孔治國 孫旭冉 李 赫 范艷佳 張 林

(吉林師范大學(xué)化學(xué)學(xué)院，吉林師范大學(xué)環(huán)境友好材料制備與應(yīng)用省部共建教育部重點實驗室，四平 136000)

0 Introduction

Recently,extensive attention has been focused on the design and synthesis of coordination polymers for their fascinating motifs and potential applications[1-5].Up to now,a wide range of one-,two-and three-dimensional infinite solid-state coordination architectures have been reported in the last decade[6-8]．Particularly, aromatic multi-benzenecarboxylate ligands together with N-based ligands have been extensively utilized in the construction of mixedligand coordination polymers[9-17]．Nevertheless,the coordination chemistry and structural properties of coordination polymers constructed by fatty carboxylates and chelating N,N-based ligands have been documented relatively little to date[8-17]．The succinic acid (H2L1),as a good candidate for the construction of coordination polymer,has two-CH2-spacers．Therefore,it can coordinate with metals in a flexible coordination mode and yield fascinating architectures．

On the other hand,1,10-phenanthroline(phen)and its derivatives have been used to construct supramolecular architectures owing their excellent coordination ability and large conjugated system that can easily form π-π interactions[8,10]．However,the combination of the phen derivatives and the different fatty dicarboxylates has not been well studied in coordination chemistry[11]．In this work,we report a new Pb（Ⅱ）coordination polymer based on L1 anion and 2-(4-fluorophenyl)- 1H-imidazo [4,5-f][1,10]phenanthroline(L2),[Pb2(L1)2(L2)2](1)．

1 Experimental

1.1 General

All materials were analytical reagent grade and used as received without further purification．Elemental analysis was carried out with a Perkin-Elmer 240C analyzer;IR spectrum was obtained on a Perkin-Elmer 2400LSII spectrometer．Thermogravimetric analysis(TGA)was performed on a Perkin-Elmer TG-7 analyzer in the rangefrom40 to800 ℃ under nitrogen gas．

1.2 Synthesis and crystal growth

A mixture of H2L1(1 mmol),Pb(NO3)2(1 mmol)and L2 (1 mmol)were dissolved in distilled water(10 mL)and ethanol (3 mL),which was heated at 170℃in a Teflon-lined stainless steel autoclave for 4 days．After the mixture had been cooled to room temperature at a rate of 10 ℃·h-1,crystals of 1 suitable for single-crystal X-ray diffraction analysis were collected by filtration,washing several times with distilled water and drying in air at ambient temperature．Yield:19%based on Pb（Ⅱ）．Anal．for C46H30F2N8O8Pb2(%):Calcd．:C 43．33,H 2．37,N 8．79;Found:C 43．21,H 2．17,N 8．63．IR (KBr,cm-1):ν=3471s,1 643m,1 564m,1 481w,1 415m,1 218w,1 132s,991w,826w,743w,618w,542w．

1.3 X-ray structure determination

A single crystal with dimension of 0．15 mm×0．12 mm×0．11 mm was selected and mounted on a Bruker Smart Apex CCD diffractometer equipped with a graphite-monochromatized Mo Kα (λ=0．071 073 nm)radiation by using an ω-2θscanning method at a temperature of 20±2 ℃ ．Out of the total 21284 reflections collected in the 1．29 ≤θ≤25．05°range,7332 were independent with Rint=0．0509,of which 5380 were considered to be observed (I＞2σ (I))and used in the succeeding refinement．

Absorption corrections were applied by using a multi-scan technique．The structure was solved by Direct Method with SHELXS-97 program[18]and refined with SHELXL 97[19]by full-matrix leastsquares techniques on F2．All non-hydrogen atoms were refined anisotropically and hydrogen atoms isotropically．All H atoms were positioned geometrically (N-H=0．086 nm and C-H=0．093 nm)and refined as riding,with Uiso(H)values set at 1．2 times Ueq(carrier)．The maximum residual electron density is 1 910 e·nm-3at 0．099 nm from Pb．The residual electron density can be interpreted as Fourier truncation error．The final R=0．038 0 and wR=0．084 5 (w=1/[σ2(Fo2)+(0．042 6P)2+0．000 0P],where P=(Fo2+2Fc2)/3)．S=0．968, (Δρ)max=1．909, (Δρ)min=-0．540 e·nm-3and(Δ/σ)max=0．003．

2 Results and discussion

2.1 Description of crystal structure

Selected bond lengths and angles for 1 are given in Table 1．As shown in Fig．1,the asymmetric unit of 1 has two crystallographically independent Pb（Ⅱ）atoms,two unique L1 anions,and two unique L2 ligands．Each Pb（Ⅱ） atom is six-coordinated by twonitrogen atoms from one L2 ligand,and four carboxylate oxygen atoms from two different L1 anions．The Pb-O distances range from 0．244 9(5)to 0．268 0(5)nm,which are comparable to the reported Pb-O distances found in related coordination polymer[Pb(ndc)(ptcp)]·0．5H2O(ndc=1,4-naphthalenedicarboxylate and ptcp=2-phenyl-1H-1,3,7,8-tetraazacyclopenta[l]phenanthrene)[6]．Each L1 anion coordinates with two Pb（Ⅱ） atoms in a bis-chelating mode．In this fashion,the L1 anions bridge neighboring Pb（Ⅱ）atoms to generate a 1D chain structure (Fig．2)．Interestingly,the L2 ligands are attached on both sides of the chain．Moreover,neighboring 1D chains are linked together by π-π stackings between the quinoline ring systems[N1/C20-C31 at(x,y,z)and N5/C1-C12 (1-x,1-y,2-z)]of the L ligands(centroid-to-centroid distance of ca．0．354 nm and face-to-face distance of 0．347 nm)among L2 ligands from neighboring chains to yield a fascinating 3D supramolecular architecture(Fig．3)．As listed in Table 2,the N-H…O hydrogen-bonding interactions further consolidate the 3D supramolecular architecture of 1．

Table 1 Selected bond distances(nm)and angles(°)

Table 2 Hydrogen bonds for complex 1(nm)and angles(°)

Fig.1 View of the coordination environments of Pb（Ⅱ）atoms in 1(displacement ellipsoids at the 15%probability level)

Fig．2 View of the one-dimensional chain structure of 1

Fig．3 View of the three-dimensional supramolecular architecture of 1 formed by π-π interactions

Fig．4 IR spectrum of the complex 1

Fig．5 TGcurve of complex 1

2.2 IR analysis

The solid-state IR spectrum of 1 is shown in the region of 4 000～400 cm-1(Fig．4)．The strong peaks at 1 643 and 1 564 cm-1correspond to the asymmetric and symmetric vibrations of carboxylate groups of the L1．The broad band at 3 471 cm-1may come from the stretching vibrations of N-H bond of L2 ligand．The C-N and C=N stretching vibrations of L2 ligand are observed at 1 132 and 1 415 cm-1[20]．

2.3 Thermogravimetric analysis

In order to characterize the compound more fully in terms of thermal stability,thermogravimetric property of compound 1 was performed．The experiment was conducted under N2atmosphere with a heating rate of 10℃·min-1from room temperature to 800 ℃ (Fig．5)．The first weight loss in 150～405 ℃(Obsd．17．6%,Calcd．18．2%)can be attributed to the release of L1 anion．The next weight loss from 405 to 575℃corresponds to the decomposition of L ligand(Obsd．48．2%,Calcd．49．3%)．

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