Synthesis,Crystal Structure of Uranium-Potassium Heteronuclear Coordination Polymer

WANG JuanL XinLI Zi-YingZHANG Yu-YanCHENG Shi-Yuan

(1School of Chemistry and Chemical Engineering,Hubei University,Wuhan 430062,China)

(2Beijing Research Insititute of Uranium Geology,Beijing 100029,China)

Synthesis,Crystal Structure of Uranium-Potassium Heteronuclear Coordination Polymer

WANG Juan＊,1LXin1LI Zi-Ying＊,2ZHANG Yu-Yan2CHENG Shi-Yuan1

(1School of Chemistry and Chemical Engineering,Hubei University,Wuhan430062,China)

(2Beijing Research Insititute of Uranium Geology,Beijing100029,China)

A novel U（Ⅵ）-K heteronuclear coordination polymer UO2K2(pdc)2·3H2O(H2pdc=pyridine-2,6-dicarboxylic acid)has been synthesized hydrothermally and determined by means of IR,UV and X-ray single-crystal diffraction methods.The single-crystal X-ray analysis of the complex reveals that the crystal belongs monoclinic,space group C2/c with a=1.888 5(6)nm,b=1.490 0(5)nm,c=0.740 2(2)nm,β=111.104(10)°.The centered uranium atom and potassium atoms are bonded to two pdc ligands via two nitrogen atoms and six oxygen atoms.Different[UO2K2(pdc)2· 3H2O]units are bridged by oxygen atoms to form three-dimensional chain coordination polymer.In addition,there are π…π stacking interactions and hydrogen bonds in the coordination polymer.CCDC:727858.

uranium;pyridine-2,6-dicarboxylic acid;coordination polymer;crystal structure

The chemistry ofmetal-organic coordination assemblies has been enriched enormously in the past two decades,and a variety of coordination assembly polymers have been discovered[1].Uranium ions have attracted considerable interestbecause oftheir reactivity,coordination behavior,bonding interactions between the metal center and ligand and their possible applications[2].

Recently,the construction ofuranyl-organic assemblies has attracted increasing interest,and a number of coordination compounds formed through the connection of uranyl units with various organic ligands have been prepared and structurally characterized. From a structural point of view,the uranyl ion is likely to form U-O (or U-F,U-N)polyhedra,which may be cross-linked by organic and/or inorganic components into chains,sheets,or three-dimensional frameworks. Furthermore,the U-O (or U-F,U-N)polyhedra havestrong tendency to polymerize into various polynuclear clusters such as dinuclear,trinuclear,and tetranuclear clusters,infini te chains,or sheets of different local structures.As a result,a very rich structural chemistry may be found for uranyl-organic assembly polymers.Recently the synthesis and crystal structures of mixed uranyl/alkali metal ions complexes with homooxacalixarenes have been published[3-4].H2pdc(pyridine-2,6-dicarboxylic acid)is an effcient ligand which is usually used as a tridentate ligand,as well as a bridging linker in the chemical design of metal-organic molecular assemblies[5-9].

1 Experimental section

1.1 Materials and physical measurements

Allmaterialsand organic solventswere of analyticalgrade and were used withoutfurther purification.Distilled deionized water was used throughout.Elemental analyses (C,H,and N)were performed on a Perkin-Elmer 2400ⅡCHNSO elemental analyzer.The infrared spectrum was recorded as a KBr pellet on a Nicolet 170SXFTIR spectrometer in the range 400～4 000 cm-1.Thermogravimetric analyses (TG/DTA)were performed in flowing nitrogen gas on a Perkin-Elmer-7 instrument with a heating rate of 10℃· min-1from room temperature to 900℃.The electronic absorption spectra were taken on a Shimadzu UV-240 spectrophotometer.

1.2 Synthesis of the complexes

UO2(0.134 0 g)was solved in hot HCl(38%), H2pdc was added into this solution.The mixture was stirred for half an hour in air,and the solution pH was adjusted to 4.8 by the addition of KOH (2 mol·L-1) solution.The mixture was then transferred to a Teflonlined stainless steel autoclave(25 mL)and kept at 170℃ for 5 d.After the autoclave had cooled to room temperature,giving a blue solution.The resulting solution was evaporated slowly at room-temperature.After several days,crystals of this polymer were formed.Dry crystals disintegrated in air.Anal.Calc.for C14H12K2N2O13U(%):C,22.94;H,1.64;N,3.82.Found (%):C,23.90;H,1.56;N,3.86.

1.3 X-ray crystal structure determination

Single-crystal X-ray crystallographic analyses was performed at 291(2)K on a Bruker SMART APEX CCD diffractometer with graphite monochromated Mo Kα(λ= 0.071 073 nm)radiation.Data collection,indexing,and initial cell refinements were carried out using SMART software[10].Frame integration and final cell refinements were carried out using SAINT software[11].Absorption corrections for each data set were applied using SADABS program[12].The single Crystal structure of title compound was solved by direct methods using the SHELXS[13]and refined on F2by the full-matrix leastsquares methods using the SHELXL program[13],All non-hydrogen atoms were refined anisotropically and hydrogen atoms were located at their ideal positions as a riding mode.A summary of the crystallographic data and structural determination for the title polymer is listed in Table 1.Selected bond lengths and bond angles are provided in Table 2.More details on the crystallographic studies as well as atom displacement parameters are presented in the Supporting Information.

CCDC:727858.

Table 1 Crystallographic parameters of the title complex

Table 2 Main bond length(nm)and bond angles(°)of the title complex

2 Results and discussion

2.1 Description of the crystal structure

Single-crystal X-ray structural analysis reveals that the uranium ion is eight coordinated.The axial positions of the dodecahedron are occupied by O5 atoms.The local coordination environment around U is depicted in Fig.1.Two ligands coordinate to uranium ion through four oxygen atoms and two nitrogen atoms. The U1-O3(pdc),U1-O1(pdc)bond distances ranging from 0.244 1(6)to 0.245 6(6)nm.U1-N1 bond distance is 0.266 5(8)nm.Both of uranium ion and two pdc ring are in the same plane,two O5 atoms at“polar”position and two pdc ligands at“equator”position.U1-O5 bond distance is 0.175 9(6)nm.While the O5-U1-O5 angles is 180.0(6)°.K+is eight-coordinated.O1,O3,O5 still connect with K1,K1-O1,K1-O3,K1-O5 bond distances ranging from 0.310 0(7)to 0.295 6(7)nm,the U1-O1-K1,U1-O3-K1,U1-O5-K1 angles are 88.21(19)°, 91.86(19)°,107.9(3)°.The four O atoms of pdc all ligate diffrentpotassium atoms.O1-K1-O3 angles is 48.13(17)°.K1-O4(pdc),K1-O2(pdc)bond distances ranging from 0.286 3(7)to 0.302 3(6)nm.O2-K1-O4 angles is 163.38(19)°. Potassium atoms connect with each other through O7,O6.K1-O7 distance is 0.2782(7)nm,K1-O6 is 0.2713(6)nm.K1-O6-K1,K1-O7-K1 angles are 97.6(3)°,103.6(2)°

Fig.1 Crystal structure of the coordination polymer

One U1 and two K1 atoms are bridged by three oxygen atoms,two free oxygen atoms and an oxygen atom from the pdc.Two potassium atoms are bridged by one oxygen atom from water.The interesting structural feature is to note that different[UO2K2(pdc)2·3H2O] units are linked by O4 from pdc and O6 from water to form a one-dimensional chain coordination polymer down c axis(Fig.2).Meanwhile,different[UO2K2(pdc)2· 3H2O]units are also bridged by O7 from water to form another one-dimensional chain coordination polymer down a axis.Furthermore,the two-dimensional chain structures are associated with each other via O6,so that a 3D framework is formed(Fig.3).

Fig.2 1D chain coordination polymer structure of the coordination polymer down c axis

The important intermolecular interaction is the offset face-to-face π…π stacking interaction between the benzene rings.The shortest π…π centroid-tocentroid distance between the offsetface-to-face (dihedral angle between the two benzene rings is 5.85°) aromatic rings of neighbouring pdc ring is 0.370 2 nm, hence,the π…π stacking interactions are very strong, lying in the range of reported distance 0.33～0.38 nm[14].The hydrogen bonds have also been observed,which is shown in Table 3.The existences of hydrogen bonds increase the stability of the structure.

Fig.3 Packing of the molecules in a unit cell of the coordination polymer

Observed alonga* axis,polymershowed a network structure,we can see same quadrilateral holes.The hole′s area is 0.4229 nm×0.2441 nm.This structure may have potential application value for the screening of match size of the molecules or molecular recognition.

Table 3 Hydrogen bonds length and bond angles of the title compound

2.2 IR/UV spectra

The FTIR spectrum of the complex is consistent with the structural data.Characteristic bands of the dicarboxylate groups are at 1625 and 1586 cm-1due to the asymmetric stretching.The strong band at the 3406 cm-1(O-H stretching vibration)indicates the presence of uncoordinated water molecules.The peak at 1 425 cm-1is assigned to the absorption of C=N group of pdc.

The UV spectrum of the complex was obtained in H2O solution with H2O as a reference.Two absorption bands at 225 and 267 nm were observed,they are strong and sharp,which may arise from the π→π* transition of ligands.

2.3 TG analyses

The TGA measure (Fig.4)shows a three-step weight loss:the first loss of 4.48%occurs between room temperature and 71.5℃,corresponding to the loss of two coordinated water molecules,(calc.4.37%).The second weight loss of 23.43%occurs in the range of 300～413℃,resulting from the release of one pdc molecule(calc.22.26%).The third step was attributed to the removal of another pdc ligand and Inorganic components from 448 to 689℃with the lost weight of 58.50%.

Fig.4 TG curve of the coordination polymer

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铀-钾异核配位聚合物的合成及晶体结构

王 娟＊,1吕 鑫1李子颖＊,2张玉燕2程时远1

(1湖北大学化学化工学院，武汉 430062)
(2核工业部北京地质研究院，北京 100029)

在水热反应条件下合成了1种新颖的U（Ⅵ）-K异核配位聚合物[UO2K2(pdc)2(H2O)3]n(H2pdc=吡啶-2，6-二羧酸)，通过元素分析、红外、紫外光谱及热重对该配合物进行了表征。单晶结构表明：配合物属于单斜晶系，C2/c空间群；晶胞参数分别为a= 1.8885(6)nm，b=1.4900(5)nm，c=0.7402(2)nm，β=111.104(10)°。中心铀及钾原子通过2个氮原子和6个氧原子与吡啶-2,6-二羧酸配体结合。不同的[UO2K2(pdc)2]·3H2O单元通过氧原子桥联组成三维链状配位聚合物。配位聚合物中存在π…π相互作用及氢键作用。CCDC：727858。

铀；吡啶-2，6-二羧酸；配位聚合物；晶体结构

O614.62；O614.113

A

1001-4861(2011)03-0580-05

2010-04-06。收修改稿日期：2010-11-19。

国防基础项目(No.A0120060596-06)，湖北省自然科学基金(No.2009CDB164)资助。＊

。E-mail：wangjuan_hd@163.com