孫月霞 張志斌 孫 琪＊, 許 巖＊,,

(1遼寧師范大學(xué)化學(xué)化工學(xué)院，化學(xué)功能材料研究所，大連116029)

(2南京工業(yè)大學(xué)化學(xué)化工學(xué)院，材料化學(xué)工程國家重點實驗室，南京210009)

兩個新的Dowson結(jié)構(gòu)硫鉬多酸鹽合成，表征以及催化性質(zhì)

孫月霞1張志斌2孫 琪＊,1許 巖＊,1,2

(1遼寧師范大學(xué)化學(xué)化工學(xué)院，化學(xué)功能材料研究所，大連116029)

(2南京工業(yè)大學(xué)化學(xué)化工學(xué)院，材料化學(xué)工程國家重點實驗室，南京210009)

通過水熱技術(shù)合成了兩種新的Dowson結(jié)構(gòu)硫鉬多酸鹽[C5N2H14]2[S2MoⅥ18O62]·8H2O(1)和[C5N2H14]8(H3O)2[S2MoⅤ2MoⅥ16O62]3·(C5H5N)2(2)，并通過X射線分析、紅外光譜和元素分析其進行了表征。X射線晶體結(jié)果分析，化合物1結(jié)晶于正交晶系，Pmmn空間群，a=1.79929(17)nm，b=1.35804(13)nm，c=1.41926(13)nm，V=3.4680(6)nm3，Z=2?；衔?結(jié)晶于單斜晶系，C2/m空間群，a=2.2665(3)nm，b=1.3749(2)nm，c=3.2912(5)nm，β=104.31(0)°，V=9.938(2)nm3，Z=4。化合物1和2都含有Dawson結(jié)構(gòu)的硫鉬多酸陰離子和質(zhì)子化的N-甲基哌嗪陽離子。并且由苯乙烯的氧化催化結(jié)果中看出混價鉬的化合物2的催化活性要比化合物1略高。

硫鉬酸鹽；晶體結(jié)構(gòu)；水熱合成；催化

Many researchers are endeavoring to study the structuralchemistryofvanadiumphosphates, polyoxomolybdenum and silicomolybdenum,and have paid a great deal of attention to heteropolyanions containing organic-inorganic cationic ligands in recent years[1-2],which is not only because of diverse structures,but also the potential applications,such as medicine,as well as electrochemistry,magnetism,and catalysis in particular[3-11].Compared with lots of reported molybdoarsenates and molybdophosphates[12-21],molybdosulfates are much less developed.Among these polyoxoanions, Dawsonpolyoxoanionsofthemolybdenum-sulfate chemistry has not been reported extensively,which may be caused because it has the large size to decrease the electronic density and the oxygen coordination on its surface[22-23].However,in view of the environmental problem,it has potential for fixing and absorbing Sulfur dioxides[24],and exploring the possibility of the frameworks with pyramidal sulfate anions,which could result innovelstructuralfeaturesandunprecedented properties for these frameworks[25-28].Here,we report the synthesis,structure,and catalytic property of two new molybosulfates[C5N2H14]2[S2MoⅥ18O62]·8H2O(1)and [C5N2H14]8(H3O)2[S2MoⅤ2MoⅥ16O60]3·(C5H5N)2(2).Both compounds contain Dawson Mo-S anions,but with different oxidation states of Mo.

1 Experimental section

1.1 Materials and methods

All chemicals purchased were of reagent grade and used without further purification.Element analyses (C,H and N)were performed on a Perkin-Elemer 2400 elemental analyzer.IR spectra were recorded on a Nicolet Impact 410 FTIR spectrometer using KBr pellets in the 4000~400 cm-1region.

1.2.1 Synthesis and characterization of compound 1

A mixture of MoO3(0.288 0 g),Fe2O3(0.159 9 g), NaHSO3(0.107 2 g),N-methylpiperazine(0.102 0 g), H2SO4(50%)(0.6325 g)was dissolved in distilled water (10 mL),and was stirred for 5 h.The resulting solution was sealed into Teflon-lined steel autoclave and heated at 160℃for 7 d.After cooling to room temperature in air,brown crystals were washed and filtered by distilled water and dried in air,yield:35%based on Mo.The elemental analysis calcd.for C10H44Mo18N4O70S2(%):C, 3.83;H,1.41;N,1.79.Found(%):C,3.80;H,1.34;N, 1.72.

1.2.2 Synthesis and characterization compound 2

A mixture of MoO3(0.2892 g),NaHSO3(0.1078 g), N-methylpiperazine(0.106 6 g),H2SO4(50%)(0.584 9 g)and pyridine(0.201 2 g)was dissolved in distilled water(10 mL),and was stirred for 5 h.The resulting solution was sealed into Teflon-lined steel autoclave and heated at 160℃for 7 d.After cooling to room temperature in air,black-rod crystals were washed and filtered by distilled water and dried in air,yield:42% based on Mo.The elemental analysis calcd.for C50H128Mo54N18O188S6(%):C,6.41;H,1.37;N,2.63.Found(%): C,6.45;H,1.40;N,2.67.

1.3 Determination of crystal structure

The crystals of both compound 1 and 2 were carefully singled out under a microscope and glued at the tip of a thin glass fiber with cyanoacrylate adhesive. Single-crystal structure determination was performed on a Bruker Smart ApexⅡCCD diffractometer at 293(2)K,with a sealed tube X-ray source Mo Kα(λ= 0.071 073 nm)operating at 50 kV and 30 mA.The crystal structure was solved by the direct method and refined on F2by full-matrix least-squares using the SHELX97 program package[29].All non-hydrogen atoms were refined anisotropically.All hydrogen atoms for organic molecules were placed in the calculation position.While the H atoms of water(or H3O+)were located from the different Fourier maps.Further details of the X-ray structural analyses for compound 1 and 2 are given in Table 1.

CCDC:783378,1;783379,2.

Table 1Crystallographic data for 1 and 2

Continued Table 1

2 Description of structures

The IR spectrum of compound 1 shows intense absorption at 945,793,668 and 559 cm-1are attributed to ν(Mo-Ot)or ν(Mo-Ob),the band at 1 149 cm-1can be attributed to ν(S-Oa).The wild band at 3432 cm-1is featured of ν(O-H)in water,3083,1601,1450,1383, 450 cm-1are characteristic bands for N-methylpiperazine.As shown in Fig.1,the polyanion of compound 1 is the well-known Dawson-type structure[X2Mo18O62]n-[28], consisting of eighteen octahedral MoO6and two SO4pyramid.The Mo-O distances range from 0.1681(3)to 0.2507(3)nm,and the central SO4is a pyramid with SO bond distances of 0.1455(3)~0.1503(4)nm and O-SO angles ranging from 108.1(2)°to 110.62(15)°.All the bond angles and lengths above are consistent with the reported Dawson-type polyanions.The SO4pyramid and nine MoO6octahedra from three capped molybdenum atoms and six equatorial belt molybdenum atoms are linked together by μ4-O atom and μ3-O atom,and further joint the other hemisphere.The most interesting aspect of compound 1 is that there is complex hydrogen bondingbetweenprotonatedN-methylpiperazine cations and the Dawson structural molybdosulfate anions.As shown in Fig.2,each N-methylpiperazine links two polyanions by using N-H…O hydrogen bonding interactions to generate a 1D chain(Table 2). The distance of N…O is 0.294 4(10)~0.308 3(15)nm, while the angle of N-H…O is from 131°to 134°.The water molecules are located between the chains,and making the chains are more stable.Although Fe2O3was not included in the final product,it is necessary as the oxidant of SⅣ→SⅥ.

Fig.1Molecular structure of 1

Table 2Hydrogen bonds lengths and bonds angles

Fig.2N-methylpiperazine molecules link polyanions by using N-H…O hydrogen bonding interactions to generate a 1D chain in 1

Fig.4Polyanions are linked by protonated water H3O+and N-methylpiperazine cations by using hydrogen bonding interactions to form a soft 3D framework along the c axis

When we replaced Fe2O3with pyridine,the mixed MoⅤ/MoⅥmolobdosulfate 2 was obtained.The IR spectra of compound 2 shows intense absorption at 952, 801 and 685 cm-1are attributed to ν(Mo-Ot)or ν(Mo-Ob),the band at 1146 cm-1can be attributed to ν(S-Oa). The wild band at 3427 cm-1is featured of ν(O-H)in water,3083,1619,1451,1382,450 cm-1are characteristic bands for N-methylpiperazine and bipy.As shown in Fig.3,the asymmetric unit of 2 contains 103 non-hydrogen atoms.15 Mo,3 S and 56 O atoms belong tothetwocrystallographicindependentDawson structuralmolybdosulfatepolyanions.Themost significant aspect of compound 2 is that the polyanions are linked by protonated water H3O+and N-methylpiperazine cations by using hydrogen bonding interactions to form a soft 3D framework along the c axis (Table 2),as shown in Fig.4.The guest pyridine molecules are located in the channels.The assignment of the oxidation state of Mo atoms is based on the bond valence sum calculations[30],which gives the averagevalue 5.895 for oxidation state of Mo(expected value for 2 is 5.889),and the calculation result is consistent with the formula of 2.

3 Catalytic properties

According to our previous work,compounds 1,2 (100 mg)and styrene(0.75 mL,6.4 mmol)were stirred respectively and reacted in the 50 mL two-neck reaction flask with 7.5 mL acetonitrile as the solvent. The oxidation was performed in water constant reflux, and heated at 60℃by adding 2.1 mL hydrogen peroxide(30%)under the conditions of constant temperature in water bath.After 3 h,we sampled and used gas chromatography(GC-6890,FID;30 m×0.32 mm capillary column)to analyze products distribution,and the yields of epoxides were determined by GC analysis using internal standards,based on the Nitrobenzene. Under the same conditions,we did the blank compared test.The results showed the main products are benzaldehyde,and a small amount of benzoic acid.The conversions of styrene oxidation were represented in Table 3.The catalytic result indicates that the mixed MoⅤ/MoⅥcompound 2 has higher catalytic activity than 1.

Table 3Catalytic activity of compound 1 and 2 in the oxidation of styrene

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Syntheses,Characterization and Catalytic Properties of Two New Wells-Dawson Molybdosulfates

SUN Yue-Xia1ZHANG Zhi-Bin2SUN Qi＊,1XU Yan＊,1,2
(1Institute of Functionalized Chemistry Materials,Faculty of Chemistry and Chemical Engineering, Liaoning Normal University,Dalian,Liaoning 116029,China)
(2College of Chemistry and Chemical Engineering,State Key Laboratory of Materials-oriented Chemical Engineering,Nanjing University of Technology,Nanjing 210009,China)

Twonewwells-Dawsoncompounds[C5N2H14]2[S2MoⅥ18O62]·8H2O(1)and[C5N2H14]8(H3O)2[S2MoⅤ2MoⅥ16O62]3· (C5H5N)2(2)have been synthesized and characterized by single crystal X-ray analysis,IR spectra and elemental analysis.Single crystal X-ray diffraction confirms that compound 1 crystallizes in orthorhombic,a=1.799 29(17) nm,b=1.35804(13)nm,c=1.41926(13)nm,V=3.4680(6)nm3,Z=2.Compound 2,monoclinic,a=2.2665(3)nm, b=1.3749(2)nm,c=3.2912(5)nm,β=104.31(0)°,V=9.938(2)nm3,Z=4.Both compound 1 and 2 are built up of the Dawson-type molybdosulfate anions,full protonated N-methylpiperazine cations.The catalytic result in the oxidation of styrene indicates that the mixed MoⅤ/MoⅥcompound 2 has higher catalytic activity than 1.CCDC: 783378,1;783379,2.

molybdosulfate;crystal structure;hydrothermal synthesis;catalysis

O614.61+2

A

1001-4861(2011)03-0556-05

2010-09-20。收修改稿日期：2010-12-02。

國家自然科學(xué)基金(No.20771050、20971068)，遼寧省教育廳基金(No.2008T106)資助項目。

＊通訊聯(lián)系人。E-mail：yanxu@lnnu.edu.cn