Preparation, luminescent properties of N-phenyl-2-{2′-[(phenyl-ethyl-carbamoyl)-methoxy]-biphenyl-2-yloxy}-N-ethyl-acetamide (L) lanthanide complexes and the supramolecular structures of [La(pic)3L] and 2[La(NO3)3L(H2O)] · H2O · 0.5C2H5OH

Article abstract of DOI:10.1016/j.poly.2006.12.019

A new amide-based ligand, N-phenyl-2-{2′-[(phenyl-ethyl-carbamoyl)-methoxy]-biphenyl-2-yloxy}-N-ethyl-acetamide (L) was synthesized. Solid complexes of lanthanide picrates with this new ligand were prepared and characterized by elemental analysis, conductivity measurements, IR, electronic and ¹H NMR spectroscopies. Under excitation, the europium picrate complex exhibited strong characteristic emissions. The europium nitrate complex exhibited quite weak characteristic emissions. The counter anion factor influencing the fluorescence properties was discussed. The lowest triplet state energy level of the ligand in the picrate complex matches better to the resonance level of Eu(III) than Tb(III) ion. The crystal structures of the complex La(Pic)₃L and 2[La(NO₃)₃L(H₂O)] · H₂O · 0.5C₂H₅OH have been determined by single-crystal X-ray diffraction. The La(Pic)₃L crystal structure shows that the La(III) ion is coordinated with four oxygen atoms from the ligand L and six from three bidentate picrates. Furthermore, the La(Pic)₃L complex units are linked by the significant intermolecular π-π interactions between coordinate picrates to form a one-dimensional (1-D) supramolecular zigzag chain. The 2[La(NO₃)₃L(H₂O)] · H₂O · 0.5C₂H₅OH crystal structure shows that L gives two different arrangements around La(III) ions and induces axial chirality directed by metal ions in the assembly process of the organic ligands with metal ions, each La(III) ion is coordinated with four oxygen atoms from the ligand L, six oxygen atoms from three bidentate nitrate groups and one coordinate water molecule. Furthermore, the [La(NO₃)₃L(H₂O)] complex units are linked by the intermolecular hydrogen bonds and π-π interaction to form a three-dimensional (3-D) netlike supramolecule.

Full text of DOI:10.1016/j.poly.2006.12.019

Polyhedron 26 (2007) 1699–1710
www.elsevier.com/locate/poly
Preparation, luminescent properties of
N-phenyl-2-{20-[(phenyl-ethyl-carbamoyl)-methoxy]-biphenyl-2-yloxy}-
N-ethyl-acetamide (L) lanthanide complexes and the supramolecular
structures of [La(pic)3L] and 2[La(NO3)3L(H2O)] Æ H2O Æ 0.5C2H5OH
a
a
a
a,b,
c
Yan-Ling Guo , Wei Dou , Ya-Wen Wang , Wei-Sheng Liu
*, Da-Qi Wang
a
Department of Chemistry and State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 210093, China
b
State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 730000, China
c
Department of Chemistry, Liaocheng University, Liaocheng 252000, China
Received 21 October 2006; accepted 6 December 2006
Available online 21 December 2006
Abstract
A new amide-based ligand, N-phenyl-2-{20-[(phenyl-ethyl-carbamoyl)-methoxy]-biphenyl-2-yloxy}-N-ethyl-acetamide (L) was synthe-
sized. Solid complexes of lanthanide picrates with this new ligand were prepared and characterized by elemental analysis, conductivity
measurements, IR, electronic and 1H NMR spectroscopies. Under excitation, the europium picrate complex exhibited strong character-
istic emissions. The europium nitrate complex exhibited quite weak characteristic emissions. The counter anion factor influencing the
fluorescence properties was discussed. The lowest triplet state energy level of the ligand in the picrate complex matches better to the res-
onance level of Eu(III) than Tb(III) ion. The crystal structures of the complex La(Pic)3L and 2[La(NO3)3L(H2O)] Æ H2O Æ 0.5C2H5OH
have been determined by single-crystal X-ray diffraction. The La(Pic)3L crystal structure shows that the La(III) ion is coordinated with
four oxygen atoms from the ligand L and six from three bidentate picrates. Furthermore, the La(Pic)3L complex units are linked by the
significant intermolecular p–p interactions between coordinate picrates to form a one-dimensional (1-D) supramolecular zigzag chain.
The 2[La(NO3)3L(H2O)] Æ H2O Æ 0.5C2H5OH crystal structure shows that L gives two different arrangements around La(III) ions and
induces axial chirality directed by metal ions in the assembly process of the organic ligands with metal ions, each La(III) ion is coordi-
nated with four oxygen atoms from the ligand L, six oxygen atoms from three bidentate nitrate groups and one coordinate water mol-
ecule. Furthermore, the [La(NO3)3L(H2O)] complex units are linked by the intermolecular hydrogen bonds and p–p interaction to form a
three-dimensional (3-D) netlike supramolecule.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Keywords: Lanthanide complexes; Luminescent properties; Supramolecular structure; p–p Interaction; Hydrogen bonds
1. Introduction
crystalline materials, optical fiber lasers and amplifiers,
luminescent label design for specific biomolecule interac-
tions, magnetic molecular materials and electroluminescent
materials [1–6].
Amide-based open-chain crown ethers offer many
advantages in extraction and analysis of the rare earth ions
because of their ring-like coordination structure and termi-
nal group effects [7,8]. However, luminescent properties on
open-chain crown ethers with lanthanide complexes have
Over the past decades, considerable attention has been
devoted to the design and synthesis of luminescent lantha-
nide complexes due to their interesting photophysical prop-
erties, which have potential applications in sensors, liquid
*
Corresponding author. Tel.: +86 931 8912552; fax: +86 931 8912582.
E-mail address: liuws@lzu.edu.cn (W.-S. Liu).
0277-5387/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2006.12.019

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Y.-L. Guo et al. / Polyhedron 26 (2007) 1699–1710
been rarely reported [9]. Our group is interested in the
supramolecular coordination chemistry of lanthanide ions
with amide-based open-chain crown ethers that have
strong coordination capability to the lanthanide ions and
terminal group effects [10]. So we have designed a series
of multi-functional amide-based open-chain crown ethers
having the ability to coordinate lanthanide ions and thus
enhance luminescence of lanthanide complexes by provid-
ing chromophores suitable for energy transfer, i.e., aryl
substitutes.
2. Experimental
2.1. Materials
Lanthanide picrate [11] and N-ethyl-N-phenylchloroace-
tamide [12] were prepared according to the literature meth-
ods. All commercially available chemicals were of A.R.
grade and were used without further purification.
2.2. Methods
In this work, we introduced biphenyl groups as the basic
molecular frame and obtained a new open-chain crown
ether ligand, N-phenyl-2-{20-[(phenyl-ethyl-carbamoyl)-
methoxy]-biphenyl-2-yloxy}-N-ethyl-acetamide (L), and
reported the synthesis, luminescent properties of lanthanide
complexes with the new ligand and the supramolecular
structures of La(pic)3L and 2[La(NO3)3L(H2O)] Æ H2O Æ
0.5C2H5OH. The results indicate that under excitation, the
Eu(III) picrate complex had strong characteristic lumines-
cence whereas the terbium picrate complex showed no
luminescence. The lowest triplet state energy level of the
ligand in the picrate complex which was calculated from
the phosphorescence spectrum of the Gd(III) picrate
complex at 77 K, and indicates that the triplet state energy
level of the ligand matches better to the resonance level of
Eu(III) than Tb(III) ion. The Eu(III) nitrate complex exhib-
ited quite weak characteristic emissions. The La(Pic)3L crys-
tal structure shows that the La(III) ion could be effectively
encapsulated and protected by the coordinated ligand.
Furthermore, the La(Pic)3L complex units are linked by
the significant intermolecular p–p interactions between
coordinate picrates to form a one-dimensional (1-D) supra-
molecular zigzag chain. The 2[La(NO3)3L(H2O)] Æ H2O Æ
0.5C2H5OH crystal structure shows that L gives two differ-
ent arrangements around La(III) ions, and induces axial
chirality directed by metal ions in the self-assembly process.
Each La(III) ion is coordinated with four oxygen atoms
from the ligand L, six oxygen atoms from three bidentate
nitrate groups and one coordinate water molecule.
Furthermore, the [La(NO3)3L(H2O)] complex units are
linked by the intermolecular hydrogen bonds and p–p
interaction to form a three-dimensional (3-D) netlike
supramolecule.
The metal ions were determined by EDTA titration using
xylenal orange as indicator. C, H and N were determined
using an Elementar Vario EL. Conductivity measurements
were carried out with a DDS-307 type conductivity bridge
using 10ꢀ3 mol dmꢀ3 solutions at 25 ꢁC. IR spectra were
recorded on Nicolet FT-170SX instrument using KBr discs
1
in the 400–4000 cmꢀ1 region, H NMR spectra were mea-
sured on a Varian Mercury plus 300 M spectrometer in
CDCl3 solution with TMS as internal standard. Fluores-
cence and phosphorescence measurements were made on a
Hitachi F-4500 spectrophotometer. Mass spectra were
obtained on a VG-ZAB-HS mass spectrometer.
2.3. Synthesis of the ligand
The synthetic route for the ligand is shown in Scheme 1.
Anhydrous K2CO3 (5.6 g, 41 mmol) was added into the
15 mL DMF solution of 2,20-dihydroxybiphenyl (1.86 g,
10 mmol) at 100 ꢁC. After 1 h, a solution of N-ethyl-N-phe-
nylchloroacetamide (5.92 g, 30 mmol) in 10 mL DMF was
added dropwise to the mixture and maintained at 110 ꢁC
for 7 h. When cool, distilled water (60 ml) was added and
the turbid solution was extracted with chloroform
(3 · 40 mL). The combined organic phases were washed
with water and dried with anhydrous Na2SO4. The solvent
was removed and the residue was chromatographed to
afford the ligand L; yield: 85%.
2.4. Synthesis of the lanthanide picrate complexes
To a solution of 0.2 mmol lanthanide picrate in 5 ml of
ethanol was added dropwise the solution of 0.2 mmol L in
Cl
N
O
N
O
O
N
DMF, K2CO3, 110 ºC, 7h
OH
OH
O
O
L
Scheme 1. The synthetic route for the ligand L.

Y.-L. Guo et al. / Polyhedron 26 (2007) 1699–1710
1701
10 ml of ethanol. The mixture was stirred at room tempera-
ture for 5 h. The precipitated solid complex was filtered,
washed with ethanol and dried in vacuum over P2O5 for
48 h. All the complexes were obtained as yellow powders in
a yield of 80–85%. Slowly evaporating a solution of the lan-
thanum complex in CHCl3/CH3CH2OH at room tempera-
ture, resulted in the formation of block crystals after 2 weeks.
ductances of the picrate complexes in acetone and
Eu(NO3)3L in DMF (see Table 1) indicate that all the pic-
rate complexes and Eu(NO3)3L act as non-electrolytes [13],
implying that all the picrate groups and nitrate groups are
in the coordination sphere.
3.2. Crystal structure of La(Pic)3L
2.5. Synthesis of the lanthanide nitrate complex
A summary of crystallographic data and details of the
structure refinements are listed in Table 2. The selected
bond lengths and bond angles are given in Table 3.
To a solution of 0.2 mmol lanthanide lanthanide nitrate
in 5 ml of ethanol was added dropwise the solution of
0.2 mmol L in 10 ml of ethanol. The mixture was stirred
at room temperature for 10 h and a clear solution obtained.
The clear solution of lanthanum nitrate complex was fil-
tered and left to crystallise. After about a month, a color-
less crystal formed from the solution. After solvent
evaporation from the solution of europium nitrate complex
in vacuum, a white precipitate obtained, washed with little
ethanol and dried in vacuum over P2O5 for 72 h.
The single-crystal X-ray analysis of the complex
La(Pic)3L reveals that the La(III) ion is coordinated with
10 oxygen donor atoms, six of which belong to three biden-
tate picrate groups and the remaining four to the tetraden-
tate ligand L (Fig. 1). The coordination polyhedron
around La(III) ion is a distorted bicapped square antiprism
(Fig. 2). The two phenyl rings about the central bond in the
molecule have a drastic twisting, with the dihedral angle
between them being 62.49ꢁ. The LaAO (C@O) distances
˚
(mean 2.461 A) are significantly shorter than the La–O
˚
2.6. Crystal structure determination
(C–O–C) distances (mean 2.701 A). This suggests that the
LaAO (C@O) bond is stronger than the La–O (C–O–C)
bond.
X-ray diffraction data of La(pic)3L and 2[La(NO3)3L-
(H2O)] Æ H2O Æ 0.5C2H5OH were collected on a Bruker
Smart-1000 CCD area detector diffractometer, using
In the complex, the requirement of high coordination
number of the lanthanide ion is satisfied by the tetradentate
ligand and three bidentate picrate groups. Due to the space
obstacle of coordinated picrates, no coordinated solvent
molecules exist in the complex, which can efficiently quench
lanthanide luminescence, this is important in the design of
supramolecular photonic devices.
˚
graphite-monochromatized Mo Ka (k = 0.71073 A) at
298(2) K. The structures were solved by direct method
and refined by full matrix least-squares techniques on F2
with all non-hydrogen atoms treated anisotropically. All
calculations were performed with the program package
SHELXTL. The hydrogen atoms were assigned with common
isotropic displacement factors and included in the final
refinement by using geometrical restrains.
Interestingly, the complex has significant intermolecular
p–p interaction [14] between two picrates of one complex
molecule and equivalent picrates of the adjacent molecules
with the dihedral angles between them being 0ꢁ and 0ꢁ, and
˚
3. Results and discussion
the distances between their centroids being 3.774, 4.019 A,
respectively, thus, producing a one-dimensional (1-D)
supramolecular zigzag chain (Fig. 3).
3.1. Properties of the complexes
Analytical data for the complexes, listed in Table 1, indi-
cate that the seven complexes of rare earth picrates and
europium nitrate conform to a 1:1 metal-to-ligand stoichi-
ometry Ln(pic)3L and Eu(NO3)3L. All the picrate com-
plexes are soluble in DMF, DMSO, acetonitrile, acetone
and CHCl3, but slightly soluble in ethanol. The molar con-
3.3. Crystal structure of
2[La(NO3)3L(H2O)] Æ H2O Æ 0.5C2H5OH
A summary of crystallographic data and details of the
structure refinements are listed in Table 2. The selected
bond lengths and bond angles are given in Table 4.
Table 1
Analytical and molar conductance data for the complexes (calculated values in parentheses)
Complex
Analysis (%)
C
Km (cm2 Xꢀ1 molꢀ1
)
H
N
Ln
La(pic)3L
Nd(pic)3L
Eu(pic)3L
Gd(pic)3L
Tb(pic)3L
Y(pic)3L
44.78(45.08)
44.63(44.91)
44.17(44.64)
44.16(44.48)
44.12(44.41)
46.56(46.84)
45.78(45.39)
3.01(2.86)
3.04(2.84)
2.70(2.83)
2.94(2.82)
2.72(2.81)
2.68(2.97)
3.08(3.78)
11.43(11.57)
11.38(11.53)
11.32(11.46)
11.14(11.42)
11.26(11.40)
12.08(12.02)
8.63(8.27)
10.21(10.44)
10.53(10.78)
11.13(11.31)
11.28(11.64)
11.32(11.77)
6.64(6.95)
34.0
31.7
29.8
32.7
31.2
34.6
50.3
Eu(NO3)3L
17.49(17.97)

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Y.-L. Guo et al. / Polyhedron 26 (2007) 1699–1710
Table 2
Crystal data and structure refinements for lanthanum picrate and lanthanum nitrate complexes
Empirical formula
Temperature (K)
Crystal color
C50H38LaN11O25
298(2)
yellow
C65H73La2N10O29.50
293(2)
colourless
Crystal size (mm)
Formula weight
Crystal system
Space group
Unit cell dimensions
0.45 · 0.38 · 0.19
1331.82
triclinic
0.53 · 0.48 · 0.45
1744.15
monoclinic
P2(1)/c
ꢀ
P1
˚
a (A)
10.9574(18)
15.381(3)
16.877(3)
25.733(8)
11.978(4)
28.383(8)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
95.734(3)
90.664(2)
107.748(2)
2692.8(8)
90
116.452(4)
90
7832(4)
3
˚
V (A )
Z
2
4
Dcalc (mg/m3)
F(000)
1.643
1344
0.71073
14193
1.479
3532
0.71073
39525
˚
Radiation, graphite-monochromatized, k (A)
Reflections collections
Independent reflection
9335
13698
h Range for data collection (ꢁ)
Index range
1.95–25.01
ꢀ13 6 h 6 12
ꢀ9 6 k 6 18
ꢀ20 6 l 6 19
1.081
R = 0.0519, wR = 0.1132
R = 0.0825, wR = 0.1327
1.148, ꢀ0.612
1.92–25.01
ꢀ28 6 h 6 30
ꢀ8 6 k 6 14
ꢀ33 6 l 6 33
1.081
R = 0.0657, wR = 0.1641
R = 0.1687, wR = 0.2313
1.388, ꢀ1.009
Goodness-of-fit on F2
R[I > 2r (I)]
R(all data)
Largest difference peak and hole [e A
ꢀ3
˚
]
˚
Table 3
Selected bond lengths (A) and bond angles (ꢁ) for La(pic)3L
(C@O) is 2.525 A and the average distance between La(2)
˚
˚
and oxygen atoms (C–O–C) is 2.781 A. It is interesting that
La(1)–O(12)
La(1)–O(5)
La(1)–O(19)
La(1)–O(2)
La(1)–O(4)
2.404(4)
2.419(4)
2.423(4)
2.429(3)
2.492(3)
La(1)–O(3)
La(1)–O(1)
La(1)–O(20)
La(1)–O(13)
La(1)–O(6)
2.700(3)
2.700(3)
2.794(4)
2.842(5)
2.937(5)
the free ligand is achiral, but upon metal coordination, it
induces axial chirality. As shown in Fig. 4, the ligand exhibits
(S) configuration in structure A and (R) configuration in
structure B in the unit cell, which is contributed to the
metal-directed self-assembly process of the ligands with the
metal ions [15].
O(2)–La(1)–O(4)
O(4)–La(1)–O(3)
O(2)–La(1)–O(1)
O(4)–La(1)–O(1)
124.8(1)
O(3)–La(1)–O(1)
O(19)–La(1)–O(20)
O(12)–La(1)–O(13)
O(5)–La(1)–O(6)
65.9(1)
60.5(1)
59.1(1)
58.4(1)
60.1(1)
60.1(1)
73.3(1)
In structure A, atom O(14) acts as hydrogen bond donor
to form O–Hꢁ ꢁ ꢁO with the oxygen atom O(12) of the adja-
˚
cent equivalent molecule [O(12)ꢁ ꢁ ꢁH(68), 2.268 A and
O(14)–H(68)ꢁ ꢁ ꢁO(12), 144.34ꢁ], thus, generating a one-
dimensional (1-D) supramolecular zigzag chain along the
b axis as shown in Fig. 5a.
The 2[La(NO3)3L(H2O)] Æ H2O Æ 0.5C2H5OH crystal
structure reveals that there are two independent molecules
in the unit cell. Each La(III) ion is coordinated with 11
oxygen donor atoms. Six of them belong to three bidentate
nitrate groups, one of them belongs to one coordinate water
molecule, and the remaining four are from the tetradentate
ligand L (Fig. 4). Upon coordination, L gives two different
arrangements (A and B) around La(III) ions in the unit cell.
In structure A, the two phenyl rings about the central bond in
the molecule have a drastic twisting, with the dihedral angle
between them being 56.75ꢁ. Again, the La(1)AO (C@O) dis-
tances (mean 2.512 A) are shorter than the La–O (C–O–C)
distances (mean 2.764 A), suggesting that LaAO (C@O)
bond is stronger than the La–O (C–O–C) bond. The same sit-
uation occurs in structure B, where the dihedral angle
between the two phenyl rings in the molecule is 58.61ꢁ, the
average distance between La(2) atom and oxygen atoms
In structure B, atom C(51) acts as hydrogen bond donor
to form C–Hꢁ ꢁ ꢁO with the oxygen atom O(22) of the adja-
˚
cent equivalent molecule [O(22)ꢁ ꢁ ꢁH(51), 2.604 A and
C(51)–H(51)ꢁ ꢁ ꢁO(22), 134.33ꢁ] [16], thus, generating a
dimer as shown in Fig. 5(b); furthermore, the dimeric
blocks are linked by the intermolecular hydrogen bond
˚
O(28)–H(70)ꢁ ꢁ ꢁO(26) [O(26)ꢁ ꢁ ꢁH(70), 2.222 A and O(28)–
H(70)ꢁ ꢁ ꢁO(26), 150.84ꢁ] to form a two-dimensional (2-D)
supramolecular layer with hydrogen bonded channels as
shown in Fig. 5c and d.
˚
˚
In addition, intermolecular p–p interaction [14] between
one phenyl ring of one ligand frame from one chain and
another phenyl ring of the adjacent ligand frame from
the adjacent layer with the dihedral angle between them
being 6.01ꢁ and the distance between their centroids being

Y.-L. Guo et al. / Polyhedron 26 (2007) 1699–1710
1703
Fig. 1. ORTEP diagram (30% probability ellipsoids) showing the coordination sphere of [La(pic)3L]. Hydrogen atoms are omitted for clarity.
L exhibits two absorption bands at 1676 and 1126 cmꢀ1
which are assigned to m(C@O) and m(C–O–C), respectively.
In picrate complexes, the m(C@O) and m(C–O–C) of the
free ligand shift by ca. 57 and 46 cmꢀ1 towards lower wave
numbers, thus indicating that the C@O and ether O-atoms
take part in coordination to the metal ions.
The OH out-of-plane bending vibration of the free Hpic
at 1151 cmꢀ1 disappears in the spectra of the complexes
indicating that the H atom of the OH group is replaced
by Ln(III) ions. The vibration m(C–O) at 1265 cmꢀ1 is
shifted towards higher frequency by ca. 10 cmꢀ1 in the
complexes. This is due to the following two effects. First,
the hydrogen atom of the OH group is replaced by Ln(III),
increasing the p-bond character in the C–O bond. Sec-
ondly, coordination of the oxygen atom of L to Ln(III)
causes the p-character to be weakened [10b]. The free Hpic
has mas(NO2) and ms(NO2) at 1555 and 1342 cmꢀ1, respec-
tively, which splits into two bands at 1584, 1545 cmꢀ1
and 1352, 1331 cmꢀ1 in the complexes. This indicates that
some of the O-atoms in the nitro group of Picꢀ take part
in coordination [17]. On the basis of the similarity of their
IR spectra, it may be assumed that the picrate complexes
have the similar structures.
Fig. 2. Coordination polyhedron of La(III) ion in La(pic)3L.
In the europium nitrate complex, the m(C@O) and m(C–
O–C) of the free ligand shift by ca. 50 and 54 cmꢀ1 towards
lower wave numbers, thus indicating that all the C@O and
ether O atoms take part in coordination to the metal ion.
The absorption bands assigned to the coordinated nitrate
groups (C2v) are observed at about 1495 cmꢀ1 (m1),
1308 cmꢀ1 (m4), 1030 cmꢀ1 (m2) and 815 cmꢀ1(m3) [18] for
the nitrate complex. In addition, the separation of the
˚
4.058 A, further produce a three-dimensional (3-D) netlike
supramolecule as shown in Fig. 6.
3.4. IR spectra
The main infrared bands of the ligand and their com-
plexes are presented in Tables 5 and 6. The ‘‘free’’ ligand

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Y.-L. Guo et al. / Polyhedron 26 (2007) 1699–1710
Fig. 3. The zigzag chain of [La(pic)3L] linked by intermolecular p–p stacking interactions. All the N-ethylanilines are omitted for clarity.
1
3.5. H NMR spectra and mass spectra
Table 4
˚
Selected bond lengths (A) and bond angles (ꢁ) for 2[La(NO3)3L(H2O)] Æ
H2O Æ 0.5C2H5OH
1
L: H NMR (CDCl3): d 7.34–7.18(m, 10H, ArH and
La(1)–O(1)
La(1)–O(3)
La(1)–O(14)
La(1)–O(11)
La(1)–O(12)
La(1)–O(8)
La(1)–O(6)
La(1)–O(9)
La(1)–O(5)
La(1)–O(4)
La(1)–O(2)
2.492(7)
2.532(7)
2.538(7)
2.636(8)
2.639(7)
2.646(8)
2.649(9)
2.662(8)
2.715(9)
2.722(6)
2.807(7)
La(2)–O(15)
La(2)–O(17)
La(2)–O(28)
La(2)–O(22)
La(2)–O(20)
La(2)–O(19)
La(2)–O(26)
La(2)–O(25)
La(2)–O(23)
La(2)–O(18)
La(2)–O(16)
2.523(8)
2.527(7)
2.560(7)
2.576(9)
2.623(9)
2.631(8)
2.633(8)
2.690(8)
2.698(9)
2.723(7)
2.839(7)
C12H8–), 7.07(q, J = 7.8 Hz, 4H, ArH), 6.96(t, J =
7.5 Hz, 2H, ArH), 6.73(d, J = 7.8 Hz, 2H, ArH), 4.21(s,
4H, –O–CH2–CO–), 3.71(q, J = 7.2 Hz, 4H, –N–CH2–),
1.08(t, J = 7.2 Hz, 6H, –CH3).
[La(pic)3 Æ L]: 1H NMR (CDCl3): d8.94(s, 6H, pic-),
7.39–7.07(m, 18H, ArH and C12H8–), 4.45(d, J =
14.7 Hz, 2H, –O–CH2–CO–), 4.09(d, J = 14.7 Hz, 2H,
–O–CH2–CO–), 3.51(q, J = 6.9 Hz, 4H, –N–CH2–),
0.91(t, J = 6.9 Hz, 6H, –CH3).
[Y(pic)3 Æ L]: 1H NMR (CDCl3): d8.84(s, 6H, pic-),
7.42–7.19(m, 18H, ArH and C12H8–), 4.80(d, J =
15.3 Hz, 2H, –O–CH2–CO–), 4.11(d, J = 15.3 Hz, 2H,
–O–CH2–CO–), 3.51(q, J = 6.9 Hz, 4H, –N–CH2–),
0.91(t, J = 6.9 Hz, 6H, –CH3).
O(1)–La(1)–O(3)
O(1)–La(1)–O(14)
O(3)–La(1)–O(14)
O(11)–La(1)–O(12)
O(8)–La(1)–O(9)
O(6)–La(1)–O(5)
O(1)–La(1)–O(4)
O(3)–La(1)–O(4)
O(14)–La(1)–O(4)
O(1)–La(1)–O(2)
O(3)–La(1)–O(2)
O(14)–La(1)–O(2)
O(4)–La(1)–O(2)
125.1(2)
O(15)–La(2)–O(17)
O(15)–La(2)–O(28)
O(17)–La(2)–O(28)
O(20)–La(2)–O(19)
O(26)–La(2)–O(25)
O(22)–La(2)–O(23)
O(15)–La(2)–O(18)
O(17)–La(2)–O(18)
O(28)–La(2)–O(18)
O(15)–La(2)–O(16)
O(17)–La(2)–O(16)
O(28)–La(2)–O(16)
O(18)–La(2)–O(16)
128.2(2)
70.0(2)
123.7(2)
47.5(2)
46.6(3)
46.2(3)
75.4(2)
59.3(2)
79.2(2)
57.9(2)
73.0(2)
119.7(2)
60.9(2)
125.1(3)
73.1(2)
47.9(3)
47.7(3)
47.3(3)
81.4(2)
58.5(2)
70.1(2)
57.3(2)
74.3(2)
130.7(2)
61.5(2)
1
The H NMR spectra of the ‘‘free’’ ligand L, the dia-
magnetic Ln(III) picrate complexes La(Pic)3L and
Y(Pic)3L were measured in CDCl3. The spectrum of L
exhibits a multiplet at ca. 7.26 ppm, a quadruplet at
7.07 ppm (J = 7.8 Hz), a triplet at 6.96 ppm (J = 7.5 Hz)
and a doublet at 6.73 ppm (J = 7.8 Hz) assigned to
C12H8– and –C6H5 protons, a singlet at 4.21 ppm, a qua-
druplet at 3.71 ppm (J = 7.2 Hz), and
a triplet at
1.08 ppm (J = 7.2 Hz) assigned to –O–CH2–CO– protons,
–N–CH2– protons, –CH3 protons, respectively.
two strongest frequencies jm1–m4j is approximately
187 cmꢀ1, clearly establishing that the NO3 groups in
Upon coordination, the proton signal of –O–CH2–CO– in
the lanthanum and yttrium complexes split into two doublets
at 4.45 ppm (J = 14.7 Hz), 4.09 ppm (J = 14.7 Hz) and
4.80 ppm (J = 15.3 Hz), 4.11 ppm (J = 15.3 Hz), respectively.
The signal of –N–CH2– and –CH3 are shifted to higher field
by 0.20 and 0.17 ppm, respectively. The reason is not clear.
ꢀ
the solid complex coordinate to the rare earth ion as biden-
tate ligands [19]. Also no bands at 1380, 820 and 720 cmꢀ1
in the spectrum of complex indicates that free nitrate
groups (D3h) are absent, in agreement with the result of
the conductivity experiment.

Y.-L. Guo et al. / Polyhedron 26 (2007) 1699–1710
1705
Fig. 4. ORTEP diagram (30% probability ellipsoids) showing the coordination sphere of [La(NO3)3L(H2O)] and coordination modes of L in the nitrate
complex.
The proton signal of the OH group in free HPic disap-
pears in the complexes, indicating that the H atom of the
OH group is replaced by Ln(III). The benzene ring protons
of the free HPic exhibit a singlet at 9.12 ppm. Upon coor-
dination, the signal moves to higher field. Only one singlet
is observed for the benzene ring protons of the three coor-
dination picrate groups, indicating fast exchange among
the groups in solution [20].
The mass spectrum of Lshows a molecular ion at
m/z = 509 (M + H), confirming the molecular formula of
L as C32H32N2O4. Above the mass of C12H8 (m/z = 152)
are observed three major fragment ions at m/z = 360
(Mꢀ[–CO–NC6H5(C2H5)]),
330
(Mꢀ[–O–CH2–CO–
NC6H5(C2H5)]), and 181 (Mꢀ[O–CO–NC6H5(C2H5)]–[–
O–CH2–CO–NC6H5(C2H5)]).

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Y.-L. Guo et al. / Polyhedron 26 (2007) 1699–1710
Fig. 5. Hydrogen bonding architecture in lanthanum nitrate complex: (a) 1-D zigzag chain of structure A generated by intermolecular O(14)–H(68) ꢁ ꢁ ꢁ O(12)
hydrogen bonds [symmetry code is ꢀx, ꢀ1/2 + y, 1/2 ꢀ z; and the hydrogen bonds are indicated by the purple dashed lines]; (b) the dimer of structure B
generated by intermolecular C(51)–H(51)ꢁ ꢁ ꢁO(22) hydrogen bonds [symmetry code is 1 ꢀ x, 2 ꢀ y,1 ꢀ z; and the hydrogen bonds are indicated by the blue
dashed lines]; (c) 2-D layer of structure B generated by intermolecular O(28)–H(70)ꢁ ꢁ ꢁO(26) hydrogen bonds [symmetry code is 1 ꢀ x, 1/2 + y, 1/2 ꢀ z; and the
hydrogen bonds are indicated by the purple dashed lines] and C(51)–H(51)ꢁ ꢁ ꢁO(22) hydrogen bonds (the hydrogen bonds are indicated by the blue dashed lines);
(d) 2-D layer of structure B viewed down the crystallographic b-axis showing the hydrogen bonded channels. Some atoms of the ligand are omitted for clarity.

Y.-L. Guo et al. / Polyhedron 26 (2007) 1699–1710
1707
Fig. 6. The intermolecular p–p stacking interactions between the chains and the layers in lanthanum nitrate complex: (a) viewing of the packing diagram
of networks along the b-axis; (b) packing diagram of the chains and the layers along a-axis. Some atoms of the ligand are omitted for clarity.
3.6. Electronic spectra
covalent character of the metal–ligand bond, assessed by
Sinha’s parameter (d), the nephelauxetic ration (b) and the
bonding parameter (b1/2) [21]. Absorption spectrum of the
Nd(III) complex was recorded in chloroform solution at
room temperature and the covalent parameters were calcu-
lated (Table 7). The values of b, which are less than unity,
and positive values of d and b1/2 support the existence of par-
tial covalent bonding between metal and ligand [22].
The electronic spectra in the visible region of the Ln(III)
complexes exhibit alternations in intensity and shifts in posi-
tion of the absorption bands relative to the corresponding
Ln(III) aquo ions. The shift has been attributed by Jorgen-
sen to the effect on the crystal field of interelectronic repul-
sion between the 4f electrons, and is related to the

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Y.-L. Guo et al. / Polyhedron 26 (2007) 1699–1710
Table 5
The most important IR bands of the rare earth picrate complexes (cmꢀ1
)
Complex
m(C@O) m(C–O–C) m(C–O) mas(–NO2)
ms(–NO2)
1342
Hpic
1265
1555
L
1676
1618
1126
1080
1081
1079
1081
1081
1080
La(pic)3L
1274
1276
1275
1275
1279
1274
1584, 1545 1359, 1330
1584, 1545 1358, 1329
1585, 1541 1352, 1331
1577, 1541 1352, 1332
1586, 1547 1357, 1328
1578, 1542 1352, 1333
Nd(pic)3L 1617
Eu(pic)3L 1619
Gd(pic)3L 1619
Tb(pic)3L
Y(pic)3L
1618
1620
Table 6
The most important IR bands of europium nitrate complexes (cmꢀ1
)
Complex
m(C@O) m(C–O–C) mðNOꢀ3 Þ
Fig. 8. The emission spectrum of the europium picrate complex in
different solutions at room temperature: (1) in CHCl3, (2) in acetone, and
(3) in acetonitrile solution.
m1
m2
m3
m4
jm1–m4j
L
1676
1126
1072
Eu(NO3)3L 1626
1495 1030 815 1308 187
tion (the excitation and emission slit widths were 5.0 nm,
Fig. 8) were recorded at room temperature. The lumines-
cence characteristics of the europium picrate complex in
solid state and in CHCl3, acetone, acetonitrile, and DMF
solutions (concentration: 1.0 · 10ꢀ3 mol L ꢀ1) are listed in
Table 8. It can be seen that the europium picrate complex
shows strong emission when excited with 451 nm in the
solid state. The highest intensity ratio value g(5D0 !
Table 7
Covalent parameters for the neodymium picrate complex
Complex
Frequency (cmꢀ1
)
Assignment
Covalent parameters
Nd(pic)3L
11429
12453
13387
13531
17182
17421
19048
4I9/2–4F3/2
b = 0.9999
d = 0.0100
4F5/2
4F7/2
b
1/2 = 0.0071
4S3/2
4G5/2
2G7/2
4G7/2
7
7F2/5D0 ! F1) is 7.7, indicative of the Eu(III) ion not
lying in a centro-symmetric coordination site [23]. It could
also be seen that in DMF solution, the luminescence of
europium was quenched which is ascribed to the decompo-
sition of the europium picrate complex in this solvent. In
the other three solvents, the europium picrate complex
has the similar excitation and emission wavelengths.
In CHCl3 solution, the europium picrate complex has
the strongest luminescence, followed by acetone and then
acetonitrile. This is due to the coordinating effects of the
solvents, namely solvate effect [24] where vibrational
quenching of the complex excited state may occur through
high energy oscillators on the solvent molecule.
3.7. Fluorescence studies
Monitored by the emission band at 600 nm, the euro-
pium picrate complex exhibits broad excitation bands
around 450 nm. The luminescence emission spectra of the
europium picrate complex in solid state (the excitation
and emission slit widths were 1.0 nm, Fig. 7) and in solu-
The fluorescence quantum yield U of the europium pic-
rate complex in CHCl3 (concentration: 1.0 · 10ꢀ5 mol Lꢀ1
)
was found to be 5.81 · 10ꢀ3 with quinine sulfate as Ref.
[25].
Table 8
Fluorescence data for the europium picrate complex
Complex
Eu(pic)3L
Solvent
kex (nm)
kem (nm)
RFI
assignment
7
Solid state
451
595
614
594
615
594
615
594
615
551
4233
277
2260
106
453
34
5D0 ! F1
7
5D0 ! F2
7
CHCl3
463
463
463
5D0 ! F1
7
5D0 ! F2
7
Acetone
Acetonitrile
DMF
5D0 ! F1
7
5D0 ! F2
7
5D0 ! F1
7
92
5D0 ! F2
Fig. 7. The emission spectrum of the europium picrate complex in solid
state.

Y.-L. Guo et al. / Polyhedron 26 (2007) 1699–1710
1709
The characteristic luminescence of the terbium picrate
complex was not observed, either in solid state or in solu-
tions. The reason is probably that the energy gap between
the triplet state levels of the ligand in picrate complex and
the lowest resonance level of the europium favor the
energy transfer process for europium. In order to acquire
the triplet excited state T1 of the ligand L in the picrate
complex, the phosphorescence spectrum of the Gd(III)
picrate complex was measured at 77 K in a chloroform–
methanol–ethanol mixture (v:v:v, 1:5:5). The triplet state
energy levels T1 of the ligand L in picrate complex, which
was calculated from the shortest wavelength phosphores-
cence band [26] of the Gd(III) picrate complex, is
21186 cmꢀ1. This energy level is above the lowest excited
resonance level 5D0 of Eu(III) (17300 cmꢀ1) and 5D4
(20500 cmꢀ1) of Tb(III). Thus the absorbed energy could
be transferred from ligand to the Eu(III) or Tb(III) ions.
The triplet state energy level T1 of this ligand L in picrate
complex matches better to the lowest resonance level of
We deduce that this is due to the following three effects.
First, the coordinated picrates participate in the energy
absorption and transfer process for the Eu(III) ion, make
the three-component complex system an optimal state for
the luminescence of europium, accordingly enhancing the
relative fluorescence intensity of the europium picrate
complex. Secondly, the intermolecular p–p stacks between
picrates favor to the energy transfer for europium. How-
ever, the coordinated nitrates do not play these roles like
picrates in the europium complex. Thirdly, the non-radia-
tive deactivation of the europium emitting state could
quench the luminescence of the Eu(III) nitrate complex
[27].
4. Conclusion
In this paper, we reported the preparation, luminescent
properties of N-phenyl-2-{20-[(phenyl-ethyl-carbamoyl)-
methoxy]-biphenyl-2-yloxy}-N-ethyl-acetamide (L) lantha-
nide complexes and the supramolecular structures of
[La(pic)3L] and 2[La(NO3)3L(H2O)] Æ H2O Æ 0.5C2H5OH
which are the assemblies of the complex units via the inter-
molecular hydrogen bonds and p–p stacking interactions.
The free ligand is achiral, but it induces axial chirality in
the lanthanum nitrate complex, which is directed by the
metal ions in the assembly process of the organic ligands
with the metal ions. The europium picrate complex exhib-
ited strong characteristic fluorescence whereas the terbium
picrate complex showed no luminescence. The lowest trip-
let state energy level of the ligand in the picrate complex
matches better to the resonance level of Eu(III) than
Tb(III) ion. The Eu(III) nitrate complex exhibited quite
weak characteristic fluorescence. So we can see that the
counter anion of complexes is very essential in determining
the fluorescent properties of the rare earth complexes. Fur-
ther studies on the ligand and their complexes are in
proceeding.
Eu(III) (Dm = 3886 cmꢀ1) than Tb(III) (Dm = 686 cmꢀ1
)
5
ion, because such small Dm(T1 ꢀ D4) could result in a
back-energy transfer process from the excited resonance
5
level D4 of Tb(III) to the triplet state energy level T1 of
this ligand L and quench the luminescence of the Tb(III)
picrate complex [27].
In contrast with the strong emission of the europium
picrate complex, the europium nitrate complex exhibited
weak characteristic emission (the excitation and emission
slit widths were 2.5 nm, Fig. 9). The phosphorescence
spectrum of the Gd(III) nitrate complex was measured
at 77 K in a methanol–ethanol mixture (v:v, 1:1), the trip-
let state energy levels T1 of the ligand L in the nitrate
complex, which was calculated from the shortest wave-
length phosphorescence band [26] of the Gd(III) nitrate
complex, is 22075 cmꢀ1. The results indicate that the
counter anions of complexes hardly influence the triplet
state energy level T1 of this ligand L, but notably affect
the fluorescence properties of the europium complexes.
Acknowledgements
We are grateful to the NSFC (Grants 20371022,
20431010 and 20021001), and the Specialized Research
Fund for the Doctoral Program of Higher Education
(200307300015) for financial support.
Appendix A. Supplementary material
CCDC 622187 and 622188 contain the supplementary
crystallographic data for lanthanum picrate complex and
lanthanum nitrate complex. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.
ac.uk. Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/j.poly.
2006.12.019.
Fig. 9. The emission spectrum of the europium nitrate complex in solid
state.

1710
Y.-L. Guo et al. / Polyhedron 26 (2007) 1699–1710
[15] B. Wu, D. Yuan, F. Jiang, R. Wang, L. Han, Y. Zhou, M. Hong, Eur.
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