ORIGINAL PAPER

A New Two-Dimensional Lead(II) Coordination PolymerContaining Left- and Right-Handed Helical Chains Constructedfrom 1H-Benzimidazole-2-carboxylic Acid

Jun Wang • Jian-hua Nie • Ping-hui Li

Received: 4 July 2013 / Accepted: 8 January 2014 / Published online: 22 January 2014

� Springer Science+Business Media New York 2014

Abstract A new two-dimensional lead(II) coordination

polymer, [Pb(C10H5N3O4)]n, was prepared by reacting lead

nitrate with 1H-benzimidazole-2-carboxylic acid (H2BI2C)

under solvothermal conditions. The asymmetric unit of the

compound contains one crystallographically independent

PbII cation and one unique BI2C2- dianion. The PbII ion is

five-coordinated by three carboxylate O atoms and two

imidazole N atoms from three different BI2C2- dianions,

displaying an interesting hemidirected coordination. It is

worth noting that the BI2C2- group acts as a l3-bridging

ligand to link the PbII ions into a two-dimensional layer,

which is composed of left- and right-handed helical chains.

This two-dimensional layer can be simplified as a 3-con-

nected fes topology with the Schlafli symbol of (4�82). In

addition, the title compound shows an intense emission at

549 nm when excited at 353 nm, and it displays a high

thermal stability up to 410 �C.

Keywords Lead � 1H-benzimidazole-2-carboxylic acid �Coordination polymer � Crystal structure � Helical �Solvothermal synthesis

Introduction

The rational design and construction of metal–organic

coordination polymers have attracted considerable attention

in the recent decades, not only for their structural diversity

and intriguing topologies, but also for their potential appli-

cations as important solid-state materials in the fields of gas

storage, catalysis, separation, chemical sensors, and so on

[1–4]. In order to prepare such materials, judicious selection

of multifunctional organic ligands containing suitable

coordination sites is one of the various factors to be taken

into consideration. Recently, 1H-benzimidazole-5-car-

boxylic acid (H2BI5C), a kind of N-Heterocyclic carboxylic

acid ligand that contains two N atoms of an aromatic group

and one carboxylate group, has received significant interest

in construction of new metal–organic coordination polymers

due to its outstanding features of versatile coordination

modes under hydro(solvo)thermal conditions. Up to now, a

great number of one-, two- and three-dimensional coordi-

nation polymers based on the H2BI5C ligand have been

reported [5–8]. In contrast to the well-studied H2BI5C, 1H-

benzimidazole-2-carboxylic acid (H2BI2C), another benz-

imidazole carboxylate ligand bearing the carboxylate group

on the 2-position rather than 5-position, remains still unex-

plored until now [9, 10]. The H2BI2C ligand also can be

successively deprotonated to yield HBI2C- and BI2C2-

species under certain conditions, thus it will be an ideal

candidate for preparing new coordination polymers.

On the other hand, most of the new coordination poly-

mers reported so far are assembled from transition metals

or lanthanide metals, whereas coordination polymers built

from main group metals, especially the lead(II) metal ion,

remain less developed. The lead(II) ion, which bears a

stereochemically active electron lone-pair and large ionic

radius, can display both hemidirected and holodirected

coordination geometries with various coordination num-

bers ranging from two to ten. Therefore, the coordination

chemistry of lead(II) ion has recently been investigated and

it is also proved to be a good choice for constructing new

coordination polymers with structural diversity [11–13].

J. Wang � J. Nie � P. Li (&)

Zhongshan Polytechnic, Zhongshan, Guangdong 528404,

People’s Republic of China

e-mail: lipinghui200@163.com

123

J Chem Crystallogr (2014) 44:103–107

DOI 10.1007/s10870-014-0490-x

On the basis of the arguments above, we decide to

choose H2BI2C as a multidentate organic ligand and lea-

d(II) salt as a metal source to construct new coordination

polymers. As expected, a two-dimensional lead(II) coor-

dination framework, formulated as [Pb(C10H5N3O4)]n, has

been successfully prepared by the reaction of Pb(NO3)2

with H2BI2C ligand under solvothermal conditions. The

as-synthesized sample was characterized by single crystal

X-ray diffraction study, infrared spectra, as well as ele-

mental analysis. In addition, the thermal stability and

photoluminescent properties of this compound were also

studied in this paper.

Experimental

Materials and Methods

All reagents were purchased from commercial sources and

used without further purification. C, H, and N microanal-

yses were carried out on a Perkin–Elmer 240 elemental

analyzer. The FT-IR spectra were recorded by using a

Nicolet 5DX spectrometer in KBr pellets.

Synthesis of the Compound, [Pb(C10H5N3O4)]n

A mixture of PbNO3 (99.3 mg, 0.300 mmol), H2BI2C

(48.6 mg, 0.300 mmol), and CH3CN/H2O (1/1, 6 mL) was

sealed in a 15 mL Teflon-lined stainless steel autoclave and

then heated at 393 K for 48 h under autogenous pressure.

After cooling to room temperature, yellow block-shaped

crystals of the title compound were collected (yield: 46 %).

Anal. Calcd. for C8H4N2PbO2: C, 26.16, H, 1.10, N,

7.63 %; Found: C, 26.24, H, 1.07, N, 7.55 %. FT-IR (KBr

pellet, cm-1): 2,924 (m), 2,852 (w), 1,572 (s), 1,561 (s),

1,485 (m), 1,421 (s), 1,413 (s), 1,334 (m), 1,298 (w), 1,258

(w), 1,119 (w), 993 (w), 909 (w), 862 (w), 808 (w), 741 (s),

638 (w), 590 (w), 450 (w), 422 (w).

Fluorescence Studies

Solid-state fluorescent spectra were measured with an

Edinburgh FLS920 spectrophotometer at room tempera-

ture. A bulk of single crystalline sample of the title com-

pound was well ground and then slightly pressed into a

piece of glass to get a film for fluorescence measurement.

In the measurements of emission and excitation spectra, the

pass width was 5 nm.

Thermogravimetric Analysis (TGA)

TGA experiment was performed on a Perkin–Elmer TGA7

analyzer under a flow of air. The flow rate of the air was

controlled at about 80 mL min-1. A total of 15.828 mg of

the ground single crystalline sample was heated at a rate of

10 �C min-1 from room temperature to 800 �C.

Table 1 Crystallographic data and structure refinement of the title

compound

CCDC deposit no. CCDC-948393

Empirical formula C8H4N2O2Pb

Formula weight 367.32

Temperature (K) 298 (2)

Wavelength (A) 0.71073

Crystal system Monoclinic

Space group P2(1)/c

a (A) 16.125 (6)

b (A) 5.4005 (19)

c (A) 9.078 (3)

a (�) 90

b (�) 104.108 (4)

c (�) 90

V (A3) 766.8 (5)

Z 4

Dc (g cm-3) 3.182

l (mm- 1) 21.962

F (000) 656

Crystal size/mm 0.32 9 0.25 9 0.20

h range for data collection (�) 2.60–25.25

Max., min. transmission 0.0965, 0.0539

Reflections collected 2721

Unique reflections 1,347

Number of parameters 118

Rint 0.0395

Final R indices [I [ 2r(I)] R1 = 0.0797, wR2 = 0.2563

R indices (all data) R1 = 0.0881, wR2 = 0.2700

Goodness-of-fit 1.098

R1 =P

||F0| - |Fc||/P

|F0|, wR2 = {P

[w(F02-Fc

2)2]/P

(F02)2}1/2

Table 2 Selected bond lengths (A) and angles (�) for the title

compound

Bond lengths (A)

Pb1–O1 2.328(7) Pb1–N2#1 2.448(12)

Pb1–O2#1 2.567(7) Pb1–N1 2.573(9)

Pb1–O1#2 2.712(6)

Bond angles (�)

O1–Pb1–N2#1 79.0(3) O1–Pb1–O2#1 81.3(3)

N2#1–Pb1–O2#1 67.9(3) O1–Pb1–N1 69.4(3)

N2#1–Pb1–N1 81.1(3) O2#1–Pb1–N1 140.8(3)

O1–Pb1–O1#2 64.5(2) N2#1–Pb1–O1#2 124.8(3)

O2#1–Pb1–O1#2 66.8(3) N1–Pb1–O1#2 118.5(3)

Symmetry transformations used to generate equivalent atoms: #1 x,

-y ? 3/2, z-1/2; #2 -x, -y ? 1, -z

104 J Chem Crystallogr (2014) 44:103–107

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X-ray Crystallography

Intensities of reflections were measured by using graphite

monochromatized Mo Ka radiation (k = 0.71,073 A) at

298(2) K. Multiscan absorption corrections were applied

with the SADABS program [14]. The structure was solved

by direct methods using the program SHELXS 97 [15] and

refined by full-matrix least-squares on F2 using SHELXL

97 [15]. All non-hydrogen atoms were treated anisotropi-

cally. The H atoms bonded to C atoms were placed at

calculated positions (C–H = 0.93 A) and refined as riding

atoms with Uiso(H) = 1.2Ueq(C). Crystallographic data and

experimental details for structural analysis are summarized

in Table 1. Selected bond lengths and angles are listed in

Table 2.

Results and Discussion

Crystal Structure

Single crystal X-ray diffraction shows that the title com-

pound crystallizes in the monoclinic space group P21/c,

and the asymmetric unit consists of only one crystallo-

graphically independent PbII cation and one unique BI2C2-

dianion. As it depicted in Fig. 1, the PbII cation is penta-

coordinate by three carboxylate oxygen atoms and two

imidazole nitrogen atoms from three individual BI2C2-

dianions. Obviously, the coordination environment of the

PbII atom is hemidirected, indicating that the empty space

around the metal center may be filled by the stereochem-

ically active 6S2 electron pair [16]. The Pb–N bond lengths

are ranging from 2.448(12) to 2.573(9) A, and the Pb–O

bond distances are varying from 2.328(7) to 2.712(6) A, all

of which are comparable to those observed for other Pb(II)

coordination polymers with nitrogen and oxygen donor

ligands [11, 12]. It is noteworthy to mention that the unique

BI2C2- anion, in which both the carboxyl group and the

imidazole N–H group are all deprotonated, adopts an

interesting coordination mode named l3-kN,O:kO:kN0,O0

coordinated mode to connect three PbII ions in bis-N,O-

chelating and O-bridging fashions, as described in

Scheme 1.

On the basis of the above-mentioned coordination

mode of BI2C2- ligand, every PbII ion links to three l3-

BI2C2- ligands and every l3-BI2C2- ligand connects to

three PbII ions, thus resulting in the formation of a new

two-dimensional [Pb(BI2C)]n layer in the bc plane, as

illustrated in Fig. 2b. Further investigation indicates that

this two-dimensional layer involves two types of inter-

esting one-dimensional helical infinite chains (Fig. 2a),

where the right-handed and left-handed helical chains are

in an alternate array by sharing the l3-BI2C2- bridging

ligands (Fig. 2b). In both the right-handed and left-handed

helical chains, the pitch is equivalent as the length of the

b-axis, while the adjacent nonbonding Pb���Pb distance is

equal to 5.833(2) A. The overall structure is apparently

achiral because the chirality is offseted by the pairs of

right-handed and left-handed helical chains. Moreover, the

benzimidazole rings project from both sides of the two-

dimensional [Pb(BI2C)]n layer. These two-dimensional

layers are stacked along the a direction in an –AAAA-

sequence (Fig. 3) and it is discovered that no noticeable

interaction is existing between the neighbouring layers.

To better understand the two-dimensional structure of

this compound, the topology analysis is employed to

describe the architecture. If both the PbII ion and l3-

BI2C2- ligand are regarded as 3-connected nodes, the

overall framework of the title compound can be described

as a 3-connected fes topology [17] with the Schlafli symbol

of (4�82), as presented in Fig. 4.

IR Spectrum

The IR spectrum of the title compound displays strong

typical bands of the carboxyl group at 1,572 and

1,561 cm-1 for the antisymmetric stretching vibration, and

Scheme 1 The coordination mode of H2BI2C ligand

Fig. 1 The structure of the title compound, showing the atom-

numbering scheme. Displacement ellipsoids are drawn at the 30 %

probability level [symmetry codes: (i) x, -y ? 3/2, z - 1/2; (ii) -x,

-y ? 1, -z]. Inset the geometry of the pentacoordinate PdII cation,

showing that PdII cation is in the hemidirected coordination

environment

J Chem Crystallogr (2014) 44:103–107 105

123

at 1,421 and 1,413 cm-1 for symmetric stretching vibra-

tion, respectively. The absence of strong characteristic

absorption around 1,700 cm-1 indicates that the carboxylic

group is deprotonated. The IR spectrum of the compound is

consistent with the crystal structure.

Fluorescence Properties

The photoluminescent behaviors of the title compound and

free ligand H2BI2C were investigated in the solid state at

room temperature. As presented in Fig. 5, the compound

exhibits strong green photoluminescence with a maximum

emission band at 549 nm when excited at 353 nm. While

Fig. 2 a A space-filling view of the right-handed and left-handed one-dimensional helical chains in the compound. b The two-dimensional

[Pb(BI2C)]n achiral layer of the compound in the bc plane (phenyl units of the BI2C2- ligands have been omitted for clarity)

Fig. 3 A view of the packing of the compound, viewed along the

b axis

Fig. 4 Schematic illustrating the 3-connected fes network with the

Schlafli symbol of (4�82) in the compound

Fig. 5 The photoluminescent spectra of H2BI2C ligand (blue line)

and the title compound (black line) in the solid state at room

temperature (Color figure online)

106 J Chem Crystallogr (2014) 44:103–107

123

the free H2BI2C ligand exhibits a maximum emission at

440 nm upon excitation at 350 nm. Compared with the free

ligand, the largely red-shifted emission for the compound

may be attributed to the ligand-to-metal charge transfer

(LMCT) [18].

Thermal Analysis

In order to examine the thermal stability of the title com-

pound, we carried out TGA. The crystal sample of the

compound was heated up to 800 �C in air atmosphere at the

rate of 10 �C min-1, and the result is shown in Fig. 6. It

can be seen from the TGA curve that there is no noticeable

weight loss below the temperature of 410 �C. Heating

above this temperature resulted in the decomposition of the

compound. This thermal behavior indicates that this com-

pound is endowed with a high thermal stability, which may

be attributed to the lack of solvent molecules in the crystal

structure. To the best of our knowledge, only a few coor-

dination polymers displaying such excellent thermal sta-

bilities have been reported [19, 20].

Supporting Information

CCDC-948393 contains the supplementary crystallo-gra-

phic data for this paper. Copy of the data can be obtained

free of charge via www.ccdc.cam.ac.uk/data_request/cif by

e-mailing data_request@ccdc.cam.ac.uk, or by contacting

The Cambridge Crystallographic Data Centre (CCDC), 12

Union Road, Cambridge CB2 1EZ, UK; fax: ?44-1223-

336033.

Acknowledgments The authors gratefully acknowledge the Science

and Technology Research Project of Zhongshan City (Grant No.

20114A256).

References

1. Kreno LE, Leong K, Farha OK, Allendorf M, Duyne RPV, Hupp

JT (2012) Chem Rev 112:1105–1125

2. Li JR, Sculley J, Zhou HC (2012) Chem Rev 112:869–932

3. Suh MP, Park HJ, Prasad TK, Lim DW (2012) Chem Rev

112:782–835

4. Yoon M, Srirambalaji R, Kim K (2012) Chem Rev

112:1196–1231

5. Chen LC, Huo SM, Chen HZ, Yang YQ, Zeng RH (2011) Acta

Cryst E 67:m1312–m1313

6. Guo ZG, Li XJ, Gao SY, Li YF, Cao R (2007) J Mol Struct

846:123–127

7. Peng G, Qiu YC, Liu ZH, Liu B, Deng H (2010) Cryst Growth

Des 10:114–121

8. Yao YL, Che YX, Zheng JM (2008) Inorg Chem Commun

11:883–885

9. Fan J, Cai SL, Zheng SR, Zhang WG (2011) Acta Cryst C

67:m346–m350

10. Małecki JG, Maron A (2012) Polyhedron 40:125–133

11. Xu H, Chao ZY, Sang YL, Hou HW, Fan YT (2008) Inorg Chem

Commun 11:1436–1440

12. Yang J, Ma JF, Liu YY, Ma JC, Batten SR (2009) Cryst Growth

Des 9:1894–1911

13. Zhang KL, Chang Y, Hou CT, Diao GW, Wu RT, Ng SW (2010)

CrystEngComm 12:1194–1204

14. Sheldrick GM (1997) SADABS. University of Gottingen, Got-

tingen, Germany, Program for Bruker Area Detector Absorption

Correction

15. Sheldrick GM (1977) SHELXS 97. University of Gottingen,

Gottingen, Germany, Program for the Solution of Crystal

Structures

16. Shimoni-Livny L, Glusker JP, Bock CW (1998) Inorg Chem

37:1853–1867

17. Gong Y, Wu T, Li JH, Lin JH (2012) Inorg Chem Commun

19:39–42

18. Allendorf MD, Bauer CA, Bhakta RK, Houk RJT (2009) Chem

Soc Rev 38:1330–1352

19. Liu YY, Zhang J, Sun LX, Xu F, You WS, Zhao Y (2008) Inorg

Chem Commun 11:396–399

20. Wu MF, Xu G, Zheng FK, Liu ZF, Wang SH, Guo GC, Huang JS

(2011) Inorg Chem Commun 14:333–336

Fig. 6 The TGA curve for the title compound

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