Structural and selectivity of 18-crown-6 ligand in lanthanide-picrate complexes

Article abstract of DOI:10.1016/j.jorganchem.2008.04.046

The selectivity factor in the separation of lanthanide could be associated with the coordination behaviour. Thus, we observed the study in the solid phase to understand the coordination pattern of Ln(III) with the 18-crown-6 (18C6) ligand. Good selectivity of the rigid 18C6 ligand toward Ln(III) depends on gradually smaller their ionic radii of Ln(III) in the complexes formation in the presence of picrate anion (Pic^-), i.e. lanthanide contraction and steric effects as clearly shown in the series of [Ln(Pic)₂(18C6)]⁺(Pic)^- {Ln = La, Ce, Pr, Nd, Sm, Gd} and [Ln(Pic)₃(OH₂)₃] · 2(18C6) · 4H₂O {Ln = Tb, Ho} complexes. The La-Gd complexes crystallized in an orthorhombic with space group Pbca, while the Ho complex crystallized in triclinic with space group P over(1, ?). The lighter lanthanides complexes [La-Sm] had a 10-coordination number from the 18C6 ligand and the two picrates, forming a bicapped square-antiprismatic geometry. Meanwhile, the middle lanthanide complex [Gd] had a nine-coordination number from the 18C6 ligand and the two picrates, forming a tricapped trigonal prismatic geometry. The heavier lanthanide [Ho] is rather unique, since Ho(III) coordinated with nine oxygen atoms from three picrates and three water molecules in the opposite direction whereas three 18C6 molecules surrounded in the inner coordination sphere, forming a trigonal tricapped prismatic geometry. The 18C6 ligand is effective in controlling the molecular geometry and coordination bonding of Ln-O and can use a crystal engineering approach. No dissociation of Ln-O bonds in solution was observed in NMR studies conducted at different temperatures. The photoluminescence spectrum of the Pr complex has typical 4f-4f emission transitions, i.e. ³P₀ → ³F₂ (650 nm), ¹D₂ → ³F₂ (830 nm) and ¹D₂ → ³F₄ (950 nm).

Full text of DOI:10.1016/j.jorganchem.2008.04.046

Journal of Organometallic Chemistry 693 (2008) 2561–2571
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Structural and selectivity of 18-crown-6 ligand in lanthanide–picrate complexes
a
b
c
Muhammad I. Saleh a, , Eny Kusrini , Hoong K. Fun , Bohari M. Yamin
*
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, University 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 selectivity factor in the separation of lanthanide could be associated with the coordination behaviour.
Thus, we observed the study in the solid phase to understand the coordination pattern of Ln(III) with the
18-crown-6 (18C6) ligand. Good selectivity of the rigid 18C6 ligand toward Ln(III) depends on gradually
smaller their ionic radii of Ln(III) in the complexes formation in the presence of picrate anion (PicÀ), i.e.
lanthanide contraction and steric effects as clearly shown in the series of [Ln(Pic)2(18C6)]+(Pic)À {Ln = La,
Ce, Pr, Nd, Sm, Gd} and [Ln(Pic)3(OH2)3] Á 2(18C6) Á 4H2O {Ln = Tb, Ho} complexes. The La–Gd complexes
crystallized in an orthorhombic with space group Pbca, while the Ho complex crystallized in triclinic with
Received 20 November 2007
Received in revised form 14 March 2008
Accepted 22 April 2008
Available online 10 May 2008
Keywords:
18-Crown-6
Lanthanide contraction
Picrate complexes
Selectivity
ꢀ
space group P1. The lighter lanthanides complexes [La–Sm] had a 10-coordination number from the 18C6
ligand and the two picrates, forming a bicapped square-antiprismatic geometry. Meanwhile, the middle
lanthanide complex [Gd] had a nine-coordination number from the 18C6 ligand and the two picrates,
forming a tricapped trigonal prismatic geometry. The heavier lanthanide [Ho] is rather unique, since
Ho(III) coordinated with nine oxygen atoms from three picrates and three water molecules in the oppo-
site direction whereas three 18C6 molecules surrounded in the inner coordination sphere, forming a tri-
gonal tricapped prismatic geometry. The 18C6 ligand is effective in controlling the molecular geometry
and coordination bonding of Ln–O and can use a crystal engineering approach. No dissociation of Ln–O
bonds in solution was observed in NMR studies conducted at different temperatures. The photolumines-
cence spectrum of the Pr complex has typical 4f–4f emission transitions, i.e. 3P0
1D2 3F2 (830 nm) and 1D2 3F4 (950 nm).
?
3F2 (650 nm),
?
?
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
one of the possible geometric configurations of the molecules [4].
In addition, hydrogen bonding can produce supramolecular struc-
ture [6] such as rows or helices (simulating regular polymer
chains), layers, sheets and networks and induce supramolecular
polar ordering [7]. These features are potentially important in sev-
eral fields of material sciences [5].
Designing solid crystal architecture by using principles of crys-
tal engineering is a new, growing area of inorganic, coordination
and supramolecular chemistry [1–3]. These designs may be used
for the rational development of novel functional materials with
predictable bulk structure [4]. The main aim of crystal engineering
is the non-casual synthesis of crystal complexes with deliberate re-
ciprocal arrangement of the molecules in the crystal. Such crystal
have intra and intermolecular covalent interaction i.e. coordination
Molecular coordination complexes of Ln(III) have attracted con-
siderable attention, due to their applications in analytical and
material chemistry [8–10]. Ln(III) forms various complexes with
a high coordination numbers, usually >6 and sometimes as high
as 9–10, with small donor atoms, such as oxygen and nitrogen a
coordination number 12 can be achieved [11–17]. The coordina-
tion sphere of a central metal ion depends on the interplay be-
tween the ionic radius and the ion charge [18]. Generally, large
ions can form a complex with the high coordination number. The
most common ligands contain several oxygen donor atoms, for
example, nitrates, phosphates, sulfates, oxalates, carboxylates,
alcohols, crown ethers, Schiff bases and water molecules [19,20].
Complexes of Ln(III) and crown ethers and their derivatives in
the presence of picric acid (Pic) have been previously described.
These complexes include the benzo-15-crown-5 [21,22] and
bonding, and non-covalent interactions i.e. hydrogen bonding, p–p
interactions and van der Waals interactions. However, the rela-
tively high energy of the interaction and its ability to generate
recurrent patterns of intermolecular interactions in ways that gov-
ern the relative orientation of molecules entering the crystal [5].
The strategy of supramolecular synthesis includes the coordina-
tion centers and the bitopic connectors such as ligand and anion
[2]. These bitopic connectors may be a relatively flexible structure
that is sensitive to the environment in the crystal. These ap-
proaches can be used to design molecular structure and stabilize
1,3-phenylenebis(formyloxyacetyl-4’-benzo-15-crown-5)
The cyclic polyether 18C6 ligand that is thought to control
[23].
* Corresponding author. Tel.: +60 4 6533888x3108; fax: +60 4 656646.
E-mail address: midiris@usm.my (M.I. Saleh).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.04.046

2562
M.I. Saleh et al. / Journal of Organometallic Chemistry 693 (2008) 2561–2571
molecular structure has been reported in alkaline–18C6 complexes
[24–27]. The structure of the [alkaline–18C6]+ fragment with the
largest size metal ion is relatively rigid and exists as a half-
sandwich encapsulate [24,27], with the small metal ion situated
out of the crown ligand plane [27–30]. This distortion results from
a mismatch between the metal ion and the crown ether cavity
sizes [26,27], a demand for the most efficient interaction of the
metal ion with the counter anion, a demand for dense packing of
the structural component [24] and the dissymmetry of the envi-
ronment of the inner coordination sphere from the two axial
sides [4].
spectra were scanned from 330 to 1000 nm. An incident laser
(20 mW) was used as an excitation source. A microscope objective
lens (UV40Â) was used to focus the laser on the sample surface.
The emitted light was dispersed by a double grating monochroma-
tor (0.8 m focal length) equipped with an 1800 grove/mm holo-
graphic plane grating. Signals were detected with a Peltier-cooled
CCD4 array detector.
2.3. X-ray crystallography analyses
X-ray single crystal data collected by using a Bruker APEX area-
The selectivity of crown ether for Ln(III) has been used when to
separate the lanthanides followed by quantitative determination of
La(III) from rare earth bearing mineral by liquid–liquid extraction
with dibenzo-24-crown-8 as the complexing agent [31]. With this
selectivity in the liquid phase, the study continued in the solid
phase to understand the coordination pattern of Ln(III) with oxy-
gen donor atoms of the 18C6 ligand. The 18-crown-6 ligand has
cavity diameter of 2.6–3.2 Å [24] and which matches the ionic
diameter of the lanthanides (ionic diameter between 1.73 and
2.06 Å) [31]. We think that the coordination behaviour will be able
to explain the selectivity factor in the separation. The similarities
and the differences in the formation of coordination bonding of
lanthanide–picrate complexes in the 18C6 closed system will be
the main discussion in this paper.
detector diffractometer with a graphite monochromatic Mo K
a
radiation at a detector distance of 5 cm and with APEX software
[34]. The collected data were reduced by using SAINT program and
the empirical absorption corrections were performed with the SAD-
ABS program [34]. The structures were solved by direct methods
and refined by least-squares using the SHELXTL software package
[35]. All non-hydrogen atoms were refined anisotropically. Hydro-
gen atoms were located from difference Fourier maps and were
isotropically refined. The final refinements converged well. Data
for publication were prepared by using SHELXTL [35] and PLATON
[36]. The structures of complexes were solved by direct methods
and refined using the full-matrix least-squares method on Fo2bs as
implemented by the SHELXTL program [35].
3. Results and discussion
2. Experimental
3.1. Physical properties and spectral analysis
2.1. Preparation of 18C6–(Ln–Pic) complexes
La2O3 and 18-crown-6 [C12H24O6] was purchased from Fluka
The complexes are air-stable in solid state, soluble in dimethyl
sulfoxide; moderately soluble in acetone, acetonitrile, tetrahydro-
furan, methanol, water and ethanol and insoluble in chloroform,
toluene and carbon tetrachloride. The elemental analyses of all of
the cyclic complexes are consistent with the molecular formula de-
rived from the single crystal X-ray diffraction (Table 1).
The solubility of all the complexes in common solvents is low
which has made it difficult to do studies in solution and has pre-
vented the measurement of conductivity. The molar conductance
of the complexes in DMSO solution (see Table 1) indicates that
the La–Gd complexes can act as ionic compounds [37], implying
that only two PicÀ ions are in the coordination sphere and that
third PicÀ ion is a counter anion. The Tb and Ho complexes are
non-electrolyte compounds.
Chemika (Buchs, Switzerland), Pr6O11, Nd2O3, Sm2O3, Gd2O3,
Tb4O6 from Sigma (St. Louis, USA), Ho2O3 from RDH (Steinheim,
Germany), picric acid (Pic) [(NO2)3C6H2OH] from BDH (Poole, Eng-
land). Ce(NO3)3.6H2O was obtained from Johnson Matthey Elec-
tronics (New Jersey, USA). All chemicals and solvents were of
analytical grade and were used without further purification.
Lanthanide picrates of [Ln(Pic)2(OH2)6]+(Pic)À Á 6H2O {Ln = La–
Ho} were prepared as previously described [32], as were the cyclic
complexes [33].
A
mixture of [Ln(Pic)2(OH2)6]+(Pic)À Á 6H2O
(0.220 g, 0.21 mmol) was mixed with 18C6 (0.264 g, 1 mmol) in
20 mL CH3CN. The solution was heated in a water bath with con-
tinuous stirring for 10–15 min at 80–90 °C. The mixture was left
to stand for one day and single crystals for La (96%); Ce (80%); Pr
(96%); Nd (96%); Sm (94%); Gd (50%) and Ho (50%) suitable for
X-ray diffraction determination were collected. However, the reac-
tions of [Tb(Pic)2(OH2)6]+(Pic)À Á 6H2O with the 18C6 ligand in aceto-
nitrile did not result in single crystal products.
The infrared spectra of the 18C6 ligand and its complexes show
the common behaviour [33]. On the basis of the similarity of their
IR spectra, the La–Gd complexes are thought to have similar struc-
tures. On the other hand, the Tb and Ho complexes are analogs.
Generally, the m(C–C) and m(C–O) stretching of the 18C6 ligand at
2.2. Physical measurements
1280 and 1107 cmÀ1 was shifted to a lower frequency in the com-
plexes at 1268 and 1105 cmÀ1, respectively. The strong absorption
at 2892 cmÀ1 weaken in complexes and was shifted to a lower fre-
The percentages of carbon, hydrogen and nitrogen were per-
formed on a Perkin–Elmer 2400II Elemental Analyzer. Conductivity
measurements were carried out in dimethyl sulfoxide (DMSO)
solution at 26.3 0.91 °C using a Scan500 conductivity meter. IR
spectra were recorded on a Perkin–Elmer FTIR 2000 spectropho-
tometer in KBr pellets in the 4000–400 cmÀ1 regions. 1H and 13C
NMR spectra were measured on a Bruker 400 MHz and 300 MHz
spectrometer, respectively, with tetramethylsilane (TMS) as inter-
nal standard. Thermogravimetric analysis was recorded on a Per-
kin–Elmer TGA-7 series thermal analyzer (under nitrogen
atmosphere) with a heating rate at 20 °C/min.
quency, indicating that the m(C–H) stretching is affected by neigh-
boring Oetheric bonded to Ln(III). The new sharp peak appearing at
1650–1300 cmÀ1 region was assigned to the asymmetric and sym-
metric of m(N–O) observed in the complexes. This indicates that the
presence of PicÀ ions and coordination with an oxygen atom from
ortho-nitro group occurred. The IR spectra of the complexes show
the disappearance OH out-of-plane bending vibration of the free
Pic molecule at 1151 cmÀ1 indicating that the OH groups take part
in coordination and the hydrogen atoms are substituted by Ln(III)
[33,38–42]. The sharp bands at 1555 and 1342 cmÀ1 of the free Pic
molecule were split into two double peaks at 1578; 1537 and
1368; 1334 cmÀ1, respectively [33]. This results indicates that the
PicÀ ions were coordinated with Ln(III) in a bidentate manner
[33,39–49]. Additionally, the broad bands at 3412–3413 cmÀ1
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

M.I. Saleh et al. / Journal of Organometallic Chemistry 693 (2008) 2561–2571
2563
Table 1
Elemental analysis of the 18C6–(Ln–Pic) complexes
Complex
C%, found (Calc.)
H%, found (Calc.)
N%, found (Calc.)
Decomposition point (°C)
Molar
conductivity
À1 molÀ1 cm3)
(X
La
Ce
Pr
Nd
Sm
Gd
Tb
Ho
33.29 (33.01)
33.33 (32.97)
33.45 (32.95)
32.61 (32.84)
32.29 (32.66)
32.72 (32.55)
35.44 (32.94)
34.28 (32.81)
2.52 (2.75)
2.48 (2.75)
2.59 (2.74)
2.80 (2.74)
2.64 (2.72)
2.26 (2.71)
4.41 (4.44)
3.70 (4.43)
11.68 (11.55)
11.62 (11.54)
11.29 (11.53)
11.21 (11.49)
11.23 (11.43)
11.10 (11.39)
7.51 (8.23)
293.0–304.5
285.0–298.5
288.5–294.8
289.0–294.0
271.5–294.9
284.4–298.8
92.9–210.0
150
115
94
319
195
123
44
8.13 (8.20)
108.3–232.3
48
indicate that water is present in the Tb and Ho complexes, confirm-
ing the elemental analysis and decomposition point.
a
25
50
75
100
3.6
3.2. Thermal analysis
3.57
The results of thermal analysis studies identify the presence of
the cyclic 18C6 ligand and the PicÀ ions. Only the thermogram of
the La–Sm complexes was obtained because of the explosive
behaviour of the PicÀ ion due to the presence of nitro groups. These
complexes have a decomposition pattern similar to that as re-
ported for the other lanthanide–picrate complexes [39–42,49].
The first step indicates decomposition of 18C6 ligand, which occurs
between 105 and 250 °C. There was a rapid decomposition at 300–
350 °C consistent with the removal of the 18C6 ligand and three
picrates with the total mass reduction of 91% (Calc. 85%), giving
the final products as lanthanide oxides at 600 °C. However, the
Sm complex was more stable than the other Ln(III) complexes be-
cause it began to decompose at 250 °C and rapid decomposition
occurred at 310–325 °C (40%).
3.54
3.51
18C6
La
Ce
Pr
Nd
Sm
Gd
Tb
Ho
Ligand and its complexes
25
50
75
100
b
8.68
8.64
8.6
3.3. NMR studies
The 1H NMR study on the complexes verified the insertion of
Ln(III) in the 18C6 ligand. NMR spectra were taken of the free
18C6 ligand and its complexes in dimethyl sulfoxide-d (DMSO-
d6). The 1H NMR spectrum of the Pic molecule [40] shows two sin-
glet 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
Pic disappeared in all of the complexes, indicating that Ln(III) re-
placed the hydrogen atom via deprotonization or substitution [40].
At 25 °C, the 18C6 ligand has only one singlet peak at 3.519 ppm
assigned to etheric groups (24H) due to its symmetric nature. The
protons of the etheric groups peak in the Pr, Nd and Gd complexes
were shifted downfield by 0.001 ppm and for the Tb complex this
peak was also shifted downfield by 0.024 ppm. The protons from
the etheric groups in the La, Ce and Sm complexes were shifted up-
field by 0.02–0.03 ppm relative to the chemical shift of the free
18C6 ligand. No shifts was observed in the Ho complex, indicating
that Ho(III) did not coordinate with the 18C6 ligand. These data are
consistent agreement with the X-ray diffraction data. It can be con-
cluded that the presence of Ln(III) in the complexes enable the
etheric proton’s peak were shifted downfield, due to the electronic
effect between the 18C6 ligand and Ln(III), thus the electron den-
sity around the etheric proton decreased and deshielding.
8.56
8.52
La
Ce
Pr
Nd
Sm
Gd
Tb
Ho
Complex
Fig. 1. Chemical shift of the free 18C6 ligand and its complexes at increasing
temperature from 25 to 100 °C for the etheric proton of the 18C6 ligand (a) and
protons from the aromatic rings of PicÀ anion (b).
tion bond of Ln–O18C6 is stronger than what was found at room
temperature. Decreasing of temperature was implemented in all
of the complexes had similar spectra, indicating that the reversible
behaviour may be due to no dissociation of Ln–O bonds in the
complexes.
3.4. X-ray studies
We structurally characterized new lanthanide–picrate com-
plexes with the 18C6 ligand to form complexes with molecular for-
mula of [Ln(Pic)2(18C6)]+(Pic)À {Ln = La, Ce, Pr, Nd, Sm and Gd} and
[Ho(Pic)3(OH2)3] Á 2(18C6) Á 4H2O have been presented (Table 2).
The La–Gd complexes crystallized in an orthorhombic with space
group Pbca. From La to Ho, the ionic radii became gradually smal-
ler. Therefore, the coordinated atoms around the different lantha-
nide ions are selective in number and type. Gd is located in the
middle of the lanthanide series. The central Ln(III) has 10-coordi-
nates with six oxygen atoms from the 18C6 ligand, four oxygen
atoms from the two picrates, which are opposite one another with
in the inner coordination sphere and almost perpendicular to each
The dynamic properties and reversible behaviour of the com-
plexes were also undertaken by using 1H NMR spectrometer at
increasing temperature from 25 to 100 °C as shown in Fig. 1a
and b. Similar 1H NMR spectra were obtained when the tempera-
ture was reduced from 100 to 25 °C. The proton of the etheric
group peaks was a consistent singlet peak regardless of increasing
temperature and shifted downfield that indicating the coordina-

Table 2
Crystallography data and their refinement of the 18C6–(Ln–Pic) complexes
Parameter
Complex
La
Ce
Pr
Nd
Formula
Molecular weight
T (K)
C
30H30N9O27La
C30H30N9O27Ce
1088.12
293
C30H30N9O27Pr
1089.54
293
C30H30N9O27Nd
1092.24
293
1086.91
293
Crystal system
Space group
Unit cell dimensions
a (Å)
Orthorhombic
Pbca
Orthorhombic
Pbca
Orthorhombic
Pbca
Orthorhombic
Pbca
11.122(6)
11.138(3)
11.122(2)
11.068(2)
b (Å)
c (Å)
23.870(12)
30.051(15)
90
23.794(5)
30.049(7)
90
7964.0(3)
23.722(4)
30.011(5)
90
7918.0(2)
23.607(3)
29.873(4)
90
7805.0(2)
a
= b =
c
(°)
Volume (Å3)
7978.0(7)
Z
8
8
8
8
Dcalc (g/cm3)
1.185
1.811
4386
1.257
1.816
4376
1.346
1.828
4384
1.447
1.860
4392
Absorption coefficient (mmÀ1
F(000)
)
Crystal size (mm)
h Range (°)
h, k, l
Reflections collected/unique [Rint
Data/restraint/parameter
Goodness-of-fit on F2
0.15 Â 0.25 Â 0.44
1.36–27.00
À12/14, À30/26, À38/38
38650/8509 [0.056]
8509/1/632
1.043
0.08 Â 0.43 Â 0.50
1.70–27.50
À13/14, À30/29, À29/38
44863/9094 [0.042]
9094/0/641
1.164
0.15 Â 0.25 Â 0.44
1.36–27.00
À13/14, À29/30, À32/38
43753/8647 [0.043]
8647/0/614
1.032
0.31 Â 0.32 Â 0.49
1.36–27.60
À13/14, À30/27, À38/38
72019/9022 [0.031]
9022/0/604
1.069
]
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.048, wR2 = 0.142
R1 = 0.080, wR2 = 0.178
R1 = 0.047, wR2 = 0.092
R1 = 0.062, wR2 = 0.098
R1 = 0.037, wR2 = 0.072
R1 = 0.060, wR2 = 0.080
R1 = 0.033, wR2 = 0.086
R1 = 0.040, wR2 = 0.090
Parameter
Complex
Sm
Gd
Ho
Formula
Molecular weight
T (K)
C
30H30N9O27Sm
C30H30N9O27Gd
1105.88
100
C42H68N9O40Ho
1503.98
100
1098.98
100
Crystal system
Space group
Orthorhombic
Pbca
Orthorhombic
Pbca
Triclinic
P1
ꢀ
Unit cell dimensions
a (Å)
b (Å)
c (Å)
10.976(2)
23.512(3)
29.683(4)
90
90
90
7660.2(2)
8
10.883(1)
23.360(3)
30.046(4)
90
90
90
7638.6(2)
8
1.856
1.923
4424
13.894(3)
13.929(3)
17.362(3)
75.979(1)
70.844(1)
81.620(1)
3071.2(1)
2
a
(°)
b (°)
(°)
c
Volume (Å3)
Z
Dcalc (g/cm3)
1.652
1.906
4408
1.400
1.626
1540
Absorption coefficient (mmÀ1
F(000)
)
Crystal size (mm)
h Range (°)
h, k, l
Reflections collected/unique [Rint
Data/restraint/parameter
Goodness-of-fit on F2
0.05 Â 0.26 Â 0.34
0.21 Â 0.34 Â 0.50
0.22 Â 0.50 Â 0.50
1.27–35.00
À22/22, À22/22, À28/28
103345/26883 [0.027]
26883/2/841
1.074
1.37–38.01
1.36–41.04
À18/18, À40/40, À51/51
171986/20804 [0.050]
20804/0/604
1.035
À20/19, À43/43, À55/52
422992/25145 [0.051]
25145/0/605
]
1.075
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.033, wR2 = 0.064
R1 = 0.055, wR2 = 0.070
R1 = 0.031, wR2 = 0.075
R1 = 0.043, wR2 = 0.082
R1 = 0.037, wR2 = 0.099
R1 = 0.042, wR2 = 0.106

M.I. Saleh et al. / Journal of Organometallic Chemistry 693 (2008) 2561–2571
2565
other with dihedral angles of 84.0(3)–84.4(7)° for the La–Sm com-
plexes (Fig. 2a). Outside the coordination sphere, there one picrate
anion is a counter anion. Molecular structures of the La–Sm com-
plexes are isostructural with the Eu complex [33].
The Gd complex has the same inner coordination sphere and
similar outer coordination sphere with the La–Sm complexes ex-
cept the nine-coordination number in the Gd complex. The Gd(III)
ion is coordinated to the nine oxygen atoms from the 18C6 ligand
in a hexadentate manner and the two picrates in each bidentate
and monodentate manners through the phenolic oxygen and an
oxygen of the ortho-nitro group in the opposite direction
(Fig. 2b). The aromatic part of the coordinated picrates formed a
dihedral angle of 82.7(6)°.
metrically one 18C6 molecule surrounding the inner coordination
sphere of [Ho(Pic)3(OH2)3] due to a steric effect from three coordi-
nated PicÀ ions (Fig. 2c). The central Ho(III) ion in Fig. 2c is nine
coordinated with six oxygen atoms from three PicÀ ions and three
oxygen atoms from three water molecules. Outside the coordina-
tion sphere, there are four water and three 18C6 molecules in-
volved in structure act as solvated molecules. The Ho(III) ion has
the smallest radius of the La–Gd ions, which requires smaller
ligands and relatively fewer coordinated atoms around it because
of the steric effects.
These clearly shows the lanthanide contraction effect because
the Ln(III) coordination centers have large ionic radii, which influ-
ence the coordination number at the central atom and the geome-
try of the complex. Good selectivity of the rigid 18C6 ligand toward
Ln(III) in the presence of PicÀ ion which depends on the lanthanide
contraction and steric effects were observed (Fig. 3a and b). The
Unlike the La–Gd complexes, the Ho complex crystallized in a
ꢀ
triclinic system with space group P1 (Table 2). The Ho complex
has centrosymmetrically two 18C6 molecules and non-centrosym-
Fig. 2. Molecular structures of the La (a), Gd (b) and Ho (c) complexes with atom numbering scheme at the 50% probability level. All the hydrogen atoms were omitted for
clarity.

2566
M.I. Saleh et al. / Journal of Organometallic Chemistry 693 (2008) 2561–2571
and displaces by 1.030(3) Å for O1 atom, À1.291(3) Å for O5 atom
a
b
[Ln(Pic)2(OH2)6]+[Pic]-.6H2O
and 0.188(3) Å for O6 atom. For the Sm complex, the Sm1 atom is
also only coplanar with the O1, O2 and O6 atoms and deviates by
1.055(1) Å for O3 atom, 0.256(1) Å for O4 atom and À1.383(1) Å for
O5 atom. For the Gd complex, the Gd1 atom is also coplanar with
the O1, O2 and O6 atoms and displaces by À1.330(1) Å for O3
atom, 0.596(1) Å for O4 atom and 1.101(1) Å for O5 atom.
[Ln(Pic)2(OH2)6]+[Pic]-.6H2O
Acetonitrile
[Ln(Pic)2]+
Acetonitrile
Heat
Heat
Water molecules may coordinate to the Ln(III) ions with small
ionic radii e.g. Tb and Ho. These coordination results from the
favorable matching between small ionic radii of Tb(III) and Ho(III)
ions and the coordination binding, sometimes too long to be coor-
dinated as an inner sphere ligand. Thus, the outer sphere of the
complexes is obtained and the necessary coordination number is
attained with three water molecules. The lack of saturation of
[Ln(Pic)2(OH2)3]++ m H2O +
[Pic]-
mH2O
+
+ [Pic]-
Added
Added
O
O
18C6
O
O
O
O
O
O
O
O
O
Heat
Heat
18C6
O
Slow evaporation
After one day
Slow evaporation
After one day
[Ln(Pic)2(18C6)]+[Pic]-
Noted : for Ln = La - Gd
+ Solvent
[Ln(Pic)3(OH2)3].2.(18C6).4H2O + Solvent
Noted: for Ln = Tb and Ho
Fig. 3. Mechanism of reaction between lanthanide–picrate and the 18C6 ligand in
acetonitrile for the La–Gd complexes (a) and the Tb and Ho complexes (b).
ionic radius of La(III), which is greater than the ionic radius of
Gd(III), enabled interaction with more oxygen donor atoms to form
a 10-coordinated complex while the smaller Gd(III) forms only a
nine-coordinated complex. The steady decrease in Ln(III) radius
can result in structural changes, with complexes of the early Ln(III)
having higher coordination numbers than do the heavier lantha-
nide elements. The electronegativity also decreases as the lantha-
nide coordination number increases, and increases with the
lanthanide atomic number. The Ln–O bond length decreases as
the lanthanide atomic number increases and increases as the lan-
thanide coordination number increases. The hard polyether Lewis
base crown ether saturates the coordination sphere and increases
the coordination number, competing with complex formation
reaction and the hydration side process to ultimately reach steric
saturation around the Ln(III) central metal ion [18]. Thus, it is
clearly observed that the small differences in the ionic radii play
an important role in the selection of electron rich atoms for the for-
mation of coordination bond.
The significant observations for the entire lanthanide series can
be seen in the three representative structures that clearly indicate
the changes in the 18C6 ligand to accommodate the decreasing
sizes of the ionic radii (Fig. 2a–c). The La(III) ion has the largest
effective ionic radius of 1.27 Å for a 10-coordination number
[50], thus the 18C6 ligand could formed complexes without dis-
torting as much as in complexes with the smaller Ln(III) ions.
The La1 atom is coplanar with the O1, O3, O4 and O5 atoms and
deviates by À1.218(4) Å for O2 atom and 0.991(4) Å for O6 atom
from the ring 18C6 ligand in inner coordination sphere. For the
Ce–Gd complexes, the Ln(III) ions in the ring 18C6 ligand of inner
coordination spheres are only coplanar with three oxygen ether
atoms of the 18C6 ligand and the other oxygen ether atoms of
the 18C6 ligand are not coplanar. For the Ce complex, the Ce1 atom
is coplanar with the O1, O5 and O6 atoms and displaces by
À1.252(3) Å for O2 atom, 0.155(2) Å for O3 atom and 1.011(2) Å
for O4 atom. For the Pr complex, the Pr1 atom is also coplanar with
the O1, O2 and O6 atom and deviates by 1.029(2) Å for O3 atom,
0.174(2) Å for O4 atom and À1.276(3) Å for O5 atom. For the Nd
complex, the Nd1 atom is coplanar with the O2, O3 and O4 atoms
Fig. 4. The inner coordination spheres of [La(Pic)2(18C6)]+ (a), [Gd(Pic)2(18C6)]+ (b)
and [Ho(Pic)3(OH2)3] (c).

M.I. Saleh et al. / Journal of Organometallic Chemistry 693 (2008) 2561–2571
2567
picrate anion. Thus, the chloride and nitrate anion did not control
and give an effect the inner coordination sphere of their complexes
alike the picrate anion.
The inner coordination sphere of [Ln(Pic)2(18C6)]+ contains un-
equal bond lengths and forms a bicapped square antiprismatic
geometry with the O1 and O4 atoms as the peak in the capping po-
sition (Fig. 4a). This geometry is slightly distorted due to the bond
angle of two etheric oxygen atoms at the top in the capping posi-
tion that is close to 180° (Fig. 5a). Gd(III) has a slightly distorted tri-
capped trigonal prismatic geometry with the O1, O3 and O5 atoms
as the peaks in the capping position (Fig. 4b). The inner coordina-
tion sphere of [Ho(Pic)3(OH2)3] has a trigonal tricapped prismatic
geometry with the O2, O9 and O21 atoms coplanar and at the
top in the capping position (Figs. 4c and 5b). The Ho1 atom lies
on the base of the triangle (Fig. 4c).
The volume of the orthorhombic complexes generally decreases
with increasing atomic number due to lanthanide contraction
(Table 2). From the La–Gd complexes, the bond lengths between
the Ln(III) ions and the coordinated atom from the same ligand tend
to become shorter. The average bond length in the La–Gd com-
plexes is 2.596(4), 2.584(3), 2.571(2), 2.550(2), 2.545(1) and
2.506(1) Å for Ln–O18C6 bonds, respectively, indicating the effect
of lanthanide contraction on molecular structure. These bond
lengths were similar with those found in the 18C6–Ln–Cl com-
plexes [51–53] and were shorter than what was found in the
18C6–Ln–NO3 complexes [54,55]. The Ln–O15 bond length for
one of the coordinated oxygen-nitro groups in the range
2.734(4)–2.789(1) Å was elongated by 0.055 Å in the La–Sm com-
plexes (Table 3). In the Eu complex has the same inner coordination
sphere and similar outer coordination sphere with the Gd complex
except that the nine-coordination number for Gd issued [33]. The
Eu–O15 bond length is 2.934(7) Å [33], while the non-bonding
Gd–O15 bond length is 3.364 Å with an elongation distance of
0.43 Å (Fig. 4b).
The [Ln(Pic)2(18C6)]+(Pic)À complexes have an average C–O
bond length of 1.427(8)–1.442(2) Å, but the average C–C bond
length of 1.432(1)–1.499(2) Å. The coordination of Ln–O18C6 in
the inner coordination sphere is very much affected by the bond
length and with the C–O bond length increasing while the C–C
bond length decreasing. The O–Ln–O bond angles in all of the
[Ln(Pic)2(18C6)]+(Pic)À complexes are equivalent (slightly bigger
than 60°) (Table 4). The average C–O–C bond angle decreases with
the size of the Ln(III) ions, namely 115.0(6)–112.6(1)° for the La–
Gd complexes. The average O–C–C bond angle also decrease with
the increase in the atomic number of lanthanides for the La–Gd
complexes, namely 110.7(6)–107.0(1)°.
Fig. 5. Bicapped square antiprismatic geometry around La(III) (a) and tricapped
trigonal prismatic geometry around Ho(III) (b).
the inner coordination sphere enables easy reactions either with a
donor solvent or with a nucleophilic impurity such as water that
ultimately leads to a poorly volatile or involatile hydroxo-complex.
All of the complexes we observed were mononuclear and the
18C6 ligand coordinated with Ln(III) in the hexadentate mode
(for the La–Gd complexes). This pattern may be due to the pres-
ence of a second large ligand, i.e. the picrate anion, which coordi-
nates with Ln(III) in a bidentate or monodentate chelating mode,
making it difficult to form a polymer or a dimer. There is an unco-
ordinating picrate anion in the lattice as a counter anion in the La–
Gd complexes. From our studies, the picrate anion is also signifi-
cantly contributed to change of the geometries and formation of
the complexes. Because of the picrate anion has higher steric hin-
drance to control the inner coordination sphere of the complexes
than those found in the 18C6–Ln–Cl and 18C6–Ln–NO3 complexes
[51–55]. For the [LnCl(OH2)2(18C6)]Cl2 Á 2H2O complexes {Ln = Pr–
Tb} are isostructural with a nine-coordination number [51–53].
These similarities structures of the complexes did not show differ-
ence of ionic radii of the Ln(III) central ions. The chloride and ni-
trate anions have smaller steric hindrance than that found in the
The O–C–C–O torsion angle [average of 49.2(6)–54.3(2)°] for the
[Ln(Pic)2(18C6)]+(Pic)À complexes occur different conformational
patterns in the respective order gÀ gÀ gÀ g+ gÀ g+; g+ gÀ g+ gÀ g+ gÀ g+;
gÀ g+ gÀ g+ g+ g+; g+ gÀ g+ g+ g+gÀ; g+ gÀ g+ gÀ gÀ gÀ and g+ gÀ gÀ gÀ g+ gÀ
for the La–Gd complexes (Table 4). The average C–O–C–C torsion
angle in ranges from 145.4(7)–158.9(5)° and was observed in the
La–Gd complexes. The average O–C–C–O torsion angle of the sol-
vated 18C6 A with g+ gÀ g+ gÀ g+ gÀ pattern [77.3(3)°], centrosym-
metry B with g+ g+ pattern [61.5(4)°] and centrosymmetry C with
g+ gÀ g+ patterns [176.6(3)°] and observed in the Ho complex. The
average C–O–C–C torsion angle of the solvated 18C6 for A, B and
C fragments are 158.5(2), 140.7(2) and 176.6(3)°, respectively.
The crystal packing of the complexes shows the intra- and inter-
molecular C–HÁ Á ÁO hydrogen bonding with one-dimensional (1-D)
networks for the La–Gd complexes (Fig. 6a). Hydrogen bonding
which is a non-covalent bond interaction will facilitate the forma-
tion of supramolecular architecture. Because of the different inner
coordination spheres and outer spheres, the La–Gd and Ho com-
plexes have different crystal structures. Their supramolecular
architectures are built in different ways.

2568
M.I. Saleh et al. / Journal of Organometallic Chemistry 693 (2008) 2561–2571
Table 3
Selected bond length (Å) in the 18C6–(Ln–Pic) complexes
Bond
Complex
Length (Å)
La
Ce
Pr
Nd
Sm
Gd
Ho
Ln1–O1
Ln1–O2
Ln1–O3
Ln1–O4
Ln1–O5
Ln1–O6
Ln1–O14
Ln1–O7
Ln1–O1
Ln1–O8
Ln1–O15
Ln1–O21
Ln1–O1W
Ln1–O2W
Ln1–O3W
2.586(4)
2.614(4)
2.604(4)
2.647(4)
2.560(4)
2.567(4)
2.419(4)
2.449(3)
–
2.637(4)
2.734(4)
–
–
–
2.549(3)
2.551(3)
2.570(3)
2.601(3)
2.602(3)
2.633(3)
2.410(2)
2.382(3)
–
2.738(3)
2.624(3)
–
–
–
2.623(2)
2.531(3)
2.536(2)
2.555(2)
2.592(3)
2.586(2)
2.390(2)
2.356(2)
–
2.749(3)
2.604(3)
–
–
–
2.513(2)
2.510(2)
2.606(2)
2.565(2)
2.574(2)
2.533(2)
2.341(2)
2.374(2)
–
2.576(2)
2.744(3)
–
–
–
2.614(1)
2.504(1)
2.489(1)
2.520(1)
2.584(1)
2.557(1)
2.312(1)
2.354(1)
–
2.521(1)
2.789(1)
–
–
–
2.580(1)
2.508(1)
2.567(1)
2.448(1)
2.462(1)
2.471(1)
2.263(1)
2.331(1)
–
2.474(1)
–
–
–
–
–
–
–
–
–
–
2.284(2)
2.290(2)
2.285(1)
2.571(2)
2.582(2)
2.562(2)
2.305(2)
2.326(2)
2.321(1)
–
–
–
–
–
–
Table 4
Selected bond angle and torsion angle (°) in the 18C6–(Ln–Pic) complexes
Bond
Complex
Angle (°)
La
Ce
Pr
Nd
Sm
Gd
O1–Ln1–O2
O2–Ln1–O3
O3–Ln1–O4
O4–Ln1–O5
O5–Ln1–O6
O6–Ln1–O1
61.8(1)
62.5(1)
62.2(1)
61.7(1)
63.9(1)
61.8(1)
64.0(1)
61.8(1)
62.1(1)
62.8(1)
62.2(9)
61.9(9)
62.0(8)
64.4(9)
61.8(9)
62.2(9)
62.9(8)
62.4(8)
64.4(7)
62.0(7)
62.4(7)
63.0(8)
62.4(8)
62.0(8)
62.4(3)
65.3(3)
62.1(4)
62.9(4)
63.5(4)
63.0(3)
64.0(3)
63.6(3)
63.0(3)
63.3(3)
65.3(3)
62.9(3)
Bond
Torsion angle (°)
O1–C1–C2–O2
O2–C3–C4–O3
O3–C5–C6–O4
O4–C7–C8–O5
O5–C9–C10–O6
O6–C11–C12–O1
À41.2(12)
À56.4(7)
À48.8(9)
46.8(10)
À55.8(8)
50.6(8)
À55.6(5)
50.7(5)
À48.7(5)
54.7(5)
À50.4(5)
45.4(6)
56.9(4)
51.1(5)
55.0(4)
À49.2(5)
52.2(4)
56.9(4)
47.6(5)
53.8(2)
À55.3(2)
50.3(2)
À52.5(2)
À58.7(2)
À55.1(2)
À55.2(1)
À57.2(2)
À48.7(2)
51.0(1)
À43.8(8)
47.5(5)
À50.0(6)
47.9(7)
À52.6(1)
À50.5(4)
51.9(2)
The intermolecular O–HÁ Á ÁO hydrogen bonding between the lat-
tice water and the coordinating water or between the lattice water
molecules form an infinite, one-dimensional (1-D) network with
symmetry direction [010] and was observed only in the crystal
packing of the Ho complex (Fig. 6b). One weak intramolecular
C23–H23BÁ Á ÁO22 [2.589 Å] hydrogen bond also was observed
(Table 5). The van der Walls interactions of C19–H19AÁ Á ÁCg1
[3.009 Å] and C39–H39BÁ Á ÁCg3 [2.979 Å] with symmetry codes x,
y, z and 1 À x, 1 À y, 1 À z, respectively, was observed only in the
Ho complex where Cg1 = aromatic ring of (C1–C6) and Cg3 = aro-
matic ring of (C13–C18). A long contact of OÁ Á ÁO and OÁ Á ÁN also
contributed to the strength of the hydrogen bonding.
ever, the T1(L) is below of the lowest excited resonance level 5D4
(about 20400 cmÀ1) of Tb(III) ion, not matched with the lowest ex-
cited level of Tb(III). Thus, the intramolecular energy transfer from
the 18C6 ligand to Tb(III) is probably not occurred. To improve en-
ergy transfer to the lanthanide ion, the lowest triplet state energy
level (T1) of the ligand must be closely matched or slightly above
the metal ion’s emitting resonance levels. The suitability of the en-
ergy gap between the excited triplet energy level of the ligand and
the lowest excited energy level of Ln(III) is a critical factor for sen-
sitized luminescence of the central Ln(III) ion [56].
Three possibilities of the lowest excited resonance levels 3P0
(20300 cmÀ1), 1D2 (17000 cmÀ1) and 1G4 (9700 cmÀ1) of Pr(III)
have taken place. However, the energy gap for 1D2 level is twice
as large as for the other two levels, namely 3P0 and 1G4. Thus, it
shown that the Pr(III) ion would only emit from 1D2 level due to
the intramolecular energy transfer process between the oxygen
atom of 18C6 ligand and Pr(III). The Pr(III) complex emits the
visible and infrared luminescence in the solid state at room temper-
ature (Fig. 7). Typical features of 3P0 ? 3F2, 1D2 ? 3F2 and 1D2 ? 3F4
transitions at 650, 830 and 950 nm were observed in the Pr com-
plex [57].
3.5. Photoluminescence (PL) studies
The ability of the cyclic 18C6 ligand to satisfy the coordination
requirements of Ln(III) centre with a high coordination number is
an important criterion in the design of supramolecular photonic de-
vices. The PL spectra of the free 18C6 ligand and its complexes were
obtained when excited by absorption at 325 nm. The lowest triplet
state energy level (T1) of the 18C6 ligand which was calculated from
the phosphorescence spectrum of the Gd complex indicates that the
T1(L) of 18762 cmÀ1 matches the resonance level of Sm(III) ion. This
The La, Ce, Nd, Sm, Gd, Tb and Ho complexes had broad bands
with the center peak at 535 nm (green) due to the 18C6 ligand
and picrate anion. The picrate anion acts as quencher in the
18C6–(Ln–Pic) complexes due to the nitro withdrawing groups.
4
energy level is above the lowest excited resonance level G5/2
(17900 cmÀ1) of Sm(III) and 3S2 (18182 cmÀ1) of Ho(III) ions. How-

M.I. Saleh et al. / Journal of Organometallic Chemistry 693 (2008) 2561–2571
2569
Fig. 6. Crystal packing of the La complex viewed down the b-axis, the dashed lines (—) show C–HÁ Á ÁO hydrogen bonding (a) and crystal packing of the Ho complex viewed
down the a-axis, the dashed lines (—) show O–HÁ Á ÁO and C–HÁ Á ÁO hydrogen bonding (b).
Near infrared (NIR) luminescence of Ln(III) ions can be quenched
by O–H vibrations [58]. Due to the limitation of our equipment,
we could not measure the excitation (monitored at 1540 nm) spec-
trum and the NIR luminescence lifetime of the Nd complex. Only
the Sm, Tb and Ho complexes had a typical 4f–4f emission transi-
tions in the visible region. For further study, only the Tb complex
with the 18C6 ligand in the presence of nitrate anion was also
prepared in our laboratory. The crystal structure of [Tb(NO3)3-
(OH2)3](18C6) complex has been reported by Roger and Rollins
[59], nevertheless the luminescence property of the this complex
was not observed. Thus, we studied luminescence property of the
[Tb(NO3)3(OH2)3](18C6) complex compared with the 18C6–(Tb–
Pic) complex.
A
strong characteristic emissions of Tb(III) for the
[Tb(NO3)3(OH2)3](18C6) complex was observed. This may be due
to the following factors, i.e. (i) the symmetry alteration of Tb(III)
in the [Tb(NO3)3(OH2)3](18C6) complex, (ii) the good rigid struc-
ture of the complex was formed by three nitrate anions and three
water molecules surrounding of the Tb(III) ion and (iii) the equiv-
alent distances between the central Tb(III) ion and the oxygen
donor atoms ranged from 2.371 to 2.446 Å. The [Tb(NO3)3(OH2)3]-
(18C6) complex has a typical features of the 5D4 ? 7FJ (J = 0, 1, 2, 3,
4, 5, 6) luminescence transitions that is similar with its salt and
oxide (Fig. 8). The presence of the 18C6 molecule in the complex
that acts as solvated or hexadentate coordinated ligand in the in-
ner coordination sphere influenced the luminescent peaks. The

2570
M.I. Saleh et al. / Journal of Organometallic Chemistry 693 (2008) 2561–2571
hypersensitive peak of the 5D4 ? 7F5 transition for the
[Tb(NO3)3(OH2)3](18C6) complex [544.2 nm; 2439 Â 102 a.u.] is
higher than that was found in Tb(NO3)3 Á 6H2O [541.4 nm;
298.7 Â 102 a.u.] and Tb4O7 [542.1 nm; 41.1 Â 102 a.u.]. Addition-
ally, the purity of green emission from the [Tb(NO3)3(OH2)3](18C6)
complex is higher than that was found in its salt and oxide.
Table 5
Hydrogen bonding in the [Ho(Pic)3(OH2)3] Á 2(18C6) Á 4(H2O) complex
D–HÁ Á ÁA
D–H (Å)
HÁ Á ÁA (Å)
DÁ Á ÁA (Å)
D–HÁ Á ÁA(°)
O1W–H11WÁ Á ÁO7W
O2W–H12WÁ Á ÁO28
O3W–H13WÁ Á ÁO30
O4W–H14WÁ Á ÁO25
O5W–H15WÁ Á ÁO33i
O6W–H16WÁ Á ÁO27
O7W–H17WÁ Á ÁO1W
O1W–H21WÁ Á ÁO5W
O2W–H22WÁ Á ÁO6W
O3W–H23WÁ Á ÁO29ii
O5W–H25WÁ Á ÁO1W
O6W–H26WÁ Á ÁO24
O7W–H27WÁ Á ÁO31i
O7W–H27WÁ Á ÁO32i
C23–H23BÁ Á ÁO22a
C26–H26BÁ Á ÁO17iii
C32–H32AÁ Á ÁO13iii
C32–H32BÁ Á ÁO5W
C35–H35AÁ Á ÁO7W
C35–H35BÁ Á ÁO10ii
C37–H37AÁ Á ÁO20i
C40–H40BÁ Á ÁO5iv
0.860(4)
0.850
0.849
0.850
0.851
0.851
0.850
0.840(3)
0.850
0.849
0.850
0.851
0.850
0.850
0.970
0.970
0.970
0.970
0.970
0.970
0.960
0.969
1.850(4)
1.985
1.873
2.080
2.167
2.062
2.319
1.810(3)
1.841
1.928
1.900
2.000
2.006
2.494
2.589
2.530
2.532
2.573
2.439
2.475
2.465
2.510
2.693(2)
2.744(2)
2.722(2)
2.867(4)
2.923(4)
2.803(3)
2.693(2)
2.609(4)
2.689(3)
2.753(2)
2.609(4)
2.824(3)
2.832(4)
2.968(3)
3.206(3)
3.435(4)
3.278(4)
3.541(4)
3.257(3)
3.418(4)
3.255(5)
3.431(4)
167.0(5)
148.1
178.2
153.7
147.9
145.1
107.0
157.0(4)
174.7
163.3
140.1
162.4
163.6
116.1
121.6
155.2
133.6
175.0
141.9
164.1
139.5
158.6
4. Conclusion
The rigid 18C6 ligand governs the selectivity in the formation of
the complexes with Ln(III) ions in the presence of picrate anion.
The Ln–O bond length is greatly influenced by the size of the Ln(III)
ionic radius of due to lanthanide contraction. The contraction of
the radii of the metal ions necessitates a change in the coordination
environment. Different coordination environments and species in
the lattice result in different non-covalent interactions which final-
ly generate different supramolecular architectures. The picrate an-
ion has a high steric effect to control in the inner coordination
sphere of the complexes. The photoluminescence spectrum of the
Pr complex has 4f–4f emission, i.e. 3P0 ? 3F2, 1D2 ? 3F2 and
1D2 ? 3F4transitions.
Symmetry codes: (i) 1 À x, 1 À y, 1 À z; (ii) 1 À x, Ày, 1 À z; (iii) À1 + x, y, z; (iv)
À1 + x, y, 1 + z.
Acknowledgements
a
Intramolecular hydrogen bonding.
We thank Universiti Sains Malaysia and the Malaysian Govern-
ment for the research Grants IRPA No. 305/PKIMIA/612906, FRGS
No. 304/PKIMIA/670006, SAGA No. 304/PKIMIA/653010/A118 and
FRGS No. 203/PKIMIA/671020.
6000
4000
2000
0
Appendix A. Supplementary material
CCDC 237057, 667007, 667008, 667009, 667010, 667011,
667012 contains the supplementary crystallographic data for Nd,
La, Ce, Gd, Ho. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.
uk/data_request/cif.
References
[1] P.J. Hagman, D. Hagan, J. Zubieta, Angew. Chem., Int. Ed. Engl. 38 (1999) 2638.
[2] B. Moulton, M.J. Zaworotko, Chem. Rev. 101 (2001) 1629.
[3] M. O’Keeffe, M. Eddaoudi, H. Li, T. Reineke, O.M. Yaghi, J. Solid State Chem. 152
(2000) 3.
[4] V.V. Ponomarova, K.V. Domasevitch, Crystal. Eng. 5 (2002) 137.
[5] R. Centore, A. Tuzi, Crystal. Eng. 6 (2003) 87.
[6] G.R. Desiraju, Angew. Chem., Int. Ed. Engl. 34 (1995) 2311.
[7] P.K. Thalapally, G.R. Desiraju, M. Bagieu-Beucher, R. Masse, C. Bourgogne, J.F.
Nicoud, Chem. Commun. (2002) 1052.
500
600
700
800
900
1000
Wavelength (nm)
Fig. 7. The photoluminescence of the Pr complex in the solid state at room
temperature.
[8] J. Ramkumar, Spectrochim. Acta, Part A 65 (2006) 993.
[9] J. Gao, G. Zhao, J. Kang, Talanta 42 (1995) 1497.
[10] R.C. Evans, P. Douglas, C.J. Winscom, Coord. Chem. Rev. 250 (2006) 2093.
[11] J. Li, L. Zhang, L. Liu, G. Liu, D. Jia, G. Xu, Inorg. Chim. Acta 360 (2007) 1995.
[12] S.A. Cotton, in: R.B. King (Ed.), Encyclopedia of Inorganic Chemistry, 7, Wiley,
New York, 1994, p. 3595.
3000
2500
2000
1500
1000
500
[13] S.A. Cotton, Coord. Chem. Rev. 160 (1997) 93.
[14] S. Isiguro, Y. Umebayashi, K. Komiya, Coord. Chem. Rev. 226 (2002) 103.
[15] L. Helm, A.E. Merbach, Coord. Chem. Rev. 187 (1999) 151.
[16] S. Zhang, K. Wu, A.D. Sherry, J. Am. Chem. Soc. 124 (2002) 4226.
[17] J.-C.G. Bünzli, N. Andre’, M. Elhabiri, G. Muller, C. Piguet, J. Alloy. Compd. 303–
304 (2000) 66.
[18] G. Malandrino, I.L. Fragalà, Coord. Chem. Rev. 250 (2006) 1605.
[19] P.L. Jones, A.J. Amoroso, J.C. Jeffery, J.A. McCleverty, E. Psillakis, L.H. Rees, M.D.
Ward, Inorg. Chem. 36 (1997) 10.
[20] D. Xue, S. Zuo, H. Ratajczak, Physica B 352 (2004) 99.
[21] Z.X. Zhou, W.C. Zheng, Y.Z. Li, Z.H. Mao, Z.H. Zhou, Z. Hong, Polyhedron 15
(1996) 3519.
[22] D. Wang, X. Sun, H. Hu, Y. Liu, B. Chen, Z. Zhou, K. Yu, Polyhedron 8 (1989)
2051.
[23] Z. Zhou, Y. Zhou, Y. Li, K. Ding, Polyhedron 14 (1995) 3033.
[24] J.W. Steed, Coord. Chem. Rev 215 (2001) 171.
[25] A.V. Bajaj, N.S. Poonia, Coord. Chem. Rev 87 (1988) 55.
[26] F.R. Fronczek, R.D. Gandour, in: Y. Inone, G.W. Goke (Eds.), Cation Binding by
Macrocycles: Complexation of Cationic Species by Crown Ethers, M. Dekker
Inc., New York, 1990.
0
500
550
600
650
700
Wavelength (nm)
Fig. 8. The photoluminescence of the [Tb(NO3)3(OH2)3](18C6) complex in the solid
state at room temperature.

M.I. Saleh et al. / Journal of Organometallic Chemistry 693 (2008) 2561–2571
2571
[27] R.M. Izatt, J.S. Bradshaw, S.A. Nielson, J.D. Lamb, J.J. Christensen, Chem. Rev. 85
(1985) 271.
[28] A.Y. Tsivadze, A.A. Varnek, V.E. Khutorsky, Coordination Compounds of Metals
with Crown Ligands, Nauka, Moscow, 1991.
[29] I.A. Kahva, D. Miller, M. Mitchel, F. Fronczek, R.G. Goodrich, D.J. Willias, C.A.
O’Mahoney, A.M. Slawin, S.V. Ley, C.G. Groombridge, Inorg. Chem. 31 (1992)
3963.
[30] R.D. Rogers, M.M. Benning, Acta Crystallogr., Sect. C 44 (1988) 1397.
[31] M.I. Saleh, A. Salhin, B. Saad, Analyst 120 (1995) 2861.
[32] J.M. Harrowfield, W. Lu, B.W. Skelton, A.H. White, Aust. J. Chem. 47 (1994) 321.
[33] M.I. Saleh, E. Kusrini, B. Saad, R. Adnan, A.S. Mohamed, B.M. Yamin, J. Lumin.
126 (2007) 871.
[44] N.F. Curties, Y.M. Curties, Inorg. Chem. 4 (1965) 801.
[45] L.F. Delboni, G.O. Livia, E.E. Castellano, L.B. Zinner, S. Braun, Inorg. Chim. Acta
221 (1994) 169.
[46] A.G. Silva, G. Vicentini, J. Zukerman-Schpector, E.E. Castellano, J. Alloy. Compd.
225 (1995) 354.
[47] T. Yongchi, L. Yingqiu, N. Jiazan, J. Mol. Sci. 5 (1987) 83.
[48] K. Nakagawa, K. Amita, H. Mizuno, Y. Inoue, T. Hakushi, Bull. Chem. Soc. Jpn. 60
(1987) 2037.
[49] J.C. Fernandes, J. R Matos, L. B Zinner, G. Vicentini, J. Zukerman-Schpector,
Polyhedron 19 (2000) 2315.
[50] R.D. Shannon, Acta Crystallogr. A 32 (1976) 751.
[51] R.D. Rogers, A.N. Rollins, R.D. Etzenhouser, E.J. Voss, C.B. Bauer, Inorg. Chem. 32
(1993) 3451.
[34] Bruker, SADABS (Version 2.01), SMART (V5.603) and SAINT (V 6.36a). Bruker AXS
Inc., Madison, Wisconsin, USA, 2000.
[35] G.M. Sheldrick, SHELXTL V5.1. Bruker AXS Inc., Madison, Wisconsin, USA, 1997.
[36] A.L. Spek, J. Appl. Crystallogr. 36 (2003) 7.
[52] R.D. Rogers, A.N. Rollines, R.F. Henry, J.S. Murdoch, R.D. Etzenhouser, S.E.
Huggins, L. Nunez, Inorg. Chem. 30 (1991) 4946.
[53] R.D. Rogers, L.K. Kurihara, Inorg. Chem. 26 (1987) 1498.
[54] R.D. Rogers, A.N. Rollins, Inorg. Chim. Acta 230 (1995) 177.
[55] R.D. Rogers, C.B. Bauer, in: J.L. Atwood (Ed.), Comprehensive Supramolecular
Chemistry, vol. 1, Pergamon Express, United State American, 1996, pp. 315–
355.
[37] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.
[38] N. Yang, J. Zheng, W. Liu, N. Tang, K. Yu, J. Mol. Struct. 657 (2003) 180.
[39] M.I. Saleh, E. Kusrini, R. Adnan, I.A. Rahman, B. Saad, A. Usman, H.-K. Fun, B.M.
Yamin, J. Chem. Crystallogr. 35 (2005) 469.
[40] M.I. Saleh, E. Kusrini, R. Adnan, B. Saad, B.M. Yamin, H.K. Fun, J. Mol. Struct. 837
(2007) 169.
[56] Y.S. Yang, M.L. Gong, Y.Y. Li, H.Y. Lei, S.L. Wu, J. Alloy. Compd. 207–208 (1994)
112.
[41] Y. Tang, D.-B. Liu, W.-S. Liu, M.-Y. Tan, Spectrochim. Acta, Part A 63 (2006) 164.
[42] L. Fan, W. Liu, X. Gan, N. Tang, M. Tan, W. Jiang, K. Yu, Polyhedron 19 (2000)
779.
[43] P. Miranda Jr., J. Zukerman-Schpector, P.C. Isolani, G. Vicentini, L.B. Zinner, J.
Alloy. Compd. 323–324 (2001) 14.
[57] A.I. Voloshin, N.M. Shavaleev, V.P. Kazakov, J. Lumin. 93 (2001) 199.
[58] A. Beeby, I.M. Clarkson, R.S. Dickins, S.F. Aulkner, D. Parker, L. Royle, A.S. de
Sousa, J.A.G. Williams, M. Woods, J. Chem. Soc., Perkin Trans.
493.
2 (1999)
[59] R.D. Rogers, A.N. Rollins, J. Chem. Crystallogr. 24 (1994) 321.