Structures and luminescent properties of Sm(III) and Dy(III) coordination polymers with 2,4,6-pyridinetricarboxylic acid

Article abstract of DOI:10.1080/00958972.2010.531130

Two rare earth coordination compounds with 2,4,6-pyridinetricarboxylic acid (H₃pta) have been synthesized by the hydrothermal method; the formula is {[RE(pta)(H₂O)₃] H₂O}n [RE = Sm (1) and Dy (2)]. Complexes 1 and 2 are crystallized in the monoclinic crystal system with P2₁/c space group. X-ray structure analyses show the two complexes have the same structure. Each pta^3- connects three rare earth ions. Both the Sm(III) and Dy(III) complexes exhibit characteristic luminescence in the visible region upon excitation with UV-rays.

Full text of DOI:10.1080/00958972.2010.531130

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Structures and luminescent
properties of Sm(III) and Dy(III)
coordination polymers with 2,4,6-
pyridinetricarboxylic acid
Hong-Sheng Wang a b , Gong-Chun Li a , Yao Chen b , Zhen-Jie
Zhang b & Ming-Li Liu b
a College of Chemistry and Chemical Engineering, Xuchang
University, Xuchang, Henan 461000, P.R. China
b Department of Chemistry, Nankai University, Tianjin 300071, P.R.
China
Version of record first published: 05 Nov 2010.
To cite this article: Hong-Sheng Wang, Gong-Chun Li, Yao Chen, Zhen-Jie Zhang & Ming-Li Liu
(2010): Structures and luminescent properties of Sm(III) and Dy(III) coordination polymers with
2,4,6-pyridinetricarboxylic acid, Journal of Coordination Chemistry, 63:23, 4068-4076
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Journal of Coordination Chemistry
Vol. 63, No. 23, 10 December 2010, 4068–4076
Structures and luminescent properties of Sm(III) and Dy(III)
coordination polymers with 2,4,6-pyridinetricarboxylic acid
HONG-SHENG WANG*yz, GONG-CHUN LIy, YAO CHENz,
ZHEN-JIE ZHANGz and MING-LI LIUz
yCollege of Chemistry and Chemical Engineering, Xuchang University, Xuchang,
Henan 461000, P.R. China
zDepartment of Chemistry, Nankai University, Tianjin 300071, P.R. China
(Received 23 June 2010; in final form 22 September 2010)
Two rare earth coordination compounds with 2,4,6-pyridinetricarboxylic acid (H3pta) have
been synthesized by the hydrothermal method; the formula is {[RE(pta)(H2O)3] ꢀ H2O}n
[RE ¼ Sm (1) and Dy (2)]. Complexes 1 and 2 are crystallized in the monoclinic crystal system
with P21/c space group. X-ray structure analyses show the two complexes have the same
structure. Each pta3ꢁ connects three rare earth ions. Both the Sm(III) and Dy(III) complexes
exhibit characteristic luminescence in the visible region upon excitation with UV-rays.
Keywords: 2,4,6-Pyridinetricarboxylic acid; Photoluminescence; Samarium; Dysprosium;
Lanthanide
1. Introduction
Design and synthesis of metal organic frameworks (MOFs) with trivalent lanthanide
cations and carboxylic acids have attracted much attention due to their luminescent
properties and potential applications in luminescent materials [1–4]. Multicarboxylic
acids containing phenyl have been widely used as organic linkers in the syntheses of
MOFs because they have two or more carboxyl groups and are inclined to forming
multidimensional structure [5–10]. The pyridine- and tri-carboxylic acids are also
important organic ligands for constructing MOFs as the nitrogen can also coordinate
with metal ions in addition to oxygens of carboxyl groups. Much attention has been
paid to this field [11–14]. The structures and photoluminescent properties of nine rare
earth complexes with 2,4,6-pyridinetricarboxylic acid have been reported by us [15].
They were all synthesized at room temperature and showed three different 1-D chain
structures. Furthermore, seven 3-D lanthanide coordination polymers were reported,
synthesized mostly with rare earth oxide and 2,4,6-pyridinetricarboxylic acid by the
hydrothermal method [16]. New coordination polymers containing three metal ions
with 2,4,6-pyridinetricarboxylic acid were also reported [17]. These show that the ligand
is a good connector for rare earth ions to construct coordination polymers.
*Corresponding author. Email: xcuwaller@163.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2010 Taylor & Francis
DOI: 10.1080/00958972.2010.531130

Sm(III) and Dy(III) coordination polymers
4069
In this article, we report two new rare earth complexes synthesized with rare earth
perchlorate or rare earth chloride and 2,4,6-pyridinetricarboxylic acid at hydrothermal
conditions. The two complexes obtained have the same structure. Their photolumines-
cent properties show that the two complexes display strong characteristic emission in
visible region with excitation of UV radiation.
2. Experimental
2.1. Synthesis of 2,4,6-pyridinetricarboxylic acid
2,4,6-Pyridinetricarboxylic acid was synthesized by oxidization of 2,4,6-trime-
thylpyridine with potassium permanganate [18]. Anal. Calcd for C8H5NO6 (%):
C, 45.51; H, 2.39; N, 6.63. Found (%): C, 45.74; H, 2.08; N, 6.49. The rare earth salts
were obtained by reacting hydrochloric acid with the corresponding rare earth oxides
(ꢂ99.95%) purchased from Grirem Advanced Materials Co. Ltd., Beijing.
2.2. Preparation of [Sm(pta)3(H2O)]n (1)
A mixture of 2,4,6-pyridinetricarboxylic acid (0.0422 g, 0.2 mmol), SmCl3 ꢀ 6H2O
(0.0728 g, 0.2 mmol), and 15 mL deionized water was placed in a 25 mL Teflon-lined
bomb, which was heated to 180ꢃC for 96 h. After the mixture was cooled to room
temperature at a rate of 1.5ꢃC hꢁ1, the products were filtered, washed by ethanol, and
dried in air. Yellow block crystals of 2 were obtained in 52% yield. Anal. Calcd for
C8H10NO10Sm (%): C, 22.32; H, 2.34; N, 3.25. Found (%): C, 22.25; H, 2.33; N, 3.28.
IR bands (KBr pellets, cmꢁ1): 3603s, 3388sb, 1631s, 1607s, 1580s, 1548s, 1453s, 1393s,
1351s, 1276m, 1235w, 1110w, 1024w, 930w, 818w, 790w, 739s, 623w, 586w, 479w, 434w.
2.3. Preparation of [Dy(pta)3(H2O)]n (2)
Synthesis of 2 was similar to 1. The products were filtered and washed by ethanol, then
dried in air. Colorless block crystals of 3 were obtained in 65% yield. Anal. Calcd for
C8H10NO10Dy (%): C, 21.71; H, 2.28; N, 3.16. Found (%): C, 21.44; H, 2.37; N, 3.14.
IR bands (KBr pellets, cmꢁ1): 3609s, 3383sb, 1632s, 1609s, 1583s, 1551s, 1446s, 1396s,
1352s, 1278m, 1236w, 1110w, 1025w, 931w, 819w, 791w, 740s, 671w, 622w, 586w, 545w,
478w, 436w.
2.4. General characterization
Elemental analyses were performed in a Perkin-Elmer 240 analyzer. IR spectra were
recorded with a Tensor 27 FTIR spectrophotometer (KBr pellets, 4000–400 cmꢁ1).
Emission spectra in the visible region were tested on a Cary Eclipse fluorescence
spectrophotometer.

4070
H.-S. Wang et al.
Table 1. Crystallographic data for 1 and 2.
1
2
Empirical formula
Crystal system
Space group
C8H10NO10Sm
Monoclinic
P21/c
C8H10NO10Dy
Monoclinic
P21/c
ꢃ
˚
Unit cell dimensions (A, )
a
b
c
ꢁ
ꢂ
ꢃ
Z
11.959(6)
7.337(4)
13.526(7)
90
96.593(7)
90
4
5.036
11.826(4)
7.245(3)
13.462(5)
90
96.175(5)
90
4
6.564
ꢄ (mmꢁ1
F(000)
)
828
1.089
844
0.982
Goodness-of-fit on F2
Final R indices [I 4 2ꢅ(I)]
R indices (all data)
R1 ¼ 0.0361, wR2 ¼ 0.1171
R1 ¼ 0.0184, wR2 ¼ 0.0445
R1 ¼ 0.0411, wR2 ¼ 0.1207
R1 ¼ 0.0213, wR2 ¼ 0.0450
2.5. X-ray diffraction analysis
Crystallographic data of 1 were collected with a Bruker SMART 1000 CCD
diffractometer and the data of 2 with a Rigaku Saturn diffractometer. The two
diffractometers were equipped with a graphite monochromator, and Mo-Ka radiation
˚
(ꢀ ¼ 0.71073 A) was used. The two structures were solved by the direct method and
refined with the full-matrix least-squares technique using the SHELXS-97 and
SHELXL-97 programs [19]. All non-hydrogen atoms were refined anisotropically
and hydrogens located and refined isotropically. Crystallographic data for the two
compounds are listed in table 1 and selected bond lengths and angles are listed in tables
2 and 3.
3. Results and discussion
3.1. Structures of the two complexes
Complexes 1 and 2 are isostructural and 1 is taken as an example to describe the
structure in detail, as shown in figure 1. The coordination number of Sm(III) is nine,
with three oxygens (O(7), O(8), and O(9)) from water having Sm–O bond lengths of
˚
2.442(6), 2.474(5), and 2.472(5) A, respectively; the other five oxygens (O(1), O(6),
O(2A), O(3A), and O(4A)) are from carboxylate groups and the Sm–O bond lengths are
˚
2.465(5), 2.400(5), 2.335(5), 2.538(5), and 2.528(5) A, respectively; the nitrogen N(1) is
˚
from the pyridyl ring with a Sm–N bond length of 2.499(5) A. The bond angles of
O–Sm–O range between 71.06(16)ꢃ and 150.29(18)ꢃ and that of O–Sm–N between
64.03(17)ꢃ and 128.67(19)ꢃ. The coordination mode of pta3ꢁ is shown in scheme 1. The
O(1), O(6), and N(1) chelate one Sm(III) through tridentate coordination. O(3) and
O(4) of the 4-carboxyl group are bonded to one Sm(III) and O(2) connects another
Sm(III), while O(5) does not coordinate with Sm(III) ion. So the ligand in the complex

Sm(III) and Dy(III) coordination polymers
4071
ꢃ
˚
Table 2. Selected bond lengths (A) and angles ( ) for 1.
Sm(1)–O(2)#1
Sm(1)–O(6)
Sm(1)–O(7)
Sm(1)–O(1)
Sm(1)–O(9)
2.335(5)
2.400(5)
2.442(6)
2.465(5)
2.472(5)
Sm(1)–O(8)
2.474(5)
2.499(5)
2.528(5)
2.538(5)
Sm(1)–N(1)
Sm(1)–O(4)#2
Sm(1)–O(3)#2
O(2)#1–Sm(1)–O(6)
O(2)#1–Sm(1)–O(7)
O(6)–Sm(1)–O(7)
O(2)#1–Sm(1)–O(1)
O(6)–Sm(1)–O(1)
O(7)–Sm(1)–O(1)
O(2)#1–Sm(1)–O(9)
O(6)–Sm(1)–O(9)
O(7)–Sm(1)–O(9)
O(1)–Sm(1)–O(9)
O(2)#1–Sm(1)–O(8)
O(6)–Sm(1)–O(8)
O(7)–Sm(1)–O(8)
O(1)–Sm(1)–O(8)
O(9)–Sm(1)–O(8)
O(2)#1–Sm(1)–N(1)
O(6)–Sm(1)–N(1)
O(7)–Sm(1)–N(1)
150.29(18)
98.26(19)
74.24(19)
75.36(16)
128.01(16)
141.95(18)
74.96(17)
93.82(18)
143.39(19)
72.20(17)
76.25(17)
74.09(18)
72.10(18)
138.30(17)
71.34(18)
132.67(17)
64.03(17)
128.67(19)
O(1)–Sm(1)–N(1)
O(9)–Sm(1)–N(1)
O(8)–Sm(1)–N(1)
64.11(16)
70.32(18)
119.63(18)
124.80(16)
82.13(18)
76.51(19)
77.07(17)
137.13(18)
144.63(17)
69.65(17)
74.44(16)
126.87(17)
71.11(18)
71.06(16)
136.79(17)
128.24(17)
111.65(17)
51.56(15)
O(2)#1–Sm(1)–O(4)#2
O(6)–Sm(1)–O(4)#2
O(7)–Sm(1)–O(4)#2
O(1)–Sm(1)–O(4)#2
O(9)–Sm(1)–O(4)#2
O(8)–Sm(1)–O(4)#2
N(1)–Sm(1)–O(4)#2
O(2)#1–Sm(1)–O(3)#2
O(6)–Sm(1)–O(3)#2
O(7)–Sm(1)–O(3)#2
O(1)–Sm(1)–O(3)#2
O(9)–Sm(1)–O(3)#2
O(8)–Sm(1)–O(3)#2
N(1)–Sm(1)–O(3)#2
O(4)#2–Sm(1)–O(3)#2
Symmetry transformations used to generate equivalent atoms: #1 ꢁx þ 1, y þ 1/2, ꢁz þ 1/2; #2 x, ꢁy þ 1/2, z þ 1/2.
ꢃ
˚
Table 3. Selected bond lengths (A) and angles ( ) for 2.
Dy(1)–O(2)#1
Dy(1)–O(5)
Dy(1)–O(9)
Dy(1)–O(1)
Dy(1)–O(7)
2.3030(19)
2.356(2)
2.406(2)
2.425(2)
2.452(2)
Dy(1)–O(8)
2.459(3)
2.503(2)
2.462(2)
2.5146(19)
Dy(1)–O(4)#2
Dy(1)–N(1)
Dy(1)–O(3)#2
O(2)#1–Dy(1)–O(5)
O(2)#1–Dy(1)–O(9)
O(5)–Dy(1)–O(9)
O(2)#1–Dy(1)–O(1)
O(5)–Dy(1)–O(1)
O(9)–Dy(1)–O(1)
O(2)#1–Dy(1)–O(7)
O(5)–Dy(1)–O(7)
O(9)–Dy(1)–O(7)
O(1)–Dy(1)–O(7)
O(2)#1–Dy(1)–O(8)
O(5)–Dy(1)–O(8)
O(9)–Dy(1)–O(8)
O(1)–Dy(1)–O(8)
O(7)–Dy(1)–O(8)
O(2)#1–Dy(1)–N(1)
O(5)–Dy(1)–N(1)
O(9)–Dy(1)–N(1)
149.52(7)
O(1)–Dy(1)–N(1)
O(7)–Dy(1)–N(1)
O(8)–Dy(1)–N(1)
65.01(7)
69.75(8)
117.30(8)
125.71(7)
81.16(7)
77.32(7)
77.26(7)
136.59(7)
144.70(8)
69.63(7)
74.45(7)
125.82(7)
70.28(7)
70.77(6)
136.74(7)
129.75(7)
112.48(7)
52.41(6)
96.39(8)
73.95(8)
75.45(7)
129.88(7)
140.96(7)
75.15(7)
95.25(7)
143.41(8)
72.30(7)
76.87(7)
72.66(8)
73.01(8)
137.96(7)
70.40(8)
133.11(7)
65.15(7)
130.19(9)
O(2)#1–Dy(1)–O(4)#2
O(5)–Dy(1)–O(4)#2
O(9)–Dy(1)–O(4)#2
O(1)–Dy(1)–O(4)#2
O(7)–Dy(1)–O(4)#2
O(8)–Dy(1)–O(4)#2
N(1)–Dy(1)–O(4)#2
O(2)#1–Dy(1)–O(3)#2
O(5)–Dy(1)–O(3)#2
O(9)–Dy(1)–O(3)#2
O(1)–Dy(1)–O(3)#2
O(7)–Dy(1)–O(3)#2
O(8)–Dy(1)–O(3)#2
N(1)–Dy(1)–O(3)#2
O(4)#2–Dy(1)–O(3)#2
Symmetry transformations used to generate equivalent atoms: #1 ꢁx þ 1, y ꢁ 1/2, ꢁz þ 3/2; #2 x, ꢁy þ 3/2, z ꢁ 1/2.

4072
H.-S. Wang et al.
Figure 1. The ORTEP representation of 1 showing the coordination environment of Sm(III) with 30%
probability thermal ellipsoids. All hydrogens were omitted for clarity.
Scheme 1. The coordination modes of pta3ꢁ in 1 and 2.
bonds only three metal ions. By connection of pta3ꢁ and Sm(III) 2-D layered
framework is formed, as shown in figure 2. The 2-D layers are connected by hydrogen
bonds formed among coordinated water molecules and carboxyl groups to form a 3-D
network (figure 3).
Nine coordination atoms of the central ions form a polyhedron of distorted
monocapped square anti-prism, as shown in figure 4. The average bond lengths of RE–
˚
O (RE ¼ Sm(III) and Dy(III)) are 2.457 and 2.427 A, respectively. They become shorter
with increasing atomic number, ascribed to lanthanide contraction because they have
the same crystal structure.
3.2. Photoluminescent properties of 1 and 2
Luminescent materials containing europium and terbium ions have been deeply studied
and some of them have been applied [20–22]. Both Sm(III) and Dy(III) can form

Sm(III) and Dy(III) coordination polymers
4073
Figure 2. 2-D layered structure formed by pta3ꢁ and Sm(III) in 1.
Figure 3. 3-D structure constructed by 2-D layers with hydrogen bonds formed among coordinated water
molecules and carboxylates.
Figure 4. The distorted monocapped tetragonal anti-prism formed by coordinating oxygen and nitrogen.

4074
H.-S. Wang et al.
Figure 5. Emission spectra of (a) 1 and (b) 2 with the excitation at 295 nm.
analogous luminescent materials, but they are not used widely due to the weak
emission. Here the solid-state photoluminescent spectra of 1 and 2 at ambient
temperature were recorded under the excitation at 295 nm. The emission bands of 1 are
shown in figure 5(a). The four peaks at 563, 598, 644, and 708 nm corresponded to

Sm(III) and Dy(III) coordination polymers
4075
4
6
transitions of Sm(III) from G5/2 to HJ (J ¼ 5/2, 7/2, 9/2, 11/2), respectively [23–26].
In the luminescence spectra of 2, as shown in figure 5(b), three emitting peaks of Dy(III)
4
6
complex at 481, 573, and 661 nm are assigned to the transitions F9/2 ! H15/2
,
4F9/2 ! H13/2, and F9/2 ! H11/2, respectively [27–29]. The transitions of G5/2 to
6H11/2 of Sm(III) ion and 4F9/2 to 6H11/2 of Dy(III) ion are usually weak, rarely seen in
the corresponding luminescence spectra. Fortunately the two emission bands are clearly
shown in emission spectra of 1 and 2. The two complexes have relatively strong
emission intensity in the visible region probably due to [30–35] the pta3ꢁ ligands
absorbing excitation energy by pyridyl rings and transferring energy to Sm(III) or
Dy(III) and the double-layered 2-D structure is a rigid structure and less energy was lost
with the vibrations of the crystal lattice.
6
4
6
4
In summary, we have synthesized two new coordination polymers of samarium and
dysprosium using pta3ꢁ as the organic linker. The two complexes are isostructural.
The ligand connects three lanthanides. Both complexes show strong characteristic
emissions in the visible region.
Supplementary material
Crystallographic data for the two complexes with CCDC Nos. are 705528 and 705529,
respectively, in this article have been deposited at the Cambridge Crystallographic
Data Center. These data can be obtained free of charge via www.ccdc.cam.ac.uk/
conts/retrieving.html (or from the Cambridge Crystallographic Data Center, 12 Union
Road, Cambridge CB2 1EZ, UK; Fax: (þ44) 1223-336-033; or E-mail:
deposit@ccdc.cam.ac.uk).
Acknowledgments
This work was supported by Education Department of Henan Province (2009B150026).
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