Crystal structures and luminescent properties of lanthanide nitrate coordination polymers with structurally related amide type bridging podands

Article abstract of DOI:10.1016/j.jssc.2010.11.011

A one-dimensional linear chain coordination polymer [ErL ^I(NO₃)₃(CH₃CO₂Et)] _n (L^I=1,2-bis{[(2'-furfurylaminoformyl)phenoxyl]methyl} benzene) and a one-dimensional zig-zag coordin

Full text of DOI:10.1016/j.jssc.2010.11.011

Journal of Solid State Chemistry 184 (2011) 164–170
Contents lists available at ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Crystal structures and luminescent properties of lanthanide nitrate
coordination polymers with structurally related amide type bridging podands
Qing Wang, Xuhuan Yan, Hongrui Zhang, Weisheng Liu, Yu Tang n, Minyu Tan
Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical
Engineering, Lanzhou University, Lanzhou 730000, PR China
a r t i c l e i n f o
a b s t r a c t
A one-dimensional linear chain coordination polymer [ErLI(NO3)3(CH3CO2Et)]n (LI¼1,2-bis{[(2’-furfur-
Article history:
Received 13 July 2010
Received in revised form
15 October 2010
ylaminoformyl)phenoxyl]methyl}benzene) and
a one-dimensional zig-zag coordination polymer
{[TbLII(NO3)3(H2O)] ꢀ (H2O)}n (LII¼1,2-bis{[2’-(2-pyridylmethylaminoformyl)phenoxyl]methyl}benzene)
were assembled by two structurally related bridging podands LI and LII which have uniform skeleton and
different terminal groups. In {[TbLII(NO3)3(H2O)] ꢀ (H2O)}n, the neutral chains were linked by the hydrogen
bonding interactions between the free and coordinated water molecules from two different directions to
interpenetrate into a 3D supramolecular structure. At the same time, the luminescent properties of the
solid Tb(III) nitrate complexes of these podands were investigated at room temperature. The lowest triplet
state energy levels T1 of the podands LI and LII indicate that the triplet state energy levels of the antennae
are both above the lowest excited resonance level of 5D4 of Tb3+ ion. Thus the absorbed energy could be
transferred from ligands to the central Tb3+ ions. And the influence of the hydrogen bonding on the
luminescence efficiencies of the coordination polymers was also discussed.
Accepted 8 November 2010
Available online 13 November 2010
Keywords:
Lanthanide
Coordination polymers
Podand
Luminescent properties
& 2010 Elsevier Inc. All rights reserved.
1. Introduction
Amide type podands have been attracting more attentions in
preparing lanthanide complexes possessing strong luminescent
Lanthanide have been extensively employed in the metal
directed synthesis in functional supramolecular structures and
self-assemblies due to their unique luminescent, magnetic, and
coordination properties [1–4]. The applications of the lanthanide
complexes in luminescent sensing and imaging technology, and as
contract agents for MRI are very well established [5–10]. Among
the luminescent complexes studied, europium(III) and terbium(III)
complexes appear to be the most attractive in view of the high
photoluminescent (PL) efficiency and the narrow band red/green-
emission ability, which may exploited in the full-color displays
[11–14] and a variety of applications ranging from chemosensors
for bioactive species to active components in time resolved assays.
Since the f–f transitions are spin- and parity-forbidden, the design
of efficient luminescent lanthanide(III) complexes continues to be
an active area of research. The weak absorbance can be overcome
by coordinating ligands containing chromophores to the lantha-
nide ion, which upon irradiation, transfers energy to the central
metal ions, typically via the ligand triplet excited state, populating
the lanthanide(III) emitting levels in a process known as the
antenna effect [15–18].
properties. It is expected that the amide type podands which have
flexible arms and ‘‘terminal-group effects’’ [19], will shield the
encapsulated lanthanide ions from interaction with the surroundings
effectively, and thus to have novel coordination structures and exhibit
good luminescent properties. Our group has been interested in
employing self-assembly strategies for luminescent lanthanide coor-
dination polymers, and has recently used podands as sensitizers for
lanthanide luminescence. As a part of our systematic studies,
this work reports the assembly of two lanthanide coordination
polymers including a one-dimensional (1D) linear chain coordina-
tion polymer [ErLI(NO3)3(CH3CO2Et)]n and
a one-dimensional
(1D) zig-zag coordination polymer {[TbLII(NO3)3(H2O)] ꢀ (H2O)}n
(LI¼1,2-bis{[(20-furfurylaminoformyl)phenoxyl]methyl}benzene, LII¼
1,2-bis{[2’-(2-pyridylmethylaminoformyl)phenoxyl]methyl}benzene
[20], Scheme 1) by two structurally related amide type bridging
podands which have uniform skeleton and different terminal groups,
and the luminescent properties of the Tb(III) complexes. The lowest
triplet state energy levels of the two ligands which were calculated
from the phosphorescence spectra of the Gd(III) complexes at 77 K
indicate that the triplet state energy levels of the antennae are both
above the lowest excited resonance level of 5D4 (20,545 cm–1) of Tb(III),
and the absorbed energy could be transferred from podand LI or LII to
the Tb(III). And the influence of the structures of the coordination
polymers on the luminescent intensities of the complexes was also
discussed.
n Corresponding author. Fax: +86 931 8912582.
E-mail address: tangyu@lzu.edu.cn (Y. Tang).
0022-4596/$ - see front matter & 2010 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2010.11.011

Q. Wang et al. / Journal of Solid State Chemistry 184 (2011) 164–170
165
2. Experimental
as the excitation source. Reported luminescence lifetimes are
averages of at least three independent determinations.
2.1. Materials
2.3. Crystal structure determination
Furfurylsalicylamide [21] were prepared according to the
literature methods. The other commercially available chemicals
were of A.R. grade and were used without further purification.
Suitable single crystal of the nitrate complexes were carefully
selected under an optical microscope and subsequently glued to the
tip of a glass fiber. Intensity data were collected on a Bruker SMART
˚
2.2. Methods
1000 CCD diffractometer using MoKa radiation (l¼0.71073 A) and
integrated using the SAINT suite of software. The absorption correc-
tions were calculated using SADABS. Primary non-hydrogen atoms
were solved by direct method and refined anisotropically by full-
matrix least-squares methods on F2. Hydrogen atoms were placed in
calculated positions and included in the final cycles of refinement
using a riding model. The programs for structure solution and
refinement were SHELXS-97 and SHELXL-97, respectively [22].
The crystal data and refinement results are summarized in Table 1,
and selected bond lengths and angles are given in Tables 2 and 3
respectively. CCDC reference numbers 783278 and 783279.
Carbon, nitrogen and hydrogen were determined on an Ele-
mentar Vario EL. Powder X-ray diffraction patterns (PXRD) were
determined with Rigaku-Dmax 2400 diffractometer using CuK
a
radiation. The FT-IR spectra were recorded on a Nicolet 360 FT-IR
instrument using KBr disks in the 4000–400 cmꢁ1 region. 1H NMR
spectra were measured on a Bruker AM400 spectrometer in
d-chloroform solutions, with TMS as internal standard. Lumines-
cence spectra and phosphorescence spectra were obtained on a
Hitachi F-4500 fluorescence spectrophotometer. The quantum
yields of the terbium samples were determined by an absolute
method using an integrating sphere (150 mm diameter, BaSO4
coating) from Edinburgh Instruments FLS920. The lifetime
measurements were measured on an Edinburgh Instruments
FLS920 Fluorescence Spectrometer with Nd pumped OPOlette laser
2.4. Syntheses of the ligands
The
podand
1,2-bis{[(2’-furfurylaminoformyl)phenoxyl]-
methyl}benzene (LI) was prepared by the following synthetic
route. Furfurylsalicylamide [21] (7.5 mmol) and anhydrous potas-
sium carbonate (8.1 mmol) were refluxed in acetone (50 cm3) for
30 min, then the o-xylene dibromide (3.4 mmol) was added to the
solution. The reaction mixture was refluxed for 12 h. After cooling
down, the mixture was filtered and the solvent was distilled off.
Then the resulted solid was recrystallized with acetone to get the
ligand LI; Yield: 81%; m.p.: 143–144 1C; 1H NMR (CDCl3, 400 MHz):
4.50(d, 4H), 5.15(s, 4H), 6.01(d, 2H), 6.21(d, 2H), 6.94(d, 2H), 7.06–
7.48(m, 10H), 8.00(s, 2H), 8.21(t, 2H) ppm. IR (KBr,
n
, cmꢁ1):
3386(m), 3062(m), 1639(s, C¼O), 1600(m), 1537(s), 1299(s),
1245(s), 1115(m), 754(s), 695(m). Anal. Calcd. for C32H28N2O6
(%): C, 71.63; H, 5.26; N, 5.22; Found (%): C, 71.75; H, 5.16; N, 5.20.
Scheme 1. The schematic illustration of the ligands LI and LII.
Table 1
Crystal data and structure refinements for the Er(III) and Tb(III) complexes.
Empirical formula
Formula weight
Temperature (K)
C36H36N5O17Er
977.96
C34H34N7O15Tb
939.6
296(2)
296(2)
0.71073
0.71073
˚
Wavelength (A)
Crystal system, Space group
Triclinic, Pꢁ1
Orthorhombic, Pbca
11.7595(16)
17.818(4)
˚
a (A)
12.994(2)
13.930(2)
17.818
˚
b (A)
23.674(6)
˚
c (A)
a
b
g
(deg)
89.367(6)
74.859(6)
75.365(6)
1984.5(5)
90.00
90.00
(deg)
(deg)
90.00
3
7516(3)
˚
Volume (A )
Z
Dcalc (Mg mꢁ3
Absorption coefficient (mmꢁ1
F(000)
2
8
)
1.637
1.661
)
2.196
1.962
982
3776
Crystal size (mm)
0.38 ꢂ 0.35 ꢂ 0.29
1.52–26.00
0.38 ꢂ 0.34 ꢂ 0.30
2.36–27.65
y
range for data collection (deg)
Index ranges
ꢁ14rhr14, ꢁ15rkr16, ꢁ16rlr17
7710
ꢁ22rhr23, ꢁ23rkr20, ꢁ29rlr29
6008
Reflections collected
Independent reflections(Rint
Data/restraints/parameters
Absorption correction
Refinement method
Goodness-of-fit on F2
R indices (all data)
)
6712(0.0566)
8836(0.0518)
7710/0/466
8836/6/531
Semi-empirical from equivalents
Full-matrix least-squares on F2
1.080
Semi-empirical from equivalents
Full-matrix least-squares on F2
1.002
R1¼0.0408, wR2¼0.1079
R1¼0.0468, wR2¼0.1121
R1¼0.0604, wR2¼0.0727
R1¼0.0304, wR2¼0.0613
Final R indices [I42s(I)]

166
Q. Wang et al. / Journal of Solid State Chemistry 184 (2011) 164–170
Table 2
I
˚
Selected bond lengths (A) and angles (deg) for the complex [ErL (NO3)3(CH3CO2Et)]n.
Er(1)–O(5)
2.286(2)
Er(1)–O(2)
2.291(2)
Er(1)–O(16)
2.366(3)
Er(1)–O(13)
2.398(3)
Er(1)–O(9)
2.414(3)
Er(1)–O(10)
2.426(3)
Er(1)–O(15)
2.431(3)
Er(1)–O(12)
2.442(3)
Er(1)–O(7)
2.447(3)
O(5)–Er(1)–O(2)
O(16)–Er(1)–O(13)
O(5)–Er(1)–O(10)
O(13)–Er(1)–O(10)
O(2)–Er(1)–O(15)
O(9)–Er(1)–O(15)
O(2)–Er(1)–O(12)
O(9)–Er(1)–O(12)
O(5)–Er(1)–O(7)
O(13)–Er(1)–O(7)
O(15)–Er(1)–O(7)
86.77(9)
O(5)–Er(1)–O(16)
O(5)–Er(1)–O(9)
O(2)–Er(1)–O(10)
O(9)–Er(1)–O(10)
O(16)–Er(1)–O(15)
O(10)–Er(1)–O(15)
O(16)–Er(1)–O(12)
O(10)–Er(1)–O(12)
O(2)–Er(1)–O(7)
O(9)–Er(1)–O(7)
O(12)–Er(1)–O(7)
148.76(10)
81.64(10)
141.32(9)
85.02(11)
72.11(9)
O(2)–Er(1)–O(13)
O(2)–Er(1)–O(9)
O(16)–Er(1)–O(10)
O(5)–Er(1)–O(15)
O(13)–Er(1)–O(15)
O(5)–Er(1)–O(12)
O(13)–Er(1)–O(12)
O(15)–Er(1)–O(12)
O(16)–Er(1)–O(7)
O(10)–Er(1)–O(7)
125.31(10)
81.49(10)
71.74(10)
77.05(9)
75.71(10)
126.84(9)
82.69(10)
72.63(9)
52.69(9)
147.11(11)
151.14(10)
73.73(11)
130.71(10)
146.59(11)
131.90(10)
127.86(10)
118.21(10)
51.53(9)
75.34(9)
74.96(11)
123.28(10)
76.17(10)
71.61(11)
71.44(10)
52.37(10)
103.33(11)
Table 3
II
˚
Selected bond lengths (A) and angles (deg) for the complex {[TbL (NO3)3(H2O)] ꢀ (H2O)}n.
Tb(1)–O(1)
2.486(2)
2.524(3)
2.334(2)
86.34(9)
83.98(8)
155.80(8)
118.83(8)
149.62(9)
81.41(8)
51.52(7)
74.09(9)
73.61(8)
121.69(8)
99.79(9)
68.35(10)
Tb(1)–O(2)
2.460(2)
2.486(2)
2.314(2)
80.23(8)
148.82(8)
77.60(8)
125.21(10)
79.34(9)
154.68(8)
105.79(8)
75.23(9)
118.01(9)
147.31(9)
68.72(8)
67.72(9)
Tb(1)–O(3)
2.465(2)
2.475(2)
2.310(2)
83.36(8)
123.74(8)
80.02(8)
82.29(9)
70.81(9)
72.79(8)
122.80(8)
147.31(8)
51.16(10)
126.29(9)
51.00(8)
112.76(9)
Tb(1)–O(4)
Tb(1)–O(7)
Tb(1)–O(10)
Tb(1)–O(11)
Tb(1)–O(13)
Tb(1)–O(17)
O(17)–Tb(1)–O(13)
O(17)–Tb(1)–O(2)
O(17)–Tb(1)–O(3)
O(2)–Tb(1)–O(3)
O(11)–Tb(1)–O(10)
O(17)–Tb(1)–O(1)
O(2)–Tb(1)–O(1)
O(17)–Tb(1)–O(7)
O(2)–Tb(1)–O(7)
O(1)–Tb(1)–O(7)
O(11)–Tb(1)–O(4)
O(10)–Tb(1)–O(4)
O(17)–Tb(1)–O(11)
O(13)–Tb(1)–O(2)
O(13)–Tb(1)–O(3)
O(17)–Tb(1)–O(10)
O(2)–Tb(1)–O(10)
O(13)–Tb(1)–O(1)
O(3)–Tb(1)–O(1)
O(13)–Tb(1)–O(7)
O(3)–Tb(1)–O(7)
O(17)–Tb(1)–O(4)
O(2)–Tb(1)–O(4)
O(1)–Tb(1)–O(4)
O(13)–Tb(1)–O(11)
O(11)–Tb(1)–O(2)
O(11)–Tb(1)–O(3)
O(13)–Tb(1)–O(10)
O(3)–Tb(1)–O(10)
O(11)–Tb(1)–O(1)
O(10)–Tb(1)–O(1)
O(11)–Tb(1)–O(7)
O(10)–Tb(1)–O(7)
O(13)–Tb(1)–O(4)
O(3)–Tb(1)–O(4)
O(7)–Tb(1)–O(4)
The podand 1,2-bis{[2’-(2-pyridylmethylaminoformyl)phenox-
yl]methyl}benzene (LII) was synthesized and characterized as
reported in our previous paper [20].
2.5. Syntheses of the complexes
The 0.1 mmol lanthanide nitrate (Ln¼Gd, Tb, Er) was dissolved
in 5 cm3 of ethyl acetate, then the solution of 0.1 mmol ligand LI in
5 cm3 of ethyl acetate was added dropwise. The mixture was stirred
at room temperature for 4 h. And then the precipitated solid
complex was filtered, washed with ethyl acetate, dried in vacuum
over P4O10 for 48 h and submitted for elemental analysis.
[GdLI(NO3)3]ꢀ CH3CO2Et yield 67%. Anal. Calcd for C36H36N5O17Gd
(%): C, 44.67; H, 3.75; N, 7.24; Found (%): C, 44.72; H, 3.64; N, 7.55.
Major IR bands (KBr; cmꢁ1),
1296,
2(NO3ꢁ): 1028,
n
(C¼O): 1617,
n n
1(NO3ꢁ): 1503, 4(NO3ꢁ):
n(C¼O ethyl acetate): 1681.
n
n
5(NO3ꢁ): 815,
[TbLI(NO3)3]ꢀ CH3CO2Et yield 70%. Anal. Calcd for C36H36N5O17Tb (%):
Fig. 1. The powder X-ray diffraction patterns for Tb (upper) and Er (lower)
complexes with the ligand LI.
C, 44.59; H, 3.74; N, 7.22; Found (%): C, 44.89; H, 3.71; N, 7.33. Major IR
bands (KBr; cmꢁ1),
n
(C¼O): 1618,
n n
1(NO3ꢁ): 1504, 4(NO3ꢁ): 1297,
n(C¼O ethyl acetate): 1681.
n
2(NO3ꢁ): 1028,
n
5(NO3ꢁ): 815,
[ErLIꢁ(NO3)3]ꢀ CH3CO2Et yield 61%. Anal. Calcd. for C36H36N5O17Er
3. Results and discussion
(%): C, 44.21; H, 3.71; N, 7.16; Found (%): C, 44.28; H, 3.56; N, 7.21.
Major IR bands (KBr; cmꢁ1),
n
(C¼O): 1620,
n
1(NO3ꢁ): 1507,
n
4(NO3ꢁ):
3.1. Physical measurements
1299,
n
2(NO3ꢁ): 1029,
n
5(NO3ꢁ): 815,
n(C¼O ethyl acetate): 1682.
The new complexes gave satisfactory microanalytical results,
justifying their purity. Analytical data for the complexes with the
ligand LI conform to a 1:1 (metal:L) stoichiometry [LnLI(NO3)3]ꢀ
CH3CO2Et (Ln¼Gd, Tb, Er). All the complexes are soluble in DMF,
General procedure for the synthesis of lanthanide complexes
[TbLII(NO3)3] ꢀ 2H2O and [GdLII(NO3)3] ꢀ 2H2O, the elemental ana-
lyses and IR spectra characterization of the complexes were
reported before [20].

Q. Wang et al. / Journal of Solid State Chemistry 184 (2011) 164–170
167
DMSO, methanol, ethanol, acetone, but slightly soluble in acetonitrile,
THF and ethyl ether.
The complexes have the similar powder X-ray diffraction pat-
terns and IR spectra, of which the characteristic bands have similar
shifts, suggesting that they have a similar coordination structure.
The room temperature PXRD patterns of the Tb(III) and Er(III)
complexes with the ligand LI are unfolded from 51 to 401 as shown
in Fig. 1, and the IR spectra of the complexes are presented in Fig. 2.
The characteristic bands of the
n(C¼O), n(C–O–C) of free ligand
LI are shown at 1639 and 1115 cmꢁ1, respectively. In the IR spectra
of the complexes, the low-energy bands remain unchanged, but the
high-energy bands of the complexes red shift to about 1618 cmꢁ1
(D
n
¼21 cmꢁ1) as compared to the free ligand, thus indicating that
only the oxygen atoms of C¼O take part in coordination to the
lanthanide ions. The band at about 1681 cmꢁ1 may be assigned to
the
complexes assigned to the coordinated nitrate groups (C2v) are
observed at about 1503 cmꢁ1 1), 1296 cmꢁ1 4), 1028 cmꢁ1
and 815 cmꢁ1
5) [23]. The separation of two strongest frequency
bands 9n1
n(C¼O) of the ethyl acetate molecules. The absorption bands of
(
n
(
n
(n2)
(
n
–n
49 lies at about 200 cmꢁ1, clearly establishing that the
NO–3 groups in the solid complexes coordinate to the lanthanide
ions as bidentate ligands [24].
3.2. Crystal structure descriptions
[ErLI(NO3)3(CH3CO2Et)]n Pink crystals suitable for X-ray diffrac-
tion were obtained by slow evaporation of the methanol and
ethyl acetate mixture (V:V¼1:2) solution of the Er(III) complex.
The single-crystal X-ray analysis of the complex [ErLI(NO3)3
(CH3CO2Et)]n reveals that the crystal crystallizes in triclinic Pꢁ1
space group and each Er3+ is coordinated with nine oxygen donor
atoms, six of which belong to three bidentate nitrate groups, two
belong to carbonyl groups from two bridging podands and the
remaining one to coordinated ethyl acetate molecule, with Er–O
Fig. 2. The IR spectra of Tb (upper) and Er (lower) complexes with the
ligand LI.
˚
distances range from 2.286(2) to 2.447(3) A (Fig. 3). The coordina-
tion polyhedron around the Er(III) is a distorted tricapped triprism.
At the same time, each ligand binds to two Er(III) using its two
oxygen atoms of the amide groups. So the whole structure consists
of an infinite array of Er(III) bridged by bidentate ligands and a one-
dimensional (1D) coordination polymeric linear chain is formed
(Fig. 4).
Many lanthanide complexes based on the same ligand usually
have alike building blocks due to similar valence shell electron
configurations [25–27], thus we may deduce that the structure of
Tb3+ complex is similar to Er3+ complex, which can also be proved
by the PXRD patterns and IR spectra.
{[TbLII(NO3)3(H2O)] ꢀ (H2O)}n Colorless crystals suitable for
X-ray diffraction were obtained by slow evaporation of the
methanol and ethyl acetate mixture (V:V¼1:2) solution of the
Tb3+ complex. The single-crystal X-ray analysis of the complex
{[TbLII(NO3)3(H2O)] ꢀ (H2O)}n reveals that each Tb3+ ion is coordi-
nated with nine oxygen donor atoms, six of which belong to three
bidentate nitrate groups, two belong to carbonyl groups from two
bridging podands and the remaining one to coordinated water
molecule (Fig. 5). The coordination polyhedron around Tb3+ is a
distorted tricapped triprism. Every asymmetric unit contains one
crystal water molecule. At the same time, each ligand binds to
two Tb3+ ions using its two oxygen atoms of the amide groups.
So the whole structure consists of an infinite array of Tb3+ ions
bridged by bidentate ligands and a one-dimensional (1D) zig-zag
coordination polymeric chain is formed (Fig. 6). The Tb–Tb
Fig. 3. Structure of [ErLI(NO3)3(CH3CO2Et)]n showing the coordination sphere
of Er3+ along with atom labeling schemes (hydrogen atoms are omitted for
clarity).
Fig. 4. 1D coordination polymer linear chain of [ErLI(NO3)3(CH3CO2Et)]n (hydrogen atoms are omitted for clarity).

168
Q. Wang et al. / Journal of Solid State Chemistry 184 (2011) 164–170
˚
separations linked by the same bridging ligand are about 16.007 A
and the separations between alternate Tb(III) centers (on the same
polymer. As a result, neutral chains are interpenetrated into a 3D
supramolecular structure (Fig. 7).
˚
side of the zig-zag) are about 17.818 A. The Tb–Tb–Tb internal
There were also strong intramolecular hydrogen bonding
between the amide nitrogen atoms (N4 and N5) and the etheric
oxygen atoms (O14 and O15), as well as the oxygen atoms of the
coordinated water molecules (O17) and the nitrogen atoms of
terminal pyridyl groups (listed in Table 4) within Tb(III) complex. It
is no doubt to note that the robust intramolecular hydrogen bond
have a template effect and participate in the stabilization of the
complete architecture.
angle of 67.641. Furthermore, the zig-zag coordination chains are
formed through the p–p interaction between the benzyl groups of
the two arms of neighboring ligands which are almost parallel (the
centroid-to-centroid distance and dihedral angle between them
˚
are 3.802 A and 4.691).
In the context of inorganic crystal engineering, the combination
of coordination chemistry with non-covalent interactions, such as
hydrogen bonding, provides a powerful method for generating
supramolecular architectures from simple building blocks. The
oxygen atoms of the nitrate anions and crystal water molecules (O3
and O16), the nitrogen atoms of the terminal pyridyl groups (N6)
act as hydrogen bond acceptors while the oxygen atoms of the
crystal and coordinated water molecules (O16 and O17) act as
donors (listed in Table 4), constitute complementary hydrogen
bonding recognition sites on the backbone of the 1D coordination
3.3. Luminescent properties of the complexes
Monitored by the emission band at 545 or 543 nm, the Tb(III)
complexes [TbLI(NO3)3(CH3CO2Et)]n and {[TbLII(NO3)3(H2O)] ꢀ
(H2O)}n both exhibit broad excitation bands around 320 nm. The
luminescence emission spectra of these two Tb(III) complexes in
solid state (the excitation and emission slit widths were 1.0 nm
(Fig. 8)) were recorded at room temperature. It can be seen from
Fig. 8 that the complexes show the characteristic f–f transition
emissions of Tb(III) when excited with 321 and 322 nm, respec-
tively, in the solid state (the data listed in Table 5). These indicate
Fig. 5. Structure of {[TbLII(NO3)3(H2O)] ꢀ (H2O)}n showing the coordination sphere
of Tb3+ along with atom labeling schemes (hydrogen atoms and crystalline water
molecule are omitted for clarity).
Fig. 7. The 3D supramolecular structure of {[TbLII(NO3)3(H2O)] ꢀ (H2O)}n con-
structed by hydrogen bonds. (The nitrate anions without formed hydrogen bonds
are omitted for clarity.)
Fig. 6. 1D zig-zag coordination polymer of {[TbLII(NO3)3(H2O)] ꢀ (H2O)}n (hydrogen atoms and crystalline water molecules are omitted for clarity).
Table 4
II
˚
Hydrogen bonds in crystal packing (A, deg) of {[TbL (NO3)3(H2O)] ꢀ (H2O)}n.
D–H?A
d(D–H)
d(H?A)
d(D?A)
+DHA
Symmetry code
O(16)–H(16C)?N(6) (inter)
O(16)–H(16D)?O(3) (inter)
O(17)–H(17D)?O(16) (inter)
N(4)–H(4)?O(14) (intra)
O(5)–H(5)?O(15) (intra)
O(17)–H(17C)?N(7) (intra)
0.86
0.86
0.87
0.86
0.86
0.84
2.01
2.04
1.78
1.98
2.01
1.95
2.8350
2.8757
2.6353
2.6322
2.6700
2.7796
160
164
167
132
132
173
ꢁx, ꢁ1/2+y, 1/2ꢁz
ꢁ1/2+x, 1/2ꢁy, 1ꢁz

Q. Wang et al. / Journal of Solid State Chemistry 184 (2011) 164–170
169
complex without water molecule. It is well-known that the O–H
oscillator of the solvent coordinated to the metal center can provide
an efficient nonradiative path [29,30]. On the basis of the crystal
structure analysis, we may deduce that the nonradiative transitions
due to the O–H oscillators and the vibration of the ligands in the
Tb(III) first coordination shell of the LII complex, which may quench
the luminescence of the central ions, were weakened and
restrained to some extent by the hydrogen bonding interactions
between the coordinated water molecule, the terminal picolyl
group and the crystallized water molecules, thus bringing the
excellent luminescence efficiency of the hydrated LII complex.
4. Conclusion
This study demonstrates that two structure-related bridging
podands with terminal groups from furan to pyridine of salicylamide,
1,2-bis{[(2’-furfurylaminoformyl)phenoxyl]methyl}benzene (LI) and
1,2-bis{[2’-(2-pyridylmethylaminoformyl)phenoxyl]methyl}benzene
(LII), form 1D linear chain and zig-zag coordination polymers [ErLI
(NO3)3(CH3CO2Et)]n and {[TbLII(NO3)3(H2O)] ꢀ (H2O)}n with lanthanide
cations via the carbonyl oxygen donors. In {[TbLII(NO3)3(H2O)] ꢀ
(H2O)}n, the free and coordinated water molecules play an important
role in the structure, which links the neutral chains with two hydrogen
bonds from two different directions, as a result, the neutral chains are
interpenetrated into a 3D supramolecular structure. The luminescent
properties of the Tb(III) complexes in solid state were investigated. And
the lowest triplet state energy levels of the podands LI and LII indicate
that the antennae with different terminal groups are both good organic
chelators to absorb energy and transfer them to central Tb3+ ions. The
complex {[TbLII(NO3)3(H2O)] ꢀ (H2O)}n which contains coordinated and
crystal water molecules displays better fluorescence quantum yield
and longer lifetime than the LI complex [TbLI(NO3)3(CH3CO2Et)]n. This
phenomenon may be produced by that the nonradiative transitions
due to the O–H oscillators and the vibration of the ligands in the Tb(III)
first coordination shell of the LII complex were restrained to some
extent by the hydrogen bonding interactions.
Fig. 8. Emission spectra of the Tb3+ complexes with the ligand LI (weak) and LII
(strong).
Table 5
Luminescence data for the Tb(III) complexes in solid state at room temperature.
Complexes
RFIa
Assignments
lEx (nm)
lEm (nm)
[TbLI(NO3)3(CH3CO2Et)]n
321
492
545
583
620
40
5D4-7F6
5D4-7F5
5D4-7F4
5D4-7F3
116
6
2
{[TbL99(NO3)3(H2O)] ꢀ H2O}n
322
489
543
581
620
581
1321
72
5D4-7F6
5D4-7F5
5D4-7F4
5D4-7F3
21
a
RFI: relative luminescence intensity.
Supplementary material
that the ligands LI and LII are comparatively good organic chelators
to absorb and transfer the energy to the central Tb3+ ions.
An intramolecular energy transfer from the triplet state of the
ligand to the resonance level of the Ln(III) ion is one of the most
important process having influence on the Ln(III) luminescent
properties of Ln(III) chelates [28]. A triplet excited state T1 which is
localized on one ligand only and is independent of the nature of the
lanthanide ions [28]. The triplet state energy levels T1 of the ligands
LI and LII, which were calculated from the shortest-wavelength
phosphorescence bands [28], are 24,449 and 24,814 cmꢁ1 [20].
These energy levels are both above the lowest excited resonance
level 5D4 (20,545 cmꢁ1) of Tb(III). Thus, the absorbed energy could
be transferred from ligands to the Tb3+ ions.
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Center, CCDC
nos. 783278 and 783279. Copies of this information may be
obtained free of charge from the director, CCDC, 12 Union Road,
Cambridge CB2 IEZ, UK (e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
Acknowledgments
This work was supported by the National Natural Science
Foundation of China (Project No. 20931003) and the program for
New Century Excellent Talents in University (NCET-06-0902).
The fluorescence quantum yield
F
of the complex {[TbLII(NO3)3
(H2O)] ꢀ H2O}n in solid state was found to be 41.170.1% using
an integrating sphere, which is higher than the complex
[TbLI(NO3)3(CH3CO2Et)]n (28.870.1%). And the luminescence
decay of the two Tb(III) complexes are best described by a
single-exponential process with significantly longer lifetimes of
Appendix A. Supplementary material
Supplementary data associated with this article can be found in
the online version at doi:10.1016/j.jssc.2010.11.011.
t
¼1.42570.001 ms ({[TbLII(NO3)3(H2O)] ꢀ H2O}n) and
t¼1.3727
0.001 ms ([TbLI(NO3)3(CH3CO2Et)]n), indicating the presence of one
distinct emitting species, respectively. From the crystal structures
of the complexes, we could find that the coordination environ-
ments of the Tb3+ ions are similar with the two ligands LI and LII, but
the luminescent properties of the LII complex which contain
coordinated water and crystal water is greatly better than the LI
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