Synthesis of two-dimensional metal-organic networks from 1,10-phenanthroline-chelated cadmium complex and polycarboxylate

Article abstract of DOI:10.1016/j.molstruc.2006.03.078

The design of two 2D metal-organic frameworks using a 1,10-phenanthroline-chelated cadmium complex as precursor and a bridging polycarboxylate as linker is described. The reaction of Cd(NO₃)₂·4H₂O with the chelating ligand 1,10-phenanthroline (phen) at room temperature gave [Cd(phen)(NO₃)₂] (1) in high yield. Treatment of the inorganic precursor 1 with the polycarboxylate bridge ligand, benzene-1,4-dicarboxylic acid (H₂BDC) or benzene-1,2,4,5-tetracarboxylic acid (H₄btec), under mild hydrothermal conditions led to the formation of two metal-organic networks {[Cd(BDC)(phen)]·DMF}_n (2) and [Cd₂(btec)(phen)₂]_n (3). Single-crystal X-ray diffraction analyses showed that both products have two-dimensional sheet architectures. Compound 2 was constructed via the use of [Cd₂(O₂C{single bond})₄] unit and BDC linker, whereas compound 3 involved the use of [CdO₄] core and btec bridge. The cadmium ions in compounds 2 and 3 are hepta- and hexa-coordinated, respectively. Thermogravimetric (TG) analyses showed that 2 and 3 are thermally stable (T_decomp. > 360 °C). Photoluminescence studies revealed that compounds 1-3 displayed a strong fluorescent emission in the solid state at room temperature.

Full text of DOI:10.1016/j.molstruc.2006.03.078

Journal of Molecular Structure 796 (2006) 69–75
www.elsevier.com/locate/molstruc
Synthesis of two-dimensional metal–organic networks from
1,10-phenanthroline-chelated cadmium complex and polycarboxylate
a
b
a,
*
Jing-Yun Wu , Che-Hao Chang a,b, Tien-Wen Tseng , Kuang-Lieh Lu
a
Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan
Department of Chemical Engineering, National Taipei University of Technology, Taipei 106, Taiwan
b
Received 15 January 2006; received in revised form 20 March 2006; accepted 25 March 2006
Available online 22 May 2006
Abstract
The design of two 2D metal–organic frameworks using a 1,10-phenanthroline-chelated cadmium complex as precursor and a bridging
polycarboxylate as linker is described. The reaction of Cd(NO3)2Æ4H2O with the chelating ligand 1,10-phenanthroline (phen) at room
temperature gave [Cd(phen)(NO3)2] (1) in high yield. Treatment of the inorganic precursor 1 with the polycarboxylate bridge ligand,
benzene-1,4-dicarboxylic acid (H2BDC) or benzene-1,2,4,5-tetracarboxylic acid (H4btec), under mild hydrothermal conditions led to
the formation of two metal–organic networks {[Cd(BDC)(phen)]ÆDMF}n (2) and [Cd2(btec)(phen)2]n (3). Single-crystal X-ray diffraction
analyses showed that both products have two-dimensional sheet architectures. Compound 2 was constructed via the use of [Cd2(O2CA)4]
unit and BDC linker, whereas compound 3 involved the use of [CdO4] core and btec bridge. The cadmium ions in compounds 2 and 3
are hepta- and hexa-coordinated, respectively. Thermogravimetric (TG) analyses showed that 2 and 3 are thermally stable
(Tdecomp. > 360 ꢀC). Photoluminescence studies revealed that compounds 1–3 displayed a strong fluorescent emission in the solid state
at room temperature.
ꢁ 2006 Elsevier B.V. All rights reserved.
Keywords: Cadmium; Metal–organic networks; Chelate ligand; Bridge ligand; Photoluminescence
1. Introduction
coordination polymers. The strategy for the design lies in
the use of a 1,10-phenanthroline-chelated metal complex
as a precursor that is terminated in one dimension by a che-
lating aromatic ligand and the utilization of a bridging
polycarboxylate ligand as propagating linker between the
inorganic moieties.
Over the past decade, low dimensional coordination
polymers [1–7] have attracted considerable interest, due
to their intriguing structural features and unique electro-
conductive, nonlinear optic, and magnetic properties,
which are different from those of 3D frameworks [8–10].
The combination of a chelating ligand and polycarboxylate
ligands at the metal center has been published as a rational
strategy for the preparation of 1D chainlike and 2D layer-
like structures [6b,8,11–17], since a bulky aromatic chelat-
ing ligand would prevent the occurrence of higher
dimensions of the overall framework by ‘‘passivating’’
vacant sites and increasing steric hindrance at the metal
center [8]. Herein we report on the synthesis of two 2D
2. Experimental
2.1. General remarks
All reagents were purchased from commercial sources
and were used as received without further purification. Ele-
mental analyses were conducted on a Perkin-Elmer 2400
CHN elemental analyzer. All thermogravimetric (TG)
analyses were performed under a flow of nitrogen on a Per-
kin-Elmer TGA-7 analyzer at a heating rate of 10 ꢀC/min.
Photoluminescence spectra were obtained on a Hitachi
F-4500 fluorescence spectrophotometer.
*
Corresponding author. Tel.: +886 2 27898518; fax: +886 2 27831237.
E-mail address: lu@chem.sinica.edu.tw (K.-L. Lu).
0022-2860/$ - see front matter ꢁ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2006.03.078

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J.-Y. Wu et al. / Journal of Molecular Structure 796 (2006) 69–75
Table 1
2.2. Synthesis of [Cd(phen)(NO3)2] (1)
Crystal structure refinement data for 3
Empirical formula
Formula weight
Crystal system
Space group
C34H18Cd2N4O8
835.338
Monoclinic
P21/c
7.5768(2)
20.1802(6)
9.8192(3)
111.9101(12)
1392.93(7)
2
A solution of 1,10-phenanthroline (phen, 0.01 mmol)
in EtOH (12 mL) was added into
a solution of
Cd(NO3)2Æ4H2O (0.01 mmol) in EtOH (45 mL) at room
temperature. The mixture was allowed to stir for 3 h. The
resulting white precipitates were isolated by filtration and
washed with ethanol, and then dried under vaccum. Yield
80%. Anal. Found: C, 35.11; H, 2.09; N, 13.63%. Calcd.
for C12H8CdN4O6: C, 34.59; H, 1.94; N, 13.45%.
˚
a (A)
˚
b (A)
˚
c (A)
b (ꢀ)
3
˚
V (A )
Z
˚
T (A)
298
2.3. Synthesis of {[Cd(BDC)(phen)]ÆDMF}n (2)
Diffractometer
Kappa CCD
0.71073
1.992
1.594
820
2.45–25.05
8207
2397 (Rint = 0.0630)
1933
217
0.0356
˚
k (A)
Dcalcd (g cmꢀ3
)
A mixture of [Cd(phen)(NO3)2] (0.15 mmol), H2BDC
(0.15 mmol), and DMF (12 mL) was conducted in an acid
digestion bomb at 80 ꢀC for 96 h. Colorless crystals were
collected in 76% yield by filtration and washed with etha-
nol, and then dried at room temperature. Anal. Found:
C, 51.62; H, 3.82; N, 8.07%. Calcd. for C23H19CdN3O5:
C, 52.14; H, 3.61; N, 7.93%.
l (mmꢀ1
F000
)
h (ꢀ)
Reflns measured
Reflns indep.
Reflns observed [I > 2r(I)]
Parameters
R1a [I > 2r(I)]
wR2a [I > 2r(I)]
R1 (all data)
0.1010
0.0535
2.4. Synthesis of [Cd2(btec)(phen)2]n (3)
wR2 (all data)
0.1321
0.964
Goodness-of-fit oꢀn3F2
A mixture of [Cd(phen)(NO3)2] (0.15 mmol), H4btec
(0.32 mmol), and DMF (12 mL) was conducted in an acid
digestion bomb at 80 ꢀC for 96 h. Colorless crystals were
collected in 84% yield by filtration and washed with etha-
nol, and then dried at room temperature. Anal. Found:
C, 48.66; H, 2.35; N, 7.02%. Calcd. for C34H18Cd2N4O8:
C, 48.89; H, 2.17; N, 6.71%.
˚
Dqmax/Dqmin (e A
)
0.846/ꢀ1.077
h
.
i
1=2
a
P
P
P
P
2
2
R1 = iFoj ꢀ jFci/ jFoj, wR2 ¼
wðF 2o ꢀ F 2c Þ
wðF 2oÞ
.
Table 2
˚
Selected bond lengths (A) and angles (ꢀ) for 3
Cd(1)–O(4b)
Cd(1)–O(2a)
Cd(1)–O(3)
2.225(4)
2.293(4)
2.383(4)
2.5. X-ray crystallography
O(4b)–Cd(1)–O(1)
O(1)–Cd(1)–O(2a)
O(1)–Cd(1)–N(2)
O(4b)–Cd(1)–O(3)
O(2a)–Cd(1)–O(3)
O(4b)–Cd(1)–N(1)
O(2a)–Cd(1)–N(1)
O(3)–Cd(1)–N(1)
Cd(1)–O(1)
111.17(16)
101.31(14)
154.09(14)
95.57(16)
174.53(16)
149.46(16)
87.45(17)
98.02(15)
2.255(4)
Suitable single crystal of 3 was selected for indexing
and the collection of intensity data. Measurements were
performed using graphite-monochromatized Mo-Ka radi-
˚
ation (k = 0.71073 A) on a Kappa CCD diffractometer.
Compound 3 crystallizes in the monoclinic system with
space group P21/c. Intensity data were collected at
298 K within the limits 2.45ꢀ < h < 25.05ꢀ. The structure
was solved by direct methods and refined by full-matrix
least-squares method on F2 using the WINGX [18] and
SHELX-97 [19] program packages. An empirical absorp-
tion correction, based on multi-scan method, was applied.
Anisotropical thermal factors were assigned to non-
hydrogen atoms. The positions of hydrogen atoms were
generated geometrically, assigned isotropic thermal
parameters. Basic information pertaining to the crystal
parameters and structure refinements for 3 are summa-
rized in Table 1, and selected bond distances and angles
are provided in Table 2.
Cd(1)–N(2)
Cd(1)–N(1)
2.354(5)
2.384(4)
O(4b)–Cd(1)–O(2a)
O(4b)–Cd(1)–N(2)
O(2a)–Cd(1)–N(2)
O(1)–Cd(1)–O(3)
N(2)–Cd(1)–O(3)
O(1)–Cd(1)–N(1)
N(2)–Cd(1)–N(1)
79.47(17)
85.08(17)
101.46(16)
78.25(13)
80.25(14)
98.34(16)
70.55(15)
Symmetry transformations used to generate equivalent atoms: a, ꢀx, ꢀy,
ꢀz; b, ꢀx + 1, ꢀy, ꢀz.
3. Results and discussion
CCDC-600560 (3) contains the Supplementary crystal-
lographic data for this paper. These data can be obtained
free of charge at www.ccdc.cam.ac.uk/conts/retrieving.htm
[or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB21EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk].
3.1. Synthesis of compounds 2 and 3
Compound [Cd(phen)(NO3)2] (1) was prepared in
high yield by treating Cd(NO3)2Æ4H2O with the chelating
ligand, 1,10-phenathroline (phen), at room temperature.

J.-Y. Wu et al. / Journal of Molecular Structure 796 (2006) 69–75
71
O
O
-
-
O
O
80 ˚C
N
O
N
Cd(NO3)2
2
+
Cd
O
O
N
N
O
O
-
-
N
N
O
O
O
-
O
O
-
O
O
1
O
O
80 ˚C
3
Scheme 1.
Compound 1 was characterized by elemental analysis. In
order to control the propagating process of a self-assembly
reaction, compound 1 is used as an inorganic precursor
in assembling polycarboxylate bridging ligands to form
extended 2D coordination polymers. The bulky aromatic
chelating ligand would be expected to passivate the vacant
sites and increase the extent of steric hindrance at the
cadmium metal center, thereby reducing the dimensions
of the resulting net. Two-dimensional compounds
{[Cd(BDC)(phen)]ÆDMF}n (2) and [Cd2(btec)(phen)2]n (3)
were successfully synthesized using this strategy by reacting
the cadmium–phen building unit 1 with the bridging aro-
matic polycarboxylic acid (benzene-1,4-dicarboxylic acid
(H2BDC) for 2 and benzene-1,2,4,5-tetracarboxylic acid
(H4btec) for 3) under mild hydro(solvo)thermal conditions
(Scheme 1).
3.2. Structural description of {[Cd(BDC)(phen)]ÆDMF}n
(2)
Compound 2 is crystallographically characterized as a
known coordination polymer {[Cd(BDC)(phen)]ÆDMF}n
[20]. This species is constructed from dinuclear Cd2(O2C)4
(phen)2 secondary building units (SBUs), in which two CdII
centers, each having seven-coordinated CdN2O5 cores, are
bridged by two carboxylates in a chelating-bridging
bidentate mode. Each SBU acts as a building node for
connecting four adjacent SBUs through BDC linkers
in a head-to-tail arrangement, generating a 2D sheet
architecture in a grid-like (4,4)-net, which is stabilized
Fig. 1. (a) The 2D sheet architecture of 2 showing the (4,4)-net topology
by regarding Cd2N4O8 cores as nodes, which is stabilized by alternative
intra- and inter-node p–p interactions between aromatic rings of phen
ligands (space-filling model). (b) Crystal packing of 2 showing an inter-
digitated arrangement of stacked sheets with the lattice DMF molecules
located between sheets.
˚
by alternating intra- (av. Cꢁ ꢁ ꢁC distance 3.46 A) and
˚
inter-node (av. Cꢁ ꢁ ꢁC distance 3.51 A) p–p interactions
between the aromatic rings of the phen ligands (Fig. 1a).
The crystal packing of 2 shows an inter-digitated arrange-
ment of sheets stacked in the bc-plane, in which the lattice
DMF molecules are located in the inter-sheet spaces
(Fig. 1b). In 2, the carboxylate groups of the BDC ligand
exhibit two different coordination modes, i.e. bis(chelating
bidentate) and bis(chelating–bridging bidentate), as shown
in Fig. 2.
3.3. Structural description of [Cd2(btec)(phen)2]n (3)
Solid-state structure analysis shows that compound 3
has a 2D sheet architecture and crystallizes in the
monoclinic space group P21/c. There is one cadmium
atom, one phen ligand, and half of a btec ligand in each

72
J.-Y. Wu et al. / Journal of Molecular Structure 796 (2006) 69–75
maintained in a pseudo-chain arrangement with a Cdꢁ ꢁ ꢁCd
˚
distance of 4.69 A.
It is noteworthy that the four carboxylates in the btec
ligand exhibit different orientations (Fig. 4a). One set of
carboxylate groups that are para with respect to each other
is almost parallel to the central phenyl ring (dihedral angle
6.59ꢀ), while the other set is nearly orthogonal (dihedral
angle 94.42ꢀ) to the phenyl plane. The adjacent carboxylate
groups are perpendicular to each other with a dihedral
angle of 91.82ꢀ. This is most likely due to the ring strain
of the metal-containing seven-membered ring (CdO2C4)
and steric hindrance imposed by two adjacent carboxylate
groups in the btec ligand. Owing to the aromatic nature of
the chelated phen ligand, adjacent 2D sheets are intercalat-
ed with each other to form a 3D supramolecular network
through face-to-face p–p stacking between phen moieties
Fig. 2. Coordination modes of BDC in 2, (left) bis(chelating bidentate)
and (right) bis(chelating–bridging bidentate).
asymmetric unit. As shown in Fig. 3, the cadmium atom is
coordinated by one chelated phen ligand and four carbox-
ylate oxygen atoms from three distinct btec ligands, form-
ing a distorted octahedral CdN2O4 core. Each btec ligand
bridges to six cadmium atoms in a tetrakis(bidentate) fash-
ion to generate a 2D sheet architecture (Fig. 4), in which
the carboxylate groups of the btec ligand all display a
syn, anti-bidentate bridging mode. Along the crystallo-
graphic a-axis, the cadmium atoms in the 2D sheet are
˚
with a Cꢁ ꢁ ꢁC separation of 3.30–3.63 A (Fig. 5).
3.4. Thermogravimetric (TG) analysis of compounds 2 and 3
As shown in Fig. 6, a thermogravimetric (TG) analysis
of compound 2 showed that a weight loss of 14.3%
occurred over the temperature range 75–144 ꢀC, which
Fig. 3. ORTEP plot of the coordination environment around cadmium ion with the atom-labeling scheme in 3.
Fig. 4. (a) Coordination mode of btec ligand in 3. (b) The 2D sheet architecture of 3 constructed by [CdN2O4] cores (polyhedra) and btec bridges.

J.-Y. Wu et al. / Journal of Molecular Structure 796 (2006) 69–75
73
Fig. 5. The 3D supramolecular network of 3 showing the face-to-face p–p stacking between aromatic rings of phen ligands.
×3
×20
Fig. 6. Thermogravimetric (TG) analysis diagrams of 2 (solid line) and 3
(dash-dot line).
Fig. 7. Photoluminescence spectra of 1–3 in the solid state at room
temperature.
corresponds to the removal of a free DMF molecule per
formula unit (calcd. 13.8%). The solvent-free phase,
[Cd(BDC)(phen)], subsequently shows no weight loss until
the temperature reaches 365 ꢀC. On the other hand, the TG
curve for 3 showed that the compound is thermally stable
at temperature up to 370 ꢀC, followed by a multi-step
decomposition process.
shoulder bands at 386, 481, and 508 nm upon excitation
at 320 nm. The free 1,10-phenanthroline shows fluores-
cence emission bands at 365 and 388 nm in the solid state
(kex = 310 nm), which correspond to p fi p transition
*
[15]. Therefore, the strong structureless emission band at
402 nm for 1 is tentatively assigned to the intraligand
fluorescence of coordinated phen ligands due to the
planar configuration of the excimeric phen molecules
maintained by the cadmium metal center [15,20,21].
Compound 2 exhibits structured emission bands at 370,
3.5. Fluorescent properties of compounds 1–3
The photoluminescent properties of compounds 1–3, in
the solid state, were examined at room temperature and
relevant spectra are shown in Fig. 7. The fluorescent emis-
sion band for 1 is mainly located at 402 nm with three
389, and 405(sh), which are assigned to p fi p transition
*
of the coordinated phen ligand, as reported by Qiu and

74
J.-Y. Wu et al. / Journal of Molecular Structure 796 (2006) 69–75
[3] (a) N.L. Toh, M. Nagarathinam, J.J. Vittal, Angew. Chem., Int. Ed.
44 (2005) 2237;
co-workers [20]. A further weak emission band at 495 nm
for 2 may not be related to n fi p transition of the
*
(b) B. Sreenivasulu, J.J. Vittal, Angew. Chem., Int. Ed. 43 (2004)
5769.
[4] (a) G.F. Swiegers, T.J. Malefetse, Chem. Rev. 100 (2000) 3483;
(b) K. Uemura, S. Kitagawa, K. Fukui, K. Saito, J. Am. Chem. Soc.
126 (2004) 3817;
(c) C.-Y. Su, M.D. Smith, H.-C. zur Loye, Angew. Chem., Int. Ed. 42
(2003) 4085.
[5] (a) B.D. Wagner, G.J. McManus, B. Moulton, M.J. Zaworotko,
Chem. Commun. (2002) 2176;
BDC ligand but may simply arise from a charge-
transfer transition [22–24], since the free H2BDC exhibits
only one emission band located at about 390 nm
(kex = 350 nm) [23]. In the case of 3, photoluminescence
with two main peaks at 386 and 400 nm and several
shoulders in the region 450–500 nm, as well as one broad
band at 533 nm (kex = 330 nm) are observed (Fig. 7). In
comparison, the free H4btec ligand also shows similar
multiple emission bands at 360, 381, 455, and 470 nm
with shoulders at 494 and 523 nm upon excitation at
(b) E. Burkholder, V. Golub, C.J. O’Connor, J. Zubieta, Inorg.
Chem. 42 (2003) 6729;
(c) L. Carlucci, G. Ciani, D.M. Proserpio, F. Porta, Angew. Chem.,
Int. Ed. 42 (2003) 317.
320 nm, which can be attributed to n fi p transition
*
[6] (a) C.-D. Wu, W. Lin, Inorg. Chem. 44 (2005) 1178;
(b) X.-M. Chen, G.-F. Liu, Chem. Eur. J. 8 (2002) 4811;
(c) Y.-C. Yang, L.-I. Hung, S.-L. Wang, Chem. Mater. 17 (2005)
2833;
(d) Y.-C. Jiang, S.-L. Wang, S.-F. Lee, K.-H. Lii, Inorg. Chem. 42
(2003) 6154.
[7] T.-T. Yeh, J.-Y. Wu, Y.-S. Wen, Y.-H. Liu, J. Twu, Y.-T. Tao, K.-L.
Lu, Dalton Trans. (2005) 656.
[23]. This indicates that the btec ligands make a significant
contribution to fluorescent emission of 3 in addition to
that from the coordinated phen ligands. Therefore, the
emission bands for 3 are rationally assigned to the combi-
nation of strong p fi p transition of the coordinated
*
phen ligand [15,20] and weak n fi p transition of the
*
btec ligand.
[8] (a) X.-L. Wang, C. Qin, E.-B. Wang, L. Xu, Z.-M. Su, C.-W. Hu,
Angew. Chem., Int. Ed. 43 (2004) 5036;
(b) Y. Li, N. Hao, Y. Lu, E. Wang, Z. Kang, C. Hu, Inorg. Chem. 42
(2003) 3119;
4. Conclusions
(c) Y. Li, H. Zhang, E. Wang, N. Hao, C. Hu, Y. Yan, D. Hall, New
J. Chem. 26 (2002) 1619.
[9] (a) C. Mellot-Draznieks, J. Dutour, G. Ferey, Angew. Chem., Int. Ed.
43 (2004) 6290;
The synthesis of two 2D networks is described. A 1,10-
phenanthroline-chelated cadmium metal complex was
successfully used as an inorganic subunit to react with
polycarboxylate bridging ligands to form 2D coordination
polymers in high yields under mildly hydrothermal reaction
conditions.
(b) N.L. Rosi, J. Kim, M. Eddaoudi, B. Chen, M. O’Keeffe, O.M.
Yaghi, J. Am. Chem. Soc. 127 (2005) 1504;
(c) C.N.R. Rao, S. Natarajan, R. Vaidhyanathan, Angew. Chem., Int.
Ed. 43 (2004) 1466;
(d) S. Tashiro, M. Tominaga, M. Kawano, B. Therrien, T. Ozeki,
M. Fujita, J. Am. Chem. Soc. 127 (2005) 4546;
(e) J.S. Seo, D. Whang, H. Lee, S.I. Jun, J. Oh, Y.J. Jeon, K. Kim,
Nature 404 (2000) 982.
Acknowledgements
[10] (a) T.-T. Luo, H.-L. Tsai, S.-L. Yang, Y.-H. Liu, R.D. Yadav, C.-C.
Su, C.-H. Ueng, L.-G. Lin, K.-L. Lu, Angew. Chem., Int. Ed. 44
(2005) 6063;
We thank Academia Sinica and the National Science
Council of Taiwan for financial support. We also express
our gratitude to Mr. Ting-Shen Kuo, National Taiwan
Normal University, for assistance with the X-ray structure
analysis.
(b) Y.-H. Liu, H.-C. Wu, H.-M. Lin, W.-H. Hou, K.-L. Lu, Chem.
Commun. (2003) 60;
(c) Y.-H. Liu, Y.-L. Lu, H.-C. Wu, J.-C. Wang, K.-L. Lu, Inorg.
Chem. 41 (2002) 2592;
(d) Y.-H. Liu, H.-L. Tsai, Y.-L. Lu, Y.-S. Wen, J.-C. Wang, K.-L.
Lu, Inorg. Chem. 40 (2001) 6426.
Appendix A. Supplementary data
[11] Y.B. Go, X. Wang, E.V. Anokhina, A.J. Jacobson, Inorg. Chem. 43
(2004) 5360.
[12] Y. Qi, Y. Wang, C. Hu, M. Cao, L. Mao, E. Wang, Inorg. Chem. 42
(2003) 8519.
[13] X.-M. Zhang, M.-L. Tong, M.-L. Gong, X.-M. Chen, Eur. J. Inorg.
Chem. (2003) 138.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.
2006.03.078.
References
[14] D. Sun, R. Cao, Y. Liang, Q. Shi, W. Su, M. Hong, J. Chem. Soc.,
Dalton Trans. (2001) 2335.
[15] X. Shi, G. Zhu, Q. Fang, G. Wu, G. Tian, R. Wang, D. Zhang, M.
Xue, S. Qiu, Eur. J. Inorg. Chem. (2004) 185.
[16] Q. Shi, R. Cao, D.-F. Sun, M.-C. Hong, Y.-C. Liang, Polyhedron 20
(2001) 3287.
[17] D.-Q. Chu, J.-Q. Xu, L.-M. Duan, T.-G. Wang, A.-Q. Tang, L. Ye,
Eur. J. Inorg. Chem. (2001) 1135.
[1] (a) J.L. Atwood, J.E.D. Davies, D.D. MacNicol, F. Vo¨gtle, J.-M.
Lehn, Comprehensive Supramolecular Chemistry, vol. 9, Pergamon
Press, New York, 1996;
(b) S.R. Batten, R. Robson, Angew. Chem., Int. Ed. 37 (1998) 1460;
(c) J.C. Noveron, A.M. Arif, P.J. Stang, Chem. Mater. 15 (2003) 372;
(d) D.-L. Long, A.J. Blake, N.R. Champness, C. Wilson,
[18] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.
[19] G.M. Sheldrick, SHELX-97 (including SHELXS and SHELXL),
University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[20] X. Shi, G. Zhu, X. Wang, G. Li, Q. Fang, G. Wu, G. Tian, M.
Xue, X. Zhao, R. Wang, S. Qiu, Cryst. Growth Des. 5 (2005)
207.
M. Schro¨der, Chem. Eur. J.
[2] (a) M. Ruben, U. Ziener, J.-M. Lehn, V. Ksenofontov, P. Gutlich,
¨
8 (2002) 2026.
G.B.M. Vaughan, Chem. Eur. J. 11 (2005) 94;
(b) M.W. Hosseini, Acc. Chem. Res. 38 (2005) 313;
(c) T.J. Prior, M.J. Rosseinsky, Chem. Commun. (2001) 1222;
(d) G.R. Desiraju, Nature 412 (2001) 397.

J.-Y. Wu et al. / Journal of Molecular Structure 796 (2006) 69–75
75
[21] (a) J. Zhang, Y.-R. Xie, Q. Ye, R.-G. Xiong, Z. Xue, X.-Z. You, Eur.
J. Inorg. Chem. (2003) 2572;
G. Tian, S.-L. Qiu, L. Fang, Inorg. Chem. Commun. 7 (2004) 31;
(c) J. Tao, M.-L. Tong, J.-X. Shi, X.-M. Chen, S.W. Ng, Chem.
Commun. (2000) 2043.
(b) X.-M. Ouyang, D.-J. Liu, T.-a. Okamura, H.-W. Bu, W.-Y. Sun,
W.-X. Tang, N. Ueyama, Dalton Trans. (2003) 1836.
[22] (a) J.-C. Dai, X.-T. Wu, Z.-Y. Fu, S.-M. Hu, W.-X. Du, C.-P. Cui,
L.-M. Wu, H.-H. Zhang, R.-Q. Sun, Chem. Commun. (2002) 12;
(b) X.-J. Liu, Q.-R. Fang, G.-S. Zhu, M. Xue, X. Shi, G. Wu,
[23] W. Chen, J.-Y. Wang, C. Chen, Q. Yue, H.-M. Yuan, J.-S. Chen,
S.-N. Wang, Inorg. Chem. 42 (2003) 944.
[24] J. Tao, J.-X. Shi, M.-L. Tong, X.-X. Zhang, X.-M. Chen, Inorg.
Chem. 40 (2001) 6328.