Coordination of trivalent lanthanum with polyethylene glycol in the presence of picrate anion: Spectroscopic and X-ray structural studies

Article abstract of DOI:10.1016/j.jallcom.2008.06.101

The effect of polyethylene chain length on molecular structures of lanthanum-picrate-polyethylene glycol (PEG) complexes has been studied. The change in the ability of the inner coordination sphere to accommodate the largest size of La³⁺ has be

Full text of DOI:10.1016/j.jallcom.2008.06.101

Journal of Alloys and Compounds 474 (2009) 428–440
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Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Coordination of trivalent lanthanum with polyethylene glycol in the presence
of picrate anion: Spectroscopic and X-ray structural studies
Muhammad I. Saleha,∗, Eny Kusrinia, Bahruddin Saada, Hoong-Kun Funb, Bohari M. Yaminc
a School of Chemical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia
b School of Physics, Universiti Sains Malaysia, 11800 Penang, Malaysia
c School of Chemical Sciences and Food Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history:
The effect of polyethylene chain length on molecular structures of lanthanum–picrate–polyethylene glycol
(PEG) complexes has been studied. The change in the ability of the inner coordination sphere to accommo-
date the largest size of La3+ has been investigated in complexes with the ligands triethylene glycol (EO3),
tetraethylene glycol (EO4), and pentaethylene glycol (EO5). The X-ray studies demonstrated that the com-
plexes [La(Pic)2(EO3)2]+(Pic)− (I and II), [La(Pic)2(OH2)(EO4)]+(Pic)−·H2O (III), and [La(Pic)2(EO5)]+(Pic)−
(IV) crystallized in the monoclinic system in space groups P21/c (I and IV), Pn (II), and C2/c (III). Com-
pounds I and II are polymorphs. The La3+ coordination with the PEG ligand in the presence of picrate anion
(Pic) showed a coordination number of 10. The number of oxygen donor atoms dictated the geometry of
the inner coordination sphere and the formation of additional inner-sphere ligands through the incorpo-
ration of water molecules, especially in III. The result with III is due to the availability of free space in the
complex and to the lack of saturation of the inner coordination sphere. All crystals were further stabilized
by ␲–␲ interactions stacking along the a-axis. No dissociation of La–O bonds in solution was observed in
NMR studies conducted at different temperatures.
Received 27 February 2008
Received in revised form 23 June 2008
Accepted 24 June 2008
Available online 31 July 2008
Keywords:
Crystal structure
Thermal analysis
X-ray diffraction
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
effectively control the geometry of the coordination sphere [8].
In addition, the Pic anion dictates the structure of the complexes
The study of coordination and structural chemistry of trivalent
lanthanide (Ln3+) complexes with oxygen donor atoms of polyether
ligands has attracted interest in recent decades due to their unique
structural characteristics as well as their ability to adopt different
geometries and thereby give rise to structural diversity [1–3]. The
physical and chemical properties of the host–guest complexes are
determined not only by the nature of the Ln–Oligand coordination
but also by the geometrical arrangement of the ligands around the
Ln3+ ion. The Ln3+ ion forms various complexes with a high coor-
dination number, usually >6 and sometimes as high as 9–10; with
small donor atoms, such as oxygen and nitrogen, a coordination
number of 12 can be achieved [4].
through strong steric effects [7,8]. Lanthanide complexes with
PEG have previously been reported [1,9–19], while complexes of
PEG–Pic coordinated to the lanthanides in the coordination sphere
have yet to be described in the literature. Previous work empha-
sized the structure of lanthanide complexes with PEG but did not
report any studies on the spectroscopic and luminescence proper-
ties of the compounds.
To gain deeper understanding into the coordination behavior
of the PEG acyclic polyether system, this paper reports the struc-
tural and spectral characterization of lanthanum complexes with
different ether linkages and therefore different numbers of oxy-
gen donor atoms. Lanthanum was chosen because it has the largest
ionic radius in the series. The thermal properties of the complexes
in relation to their crystal structure is also discussed and correlated
with the structural arrangement and chemical bonding.
The effecton the structure of different polyethylene glycol (PEG)
chain lengths and counteranion such as Cl−, SCN−, and NO3 has
−
been reported by Rogers et al. [1] for the series of lanthanide
complexes. The use of PEG as a ligand coordinated to Ln3+ in the
presence of picrate anion (Pic) has been structurally characterized
in our laboratory [5–8]. The light and heavy rare-earth elements
2. Experimental
2.1. Materials
All chemicals and solvents were of analytical grade and were used without fur-
ther purification. Triethylene glycol (EO3, 99% purity) and tetraethylene glycol (EO4,
99.5% purity) were purchased from Acros (NJ, USA). Pentaethylene glycol (EO5, >97%
∗
Corresponding author. Tel.: +60 4 6533888x3108; fax: +60 4 656646.
E-mail address: midiris@usm.my (M.I. Saleh).
0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2008.06.101

M.I. Saleh et al. / Journal of Alloys and Compounds 474 (2009) 428–440
429
Table 1
Elemental analysis for the lanthanum complexes and their molar conductivity
Compound
Colour
Decomposition (◦C)
Found (calculated) (%)
C
Molar conductivity (ꢀ−1 mol−1 cm3)
H
N
I
II
III
IV
Red
128.4–202.7
117.3–173.2
244.2–289.7
262.6–290.1
31.26 (32.07)
32.02 (32.07)
30.25 (29.53)
31.49 (31.56)
2.81 (3.05)
2.73 (3.05)
2.37 (2.37)
2.56 (2.54)
11.08 (11.22)
11.50 (11.22)
11.79 (11.93)
11.93 (11.84)
133
181
124
140
Yellow
Yellow
Yellow
purity) and La(NO3)3·7H2O (98% purity) were purchased from Fluka (Buchs, Switzer-
land). Picric acid (HPic) [(NO2)3C6H2OH, >98% purity) was purchased from BDH
(Poole, England).
2.5. Synthesis of the [La(Pic)2(EO3)2]+(Pic)− complex, II
The preparation of II was carried out using a method similar to that used to
make I. Acetonitrile was the solvent used, followed by reflux for 10 h. Precipitate
was obtained after 3 days. Yellow crystalline complex was recrystallized in CH3CN,
hot CH3CN, hot CH3OH and CH3OH. Single crystals were obtained from CH3OH with
90% yield after 11 months.
2.2. Apparatus
The percentages of carbon, hydrogen, and nitrogen were determined using a
PerkinElmer 2400II elemental analyzer. Conductivity measurements were carried
out in DMSO solution at 26.3 0.91 ◦C using a Scan500 conductivity meter. IR spec-
tra were recorded on a PerkinElmer 2000 FTIR spectrophotometer in the region of
4000–400 cm−1 using the conventional KBr pellet method for solid samples. For
liquid samples, i.e. PEG ligands, a thin layer of sample was applied to the surface
of a KRS-5 (Thallium bromoiodide). 1H and 13 C NMR spectra were recorded on a
Bruker 400 and 300 MHz spectrometer, respectively. Thermogravimetric analysis
was performed on a PerkinElmer TGA-7 series thermal analyzer under a nitrogen
atmosphere, with a heating rate of 20 ◦C/min.
2.6. Synthesis of the [La(Pic)2(OH2)(EO4)]+(Pic)−·H2O, III and
[La(Pic)2(EO5)]+(Pic)−, IV complexes
Compounds III and IV were synthesized in a manner similar to I, except that the
solution mixture was acetonitrile:methanol (3:1, v/v).
For III, a light yellow single crystal was observed after 2 days with 80% yield,
while for IV, a yellow single crystal was visible after 5 days with 85% yield. Both
compounds were isolated and characterized.
Photoluminescence (PL) measurements were made at room temperature using
a Jobin Yvon HR800UV system. The data were collected and processed with Labspec
Version 4 software. An HeCd laser was used for excitation at 325 nm, and the emis-
sion spectra were scanned from 330 to 1000 nm. An incident laser (20 mW) was used
as the excitation source. The microscope objective lens of UV40 was used to focus
the laser on the sample surface. The emitted light was dispersed by a double grating
monochromator (0.8 m focal length) equipped with an 1800 grove/mm holographic
plane grating. Signals were detected with a Peltier-cooled CCD4 array detector.
3. Results and discussion
3.1. Preparation and spectral analysis
The elemental analysis of the lanthanum complexes is consis-
tent with the molecular formula obtained from single-crystal X-ray
diffraction (Table 1). All complexes are stable when exposed to the
atmosphere and are also thermally stable. While they are almost
insoluble in many common solvents, such as methanol, acetoni-
trile, ethyl acetate, and ethanol, they are very soluble in dimethyl
sulfoxide.
The solubility of I–IV in common solvents is low, which made
solution studies difficult and prevented the measurement of con-
ductivity. Measurement of the molar conductance of the complexes
in DMSO solution (see Table 1) indicates that the lanthanum com-
plexes are ionic [23], suggesting that only two Pic ions are in the
inner coordination sphere, whereas the third Pic ion is a counteran-
ion.
The infrared spectra of the free PEG ligands showed broad bands
stretching from ꢁ(O–H) at 3368, 3402, and 3429 cm−1 and ꢁ(C–O–C)
at 1115, 1102, and 1102 cm−1 (Table 2). The stretching vibration of
ꢁ(O–H) was shifted to higher frequency (∼12 cm−1) for III; for I, II,
and IV, in contrast, the band shifted to the lower frequency (∼21,
19, and 17 cm−1, respectively). This indicates the existence of free
OH groups from water molecules in III. The OH groups in I, II, and
IV were involved in the formation of hydrogen bonding that orig-
inated from the terminal alcoholic group. The stretching band of
ꢁ(C–O–C) was shifted toward lower frequency by about 35, 37, 31,
2.3. X-ray crystallographic study
X-ray diffraction data were collected from single crystals 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
[20]. The collected data were reduced using the SAINT program and the empirical
absorption corrections were applied using the SADABS program [20]. The structures
of I, III, and IV were solved by direct methods and refined by XL command with the
full-matrix least-squares method on F2
using the SHELXTL program [21]. Mean-
obs
while, the structure of II was solved using similar methods and refined using XH
command. Due to the very large atoms in II, the usual refinement XL command
could not be used. 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 using SHELXTL
[21] and PLATON [22].
2.4. Synthesis of the [La(Pic)2(EO3)2]+(Pic)− complex, I
The preparations of the complexes were carried out as described pre-
viously [5–8].
A mixture of EO3 (0.454 g, 3.0 mmol), HPic (0.917 g, 4 mmol),
and [La(NO3)3·7H2O] (0.434 g, 1 mmol) was dissolved in 30 mL acetoni-
trile:methanol:water (3:3:1, v/v). The solution mixture was stirred for 5–10 min.
The clear yellow solution was filtered into a 100 mL beaker. The beaker was covered
with aluminum foil to enable slow evaporation at room temperature. The red crys-
talline complex was obtained by recrystallization from acetonitrile after 6 months
with 75% yield.
Table 2
IR data of the free PEG ligands and their lanthanum complexes
Compound
Wavenumber (cm−1
)
ꢁ(O–H)
ꢁ(C–H) Ar
ꢁ(C–H) Met
ı(O–H)
ꢁas(NO2)
ꢁs(NO2)
ꢁ(C–O)
ı(C–O) Ar
ꢁ(C–O–C)
ꢁ(C–N)
EO3
EO4
EO5
I
II
III
3368b
3402b
3429b
3347b
3349b
3414b
3412b
–
–
–
2879s
1651s
1633s
1650st
1630st
1613st
1615st
1611s
–
–
–
–
–
–
1247s
1248s
1249s
1270s
1276s
1277s
1278s
–
–
–
1115b
1102b
1102b
1080s
1078s
1071s
1064s
–
–
–
2873st
2874st
2956m
2954s
2954w
2949w
3086w
3092w
3087w
3095m
1562s; 1551s
1576s; 1540s
1573s; 1536s
1576s; 1533s
1370s; 1330s
1367s; 1333s
1349s; 1335s
1354s; 1342s
1163s
1165s
1169s
1167s
936s; 795m
937m, 795s
945b; 789w
938s; 788s
IV
Note: b = broad, st = strong, s = sharp, m = medium, and w = weak, ꢁ = stretching, ı = deformation (bending), Ar = aromatic, and Met = methylene.

430
M.I. Saleh et al. / Journal of Alloys and Compounds 474 (2009) 428–440
Table 3
Summary of crystallographic data and refinement for the lanthanum complexes
Parameter
Compound
I
II
III
IV
Formula
C30H34N9O29La
1123.57
293(2)
Monoclinic
P21/c
C30H34LaN9O29
1123.57
100
Monoclinic
Pn
C26H28N9O28La
1053.48
293(2)
Monoclinic
C2/c
C28H28N9O27La
1061.50
293(2)
Monoclinic
P21/c
Formula weight
Temperature (K)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
9.33250(10)
19.1971(3)
23.6383(3)
90
90.4900(10)
4234.81(10)
4
9.4974(2)
38.658(9)
8.755(2)
23.887(6)
90
107.890(6)
7694(3)
8
17.9505(9)
9.0440(5)
23.5433(12)
90
93.3540
3815.6(3)
4
37.5821(7)
22.7915(4)
90
91.8140(10)
8130.9(3)
c (Å)
˛ = ␥ (◦)
ˇ (◦)
Volume (Å3)
Z
8
F(0 0 0)
2264
1.762
1.123
4528
1.836
1.169
4208
1.819
1.227
2128
1.848
1.236
Dx (g/cm3)
ꢂ (mm−1
)
Crystal size (mm)
0.38 × 0.41 × 0.50
1.71–32.50
99.8
−15/15, −28/30, −38/38
104,668/15,302
0.0288
0.50 × 0.38 × 0.37
1.05–40.00
98.4
−17/17, −67/66, −41/41
465,489/95,739
0.0590
0.50 × 0.43 × 0.38
0.20 × 0.20 × 0.10
2.41–28.30
98.3
−21/23, −11/12, −30/20
23,165/9300
0.0502
ꢃ range (◦)
1.79–26.00
Completeness to theta (%)
h, k, l
Reflections collected/unique
R (int)
99.7
−47/47, −10/10, −29/29
37,805/7540
0.0181
Data/restraints/parameters
Final R indices [I > 2ꢄ(I)]
R indices (all data)
Goodness of fit
15,302/0/604
R1 = 0.0618, wR2 = 0.1753
R1 = 0.0749, wR2 = 0.1998
1.078
95,739/2/2321
R1 = 0.0767, wR2 = 0.1292
R1 = 0.1015, wR2 = 0.1414
1.091
7540/0/656
R1 = 0.0343, wR2 = 0.0916
R1 = 0.0372, wR2 = 0.0938
1.103
6916/0/586
R = 0.0682, wR = 0.1186
R1 = 0.0974, wR2 = 0.1283
1.113
´
˚
−3
Largest difference peak and hole, e (A
)
4.086 and −2.269
3.492 and −2.822
0.862 and −0.589
0.994 and −2.278
and 38 cm−1, indicating that all the ether oxygen atoms of the PEG
ligands were involved in the coordination of the La3+ ion.
The absorption band due to the ꢁ(C–H) symmetric stretching
at 2879–2874 cm−1 was significantly shifted to the higher wave-
length, namely 2954–2949 cm−1, indicating that the PEG ligands
rearranged to the cyclic conformation [5–8,24]. The stretching
bands from ꢁs(NO2) were split into two bands, which indicates
that the Pic anion was coordinated to La3+ through the phenolic
oxygen and the oxygen of one ortho-nitro group, forming a biden-
tate ligand [5–8,25–27]. The absorption band assigned to ꢁ(C–N) at
920–940 cm−1 was shifted to 936–945 cm−1, indicating that the
coordinated Pic anion affected the C–N bonds. In addition, the
out-of-plane due to the phenolic bending vibration on the free
HPic molecule at 1155 cm−1 was shifted to 1163, 1165, 1169, and
1167 cm−1 for I–IV, respectively. This suggests that the hydrogen
atom of the phenolic group in the Pic anion was substituted by La3+
[28–30].
moieties of symmetry 2/m at Wyckoff position a in the coordinates
of equivalent positions (0, 0, 0), compared to space group Pn with
moiety of symmetry m at Wyckoff positions n. The space group of
P21/c is symmorphic, whereas C2/c is non-symmorphic [32].
Compound I forms on slow evaporation of the solution within a
relatively short time (6 months), whereas compound II crystallizes
on slow evaporation after a long time (11 months), suggesting that
the latter is thermodynamically more stable than compound I. Con-
sistent with this idea, compound II has higher density (1.836 g/cm3
vs. 1.762 g/cm3 for compound I), thus suggesting more efficient
packing. The calculated density of I is the smallest. Meanwhile the
calculated density of II–IV are almost similar, namely 1.836, 1.819,
and 1.848 g/cm3, respectively (Table 3).
As the polyethylene chain length of the PEG ligand increases, the
number of oxygen donor atoms of the PEG ligand also increases,
leading to a structural change to accommodate the largest ionic
radius of La3+ in the ring PEG ligand to form a stable complex. Nev-
ertheless, the coordination number of the complex does not depend
on the PEG ligand: all of the lanthanum complexes examined here
maintain a coordination number of 10.
3.2. X-ray studies
The coordination of La3+ with the PEG ligands in the presence of
Pic anion involved a coordination number of 10. All of the complexes
crystallized in a monoclinic system with different space groups, i.e.
P21/c (I and IV), Pn (II), and C2/c (III) (Table 3). Molecular struc-
tures of the complexes reported here are unique because of the
different inner coordination spheres and outer spheres. As a result,
the lanthanum complexes have different crystal structures. In vir-
tually all cases the change in cell type or crystal system are due to
the insertion of a specific ligand or guest, as well as the changing of
the central metal ion [31]. The differences in space group of these
complexes are not due to the differences in chain length of the PEG
ligands, but are instead governed by the point symmetry and the
crystal system. The space group is determined by the chemical moi-
ety and the orientation of the atoms around each point of a Bravais
lattice [32]. The low symmetry for the primitive unit cell and cen-
tered unit cell were observed for space groups P21/c and C2/c with
All of the complexes studied here are mononuclear and the
PEG ligands are coordinated to La3+ in the bi-, tetra-, penta-, and
hexadentate modes. This pattern may be due to the presence of a
second large ligand, i.e. the picrate anion, which coordinates to La3+
in a bidentate chelating mode, making it difficult to form a polymer
or a dimer. There is an uncoordinated picrate anion in the lattice as a
counteranion. The results also indicate that the picrate ligand main-
tains a coordination number of 10 in the lanthanum complexes.
This contrasts with the La–PEG–chloride and La–PEG–nitrate com-
plexes, where the coordination polyhedron is inconsistent with a
coordination number of 10, but instead a coordination number of
9–12 [1,9–18].
Both polymorphs of I and II have similar molecular structures,
even though the crystals differ in space group, unit cell dimen-
sions, unit cell volume, and number of molecules in one unit cell
(Z) (Table 3). Meanwhile for the [Ce(Pic)(NO3)(H2O)2(EO3)]+(Pic)−

M.I. Saleh et al. / Journal of Alloys and Compounds 474 (2009) 428–440
431
complexes isolated from the same preparation we observed slight
difference in the crystal parameters, significant difference was in
the coordination of the Pic anion one was monodentate and the
other one was bidentate [33]. It may be that the method of prepa-
ration, the central metal ion, the type of solvent (protic or aprotic),
and length of the complexation reaction affect the formation of
complex. In this way, the use of aprotic solvents seems to favor the
formation of compounds in hydrophobic conformations.
side chains pointing directly in each other’s direction (Fig. 2(a)).
Positioned across from each other, the two Pic anions were coor-
dinated to La3+ in a bidentate manner, and the inner coordination
sphere had a dihedral angle of 83.5(2)◦ for I. This unusual sandwich
complexation involving an EO3 ligand has also been observed in the
complexes [LaCl(OH2)(EO3)2]Cl2 [15] and [La(ClO4)3(EO3)2]·xH2O
[19].
Supramolecular materials that contain two or more components
linked weakly by non-covalent interactions exhibit remarkable
structural adaptability [31]. Compound II was shown to have
greater chances of forming a supramolecular complex through
abundant non-covalent interactions, namely intra- and intermolec-
ular hydrogen bonds and also ␲–␲ interactions. Formation of
polymeric chain complex was not observed. One asymmetric unit
of the monoclinic structure comprises four crystallographically
independent molecules A–D, whereas the asymmetric unit in I
contains only one molecule (Fig. 1(a) and (b)). Changes in crys-
tal packing and complex structure may take place even without a
The La3+ ion can form a sandwich complex with short ether link-
ages and four oxygen donor atoms, which is the situation with the
EO3 ligand. In our study, the La3+ ion was coordinated to two EO3
ligands and two Pic anions and was neutralized by one Pic anion
as counteranion. One of the EO3 ligands was coordinated to La3+
through all four oxygen donor atoms in a tetradentate manner; the
second EO3 ligand was chelated to La3+ in a bidentate manner via
the terminal alcoholic oxygen (O5) and the adjacent etheric oxygen
(O6) atoms, leaving the remaining chain like a hanging tail (Fig. 1(a)
and (b)). Both the EO3 ligands surround the La1 atom with their
Fig. 1. Molecular structure of compounds I (a), II (b), III (c), and IV (d) with the atomic numbering schemes of 30, 80, 50, and 50%, respectively. All the hydrogen atoms have
been omitted for clarity.

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M.I. Saleh et al. / Journal of Alloys and Compounds 474 (2009) 428–440
Fig. 1. (Continued ).
To complete the formation of III, the La3+ ion was coordinated
to the EO4 ligand in a pentadentate mode, with the two picrates
coordinating in a bidentate manner and one water molecule also
participating (Fig. 1(c)). The coordinated water molecule positioned
itself centrally between O1 and O5 of the terminal alcoholic groups
(Fig. 2(b)). Complex formation is easier with long-chain PEG ligands
than with short-chain ones. The aromatic part of the coordinated
Pic anion, i.e. the aromatic rings of (C9–C14) and (C15–C20), was
planar and showed a maximum deviation of 0.022(4) Å for the C9
atom. Both the aromatic rings of the coordinated Pic anion formed
a dihedral angle of 87.6(2)◦. This is in contrast to I, II and IV where
water molecules were not involved in III. This may reflect the over-
lapping orbital between the central metal ion and the PEG ligand,
which reduced the space available in these complexes.
change in composition [31]. The aromatic ring of the bidentate Pic
anion between (C13–C18) and (C19–C24) formed dihedral angles
of 77.7(2)◦, 80.2(3)◦, 75.7(3)◦, and 80.1(2)◦ in the structures of A–D,
respectively. Both aromatic rings of the coordinated Pic anion were
planar with maximum deviations, respectively, on the order of
−0.046(5), −0.056(5), −0.030(6), and −0.035(5) Å for the C19A,
C19B, C17C, and C23D atoms.
The lack of saturation of the La-EO4 inner coordination sphere
enables easy reactions, either with a donor solvent or with a nucle-
ophilic impurity such as water, which ultimately leads to a poorly
volatile or non-volatile hydroxo-complex. The fact that the inner
coordination sphere in III is less crowded, allows the coordinated
water molecule and a solvated water molecule to participate in
complex formation. This coordination results from the favorable
matching between the coordination ligands and La3+, which is
sometimes too large to be coordinated as an inner-sphere ligand.
Thus, the outer sphere of the complex is obtained and the neces-
sary coordination number is reached with one water molecule. The
inner coordination sphere of [La(Pic)2(OH2)(EO4)]+ is hydrophilic.
As expected, the PEG ligand has a profound effect on the inner
coordination sphere in complex formation. In contrast to the five
donor atoms of EO4, the six donor atoms of EO5 formed a com-
plex with a hydrophobic environment (IV) such as I and II. La3+
was chelated to ten oxygen donor atoms from the EO5 ligand in a

M.I. Saleh et al. / Journal of Alloys and Compounds 474 (2009) 428–440
433
of the PEG ligand and the characteristics of its coordination with
La3+ make it very suitable for the formation of complexes.
All of the complexes had a bicapped square antiprismatic geom-
etry around La3+. This geometry was slightly distorted due to the
bond angle nearly equal to 180◦ for pairs of etheric oxygens at the
top in the capping position, i.e. (O3, O5), (O2, O5), (O2, O5), and (O3,
O6) atoms for I–IV, respectively. The lanthanum complexes showed
point symmetry C2h with two-element symmetries, i.e. C2 and ꢄh.
This symmetry is typical of the monoclinic crystal system [32].
Increasing the number of oxygen donor atoms in PEG slightly
increased the average La–OPEG bond length by 2.608(3), 2.610(2),
and 2.623(4) Å for I, III and IV, respectively (Table 4). In contrast,
the average bond lengths in II of La–OEO3A, La–OEO3B, La–OEO3C
,
and La–OEO3D were approximately 2.608(4), 2.608(4), 2.611(5), and
2.606(5) Å, respectively. This bond was significantly longer than
those reported in the complexes [Pr(Pic)2(EO5)]+(Pic)− [2.557(4) Å]
[5] and [Ho(Pic)2(EO5)]+(Pic)− [2.432(3) Å] [7]. The La–OPEG bonds
in the inner coordination sphere were of two types: La–Oalcoholic
and La–Oetheric. As expected, the La–Oalcoholic bond lengths were
shorter than the La–Oetheric bond lengths (Table 4). The average
La–Oalcoholic bond length in I, III, and IV was 2.557(3), 2.588(3),
and 2.594(4) Å. Meanwhile, the average La–Oetheric bond length
in these three compounds was 2.659(3), 2.625(2), and 2.637(4) Å.
In IV, the difference of 0.045 Å between the average La–Oetheric
and La–Oalcoholic bond lengths was similar to the corresponding
difference in the chloride complex of [LaCl2(OH2)(EO5)]Cl·H2O,
reported to be 0.042 Å [17]. The difference in La–Oetheric and
La–Oalcoholic bond lengths for I and III, ∼0.11–0.12 Å, was greater
than in IV, but similar to that reported in [LaCl3(EO4)]2 [14]
and [LaCl(OH2)(EO3)2]Cl2 [15]. However, the difference between
the average La–Oetheric and La–Oalcoholic bond lengths in the
three La–PEG complexes was shorter by 0.106, 0127, 0.104, and
0.125 Å, respectively, compared to the difference in the thiocyanate
and nitrate complexes in the [La(NCS)3(OH2)2(EO3)].0.5(H2O),
[La(NCS)3(OH2)(EO4)], [La(NCS)3(EO5)] [1], and−[La(NO3)3(EO4)]
[18]. Thus, bidentate ligands such as Pic and NO3 coordinate La3+
more tightly than monodentate ligands such as Cl− and SCN−.
The average La–Ophenolic bond lengths were the shortest,
i.e. 2.426(3), 2.410(4), 2.431(2), and 2.470(4) Å for I–IV, respec-
tively. The shortness of these bond length is caused by the
higher electron density of the phenolic oxygen of the Pic
anion [6–7,29]. However, the average La–Onitro bond length was
the longest, growing longer from I to IV: 2.741(4), 2.745(4),
2.802(3), and 2.686(4) Å. The same trend was observed in
the analogous complexes [Pr(Pic)2(EO5)]+(Pic)− [2.582(4) Å] [5],
[Sm(Pic)2(EO5)]+(Pic)− [2.519(3) Å] [7], and [Eu(Pic)2(EO5)]+(Pic)−
[2.496(2) Å] [6]. The La–Onitro bond length was the longest, reflect-
ing the fact that the electron density of the ortho-nitro group is
lower than that of the phenolic group of the Pic anion.
Along the chain of the acyclic PEG ligand, the bond lengths of C–C
and C–O, and the bond angles in C–O–C and O–C–C were unchanged
and were comparable to the values seen in the other La–PEG
complexes. For I–IV, bond angles between the adjacent terminal
alcoholic groups in the complexes were significantly reduced, i.e.
145.7(1)◦, 148.0(1)◦, 123.8(8)◦, and 66.4(1)◦, respectively (Table 4).
However, the O–La–O bond angle between the adjacent oxygen
atoms in the inner coordination sphere of all of the complexes was
approximately the same, slightly larger than 60◦. The O6-La–O1
bond angle in IV was quite close to the other bond angles because
its inner coordination sphere was more symmetrical than that of
complexes I–III.
Fig. 2. The inner coordination spheres of I (a), III (b), and IV (c).
hexadentate manner and the two picrates in a bidentate manner,
and the positive charge was balanced by one Pic as counteranion
(Fig. 1(d)). Both aromatic rings of the coordinated Pic anions were
planar, with a maximum deviation of 0.037(5) Å for C11 atom and
forming a dihedral angle of 85.7(3)◦ in the opposite direction. The
conformation in the inner coordination sphere of [La(Pic)2(EO5)]+
(Fig. 2(c)) is similar to that of the 18-crown-6 complexes [1,5–8,17].
The acyclic PEG ligand was coordinated to La3+ in I–IV, which exhib-
ited pseudo-cyclic behavior (Fig. 2(a–c)) [5–7,9–19]. The flexibility
One particularity of the coordinated Pic anion structure is the
shortening of the C–Ophenolic bonds relative to these bonds in the
acid structure of 1.322(3) Å [34]. The average C–Ophenolic bond
lengths of the coordinated Pic anion were in the order 1.270(6),

434
M.I. Saleh et al. / Journal of Alloys and Compounds 474 (2009) 428–440
Table 4
Bond length (Å), bond angle, and torsion angle (◦) of all the complexes
Bond
Compound
I
II*
III
IV
Length (Å)
La1–O1
La1–O2
La1–O3
La1–O4
2.570(3)
2.646(3)
2.657(3)
2.563(3)
2.538(3)
2.675(3)
2.418(3)
2.434(3)
2.744(4)
2.737(3)
–
2.563(4)
2.686(5)
2.640(4)
2.558(4)
2.557(4)
2.644(4)
2.423(4)
2.396(4)
2.703(3)
2.786(4)
–
2.591(3)
2.642(2)
2.636(2)
2.598(3)
2.584(2)
–
2.429(2)
2.433(2)
2.709(3)
2.894(3)
2.537(2)
1.442(8)
1.449(8)
2.539(4)
2.659(4)
2.641(4)
2.656(4)
2.592(4)
2.649(4)
2.471(4)
2.468(4)
2.708(4)
2.667(4)
–
La1–O5
La1–O6
La1–Ophenolic
La1–Ophenolic
La1–Onitro
La1–Onitro
La1–Owater
Average C–O
Average C–C
1.431(6)
1.485(8)
1.436(7)
1.511(9)
1.432(7)
1.439(10)
Angle (◦)
O1–La1–O2
O2–La1–O3
O3–La1–O4
O4–La1–O5
O5–La1–O6
O4–La1–O1
O5–La1–O1
O6–La1–O1
Average C–O–C
Average O–C–C
62.3(9)
59.6(9)
60.2(9)
–
61.2(1)
145.7(1)
–
59.5(1)
59.2(1)
62.4(1)
–
62.9(1)
148.0(1)
–
60.3(8)
60.8(8)
61.0(8)
61.7(8)
–
62.4(1)
61.0(1)
61.1(1)
61.3(1)
62.6(1)
–
–
123.8(8)
–
113.1(4)
108.0(6)
–
–
–
66.4(1)
114.3(5)
110.3(6)
112.4(3)
107.7(6)
111.4(5)
107.3(5)
Torsion angle (◦)
O1–C1–C2–O2
O2–C3–C4–O3
O3–C5–C6–O4
O4–C7A–C8A–O5
O4–C7B–C8B–O5
O4–C5–C6–O5
O5–C5–C6–O6
Average O–C–C–O
Average C–O–C–C
54.0(5)
−51.6(8)
−54.1(5)
56.7(4)
−50.4(7)
51.7(12)
−58.9(11)
–
−51.6(8)
−31.8(2)
55.9(7)
–
−53.5(5)
48.7(6)
49.1(8)
−53.4(5)
–
–
–
–
–
–
–
–
−57.2(6)
−54.5(7)
50.2(6)
152.6(5)
–
–
52.2(6)
173.6(4)
51.2(6)
169(5)
54.4(8)
161.2(6)
The second EO3 ligand
Average C–O
Average C–C
Average C–O–C
Average O–C–C
Average O–C–C–O
Average C–O–C–C
1.427(5)
1.488(2)
112.4(7)
109.2(6)
59.1(5)
1.419(7)
1.522(9)
114.3(5)
109.5(5)
59.4(7)
–
–
–
–
–
–
–
–
–
–
–
–
132.0(11)
139.5(6)
Note: (*) for molecular structure of A in II.
The acyclic polyether stand of the molecule displayed a series
of anti and gauche torsion angles for C–O and C–C bonds. In I, the
average O–C–C–O torsion angle was 52.2(6)◦ and the first EO3 lig-
and showed a geometric conformational pattern of g+ g− g+ in a
tetradentate mode. However, the O–C–C–O torsion angle of the
second EO3 ligand in a bidentate mode took on a different confor-
mation, namely g− g+ g− or g+, due to the disorder in the positions
of the C7 and C8 atoms. For II, the structures A–D showed the fol-
lowing average O–C–C–O torsion angles and conformation patterns
in the first EO3 ligand in a tetradentate mode: g− g+ g− [51.3(6)◦],
g− g+ g− [51.5(6)◦], g+ g− g+ [54.1(6)◦], and g+ g− g+ [55.2(7)◦],
respectively. In contrast, the average O–C–C–O torsion angles for
the second EO3 ligand in a bidentate mode for structures A–D was
larger, and the geometric conformational patterns different, com-
pared to the first EO3 ligand: g+ g+ g+ [59.4(7)◦], g+ g+ g+ [61.7(7)◦],
g− g− g− [61.4(8)◦], and g− g− g− [61.5(7)◦]. In III, the average
O–C–C–O torsion angle and conformation pattern of g− g+ g− g+
or g− is due to the disorder in the position of the C7 and C8 atoms.
In IV, the O–C–C–O torsion angle with conformation patterns of g−
g− g+ g− g− occurred. The O–C–C–O torsion angles for overall com-
pounds showed minor differences less than 60◦ (Table 4). However,
1.268(4), and 1.264(6) Å for I, III, and IV. This is due to the replace-
ment of the hydrogen atom by La3+ and the increase in the ␲-bond
due to the greater electron density of the phenolic oxygen. In II, the
C–Ophenolic bond lengths of the coordinated Pic anion, i.e. 1.273(6),
1.331(9), 1.345(10), and 1.271(7) Å were longer than the C–Ophenolic
bond lengths in the Pic counteranion, which measured 1.212(8),
1.319(8), 1.300(7), and 1.215(8) Å in the structures of A–D.
The C and N atoms of the Pic anions were coplanar with a
maximum deviation of 0.117(8) Å for N8 (I); −0.107(4), −0.122(7),
−0.133(6), −0.130(7), −0.105(7), and 0.120(7) Å for N1B, N2C, N5A,
N6B, N4D, and N7A (II); 0.121(4) Å for N2 (III); −0.140(6) and
0.119(5) Å for N1 and N5 (IV), respectively. The para-nitro groups
of all the Pic anions were coplanar with their aromatic ring. The
distances from the oxygen of the phenolic group to the adjacent
coordinated oxygen atoms of the ortho-nitro groups in the coor-
dinated Pic anion (2.650–2.662 Å) were significantly shorter than
those between the free oxygen atoms of the ortho-nitro groups of
the Pic anion (2.835–3.029 Å). In contrast, the free and coordinated
forms of the Pic counteranion showed similar distances between
the oxygen of the phenolic group and the adjacent oxygen atoms of
the ortho-nitro groups, i.e. 2.706 and 2.725 Å, respectively.

M.I. Saleh et al. / Journal of Alloys and Compounds 474 (2009) 428–440
435
Table 5
Table 5 (Continued )
Geometrical parameter of intra- and intermolecular hydrogen bonding involved in
supramolecular construction of the lanthanum complexes
D–H· · ·A
D–H (Å)
H· · ·A (Å)
D· · ·A (Å)
D–H· · ·A (◦)
D–H· · ·A
(a) I
D–H (Å)
H· · ·A (Å)
D· · ·A (Å)
D–H· · ·A (◦)
O1W–H21W· · ·O20i
0.850
0.850
0.850
0.849
0.970
0.972
0.972
0.930
0.930
0.930
0.930
0.843
2.236
2.300
2.254
2.331
2.591
2.587
2.267
2.530
2.569
2.569
2.434
2.519
2.633(4)
2.84(3)
2.92(3)
3.061(11)
3.240(6)
3.21(2)
2.97(3)
3.16(3)
3.08(3)
3.22(3)
3.27(3)
2.97(3)
108.5
121.7
135.6
144.4
124.4
122.2
128.8
124.9
114.8
127.7
150.3
114.9
O1W–H21W· · ·O21Ai
O1W–H21W· · ·O21Bi
O2W–H22W· · ·O18v
C5–H5B· · ·O23vi
O4–H4C· · ·O7a
0.850(3)
0.840(5)
0.840(5)
0.850(6)
0.850(6)
0.970
0.970
0.970
0.970
1.810
2.639(5)
2.629(6)
2.706(6)
3.116(10)
2.861(7)
3.043(7)
3.151(11)
3.153(7)
3.216(11)
168(6)
165(5)
175(9)
132(8)
152(8)
116
132
117
133
O1–H1C· · ·O25
O5–H5C· · ·O8i
O8–H8C· · ·O24ii
O8–H8C· · ·O25ii
C1–H1B· · ·O10a
C6–H6A· · ·O26
C4–H4A· · ·O11a
C9–H9A· · ·O12
1.800(5)
1.87(5)
2.480(7)
2.080(8)
2.490
2.420
2.590
2.470
C8A–H8A· · ·O26Ai
C8A–H8A· · ·O26Bi
C13–H13A· · ·O19Bvi
C19–H19A· · ·O12Aviii
C19–H19A· · ·O12Bviii
C23–H23A· · ·O16Aix
C8A–H81· · ·O26Bi
(b) II
O1A–H1AC· · ·O7Aa
O4A–H4AC· · ·O8Ai
O4A–H4AC· · ·O27Cii
O5A–H5AC· · ·O8Ai
O8A–H8AC· · ·O5Aiii
O1B–H1BC· · ·O8Bi
O1B–H1BC· · ·O27Biv
O4B–H4BC· · ·O7Ba
O5B–H5BC· · ·O8Bi
O8B–H8BC· · ·O5Biii
O1C–H1CC· · ·O7Ca
O4C–H4CC· · ·O8Ciii
O4C–H4CC· · ·O27Av
O5C–H5CC· · ·O8Ciii
O8C–H8CC· · ·O5Ci
O1D–H1DC· · ·O8Diii
O1D–H1DC· · ·O27Dv
O4D–H4DC· · ·O7Da
O5D–H5DC· · ·O8Diii
O8D–H8DC· · ·O5Di
C11B–H11D· · ·O19Dvi
C12B–H12C· · ·O25Bvii
C15B–H15B· · ·O13Ba
C15B–H15B· · ·O14Ba
C15C–H15C· · ·O9Ca
C2A–H2AB· · ·O15D
C21D–H21D· · ·O18Da
C6A–H6AA· · ·O10Aa
C27A–H27A· · ·O24Aa
C27C–H27C· · ·O23Ca
C6A–H6AB· · ·O24Cii
C29B–H29B· · ·O23Ba
C8A–H8AA· · ·O12Cii
C9A–H9AB· · ·O12Aa
C1B–H1BA· · ·O11Ba
C1B–H1BA· · ·O21Ci
C1B–H1BB· · ·O29Biv
C4B–H4BB· · ·O10Ba
C5B–H5BB· · ·O8Ba
C6B–H6BA· · ·O13Biii
C6B–H6BB· · ·O21Ca
C7B–H7BB· · ·O11Ba
C9B–H9BB· · ·O10Ba
C3C–H3CA· · ·O16Ca
C6C–H6CB· · ·O23Av
C8C–H8CB· · ·O19Bviii
C1D–H1DA· · ·O24Dv
C4D–H4DA· · ·O10Da
C5D–H5DA· · ·O14Aa
C5D–H5DB· · ·O10Da
C5D–H5DB· · ·O13Di
C6D–H6DA· · ·O12Di
C9D–H9DA· · ·O10Da
0.819
0.820
0.820
0.821
0.820
0.821
0.821
0.820
0.821
0.819
0.820
0.819
0.819
0.819
0.820
0.821
0.821
0.821
0.821
0.820
0.970
0.970
0.930
0.930
0.931
0.971
0.930
0.972
0.931
0.931
0.969
0.931
0.971
0.971
0.970
0.970
0.969
0.970
0.970
0.970
0.969
0.971
0.970
0.969
0.971
0.972
0.970
0.971
0.971
0.970
0.970
0.970
0.970
1.842
2.405
2.254
1.892
1.883
2.279
2.315
1.856
1.914
1.924
1.786
2.444
2.288
1.995
1.984
2.366
2.305
1.785
2.000
1.993
2.533
2.539
2.466
2.386
2.300
2.402
2.315
2.501
2.322
2.322
2.452
2.304
2.575
2.552
2.566
2.593
2.533
2.495
2.521
2.364
2.435
2.596
2.480
2.510
2.468
2.589
2.519
2.408
2.377
2.479
2.259
2.476
2.575
2.656(7)
3.217(6)
2.589(6)
2.698(6)
2.698(6)
3.090(6)
2.589(6)
2.670(7)
2.722(7)
2.722(7)
2.600(7)
3.252(8)
2.630(7)
2.800(8)
2.800(8)
3.175(7)
2.627(6)
2.599(6)
2.808(6)
2.808(6)
3.227(10)
3.122(11)
2.806(13)
2.772(9)
2.634(9)
3.251(9)
2.642(7)
3.036(6)
2.662(10)
2.653(10)
3.155(8)
2.634(9)
3.177(8)
3.300(8)
3.104(9)
3.220(7)
3.189(10)
3.062(7)
3.206(7)
3.297(8)
3.164(6)
3.140(9)
3.061(8)
3.099(7)
3.137(10)
3.146(11)
3.101(10)
2.983(8)
3.200(10)
3.001(11)
3.151(13)
3.241(10)
3.140(9)
173.1
170.4
104.9
167.2
172.7
169.3
100.2
170.9
167.8
164.5
171.6
168.9
105.7
167.8
173.5
168.6
104.0
170.6
168.0
172.7
128.5
118.6
101.6
104.7
100.5
146.0
100.1
114.6
101.0
100.5
129.2
100.3
120.3
133.9
115.0
122.5
125.0
117.2
127.6
161.4
131.8
115.5
118.3
119.1
125.9
116.6
118.5
117.5
142.1
114.0
152.5
135.6
117.3
(d) IV
O1–H1C· · ·O21a
O1–H1C· · ·O27a
O6–H6C· · ·O21a
C1–H1A· · ·O27a
C5–H5A· · ·O7a
0.931
0.931
0.929
0.970
0.971
0.969
0.970
0.929
0.929
1.767
2.346
2.087
2.472
2.550
2.552
2.552
2.465
2.451
2.669(6)
2.884(7)
2.778(6)
3.092(10)
3.091(8)
3.167(8)
3.213(6)
3.039(7)
3.059(8)
162.3
116.5
130.0
121.5
115.3
121.3
125.4
120.1
123.0
C7–H7B· · ·O25i
C8–H8B· · ·O8a
C15–H15A· · ·O16ii
C25–H25A· · ·O11iii
D = donor and A = acceptor. (a) Symmetry codes: (i) 1 + x, y, z; (ii) x − 1, y, z; (iii) −x,
2 − y, 1 − z; (b) symmetry codes: (i) −1 + x, y, z; (ii) −1/2 + x, 1 − y, −1/2 + z; (iii) 1 + x,
y, z; (iv) −1 + x, y, −1 + z; (v)1/2 + x, 1 − y, 1/2 + z; (vi) 1/2 + x, 1 − y, −1/2 + z; (vii) x,
y, −1 + z; (viii) 1/2 + x, 2 − y, 1/2 + z; (c) symmetry codes: (i) x, −1 + y, z; (ii) −x, −y,
1 − z; (iii) −x, y, 1/2 − z; (iv) −x, 1 − y, 1 − z; (v) x, 1 + y, z; (vi) x, 1 − y, 1/2 + z; (vii) x,
−y, 1/2 + z; (viii) x, 1 − y, −1/2 + z; (ix) 1/2 − x, 1/2 + y, 1/2 − z; (d) symmetry codes:
(i) x, 1/2 − y, −1/2 + z; (ii) x, −1/2 − y, 1/2 + z; (iii) 1 − x, 1/2 + y, 1/2 − z.
a
Intramolecular hydrogen bonding.
the O–C–C–O torsion angle patterns in IV were different from those
measured in the other derivative complexes involving Pr [5], Eu [6]
and Sm, Dy, and Ho [7]. Among the different lanthanide ion com-
plexes, the inner coordination sphere and geometrical arrangement
also influence the torsion angle sequence [7,8,17].
All of the C–O–C–C torsion angles were anti, except for
C8–O6–C9–C10, and they measured 58.7(6)◦, 60.8(6)◦, −63.4(8)◦,
and −65.1(7)◦, respectively, for structures A–D. The angle was
very close to the gauche (g) conformation in II. For I, III, and
IV, the torsion angles C8A-O6-C9-C10 [−62.5(16)◦], C8B-O6-C9-
C10 [−92.6(12)◦], C6-O4-C7B-C8B [−101.1(9)◦], and C8-O5-C9-C10
[−87.5(6)◦] were not anti and were close to the g− conformation,
respectively.
The supramolecular architectures of the complexes were built in
different ways. In general, hydrogen bonding is possible with highly
electronegative atoms such as oxygen, nitrogen, and fluorine, with
the limitation that the distance between these atoms and hydro-
gen must be less than 2.8 Å. In C–H· · ·O hydrogen bonding, the C· · ·O
bond length must have a distance less than 3.3 Å (Table 5(a–d)). In I,
despite the disorder in the positions of C7 and C8 atoms in the sec-
ond EO3 ligand, there was one strong intramolecular O4-H4C· · ·O7
hydrogen bond interaction, with the O4-H4C· · ·O7 angle close to
170◦. Generally, the strength of the hydrogen bond is greatest when
the D–H· · ·A angle is 180◦, where D = donor atom and A = acceptor
atom [35,36]. In addition, the nitro group in I accepted a few
weak intermolecular O–H· · ·O and C–H· · ·O hydrogen bonds with
D–H· · ·A angles of 132–152◦. Some weak intramolecular C–H· · ·O
contacts were also observed, but they seemed to be insignificant
and more or less repulsive in nature (Table 5(a)). The dominant
packing feature of both polymorphs of I and II was hydrogen bond-
ing between the terminal alcohol groups of the EO3 ligand and
the oxygen atoms of the Pic anion and the bidentate EO3 ligand.
For I and II, the intra- and intermolecular hydrogen bonding stabi-
lized the crystal packing of the complexes in the one-dimensional
(c) III
O1–H1C· · ·O2Wi
0.850
0.850
0.850
0.850
0.850
0.851
0.851
2.448
2.237
1.938
2.478
2.328
1.900
2.429
2.798(10)
2.997(5)
2.709(4)
3.067(17)
2.94(2)
105.5
148.9
150.2
127.2
129.5
122.5
109.0
O1–H1C· · ·O9ii
O5–H5C· · ·O20i
O5–H5C· · ·O26Ai
O5–H5C· · ·O26Bi
O2W–H12W· · ·O2Wiii
O2W–H12W· · ·O10iv
2.465(12)
2.833(10)

436
M.I. Saleh et al. / Journal of Alloys and Compounds 474 (2009) 428–440
(1D) network with a symmetry direction of [1 0 0] parallel to the
bc plane along the b-axis (Fig. 3(a) and (b)). In II, only one terminal
alcohol group was involved in the intramolecular hydrogen bond-
ing, i.e. O1A-H1AC· · ·O7A [1.842 Å], O4B-H4BC· · ·O7B [1.856 Å],
O1C-H1CC· · ·O7C [1.786 Å], and O4D-H4DC· · ·O7D [1.785 Å] in the
structures A–D, respectively (Table 5(b)).
The number of hydrogen bonds formed in the complex was
greater when water molecules were involved either in the inner
or outer coordination spheres forming the intermolecular hydrogen
bonding in 1D chain along symmetry direction of [0 0 1] (Table 5(c)).
The crystal structure consisted of a layer of molecules parallel to
the bc plane. The disordered positions of the C7, C8, O12, O16, O19,
O21, O25, and O26 atoms in III were stabilized by intermolecu-
lar O–H· · ·O and C–H· · ·O hydrogen bonds along the b-axis. Also
observed in III were the four bifurcated and one trifurcated hydro-
gen bond along the long b-axis with channels occupied by water
molecules. The bifurcated and trifurcated hydrogen bonds required
a very high electron density in the acceptors or at least locally
in the hydrogen bond itself [36]. The solvated water molecules
linked together between two layers in the stacks of the molecules
(Fig. 3(c)). One strong intramolecular O1-H1C· · ·O21 hydrogen bond
was observed in IV with a distance of 1.767 Å and the O1-H1C· · ·O21
angle of 162.3◦ (Table 5(d)). Two molecules in adjacent layers of
IV were linked by two hydrogen bonds, i.e. C25-H25A· · ·O11-N2
[2.451 Å] and C1-H1A· · ·O17-N6 [2.582 Å] (Fig. 3(d)). For IV, the
intra- and intermolecular hydrogen bonding stabilized the crystal
Fig. 3. 1D network of compounds I (a), II (b), III (c), and IV (d) view down the b-axis. Hydrogen bonds are shown in dashed lines (– – –).

M.I. Saleh et al. / Journal of Alloys and Compounds 474 (2009) 428–440
437
Fig. 3. (Continued ).
packing of the complex in the 1D chains with a symmetry direction
of [0 0 1].
on our studies in one asymmetric unit, the Pic counteranion occu-
pied different positions in the complexes, reflecting the influence
of ␲–␲ interactions. The stacking layer between aromatic Pic rings
caused ␲–␲ interactions in the absence of the coplanarity of all
three nitro groups with their aromatic ring. Similar interactions
have been reported in picrate complexes with other metal ions
[37].
In I, the aromatic ring of the Pic counteranion was exactly copla-
nar and packed in a face-to-face orientation with the aromatic ring
of the coordinated Pic anion; the centroids of the two rings were
separated by 3.825 Å (Fig. 3(a)). The Pic counteranion was not copla-
nar with the inner coordination sphere of [La(EO3)2(Pic)2]+ in II.
Thus, it was separated by a long distance from the inner coordi-
In II, van der Waals interactions were observed as follows: C1A-
H1AA· · ·Cg5 [2.799 Å], C5B-H5BA· · ·Cg6 [2.635 Å], C1C-H1CB· · ·Cg3
[3.026 Å], and C6D-H6DB· · ·Cg8 [2.866 Å] with symmetry code x, y,
and z, where Cg5 corresponds to (C19A–C24A), Cg6 to (C19B–C24B),
Cg3 to (C13C–C18C), and Cg8 to (C19D–C24D). For IV, a van der
Waals interaction was observed between C3-H3A· · ·Cg2 [3.242 Å]
with symmetry code −x, −y, and −z and Cg2 = aromatic ring of
(C17–C22). The presence of O· · ·O interactions in the complexes,
with distances ranging from 2.463 to 2.908 Å, was taken to indicate
hydrogen bonding situations. In addition, a long contact length of
N· · ·O in the range of 2.876–2.945 Å was observed for II–IV. Based

438
M.I. Saleh et al. / Journal of Alloys and Compounds 474 (2009) 428–440
Table 6
1H NMR data of the free PEG ligands and their complexes at 25 ◦
C
Compound
ı[OH]
ı[C(1)H2–C(2)]
ı[C(1)–C(2)H2]
ı[C(3)H2–C(3)H2]
ı[H2O]
ı[Ar]
EO3
EO4
EO5
I
II
III
4.557
4.425
4.142
4.567
3.813
4.510
4.560
3.417
3.430
3.414
3.414
3.411
3.430
3.414
3.486
3.494
3.491
3.481
3.486
3.477
3.480
3.520
3.516
3.510
3.527
3.512
3.518
3.514
–
–
–
–
–
–
–
8.592
8.589
8.597
8.593
–
3.340
–
IV
nation sphere and the distance between the free and coordinated
Pic rings was 11.059 Å. In I and II, the adjacent aromatic rings of
the Pic counteranion and the coordinated Pic anion were separated
by 3.851(3) Å with symmetry codes x, y, and z and −1 + x, y, −1 + z,
respectively, with stacking along the a-axis. In III and IV, the aro-
matic ring of the Pic counteranion was coplanar and positioned
relative to the aromatic ring of the coordinated Pic anion with a cen-
troid distance of 4.207 and 5.449 Å, respectively. In IV, the oxygen
of the phenolic group from the Pic counteranion was slightly copla-
nar with the La3+ and situated at a distance of 4.280 Å from the ion.
The ␲–␲ interaction in III was longer than those found in I, II, and
IV with a centroid separation of 4.189(3) Å; in addition, a symme-
try code x, y, and z stack along the a-axis was observed. The crystal
structure of IV was also stabilized by ␲–␲ interactions of 4.134(3) Å
along the a-axis and symmetry code x, −1 + y, z. These values were
longer than those found in the [La(Pic)3L] complex of 3.774 and
4.019 Å [38], where L = N-phenyl-2-{2ꢀ-[(phenyl-ethyl-carbamoyl)-
methoxy]-biphenyl-2-yloxy}-N-ethyl-acetamide.
For I and II, the terminal alcoholic group peak was shifted
upfield, and its signal broadened when the temperature was raised
the shifts reached 4.033 and 3.293 ppm at 100 ◦C, respectively. At
the same time, the etheric protons were significantly split and
shifted downfield to 3.568 and 3.567 ppm at 100 ◦C. No splitting
of the aromatic peak of the Pic anion was observed in the com-
plexes, but the peak was shifted upfield (to ∼8.545 and 8.540 ppm)
at 100 ◦C for I and II, respectively. In contrast, the signal of the aro-
matic Pic anion in III and IV was shifted upfield due to the stronger
interaction between the adjacent aromatic Pic anions. The peak of
the terminal alcoholic group was shifted upfield at a high tempera-
ture, causing the chemical shift in I to exceed that in IV (Fig. 4). This
indicates that at high temperature, hydrogen bonding is weaker
and may be broken [39,40]. In III, the signal of the terminal alco-
holic groups disappeared at 50–100 ◦C, even though the signal of
the water molecules was shifted upfield to about 2.949 ppm at
100 ◦C. The peak for the terminal alcoholic group in IV was shifted
upfield as a triplet signal and it reached ∼3.951 ppm at 100 ◦C. The
etheric proton peaks of lanthanum complexes were shifted slightly
downfield. The results show that the La–Oetheric bond lengths are
shorter at higher temperatures than at room temperature because
of a decrease in the shielding effect. Interestingly, the aromatic peak
of Pic anion was shifted significantly upfield by 0.05 ppm for the
lanthanum complexes, indicating stronger ␲–␲ interactions due to
the rearrangement of three Pic anions in the crystal packing of the
complexes [41].
3.3. 1H and 13 C NMR studies
The 1H NMR study on the lanthanum complexes verified the
coordination of La3+ in the PEG ligands. NMR spectra were taken of
the free PEG ligands and their complexes in dimethyl sulfoxide-d
(DMSO-d6) using tetramethylsilane (TMS) as an internal standard
(Table 6). The 1H NMR spectrum of the Pic molecule [7] shows two
singlet peaks at 8.593 and 4.577 ppm assigned to the equivalents of
two protons from the aromatic ring and one proton from the phe-
nolic group, respectively. The proton peak of the phenolic group
in HPic disappeared in all of the complexes, indicating that La3+
replaced the hydrogen atom via deprotonization or substitution
[7].
The 13C NMR spectra of the complexes showed no signifi-
cant change compared to the free PEG ligand and HPic molecule
(Table 7), because the coordination bonding did not directly affect
the carbon atoms. However, the ipso aromatic carbon (ipso C)
from the Pic anion was shifted downfield (1.17–1.32 ppm), proba-
bly due to the deprotonation and coordination bonding. In contrast,
the ortho C and meta C from the Pic anion were shifted upfield
(1.69–1.80 ppm) and (1.24–1.57 ppm), respectively, relative to the
free HPic molecule.
At 25 ◦C, the peak for the terminal alcoholic groups in I, III
and IV was shifted downfield by 0.01, 0.385, and 0.437 ppm rel-
ative to the chemical shift of each free PEG ligand. This indicates
that the terminal alcoholic groups were coordinated to La3+ and
their bond lengths were shorter than that of the La–Oetheric bond.
1H NMR data suggesting direct coordination of Ln(III) to the oxy-
gen atoms of the acyclic PEG and the Pic ligands in the complexes
were consistent with the X-ray studies carry out in this paper. In
II, the peak of the terminal alcoholic group of the EO3 ligand was
shifted upfield by 0.744 ppm relative to the chemical shift of the free
EO3 ligand. This may reflect the conformation of the supramolecu-
lar sandwich complex (2:1 = ligand:metal), causing the peak to be
more shielded. Meanwhile, small or no shifts were seen for the
etheric proton from the PEG ligand or the proton in the aromatic
Pic anion. Nevertheless, the PEG ligand and the Pic anion were
still coordinated to La3+ in the DMSO-d6 solution. To investigate
this phenomenon, a study was undertaken using 1H NMR to mea-
sure chemical shifts at increasing temperature 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 the
complexes.
Fig. 4. Effect variable temperatures on the terminal alcoholic groups at 25–100 ◦C.

M.I. Saleh et al. / Journal of Alloys and Compounds 474 (2009) 428–440
439
Table 7
13 C NMR data of the free PEG ligands and their complexes at 25 ◦
C
Compound
C1
C2
C3
meta C
ortho C
para C
ipso C
EO3
EO4
EO5
I
II
III
60.04
60.40
60.39
60.39
60.45
60.23
60.22
69.95
69.95
69.93
69.95
70.04
69.78
69.81
72.48
72.48
72.44
72.48
72.59
72.35
72.35
–
–
–
–
–
–
–
–
–
–
–
–
124.40
124.71
124.07
124.27
125.32
125.44
125.21
125.22
142.03
142.03
141.86
141.86
160.96
161.05
160.81
160.81
IV
3.4. Photoluminescence studies
5. Supplementary material
Photoluminescence spectra of the diamagnetic lanthanum com-
plexes produced similarly broad bands with the center at 534.6 nm
resulting from only the PEG ligand and the Pic anion [7]. Thus,
the emission peak in La3+, which has no electron in the 4f orbital,
occurred due to relaxation. This observation suggests that the nitro
electron withdrawing groups of the Pic anion acts as a quencher
CCDC 295232, 667496, 667497, and 247724 supplementary crys-
tallographic data for compounds I, II, III, and IV, respectively. These
data can be obtained free of charge from the Cambridge Crystallo-
graphic Data Center via www.ccdc.cam.ac.uk/data request/cif.
Acknowledgements
[42]. Usually, the non-luminescent lanthanides such as La3+, Gd3+
,
and Y3+ can show increased emission intensity in the presence of
the activator Eu3+, in what is termed the “co-fluorescence effect”
[43].
We are grateful to the Malaysian Government for supporting this
research with grants SAGA No. 304/PKIMIA/653010/A118 and FRGS
No. 203/PKIMIA/671020. A postdoctoral fellowship from Universiti
Sains Malaysia to one of us (E.K.) is also greatly appreciated.
3.5. Thermal analysis
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Only thermograms of III and IV were obtained because of the
explosive nature of the Pic anion due to the presence of the nitro
groups. These complexes showed a decomposition pattern simi-
lar to that reported for the other Ln–Pic complexes [5,7,8,44,45]. In
III, a gradual decomposition of the two water molecules occurred
at 100–200 ◦C with a weight loss of 3.6% (calc. 3.4%), followed by
decomposition of the EO4 ligand and the three Pic anions between
225 and 300 ◦C, with a corresponding weight loss of 87.9% (calc.
86.6%). However, compound IV was more thermally stable than
III. It began to decompose at 180 ◦C, and decomposition rapidly
went to completion at 290 ◦C due to loss of the EO5 ligand and the
three Pic anions, with a corresponding weight loss of 89.1% (calc.
87.2%). Further decomposition of the complexes at ∼895 ◦C resulted
in lanthanum oxide as the final product. Both compounds exhibit
good thermal stability due to the high coordination number of the
complexes, the strong metal–oxygen bonds, and ␲–␲ interactions.
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