Coordination of Ce(III) and Nd(III) with pentaethylene glycol in the presence of picrate anion: Spectroscopic and X-ray structural studies

Article abstract of DOI:10.1016/j.saa.2009.05.024

¹H NMR evidence for direct coordination between the Ln(III) ion and the oxygen atoms of the pentaethylene glycol (EO5) ligand and the picrate anion (Pic) in [Ln(Pic)₂(EO5)][Pic] {Ln = Ce and Nd} complexes are confirmed by single X-ra

Full text of DOI:10.1016/j.saa.2009.05.024

Spectrochimica Acta Part A 74 (2009) 120–126
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Coordination of Ce(III) and Nd(III) with pentaethylene glycol in the presence
of picrate anion: Spectroscopic and X-ray structural studies
Eny Kusrinia,∗, Muhammad Idiris Salehb,∗, Claude Lecomtec
a Department of Chemical Sciences, Faculty of Science and Technology, Universiti Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia
b School of Chemical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia
c Laboratoire de Chimie du Solide Minéral, UMR 7555, Université Henri Poincaré Nancy 1, BP 239, 54506 Vandoeuvre-les-Nancy Cedex, France
a r t i c l e i n f o
a b s t r a c t
1H NMR evidence for direct coordination between the Ln(III) ion and the oxygen atoms of the pentaethy-
lene glycol (EO5) ligand and the picrate anion (Pic) in [Ln(Pic)2(EO5)][Pic] {Ln = Ce and Nd} complexes
are confirmed by single X-ray diffraction. No dissociation of Ln–O bonds in dimethyl sulfoxide-d solution
was observed in NMR studies conducted at different temperatures ranging 25–100 ◦C. The Ln(III) ion was
chelated to nine oxygen atoms from the EO5 ligand in a hexadentate manner and the two Pic anions in
each bidentate and monodentate modes. Both compounds are isostructural and crystallized in monoclinic
with space group P21/c. Coordination environment around the Ce1 and Nd1 atoms can be described as
tricapped trigonal prismatic and monocapped square antiprismatic geometries, respectively. The crystal
packing of the complexes have stabilized by one dimensional (1D) chains along the [0 0 1] direction to
form intermolecular O–H· · ·O and C–H· · ·O hydrogen bonding. The molar conductance of the complexes
in DMSO solution indicated that both compounds are ionic. The complexes had a good thermal stability.
Under the UV-excitation, these complexes exhibited the red-shift emission.
Article history:
Received 19 August 2008
Received in revised form 7 May 2009
Accepted 18 May 2009
Keywords:
Cerium
Crystal structure
Neodymium
Pentaethylene glycol
Picrate complexes
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
Ln(III) ion from interaction with the surrounding atom or/and water
molecules, and (iii) its terminal alcohol groups can act not only
In some examples lanthanide complexes with the series of
polyethylene glycol (PEG) ligands, i.e. triethylene glycol (EO3),
tetraethylene glycol (EO4), pentaethylene glycol (EO5), hexaethy-
lene glycol (EO6) and heptaethylene glycol (EO7) have been
previously reported [1–9], while complexes of PEG–Pic coordinated
totheLn(III)ionsinthecoordinationspherehaveyettobedescribed
in the literature. The metal–organic coordination constructed by
mixed ligand is more adjustive than those by single ligand [10]. Lan-
thanide formed various complexes in which higher coordination
numbers, usually greater than 6 and often as high as 9–10 appear
to dominate [11,12].
as donor oxygen atom but as a hydrogen-bond donor [13–16]. The
Pic anion can minimize the water molecules involved in the inner-
coordination spheres of the complexes [16,17].
This paper continues and completes previous research on crys-
tal structure behavior in the light lanthanide ions Ce(III), and Nd(III)
was chosen as coordination center with the EO5 ligand in the pres-
ence of Pic anion. In this paper, we report the systematic synthesis of
two [Ln(Pic)2(EO5)][Pic] {Ln = Ce, Nd} complexes by using one-spot
preparation. The structures of these complexes were character-
ized and their spectroscopic, molar conductance, luminescence and
thermal stability were also investigated.
The use of PEG as a ligand coordinated to Ln(III) in the presence
of Pic anion has been structurally characterized in our laboratory
[13–17]. The light and heavy lanthanide ions effectively control the
geometry of the inner-coordination sphere [17]. The EO5 molecule
waschosenasligand, basedonthefollowingconsiderations, i.e. (i)it
is a flexible ligand and its donor oxygen atoms can be coordinated to
theLn(III)ioninahexadentatemode, (ii)shieldingtheencapsulated
2. Experimental
2.1. Materials
All chemicals and solvents were of analytical grade and
were used without further purification. Pentaethylene glycol,
EO5 (C10H22O6, >97% purity) was purchased from Fluka (Busch,
Switzerland). Picric acid (HPic) [(NO2)3C6H2OH, >98% purity] was
purchased from BDH (Poole, England). Nd(NO3)3·5H2O (99.9%
purity) from Aldrich (WI, USA). Ce(NO3)3·6H2O (99.9% purity) was
obtained from Johnson Matthey Electronic (NJ, USA).
∗
Corresponding authors. Tel.: +60 9 6683542; fax: +60 9 6683326.
E-mail addresses: eny2kus@yahoo.com (E. Kusrini), midiris@usm.my (M.I. Saleh).
1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.05.024

E. Kusrini et al. / Spectrochimica Acta Part A 74 (2009) 120–126
121
Table 1
2.2. Preparation of the complexes
1H NMR chemical shift of the free EO5 ligand and the [Ln(Pic)2(EO5)][Pic] complexes.
EO5 ligand (0.60 g, 2.52 mmol) and each [Ln(NO3)3·6H2O]
{Ln = Ce, Nd} (0.43 g, 1 mmol) were added slowly to a HPic solu-
tion (0.91 g, 3.97 mmol) into 20 mL mixture acetonitrile:methanol
(3:1, v/v) at room temperature under stirring for 5 min. The mixed
solution was covered with aluminum foil to allow a slow evapo-
ration at room temperature. Single crystals were grown after 1–5
days and were suitable for X-ray structure determination.
Peak
Chemical shift (ppm)
Ligand
EO5
Compound
Ce
Nd
(i) At 25 ◦
C
–C(1)H2–C(2)
C(1)–C(2)H2–
–C(3)H2–C(3)H2
OH
3.414
3.491
3.51
4.142
–
3.416
3.475
3.516
3.660
8.588
3.412
3.484
3.511
3.333
8.589
Pic
2.2.1. [Ce(Pic)2(EO5)][Pic]
Yield: 75%. Colour: red. Anal. Calc.: C, 31.53; H, 2.53; N,
11.82. Found: C, 32.63; H, 2.46; N, 11.97%. Decomposition point:
253.8–280.6 ◦C. Molar conductivity: 189 (−1 mol−1 cm3. Significant
peaks IR (KBr), ꢀ/cm−1: 3413, 3088, 2956, 1614, 1578, 1535, 1356,
1340, 1268, 1168, 1085, 1067, 937, 789.
(ii) At 50 ◦
C
C(1)H2–C(2)
C(1)–C(2)H2
–C(3)H2–C(3)H2
OH
3.448
3.494
3.527
3.964
–
3.431
3.482
3.524
#
3.451
3.503
3.532
3.249
8.574
Pic
8.558
(iii) At 75 ◦
C
2.2.2. [Nd(Pic)2(EO5)][Pic]
C(1)H2–C(2)
C(1)–C(2)H2
C(3)H2–C(3)H2
OH
3.457
3.523
3.542
3.764
–
3.465
3.525
3.553
3.219
8.559
3.476
3.511
3.55
3.13
Yield: 95%. Colour: brownish. Anal. Calc.: C, 31.36; H, 2.52; N,
11.76. Found: C, 31.66; H, 2.41; N, 11.52%. Decomposition point:
263.0–280.2 ◦C. Molar conductivity: 152 (−1 mol−1 cm3. Significant
peaks IR (KBr), ꢀ/cm−1: 3414, 3088, 2757, 1610, 1578, 1521, 1370,
1337, 1266, 1167, 1084; 1070, 939, 788.
Pic
8.56
(iv) At 100 ◦C
C(1)H2–C(2)
C(1)–C(2)H2
C(3)H2–C(3)H2
OH
3.476
3.540
3.559
3.570
–
3.451
3.496
3.546
3.230
8.525
3.495
3.528
3.564
2.992
8.555
2.3. Physical measurements
Pic
Elemental analyses were performed on a Perkin-Elmer 2400II
elemental analyzer. Conductivity measurements were carried
out in DMSO solution at 26.3 0.91 ◦C using a Scan500 con-
ductivity meter. IR spectra were recorded on a Perkin-Elmer
2000 FTIR spectrophotometer in the region of 4000–400 cm−1
by using the conventional KBr pellets method for solid sam-
ples. For liquid sample, i.e. the EO5 ligand, a thin layer of
sample was applied on the surface of a KRS-5 (thallium bro-
moiodide). 1H NMR spectra were measured on a Bruker 400 MHz
spectrometer by using tetramethylsilane (TMS) as an internal
standard in dimethyl sulfoxide-d. Thermogravimetric analysis
was recorded on a Perkin-Elmer TGA-7 series thermal ana-
Note: (#) overlapping peak and (–) peak is lost.
3. Results and discussion
3.1. Properties of the complexes
Preparation of the complexes is carried out by reacting each
lanthanide nitrate and HPic solution in acetonitrile–methanol, fol-
lowed by adding the EO5 ligand, without previous synthesis of the
Table 2
Crystal data of the [Ln(Pic)2(EO5)][Pic] complexes.
lyzer (under nitrogen atmosphere) with
a heating rate of
Parameter
Compound
28H28N9O27Ce
1062.71
3882.92(14)
Monoclinic
P21/c
20 ◦C/min.
Empirical formula
Formula weight
Volume (Å3)
Crystal system
Space group
Z
C
C28H28N9O27Nd
1066.83
3860.2(8)
Monoclinic
P21/c
Photoluminescence (PL) measurements were made at room
temperature by using a Jobin Yvon HR800UV system, with the data
collected and processed with Labspec Version 4 software source.
A HeCd laser was used for excitation at 325 nm and the emission
spectra were scanned from 330 to 1000 nm.
4
4
Unit cell dimensions
a (Å)
b (Å)
18.8013(4)
9.0614(2)
24.1013(5)
90
108.9750(10)
1.818
18.7757(7)
9.0337(1)
24.094(3)
90
109.160 (1)
1.836
2.4. X-ray crystallography analyses
c (Å)
˛ = ꢁ (◦)
ˇ (◦)
X-ray diffraction data were collected from single crystals by
using a Bruker APEX2 area-detector diffractometer with a graphite
monochromated Mo-K␣ radiation source and a detector distance of
5 cm. Data were processed using APEX2 software [18]. The collected
data were reduced by using the SAINT program and the empiri-
cal absorption corrections were applied with the SADABS program
[18]. The structures were solved by direct methods and refined by
least-squares method on Fo2bs using the SHELXTL program [19]. All
non-hydrogen atoms were refined anisotropically. Hydrogen atoms
were located from different Fourier maps and were isotropically
refined. The final refinement converged well. Data for publication
were prepared with SHELXTL [19] and PLATON [20]. Four oxygen
atoms (O16, O23, O25, and O27) in the Ce complex are disordered
over two positions with refined occupancies of 54:46, 70:30, 23:63,
and 49:51. While for the Nd complex, four oxygen atoms (O16, O22,
O24, and O27) are also disordered over two positions with refined
occupancies of 68:32, 56:44, 38:62, and 58:42.
Dx (g/cm3)
ꢂ (mm−1
F(000)
)
1.287
2132
1.460
2140
Crystal size (mm)
ꢃ range (◦)
h, k, l
0.20 × 0.50 × 0.50
2.80–27.44
−24/24,
0.10 × 0.20 × 0.20
1.15–30.03
−26/26, −12/12,
−33/33
−11/11, −31/31
15120/8387
[R(int) = 0.0258]
Full-matrix
least squares of
F2
Reflections collected/unique
Refinement method
20074/11254
[R(int) = 0.029]
Full-matrix least
squares of F2
Data/restraints/parameter
Final R indices [I > 2ꢄ(I)]
8387/0/626
R1 = 0.0371,
wR2 = 0.0899
R1 = 0.0608,
wR2 = 0.1009
1.017
11254/0/586
R1 = 0.044,
wR2 = 0.122
R1 = 0.075,
wR2 = 0.164
1.096
R indices (all data)
Goodness-of-fit on F2

122
E. Kusrini et al. / Spectrochimica Acta Part A 74 (2009) 120–126
Fig. 1. Molecular structure of the [Ce(Pic)2(EO5)][Pic] complex with 30% probability ellipsoids. The hydrogen atoms are omitted for clarity.
cantly shifted to the higher wavelength, namely 2956–2957 cm−1
indicating that the EO5 ligand rearranged to the pseudo-cyclic con-
formation [15,16,23].
,
Ln–Pic salt such as in the close system 18C6–Ln–Pic complexes [17].
Because of the flexibility open chain from the EO5 ligand is easier
compared to the cyclic 18C6 ligand in the formation of lanthanide
complex. The EO5 molecule is chelated to the Ln(III) ion is easier
compared to the 18C6 molecule. Analytical data for the synthe-
sized compounds indicated that both compounds confirm to a 1:1:3
(Ln:EO5:Pic) compositions with salt-type compounds. And similar
with our previous studies [13–16], both compounds are stable to air
and moisture for long-period time. The complexes were soluble in
dimethyl sulfoxide, slightly soluble in acetone, methanol, acetoni-
trile and water. However, neither was soluble in chloroform, ethyl
acetate or toluene.
The solubility of the complexes in common solvents is low,
which made solution studies difficult and prevented the measure-
ment of conductivity. The molar conductivity values for the Ce and
Nd complexes were at 189, and 152 (−1 mol−1 cm3, respectively,
indicating that the complexes were electrolytes nature in a 1:3 ratio
[21,22]. This means that the DMSO molecules have replaced the two
Pic anions from the inner-coordination sphere of the complexes and
the actual solution species are [Ln(EO5)(DMSO)3]3+·3[Pic]− [22].
The stretching bands from asymmetric and symmetric of nitro
groups ꢀ(NO2) were split into two bands, i.e. 1578, 1535; 1356,
1340 and 1578, 1521; 1370, 1337 cm−1 for the Ce and Nd com-
plexes, respectively. This splitting indicates that the Pic anion was
coordinated to Ln(III) through the phenolic oxygen and the oxygen
ortho-nitro group, forming a bidentate ligand [13–17,24–28]. The
absorption band assigned to ꢀ(N–O) at 940–988 cm−1 was shifted
to 937–939 cm−1, indicating the coordination of Pic anion through
the oxygen atoms [29]. In addition, the out-of-plane due to the phe-
nolic bending vibration on the free HPic molecule at 1155 cm−1
was shifted to higher frequencies of 1168 and 1167 cm−1 for the
Ce and Nd complexes, respectively. This shifting suggests that the
hydrogen atom of the phenolic group in the HPic molecule was
substituted by Ln(III) ion [13–17,24,25,27]. The vibration ꢀ(C–O) of
HPic molecule at 1213 cm−1 was shifted higher frequencies about
∼54–56 cm−1 in the IR spectra of both compounds. This suggested
that the Ln–Ophenolic bonds were stronger than those found in the
Ln–OEO5 bonds [15].
3.2. IR spectra
3.3. NMR studies
The IR spectrum of the free EO5 ligand shows strong absorp-
tion bands at 3429, 2874, 1249–1067 cm−1 which are assigned to
the ꢀ(O–H), ꢀ(C–H) and ꢀ(C–C–O) stretching modes of the ether
linkages in the respective order and have been reported by Saleh
et al. [14–16]. On the basis of the similarity of their IR spectra,
it may be assumed that both compounds have similar structures.
The stretching band of ꢀ(C–O–C) in the Ce and Nd complexes were
shifted higher frequencies by about 19 and 17 cm−1, respectively,
relative to the frequency of free EO5 ligand. This shifting indicates
that all of the donor oxygen atoms of the EO5 ligand were involved
in coordination bonding with the Ln(III) ion. The absorption band
due to the ꢀ(C–H) symmetric stretching at 2874 cm−1 was signifi-
Because of poor solubility of the complexes in CD3CN or D2O,
their 1H NMR spectra were obtained in d6-DMSO. The 1H NMR spec-
trum suggested the coordination interaction between the Ln(III) ion
and the EO5 ligand in the solid state and/or solution were observed.
The 1H NMR spectrum of the HPic molecule [15,16] shows two sin-
gletpeaks at8.593 and4.577 ppm assignedtothe equivalents of two
protons from the aromatic part and one proton from the phenolic
group, respectively. The proton peak of the phenolic group in HPic
molecule disappeared in both compounds, indicating that Ln(III)
replaced the hydrogen atom via deprotonization or substitution
[15–17].

E. Kusrini et al. / Spectrochimica Acta Part A 74 (2009) 120–126
123
In the lighter lanthanide complexes of Ce and Nd, all of the sig-
nals were found to be sharp and free from overlapping. At 25 ◦C,
the singlet signal of the terminal alcohol groups in the complexes
was shifted upfield (∼0482 to 0.809 ppm) relative to the chemi-
cal shift of the free EO5 ligand (∼4.142 ppm) (Table 1). This may
reflect the conformation of the complex, causing the peak to be
more shielded. Both the terminal alcohol groups were involved in
coordination bonding and also to form a strong O–H· · ·O hydrogen
bond. In addition, the terminal alcohol groups had a high mobility
in the solution [30] and when more the donor atoms are present
in the complex, they influenced each other and the chemical shift
may even have an opposite change [31].
Small shifts were seen for the etheric protons from the EO5 lig-
and or the proton in the aromatic rings of Pic anions. Nevertheless,
the EO5 and Pic ligands were still coordinated to the metal ion in
solution. To investigate this phenomenon, a study was undertaken
using 1H NMR to measure chemical shifts at increasing tempera-
ture from 25 to 100 ◦C. Similar 1H NMR spectra were obtained when
the temperature was reduced from 100 to 25 ◦C. This indicates that
the phenomenon study was reversible and no dissociation of bonds
occurred in both compounds.
The terminal alcohol groups peak was shifted upfield when the
temperature was raised and reached about 2.992–3.230 ppm at
100 ◦C. In addition, this peak signal became a broad at high temper-
ature. This indicates that at high temperature, hydrogen bonding is
weaker and may be broken [32,33]. At the same time, the peaks
of etheric protons were splitted significantly and shifted down-
field. We assume that the Ln–Oetheric bond lengths are shorter than
that found at room temperature because of decrease in the shield-
ing effect. No splitting of the aromatic Pic peak in the complexes
was observed. However, these peaks from 8.588 and 8.589 ppm at
25 ◦C were slightly shifted upfield by 8.525 and 8.555 ppm at 100 ◦C,
respectively for the Ce and Nd complexes (Table 1). In these case,
the strong ␲–␲ interactions among the adjacent aromatic rings of
the Pic anions was observed [34].
3.4. X-ray studies
Single-crystal X-ray diffraction and elemental analysis that were
performed on the Ce and Nd complexes reveal that they are identi-
cal in structure with formula [Ln(Pic)2(EO5)][Pic]. Both compounds
are crystallized in monoclinic with space group P21/c (Table 2). The
structure of complex Ce is similar with complex Nd, except the bond
lengths and angles because of different ion radii of the lanthanide
center. Single-crystal studies revealed the existence of interaction
between the Ln(III) ion and the donor oxygen atoms of the EO5
ligand in the crystalline state. Fig. 1 shows that the Ln(III) metal
center is coordinated to nine oxygen atoms from the EO5 ligand
in hexadentate mode and the remaining three oxygen atoms from
each bidentate and monodentate Pic anions. Additionally, due to
the space obstacle of coordinated Pic anion, no coordinated solvent
molecules are present in the complexes [16]. From these results,
the Pic anions prevent that the water molecule does not involve in
the inner-coordination sphere. The acyclic EO5 ligand wraps around
Ln(III) with its donor oxygen atoms and forms a ring-like coordina-
tion structure such as 18-crown-6 [1,2,4,8,14–16].
Fig. 2. Perspective view coordination polyhedron geometries around the Ce1 atom
(a) and the Nd1 atom (b).
bond lengths are slightly longer than the Ln–Oalcohol bond lengths.
The Ce–O bond lengths range from 2.371(2) to 2.605(2) Å (Table 3).
The Nd–O bond lengths range from 2.348(3) to 2.578(3) Å (Table 3).
The averages of Ln–Oether bond lengths are 2.580(3) and 2.554(3) Å
fortheCeandNdcomplexes, respectively. TheaverageofLn–Oalcohol
bond lengths are 2.548(2) and 2.519(3) Å for the Ce and Nd com-
plexes, respectively. The averages of Ln–Ophenol bond lengths are
The coordination geometry around the Ce1 atom is slightly dis-
torted a tricapped trigonal prismatic with the O1, O3, and O5 atoms
at the peak of the capping position of the three square planes was
observed in the Ce complex (Fig. 2a). The coordination environment
around the Nd1 atom can be described as a monocapped square
antiprismatic geometry with the O2 atom at the peak of the capping
position for one square O7–O8–O1–O3 plane (Fig. 2b).
the shortest, i.e. 2.370(2) and 2.352(3) Å for the Ce and Nd com-
plexes, respectively. The shortness of these bond length is caused
by a higher electron density of the phenolic oxygen of the Pic anion
[14–17]. Both the coordinated Pic anions make a dihedral angle with
the inner-coordination sphere of [Ln(Pic)2(EO5)] of about 89.4(2)◦
and 89.7(2)◦ for the Ce and Nd complexes, respectively.
The Ln–OEO5 bond lengths in the inner-coordination sphere are
of two types, i.e. Ln–Oalcohol and Ln–Oether. The average of Ln–Oether

124
E. Kusrini et al. / Spectrochimica Acta Part A 74 (2009) 120–126
Table 3
Selected bond length (Å) and bond angle (◦) in the [Ln(Pic)2(EO5)](Pic) complexes.
Atom
Bond length (Å)
Ce
Atom
Bond angle (◦)
Ce
Atom
Torsion angle (◦)
Ce
Nd
Nd
62.23(10)
Nd
48.6(6)
Ln1–O1
Ln1–O2
Ln1–O3
Ln1–O4
Ln1–O5
Ln1–O6
Ln1–O7
Ln1–O14
Ln1–O8
2.522(2)
2.589(3)
2.587(3)
2.538(3)
2.605(2)
2.573(2)
2.371(2)
2.368(2)
2.603(2)
1.436(7)
1.430(5)
2.497(3)
2.572(3)
2.567(3)
2.500(3)
2.578(3)
2.540(3)
2.355(3)
2.348(3)
2.566(3)
1.446(8)
1.436(6)
O1–Ln1–O2
O2–Ln1–O3
O3–Ln1–O4
O4–Ln1–O5
O6–Ln1–O5
O1–Ln1–O6
Average C–O–C
Average O–C–C
62.09(9)
61.72(10)
61.83(10)
60.54(8)
62.25(7)
71.41(8)
113.5(4)
110.1(4)
O1–C1–C2–O2
O2–C3–C4–O3
O3–C5–C6–O4
O4–C7–C8–O5
O5–C9–C10–O6
Average O–C–C–O
C2–O2–C3–C4
C3–O2–C2–C1
C5–O3–C4–C3
C4–O3–C5–C6
C7–O4–C6–C5
C6–O4–C7–C8
C9–O5–C8–C7
C8–O5–C9–C10
Average C–O–C–C
47.8(5)
−39.2(10)
49.7(6)
−45.1(5)
−50.0(5)
46.4(5)
169.7(6)
−171.8(5)
−171.0(6)
−174.9(5)
130.6(5)
−164.5(4)
−86.6(5)
−179.2(4)
156.0(5)
61.92(12)
62.55(11)
61.04(9)
62.76(9)
71.67(9)
113.0(4)
110.1(5)
−33.7(13)
48.8(7)
−43.6(6)
−51.4(6)
45.2(8)
164.1(8)
−173.8(6)
−171.8(8)
−175.6(6)
126.1(6)
−163.1(5)
−82.8(5)
−179.9(4)
154.7(6)
Average C–C
Average C–O
One peculiarity of the coordinated Pic anion is the shortening
of the C–Ophenol bonds relative to these bonds in the acid struc-
counteranion formed the shortest ␲–␲ interaction with their cen-
troids separation of 4.504(2) Å with dihedral angle of 3.63◦ and
symmetry code 1 − x, 1/2 + y, 1/2 − z (Fig. 3). These values are longer
than those found in the [La(Pic)3L] complex about of 3.774 and
4.019 Å [36] where L = N-phenyl-2-{2ꢀ-[(phenyl-ethyl-carbamoyl)-
methoxy]-biphenyl-2-yloxy}-N-ethyl-acetamide.
ture of 1.322(3) Å [35]. The average C–Ophenol bond lengths were
1.272(4) and 1.276(5) Å for the Ce and Nd complexes, respectively.
These lengths result from the replacement of the hydrogen atom
by Ln(III) and the increase in the ␲-bond due to the greater elec-
tron density of the phenol oxygen [14–17]. The average C–Ophenol
bond lengths of the coordinated Pic anion were quite similar to
the C–Ophenolic bond lengths in the Pic anion as a counteranion, i.e.
The van der Waals interactions of O6–H6C· · ·Cg2 [3.108 Å, x,
y, z] with an angle of 129.03◦ where Cg2 = aromatic ring of
(C17–C22) also was observed in the Ce complex. In addition, the
O· · ·O interactions in the ranges of 2.648–2.728 Å was observed
in both compounds. These interactions indicated that strong or
moderate hydrogen bonds are present in the crystal packing of
compounds.
1.280(4) and 1.264(5) Å for the Ce and Nd complexes, respectively.
The averages of C–O and C–C bond lengths of the acyclic EO5
ligand are 1.430(5); 1.436(7) and 1.436(6); 1.446(8) Å for the Ce
and Nd complexes, respectively. These distances were similar and
comparable with the derivative EO5 complexes [13–16]. The aver-
age C–O–C and O–C–C bond angles of both compounds are similar
and close to the tetrahedral angle (Table 3). The O–Ln–O bond
angles between adjacent oxygen atoms in the acyclic EO5 ligand
are slightly larger than 60◦ (Table 3). The O1–Ln–O6 bond angles
between the oxygen atoms of terminal alcohol groups in the acyclic
EO5 ligand are similar with the derivative [Ln(EO5)(Pic)2][Pic] com-
plexes [14,15], except for the [La(EO5)(Pic)2][Pic] [16]. The O–C–C–O
torsion angles from the acyclic EO5 ligand use the same conforma-
tion patterns of g+g− g+ g− g− with average values of 46.4(5)◦ and
45.2(8)◦ for the Ce and Nd complexes, respectively (Table 3). All the
C–O–C–C torsion angles are anti, except C9–O5–C8–C7 that is close
to the gauche conformation (g−) for both compounds.
Both terminal alcohol groups of the EO5 ligand are involved to
form a strong intermolecular hydrogen bond, i.e. O1–H1C· · ·O21
[1.835 Å, x, 1 + y, z] and O1–H1C· · ·O21 [1.855 Å, 1 − x, 1/2 + y,
1/2 − z], thus producing the one-dimensional (1D) supramolecule
network (Table 4). The crystal packing of the molecule units are
linked by the intermolecular O–H· · ·O and C–H· · ·O hydrogen bonds
to form 1D chain along bc plane with symmetry direction [0 0 1]
(Fig. 3). Only one the terminal alcohol group of the EO5 ligand was
involved to form bifurcated hydrogen bonds (Tables 4a and 4b). The
Pic counteranion acts not only as hydrogen-bonds acceptor but also
as hydrogen-bond donor, namely C25–H25A· · ·O17 [2.465 Å, 1 − x,
−1/2 + y, 3/2 − z] and C27–H27A· · ·O20 [2.476 Å, −1 + x, y, z] for the
Ce and Nd complexes, respectively.
Table 4
Hydrogen bonding in the Ce and Nd complexes. D = donor and A = acceptor.
D–H· · ·A
D–H (Å)
H· · ·A (Å)
D· · ·A (Å)
D–H· · ·A (◦)
(a) The Ce complex
O1–H1C· · ·O21i
O6–H6C· · ·O21i
O6–H6C· · ·O22i
C1–H1B· · ·O26i
C2–H2A· · ·O10ii
C2–H2B· · ·O26iii
C7–H7A· · ·O18iv
C8-H8A· · ·O23Bv
C9–H9A· · ·O19vi
C10–H10A· · ·O22i
C21–H21A· · ·O24vii
C25–H25A· · ·O17viii
0.930
0.931
0.931
0.970
0.970
0.970
0.971
0.970
0.971
0.971
0.929
0.930
1.835
2.007
2.346
2.356
2.569
2.589
2.435
2.493
2.599
2.481
2.568
2.465
2.642(4)
2.736(4)
2.987(4)
3.047(7)
3.339(6)
3.527(7)
3.143(6)
3.38(3)
3.315(6)
3.098(5)
3.495(6)
3.383(5)
143.6
133.9
125.8
127.6
136.4
162.8
129.5
151.4
130.8
121.3
175.5
169.2
(b) The Nd complex
O1–H1C· · ·O21i
O6–H6C· · ·O21i
O6-H6C· · ·O26i
C1–H1B· · ·O23i
C2–H2A· · ·O11ii
C2–H2B· · ·O23
0.930
0.930
0.930
0.970
0.967
0.971
0.970
0.970
0.971
0.970
0.930
0.929
1.847
1.998
2.352
2.352
2.591
2.572
2.593
2.485
2.566
2.439
2.565
2.478
2.637(5)
2.726(4)
2.983(5)
3.027(9)
3.353(8)
3.509(9)
3.501(9)
3.155(7)
3.282(7)
3.066(6)
3.493(7)
3.391(8)
141.2
133.8
124.9
126.2
135.6
162.3
155.9
126.1
130.6
122.1
175.9
167.8
C5–H5A· · ·O21iii
C7–H7A· · ·O19iv
C9–H9A· · ·O18v
C10–H10A· · ·O26i
C19–H19A· · ·O25vi
C27–H27A· · ·O20vii
Both compounds have no significant intermolecular ␲–␲ inter-
actions between two aromatic rings of the Pic anion. In the Ce
complex, between the aromatic rings of coordinated Pic anion and
Pic counteranion formed the shortest ␲–␲ interaction with their
centroids separation of 4.517(2) Å with a dihedral angle between
two planes of 3.44◦ and symmetry code x, 1 + y, z. In the Nd com-
plex, between the aromatic rings of coordinated Pic anion and Pic
(a) Symmetry codes: (i) x, 1 + y, z; (ii) x, 1/2 − y, −1/2 + z; (iii) −x, 1/2 + y, 3/2 − z; (iv)
x, 1/2 − y, 1/2 + z; (v) 1 − x, −y, 2 − z; (vi) 1 − x, 1 − y, 2 − z; (vii) 1 − x, 1/2 + y, 3/2 − z;
(viii) 1 − x, −1/2 + y, 3/2 − z.
(b) Symmetry codes: (i) 1 − x, 1/2 + y, 1/2 − z; (ii) x, 1/2 − y, −1/2 + z; (iii) 1 − x,
−1/2 + y, 1/2 − z; (iv) x, 1/2 − y, 1/2 + z; (v) 2 − x, 1 − y, 1 − z; (vi) 1 + x, y, z; (vii) −1 + x,
y, z.

E. Kusrini et al. / Spectrochimica Acta Part A 74 (2009) 120–126
125
Fig. 3. Packing diagram of [Nd(Pic)2(EO5)][Pic] complex viewed along b-axis. The dashed lines indicate the hydrogen bonds and the ␲–␲ interactions.
Fig. 4. The photoluminescence of the Ce (a) and Nd (b) complexes.
Fig. 5. Thermogram of the free EO5 ligand (
complex ( ).
), the Ce complex (. . .) and the Nd
3.5. Photoluminescence studies
The emission spectra of the free EO5 ligand and its complexes
were evaluated in the solid state at room temperature based on
D2 filter measurement. The free EO5 ligand exhibits an intense
broad emission bands at 412.1 and 492.8 nm (ꢅex = 325 nm). Mean-
while, the HPic molecule had a broad band with the center peak at
537 nm. Comparison with the free EO5 ligand, the Ce and Nd com-
plexes had red-shift emission peak, i.e. 414.1; 531.5 nm, and 414.0;
513.0 nm, respectively (Fig. 4). The red-shift emission peak is prob-
ably due to the intra-ligand fluorescent emission [37]. Meanwhile,
the PL spectra of Ce and Ne complexes that had blue-shift emission
are relative to the HPic molecule. The blue-shift emission of both
compounds is attributed to the emission of ligand-to-metal charge
transfer (LMCT).
Based on this observation the melting point of the EO5 ligand is
187 ◦C. This ligand began to decompose at 190 ◦C, with decomposi-
tion going rapidly to completion at 260–290 ◦C due to the release
of the EO5 ligand and the three Pic anions, with a corresponding
weight loss of 94.7% and 94.3% (calc. 86.7% and 86.4%) for the Ce
and Nd complexes, respectively.
Decomposition up to 600 ◦C and no mass loss is observed
under this temperature. Further decomposition of the complexes at
∼895 ◦Cresultedinalanthanideoxideasthefinalproduct. Thecom-
plexes had good thermal stability due to the role of ␲–␲ stacking
interactions, the strong metal–oxygen bonds as well as hydrogen
bonding. The Pic ligands are lost at more than 300 ◦C [30] after
which there is no ␲–␲ interaction. Similar pattern decomposition
was seen with the lanthanide–picrate complexes [13,14,16,17,38].
3.6. Thermal studies
4. Conclusion
Thermal analysis studies were carried out under N2 to evalu-
ate complex dehydration and stability. Both compounds behave
similarly (Fig. 5). The free EO5 ligand decomposed at 135–340 ◦C.
The [Ln(Pic)2(EO5)][Pic] complexes have been synthesized
by one-spot reaction of lanthanide nitrate, the EO5 and HPic

126
E. Kusrini et al. / Spectrochimica Acta Part A 74 (2009) 120–126
molecules. The lighter lanthanide ions prefer to form the complexes
withanine-coordinationnumberinwhichdependingontheacyclic
polyether chain length and number of donor oxygen atoms. Fur-
ther investigations are in progress involving other lanthanides to
get a reasonable explanation and deeper insight into this crystal
structure behavior of the Ln–EO5 complexes and the luminescence
properties.
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We are grateful to the Malaysian Government for granting
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Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2009.05.024.
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