www.elsevier.com/locate/inoche

Inorganic Chemistry Communications 8 (2005) 212–215

Synthesis and characterization of infinite coordination networksfrom a hybrid ligand N-(4-pyridylmethyl)imidazole

Zheng Liu a,b, Ping Liu a,*, Yun Chen a,b, Jian Wang a, Meihua Huang a,b

a Fujian Institute of the Research on the Structure of Matter, Chinese Academy of Sciences, 155 Yangqiao West Road, Fuzhou 350002, PR Chinab Graduate School of the Chinese Academy of Sciences, Beijing 100039, PR China

Received 13 November 2004; accepted 1 December 2004

Abstract

Three cadmium(II) coordination polymers formed from pyim [pyim = N-(4-pyridylmethyl)imidazole], namely 24[Cd(pyim)2X2]n

(X@Cl, 1; Br, 2; I, 3), have been synthesized and characterized by IR, and fluorescence spectroscopy as well as TG analysis.

� 2004 Elsevier B.V. All rights reserved.

Keywords: Metal–organic compound; Hybrid; Unsymmetrical; Flexibility; Counter anions

Design and synthesis of organic and metal–organic

compounds with unusual and tailorable structures are

fundamental steps to discover and fabricate various

functional supramolecular devices or technologically

useful materials [1]. There has been much interest and

progress recently in the study of crystal engineering of

supramolecular architectures organized and sustainedby means of ligands including pyridine and imidazole

moieties. Herein, the ligand N-(4-pyridylmethyl)imidaz-

ole (pyim) is synthesized. Pyim can be considered as a

hybrid of 4,4 0-bipyridine and 2,2 0-biimidazole, which

are versatile N-donor ligands in transition metal chemis-

try [2]. Its chemistry, which has not been explored thor-

oughly [3], is our concern here. From a structural point

of view, it should be pointed out that (1) this ligand, un-like the rigidity of bipyridine, possesses flexibility owing

to the presence of a –CH2– spacer between the pyridyl

ring and imidazole moiety; (2) if both N-donor sites

can coordinate to the metal center, the pyim can act as

l2-bridging ligand. Accordingly, a grid-like structure

may be expected by introducing metal ions favoring

1387-7003/$ - see front matter � 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.inoche.2004.12.001

* Corresponding author. Tel.: +86 591 83704960; fax: +86 591

83714648.

E-mail address: pliu@ms.fjirsm.ac.cn (P. Liu).

tetra- or hexa-coordination mode, and the flexibility of

pyim may result in a novel framework; (3) due to its

unsymmetrical nature, pyim can be considered as a

potential ligand for the construction of acentric solids

based on two-dimensional (2D) grids [4]. Among our

attempts, three polymers, namely 24[Cd(pyim)2X2]n

(X@Cl, 1; Br, 2; I, 3), were obtained as crystals suitablefor single-crystal X-ray analysis.

The crystal structure of 1 is isomorphous with those

of the bromide and iodine derivatives 2 and 3. Reason-

ably, also the most relevant molecular and conforma-

tional parameters are similar, except for the small

influence of the limited covalent radius of Cl vs. Br

and I. Therefore, a complete analysis of the bromine

and iodine derivatives were not performed.The crystallographic analysis [5] reveals that com-

pound 1 crystallizes in the centrosymmetric space group

P21/c. The asymmetric unit contains one cadmium atom

lying on a crystallographic twofold axis, one chlorine

donor and one N-(4-pyridylmethyl)imidazole bridging

group. In order to develop new second-order nonlinear

optic materials, Thompson and co-workers [6] had re-

ported an inorganic coordination polymer where mole-cules are aligned in a head-to-tail arrangement along

the polymer backbone. This bridging ligand N-(4-pyr-

Fig. 1. Local coordination environment around Cd(II) atom in 1, 2,

and 3 (X@Cl, 1; Br, 2; I, 3). Selected bond lengths (A) and angles (�):For 1: Cd(1)–N(2) 2.318(4), Cd(1)–N(1A) 2.425(4), Cd(1)–Cl(1)

2.6208(13) and N(2B)–Cd(1)–N(1A) 94.68(15), N(2B)–Cd(1)–N(1C)

85.32(15), N(2)–Cd(1)–Cl(1B) 91.46(11), N(2)–Cd(1)–Cl(1) 88.54(11),

N(1A)–Cd(1)–Cl(1B) 90.65(11), N(1A)–Cd(1)–Cl(1) 89.35(11). Sym-

metry operation: A x � 1, �y + 3/2, z � 1/2; B �x + 1, �y + 2, �z + 1;

C �x + 2, y + 1/2, �z + 3/2; For 2: Cd(1)–N(2) 2.341(4), Cd(1)–N(1A)

2.419(4), Cd(1)–Br(1) 2.7679(4) and N(2B)–Cd(1)–N(1A) 94.53(13),

N(2B)–Cd(1)–N(1C) 85.47(13), N(2)–Cd(1)–Br(1B) 91.54(9), N(2)–

Cd(1)–Br(1) 88.46(9), N(1A)–Cd(1)–Br(1B) 89.99(9), N(1A)–Cd(1)–

Br(1) 90.01(9). Symmetry operation: A x � 1, �y + 1/2, z � 1/2; B �x,

�y + 1, �z + 1; C �x + 1, y + 1/2, �z + 3/2; For 3: Cd(1)–N(2)

2.362(4), Cd(1)–N(1A) 2.426(4), Cd(1)–I(1) 2.9895(3) and N(2B)–

Cd(1)–N(1A) 94.02(16), N(2B)–Cd(1)–N(1C) 85.98(16), N(2)–Cd(1)–

I(1B) 91.67(10), N(2)–Cd(1)–I(1) 88.33(10), N(1A)–Cd(1)–I(1B)

89.45(11), N(1A)–Cd(1)–I(1) 90.55(11). Symmetry operation: A x + 1,

�y + 1/2, z + 1/2; B �x + 1, �y + 1, �z + 2; C �x, y + 1/2, �z + 3/2.

Fig. 2. The two-dimensional layer structure of 1. The grids have the same dim

about 14.215 · 16.892 A.

Z. Liu et al. / Inorganic Chemistry Communications 8 (2005) 212–215 213

idylmethyl)imidazole, which is non-equivalent and as-

sumes a head-to-tail arrangement, satisfies the funda-

mental requirements for NLO material. However,

unfortunately, the compound crystallized in the centro-

symmetric space group. According to the thoughts of ra-

tional design developed by Evans and Lin [7], wetentatively attribute the failure to the flexibility of pyim

which might increase the potential packing complexity.

The Cd(II) center lies in an octahedral {CdN4Cl2}

environment with the axial positions occupied by two

chlorine atoms and the equatorial positions occupied

by two trans imidazolium nitrogen atoms and two trans

pyridyl nitrogen atoms, each of which, respectively, be-

longs to four different N-(4-pyridylmethyl)imidazole li-gands (Fig. 1). The bond angles about the Cd1

octahedron range from 85.32� to 94.68� and deviate

slightly from those of a perfect octahedron. As pre-

dicted, this coordination fashion results in an infinite

2D rhombohedral grid containing 36-membered rings

(Fig. 2). The grid-like Cd4(pyim)4 species can be viewed

as the basic building block of the structure, in which the

apices are occupied by cadmium ions and the sides areformed by pyim ligands. Each four Cd4(pyim)4 grids

are joined together by sharing the cadmium apices to

give the final 2D layer structure with a diagonal mea-

surement of about 14.215 and 16.892 A based on the

metal–metal connections.

Noted that the basic grid is a highly distorted

square. More accurately, the dimension of the grid

can be described as hourglass-shaped. This shape isunderstandable, because the sp3 configuration of C of

–CH2– spacer forces the pyim ligand to be non-linear,

generating the nonlinear grid sides and thereby the

dumbbell-shaped grids. Actually, the N–C–C angle of

ensions with a side length of 11.039 A and a diagonal measurement of

Fig. 3. The tightly packed structure of 1 with face to face p–p stacking

interactions (dash lines); The Cd–Cd interlayer distances is 7.583 A.

the chlorine atoms are omitted for clarity.

214 Z. Liu et al. / Inorganic Chemistry Communications 8 (2005) 212–215

pyim in compound 1 is 115.18�, and the dihedral anglebetween the imidazolium and pyridyl rings is 72.6�.These data clearly depict the nonlinear configuration

of pyim in 1. Interestingly, the imidazolium rings of

one layers parallel to those of the adjacent layers to

form a three-dimensional (3D) framework by the face

to face p–p stacking interactions of the aromatic rings

of neighboring layers with the distances 3.552 A

between the centers of rings (Fig. 3). It should be notedthat the actual structure of the 2D layer is wave-like,

the convex surface of an adjacent layer to get a tightly

packed structure without any guest molecules.

To study the stability of the polymers, thermogravi-

metric analysis (TGA) was performed in the tempera-

ture range 30–800 �C under N2. Their thermal

decomposition behaviors were very similar. The TG/

DTA curves show neither weight loss nor structuralchange up to about 250 �C (257 �C for 1, 252 �C for

2, 251 �C for 3), demonstrating that these frameworks

were retained up to these high temperatures. Immedi-

ately above this point, the samples began to lose the

pyim ligands, and the whole frameworks collapsed in

continuous fashions.

The excitation and emission spectra of compound 1,

2, and 3 were measured in solid state at room tempera-ture. The results show that 1 exhibits an intense photo-

luminescence emission at 610 nm (kex = 350 nm), while 2

and 3 also exhibit intense photoluminescence emission

at 620 nm (kex = 284 nm), and 640 nm (kex = 364 nm),

respectively. These emissions may be tentatively as-

signed as ligand-to-metal charge transfer (LMCT) [8].

The slightly difference among 1, 2 and 3 should be as-

cribed to the different coordinated counter anions toCd(II) in the axial positions (Cl� for 1, Br� for 2 and

I� for 3) which suggest that the change of counter an-

ions, to some extent, exerts a significant effect on their

fluorescent properties.

A solution of pyim [3] (0.016 g, 0.10 mmol) in

MeOH (5 ml) was carefully layered on a solution of

CdX2 (X@Cl, Br, I, respectively) (0.10 mmol) in

H2O (5 ml). Diffusion between the two phases overa period of two weeks produced red block crystals.

Yield: 1, 0.020 g, 80%; 2, 0.024 g, 83%; 3, 0.029 g,

85%; Elementary analysis: Calcd. for 1,

C9H9N3Cd0.5Cl (250.84): C, 43.09; H, 3.62 ; N,

16.75%. Found: C, 43.07; H, 3.60; N, 16.74%. Calcd.

for 2, C9H9N3Cd0.5Br (295.30): C, 36.61; H, 3.07 ; N,

14.23%. Found: C, 36.63; H, 3.10; N, 14.22%. Calcd.

for 3, C9H9N3Cd0.5I (342.29): C, 31.58; H, 2.65 ; N,12.28%. Found: C, 31.55; H, 2.64; N, 12.27%. IR

(KBr, cm�1) for 1: 2922 (w), 1614 (vs), 1514 (m),

1423 (s), 1279 (m), 1237 (m), 1105 (s), 1076 (s),

1065(m), 1029 (m), 1010 (m), 931 (m), 843 (m), 800

(w), 749 (w), 658 (w), 628 (s), 481 (s); for 2: 2921

(w), 1614 (vs), 1513 (m), 1422 (s), 1281 (m), 1236

(m), 1106 (s), 1077 (s), 1064 (m), 1029 (m), 1010

(m), 930 (m), 844 (m), 800 (w), 749 (w), 657 (w),628 (s), 481 (s); for 3: 2920 (w), 1614 (vs), 1512 (m),

1422 (s), 1283 (m), 1234 (m), 1107 (s), 1079 (s),

1063 (m), 1031 (m), 1011 (m), 929 (m), 845 (m), 800

(w), 747 (w), 656 (w), 628 (s), 480 (s).

Acknowledgements

This work was financially supported by the NSFC

(Grant Nos. 20272058 and 20472085) and the program

of Science and Technology Plan of Fujian Province of

China.

Appendix A. Supplementary data

A figure showing the emission spectra of 1 is avail-

able. Supplementary data associated with this article

can be found, in the online version at doi:10.1016/

j.inoche.2004.12.001.

References

[1] J.M. Lehn, Supramolecular Chemistry: Concepts and Perspectives,

VCH, New York, 1995;

J.W. Steed, J.L. Atwood, Supramolecular Chemistry, Wiley, New

York, 2000;

M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. O�keeffe,O.M. Yaghi, Science 295 (2002) 469;

B.J. Holliday, C.A. Mirkin, Angew. Chem. Int. Ed. 40 (2001) 2022;

P.J. Hagrman, D. Hagrman, J. Zubieta, Angew. Chem. Int. Ed. 38

(1999) 2638;

C. Piguet, G. Bernardinelli, G. Hopfgartner, Chem. Rev. 97 (1997)

2005.

[2] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann,

Advanced Inorganic Chemistry, 6th ed., Wiley, New York, 1999,

pp. 350–354.

[3] G. Mago, M. Hinago, H. Miyasaka, N. Matsumoto, S. Okawa,

Inorg. Chim. Acta. 254 (1997) 145.

[4] O.R. Evans, W. Lin, Chem. Mater. 13 (2001) 3009.

[5] Crystal data. For complex 1: C9H9N3Cd0.5Cl, M = 250.84, Mono-

clinic, P21/c, a = 7.5384(6), b = 16.8918(13), c = 8.4082(6) A,

b = 112.232(2)�, V = 991.08(13) A3, Z = 4, T = 273(2) K.

R(wR) = 0.0243 (0.0338) for 1444 reflections with [I > 2r(I)].

Z. Liu et al. / Inorganic Chemistry Communications 8 (2005) 212–215 215

CCDC 251133. For complex 2: C9H9N3Cd0.5Br, M = 295.30,

Monoclinic, P21/c, a = 7.7877(4), b = 16.7015(9), c = 8.6362(4) A,

b = 113.719(2)�, V = 1028.46(9) A3, Z = 4, T = 273(2) K.

R(wR) = 0.0182 (0.0272) for 1622 reflections with [I > 2r(I)].CCDC 251134. For complex 3: C9H9N3Cd0.5I, M = 342.29,

Monoclinic, P21/c, a = 8.2156(4), b = 16.4773(4), c = 9.0405(4) A,

b = 115.909(2)�, V = 1100.81(8) A3, Z = 4, T = 273(2) K.

R(wR) = 0.0228 (0.0283) for 1742 reflections with [I > 2r(I)].CCDC 251135.

[6] W. Chiang, D.M. Ho, D.V. Engen, M.E. Thompson, Inorg. Chem.

32 (1993) 2886.

[7] O.R. Evans, W. Lin, Acc. Chem. Res. 35 (2002) 511.

[8] A. Meijerink, G. Blasse, M. Glasbeek, J. Phys. Condens. Matter 2

(1990) 6303;

R. Bertoncello, M. Bettinelli, M. Casarin, A. Gulino, E. Tondello,

A. Vittadini, Inorg. Chem. 31 (1992) 1558;

J. Tao, M.L. Tong, J.X. Shi, X.M. Chen, S.W. Ng, Chem.

Commun. (2000) 2043.