Synthesis, characterization, X-ray structure and photoluminescence properties of two Ce(III) complexes derived from pentadentate ligands

Article abstract of DOI:10.1016/j.molstruc.2015.08.016

In this study, two new Ce(III) complexes [Ce(L¹)(NO₃)₃]·H₂O and [Ce(L²)(NO₃)₃]·H₂O were synthesized and characterized by spectroscopic and analytical methods where L¹ and L² are pentadentate diimine ligands. Molecular structure of [Ce(L1)(NO3)3]·H2O was determined by single crystal X-ray diffraction study. The complex was found to crystallize as [Ce(L¹)(NO₃)₃] H₂O. In the complex, the ligand L¹ coordinates to the Ce(III) ion with the N₃O₂ donor set and the Ce(III) ion sits within the cavity of acyclic ligand. The Ce(III) ion is 11-coordinated by three nitrogen atoms from the ligand and eight O atoms, six of which come from three nitrate ions, two from the ligand. In the structure of the complex, water molecules link molecules together to form a 3D hydrogen bond network. Thermal behavior of the Schiff base ligands and their Ce(III) complexes metal complexes were studied under nitrogen atmosphere in the temperature range of 20-800 °C. Thermal stability of the ligands increased upon complexation with Ce(III) ion. In the UV-Vis spectra of Ce(III) complexes, new absorption bands appeared at 340-450 nm and these new bands were attributed to metal-ligand (M-L) charge transitions. Photoluminescence properties of the ligands and their Ce(III) complexes were examined.

Full text of DOI:10.1016/j.molstruc.2015.08.016

Journal of Molecular Structure 1101 (2015) 33e40
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Synthesis, characterization, X-ray structure and photoluminescence
properties of two Ce(III) complexes derived from pentadentate ligands
*
Muhammet K o€ se , Eyup Akgün, G o€ khan Ceyhan
Chemistry Department, Kahramanmara s¸ Sütçü Imam University, Kahmaranmara s¸ , 46050, Turkey
a r t i c l e i n f o
a b s t r a c t
1
2
Article history:
Received 4 June 2015
Received in revised form
3 3 2 3 3 2
In this study, two new Ce(III) complexes [Ce(L )(NO ) ]∙H O and [Ce(L )(NO ) ]∙H O were synthesized
and characterized by spectroscopic and analytical methods where L and L2 are pentadentate diimine
ligands. Molecular structure of [Ce(L1)(NO3)3]∙H2O was determined by single crystal X-ray diffraction
study. The complex was found to crystallize as [Ce(L )(NO
ordinates to the Ce(III) ion with the N donor set and the Ce(III) ion sits within the cavity of acyclic
ligand. The Ce(III) ion is 11-coordinated by three nitrogen atoms from the ligand and eight O atoms, six of
which come from three nitrate ions, two from the ligand. In the structure of the complex, water mol-
ecules link molecules together to form a 3D hydrogen bond network. Thermal behavior of the Schiff base
ligands and their Ce(III) complexes metal complexes were studied under nitrogen atmosphere in the
1
5
August 2015
1
1
3 3 2
) ] H O. In the complex, the ligand L co-
Accepted 5 August 2015
Available online 7 August 2015
3 2
O
Keywords:
Ce(III) complex
X-ray structure
Spectroscopy
ꢀ
temperature range of 20e800 C. Thermal stability of the ligands increased upon complexation with
Photoluminescence
Ce(III) ion. In the UVeVis spectra of Ce(III) complexes, new absorption bands appeared at 340e450 nm
and these new bands were attributed to metaleligand (MeL) charge transitions. Photoluminescence
properties of the ligands and their Ce(III) complexes were examined.
©
2015 Elsevier B.V. All rights reserved.
1. Introduction
semiconductors [22], fluorescent [23], magnetic [24], catalytic
25], and nonlinear optical materials [26]. Lanthanide complexes
[
The nitrogen-oxygen containing multidentate ligands and their
metal complexes are of special interest due to their potential ap-
plications in several fields including catalysis, transport processes
and modeling of several biological compounds [1e10]. Schiff base
compounds are used as ligands in metal coordination chemistry
and metal complexes derived from Schiff bases have occupied a
central role in the development of coordination chemistry [11e15].
There are a number of publications on Schiff base metal complexes
regarding their antimicrobial activity, thermal studies, electro-
chemical properties, as electrochemical sensors and as catalysts for
epoxidation of olefins, lactide polymerization, ring opening of ep-
oxides and Michael reactions [16e18].
usually exhibit high coordination numbers and structural diversity
[27,28]. The relatively large size of the lantanide ions usually allows
accommodation of more than six donor atoms. The solid-state co-
ordination numbers and geometries of lanthanides are difficult to
predict, especially for complexes of mono- and bi-dentate ligands
[28]. Several mono- and poly-nuclear lantanide complexes of Schiff
base ligands derived from 2,6-diacetylpyridine or 2,6-
diformylpyridine with polydentate hydrazones, semicarbazones,
and thiosemicarbazones were reported in literature [29e35].
In our previous study, the synthesis, structural characterization,
electrochemical and luminescence properties of a La(III) complex
were investigated [28]. Due to the importance of lanthanide com-
plexes and in continuance of our interest in the synthesis of triva-
lent lanthanide, we herein reported the synthesis, spectral,
electrochemical and luminescence properties of two pentadentate
Schiff base ligands (Fig. 1) and their Ce(III) complexes. The structure
of the ligands and their Ce(III) complexes were characterized by
Trivalent lanthanide complexes have received considerable
attention due to their interesting magnetism [19,20], luminescent
properties [21] and potential applications including Ln-doped
spectroscopic and analytical methods. Molecular structure of
*
Corresponding author.
E-mail addresses: muhammetkose@ksu.edu.tr, muhammetkose1987@hotmail.
1
[
Ce(L )(NO
3
)
3
2
]∙H O
was determined by single crystal X-ray
com (M. K o€ se).
diffraction study.
http://dx.doi.org/10.1016/j.molstruc.2015.08.016
0
022-2860/© 2015 Elsevier B.V. All rights reserved.

34
M. K o€ se et al. / Journal of Molecular Structure 1101 (2015) 33e40
Fig. 1. Proposed structures of synthesized ligands.
2
. Experimental
d in ppm); 163.58 (C]O), 161.40 (C]N), 153.85 (CeOH), 147.12,
ꢁ
1
137.98, 130.36, 124.00, 120.62, 115.59 (aromatic). IR (KBr, cm ):
2.1. Materials
3502, 3222, 3073, 1629, 1606, 1577, 1557, 1512, 1492, 1456, 1362,
1
325, 1264, 1174, 1107, 1075, 927, 901, 847, 804, 761, 673. Mass
2
þ
All starting materials and organic solvents were purchased from
spect(ESI): m/z 426(100%) [L þNa] .
commercial sources and used as received unless otherwise noted.
,6-Diformylpyridine was prepared by oxidation of 2,6-
2
2.4. Synthesis of the Ce(III) complexes
pyridinedimethanol using manganese dioxide according to the
literature method [36].
To a stirring solution of the ligands (1 mmol) in MeOH (20 ml),
3 3 2
Ce(NO ) 6H O (1 mmol) was added and the reaction solution was
2
.2. Physical measurements
refluxed for 4 h. Clear orange solution was left for air evaporation.
After two days, an orange powder formed was collected by filtra-
tion and dried in air. Single crystals of [Ce(L1)(NO3)3]∙H2O suitable
for X-ray diffraction study were obtained from slow diffusion of
FT-IR spectra were performed using KBr pellets on a Perkin
Elmer Paragon 1000PC. CHN analysis was performed using a CE-
4
formed on a Bruker Avance 500. ESI mass spectra were recorded on
an ESI/MS Tandem mass spectrometry. The electronic spectra in the
2
UVeVis spectrophotometer. The single-photon fluorescence
spectra were collected on a Varian Cary Eclipse fluorescence
spectrometer.
Data collection for X-ray crystallography was completed using a
Bruker APEX2 CCD diffractometer and data reduction was per-
formed using Bruker SAINT. SHELXS97 was used to solve and
SHELXL2014/6 to refine the structure [37].
1
13
40 Elemental analyser. The H and C NMR spectra were per-
diethylether into a MeOH solution of the complex.
1
[Ce(L )(NO
3
)
N
3
]∙H
2
O: Orange, Yield:%78, Elemental analysis:
12Ce (F.W.:717.51): C, 31.80; H, 2.39; N, 19.52.
Calc. for C19
H
17
10
O
ꢁ
1
00e900 nm range were obtained on a Shimadzu UV-1800
Found: C, 31.11; H, 2.14; N, 18.95%. IR (KBr, cm ): 3495, 2984, 1644,
1573, 1554, 1481, 1445, 1379, 1280, 1166, 1108, 1089, 1066, 1027, 951,
ꢁ3
925, 852, 817, 734, 693, 547, 520.
^
m
(MeOH, 10
M):
ꢁ
1
2
ꢁ1
4.25
[Ce(L )(NO
ysis: Calc. for C21
U
cm mol .
2
3
)
3
]∙H
2
O: color: Orange, Yield: %80, Elemental anal-
17 8
H N O13Ce (F.W.:747.53): C, 33.74; H, 2.56; N,
ꢁ1
14.99. Found: C, 33.12; H, 2.21; N, 14.31%. IR (KBr, cm ): 3243,
3074, 1620, 1601, 1581, 1557, 1507, 1456, 1373, 1293, 1263, 1180, 1115,
1
m
033, 943, 914, 850, 758, 742, 692, 624, 550, 523. ^ (MeOH,
1
2
ꢁ3
ꢁ1
2
ꢁ1
2
.3. Synthesis of ligands L and L
10 M): 5.48
U
cm mol .
Pyridine-4-carbohydrazide
or
4-hydroxybenzohydrazide
2.5. X-ray structure solution and refinement
(
(
10 mmol) was added to a solution of 2,6-diformylpyridine
5 mmol) in MeOH (20 ml). Resulting solution was then refluxed
Data for complex [Ce(L1)(NO3)3]∙H2O was collected at 150(2) K
on a Bruker ApexII CCD diffractometer using Mo-K radiation
¼ 0.71073 Å). Data reduction was performed using Bruker SAINT
for 4 h. Upon cooling to the room temperature, a white precipitate
formed was filtered and dried in air.
a
(l
1
2
L : color: white, Yield: %92, Elemental analysis: Calc. for
[38]. The structure was solved by direct methods and refined on F
C
19
H
15
N
7
O
2
∙2H
Found: C, 54.93; H, 4.45; N, 23.18%. H NMR (DMSO-d
in ppm); 11.92 (s, 2H, NH), 10.44 (s, 2H, OH), 8.64 (s, 2H, CH]N),
.99 (t, 1H, CH pyridine), 7.93 (d, 2H, CH pyridine), 7.84 (d, 4H, CH
2
O (F.W.:409.398): C, 55.74; H, 4.68; N, 23.95.
using all the reflections. All the non-hydrogen atoms were refined
using anisotropic atomic displacement parameters and hydrogen
atoms bonded to carbon atoms were inserted at calculated posi-
tions using a riding model. The crystal used in the measurement
was a racemic twin, with approximately equal twin components.
Hydrogen atoms bonded to the nitrogen atom (N3) and water
molecule (O7) were located from difference maps and refined with
temperature factors riding on the carrying atoms. One of the nitrate
ions in the structure is highly disordered and this was modeled over
two positions. Details of the crystal data and refinement are given
in Table 1.
1
6
as solvent,
d
7
13
aromatic), 6.94 (d, 4H, CH aromatic). C NMR (DMSO-d
d
6
as solvent,
in ppm); 163.46 (C]O), 160.25 (C]N), 148.15, 136.78, 129.38,
ꢁ
1
122.10, 119.62, 114.65 (aromatic). IR (KBr, cm ): 3401, 3104, 2891,
1662, 1603, 1554, 1492, 1455, 1410, 1322, 1298, 1221, 1146, 1061, 992,
9
63, 887, 842, 799, 746, 675. Mass spect(ESI): m/z 396(40%)
1
þ
þ
[L þNa] , 279(100%) [C14
H
11
N
6
O] .
L : color: white, Yield: %95, Elemental analysis: Calc. for
∙2H O (F.W.:439.421): C, 57.40; H, 4.82; N, 15.94.
2
C
21
H
17
N
5
O
4
2
1
Found: C, 57.11; H, 4.48; N, 15.21%. H NMR (DMSO-d
in ppm); 11.94 (s, 2H, NH), 10.24 (s, 2H, OH), 8.59 (s, 2H, CH]N),
.94 (t, 1H, CH pyridine), 7.96 (d, 2H, CH pyridine), 7.86 (d, 4H, CH
6
as solvent,
3. Result and discussion
d
7
In this work, two pentadentate Schiff base ligands and their
Ce(III) complexes were prepared and characterized by
13
6
aromatic), 6.91 (d, 4H, CH aromatic). C NMR (DMSO-d as solvent,

M. K o€ se et al. / Journal of Molecular Structure 1101 (2015) 33e40
35
Table 1
nitrogen and carbonyl oxygen atoms with the Ce(III) ion. The nitrate
group stretching frequencies were observed as split bands at the
1444e1280 cm suggesting at least one of three nitrate ions co-
Crystallographic data for the Ce(III) complex.
ꢁ1
Empirical formula
Formula weight
Crystal size (mm )
Crystal color
Crystal system
Space group
Unit cell a (Å)
b (Å)
C
19
H
17CeN10
O
12
717.55
0.27 ꢂ 0.25 ꢂ 0.04
Yellow
Monoclinic
C2
10.7314(14)
13.3180(18)
10.4986(14)
90
115.1852(17)
90
1357.8(3)
2
1.755
6221
ordination to the metal as a bidentate ligand. X-ray structure
3
1
analysis of [Ce(L )(NO
3
)
3
]∙H
2
O showed that all three nitrate ions
bind to Ce(III) as bidentate chelating ligands. The occurrence of the
ꢁ
1
1
bands at 520e547 and 523e550 cm for [Ce(L )(NO
3
)
3
]∙H
2
O and
2
[Ce(L )(NO ) ]∙H O associated with CeeO and CeeN vibrations,
3 3 2
respectively, supports the involvement of the nitrogen and oxygen
atoms in the coordination sphere of Ce(III) ions.
c (Å)
ꢀ
a
b
g
( )
ꢀ
The ESI spectrum of the ligands and their Ce(III) complexes were
( )
1
ꢀ
( )
investigated in MeOH. The ESI mass spectrum of the ligands (L and
3
2
Volume (Å )
Z
L ) showed signals at m/z 396(40%) and 426(100%) assigned to
1
2
molecular ion signals for [L þNa]þ and [L þNa], respectively
Abs. coeff. (mmꢁ1)
Refl. collected
(
Figs. S4&S5). The mass spectra of the complexes show several
¼ 28.33ꢀ
fragmentation signals and molecular ion signals were not observed
Completeness to
Ind. Refl. [Rint
R1, wR2 [I > 2
R1, wR2 (all data)
CCDC number
q
99.6%
]
s
3278 [0.0272]
0.0338, 0.0751
0.0351, 0.0761
1404489
for the complexes.
1
(I)]
Molar conductance value of the complexes [Ce(L )(NO
3
)
3
]∙H
2
O
2
ꢁ3
3 3 2
and [Ce(L )(NO ) ]∙H O in MeOH (10 M) were found to be 4.25
ꢁ ꢁ1
1
2
and 5.48
U
cm mol , respectively, indicating the nonelectrolyte
nature of the complexes in MeOH solution. The conductivity results
of the complexes show that the nitrate ions are present in the co-
ordination sphere in MeOH solution.
spectroscopic and analytical methods. Elemental analysis data of
the ligands and their Ce(III) complexes are well agreed with the
theoretical values. The purity of the ligands was checked by
Thermal behavior of the Schiff base ligands and their Ce(III)
complexes metal complexes were studied under nitrogen atmo-
1
13
ꢀ
elemental analysis, He C NMR spectra and ESI mass spectrum. In
sphere in the temperature range of 20e800 C. The thermal curve
1
1
the H NMR spectra of the ligands, azomethine group hydrogen
for the complex [Ce(L )(NO
3
)
3
]∙H
2
O is shown in Fig. 5 and rest of
1
2
atoms were observed at
d
8.64 and 8.59 ppm for L and L ,
11.92 and 11.94 ppm are due to the
the spectra are given in the supplementary file (Figs. S6eS8). The
1
respectively. Broad signals at
d
TG curve of L shows three decomposition steps and the molecular
1
2
ꢀ
NH group protons. In H spectrum of L , phenolic protons (Ph-OH)
were observed at 10.24 ppm. Aromatic proton signals were seen
at 7.99e6.94 ppm range for both ligands. In the C NMR spectra
backbone of the compound is thermally stable up to about 200 C.
ꢀ
d
The first decomposition stage appeared at 30e150 C for Cu(II)
13
d
complex, with a mass loss 3.54%, accompanied by an endothermic
ꢀ
of the ligands, the number of carbon atom signals is well agreed
peak with Tmax ¼ 110 C on the DTA curve, may be attributed to the
with their proposed structures. The carbon atoms of the carbonyl
removal of absorbed two molecules of water. In the second
decomposition step approximately 65.26% of the other organic
1
groups (C]O) were observed at
d 163.58 and 163.46 ppm, for L
2
ꢀ
and L , respectively. The azomethine group carbon atom signals
moiety decomposed within the temperature range of 200e600 C
1
2
ꢀ
were seen at
d
161.40 and 160.25 ppm, for L and L , respectively. All
with an endothermic peak in this region (Tmax ¼ 280 C). Rest of the
the other carbon atoms signals for both ligands were shown in the
organic residue decomposes gradually up to high temperature. The
1
13
2
1
range of
d
148.15 and 114.65 ppm. H and C NMR spectra of L are
complex [Ce(L )(NO
3
)
3
]∙H
2
O is thermally more stable than its free
1
given in Fig. S1 and Fig. 2, respectively.
ligand L . Thermal decomposition of the complex also contains
Two mononuclear Ce(III) complexes were prepared by the re-
action of one equivalent Schiff base ligand and one equivalent
three decomposition steps. In the first decomposition step, a water
ꢀ
molecule in the structure was lost in the range of 30e150 C. The
ꢀ
Ce(NO
3
)
3
6H
2
O in a refluxing MeOH solution. The orange colored
structure of the complex is stable up approximately 220 C. In the
complexes are stable at room temperature in the solid state without
decomposition. The complex is soluble in common organic solvents
such as MeOH, EtOH, acetonitrile, DMF and DMSO, partially soluble
in chloroform and dichloromethane, not soluble in diethylether.
The formation of the Schiff base ligands and their Ce(III) complexes
is supported by IR spectroscopy. The IR spectra of the Ce(III) com-
second step of thermal decomposition, about 44.63% mass of the
ꢀ
complex was lost in the range of 220e400 C accompanied by an
ꢀ
endothermic peak with Tmax ¼ 290 C. Rest of the organic residue of
ꢀ
the complex was lost between 400 and 700 C. No further weight
ꢀ
loss was observed above 700 C leaving metal oxides as a final
2 2 3
residue (CeO , Ce O ).
ꢁ
1
2
plexes taken in the 4000e450 cm region are very similar to one
another suggesting the same bonding fashion of the ligands in
these complexes. The infrared spectral data of the ligands and their
Ce(III) complexes are given in the experimental section, IR spectra
The thermal decomposition of the ligand L starts at around
ꢀ
300 C and approximately 35.04% of mass was lost in the range of
ꢀ
200e550 C with an endothermic peak in this region (Tmax ¼ 360).
Thermal decomposition of the ligand continues up to high tem-
1
ꢀ
2
of the ligand L and its Ce(III) complex are shown in Figs. 3 and 4,
peratures (˃800 C). Thermal study indicated that the ligand L is
2
1
respectively, and rest of the IR spectra of L and its Ce(III) complex
thermally more stable than L . This may be due to two extra
are given in supplementary file (Figs. S2&S3). In the IR spectra of
phenolic groups present involved in hydrogen bonding with
1
2
ꢁ1
the ligands L and L , the sharp bands at 1662 and 1629 cm were
assigned to O) vibrations, respectively. The broad bands in the
range of 3502 and 3104 cm were can be assigned to
(NeH) stretches, respectively. In the spectra of the Schiff base li-
neighboring molecules increasing the thermal stability. The com-
2
n
(C
]
plex [Ce(L )(NO
3
)
3
]∙H
2
O showed about 3.28% weight loss in the
ꢁ1
ꢀ
n
(OeH) and
range of 30e150 C due to an absorbed water molecule in the
n
structure. Approximately half of the total mass was lost between
ꢀ
gands, characteristic azomethine
n
(CH
2
]
N) vibration was observed
320 and 500 C. Also, the DTA curve shows an endothermic peak at
ꢁ1
1
ꢀ
at 1603 and 1606 cm , for L and L , respectively. In the spectra of
T
max ¼ 365 C in this region. Rest of the organic moiety was grad-
1
2
ꢀ
the complexes [Ce(L )(NO
methine N) and carbonyl group
ward lower wavenumbers confirming coordination of azomethine
3
)
3
]∙H
2
O and [Ce(L )(NO
3
)
3
2
]∙H O azo-
ually removed from the structure up to 800 C and no further
weight loss was observed above this temperature leaving about
n
(CH
]
(C
n ]
O) vibrations shifted to-
2 2 3
28% of total mass as a final residue (metal oxides CeO , Ce O ).

36
M. K o€ se et al. / Journal of Molecular Structure 1101 (2015) 33e40
Fig. 2. 13C NMR spectrum of L2.
1
3
.1. X-ray structure of complex [Ce(L )(NO
3
)
3
]∙H
2
O
space group with unit cell parameters a ¼ 10.7314(14), b ¼ 13.3180
3
ꢀ
(
18), c ¼ 10.4986 (14) Å,
b
¼ 115.1852 (17) , V ¼ 1357.8 (3) Å and
Single crystals of the complex suitable for X-ray diffraction
study were obtained by slow evaporation of a MeOH solution of the
complex. The complex was found to crystallize as [Ce(L )(NO
Z ¼ 2. The complex lies across a twofold crystallographic axis with
the Ce1, N1, C1, N5, O5, O6 atoms sitting on this axis. Molecular
structure of the complex molecule is shown in Fig. 6. All bond
lengths and angles are within the normal ranges. Selected bond
1
3 3
) ]
∙H
2
O. The complex crystallizes in monoclinic crystal system, P2 /n
1
Fig. 3. FTIR spectrum of L1.

M. K o€ se et al. / Journal of Molecular Structure 1101 (2015) 33e40
37
1
Fig. 4. FTIR spectrum of [Ce(L )(NO
3
)
3
]∙H
2
O.
lengths are listed in Table 2. In the complex, each Ce(III) ion is 11-
3 2
coordinated and the ligand bind to the Ce(III) ion with N O
donor set group (two imine nitrogen, one pyridine nitrogen and
two carbonyl group oxygen atoms). All three nitrate ions coordinate
to the metal ion as bidentate ligands. The CeeO bond distances are
longer than the CeeN bond distances as expected. The N2eC4 and
O1eC5 distances of 1.256(13) and 1.261(17) Å exhibits a typical C]
N and C]O double bond characters respectively.
1
Fig. 5. Thermal curves for [Ce(L )(NO
3
)
3 2
]∙H O.

38
M. K o€ se et al. / Journal of Molecular Structure 1101 (2015) 33e40
1
3 3 2
Fig. 7. Packing diagram of [Ce(L )(NO ) ]∙H O showing hydrogen bond network.
Hydrogen atoms bonded to carbon atoms are not shown for clarity.
1
3 3 2
Fig. 6. Molecular structure of the complex [Ce(L )(NO ) ]∙H O.
Water molecules in the structure make two types of hydrogen
Table 3
1
ꢀ
bonding linking complex molecules. First, water molecules involve
in hydrogen bonding with one of the oxygen atom of a nitrate ion
and pyridine nitrogen atom as donor. Second, NH group of the
ligand makes intermolecular hydrogen bond with water molecule
Hydrogen bonds for [Ce(L )(NO
3
)
3
]∙H
2
O [Å and ].
D-H … A
d(D-H)
d(H … A)
d(D … A)
<(DHA)
N(3)-H(3) … O(7)i
O(7)-H(7B) … O(6)
O(7)-H(7B) … O(6A)
O(7)-H(7A) … N(6)
0.88
0.84
0.84
0.83
2.04
1.99
2.04
1.90
2.849(11)
2.80(3)
2.80(3)
152.3
163.4
152.2
163.0
ii
(
NH∙∙∙∙∙OH
2
). These intermolecular hydrogen bonding contacts
ii
are extended between the other symmetry-related molecules in
their respective planes to form a 3D hydrogen bond network
Fig. 7). Hydrogen bond parameters are listed in Table 3. Hydrogen
2.700(7)
i: ꢁxþ1/2,yþ1/2,ꢁzþ1 ii: xꢁ1,y,zꢁ1.
(
bonded complex molecules further connected with in-
p-p
teractions. The C1eC2 atoms of central pyridine ring are stacked
with the C5*eC6* section of an adjacent molecule under symmetry
operation of 3/2 e x, 1/2 þ y, 2 e z. The C1eC5* and C2eC6* atoms
are separated by distances of 3.493 and 3.447 Å, respectively. These
interactions are shown in Fig. 8.
band was shown in the 300e350 nm range. Excitation at 320 nm
caused the Schiff base ligand L to emit at an emission maximum of
1
547 nm (Fig. 9). This emission can be attributed to p-p* transitions
1
of the ligand. In the spectra of the complex [Ce(L )(NO ) ]∙H O,
3
3
2
both excitation and emission bands shifted to shorter wavelengths
(
hypsochromic effect). Although, there is no change in the intensity
1
1
3 3 2
of excitation bands of the ligand L and [Ce(L )(NO ) ]∙H O,
3
.2. UVeVis and photoluminescence properties
emission intensity of the complex shifted to higher values. The
1
complexation of Ce(III) ion with L effected some electrons of atoms
The UVeVis absorption spectra of the Schiff base ligands and
2
2
or component of the ligand. The ligand L and [Ce(L )(NO
3 3 2
) ]∙H O
their Ce(III) complexes were investigated in the range of
ꢁ
4
complex exhibit similar excitation and emission spectra to the
2
00e800 nm in MeOH (10 M) (Fig. S9). Absorption spectra of
1
2
both ligands L and L2 show only one absorption band in the
50e350 nm range and this was assigned to the * transitions of
the ligands. In the absorption spectra of the complexes these
1
ligand
[
5
L
and its Ce(III) complex. Both the ligand
]∙H complex show an emission band at
00e550 nm range upon excitation at 280e350 nm. The excitation
L
and
2
Ce(L )(NO
3
)
3
2
O
2
p-p
p-p*
2
and emission spectra of L show no significant change upon
complexation with Ce(III) ion (Fig. 9).
transition shifted to lower wavelength values (red shift). In the
spectra of Ce(III) complexes, new absorption bands appeared at
3
The effect of the solution concentration on photoluminescence
40e450 nm and these new bands were attributed to metaleligand
ꢁ5
ꢁ7
properties were studied (1 ꢂ 10 ꢁ1 ꢂ 10 M) (Figs. S10&S11).
The emission wavelengths of the ligands their Ce(III) complexes
were shifted to lower and higher values when different
(
MeL) charge transfer. No metal induced transitions were observed
at the concentrations studied.
The photoluminescence spectra for the Schiff base ligands and
their Ce(III) complexes investigated at room temperature on a
Varian Cary Eclipse fluorescence spectrometer. All samples were
prepared in MeOH and analyzed in a 1 cm optical path quartz
cuvette [39]. The emission and excitation spectra of the ligands and
1
2
ꢁ5
metal complexes L and L in MeOH (10 M) are shown in Fig. 9
and the obtained data are given in Table 4.
1
In the excitation spectra of the L ligand in MeOH, one excitation
Table 2
1
Selected bond lengths [Å] for [Ce(L ) (NO
3
3
) ]∙H
2
O.
Ce(1)-O(1)
Ce(1)-N(2)
Ce(1)-N(1)
Ce(1)-O(2)
2.625(6)
2.747(8)
2.765(11)
2.580(4)
Ce(1)-O(4)
Ce(1)-O(6)
O(1)-C(5)
N(2)-C(4)
2.569(4)
2.57(3)
1.261(12)
1.256(10)
1
Fig. 8.
p
-
p
interactions within the structure of [Ce(L )(NO
3
)
3
]∙H
2
O. Hydrogen atoms
are not shown for clarity.

M. K o€ se et al. / Journal of Molecular Structure 1101 (2015) 33e40
39
Fig. 9. Excitation and emission spectra of the ligands and their Ce(III) complexes.
concentrations were used. The emission intensities shifted to
ꢁ7
higher values when concentrations increased from 1 ꢂ 10 to
ꢁ
5
1
1
ꢂ 10 M. In the spectrum of the ligand L , the increase in the
Table 4
concentration results in a blueshift in the emission band.
Photoluminescence data for the synthesized compounds.
max
(l )
4. Conclusion
ꢂ 10ꢁ
5
1 ꢂ 10ꢁ6
1 ꢂ 10ꢁ7
1
Exc.
Em.
Exc.
Em.
Exc.
Em.
In this study, two pentadentate Schiff base ligand and their
L1
Ce(III) complexes were synthesized. The structures of the synthe-
320
300
325
326
547
525
550
526
325
305
320
320
550
570
568
525
310
320
324
332
555
571
545
518
1
[
L
Ce(L )(NO
3
)
3
3
]∙H
]∙H
2
O
O
sized compounds were characterized by analytical and spectro-
2
1
scopic methods. Molecular structure of complex [Ce(L )(NO
3
)
3
]
2
[Ce(L )(NO
3
)
2
∙H
2
O was determined by single crystal X-ray diffraction technique.
Exc: Excitation Em: Emission.
In the complex, the Ce(III) ion is 11-coordinated by eight O atoms,

40
M. K o€ se et al. / Journal of Molecular Structure 1101 (2015) 33e40
six of which come from three nitrate ions, two from the Schiff base
ligand. The ligand L1 behaves as pentadentate ligand with N
donor set group (two imine nitrogen, one pyridine nitrogen and
two carbonyl group oxygen atoms) and the Ce(III) sits in the acyclic
cavity. Excitation and emission spectra of the prepared compounds
were studied.
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Supplementary information
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CCDC 1404489 contains the supplementary crystallographic
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