Self-assembly of 2D→2D interpenetrating coordination polymers showing polyrotaxane- and polycatenane-like motifs: Influence of various ligands on topological structural diversity

Article abstract of DOI:10.1021/ic801275w

A series of mixed-ligand coordination complexes, namely, [Cd ₂(bimb)₂(L¹)₂] (1), [Cd(bpimb) _0.5(L²)(H₂0)] (2), [Zn₅(bpib) ₂(L³)₄(OH)₂(H₂O) ₂] (3), [Zn(bpib)_0.5(L⁴)] (4), and [Cd(bib)(L⁴)] (5), where bimb = 1,4-bis((1H-imidazol-1-yl)methyl) benzene, bpimb = 1,4-bis((2-(pyridin-2-yl)-1H-imidazol-1-yl)methyl)benzene, bpib = 1,4-bis(2-(pyridin-2-yl)-1H-imidazol-1-yl)butane, bib = 1,4-bis(1H-imidazol- 1-yl)butane, H₂L¹ = 4-((4-(dihydroxymethyl)phenoxy)methyl) benzoic acid, H₂L² = 4,4′-methylenebis(oxy)dibenzoic acid, H₂L³ = 3,3′-methylenebis(oxy)dibenzoic acid, and H₂L⁴ = 4,4′-(2,2′-oxybis(ethane-2,1-diyl) bis(oxy))dibenzoic acid, have been synthesized under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric (TG) analyses. In 1, (L¹)^2- anions link the metal-neutral ligand subunits to generate a 2-fold parallel interpenetrating net with the 6³ topology. In 2-4, neutral ligands connect the various metal-carboxylic ligand subunits to give a 2-fold parallel interpenetrating net with (4,4) topology in 2, a 2-fold parallel interpenetrating net with (3,6)-connected topology in 3, and a 3-fold parallel interpenetrating net with (4,4) topology in 4. Compounds 1-4 display both polyrotaxane and polycatenane characters. Compound 5 is a 5-fold parallel interpenetrating net with (4,4) topology. By careful inspection of these structures, we find that different topological structures showing both polyrotaxane and polycatenane characters have been achieved with increase of the carboxylic ligand length. It is believed that various carboxylic ligands and N-donor ligands with different coordination modes and conformations are important for the formation of the different structures. In addition, the luminescent properties of these compounds are discussed.

Full text of DOI:10.1021/ic801275w

Inorg. Chem. 2008, 47, 10600-10610
Self-Assembly of 2Df2D Interpenetrating Coordination Polymers
Showing Polyrotaxane- and Polycatenane-like Motifs: Influence of
Various Ligands on Topological Structural Diversity
Ya-Qian Lan, Shun-Li Li, Jun-Sheng Qin, Dong-Ying Du, Xin-Long Wang, Zhong-Min Su,*
and Qiang Fu*
Institute of Functional Material Chemistry, Key Laboratory of Polyoxometalate Science of Ministry
of Education, Faculty of Chemistry, Northeast Normal UniVersity, Changchun, 130024, China
Received July 8, 2008
A series of mixed-ligand coordination complexes, namely, [Cd2(bimb)2(L1)2] (1), [Cd(bpimb)0.5(L2)(H2O)] (2),
[Zn5(bpib)2(L3)4(OH)2(H2O)2] (3), [Zn(bpib)0.5(L4)] (4), and [Cd(bib)(L4)] (5), where bimb ) 1,4-bis((1H-imidazol-1-
yl)methyl)benzene, bpimb ) 1,4-bis((2-(pyridin-2-yl)-1H-imidazol-1-yl)methyl)benzene, bpib ) 1,4-bis(2-(pyridin-2-
yl)-1H-imidazol-1-yl)butane, bib ) 1,4-bis(1H-imidazol-1-yl)butane, H2L1 ) 4-((4-(dihydroxymethyl)phenoxy)meth-
yl)benzoic acid, H2L2 ) 4,4′-methylenebis(oxy)dibenzoic acid, H2L3 ) 3,3′-methylenebis(oxy)dibenzoic acid, and
H2L4 ) 4,4′-(2,2′-oxybis(ethane-2,1-diyl)bis(oxy))dibenzoic acid, have been synthesized under hydrothermal conditions.
Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by
elemental analyses, IR spectra, and thermogravimetric (TG) analyses. In 1, (L1)2- anions link the metal-neutral
ligand subunits to generate a 2-fold parallel interpenetrating net with the 63 topology. In 2-4, neutral ligands
connect the various metal-carboxylic ligand subunits to give a 2-fold parallel interpenetrating net with (4,4) topology
in 2, a 2-fold parallel interpenetrating net with (3,6)-connected topology in 3, and a 3-fold parallel interpenetrating
net with (4,4) topology in 4. Compounds 1-4 display both polyrotaxane and polycatenane characters. Compound
5 is a 5-fold parallel interpenetrating net with (4,4) topology. By careful inspection of these structures, we find that
different topological structures showing both polyrotaxane and polycatenane characters have been achieved with
increase of the carboxylic ligand length. It is believed that various carboxylic ligands and N-donor ligands with
different coordination modes and conformations are important for the formation of the different structures. In addition,
the luminescent properties of these compounds are discussed.
Introduction
rotaxanes, and knots, respectively.6 According to the research
by Ciani and co-workers,6a polycatenation differs from
interpenetration in that the whole catenated array has a higher
dimensionality than that of the component motifs and that
each individual motif is catenated only with the surrounding
ones and not with all the others. Polythreaded structure is
Entangled systems have attracted considerable interest
because of their intriguing topological structures and potential
applications.1-4 Among different types of entanglements,
interpenetrating networks have been extensively studied.5 In
recent years, the intense interest in coordination polymers
has led to more topological types of entanglements being
discovered, such as polycatenation, polythreading, and poly-
knotting, and they are reminiscent of molecular catenanes,
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H. C. Chem. Commun. 2003, 1630. (d) Tong, M. L.; Chen, X. M.;
Batten, S. R. J. Am. Chem. Soc. 2003, 125, 16170. (e) Moulton, B.;
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M. J. Chem. Commun. 2003, 1342.
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P.; Wilson, C.; Schro¨der, M. Chem.sEur. J. 2005, 11, 1384. (b) He,
J.; Yin, Y. G.; Wu, T.; Li, D.; Huang, X. C. Chem. Commun. 2006,
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* To whom correspondence should be addressed. E-mail: zmsu@
nenu.edu.cn (Z.-M.S), fuq836@nenu.edu.cn (Q.F.). Tel: +86 431 85099108.
(1) (a) Molecular Catenanes, Rotaxanes and Knots, A Journey Through
the World of Molecular Topology; Sauvage, J. P., Dietrich-Buchecker,
C., Eds.; Wiley-VCH: Weinheim, Germany, 1999. (b) Stoddart, J. F.
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10600 Inorganic Chemistry, Vol. 47, No. 22, 2008
10.1021/ic801275w CCC: $40.75  2008 American Chemical Society
Published on Web 10/24/2008

Self-Assembly of 2Df2D Interpenetrating Coordination Polymers
Chart 1. The Carboxylate Ligands and Neutral Ligands in 1-5
characterized by the presence of closed loops, as well as of
elements that can thread through the loops, and can be
considered as extended periodic analogues of molecular
rotaxanes and pseudorotaxanes, depending on the “ideal”
possibility of being extricated. To date, although some
polycatenated or polythreaded coordination polymers have
been reported,7,8 the topological frameworks containing two
kinds of entangled motifs in one compound are still quite
rare. Only a few fascinating structures showing both poly-
rotaxane and polycatenane characters have been observed.9
However, there is an unfavorable lack of detailed investiga-
tion on different topological structures in above-mentioned
nets, such as other topological nets and various interpenetrat-
ing ones.
As shown above, it is a great challenge not only to
synthesize entangled frameworks having both polyrotaxane
and polycatenane characters but also to achieve different
topological structures in the aforementioned system. To
achieve this aim, we have designed and synthesized a series
of flexible N-donor ligands (1,4-bis((1H-imidazol-1-yl)m-
ethyl)benzene (bimb), 1,4-bis((2-(pyridin-2-yl)-1H-imidazol-
1-yl)methyl)benzene (bpimb), 1,4-bis(2-(pyridin-2-yl)-1H-
imidazol-1-yl)butane (bpib), and 1,4-bis(1H-imidazol-1-yl)-
butane (bib)) and multicarboxylic bridging ligands (4-((4-
(dihydroxymethyl)phenoxy)methyl)benzoic acid (H2L1), 4,4′-
methylenebis(oxy)dibenzoic acid (H2L2), 3,3′-methylenebis-
(oxy)dibenzoic acid (H2L3), and 4,4′-(2,2′-oxybis(ethane-2,1-
diyl)bis(oxy))dibenzoic acid (H2L4)) based on the following
considerations: (i) The use of conformationally nonrigid
ligands can favor the formation of interesting motifs with
peculiar features like new topologies and entanglements
(including polycatenanes and polyrotaxanes).6a,10 (ii) The
carboxylic bridging ligands contain the flexible -CH2- or -O-
CH2- spacer. Therefore, the two phenyl rings can freely twist
around the -CH2- group or -O-CH2- to meet the requirements
of the coordination geometries of metal atoms in the
assembly process. Conformational changes of flexible ligands
can more easily give unusual entanglements involving a
molecular unit with loops and insertion of a linear rod
through those loops. (iii) From H2L1 to H2L2 to H2L3 to H2L4
(Chart 1), the different lengths of carboxylic bridging ligands
maybe benefit the formation of different topological struc-
tures. Because an accurate prediction of the final structure
is impossible, the exploration of the influencing factors for
the ultimate structures is not trivial. In this paper, we have
tried different synthetic conditions and performed many
experiments. Fortunately, compounds [Cd2(bimb)2(L1)2] (1),
[Cd(bpimb)0.5(L2)(H2O)] (2), [Zn5(bpib)2(L3)4(OH)2(H2O)2]
(3), [Zn(bpib)0.5(L4)] (4), and [Cd(bib)(L4)] (5) have been
successfully isolated by hydrothermal methods. In addition,
the infrared spectra, thermogravimetric analyses, and lumi-
nescent properties of these compounds have been investigated
in detail.
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Experimental Section
General Procedures. Chemicals were purchased from com-
mercial sources and used without further purification. Ligands bimb,
bpimb, bpib, and bib were prepared according to literature proce-
dures.11
Synthesis of H2L1. A mixture of ethyl 4-hydroxybenzoate (8.30
g, 50 mmol) and NaOH (2.00 g, 50 mmol) in DMSO (20 mL) was
stirred at 5 °C for 2 h, then 4-(chloromethyl)benzonitrile (7.55 g,
50 mmol) was added. The mixture was cooled to room temperature
Inorganic Chemistry, Vol. 47, No. 22, 2008 10601

Lan et al.
after stirring at 50 °C for 24 h and then poured into 200 mL of
water. A yellow solid of ethyl 4-(4-cyanobenzyloxy)benzoate
formed immediately, which was isolated by filtration in 94% yield
after drying in air.
A mixture of ethyl 4-(4-cyanobenzyloxy)benzoate (14.07 g, 50
mmol) and KOH (11.20 g, 200 mmol) in H2O (200 mL) was stirred
at 100 °C for 15 h, and was cooled to room temperature. Then the
mixture was adjusted to pH ≈ 5 with HCl (1.0 mol ·L-1), and a
white solid of H2L1 formed immediately, which was isolated by
filtration in 60% yield after drying in air. IR (cm-1): 3743 (w),
3442 (w), 2985 (w), 2546 (w), 2362 (m), 1681 (s), 1606 (s), 1577
(m), 1514 (m), 1425 (s), 1385 (s), 1292 (s), 1252 (s), 1172 (s),
1047 (m), 949 (w), 854 (w), 765 (m).
Syntheses of H2L2, H2L3, and H2L4. A mixture of ethyl
4-hydroxybenzoate (8.30 g, 50 mmol) and NaOH (2.00 g, 50 mmol)
in DMSO (20 mL) was stirred at 5 °C for 2 h, and then
dichloromethane (2.12 g, 25 mmol) was added. The mixture was
stirred at 5 °C for 48 h and then poured into 200 mL of water. A
white solid of diethyl 4,4′-methylenebis(oxy)dibenzoate formed
immediately, which was isolated by filtration in 91% yield after
drying in air.
A mixture of diethyl 4,4′-methylenebis(oxy)dibenzoate (17.20
g, 50 mmol) and KOH (11.20 g, 200 mmol) in H2O (200 mL) was
stirred at 100 °C for 8 h and was cooled to room temperature. Then
the mixture was adjusted to pH ≈ 5 with HCl (1.0 mol ·L-1), and
a white solid of H2L2 formed immediately, which was isolated by
filtration in 75% yield after drying in air. IR (cm-1): 3897 (w),
3743 (m), 2982 (w), 1716 (s), 1645 (m), 1608 (s), 1539 (m), 1510
(s), 1462 (m), 1369 (m), 1314 (s), 1275 (s), 1218 (s), 1168 (s),
1105 (m), 1025 (s), 849 (w), 767 (m).
H2L3 was prepared in the same way as H2L2 by using the
corresponding ethyl 3-hydroxybenzoate instead of ethyl 4-hydroxy-
benzoate. IR (cm-1): 3887 (w), 3740 (m), 2985 (w), 1726 (s), 1645
(m), 1608 (s), 1549 (m), 1512 (s), 1462 (m), 1318(s), 1274 (s),
1218 (s), 1172 (s), 1105 (m), 1035 (s), 849 (w), 767 (m).
H2L4 was prepared in the same way as H2L2 by using the
corresponding bis(2-chloroethyl)ether instead of dichloromethane.
IR (cm-1): 3827 (m), 3745 (m), 2985 (w), 1715 (s), 1683 (s), 1606
(s), 1577 (m), 1508 (s), 1457 (m), 1366 (m), 1278 (s), 1171 (m),
1106 (s), 1052 (m), 957 (w), 851 (w), 768 (w).
Synthesis of [Cd2(bimb)2(L1)2] (1). A mixture of bimb (0.24 g,
1.00 mmol), H2L1 (0.27 g, 1.0 mmol), Cd(OAc)2 ·2H2O (0.27 g,
1.00 mmol), NaOH (0.08 g, 2.00 mmol), and H2O (10 mL) was
stirred for 1 h and then sealed in a 25 mL Teflon-lined stainless
steel container. The container was heated to 150 °C and held at
that temperature for 72 h, then cooled to 100 °C at a rate of 10
°C·h-1, held for 8 h, and further cooled to 30 °C at a rate of 5
°C·h-1. Colorless crystals of 1 were collected in 72.7% yield based
on Cd(OAc)2 ·2H2O. Anal. Calcd for C58H48Cd2N8O10 (1241.84):
C, 56.09; H, 3.90; N, 9.02. Found: C, 56.87; H, 3.86; N, 8.99%.
IR (cm-1): 3861 (s), 3741 (s), 3120 (m), 2882 (s), 2817 (s), 1836
(w), 1751 (w), 1707 (w), 1516 (m), 1395 (m), 1223 (w), 1142 (w),
1000 (m), 849 (w), 774 (w), 673 (m).
Synthesis of [Cd(bpimb)0.5(L2)(H2O)] (2). A mixture of bpimb
(0.39 g, 1.00 mmol), H2L2 (0.29 g, 1.0 mmol), Cd(OAc)2 ·2H2O
(0.27 g, 1.00 mmol), NaOH (0.08 g, 2.00 mmol), and H2O (10
mL) was stirred for 1 h and then sealed in a 25 mL Teflon-lined
stainless steel container. The container was heated to 150 °C and
held at that temperature for 72 h, then cooled to 100 °C at a rate
of 10 °C·h-1, held for 8 h, and further cooled to 30 °C at a rate of
5 °C·h-1. Colorless crystals of 2 were collected in 69.7% yield
based on Cd(OAc)2 ·2H2O. Anal. Calcd for C27H22CdN3O7 (612.88):
C, 52.91; H, 3.62; N, 6.86. Found: C, 52.85; H, 3.55; N, 6.93%.
IR (cm-1): 3731 (s), 3121 (s), 2883 (w), 1836 (w), 1798 (w), 1751
(w), 1707 (w), 1645 (w), 1596 (m), 1477 (s), 1423 (s), 1394 (s),
1298 (s), 1205 (m), 1153 (m), 1096 (m), 999 (m), 942 (w), 853
(w), 782 (m).
Synthesis of [Zn5(bpib)2(L3)4(OH)2(H2O)2] (3). A mixture of
bpib (0.34 g, 1.00 mmol), H2L3 (0.29 g, 1.00 mmol),
Zn(OAc)2 ·2H2O (0.22 g, 1.00 mmol), NaOH (0.08 g, 2.00 mmol),
and H2O (10 mL) was stirred for 1 h and then sealed in a 25 mL
Teflon-lined stainless steel container. The container was heated to
150 °C and held at that temperature for 72 h, then cooled to 100
°C at a rate of 10 °C·h-1, held for 8 h, and further cooled to 30 °C
at a rate of 5 °C·h-1. Colorless crystals of 3 were collected in 64.5%
yield based on Zn(OAc)2 ·2H2O. Anal. Calcd for C100H86N12O28Zn5
(2230.66): C, 53.84; H, 3.89; N, 7.53. Found: C, 53.79; H, 3.78;
N, 7.46%. IR (cm-1): 3731 (w), 3671 (w), 3116 (m), 2875 (m),
2788 (m), 1609 (m), 1568 (s), 1478 (s), 1445 (s), 1386 (s), 1282
(m), 1209 (s), 1167 (w), 1090 (w), 1017 (s), 896 (w), 770 (s), 674
(m).
Synthesis of [Zn(bpib)0.5(L4)] (4). A mixture of bpib (0.34 g,
1.00 mmol), H2L4 (0.35 g, 1.00 mmol), Zn(OAc)2 ·2H2O (0.22 g,
1.00 mmol), NaOH (0.08 g, 2.00 mmol), and H2O (10 mL) was
stirred for 1 h and then sealed in a 25 mL Teflon-lined stainless
steel container. The container was heated to 150 °C and held at
that temperature for 72 h, then cooled to 100 °C at a rate of 10
°C·h-1, held for 8 h, and further cooled to 30 °C at a rate of 5
°C·h-1. Colorless crystals of 4 were collected in 77.6% yield based
on Zn(OAc)2 ·2H2O. Anal. Calcd for C28H26N3O7Zn (581.89): C,
57.79; H, 4.50; N, 7.22. Found: C, 57.83; H, 4.37; N, 7.39%. IR
(cm-1): 3732 (w), 3120 (m), 2940 (m), 2882 (m), 2828 (m), 1634
(s), 1601 (s), 1500 (s), 1411 (s), 1347 (s), 1252 (s), 1168 (m), 1130
(s), 1054 (s), 948 (m), 922 (m), 854 (w), 784 (m), 742 (w), 657
(w).
Synthesis of [Cd(bib)(L4)] (5). A mixture of bib (0.19 g, 1.00
mmol), H2L4 (0.35 g, 1.00 mmol), Cd(OAc)2 ·2H2O (0.27 g, 1.00
mmol), NaOH (0.08 g, 2.00 mmol), and H2O (10 mL) was stirred
for 1 h and then sealed in a 25 mL Teflon-lined stainless steel
container. The container was heated to 150 °C and held at that
temperature for 72 h, then cooled to 100 °C at a rate of 10 °C·h-1
held for 8 h, and further cooled to 30 °C at a rate of 5 °C·h-1
,
.
Colorless crystals of 5 were collected in 78.4% yield based on
Cd(OAc)2 ·2H2O. Anal. Calcd for C28H30CdN4O7 (646.96): C,
51.98; H, 4.67; N, 8.66. Found: C, 52.02; H, 4.79; N, 8.74.% IR
(cm-1): 3742 (s), 3104 (s), 2872 (w), 1706 (w), 1596 (s), 1515 (s),
1453 (m), 1393 (s), 1298 (w), 1239 (m), 1162 (w), 1107 (w), 937
(m), 852 (m), 777 (m), 692 (m).
Physical Measurements. The C, H, and N elemental analysis
was conducted on a Perkin-Elmer 240C elemental analyzer. The
FT-IR spectra were recorded from KBr pellets in the range of
4000-400 cm-1 on a Mattson Alpha-Centauri spectrometer. TGA
was performed on a Perkin-Elmer TG-7 analyzer heated from room
temperature to 700 °C under nitrogen. The solid-state emission/
excitation spectra were recorded on a Varian Cary Eclipse
spectrometer at room temperature.
(10) (a) Carlucci, L.; Ciani, G.; Proserpio, D. M. Networks, Topologies,
and Entanglements in Making Crystals by Design - Methods,
Techniques and Applications; Braga, D., Grepioni, F., Eds.; Wiley-
VCH: Weinheim, Germany, 2007; Chapter 1.3. (b) Carlucci, L.; Ciani,
G.; Maggini, S.; Proserpio, D. M. CrystEngComm 2008, 1191.
(11) (a) Li, S.-L.; Lan, Y.-Q.; Ma, J.-F.; Yang, J.; Wei, G.-H.; Zhang, L.-
P.; Su, Z.-M. Cryst. Growth Des. 2008, 8, 675. (b) Reeder, K. A.;
Dose, E. V.; Wilson, L. J. Inorg. Chem. 1978, 17, 1071. (c) Chiswell,
B.; Lions, F.; Morris, B. S. Inorg. Chem. 1964, 3, 110. (d) Lan, Y.-
Q.; Fu, Y.-M.; Shao, K.-Z.; Su, Z.-M. Acta Crystallogr. 2006, E62,
2586. (e) Li, S.-L.; Lan, Y.-Q.; Ma, J.-F.; Fu, Y.-M.; Yang, J.; Ping,
G.-J.; Liu, J.; Su, Z.-M. Cryst. Growth Des. 2008, 8, 1610.
10602 Inorganic Chemistry, Vol. 47, No. 22, 2008

Self-Assembly of 2Df2D Interpenetrating Coordination Polymers
Table 1. Crystal Data and Structure Refinements for Compounds 1-5
1
2
3
4
5
formula
fw
crystal system
space group
a (Å)
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
C58H48Cd2N8O10
1241.84
C27H22CdN3O7
612.88
C
100H86N12O28Zn5
C28H26N3O7Zn
581.89
C28H30CdN4O7
646.96
monoclinic
P21/n
7.1680(3)
24.8870(6)
15.4390(7)
90
91.0140(10)
90
2230.66
triclinic
triclinic
triclinic
triclinic
j
j
j
j
P1
P1
P1
P1
9.7860(6)
14.7460(9)
19.8720(12)
100.7460(10)
97.9240(10)
100.6960(10)
2723.8(3)
2
10.3930(5)
11.0290(5)
12.0990(5)
110.6250(10)
105.6710(10)
93.4570(10)
1230.97(10)
2
11.5890(4)
11.7730(4)
19.6900(7)
94.4840(10)
105.2900(10)
114.1670(10)
2310.75(14)
1
8.2200(3)
12.4460(5)
13.5470(5)
98.6910(6)
98.8260(10)
109.2600(10)
1262.29(8)
2
2753.73(18)
4
1.561
Z
Dcalcd [g cm-3
F(000)
]
1.514
1256
1.654
618
1.603
1144
1.531
602
1320
reflns collected /unique
R(int)
13923/9522
0.0194
1.042
0.0458
0.0976
7599/5501
0.0115
1.034
0.0358
0.0950
14529/10619
0.0233
1.031
0.0500
0.1212
7818/5660
0.0091
1.051
0.0271
0.0687
16942/6614
0.0253
1.035
0.0390
0.0878
GOF on F2
a
R1 [I > 2σ(I)]
b
wR2
largest residuals [e Å-3
]
0.744/-0.480
0.910/-0.994
1.440/-0.559
0.341/-0.312
0.904/-0.468
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) |∑w(|Fo|2 - |Fc|2)|/∑|w(Fo )2|1/2
.
b
2
bridge adjacent CdII atoms to give a 26-membered ring
[Cd(bimb)2Cd] with the dimensions 9.265 Å × 11.708 Å
(Figure S1a, Supporting Information), which is further linked
by (L1)2- ligands in the monobidentate and bis-bidentate
modes with T conformations (considering the relative
orientations T ) trans, G ) gauche) to give a 2D undulated
layer (Figure 1b), showing a rectangular window with the
dimensions 17.460 Å × 28.589 Å. So six CdII ions are linked
by four bimb and four (L1)2- ligands to form a large
rectangular 86-membered ring [Cd6(bimb)2(L1)4] with the
distances for each edge and diagonal of 17.460, 28.589,
29.199, and 37.307 Å, respectively (Figure S1b, Supporting
Information). If each [Cd(bimb)2Cd] 26-membered ring is
considered as a 3-connected node, the structure of 1 exhibits
a 63 topology (Figure 1c).
In order to minimize the big void cavities and stabilize
the framework, the potential voids formed by a single 2D
network show incorporation of another identical network,
thus giving a 2-fold parallel interpenetrating network (Figure
1d and Figure S1c, Supporting Information). To further study
the structure, each [Cd(bimb)2Cd] 26-membered loop of each
layer is threaded by the rod of one (L1)2- ligand from the
other layer, and vice versa. In addition, the polyrotaxane
nature of this net is evident in the presence of catenated rings
by the [Cd(bimb)2Cd] 26-membered ring and the [Cd6-
(bimb)2(L1)4] 86-membered ring from adjacent layers, which
makes the nontrivial topology of the entanglement (Figure
1e,f). So the structure of 1 shows both polyrotaxane and
polycatenane characteristics.
X-ray Crystallography. Single-crystal X-ray diffraction data for
compounds 1-5 were recorded on a Bruker Apex CCD diffracto-
meter with graphite-monochromated Mo KR radiation (λ ) 0.71073
Å) at 293 K. Absorption corrections were applied using the
multiscan technique. All the structures were solved by direct
methods using SHELXS-9712 and refined by full-matrix least-
squares techniques using the SHELXL-97 program13 within
WINGX.14 Non-hydrogen atoms were refined with anisotropic
temperature parameters. The hydrogen atoms of the organic ligands
were refined on idealized positions. H atoms of water molecules
were located from different Fourier maps. The detailed crystal-
lographic data and structure refinement parameters for 1-5 are
summarized in Table 1.
Results
Structural Description of 1. As shown in Figure 1a, the
structure of 1 contains two kinds of unique CdII atoms, two
kinds of unique (L1)2- anions, and two kinds of unique bimb
ligands. The Cd1 cation shows an octahedral coordination
geometry {CdN2O4}, which is completed by four carboxylate
oxygen atoms from two (L1)2- anions, and two nitrogen
atoms from two bimb ligands. The Cd2 cation is five-
coordinated by three carboxylate oxygen atoms from two
(L1)2- anions, and two nitrogen atoms from two bimb
ligands, showing a trigonal bipyramidal geometry {CdN2O3}.
The CdII-O and CdII-N distances are quite similar to normal
CdII-O and CdII-N distances (Table S1, Supporting Infor-
mation).15 A pair of bimb ligands in the bis-monodentate
(12) Sheldrick, G. M. SHELXS-97, Programs for X-ray Crystal Structure
Solution; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(13) Sheldrick, G. M. SHELXL-97, Programs for X-ray Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(14) Farrugia, L. J. WINGX, A Windows Program for Crystal Structure
Analysis; University of Glasgow: Glasgow, UK, 1988.
(15) (a) Dai, J.-C.; Wu, X.-T.; Fu, Z.-Y.; Cui, C.-P.; Hu, S.-M.; Du, W.-
X.; Wu, L.-M.; Zhang, H.-H.; Sun, R.-Q. Inorg. Chem. 2002, 41, 1391.
(b) Wang, R.; Hong, M.; Luo, J.; Cao, R.; Weng, J. Chem. Commun.
2003, 1018. (c) Luan, X.-J.; Cai, X.-H.; Wang, Y.-Y.; Li, D.-S.; Wang,
C.-J.; Liu, P.; Hu, H.-M.; Shi, Q.-Z.; Peng, S.-M. Chem.sEur. J. 2006,
12, 6281. (d) Paz, F. A. A.; Klinowski, J. Inorg. Chem. 2004, 43,
3948. (e) Zou, R.-Q.; Bu, X.-H.; Zhang, R.-H. Inorg. Chem. 2004,
43, 5382. (f) Suresh, E.; Boopalan, K.; Jasra, R. V.; Bhadbhade, M. M.
Inorg. Chem. 2001, 40, 4078.
Structural Description of 2. When H2L1 is replaced with
longer H2L2 and bimb is replaced with bpimb, a similar
parallel interpenetrating 2D structure, 2, has been obtained.
The structure of 2 contains one kind of CdII atom, one kind
of bpimb ligand, and one kind of (L2)2- anion. Cd1 is
coordinated by three carboxylate oxygen atoms from different
(L2)2- anions, two nitrogen atoms from one bpimb ligand,
and one coordinating water molecule, showing an octahedral
geometry {CdN2O4} (Figure 2a). Different from 1, (L2)2-
Inorganic Chemistry, Vol. 47, No. 22, 2008 10603

Lan et al.
Figure 1. (a) Coordination environment of CdII atoms in 1 with the ellipsoids drawn at the 30% probability level; hydrogen atoms were omitted for clarity;
(b) ball-and-stick representation of the sheet-like structure of compound 1; (c) schematic view of the 63 topology of 1; (d) ball-and-stick representation of
interlocked nets; (e) the polyrotaxane and polycatenane motifs in 1; (f) schematic description of the interpenetrating nets of 1.
anions connect CdII ions with the mono-and-bis(mono)-
dentate coordination mode in the GG conformation to
generate a double chain, in which there exists a rectangular
32-membered ring [Cd(L2)2Cd] (Figure S2a) with distances
for each edge and diagonal of 9.206, 9.425, 12.348, and
13.953 Å, respectively. The adjacent double chains are
pillared by bpimb ligands with bis-bidentate coordination
mode to form an undulated sheet (Figure 2b), showing a
rectangular window with the dimensions 14.691 Å × 15.604
Å. Within the layer, there is a large 86-membered ring
[Cd4(bpimb)2(L2)2] with corresponding distances of 12.414,
14.691, 17.417, and 20.893 Å (Figure S2b, Supporting
Information). From the topological view, if each [Cd(L2)2Cd]
ring is considered as a 4-connected node, the structure of 2
exhibits a (4,4) topology (Figure 2c).
Similar to compound 1, two identical layers penetrate each
other in parallel interpenetrating modes to give a 2-fold
parallel interpenetrating network (Figure 2d and Figure S2c,
Supporting Information), which shows both polyrotaxane and
polycatenane character. Each bpimb as a rod threads the
[Cd(L2)2Cd] loop from the adjacent layers and two kinds of
loops of the [Cd(L2)2Cd] ring and the [Cd4(bpimb)2(L2)2] ring
from adjacent sheets catenate each other (Figure 2e,f).
Compounds 1 and 2 are 2-fold parallel interpenetrating
networks and exhibit both polyrotaxane and polycatenane
character. Comparison of two structures shows that the
distinction between them is the different compositions for
the smaller loops, such as [Cd(bimb)2Cd] in 1 and [Cd-
(L2)2Cd] in 2, which are connected to form final structures
with various topologies. In the literature, such nets with 63
and (4,4) topologies containing both polyrotaxane and
polycatenane character are quite rare.9a-e
Structural Description of 3. When H2L3 with different
angular character replaced H2L2 and the flexible bpib ligand
is selected instead of bpimb, a particularly fascinating 2D
2-fold structure of 3 has been obtained. There are three kinds
of unique ZnII atoms, two kinds of unique (L3)2- anions, and
one kind of bpib ligand (Figure 3a). The Zn1 cation shows
a trigonal bipyramidal geometry {ZnN2O3}, which is sur-
rounded by two carboxylate oxygen atoms from two (L3)2-
anions, one (OH)- group, and two nitrogen atoms from one
bpib ligand. The Zn2 cation is five-coordinated by two
carboxylate oxygen atoms from different (L3)2- anions, two
nitrogen atoms from the bpib ligand, and one water molecule,
showing a trigonal bipyramidal geometry {ZnN2O3}. Zn3
exhibits an octahedral coordination geometry with four
carboxylate atoms from different (L3)2- anions and two
(OH)- groups. The ZnII-O and ZnII-N distances are quite
similar to normal ZnII-O and ZnII-N distances.16 Two types
of (L3)2- anions with mono-and-bis(mono)-dentate coordina-
tion modes in the GG conformations connect ZnII ions to
give a double chain. Within this chain, two adjacent Zn1
atoms and one Zn3 atom are bridged by four carboxylate
groups and two (OH)- groups to give a trimetallic unit
10604 Inorganic Chemistry, Vol. 47, No. 22, 2008

Self-Assembly of 2Df2D Interpenetrating Coordination Polymers
Figure 2. (a) Coordination environment of the CdII atom in 2 with the ellipsoids drawn at the 30% probability level; hydrogen atoms were omitted for
clarity; (b) ball-and-stick representation of the sheet-like structure of compound 2; (c) schematic view of the (4,4) topology of 2; (d) ball-and-stick representation
of interlocked nets; (e) the polyrotaxane and polycatenane motifs in 2; (f) schematic description of the interlocked nets of 2.
[Zn3(CO2)4(OH)2]. In addition, four (L3)2- anions and four
ZnII ions (two Zn2 and two Zn3) assemble a large 56-
membered ring [Zn4(L3)4] (Figure S3a, Supporting Informa-
tion) with the Zn2 · · ·Zn2 distance of 5.628 Å and Zn3 · · ·Zn3
distance of 26.234 Å, respectively. The adjacent chains are
pillared by bpib ligands with the bis-bidentate coordination
mode in TTT conformation to generate a sheet (Figure 3b),
showing a window with dimensions 13.117 Å by 17.358 Å.
There is a parallelogrammic 50-membered ring [Zn4(L3)2-
(bpib)2] (Figure S3b, Supporting Information) formed by two
(L3)2- anions, two bpib ligands, and four ZnII ions with the
distances for each edge and diagonal of 12.782, 12.839,
17.545, and 18.795 Å.
bpib ligand are considered as connectors, the structure of 3
is a (3,6)-connected net with (43)(46 ·66 ·83) topology (Figure
3c). The potential windows formed by a single 2D network
show incorporation of another identical network, thus giving
a 2-fold parallel interpenetrating network (Figure 3d and
Figure S3c, Supporting Information). Although the structure
of 3 also shows both polyrotaxane and polycatenane char-
acter, it is different from those of compounds 1 and 2; in 3,
each [Zn4(L3)4] loop is threaded by two bpib ligands as rods
from the adjacent layers and the [Zn4(L3)4] ring and
[Zn4(L3)2(bpib)2] ring from adjacent layers interlock each
other (Figure 3e,f). To the best of our knowledge, this is the
first example of a 2-fold parallel interpenetrating network
with a (3,6)-connected net showing both polyrotaxane and
polycatenane character.
From the topological view, if each [Zn3(CO2)4(OH)2] unit
is considered as a 6-connected node, the Zn2 atom is
considered as a 3-connected node, and the (L3)2- anion and
In addition, the coordination water molecule donates two
hydrogen bonds to two adjacent carboxylate oxygen atoms
(Table S2 and Figure S3d, Supporting Information), which
forms a [Zn2(CO2)4(H2O)2] unit. If each [Zn2(CO2)4(H2O)2]
unit is considered as a 4-connected node and the
[Zn3(CO2)4(OH)2] unit is also a 4-connected node, the
structure of 3 is a 2-fold parallel interpenetrating network
with (4,4) topology, which is similar to the structure of 2.
(16) (a) Majumder, A.; Shit, S.; Choudhury, C. R.; Batten, S. R.; Pilet, G.;
Luneau, D.; Daro, N.; Sutter, J.-P.; Chattopadhyay, N.; Mitra, S. Inorg.
Chim. Acta 2005, 358, 3855. (b) Chen, W.; Yuan, H.-M.; Wang, J.-
Y.; Liu, Z.-Y.; Xu, J.-J.; Yang, M.; Chen, J.-S. J. Am. Chem. Soc.
2003, 125, 9266. (c) Ganesan, S. V.; Natarajan, S. Inorg. Chem. 2004,
43, 198. (d) Zhang, J.-P.; Lin, Y.-Y.; Huang, X.-C.; Chen, X.-M. Eur.
J. Inorg. Chem. 2006, 3407. (e) Bourne, S. A.; Lu, J.; Moulton, B.;
Zaworotko, M. J. Chem. Commun. 2001, 861. (f) Sun, D.; Cao, R.;
Liang, Y.; Shi, Q.; Su, W.; Hong, M. J. Chem. Soc., Dalton Trans.
2001, 2335.
Inorganic Chemistry, Vol. 47, No. 22, 2008 10605

Lan et al.
Figure 3. (a) Coordination environment of ZnII atoms in 3 with the ellipsoids drawn at the 30% probability level; hydrogen atoms were omitted for clarity;
(b) ball-and-stick representation of the sheet-like structure of compound 3; (c) schematic view of the topology of 3; (d) ball-and-stick representation of
interlocked nets; (e) the polyrotaxane and polycatenane motifs in 3; (f) schematic description of the interlocked nets of 3.
Structural Description of 4. In order to investigate the
influence of multicarboxylate ligands with different lengths
on ultimate structures, the longer H2L4 is selected instead of
H2L3, and compound 4 is obtained. The compound 4 shows
a rare 2Df2D example with 3-fold parallel interpenetration
of (4,4) layers. As shown in Figure 4a, the structure of 4
contains one kind of ZnII atom and one kind of (L4)2- and
bpib ligands (Figure 4a). The ZnII center is coordinated by
three carboxylate oxygen atoms from different (L4)2- ions
and one nitrogen atom from the bpib ligand to give the
ZnO3N tetrahedral geometry. The (L4)2- anions with the
mono-and-bis(mono)-dentate coordination mode in the TGT-
TGT conformation link ZnII atoms to give a hinged chain
containing the [Zn2(CO2)4] unit and a 40-membered ring,
[Zn2(L4)2] (Figure S4a, Supporting Information) showing the
corresponding edge and diagonal sizes of 10.455, 10.761,
13.956, and 15.982 Å. The bpib ligand with the bis-
(mono)dentate coordination mode in the TTT conformation
connects the adjacent chains to generate a 2D sheet (Figure
4b) with a window of dimensions 17.028 Å by 17.035 Å.
There is a large 62-membered loop, [Zn4(bpib)2(L4)2] (Figure
S4b, Supporting Information), formed by four ZnII ions, two
bpib, and two (L4)2- anions with the corresponding distances
of 14.540, 17.035, 20.592, and 24.065 Å.
the large window in the sheet, the other two identical layers
penetrate it in the parallel mode to form a 2Df2D 3-fold
interpenetrating network (Figure 4d and Figure S4c, Sup-
porting Information). It is interesting that this network also
shows both polyrotaxane and polycatenane characters. The
loop of [Zn2(L4)2] in one sheet is threaded by two bpib
ligands as rods from two adjacent layers. A large ring of
[Zn4(bpib)2(L4)2] from one layer is interlocked by two
[Zn2(L4)2] loops from the other two identical layers (Figure
4e,f).
When the ZnII ion and bpib ligand are selected to react
with H2L3 and H2L4, respectively, compounds 3 and 4 with
different structural types have been obtained. Based on the
different lengths for H2L3 and H2L4, they link ZnII ions to
form two kinds of hinged chains with different sized
metal-multicarboxylate loops, which are connected by bpib
ligands to form distinct structures of 3 and 4. So they exhibit
(3,6)-connected and 4-connected topological structures. H2L4
is longer than H2L3, so the structure of 4 shows a larger
window than that in 3, which can benefit formation of the
higher degrees of interpenetrating network.
Structural Description of 5. X-ray crystallography has
indicated that complex 5 is made up of one kind of CdII ion,
one kind of bib ligand, and the (L4)2- anion (Figure 5a).
CdII exhibits a distorted octahedral coordination geometry
surrounded by four carboxylate oxygen atoms from two
(L4)2- anions and two nitrogen atoms of different bib
If each [Zn2(CO2)4] unit is considered as a 4-connected
node and bpib and (L4)2- anion are considered as linkages,
the structure of 4 is a (4,4) topology (Figure 4c). Based on
10606 Inorganic Chemistry, Vol. 47, No. 22, 2008

Self-Assembly of 2Df2D Interpenetrating Coordination Polymers
Figure 4. (a) Coordination environment of ZnII atom in 4 with the ellipsoids drawn at the 30% probability level; hydrogen atoms were omitted for clarity;
(b) ball-and-stick representation of the sheet-like structure of compound 4; (c) schematic view of the (4,4) topology of 4; (d) ball-and-stick representation
of interlocked nets; (e) the polyrotaxane and polycatenane motifs in 4; (f) schematic description of the interlocked nets of 4.
molecules. The (L4)2- anions coordinate CdII atoms with the
bis-bidentate coordination mode in the TGTTTT (G )
gauche) conformation to give a chain-like structure, which
is pillared by the bib ligands with the TTT conformation to
generate a 2D (4,4) sheet (Figure 5b) with a large grid,
showing the dimensions 13.685 Å × 20.882 Å. The large
grid allows each net to be penetrated by four other
independent nets in parallel mode to form the interesting 2D
5-fold interpenetrating networks (Figure 5c and Figure S5,
Supporting Information). It is interesting that the 2D 5-fold
parallel interpenetrating networks show polycatenane char-
acter, in which there is a subunit formed by five rings from
adjacent layers interlocking each other. This kind of con-
nection mode is similar to the Olympic Rings (Figure 5d,e).
Due to different coordination modes of (L4)2- anions, they
link CdII to generate a single chain in 5 and a double chain
in 4, which are pillared by neutral ligands to form 5-fold
and 3-fold interpenetrating networks, respectively. Compari-
son of the structures of 4 and 5 with those of 1-3 reveals
more degrees of interpenetrating structures owing to the
longer carboxylic acids in 4 and 5.
(4,4) 2D layer frameworks. One of them is a covalently
connected net within the structure of the coordination
polymer [Co(NCS)2(2,5-bis(4-pyridylethynyl) thiophene)].18
The other is the 5-fold interpenetrated 2D hydrogen-bonded
rhomboid grid supramolecular architectures with the com-
positions of {[Co(Hdpa)2(BPDC)2] · 2H2O} or [Zn(dpa)2-
(HBPDC)2].19 So the structure of 5 is another example of
5-fold (4,4) 2D wavy layers formed by parallel interpenetra-
tion, which could help us deeply understand the nature of
coordination polymer frameworks and better design func-
tional materials.
As mentioned above, compounds 1-4 show both poly-
rotaxane and polycatenane character and various topological
structures by changing carboxylic acids with different
lengths, which mean that there are two kinds of motifs in
compounds 1-4, rotaxane-like species and catenated arrays.
Notably, the rotaxane-like motif in compound 1 is formed
by the metal-neutral ligand subunit as the loop and the
carboxylate ligand as a rod threading the above loop. In 2-4,
the ring composition is the metal-carboxylate ligand, and
(17) Carlucci, L.; Ciani, G.; Macchi, P.; Proserpio, D. M.; Rizzato, S.
Chem.sEur. J. 1999, 5, 237.
(18) Son, S. U.; Kim, B. Y.; Choi, C. H.; Lee, S. W.; Kim, Y. S.; Chung,
Y. K. Chem. Commun. 2003, 2528.
(19) Montney, M. R.; Supkowskib, R. M.; LaDuca, R. L. CrystEngComm
2008, 10, 111.
Interpenetration phenomena are found to frequently occur
during the self-assembly process.17 But the 2D 5-fold parallel
interpenetrating net is scarce. To the best of our knowledge,
there are only two examples for 5-fold parallel interpenetrated
Inorganic Chemistry, Vol. 47, No. 22, 2008 10607

Lan et al.
Figure 5. (a) Coordination environment of CdII atom in 5 with the ellipsoids drawn at the 30% probability level; hydrogen atoms were omitted for clarity;
(b) ball-and-stick representation of the sheet-like structure of compound 5; (c) ball-and-stick representation of 5-fold penetrating nets; (d) the polycatenane
motifs in 5; (e) schematic description of the 5-fold penetrating nets of 5.
the corresponding rod is the neutral ligand. The carboxylate
anions show the mono-and-bis(mono)-dentate coordination
modes and coordinate to three metal centers in 2-4, which
benefit the formation of various metal-carboxylate chains
with two or three metal-oxygen clusters. These chains are
pillared by neutral ligands to generate the final different
topological structures. Compound 2 shows a 2-fold parallel
interpenetrating network with the (4,4) topology. When
different angular H2L3 is selected to replace H2L2, compound
3 exhibits a 2-fold parallel interpenetrating network with the
(3,6)-connected topology. Compared with the structure of
3, 4 displays a 3-fold parallel interpenetrating network with
the (4,4) topology by using the longer H2L4. The coordination
modes of carboxylic anions in 2-4 play important roles in
forming the special structures with both polyrotaxane and
polycatenane characters.
distance of 20.882 Å, which is longer than that of 4. From
a theoretical view, the longer the distance between two metal
centers coordinated by one carboxylic anion is, the more the
number of identical interpenetrating nets may be. The 3-fold
parallel interpenetrating net of compound 4 and the 5-fold
one of compound 5 support this view well.
Four kinds of carboxylic ligands with different lengths and
angles adopt various coordination modes and conformations
in 1-5 (Scheme 1). In addition, many factors, such as the
radii of metal cations, the versatilities of the metal coordina-
tion geometries, and the donor characters of nitrogen atoms
to the metals, play fundamental roles in the formation of
the final products. These factors work together and have a
significant effect on the structures of the coordination
polymers. It is a feasible method to introduce ligands to
construct coordination polymers with different structural
types.
In 4, the (L4)2- anion with the mono-and-bis(mono)-
dentate coordination mode coordinates to metal centers in
the TGTTGT conformation with the M· · · M (metal center)
distance of 15.982 Å. Different from 4, in 5, the (L4)2- anion
with the bis-bidentate coordination mode coordinates to metal
centers in the TGTTTT conformation with the M · · · M
Luminescent Properties. Luminescent compounds are
of great current interest because of their various applica-
tions in chemical sensors, photochemistry, and electrolu-
minescent display.20 The luminescent properties of zinc
and cadmium carboxylate compounds have been investi-
10608 Inorganic Chemistry, Vol. 47, No. 22, 2008

Self-Assembly of 2Df2D Interpenetrating Coordination Polymers
is similar to the previous literature.22 The emissions of
compounds 2-4 may be attributed to a joint contribution
of the intraligand π/ f π transitions, which effectively
increase the rigidity of the ligand and reduce the loss of
energy by nonradiative decay, and charge transfer transi-
tions between the coordinated ligands and the metal
center.11a,e
Thermal Analyses. In order to characterize the com-
pounds more fully in terms of thermal stability, their thermal
behaviors were studied by TGA. The experiments were
performed on samples consisting of numerous single crystals
of 1-5 under N2 atmosphere with a heating rate of 10 °C/
min. The results of the TGA for compounds 1-5 are shown
in Figure S6 in the Supporting Information.
Figure 6. Solid-state photoluminescent spectra of 1-5 at room temperature.
Scheme 1. Schematic View of Five Compounds in This Work
For 1, the weight loss begins with decomposition
starting at 273 °C and ending above 489 °C. The remaining
weight of 21.1% corresponds to the percentage (20.7%)
of CdO. For compounds 2 and 3, the weight losses in the
range of 20-151 °C for 2 and 15-98 °C for 3 correspond
to the removal of the corresponding coordination water
molecules. The anhydrous compositions begin to decom-
pose at 203 °C ending above 487 °C for 2 and at 182 °C
ending above 479 °C for 3. The remaining weight
corresponds to the formation of CdO in 2 (obsd 21.2%,
calcd 21.0%) and ZnO in 3 (obsd 18.5%, calcd 18.3%).
The anhydrous compounds 4 and 5 begin to decompose
at 216 °C for 4 and 187 °C for 5 and end above 537 °C
for 4 and 527 °C for 5. The remaining weight of 14.5%
for 4 and 18.6% for 5 correspond to the percentage
(14.0%) of ZnO in 4 and (19.9%) of CdO in 5.
Table 2. The Wavelengths of the Emission Maximums and Excitation
(nm)
Conclusion
ligand
bimb
bpimb
bpib
bib
In summary, we have synthesized five mixed-ligand
coordination complexes under hydrothermal conditions.
Compounds 1-4 display 2Df2D parallel interpenetrating
structures with various topological types and show both
polyrotaxane and polycatenane character. Compound 5 is a
5-fold parallel interpenetrating net with (4,4) topology. By
careful inspection of these structures, we find that different
topological structures have been achieved with the increase
of carboxylic ligand length. It is believed that various
carboxylic ligands and N-donor ligands with different
coordination modes and conformations are important for the
formation of the different structures. These results suggest
that novel extended entanglements containing both polyro-
taxane and polycatenane character can be realized by
combining metal nodes with flexible N-donor ligands and
various carboxylic ligands. Investigations in this direction
are currently under way.
λem
λex
432
255
360, 506
320
532
370
436
380
compound
1
2
3
4
5
λem
λex
451
375
537
440
369
335
481
400
475
400
gated.21 The photoluminescent spectra of compounds 1-5
and N-donor ligands have been measured at room tem-
perature (Figure 6),and the wavelengths of the emission
maximums and excitation are listed in Table 2 for
compounds 1-5 and N-donor ligands. And solid
H2L1-H2L4 ligands are nearly nonfluorescent in the range
400-800 nm at ambient temperature. In comparison with
the N-donor ligands, the emission maximums of com-
pounds 1-5 have changed. This may be caused by the
following reasons: The emission peaks for 1 may arise
from π/ f π transitions of the bimb ligands because a
similar peak also appears for the free bimb ligand, which
Acknowledgment. The authors gratefully acknowledge the
financial support from the National Natural Science Founda-
(20) (a) Wu, Q.; Esteghamatian, M.; Hu, N.-X.; Popovic, Z.; Enright, G.;
Tao, Y.; D’Iorio, M.; Wang, S. Chem. Mater. 2000, 12, 79. (b)
McGarrah, J. E.; Kim, Y.-J.; Hissler, M.; Eisenberg, R. Inorg. Chem.
2001, 40, 4510. (c) Santis, G. D.; Fabbrizzi, L.; Licchelli, M.; Poggi,
A.; Taglietti, A. Angew. Chem., Int. Ed. Engl. 1996, 35, 202.
(21) Zheng, S.-L.; Yang, J.-H.; Yu, X.-L.; Chen, X.-M.; Wong, W.-T. Inorg.
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(22) (a) Zheng, S.-L.; Zhang, J.-P.; Chen, X.-M.; Huang, Z.-L.; Lin, Z.-
Y.; Wong, W.-T. Chem.sEur. J. 2003, 9, 3888. (b) Kang, Y.; Zhang,
J.; Li, Z.-J.; Cheng, J.-K.; Yao, Y.-G. Inorg. Chim. Acta 2006, 359,
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Inorganic Chemistry, Vol. 47, No. 22, 2008 10609

Lan et al.
Supporting Information Available: X-ray crystallographic files
(CIF), additional figures, selected bond distances and angles, and
TGA curves of compounds 1-5. This material is available free of
charge via the Internet at http://pubs.acs.org.
tion of China (Project Nos. 20573016 and 20703008), the
National High-tech Research and Development Program (863
Program 2007AA03Z354), Program for Changjiang Scholars
and Innovative Research Team in University (Grant IRT0714),
and the Science Foundation for Young Teachers of Northeast
Normal University (No. 20070309).
IC801275W
10610 Inorganic Chemistry, Vol. 47, No. 22, 2008