O9 are 165.38(18)°, 105.29(17)°and 89.1(2)°respectively.

Fig.4 1D chain structure of complex 2 along the a axis

Fig.5 3D network of complex 2

The considerable interesting observation is that complex 2 contains uncoordinated carboxyl groups (freecarboxylicacids)andnitrogenatomsfrom Hcmdpca-,while 1 not only keeps uncoordinated carboxyl groups but also uncoordinated nitrogen atoms from 4,4′-bpymoleculesandHcmdpca-.These uncoordinated carboxyl groups/nitrogen atoms might serve as Lewis acid/base sites in catalytic and acid-base reactions[28,31].On the other hand,the metal complexes with uncoordinated carboxyl groups could be further modified using a variety of organic and inorganic reactions to afford new metal complexes with different properties.The relative research is under way in our group.

2.3 Thermal analysis

For detecting the thermal stabilities of complexes 1 and 2,thermal gravimetric(TG)analyses were carried out from the room temperature to 850℃in a nitrogen atmosphere(see Fig.S2,supporting information).For complex 1,the initial weight loss of 12.84%occurs from 55 to 169℃,corresponding to the loss of five water molecules(Calcd.12.76%).Above 169℃,the remainingmaterialdecomposesgradually.For complex 2,the first weight loss of 12.84%which occurred from 50 to 166℃corresponds to the release of five water molecules(10.46%).Above 166℃,the remaining part begins to decompose gradually.

2.4 Luminescent properties

Luminescent compounds are currently of great interestbecauseoftheirvariousapplicationsin chemical sensors,photochemistry,and electroluminescent display.The photoluminescent behaviors of complexes 1 and 2 as well as free ligand H2cmdpca are studied in the solid state at room temperature.As illustrated in Fig.6 ,the blue emission for H2cmdpca and complexes 1 and 2 can be observed,where their maximum emission wavelengths are all at about 425 nm.Apparently,the main emission speaks of all of the complexes 1 and 2 are similar to that of the ligand H2cmdpca in terms of the position and the band shape,indicating that the emission bands of 1 and 2 may be attributed to the emission of intraligand π-π* transition[28,31].

Fig.6 Solid-state emission spectra for compounds H2cmdpca,1 and 2(excitation wavelength= 370 nm)at room temperature

3 Conclusions

Inthiswork,twozinccomplexeswith uncoordinated carbonyl groups have been successfully synthesized by the self-assembly of Zn(NO3)2·6H2O, H2cmdpca,and 4,4′-bpy in different molar ratio. Complex 1 is a mononuclear structure,and 2 shows a 1D structure.The coordination modes of Hcmdpcawith metal atoms are the same in the two complexes. The intermolecular weak interations play important roles in the formation of three-dimension supramolecular architectures of 1 and 2.Complexes 1 and 2 all display blue fluorescence in the solid state.

SupportingInformation:Supportinginformationis available at http://www.wjhxxb.cn

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Two Zinc Complexes Based on 1-Carboxymethyl-3,5-dimethyl-1H-pyrazole-4-carboxylic Acid:Syntheses,Structures,and Luminescent Properties

LIU Xiu-Xiu1CHENG Mei-Ling1REN Yan-Qiu1XIA Qing-Hong1HAN Wei1LIU Qi＊,1,2
(1School of Petrochemical Engineering and Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology,Changzhou University,Changzhou,Jiangsu 213164,China)
(2State Key Laboratory of Coordination Chemistry,Nanjing University,Nanjing 210093,China)

One monomeric complex[Zn(4,4′-bpy)(Hcmdpca)2(H2O)3]·2H2O(1)and one 1D coordination polymer [Zn(4,4′-bpy)(Hcmdpca)2(H2O)]·3H2O(2)(H2cmdpca=1-carboxymethyl-3,5-dimethyl-1H-pyrazole-4-carboxylic acid,4,4′-bpy=4,4′-bipyridine)have been synthesized and characterized by elemental analysis,IR spectra,single crystal X-ray diffraction,thermogravimetric analysis.Complexes 1 and 2 all crystallize in the monoclinic system, space group P21/c.In 1,Znion is located in distorted octahedral coordination geometry,discrete mononucleate units and water molecules are assembled into a 3D network.In 2,each Znion is located in distorted squarepyramid geometry.Each 4,4′-bpy ligand bridges two adjacent Znions,forming a 1D chain.These chains and water molecules are connected by hydrogen bonds,forming a 3D supramolecular network.The thermal stability and luminescent properties of the complexes are also investigated.CCDC:963357,1;979480,2.

zinc;1-carboxymethyl-3,5-dimethyl-1H-pyrazole-4-carboxylic acid;4,4′-bipyridine;crystal structure;photoluminescence

O614.24+1

A

1001-4861(2015)03-0611-08

10.11862/CJIC.2015.098

2014-11-02。收修改稿日期：2014-12-31。

國家自然科學(xué)基金(No.20971060、21101018)，南京大學(xué)配位化學(xué)國家重點實驗室開放課題資助項目。＊

。E-mail：liuqi62@163.com，Tel：0519-86330185；會員登記號：S060018987P。