Synthesis, structure and luminescence property of the three ternary and quaternary europium complexes

Article abstract of DOI:10.1016/S0022-2860(01)00900-0

Three binuclear europium complexes containing bidentate and tridentate bridging carboxylates with diimines, namely [Eu(m-MOBA)₂NO₃phen]₂, [Eu(2,3-DMOBA)₂NO₃phen]₂ and [Eu(2,3-DMOBA)₃

Full text of DOI:10.1016/S0022-2860(01)00900-0

Journal of Molecular Structure 607 (2002) 59±67
www.elsevier.com/locate/molstruc
Synthesis, structure and luminescence property of the three ternary
and quaternary europium complexes
a,b
X. Li , L.P. Jin , X.J. Zheng , S.Z. Lu , J.H. Zhang
a,
a
c
c
*
aDepartment of Chemistry, Beijing Normal University, Beijing 100875, People's Republic of China
bDepartment of Chemistry, Capital Normal University, Beijing 100037, People's Republic of China
cLaboratory of Excited State Processes, Chinese Academy of Sciences, Changchun 130021, People's Republic of China
Received 25 July 2001; revised 5 October 2001; accepted 5 October 2001
Abstract
Three binuclear europium complexes containing bidentate and tridentate bridging carboxylates with diimines, namely
[Eu(m-MOBA)2NO3phen]2, [Eu(2,3-DMOBA)2NO3phen]2 and [Eu(2,3-DMOBA)3bpy]2 (m-MOBA ˆ 3-methoxybenzoate,
2,3-DMOBA ˆ 2,3-dimethoxy-benzoate, phen ˆ 1,10-phenanthroline, bpy ˆ 2,20-bipyridine), have been synthesized and
characterized by X-ray diffraction. The two europium(III) ions in each dimer are bridged by the four carboxylato groups in
which two of them are the bidentate bridging mode, and the other two the tridentate bridging mode. The crystallographic data
and combination bands of infrared spectra of the [Eu(m-MOBA)2NO3phen]2 and the [Eu(2,3-DMOBA)2NO3phen]2 complexes
show that the nitrato group is bidentate, and thus each europium(III) ion in the complexes is coordinated with seven oxygen
atoms and two nitrogen atoms from phen, leading to a dimeric structure with coordination number 9. Excitation and emission
7
spectra of the europium complexes were observed at 77 K. The 5D0 ! FJ ꢀJ ˆ 0±4† luminescence spectra show that the
europium(III) ion site in the crystals of the three europium complexes has C1 symmetry. The slightly different chemical
environments of the europium(III) ions in the [Eu(2,3-DMOBA)3bpy]2 complex is con®rmed by its emission spectra.
q 2002 Elsevier Science B.V. All rights reserved.
Keywords: Europium complex; Synthesis; X-ray crystallography; Luminescence property
1. Introduction
formed when lanthanides are bonded to benzoate (or
its derivatives) and diimine ligands such as 1,10-
phenanthroline and 2,20-bipyridine [6±9]. To our
knowledge, less attention has been paid to the position
of the substituents on the benzene ring, which results
in different structures and photophysical properties of
the europium complexes [10,11]. Europium ion is a
sensitive probe in lanthanide coordination chemistry
[12]. Especially laser induced high-resolution spectra
provide detailed information of chemical environment
of the central coordinated metal ions [13]. As a part of
our systematic study of crystal structures and photo-
physical characteristics of lanthanide benzoate
Rare earth complexes with benzoic acid or its
derivatives have been reported to show chelating,
bridging and chelating±bridging modes of coordina-
tion which can be simultaneous or separate [1±4]. In
general, lanthanide coordination polymers are
commonly found in the lanthanide benzoate hydrates
[2,3,5]. However, binuclear lanthanide complexes are
* Corresponding author. Tel.: 186-1062207838; fax: 186-
1062200567.
E-mail address: lpjin@bnu.edu.cn (L.P. Jin).
0022-2860/02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-2860(01)00900-0

60
X. Li et al. / Journal of Molecular Structure 607 (2002) 59±67
Table 1
Crystal data and experimental details
Formula
Formula weight
Temperature (K)
[Eu(m-MOBA)2NO3phen]2
1392.91
293
[Eu(2,3-DMOBA)2NO3phen]2
1513.02
293
[Eu(2,3-DMOBA)3bpy]2
1703.30
293
Ê
Radiation (Mo Ka) (A)
Crystal system
0.71069
Triclinic
0.71069
Triclinic
0.71069
Triclinic
Å
P1
Å
P1
Å
P1
Space group
ꢀ
ꢀ
ꢀ
Unit cell dimensions
a ˆ 11:067ꢀ3† A
a ˆ 11:064ꢀ4† A
a ˆ 12:010ꢀ7† A
ꢀ
ꢀ
ꢀ
b ˆ 11:728ꢀ5† A
b ˆ 13:151ꢀ4† A
b ˆ 15:309ꢀ6† A
ꢀ
ꢀ
ꢀ
c ˆ 10:723ꢀ3† A
c ˆ 10:947ꢀ4† A
c ˆ 10:949ꢀ5† A
a ˆ 101:95ꢀ2†8
a ˆ 105:67ꢀ3†8
a ˆ 95:41ꢀ4†8
b ˆ 96:68ꢀ2†8
b ˆ 101:78ꢀ3†8
b ˆ 106:90ꢀ4†8
g ˆ 80:00ꢀ2†8
g ˆ 78:58ꢀ3†8
g ˆ 67:63ꢀ4†8
Ê 3
Volume (A )
1336.2(7)
1484.0(9)
1780(1)
Z
1
1
1
Density (calculated) (g cm23
)
1.731
24.03
1.693
21.8
1.588
18.2
Absorption coef®cient (cm21
)
F(000)
692.00
756.00
860.00
m (Mo Ka) (cm21
Crystal size
2umax (8)
)
24.03
21.75
18.24
0:20 £ 0:20 £ 0:30 mm
51.0
0:20 £ 0:20 £ 0:30 mm
51.0
0:20 £ 0:20 £ 0:30 mm
45.0
Index ranges
0 # h # 11; 213 # k # 14;
212 # l # 12
0 # h # 11; 215 # k # 15;
213 # l # 12
0 # h # 11; 214 # k # 16;
211 # l # 11
Re¯ections collected
Re®nement method
Independent re¯ections
No. observations
4314
4578
4459
Full-matrix least-squares on F2
4042ꢀRint ˆ 0:038†
3650
Full-matrix least-squares on F2
4275ꢀRint ˆ 0:060†
3648
Full-matrix least-squares on F2
4190ꢀRint ˆ 0:076†
2868
(I-2.50b(I))
Data/restraints/parameters
Goodness-of-®t on F2
Final R indices
3650/0/370
3648/0/406
2868/0/469
1.59
1.21
1.21
R1 ˆ 0:031; vR2 ˆ 0:039
R1 ˆ 0:032; vR2 ˆ 0:038
R1 ˆ 0:054; vR2 ˆ 0:054
Ê 23
Ê 23
Ê 23
Largest diff. peak and hole
1.37 and 20.64 e A
0.90 and 21.08 e A
0.86 and 2 1.19 e A
complexes with diimines, this paper reports the synth-
eses, crystal structures and luminescence properties of
the three europium complexes [Eu(m-MOBA)2NO3-
phen]2, [Eu(2,3-DMOBA)2NO3phen]2 and [Eu(2,3-
DMOBA)3bpy]2.
Crystals of [Eu(m-MOBA)2NO3phen]2 suitable for
X-ray analysis were obtained after 13d. Anal. Calc.
(%): C, 48.29; H, 3.18; N, 6.03. Found: C, 48.11; H,
3.00; N, 5.64. IR: 1776(w), 1733(w), 1601(vs),
1570(vs), 1483(s), 1412(vs), 1394(vs), 1294(s),
1045(m), 846(m), 732(m), 449(w), 417(m), 279(w),
225(w).
[Eu(2,3-DMOBA)2NO3phen]2. 3.0 mmol 2,3-
dimethoxybenzoic acid (2,3-DMOBAH), 0.6 mmol
1,10-phenanthroline (phen) and 1.0 mmol 8-hydroxy-
quinoline were dissolved in 20 ml 95% ethanol. Then,
0.5 mmol Eu(NO3)3 solution (dissolved in 6 ml H2O)
was added. Crystals of [Eu(2,3-DMOBA)2NO3phen]2
suitable for X-ray analysis were obtained after 29d.
Anal. Calc. (%): C, 47.63; H, 3.46; N, 5.55. Found: C,
47.43; H, 3.15; N, 5.20. IR: 1772(w), 1737(w),
1604(vs), 1573(vs), 1476(vs), 1421(vs), 1403(vs),
2. Experimental
2.1. Synthesis of europium complexes
[Eu(m-MOBA)2NO3phen]2. 3.0 mmol 3-methoxy-
benzoic acid (m-MOBAH), 0.6 mmol 1,10-phenan-
throline (phen) and 1.0 mmol 8-hydroxyquinoline
were dissolved in 20 ml C2H5OH±H2O ꢀv=v ˆ 50 :
50† solution, to which was added 0.5 mmol of
Eu(NO3)3 solution (dissolved in 10 ml 95% ethanol).

X. Li et al. / Journal of Molecular Structure 607 (2002) 59±67
61
Table 2
Selected bond lengths (A) and bond angles (8) for the [Eu(m-MOBA)2NO3phen]2 complex
Ê
Atom
Eu
Atom
O(1)
O(4)
O(5)
O(8)
N(2)
Distance
2.362(4)
2.388(4)
2.739(4)
2.448(4)
2.580(4)
Atom
Eu
Atom
O(2)p
O(5)p
O(7)
Distance
2.357(3)
2.364(3)
2.524(4)
2.631(4)
Eu
Eu
Eu
Eu
Eu
Eu
N(1)
Eu
Atom
O(1)
O(1)
O(1)
O(1)
O(1)
O(1)
O(1)
O(1)
O(2)p
O(2)p
O(2)p
O(2)p
O(2)p
O(2)p
O(2)p
O(4)
O(4)
O(4)
Atom
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Atom
O(2)p
O(4)
O(5)
O(5)p
O(7)
O(8)
N(1)
N(2)
O(4)
O(5)
O(5)p
O(7)
O(8)
N(1)
N(2)
O(5)
O(5)p
O(7)
Angle
Atom
O(4)
O(4)
O(4)
O(5)
O(5)
O(5)p
O(5)
O(5)p
O(5)
O(5)p
O(5)
O(5)p
O(7)
O(7)
O(7)
O(8)
O(8)
N(1)
Atom
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Atom
O(8)
N(1)
N(2)
O(5)p
O(7)
O(7)
O(8)
O(8)
N(1)
N(1)
N(2)
N(2)
O(8)
N(1)
N(2)
N(1)
N(2)
N(2)
Angle
136.5(1)
90.7(1)
74.5(1)
72.4(1)
126.5(1)
87.2(1)
75.8(1)
138.7(1)
82.4(1)
68.4(1)
78.7(1)
74.0(1)
125.1(1)
138.2(1)
81.4(1)
49.8(1)
128.2(1)
142.4(1)
138.6(1)
69.6(1)
77.2(1)
78.4(1)
137.5(1)
75.5(1)
160.6(1)
90.3(1)
110.5(1)
143.1(1)
120.5(1)
144.4(1)
51.3(1)
110.6(1)
70.8(1)
69.9(1)
77.6(1)
62.9(1)
p
Symmetry operators: x,y,z, 2x,2y,2z.
1305(s), 1038(m), 848(m), 733(m), 418(m), 388(w),
366(w), 277(w), 213(w).
empirical absorption correction using the program
difabs was applied [14]. The structure was solved
by heavy-atom Patterson methods [15]. The non-
hydrogen atoms were re®ned anisotropically.
Hydrogen atoms were included but not re®ned. All
calculations were performed using TEXSAN crystal-
lographic software package [16]. Information
concerning crystallographic data and structure re®ne-
ment of the three europium complexes is given in
Table 1. Selected bond lengths and angles are listed
in Tables 2±4. Additional information comprising of
atomic coordinates and thermal parameters has been
deposited with B.L.L.D as supplementary publication
SUP 26681 (14 pages).
[Eu(2,3-DMOBA)3bpy]2. 1.5 mmol 2,3-dimethoxy-
benzoic acid (2,3-DMOBAH), and 0.5 mmol 2,20-
bipyridine (bpy) were dissolved in 15 ml 95% ethanol.
The pH of the solution was adjusted to ,6 with 1 M
NaOH solution, and the mixture was added dropwise
to a 6 ml aqueous solution of 0.5 mmol Eu(NO3)3. The
mixture was heated at 50 8C with stirring for 4 h. The
solution was ®ltered. Crystals of [Eu(2,3-
DMOBA)3bpy]2 suitable for X-ray analysis were
obtained from the mother liquor after 5d. Anal.
Calc. (%): C, 52.18; H, 4.14; N, 3.29. Found: C,
52.12; H, 4.00; N, 3.21. IR: 1610(vs), 1574(vs),
1416(vs), 1391(vs), 416(w), 384(w), 351(w),
278(w), 212(w).
2.3. Spectral measurement
2.2. Crystal structure determination
The excitation and the emission spectra of the three
europium complexes were recorded at 77 K using a
YAG:Nd pumped dye laser with RG10 dye as the
excitation source and a spex 1403 double grating
X-ray data were collected for the three europium
complexes on a Rigaku AFCR diffractometer at 293 K
using graphite monochromated Mo Ka radiation. An

62
X. Li et al. / Journal of Molecular Structure 607 (2002) 59±67
Table 3
Selected bond lengths (A) and bond angles (8) for the [Eu(2,3-DMOBA)2NO3phen]2 complex
Ê
Atom
Atom
Distance
Atom
Atom
Distance
Eu
Eu
Eu
Eu
Eu
O(1)
O(5)
O(6)p
O(10)
N(1)
2.349(4)
2.391(4)
2.439(4)
2.532(4)
2.626(5)
Eu
Eu
Eu
Eu
O(2)p
O(5)p
O(9)
N(2)
2.346(4)
2.611(4)
2.461(4)
2.575(4)
Atom
O(1)
O(1)
O(1)
O(1)
O(1)
O(1)
O(1)
O(1)
O(2)p
O(2)p
O(2)p
O(2)p
O(2)p
O(2)p
O(2)p
O(5)
O(5)
O(5)p
Atom
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Atom
O(2)p
O(5)
O(5)p
O(6)p
O(9)
Angle
Atom
O(5)p
O(5)
Atom
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Atom
O(6)p
O(9)
O(10)
O(10)
N(1)
N(1)
N(2)
N(2)
O(9)
O(10)
N(1)
N(2)
O(10)
N(1)
N(2)
N(1)
N(2)
N(2)
Angle
138.0(1)
73.1(1)
74.9(1)
97.0(1)
82.6(1)
121.1(1)
75.8(1)
138.2(1)
76.6(1)
70.8(1)
79.5(1)
126.9(1)
76.1(1)
136.2(1)
81.9(1)
77.4(1)
127.8(1)
157.0(1)
50.9(1)
91.7(1)
140.4(1)
74.3(1)
105.4(1)
146.8(1)
143.2(1)
122.7(1)
138.8(1)
141.4(1)
67.2(1)
75.7(1)
51.0(1)
72.9(1)
77.7(1)
113.5(1)
71.7(1)
63.3(1)
O(5)p
O(5)
O(5)p
O(5)
O(10)
N(1)
O(5)
N(2)
O(5)p
O(6)p
O(6)p
O(6)p
O(6)p
O(9)
O(5)
O(5)p
O(6)p
O(9)
O(10)
N(1)
O(9)
N(2)
O(9)
O(5)p
O(6)p
O(9)
O(10)
O(10)
N(1)
p
Symmetry operators: x,y,z, 2x,2y,2z.
monochromator. Infrared spectra were measured with
Nicolet Nexus 670 instrument.
Evidently, the ligand 2,3-DMOBA has larger
steric effect than the ligand m-MOBA in the forma-
tion of the europium complexes, and therefore the
average distance of Eu±O(NO32) for [Eu(m-
Ê
MOBA)2NO3phen]2, 2.486 A is shorter than that for
Ê
[Eu(2,3-DMOBA)2NO3phen]2, 2.497 A. However,
3. Results and discussion
the average distances of Eu±O(carboxylato groups)
for the bidentate bridging and tridentate bridging
modes of [Eu(m-MOBA)2NO3phen]2, 2.360 and
Ê
2.497 A, are larger than those of [Eu(2,3-DMOBA)2-
Ê
NO3phen]2, 2.348 and 2.480 A, respectively, which
makes Eu´´´Eu distance in the [Eu(m-MOBA)2NO3-
3.1. Description of structures
The structure of [Eu(m-MOBA)2NO3phen]2 is
similar to that of [Eu(2,3-DMOBA)2NO3phen]2 as
shown in Figs. 1 and 2. The structures consist of
centrosymmetric dimers in which each europium(III)
ion is connected by four ligands through the carbox-
ylato groups. Two of the four carboxylato groups
simultaneously bridge two europium(III) ions and
the other two carboxylato groups chelate one euro-
pium(III) ion and at the same time bridge two euro-
pium(III) ions. Each europium(III) ion is further
chelated to one nitrato group and one molecule of
1,10-phenanthroline to form nine coordinated
Eu(III) complex.
Ê
phen]2 dimer, 3.962 A longer than that in the
Ê
[Eu(2,3-DMOBA)2NO3phen]2 dimer, 3.905 A. The
calculated results of the least square planes show
that the plane for C11, C12, N1, N2 and Eu in
[Eu(2,3-DMOBA)2NO3phen]2 is less coplanar than
that for C11, C12, N1, N2 and Eu in [Eu(m-MOBA)2-
NO3phen]2 since the 2,3-DMOBA ligand in the
former has larger steric effect than the m-MOBA
ligand in the latter.

X. Li et al. / Journal of Molecular Structure 607 (2002) 59±67
63
Table 4
Selected bond lengths (A) and bond angles (8) for the [Eu(2,3-DMOBA)3bpy]2 complex
Ê
Atom
Atom
Distance
Atom
Atom
Distance
Eu
Eu
Eu
Eu
Eu
O(1)
2.480(8)
2.426(9)
2.386(9)
2.348(9)
2.553(9)
Eu
Eu
Eu
Eu
O(5)
O(9)
O(10)
N(2)
2.352(8)
2.488(9)
2.699(9)
2.614(1)
O(2)
O(6)p
O(10)p
N(1)
Atom
O(1)
O(1)
O(1)
O(1)
O(1)
O(1)
O(1)
O(1)
O(2)
O(2)
O(2)
O(2)
O(2)
O(2)
O(2)
O(5)
O(5)
O(5)
Atom
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Atom
O(2)
Angle
Atom
O(9)
Atom
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Eu
Atom
O(10)
O(10)p
N(1)
Angle
52.9(3)
79.4(3)
120.4(3)
141.0(3)
146.0(3)
79.3(3)
72.4(3)
112.2(3)
132.4(3)
78.0(3)
139.6(3)
150.4(3)
94.4(3)
84.3(3)
73.5(3)
136.7(3)
77.1(3)
72.4(3)
49.1(3)
123.0(3)
73.3(3)
66.5(3)
75.2(3)
120.0(3)
101.2(3)
145.5(3)
149.1(3)
75.0(3)
80.6(3)
134.0(3)
97.8(3)
72.4(3)
72.3(3)
139.9(3)
77.4(3)
63.1(3)
O(5)
O(6)p
O(9)
O(9)
O(9)
O(9)
N(2)
O(10)p
O(10)
O(10)p
N(1)
O(10)
O(10)
O(10)
O(10)p
O(10)p
O(5)
N(1)
N(2)
N(2)
O(5)
O(6)p
N(1)
N(2)
O(10)p
O(9)
O(5)
N(1)
N(2)
O(10)
O(10)p
N(1)
O(5)
O(6)p
O(6)p
O(6)
O(9)
O(10)
O(10)p
N(1)
N(2)
O(6)p
O(6)p
O(6)p
N(1)
O(9)
N(2)
O(10)
N(2)
p
Symmetry operators: x,y,z, 2x,2y,2z.
The structure of (2,20-bipyridine)tris(2,3-dimethoxy-
benzoato) europium, [Eu(2,3-DMOBA)3bpy]2 is
shown in Fig. 3. The structure is composed of dimers
in which each europium(III) ion is coordinated with
two oxygen atoms from the bidentate chelating
carboxyl group, ®ve oxygen atoms from the four
carboxylato0 bridged groups and two nitrogen atoms
from a 2,2 -bipyridine molecule. The carboxylato
groups in [Eu(2,3-DMOBA)3bpy]2 act as the biden-
tate chelating, bidentate bridging and tridentate
bridging coordination modes. It is reasonable that
the average Eu±O distance of the chelating carboxyl
Ê
group, 2.453 A is larger than that of the bidentate
Ê
bridging carboxyl group, 2.369 A, but shorter than
that of the tridentate bridging carboxyl group,
Ê
2.517 A. Unlike [Eu(m-MOBA)3bpy]2 [17], the
[Eu(2,3-DMOBA)3bpy]2 complex crystallizes in
Å
triclinic, space group P1 while the latter belongs to
the monoclinic, space group Pc. The average Eu±O
MOBA)3bpy]2 complex, and the average Eu±N
Ê
distance (2.584 A) of the [Eu(2,3-DMOBA)3bpy]2
Ê
complex is shorter than that (2.618 A) of the
[Eu(m-MOBA)3bpy]2 complex. It is obvious that
the structural difference arises from differing
numbers of the methoxyl group on the benzene
ring, which makes steric effect different in the forma-
tion of complexes.
3.2. Emission spectral analysis
Emission spectrum of the complex [Eu(2,3-
DMOBA)2NO3phen]2 is composed of narrow and
7
well resolved bands corresponding to 5D0 ! FJ ꢀJ ˆ
0±4† transitions in the range 570±730 nm as shown in
Fig. 4. For the complex [Eu(2,3-DMOBA)2NO3-
7
phen]2, the 5D0 ! F0 transition could be found
though it is weak. The position of the peak is at
17,222 cm21. Three lines at 16,877, 16,867 and
16,814 cm21 were observed after 355 nm excitation.
Ê
distance (2.458 A) of the [Eu(2,3-DMOBA)3bpy]2
Ê
complex is larger than that (2.384 A) of the [Eu(m-
5
7
They are assigned to D0 ! F1 transitions. In the

64
X. Li et al. / Journal of Molecular Structure 607 (2002) 59±67
Fig. 1. Molecular structure of [Eu(m-MOBA)2NO3phen]2.
region between 15,900 and 16,300 cm21, intense
[Eu(m-MOBA)2NO3phen]2 is similar to that of
[Eu(2,3-DMOBA)2NO3phen]2 in splitting patterns
and intensity although some shifts were observed.
However, emission spectrum of the complex
[Eu(2,3-DMOBA)3bpy]2 is distinctly different from
those of the complexes [Eu(2,3-DMOBA)2NO3-
phen]2 and [Eu(m-MOBA)2NO3phen]2, as shown in
7
emission bands assigned to 5D0 ! F2 manifold
were observed. These transitions exhibit a so-called
hypersensitivity with respect to changes in the envir-
onment [12].
A few weak lines centered at
15,370 cm21 were observed in the region of the
7
5D0 ! F3 transitions (see Fig. 4). In the region of
5
7
7
the D0 ! F4 transitions one can see six relatively
Fig. 5. It is known that the 5D0 ! F0 emission band
strong lines. The splitting patterns of the emission
of Eu31 ꢀlem ˆ ,580 nm† is of particular impor-
tance since neither level ꢀJ ˆ 0† can be split by the
ligand ®eld. This demands that the resulting
transition be a single band. Multiple environments
bands, especially due to 5D0 ! FJ ꢀJ ˆ 0±2† transi-
7
tions show a single europium ion site and low
symmetry of the site [12]. Emission spectrum of

X. Li et al. / Journal of Molecular Structure 607 (2002) 59±67
65
Fig. 2. Molecular structure of [Eu(2,3-DMOBA)2NO3phen]2.
for the Eu31 ion may cause more than one electronic
of the peaks. This may be due to the fact that bpy is a
¯exible ligand since the free bpy ligand is in trans-
form but it becomes cis-form upon complexation.
Packing with different bpy conformations in the
crystal results in changes in bond lengths for Eu±O
and Eu±N bonds, which places the Eu31 ions at
different environments. This is a common phenom-
enon found in stu0dies of the ternary lanthanide
complexes with 2,2 -bipyridine [8,17,18].
7
transition to appear in the 5D0 ! F0 transition
5
7
region. Fig. 5 shows two lines for the D0 ! F0
transitions at 17,241 and 17,226 cm21, and the
7
number of emission lines for the 5D0 ! FJ ꢀJ ˆ
1; 2† transitions is more than 2J 1 1; which exhibits
a different chemical environment of the Eu31 ion site
in [Eu(2,3-DMOBA)3bpy]2. This could be evidenced
by the time resolved spectra of [Eu(2,3-
DMOBA)3bpy]2, as shown in Fig. 6. Changes in
peak shape and intensity could be found in the 5D0 !
5
7
7F1 and D0 ! F2 transitions at delay times 20 ms,
250 ms and 1 ms after 355 nm excitation, respec-
tively. Taking the splitting pattern of the 5D0 !
7F1 transitions as an example, the peaks at 16,880
and 16,850 cm21 become well resolved, and the
peak at 16,814 cm21 disappears while peaks at
16,832 and 16,802 cm21 become well developed
(Fig. 6c). This clearly shows that the Eu31 ions in
the crystal occupy sites with different environments
leading to differing lifetimes and changes in intensity
4. Conclusions
It is likely to form binuclear lanthanide complexes
if lanthanides are coordinated with carboxylic acids
and diimines such as 2,20-bipyridine and 1,10-phenan-
throline. The carboxylates of the complexes show
chelating, bidentate bridging and tridentate
chelating±bridging modes of coordination which
can be simultaneous or separate. The europium(III)
ion is a sensitive probe for determination of chemical

66
X. Li et al. / Journal of Molecular Structure 607 (2002) 59±67
Fig. 3. Molecular structure of [Eu(2,3-DMOBA)3bpy]2.
Fig. 4. Emission spectrum of the [Eu(2,3-DMOBA)2NO3phen]2
Fig. 5. Emission spectrum of the [Eu(2,3-DMOBA)3bpy]2 complex
complex at 77 K, lexc ˆ 355nm:
at 77 K, lexc ˆ 355nm:

X. Li et al. / Journal of Molecular Structure 607 (2002) 59±67
67
Natural Science Foundation of China (29971005)
and Natural Science Foundation of Beijing (2982009).
References
È
È
[1] C. Arici, D. UlkuÈ, M.N. Tahir, C. Unaleroglu, Acta Crystal-
logr. C 55 (1999) 198.
[2] J.F. Ma, Z.S. Jin, J.Z. Ni, Acta Crystallogr. C 55 (1994) 1008.
[3] J.F. Ma, Z.S. Jin, J.Z. Ni, Acta Crystallogr. C 55 (1994) 1010.
[4] L.P. Jin, S.X. Lu, S.Z. Lu, Polyhedron 15 (22) (1996) 4069.
[5] X. Li, X.J. Zheng, L.P. Jin, S.Z. Lu, W.P. Qin, J. Mol. Struct.
519 (2000) 85.
[6] Y. Zhang, L.P. Jin, S.Z. Lu, Chin. J. Inorg. Chem. 13 (3)
(1997) 280 In Chinese.
[7] Y. Zhang, L.P. Jin, S.Z. Lu, J. Chin. Rare Earth Soc. 16 (1)
(1998) 5 In Chinese.
[8] L.P. Jin, R.F. Wang, L.S. Li, S.Z. Lu, S.H. Huang, Polyhedron
18 (1999) 487.
[9] L.Y. Wang, X.J. Zheng, L.P. Jin, S.Z. Lu, Chem. J. Chin.
Univ. 20 (7) (1999) 1110 In Chinese.
[10] L.P. Jin, M.Z. Wang, G.L. Cai, S.X. Liu, J.L. Huang, R.F.
Wang, Sci. China, Ser. B 38 (1) (1995) 1.
Fig. 6. Time resolved spectra of the [Eu(2,3-DMOBA)3bpy]2
complex at 77 K, lexc ˆ 355nm: Delay time: (a) 20 ms, (b)
250 ms, (c) 1 ms.
[11] L.P. Jin, R.F. Wang, M.Z. Wang, G.L. Cai, S.X. Liu, J.L.
Huang, Chem. J. Chin. Univ. 14 (9) (1993) 1195.
[12] J.-C.G. BuÈnzli, G.R. Choppin, Lanthanide probes in life,
Chemical and Earth Science, Elsevier, Amsterdam, 1989
Chapter 7.
[13] J.-C.G. BuÈnzli, G.O. Pradervand, J. Chem. Phys. 85 (5) (1986)
2489.
environment. In general lanthanide complexes
containing bpy result in slightly different chemical
environment for the0 central metal ions because of
¯exibility of the 2,2 -bipyridine molecule. Free 2,2-
bipyridine is in trans-form while it is cis-form upon
complexation.
[14] N. Walke, D. Stuart, Acta Crystallogr. Sect. A 39 (1983) 158.
[15] P.T. Beurskens, G. Admiraal, G. Beurskens, W.P. Bosman, S.
Garcia-Granda, R.O. Gould, J.M.M. Smits, C. Smykalla, The
DIRDIF program system, Technical Report of the Crystallo-
graphy Laboratory, University of Nijmegen, The Netherlands,
1992.
[16] TEXSAN, Structure Analysis Package, Molecular Structure
Corporation, Texas, USA, 1985 & 1992.
Acknowledgements
[17] X. Li, Z.Q. Bian, L.P. Jin, S.Z. Lu, S.H. Huang, J. Mol. Struct.
522 (2000) 117.
This work was supported by the State Key Project
of Fundamental Research (G1998061308), National
[18] R.F. Wang, L.P. Jin, M.Z. Wang, S.H. Huang, X.T. Chen,
Acta Chim. Sin. 53 (1995) 39 In Chinese.