Assembly, crystal structures and luminescent properties of the lanthanide nitrate coordination polymers with 1,5-bis{[(2′-(2-picolylaminoformyl)) phenoxyl]methyl}naphthalene

Article abstract of DOI:10.1016/j.inoche.2011.01.043

A new amide type bridging ligand, 1,5-bis{[(2′-(2-picolylaminoformyl) )phenoxyl]methyl}naphthalene (L), and its complexes with lanthanide ions (LnSm, Eu, Gd, Tb, and Dy) have been designed and assembled. The crystal structures of {[EuL(NO₃)

Full text of DOI:10.1016/j.inoche.2011.01.043

Inorganic Chemistry Communications 14 (2011) 654–658
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Assembly, crystal structures and luminescent properties
of the lanthanide nitrate coordination polymers with
1,5-bis{[(2′-(2-picolylaminoformyl))phenoxyl]methyl}naphthalene
⁎
Xu-Huan Yan, Chun-Li Yi, Xiao-Guang Huang, Wei-Sheng Liu, Yu Tang , Min-Yu 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
Article history:
A new amide type bridging ligand, 1,5-bis{[(2′-(2-picolylaminoformyl))phenoxyl]methyl}naphthalene (L),
and its complexes with lanthanide ions (Ln Sm, Eu, Gd, Tb, and Dy) have been designed and assembled. The
crystal structures of {[EuL(NO3)3(CH3OH)](H2O)}n and [TbL(NO3)3(CH3OH)]n display one-dimensional (1-D)
zig-zag coordination polymeric chains. At the same time, the solid state luminescent properties of the Sm, Eu,
Tb, and Dy complexes were investigated at room temperature. The complexes all exhibit characteristic
luminescence emissions of the central metal ions under UV light excitation. The lowest triplet state energy
level (T1) of the ligand indicates that the triplet state energy level of the ligand matches better to the
resonance level of Tb(III) ion than other lanthanide ions.
Received 23 December 2010
Accepted 28 January 2011
Available online 23 February 2011
Keywords:
Amide type bridging ligand
Lanthanide
Coordination polymers
Luminescent properties
© 2011 Elsevier B.V. All rights reserved.
Over the past decade, the construction of supramolecular
coordination polymers has attracted great interest because of their
potential applications as some functional materials [1]. Remarkably,
the vast majority of the reported frameworks are based on transition
metal centers. Lanthanide centers have recently attracted the
attention of crystal engineers due to their various tantalizing
applications such as fluoroimmuno-assays, light-emitting diodes,
laser systems, and optical amplification for telecommunication and
fascinating topological architectures which can be achieved by their
higher coordination numbers and more flexible coordination geom-
etry [2]. As a consequence of the parity rule (and sometimes due to the
change in spin multiplicity), lanthanide ions are very poor at
absorbing light directly. This problem may be overcome by using a
strongly absorbing chromophore to sensitize Ln(III) emission in a
process known as the “antenna effect”. Considering this, we designed
and synthesized a new amide type bridging ligand 1,5-bis{[(2′-(2-
picolylaminoformyl))phenoxyl]methyl}naphthalene (L), because: (1)
the amide ligands that have high extinction coefficients in the near
ultraviolet-visible range provide effective absorption of excitation
energy, which promotes more effective energy transfer to the
lanthanide ions; (2) the ligands possess spheroidal cavities, therefore
stabilizing their complexes and shielding the encapsulated ions from
interaction with the surroundings; (3) the presence of O and N atoms
and aromatic rings may form hydrogen bonds and π–π stacking
interactions, thus to extend and stabilize the whole framework series
[3]. The lanthanide (Ln Sm, Eu, Gd, Tb, and Dy) complexes with this
ligand have also been synthesized. At the same time, we obtained the
crystal structures of the complexes {[EuL(NO3)3(CH3OH)](H2O)}n and
[TbL(NO3)3(CH3OH)]n, which demonstrate one-dimensional (1-D)
zig-zag coordination polymeric chain structures. Under the excitation
of UV light, Sm(III), Eu(III), Tb(III), and Dy(III) complexes all exhibit
characteristic emissions of corresponding central lanthanide ions. The
lowest triplet state (T1) energy level of the ligand L matches better to
the resonance level of Tb(III) than other lanthanide ions.
The synthetic route for the ligand L is shown in Scheme 1. A
mixture of picolylsalicylamide [4] (5 mmol, 1.142 g) and potassium
carbonate (5 mmol, 0.690 g) in 50 cm3 acetone were refluxed for
30 min, then 1,5-bis(bromomethyl)naphthalene (2.2 mmol, 0.691 g)
was added to the solution. The reaction mixture was stirred and
refluxed for 12 h and the hot solution was filtered off. The collected
organic phase was concentrated in vacuum. Then the resulted solid
was recrystallized with acetone to get the ligand L. Yield: 60%. m.p.:
113–116 °C. 1H NMR (CDCl3, 200 MHz): 4.52–4.54 (d, 4 H, ―CH2―N),
5.64 (s, 4 H, ―CH2―O), 6.97–8.29(m, 22 H, Ar―H), 8.66 (s, 2 H,
N―H). IR (KBr) ν: 3372(m), 1651(s, C O), 1596(m), 1542(s), 1446
(m), 1450(s), 1300(s), 1229(s, Ar―O―C), 1163(w), 1104(w), 984
(m), 759(s), 637(s). The lanthanide complexes were prepared by the
reaction of Ln(NO3)3∙6H2O (Ln Sm, Eu, Gd, Tb, and Dy) and L in 1:1
molar ratio in ethyl acetate and chloroform as white powder. The data
of the elemental analysis indicate that the complexes conform to a 1:1
metal-to-ligand stoichiometry [5]. The complexes have the similar IR
spectra, of which the characteristic bands have similar shifts,
suggesting that they have a similar coordination structure [5]. The
molar conductances of the complexes in methanol indicate that all
⁎
Corresponding author. Fax: +86 9318912582.
E-mail address: tangyu@lzu.edu.cn (Y. Tang).
1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2011.01.043

X.-H. Yan et al. / Inorganic Chemistry Communications 14 (2011) 654–658
655
ligands and the Tb–Tb separations linked by the bridging ligand are
ca. 15.78 and 17.46 Å. Through careful study, we found that the major
reason is the strong intermolecular hydrogen bonds between the
oxygen atoms (O14) of the coordinated methanol molecules and the
nitrogen atoms (N1) of terminal pyridyl groups. The schematic view
of this 1-D zig-zag chain is shown in Fig. 1b. A deeper view of the
compound [TbL(NO3)3(CH3OH)]n indicates that there are strong
intramolecular hydrogen bonds between the amide nitrogen atoms
(N2 and N3) and the ether oxygen atoms (O2 and O3).
Scheme 1. The synthetic route for the ligand L.
There were also intermolecular hydrogen bonds between the
coordinated ligands and nitrate groups which play an important role
in the crystal packing of the complex. In the complex, the coordination
chains are linked by intermolecular hydrogen bonds C(6)―H(6B)⋯O
(12) [H(6B)⋯O(12), 2.50 Å and C(6)―H(6B)⋯O(12), 128°] to form a
two-dimensional (2-D) layer supramolecular structure, as shown in
Fig. 2a. In addition, the layers are linked by intermolecular hydrogen
bonds C(25)―H(25A)⋯O(6) [H(25A)⋯O(6), 2.59 Å and C(25)―H
(25A)⋯O(6), 138°] to form an infinite three-dimensional (3-D)
supramolecular framework (Fig. 2b). It is no doubt to note that the
robust hydrogen bonds may have a template effect and participate in
the stabilization of the complex architectures and may enhance the
luminescent properties.
complexes act as non-electrolytes [6], implying that all nitrate groups
are in coordination sphere.
After several weeks of slow evaporation of the ethyl acetate–
methanol solution, the colorless crystals suitable for X-ray analysis of
the complexes {[EuL(NO3)3(CH3OH)](H2O)}n and [TbL(NO3)3
(CH3OH)]n were obtained [7]. The single-crystal X-ray analysis reveals
that they possess the same topological structures despite the fact that
one crystal water molecule occurs in {[EuL(NO3)3(CH3OH)](H2O)}n.
Therefore, only [TbL(NO3)3(CH3OH)]n is selected for investigation
here in detail as a representative example. The crystal analysis
unambiguously reveals that the [TbL(NO3)3(CH3OH)]n crystallizes in
the triclinic space group P-1. As shown in Fig. 1a, each Tb(III) ion is
coordinated with nine oxygen donor atoms, six of which belong to
three bidentate nitrate groups, two belong to carbonyl groups from
two bridging ligands and the remaining one to coordinated methanol
molecule. The Tb(III) center lies in a distorted tricapped trigonal prism
coordination environment. The Tb―O distances are between 2.276(2)
and 2.515(2) Å, which are comparable to the corresponding Tb―O
bond lengths found in related complexes [8]. At the same time, each
ligand binds to two Tb(III) ions using its two oxygen atoms of the
amide groups. So the whole structure consists of an infinite array of Tb
(III) ions bridged by bidentate ligands and a one-dimensional (1-D)
zig-zag coordination polymeric chain is formed. Different from
previous reports [3d, 9], an asymmetric unit of compound [TbL
(NO3)3(CH3OH)]n contains two crystallographically independent
Excited by the absorption band at 327 nm, the free ligand exhibits a
broad emission band (λmax=447 nm). And the solid state luminescent
properties of the Sm(III), Eu(III), Tb(III), and Dy(III) complexes were
investigated at room temperature (the excitation and emission slit
widths were 2.5 and 1.0 nm except for Sm(III) complex with the
excitation and emission slit widths being 2.5 and 2.5 nm). The solid
state excitation and emission spectra of the complexes at room
temperature are shown in Fig. 3. The excitation spectrum of {[EuL
(NO3)3(CH3OH)](H2O)}n has negligible contribution from the ligand
and exhibits a series of sharp lines characteristic of the Eu(III) energy-
level structure and can be assigned to transitions between the 7F0, 1 and
5
5L6, D2,1 levels [10]. The intensity of the 5D0→7F2 transition (electric
dipole) is stronger than that of the 5D0→7F1 transition (magnetic
dipole), which indicates that the coordination environment of the Eu
(III) ion is asymmetric [11], which is confirmed by crystallographic
Fig. 1. (a) The local coordination environment of Tb(III) in compound [TbL(NO3)3(CH3OH)]n. (b) 1-D coordination polymer chain of Tb(III) complex (hydrogen atoms are omitted for
clarity). The key bond distances and angles (Å and °): Tb(1)―O(4) 2.2759(18), Tb(1)―O(1) 2.2880(18), Tb(1)―O(14) 2.427(2), Tb(1)―O(13) 2.434(2), Tb(1)―O(5) 2.448(2), Tb
(1)―O(11) 2.482(2), Tb(1)―O(7) 2.484(2), Tb(1)―O(8) 2.487(2), Tb(1)―O(10) 2.515(2) and O(4)―Tb(1)―O(1) 149.29(8), O(5)―Tb(1)―O(7) 51.41(7), O(13)―Tb(1)―O(11)
51.63(7), O(8)―Tb(1)―O(10) 51.03(6).

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X.-H. Yan et al. / Inorganic Chemistry Communications 14 (2011) 654–658
Fig. 2. (a) 2-D supramolecular layer structure generated by intermolecular hydrogen bonds. (b) 3-D supramolecular structure of [TbL(NO3)3(CH3OH)]n generated by intermolecular
hydrogen bonds. (The hydrogen atoms without formed hydrogen bonds and the benzyl groups of the ligands are omitted for clarity).
analysis. For the complex [TbL(NO3)3(CH3OH)]n, the excitation spec-
trum exhibits a broad excitation band (BEB) between 250 and 500 nm,
indicating that energy can transfer efficiently from the ligand to the Tb
(III) center. There are four characteristic peaks shown in Fig. 3b, which
are assigned to the 5D4→7FJ (J=6, 5, 4, 3) transitions. The solid state
luminescence lifetime values of the Eu(III) and Tb(III) complexes were
determined to be 0.687 0.001 ms and 0.805 0.001 ms from the
luminescence decay profile at room temperature by fitting with a
monoexponential curve. For the Sm(III) and Dy(III) complexes, the
characteristic emission bands can also be observed in the emission
spectra, which are attributed to 4G5/2 →6HJ (J=5/2, 7/2) and
4F9/2→6HJ (J=15/2, 13/2) transitions respectively. The fluorescence
quantum yield, Φ, of the Sm(III), Eu(III), Tb(III), and Dy(III) complexes
in the solid state were found to be 0.39%, 3.12%, 7.97%, and 0.82% using
an integrating sphere, respectively. The emission intensity and
fluorescence quantum yield of the Tb(III) complex are the strongest
among these four complexes under the same conditions.
Sm(III) (Δν=4827 cm−1), Eu(III) (Δν=5427 cm−1), and Dy(III)
(Δν=1727 cm−1) ions, because such larger or smaller overlap
between the ligands and lanthanide ions excited states result in the
non-radiative deactivation of the lanthanide emitting state and
quench the luminescence of the complexes [13].
In summary, we have designed and synthesized a new amide type
ligand 1,5-bis{[(2′-(2-picolylaminoformyl))phenoxyl]methyl}naph-
thalene (L). Furthermore, the one-dimensional (1-D) lanthanide zig-
zag coordination polymers {[EuL(NO3)3(CH3OH)](H2O)}n and [TbL
(NO3)3(CH3OH)]n were assembled using this ligand. In addition, the
three-dimensional supramolecular structures were formed by the
hydrogen bonds between the chains. And the robust hydrogen bonds
may have a template effect and participate in the stabilization of the
architectures and enhance the luminescent properties of the
complexes. The Sm(III), Eu(III), Tb(III), and Dy(III) complexes all
exhibit characteristic emissions of the central metal ions under the UV
excitation. This indicates that the ligand L can absorb and transfer
energy to lanthanide ions. From a more general perspective, these
new complexes may have applications in luminescence materials. On
the other hand, a series of new ligands could be designed and
synthesized to optimize the luminescent properties of the lanthanide
ions based on these results.
We have investigated the energy transfer processes in order to
elucidate the phenomenon. The triplet excited energy-level T1 datum
of the ligand L is 22, 727 cm−1 (440 nm), which was calculated by the
low-temperature (77 K) phosphorescence spectrum of the complex
[GdL(NO3)3]n·3H2O in a 1:1 methanol–ethanol mixture [12]. The
triplet energy level of the ligand L is higher than the lowest excited
4
resonance levels G5/2 of Sm(III) (17,900 cm−1), 5D0 of Eu(III)
Acknowledgments
4
(17,300 cm−1), 5D4 of Tb(III) (20,500 cm−1), and F9/2 of Dy(III)
(21,000 cm−1). This therefore supports the observation of the
characteristic emissions of central Sm(III), Eu(III), Tb(III) or Dy(III)
ions in the emission spectra of the complexes. And we may deduce
that the triplet state energy level T1 of this ligand L matches better to
the lowest resonance level of Tb(III) (Δν=2227 cm−1) than that of
This work was financially supported by the National Natural
Science Foundation of China (Project 20931003, 21071068), the
Natural Science Foundation of Gansu Province (Project 1010RJZA121),
and the program for New Century Excellent Talents in University
(NCET-06-0902).

X.-H. Yan et al. / Inorganic Chemistry Communications 14 (2011) 654–658
657
Fig. 3. Excitation and emission spectra of the samples of Eu(III) complex (a), Tb(III) complex (b), Sm(III) complex (c), and Dy(III) complex (d) in the solid state at room temperature.
(g) H.L. Jiang, Y. Tatsu, Z.H. Lu, Q. Xu, Non-, micro-, and mesoporous metal–
Appendix A. Supplementary material
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Crystallographic data for the structures reported in this paper have
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allocated the deposition numbers CCDC 802510 and 802511. Copies of
the data can be obtained free of charge on application to CCDC 12
Union Road, Cambridge CB2 1EW, UK (email: deposit@ccdc.cam.ac.
uk). Supplementary data to this article can be found online at
doi:10.1016/j.inoche.2011.01.043.
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[5] Element analysis (%) for [SmL(NO3)3]·3H2O Calcd.: C 46.52, H 3.70, N 9.99; found:
C 46.66, H 3.50, N 9.54. IR (KBr pellet, cm-1) ν: ν(C=O):1611, ν1 (NO3- ): 1479, ν4
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(NO3)3]·3H2O Calcd.: C 46.45, H 3.69, N 9.98; found: C 46.37, H 3.84, N 9.69.
ν(C=O):1612, ν1 (NO3- ): 1478, ν4 (NO3- ): 1296, ν2 (NO-3): 1032, ν5 (NO-3): 814.
Elemental analysis (%) for [GdL(NO3)3]·3H2O Calcd.: C 46.20, H 3.67, N 9.92;
found: C 45.85, H 4.07, N 9.87. ν(C=O):1611, ν1 (NO-3): 1476, ν4 (NO3- ): 1299, ν2
(NO-3): 1032, ν5 (NO-3): 811. Elemental analysis (%) for [TbL(NO3)3]·3H2O Calcd.:
C 46.12, H 3.67, N 9.91; found: C 46.42, H 3.53, N 9.46. ν(C=O):1610, ν1 (NO-3):
1476, ν4 (NO-3): 1297, ν2 (NO3- ): 1031, ν5 (NO-3): 811. Elemental analysis (%) for
[DyL(NO3)3]·3H2O Calcd.: C 45.73, H 3.64, N 9.82; found: C 45.85, H 3.43, N 9.91.
ν(C=O):1611, ν1 (NO3- ): 1479, ν4 (NO3- ): 1296, ν2 (NO-3): 1031, ν5 (NO-3): 814.
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