Synthesis, crystal structure and luminescence properties of lanthanide complexes with a new semirigid bridging furfurylsalicylamide ligand

Article abstract of DOI:10.1016/j.ica.2012.04.007

We present here new lanthanide coordination polymers based on a semirigid bridging furfurylsalicylamide ligand which were synthesized and characterized by elemental analysis, X-ray powder diffraction and IR measurements. The coordination polymer [Pr₂L₃(NO₃) ₆]_∞ displays a two-dimensional honeycomb-like framework, which can be regarded as a (6,3) topological network with praseodymium atoms acting as "three-connected" centers. The photoluminescence analysis indicates that there is an efficient ligand-to-LnIII energy transfer in TbIII complex and the ligand is an efficient "antenna" for TbIII. From a more general perspective, the results demonstrated herein provide the possibility of controlling the formation of the desired lanthanide coordination structure to enrich the crystal engineering strategy and enlarges the arsenal for developing excellent luminescent lanthanide complexes of salicylamide derivatives.

Full text of DOI:10.1016/j.ica.2012.04.007

Inorganica Chimica Acta 391 (2012) 171–178
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, crystal structure and luminescence properties of lanthanide
complexes with a new semirigid bridging furfurylsalicylamide ligand
a
a
b,
Xue-Qin Song a, , Li Wang , Qing-Fang Zheng , Wei-Sheng Liu
⇑
⇑
a School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China
b College of Chemistry and Chemical Engineering and State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
We present here new lanthanide coordination polymers based on a semirigid bridging furfurylsalicylamide
ligand which were synthesized and characterized by elemental analysis, X-ray powder diffraction and IR
Received 4 February 2012
Received in revised form 3 April 2012
Accepted 3 April 2012
measurements. The coordination polymer [Pr2L3(NO3)6] displays a two-dimensional honeycomb-like
1
framework, which can be regarded as a (6,3) topological network with praseodymium atoms acting as
‘‘three-connected’’ centers. The photoluminescence analysis indicates that there is an efficient ligand-to-
LnIII energy transfer in TbIII complex and the ligand is an efficient ‘‘antenna’’ for TbIII. From a more general
perspective, the results demonstrated herein provide the possibility of controlling the formation of the
desired lanthanide coordination structure to enrich the crystal engineering strategy and enlarges the arse-
nal for developing excellent luminescent lanthanide complexes of salicylamide derivatives.
Ó 2012 Published by Elsevier B.V.
Available online 23 April 2012
Keywords:
Salicylamide ligand
Lanthanide coordination polymer
Crystal structure
Luminescence properties
1. Introduction
furfurylaminoformyl)phenoxyl]methyl}-1,2,4,5-tetramethylbenzene
(L) (Scheme 1) and the resulting lanthanide complexes to extend
Materials incorporating lanthanide ions are of great interest for
a wide range of optical applications, such as biomedical analysis
and material science [1,2]. Trivalent lanthanide ions are fascinating
in luminescence sources for their high color purity and relatively
long lifetimes of the excited states. Among the luminescent lantha-
nide complexes, EuIII and TbIII compounds show strong lumines-
cence in the visible region, making them to be good candidates
for fluoroimmunoassays and structural probes. Lanthanide ions ex-
hibit, however, low luminescence intensity due to the fact that the
4f ? 4f transitions are parity forbidden. One of the most useful
strategies that has been employed to overcome this drawback is
to combine the lanthanide ions through the coordination with or-
ganic ligands acting as sensitizers, which is the so-called ‘‘antenna
effect’’ [3,4]. The ligands absorb UV or visible light and efficiently
transfer the energy to the central lanthanide ion (intramolecular
energy transfer), ultimately resulting in sensitized Ln(III) ion
emission. Among the various organic ligands [5–10] used for con-
structing lanthanide coordination complexes, salicylamide deriva-
our systematic research .
As a result, the reaction of L with trivalent lanthanide ions affor-
ded a novel two-dimensional honeycomb-like framework, which
can be regarded as a (6,3) topological network with praseodymium
atoms acting as ‘‘three-connected’’ centers. Under the excitation of
UV light, SmIII, EuIII, TbIII and DyIII complexes exhibit characteris-
tic emissions of corresponding lanthanide ions. The lowest triplet
state energy levels of the ligand was calculated from the phospho-
rescence spectra of the GdIII complex at 77 K. The results presented
herein indicated that the new semirigid bridging ligand exhibited a
good antennae effect with respect to the TbIII ion due to efficient
intersystem crossing and ligand to metal energy transfer.
2. Experimental
2.1. Materials and instrumentation
Furfurylamine was obtained from Alfa Aesar Co. Other commer-
cially available chemicals were of analytical grade and were used
without further purification. The lanthanide nitrates [12] were pre-
pared according to the literature method.
The metal ions were determined by EDTA titration using xyle-
nol orange as indicator. Carbon, nitrogen and hydrogen analyses
were performed using an EL elemental analyzer. Melting points
were determined on a Kofler apparatus. Powder X-ray diffraction
patterns (PXRD) were determined with Rigaku-D/Max-II X-ray dif-
tives provide
a fascinating prospect in preparing lanthanide
coordination polymers possessing strong luminescence properties
[11] which prompts us to synthesize and investigate analogs
of the extensive series of these ligands. Therefore we synthesis
the new member of salicylamide derivatives namely, 3,6-bis{[(20-
⇑
Corresponding authors. Tel.: +86 931 8843385; fax: +86 931 4938755
(X.-Q. Song), tel./fax: +86 931 8915151 (W.-S. Liu).
E-mail addresses: songxq@mail.lzjtu.cn (X.-Q. Song), liuws@lzu.edu.cn (W.-S. Liu).
fractometer with graphite-monochromatized Cu Ka radiation.
0020-1693/$ - see front matter Ó 2012 Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.ica.2012.04.007

172
X.-Q. Song et al. / Inorganica Chimica Acta 391 (2012) 171–178
Table 1
Crystal data and structure refinement parameters for Pr(III) complex.
Empirical formula
C108H108N12O36Pr2
Crystal system, space group
Triclinic, P-1
Unit cell dimensions
0
11.729(6)
17.716(9)
20.360(10)
a (ÅA)
0
b (AÅ)
0
c (AÅ)
a
b (°)
c
V (AÅ3)
(°)
69.109(6)
89.186(6)
89.739(7)
3952(3)
(°)
0
Z, Calculated density (kg/m3)
Absorption coefficient (mmꢀ1
F(000)
1, 1.021
0.671
1244
)
Crystal size (mm)
Theta range for data collect (°)
0.46 ꢂ 0.45 ꢂ 0.31
2.03–25.01
Limiting indices
ꢀ13 6 h 6 13, ꢀ21 6 k 6 16,
ꢀ24 6 l 6 24
Reflections collected/unique
20017/13537 [R(int) = 0.0631]
Completeness to theta = 25.01 (%) 97.2
Data/restraints/parameters
13537/2/712
1.000
Goodness-of-fit on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0751, wR2 = 0.1580
R1 = 0.1405, wR2 = 0.1685
To a solution of 2-furfurylsalicylamide (2.28 g, 10.5 mmol)
in dry acetone was added 1.52 g (11 mmol) dried K2CO3, and
the mixture was stirred for 30 min at room temperature, 1.59 g
(5 mmol) 1,4-bis(bromomethyl)-2,3,5,6-tetramethylbenzenezene in
20 ml of dry acetone was added dropwise in 30 min and the result-
ing solution stirred and heated to reflux for 24 h. After cooling
down, inorganic salts were separated by filtration and the solvent
removed from the filtrate under reduced pressure. The crude prod-
uct was recrystallized with ethyl acetate to give a white solid.
2.55 g, Yield 86%. M.p. 151–152 °C. Anal. Calc. for C36H36N2O6: C,
72.95; H, 6.12; N, 4.73. Found: C, 72.67; H, 6.14; N, 4.76%. IR
Scheme 1. The synthetic route of the ligand L.
Infrared spectra (4000–400 cmꢀ1) were obtained with KBr discs on
a Therrno Mattson FTIR spectrometer. 1H NMR spectra were re-
corded on a Bruker DRX 300 spectrometer in CDCl3 solution with
TMS as internal standard. Fluorescence measurements of the well
grinded thick solid samples were made on a Hitachi F-4500 spec-
trophotometer equipped with a xenon lamp as the excitation
source (front-face mode). Samples were placed between two
quartz cover slips and the excitation and emission slit of 2.5 nm
were used. The 77 K solution-state phosphorescence spectra of
the Gd(III) complex was recorded with solution samples (a 1:1
ethyl acetate–MeOH (v/v) mixture) loaded in a quartz tube inside
a quartz-walled optical Dewar flask filled with liquid nitrogen in
the phosphorescence mode [13]. Quantum yields were determined
by an absolute method [14] using an integrating sphere on FLS920
of Edinburgh Instrument. The luminescence decays were recorded
using a pumped dye laser (Lambda Physics model FL2002) as the
excitation source. The nominal pulse width and the line width of
the dye-laser output were 10 ns and 0.18 cmꢀ1, respectively. The
emission of the sample was collected by two lenses in a monochro-
mator (WDG30), detected by a photomultiplier and processed by a
Boxcar Average (EGG model 162) in line with a microcomputer. Re-
ported quantum yields and luminescence lifetimes are averages of
at least three independent determinations. The estimated errors
for quantum yields and luminescence lifetimes are 10%.
(KBr, m
, cmꢀ1): 3375 (s), 2912 (m), 2886 (w), 1645 (s, C@O), 1597
(m), 1532 (s), 1481 (m), 1293 (s),1226 (s, Ar–O), 752 (s). 1H NMR
(CDCl3, 300 MHz): d: 2.25 (s, 12H, CH3), 4.41 (d, 4H, NHCH2,
J = 3.6 Hz), 5.25 (s, 4H, OCH2), 5.80 (d, 2H, furan d, J = 2.7 Hz),
6.13 (m, 2H, furan d, J = 2.1 Hz), 7.09–7.54 (m, 6H, ArH), 7.53 (t,
2H, Ar, J = 5.4 Hz), 8.11 (t, 2H, NH), 8.31 (d, 2H, Ar, J = 6.9 Hz).
2.3. Synthesis of the complexes
To a clear solution of L (0.086 g, 0.1 mmol) in CHCl3 (2 ml) was
added Ln(NO3)3ꢁ5H2O (0.15 mmol) in 10 ml of ethyl acetate. The
resulting solution was left stirring overnight at room temperature
to afford a pale white solid which was filtered off, washed three
times with ethyl acetate and CHCl3 respectively, and dried over
CaCl2 for 3 days to give the product in 70–80% yield. The single
crystals of PrIII complex were obtained as follows: 10 ml of ethyl
acetate was added to a clear solution of L (0.086 g, 0.1 mmol) in
CHCl3 (2 ml) in 30 ml test tube. The resulting solution was left
standing for about 30 min, then Pr(NO3)3ꢁ5H2O (0.15 mmol) in
10 ml of ethyl acetate was added carefully and sealed for crystalli-
zation at room temperature. After about two weeks pale green
crystals suitable for analysis were obtained.
2.2. Synthesis of the ligand
2.4. X-ray single-crystal diffraction analysis
The synthetic route for the ligand (L) is shown in Scheme 1.
2-furfurylsalicylamide was prepared according to the literature
procedure with minor modifications [15] and 1,4-bis(bromo-
methyl)-2,3,5,6-tetramethylbenzene [16] were prepared according
to the literature.
Structure diffraction intensities for PrIII complex were carried
out on a Bruker SMART Apex CCD area detector diffractometer
(Mo
Ka, k = 0.71073 Å) at 293 K. Lorentz-polarization and
absorption corrections were applied for the compound. The struc-
ture was solved with direct methods and refined with full-matrix

X.-Q. Song et al. / Inorganica Chimica Acta 391 (2012) 171–178
173
Table 2
Selected bond lengths (Å) and angles (°) for Pr(III) complex.
Pr(1)–O(8)
Pr(1)–O(17)
Pr(1)–O(14)
2.393(6)
2.541(6)
2.555(8)
Pr(1)–O(5)
Pr(1)–O(16)
2.396(5)
2.544(6)
Pr(1)–O(2)
Pr(1)–O(13)
2.422(5)
2.546(6))
Pr(1)–O(11)
Pr(1)–O(10)
2.535(7)
2.551(6)
O(8)–Pr(1)–O(5)
77.0(2)
O(8)–Pr(1)–O(2)
87.8(2)
146.3(3)
78.9(2)
128.4(2)
70.6(3)
123.2(3)
117.2(2)
147.2(2)
118.4(2)
149.5(2)
127.4(3)
49.7(2)
O(5)–Pr(1)–O(2)
82.60(19)
123.5(2)
160.40(18)
101.8(2)
48.5(2)
78.6(2)
68.8(2)
75.3(2)
110.4(2)
74.3(2)
O(8)–Pr(1)–O(11)
O(8)–Pr(1)–O(17)
O(11)–Pr(1)–O(17)
O(2)–Pr(1)–O(16)
O(8)–Pr(1)–O(13)
O(11)–Pr(1)–O(13)
O(8)–Pr(1)–O(10)
O(11)–Pr(1)–O(10)
O(13)–Pr(1)–O(10)
O(2)–Pr(1)–O(14)
O(16)–Pr(1)–O(14)
82.7(3) 77.8(8)
81.8(2) 118.7(6)
71.8(3)
143.7(2)
153.2(2)
85.6(3)
78.3(2)
48.3(2)
76.0(3)
O(5)–Pr(1)–O(11)
O(5)–Pr(1)–O(17)
O(8)–Pr(1)–O(16)
O(11)–Pr(1)–O(16)
O(5)–Pr(1)–O(13)
O(17)–Pr(1)–O(13)
O(5)–Pr(1)–O(10)
O(17)–Pr(1)–O(10)
O(8)–Pr(1)–O(14)
O(11)–Pr(1)–O(14)
O(13)–Pr(1)–O(14)
O(2)–Pr(1)–O(11)
O(2)–Pr(1)–O(17)
O(5)–Pr(1)–O(16)
O(17)–Pr(1)–O(16)
O(2)–Pr(1)–O(13)
O(16)–Pr(1)–O(13)
O(2)–Pr(1)–O(10)
O(16)–Pr(1)–O(10)
O(5)–Pr(1)–O(14)
O(17)–Pr(1)–O(14)
O(10)–Pr(1)–O(14)
78.7(2) 130.23(11)
68.2(2)
102.1(2)
123.2(2)
least squares on F2 using the SHELXL-97 program package [17]. All
non-hydrogen atoms were subjected to anisotropic refinement,
and all hydrogen atoms were added in idealized positions and re-
fined isotropically. Crystal data and details of the refinement are
summarized in Table 1, representative bond lengths (Å) and angles
(°) are presented in Table 2. CCDC reference numbers 863911.
the complete coordination of the ligand. Weak absorptions
observed in the range of 2900–2950 cmꢀ1 can be attributed to
the tCH2 of the ligand. The absorption bands assigned to the
coordinated nitrates were observed as two group bands at about
1484 cmꢀ1 1) and 1295 cmꢀ1
(m (m4) for the complexes. The differ-
ences between the strongest absorption band m1 and m4 of nitrate
group lie in ca 180 cmꢀ1, indicating that coordinated nitrate groups
in the complexes are bidentate ligands [18], the m3 of free nitrate
group disappears in the spectra of the complexes which is in agree-
ment with the results of the conductivity experiment, implying
that three nitrate groups are all in coordination sphere. The room
temperature PXRD patterns of the PrIII, SmIII, EuIII, GdIII, TbIII,
DyIII complexes with the ligand L as well as that of simulation
for PrIII complex single crystal are unfolded from 5° to 40° as
shown in Fig. 2. According to the elemental analysis, IR and PXRD,
complexes of the ligand have similar coordination structure with
PrIII complex.
3. Results and discussion
3.1. Physical measurements
Analytical data for the newly synthesized complexes, listed in
Table 3, conforms to a 2:3 metal-to-L stoichiometry for nitrate
complexes. All complexes are soluble in DMF, DMSO, ethanol,
methanol and slightly soluble in ethyl acetate. The molar conduc-
tance of the complexes in methanol (see Table 3) indicate that all
complexes act as non-electrolytes.
As shown in Table 4 and Fig. 1, the characteristic band of car-
bonyl group of free ligand L is shown at 1645 cmꢀ1. The absence
of the band round 1645 cmꢀ1 which is instead of a new band at
ca 1611 cmꢀ1 of the complex compared to the free ligand indicates
3.2. Crystal structure descriptions
The structure comprises of a covalently bonded two-dimen-
sional (2D) honeycomb of composition [Pr2(NO3)6L3]1 crystallized
Table 3
Analytical and molar conductance data for the complexes (calculated values in parentheses).
Complex
Elemental Analysis (%)a
C
m(Oꢀ1ꢁcm2ꢁmolꢀ1
)
K
H
N
Ln
Pr2L3(NO3)6
Sm2L3(NO3)6
Eu2L3(NO3)6
Gd2L3(NO3)6
Tb2L3(NO3)6
Dy2L3(NO3)6
53.18 (53.34)
53.11 (53.19)
52.74 (52.86)
52.54 (52.63)
52.67 (52.56)
52.26 (52.41)
4.46 (4.48)
4.45 (4.46)
4.42 (4.44)
4.43 (4.42)
4.40 (4.41)
4.38(4.40)
6.94 (6.91)
6.86 (6.89)
6.88 (6.85)
6.79 (6.82)
6.80 (6.81)
6.76 (6.79)
11.54 (11.59)
11.79 (11.83)
12.44 (12.38)
12.69 (12.76)
12.83 (12.88)
13.05 (13.13)
68.4
73.9
65.8
72.3
75.5
74.8
a
Data in parentheses are calculated values.
Table 4
The most important IR bands for the lanthanide nitrate complexes(cmꢀ1).
ꢀ
ꢀ
ꢀ
ꢀ
Compound
m
(C@O)
m
(C–O–C)
m
1(NO3ꢀ) (NO3ꢀ) (NO3
)
m4 (NO3
)
m2 (NO3
)
m3(NO3
)
|m1–m4|
L
1645
1611
1610
1611
1611
1611
1612
1226
1224
1221
1224
1222
1223
1222
–
–
–
–
Pr2L3(NO3)6
Sm2L3(NO3)6
Eu2L3(NO3)6
Gd2L3(NO3)6
Tb2L3(NO3)6
Dy2L3(NO3)6
1484
1485
1479
1482
1484
1484
1295
1303
1300
1303
1300
1302
1029
1028
1029
1028
1033
1020
816
815
817
817
816
815
189
182
179
179
184
182

174
X.-Q. Song et al. / Inorganica Chimica Acta 391 (2012) 171–178
Fig. 1. IR Spectra of ligand L (solid line) and it’s Tb(III) complex in solid state.
Fig. 2. Powder x-ray diffraction patterns of complexes.
ꢀ
in the triclinic P1 space group which is quite different from the
structure of PrIII complex reported recently [11g]. As shown in
Fig. 3, each Pr(III) node lies in a distorted monocapped square
antiprism coordination sphere, which is defined by three carbonyl
oxygen and six nitrate oxygen donors with Pr–O distances range
from 2.393(5) to 2.555(7) Å. The two carbonyl oxygens of the same
ligand are coordinated to the two different PrIII ion in a trans con-
figuration. Each praseodymium center, shown as green large
spheres in Fig. 4, connects three ligands, While, each ligand mole-
cule is connected to two praseodymium atoms. The combination of
bridging L and nona-coordinated praseodymium atoms build up a
two-dimensional honeycomb-like framework in the ab plane,
which can be regarded as a (6,3) topological network with praseo-
dymium atoms acting as ‘‘three-connected’’ centers (Fig. 4).
3.3. Luminescence properties
Upon UV irradiation, the free ligand emits a strong blue lumines-
cence (kmax at ca. 455 nm) that can be easily detected with naked
eyes. However, upon complexation with trivalent lanthanide this
emission is replaced by the typical luminescent color arising from
LnIII cation. The luminescence characteristics of the ligand and
lanthanide complexes in solid state were measured at room
temperature under identical experimental conditions, and the
luminescence data in solid state are listed in Table 5.
For the SmIII complex of L, the emission intensity is the weak-
est, but two characteristic bands can still be observed. They were
attributed to 4 5/2 ? 6HJ (J = 5/2, 7/2) transitions (Fig. 5). The solid
G
state excitation and emission spectrum of europium complex of L

X.-Q. Song et al. / Inorganica Chimica Acta 391 (2012) 171–178
175
Fig. 3. ORTEP plot of Pr(III) complex showing the local coordination environment with thermal ellipsoids at 30% probability (hydrogen atoms are omitted for clarity).
Fig. 4. 2D honeycomb coordination polymer of [Pr2L3(NO3)6] (hydrogen atoms are omitted for clarity).
1
Table 5
Luminescence data for the ligand and its complexes.
Slit (nm)
2.5
kex (nm)
kem (nm)
RFI
56.77
Assignment
s
(ms)a
U%a
Sm2L3(NO3)6
Eu2L3(NO3)6
319
563
598
4G5/2
4G5/2
?
?
6H5/2
6H7/2
0.043
–
74.7
2.5
2.5
2.5
397
580
593
618
12.55
76.59
187.5
5D0
?
?
?
7F0
7F1
7F2
0.314
0.49
2.4
–
5D0
5D0
Tb2L3(NO3)6
Dy2L3(NO3)6
320
320
492
546
583
376.4
1325
87.5
5D4
5D4
5D4
?
?
?
7F6
7F5
7F4
0.926
0.069
457
482
573
4.53
128.5
125.7
4I15/2
?
?
?
6H15/2
6H15/2
6H13/2
4F9/2
4F9/2
a
Luminescence lifetimes and quantum yield values are reported here with an error of 10%.
at room temperature is shown in Fig. 6 and Fig. 7 respectively. The
excitation spectrum of europium complex of L exhibited a series of
sharp lines characteristic of the EuIII energy-level structure and as-
which indicates that the EuIII luminescence is not efficiently sensi-
tized by the ligand which is similar to those reported previously
[11]. There were four characteristic peaks of EuIII shown in the
emission spectra, which were attributed to 5D0 ? 7F0 (580 nm),
7
signed to transitions between the F0,1 and 5L6, 5D2 levels [19],

176
X.-Q. Song et al. / Inorganica Chimica Acta 391 (2012) 171–178
Fig. 7. Room-temperature emission spectra for europium complex of ligand L
(kex = 397 nm, excitation and emission passes = 2.5 nm) in the solid state.
Fig. 5. Room-temperature emission spectra for samarium complex of ligand L
(kex = 319 nm, excitation and emission passes = 2.5 nm) in the solid state.
Fig. 8. Room-temperature emission spectra for terbium complex of ligand
(kex = 320 nm, excitation and emission passes = 2.5 nm) in the solid state.
L
Fig. 6. Room-temperature excitation spectra for europium complex of ligand L with
emission monitored at approximately 619 nm (excitation and emission pas-
ses = 2.5 nm) in the solid state.
5D0 ? 7F1 (593 nm), 5D0 ? 7F2 (619 nm) and 5D0 ? 7F4 (689 nm).
The sharpness of the nondegenerate transition (5D0 ? 7F0) indi-
cates that all the EuIII coordinated in the sample have essentially
identical ligand coordination and structural environments. The
intensity of the 5D0 ? 7F2 transition (electric dipole) is stronger
than that of the 5D0 ? 7F1 transition (magnetic dipole), indicating
that the coordination environment of the EuIII ion is asymmetric
[20]. For TbIII complex, the emission intensity is stronger than that
of the other three complex in the same experimental conditions.
Four characteristic peaks are shown in Fig. 8, assigned to the
5D4 ? 7FJ (J = 3,4,5,6) transitions. For DyIII complex, three charac-
teristic bands can be seen in the emission spectra (Fig. 9), which
are attributed to transitions of 456 nm (4I15/2 ? 6H15/2) 484 nm
(4F9/2 ? 6H15/2) and 574 nm (4F9/2 ? 6H13/2). Compared with the
emission spectra of the four complexes (Table 5), the relative tran-
sition intensity changes in the order of TbIII > EuIII > DyIII > SmIII.
In addition to steady-state measurements, the luminescence
lifetimes of the Sm (4G5/2), Eu (5D0), Tb (5D4) and Dy (4F9/2) excited
states and quantum yield determinations for Eu, Tb complexes
were determined with the results also summarized in Table 5.
The relatively long luminescence lifetimes and larger quantum
yield values are an indication that the bridging ligand provides a
significant level of protection from nonradiative deactivation of
lanthanide cations by the solvent molecules. The longer lifetime
and the larger quantum yield of TbIII than that of EuIII is most
likely due to the insufficient inter-system crossing (ISC) of EuIII
complexes, as further supported by the energy transfer discussed
below.
To demonstrate the energy transfer process, the phosphores-
cence spectrum of GdIII complex of L was measured for the triplet
energy-level data. From the phosphorescence spectra (Fig. 10), the
triplet energy level (3pp⁄) of GdIII complex, which corresponds to
its lower wavelength emission edge, is 25126 cmꢀ1 (398 nm). Be-
6
cause the lowest excited state, P7/2 (E(6P7/2) = 32000 cmꢀ1) of
GdIII is too high to accept energy from the ligand, the data obtained
from the phosphorescence spectra actually reveal the triplet

X.-Q. Song et al. / Inorganica Chimica Acta 391 (2012) 171–178
177
triplet energy level of the salicylamide ligand (25126 cmꢀ1) is
higher than the 5D0 level of EuIII (17 500 cmꢀ1) and the 5D4 level
of TbIII (20400 cmꢀ1). This therefore supports the observation of
stronger sensitization of the terbium complexes than the europium
complexes because of the smaller overlap between the ligand trip-
let and europium ion excited states.
For the energy gap between the excited luminescent states and
the highest J levels of the ground states of SmIII and DyIII is ca.
7500 and 7800 cmꢀ1, considerably smaller than that of EuIII and
TbIII with values around 12300 and 14800 cmꢀ1 [23]. As a result
the lifetime measurements for both the SmIII and DyIII complexes
were found to be 43 and 69 ls, respectively, based on a single-
exponential fit of the data, which are much shorter than those ob-
served with EuIII or TbIII due to the higher water sensitivity [24].
In contrast to SmIII, EuIII, TbIII and DyIII complexes of similar
ligands reported previously [11], the lifetimes are shorter slightly,
suggesting that one or more nonradiative pathways are assisting in
the deactivation of the excited state and shortening the observed
lifetimes, since the triplet energy level of the antenna only changed
slightly with the backbone group, which excludes the possibility
that the quenching of luminescence is due to a change in the nat-
ure of the antenna triplet state. The most probable explanation
may be the bulky of the backbone which could weaken the coordi-
nation bond and thus the efficiency of the energy transfer.
Fig. 9. Room-temperature emission spectra for dysprosium complex of ligand L
(kex = 320 nm, excitation and emission passes = 2.5 nm) in the solid state.
4. Conclusions
We presented here a new semirigid bridging ligand featuring
N-furfurylamide arms which can form stable coordination poly-
mers with lanthanide nitrates. The coordination polymer
{Pr2(NO3)6L3}
displays
a
two-dimensional honeycomb-like
1
framework in the ab plane, which can be regarded as a (6,3) topo-
logical network with praseodymium atoms acting as ‘‘three-con-
nected’’ centers. The luminescent properties of the SmIII, EuIII,
TbIII and DyIII complexes were investigated in detail. It is worthy
noting that the bridging ligand provides a significant level of pro-
tection from nonradiative deactivation of lanthanide cations by
the solvent molecules and exhibits a good antennae effect with re-
spect to the TbIII ion due to efficient intersystem crossing and li-
gand-to-metal energy transfer. Our present findings provide the
possibility of controlling the formation of the desired lanthanide
coordination structure to enrich the crystal engineering strategy
and enlarges the arsenal for developing excellent luminescent lan-
thanide complexes of salicylamide derivatives.
Fig. 10. Phosphorescence spectra of Gd(III) complex of ligand L in methanol–ethyl
acetate solution at 77 K.
energy level of ligand in lanthanide complexes. In general, the sen-
sitization pathway in luminescent europium complexes consists of
excitation of the ligands into their excited singlet states, subse-
quent intersystem crossing of the ligands to their triplet states
and energy transfer from the triplet state to the 5DJ manifold of
the EuIII ions, followed by internal conversion to the emitting
5D0 state. Finally, the EuIII ion emits when a transition to the
ground state occurs [21]. Moreover, electron transition from the
Acknowledgment
This work was supported by the National Natural Science
Foundation of China (Grant No. 21161011).
Appendix A. Supplementary material
CCDC 863911 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at http://dx.doi.org/10.1016/
j.ica.2012.04.007.
higher excited states, such as 5D3 (24800 cmꢀ1), 5D2 (21200 cmꢀ1
)
and 5D1 (19000 cmꢀ1) to 5D0 (17500 cmꢀ1) becomes feasible by
internal conversion, and most of the photophysical processes take
place in this excited states. Consequently, most europium com-
plexes give rise to typical emission bands at ca. 581, 593, 614,
654 and 702 nm, corresponding to the deactivation of the 5D0 ex-
cited state to the 7FJ ground states (J = 0–4). In a similar way, the
4f electrons of the TbIII ion are excited to the 5DJ ion manifold from
the ground state. Finally, the TbIII ion emits when the 4f electrons
undergo a transition from the excited state of 5D4 to the 7FJ ground
states (J = 6–3). Latva’s empirical rule [22] states that an optimal
References
[1] J.-G.G. Bünzli, S. Comby, A.-S. Chauvin, C.D.B. Vandevyver, J. Rare Earth 25
(2007) 257.
[2] (a) F.Y. Li, H. Yang, C.H. Huang, Rare Earth Coordination Chemistry (2010) 529;
(b) J. Yu, D. Parker, R. Pal, R.A. Poole, M.J. Cann, J. Am. Chem. Soc. 128 (2006)
2294.
ligand-to-metal energy transfer process for LnIII needs
D –
E = 3pp⁄
5DJ (2500–4000 cmꢀ1 for EuIII and 2500–4500 cmꢀ1 for TbIII). The
[3] J.-C. Bünzli, C. Piguet, Chem. Soc. Rev. 34 (2005) 1048.

178
X.-Q. Song et al. / Inorganica Chimica Acta 391 (2012) 171–178
[4] M. Fernandes, S.S. Nobre, M.C. Goncalves, A. Charas, J. Morgado, R.A.S. Ferreira,
L.D. Carlos, V. de Zea Bermudez, J. Mater. Chem. 19 (2009) 733.
[11] (a) J. Zhang, Y. Tang, N. Tang, M.-Y. Tan, W.-S. Liu, K.-B. Yu, J. Chem. Soc., Dalton
Trans. 14 (2002) 832;
[5] (a) M. Giraud, E.S. Andreiadis, A.S. Fisyuk, R. Demadrille, J. Pécaut, D. Imbert, M.
Mazzanti, Inorg. Chem. 47 (2008) 3952;
(b) Y. Tang, J. Zhang, W.-S. Liu, M.-Y. Tan, K.-B. Yu, Polyhedron 24 (2005)
1160;
(b) E.S. Andreiadis, R. Demadrille, D. Imbert, J. Pécaut, M. Mazzanti, Chem.-Eur.
J. 15 (2009) 9458.
(c) X.-Q. Song, W.-S. Liu, W. Dou, Y.-W. Wang, J.-R. Zheng, Z.-P. Zang, Eur. J.
Inorg. Chem. 11 (2008) 1901;
[6] F.-Y. Yi, Q. -P Lin, T. -H Zhou, J.-G. Mao, Cryst. Growth. Des. 10 (2010) 1788.
[7] (a) G.F. de Sá, O.L. Malta, C. de Mello Doneg0a, A.M. Simas, R.L. Longo, P.A.
Santa-Cruz, E.F. da Silva Jr., Coord. Chem. Rev. 196 (2000) 165;
(b) P.N. Remya, S. Biju, M.L.P. Reddy, A.H. Cowley, M. Findlater, Inorg. Chem. 47
(2008) 7396;
(d) X.-Q. Song, W.-S. Liu, W. Dou, J.-R. Zheng, X.-L. Tang, H.-R. Zhang, D.-Q.
Wang, Dalton Trans. 24 (2008) 3582;
(e) X.-Q. Song, W. Dou, W.-S. Liu, Y. -L. Guo, X. -L. Tang, Inorg. Chem.
Commun. 10 (2007) 1058;
(f) Y.-W. Wang, Y.-L. Zhang, W. Dou, A.-J. Zhang, W.-W. Qin, W.-S. Liu, Dalton
Trans. 39 (2010) 9013;
(g) Q. Wang, X. Yan, H. Zhang, W. Liu, Y. Tang, M. Tan, J. Solid State Chem.
184 (2011) 164;
(c) D.B.A. Raj, B. Francis, M.L.P. Reddy, R.R. Butorac, V.M. Lynch, A.H. Cowley,
Inorg. Chem. 49 (2010) 9055;
(d) S. Biju, D.B.A. Raj, M.L.P. Reddy, C.K. Jayasankar, A.H. Cowley, M. Findlater, J.
Mater. Chem. 19 (2009) 1425.
(h) X.-Q. Song, W.K. Dong, Y.J. Zhang, W.-S. Liu, Luminescence 25 (2010) 328.
[12] K. Nakagawa, K. Amita, H. Mizuno, Y. Inoue, T. Hakushi, Bull. Chem. Soc. Jpn. 60
(1987) 2037.
[13] F. Gutierrez, C. Tedeschi, L. Maron, J.-P. Daudey, R. Poteau, J. Azema, P. Tisnès,
C. Picard, Dalton Trans. 9 (2004) 1334.
[14] M.S. Wrighton, D.S. Ginley, D.L. Morse, J. Phys. Chem. 78 (1974) 2229.
[15] K. Michio, Bull. Chem. Soc. Jpn. 49 (1976) 2679.
[16] Z. Jiri, P. Magdalena, H. Petr, T. Milos, Synthesis 110 (1994) 1132.
[17] G.M. Sheldrick, SHELXL-97, Program for Crystal Structure Solution and
Refinement, University of Göttingen, Göttingen, Germany, 1997.
[18] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, Wiley, New York, 1978. p. 227.
[19] M. Albin, R.R. Whittle, W.D. Horrocks Jr., Inorg. Chem. 24 (1985) 4591.
[20] A.F. Kirby, D. Foster, F.S. Richardson, Chem. Phys. Lett. 95 (1983) 507.
[21] (a) R. Pavithran, N.S. Saleesh Kumar, S. Biju, M.L.P. Reddy, S. Alves Jr., R.O.
Freire, Inorg. Chem. 45 (2006) 2184;
[8] (a) M. Seitz, M.D. Pluth, K.N. Raymond, Inorg. Chem. 46 (2007) 351;
(b) E.G. Moore, C.J. Jocher, J. Xu, E.J. Werner, K.N. Raymond, Inorg. Chem. 46
(2007) 5468;
(c) E.G. Moore, J. Xu, C.J. Jocher, I. Castro-Rodriguez, K.N. Raymond, Inorg.
Chem. 47 (2008) 3105;
(d) A.P.S. Samuel, E.G. Moore, M. Melchior, J. Xu, K.N. Raymond, Inorg. Chem.
47 (2008) 7535;
(e) A.P.S. Samuel, J. Xu, K.N. Raymond, Inorg. Chem. 48 (2009) 687.
[9] A.J. Amoroso, M.W. Burrows, R. Haigh, M. Hatcher, M. Jones, U. Kynast, K.M.A.
Malik, D. Sendor, Dalton Trans. 16 (2007) 1630.
[10] (a) N. Chatterton, Y. Bretonnière, J. Pécaut, M. Mazzanti, Angew. Chem., Int. Ed.
44 (2005) 7595;
(b) G.S. Kottas, M. Mehlstäubl, R. Fröhlich, L. De Cola, Eur. J. Inorg. Chem. 22
(2007) 3465;
(c) L.J. Charbonnière, S. Mameri, D. Flot, F. Waltz, C. Zandanel, R.F. Ziessel,
Dalton Trans. 22 (2007) 2245;
(d) L.S. Natrajan, P.L. Timmins, M. Lunn, S.L. Heath, Inorg. Chem. 46 (2007)
10877;
(e) L. Benisvy, P. Gamez, W.T. Fu, H. Kooijman, A.L. Spek, A. Meijerink, J.
Reedijk, Dalton Trans. 24 (2008) 3147;
(b) R. Pavithran, M.L.P. Reddy, S. Alves Jr., R.O. Freire, G.B. Rocha, P.P. Lima, Eur.
J. Inorg. Chem. 20 (2005) 4129;
(c) M. Shi, F. Li, T. Yi, D. Zhang, H. Hu, C. Huang, Inorg. Chem. 44 (2005) 8929.
[22] M. Latva, H. Takalo, V.M. Mukkala, C. Matachescu, J.C. Rodriguez-Ubis, J.
Kanakare, J. Lumin. 75 (1997) 149.
(f) N.M. Shavaleev, F. Gumy, R. Scopelliti, J.-C.G. Bünzli, Inorg. Chem. 48 (2009)
5611;
(g) R. Feng, F.-L. Jiang, M.-Y. Wu, L. Chen, C.-F. Yan, M.-C. Hong, Cryst. Growth.
Des. 10 (2010) 2306.
[23] S.W. Magennis, S. Parsons, Z. Pikramenou, Chem. Eur. J. 8 (2002) 5761.
[24] D.R. Lide (Ed.), CRC Handbook of Chemistry and Physics, 80th ed., CRC Press,
Boca Raton, FL, 1999.