Synthesis, characterization and photoluminescence studies of new Cu(II) complex

Article abstract of DOI:10.1080/15421406.2017.1358013

In the current work, a new coordination complex, [Cu(HL)₂], 1 [H₂L = 2–((E)–(2–hydroxypropylimino)methyl)–4–nitrophenol] was successfully synthesized and characterized by IR, UV-vis and photoluminescence spectroscopic techniques, single crystal and powder X-ray diffraction measurements. In the crystalline structure of complex 1, the aliphatic –OH group of the ligand is not coordinated and points away from the metal coordination zone, and also actively participates in intermolecular bifurcated O?H...O hydrogen bonds which link the molecules to form hydrogen-bonded linear chains. C?H...π and π...π contacts also connect the molecules in the structure which form to 3D structure. This hydrogen bonded polymeric networks lie in the bc-plane and stacks along to the a-axis. Furthermore, complex 1 and its ligand H₂L display an intense navy-blue emission and blue emission in the solid state at room temperature, respectively, when they are excited under UV light.

Full text of DOI:10.1080/15421406.2017.1358013

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Synthesis, characterization and
photoluminescence studies of new Cu(II) complex
Adem Donmez, M. Burak Coban, Cagdas Kocak, Gorkem Oylumluoglu, Ulrich
Baisch & Hulya Kara
To cite this article: Adem Donmez, M. Burak Coban, Cagdas Kocak, Gorkem Oylumluoglu, Ulrich
Baisch & Hulya Kara (2017): Synthesis, characterization and photoluminescence studies of new
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Date: 21 September 2017, At: 21:05

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
https://doi.org/./..
Synthesis, characterization and photoluminescence studies of
new Cu(II) complex
Adem Donmeza,b, M. Burak Cobanc,d, Cagdas Kocaka, Gorkem Oylumluoglua,
Ulrich Baische,f, and Hulya Karaa,c
aDepartment of Physics, Molecular Nano-Materials Laboratory, Mugla Sitki Kocman University, Mugla, Turkey;
bScientific Research Projects Coordination Unit, Mugla Sitki Kocman University, Mugla, Turkey; cDepartment of
Physics, Balikesir University, Balikesir, Turkey; dCenter of Sci and Tech App and Research, Balikesir University,
Balikesir, Turkey; eDepartment of Chemistry, University of Malta, Msida, Malta; fSchool of Chemistry, Newcastle
University, Bedson Building, Newcastle upon Tyne, UK
ABSTRACT
KEYWORDS
Copper(II) complex; crystal
structure;
photoluminescence
In the current work, a new coordination complex, [Cu(HL)2], 1 [H2L = 2–
((E)–(2–hydroxypropylimino)methyl)–4–nitrophenol] was successfully
synthesized and characterized by IR, UV-vis and photoluminescence
spectroscopic techniques, single crystal and powder X-ray diffraction
measurements. In the crystalline structure of complex 1, the aliphatic
–OH group of the ligand is not coordinated and points away from the
metal coordination zone, and also actively participates in intermolec-
ular bifurcated O−H···O hydrogen bonds which link the molecules to
form hydrogen-bonded linear chains. C−H···π and π···π contacts also
connect the molecules in the structure which form to 3D structure. This
hydrogen bonded polymeric networks lie in the bc-plane and stacks
along to the a-axis. Furthermore, complex 1 and its ligand H2L display
an intense navy-blue emission and blue emission in the solid state at
room temperature, respectively, when they are excited under UV light.
1. Introduction
Schiff bases are considered as a very important class of organic compounds because of their
ability to form complexes with transition metal ions and widely used for industrial purposes
[1–6]. Due to having great interesting properties of Salen-type schiff-bases metal complexes,
they could be found various potential applications areas in the literature [7–10]. These appli-
cation and usage areas can ordered as single-molecule magnets (SMMs), luminescent probes,
catalyst in cleavage reactions for specific biological components as like DNA and RNA, non-
linear optics and as a performance enhancer of absorber or buffer layer in photovoltaic devices
[11–20].
The beneficial effect of transiton metal compounds on the crystal structure and photolu-
minescence properties of the new designed Schiff bases derived from salicylaldehyde and its
derivatives have been a subject of magnificent interest since its discovery [5]. It can be easily
seen that Schiff base complexes is used as materials during growthing OLEDs [21–23] and
is used as fluorescent sensors for the detection of certain metal ions [24] due to the having
CONTACT Dr. Adem Donmez
adonmez@mu.edu.tr
Mugla Sitki Kocman University, Mugla, , Turkey.
Department of Physics, Molecular Nano-Materials Laboratory,
©  Taylor & Francis Group, LLC

2
A. DONMEZ ET AL.
an interesting luminescence properties. One of the most promising candidates of this kind
of complexes are Schiff-base copper complexes. Since copper(II) quenches luminescence, the
examples of copper(I,II) and copper(II) luminescent complexes are rather scarce [25–27].
Over the last years, our research group and others have reported the synthesis, electronic-
optic and magnetic properties of Cu(II) complexes containing ONNO, ONO and NNO type
Schiff base ligands [28–32], but still there is need to explore the photoluminesence properties
of these complexes and to synthesize new complexes with more properties. In view of these
findings and in an effort to enlarge the library of such complexes, we report herein the syn-
thesis, structural characterizations and photoluminescence studies of new Schiff base Cu(II)
complex, [Cu(HL)2], 1.
2. Experimental
2.1. Materials and physical measurements
All chemical reagents and solvents were purchased from Sigma Aldrich and used without
further purification. Elemental (C, H, N) analyses were carried out by standard methods with
a LECO, CHNS–932 analyzer. Solid state UV-visible spectra were measured at room tem-
perature with an Ocean Optics Maya 2000Pro Spectrophotometer. FT-IR spectra were mea-
sured with a Perkin-Elmer Spectrum 65 instrument in the range of 4000–500 cm−1. The solid
state UV-vis spectra were determined by Ocean Optics Maya 2000Pro Spectrometer (230–
550 nm). Solid state photoluminescence spectra in the visible region were measured at room
temperature with an ANDOR SR500i-BL Photoluminescence Spectrometer, equipped with
a triple grating and an air-cooled CCD camera as detector. The measurements were done
using the excitation source (349 nm) of a Spectra-physics Nd:YLF laser with a 5 ns pulse
width and 1.3 mJ of energy per pulse as the source. Powder x-ray diffraction (PXRD) patterns
were recorded on a Bruker-AXS D8-Advance diffractometer by using Cu-Kα radiation (λ =
˚
1.5418 A) in the range 5° < 2θ < 50° in θ-θ mode with a step ns (5 s < n < 10 s) and step width
of 0.03°. Comparison between experimental and calculated (from CIF’s) PXRD patterns was
performed with Mercury 3.8 [33].
X-ray single crystal data for complex 1 was collected on an Oxford Diffraction Gemini
˚
a Ultra diffractometer at 150 K using MoKα radiation (λ = 0.71073 A). The data were col-
lected for Lorentz, polarization and absorption effects using the analytical numeric absorp-
tion correction technique [34]. The structures were solved by direct methods using SHELXS
[35] and refined by full-matrix least-squares based on |Fobs|2 using SHELXL [35]. The non-
hydrogen atoms were refined anisotropically, while the hydrogen atoms, generated using ide-
alized geometry, were made to “ride” on their parent atoms and used in the structure factor
calculations. Details of the supramolecular π-interactions were calculated PLATON 1.17 pro-
gram [36].
2.2. Synthesis of Schiff base ligand, H2L
The Schiff base ligand, H2L was synthesized by the reaction of 2-hydroxy-5-
nitrobenzaldehyde (1 mmol, 0.167 g) with 3-amino-1-propanol (1 mmol, 0.075 g) in
hot methanol (50 ml). The solution was stirred at 65°C for 30 min. The yellow product of
the ligand precipitated from the solution on cooling. H2L: Yellow compounds, yield 80%.
Anal. Calcd. for C10H12N2O4 (%): C, 53.57; H, 5.39; N, 12.49. Found (%): C, 53.54; H, 5.37;
N, 12.46.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
3
Scheme . The synthetic route of complex 1 evaluated in this study.
2.3. Synthesis of Complex 1
Complex 1 was prepared by addition of copper(II) acetate monohydrate (0.199 g, 1 mmol) in
hot methanol (30 cm3) to the ligand (H2L) (0.224 g, 1 mmol) in hot ethanol (30 cm3). The
resulting solution was filtered rapidly and then allowed to stand at room temperature. Several
weeks of standing led to the growth of clear green crystals of complex 1 suitable for the X-ray
analysis. The synthetic route of the complex 1 is outlined in Scheme 1. Complex 1: Clear green
crystals, yield 70%. Anal. Calcd. for C20H22CuN4O8 (%): C, 47.10; H, 4.35; N, 10.99. Found
(%): C, 47.20; H, 4.39; N, 10.96.
3. Results and discussion
3.1. X–ray structure of 1
The crystal data and structure refinement details for complex 1 are listed in Table 1. Selected
bond lengths and angles for the complex 1 are given in Table 2. A perspective ORTEP view
with the atom labelling scheme of complex 1 is shown in Fig. 1 while packing diagrams are
given in Fig. 2 and 3.
The complex 1 crystallizes in the monoclinic space group P21/c and its asymmetric unit
consists of a half of the monomeric [Cu(HL)2] unit. The CuII atom is chelated by two bidentate
Schiff base ligands by using two imine nitrogen and two phenolate oxygen atoms in a mutual
˚
trans disposition. In the equatorial plane, the bond lengths are Cu–Oalk = 1.908 (5) A and
II
˚
Cu–Nimi = 2.009 (5) A. As usually observed for four coordinate Cu ion will include addi-
i
ii
˚
tional weak interactions with axial atoms, Cu1–O1 alk = 3.322 (5) A and Cu1–O1 alk = 3.322
˚
(5) A [i = 1 + x, y, z, ii = 1 −x, 1 −y, 1 −z]. If this weak Cu···O interaction are considered as
part of the coordination geometry of the CuII ion, the geometry of CuII atom is best described
as octahedral coordination with Jahn-Teller distortion. The bond lengths and angles lie well
within the range of corresponding values reported for other mononuclear copper(II) com-
plexes [28–32, 37].

4
A. DONMEZ ET AL.
Table . Crystal data and structure refinement for complex 1.
Chemical Formula
Formula weight (g mol–)
Crystal system
CHCuNO
.
Monoclinic
P/c
Space group
˚
Unit cell dimensions
a = . () A α = °
˚
b = . () A β = . ()°
˚
c = . () A γ = °

˚
V / A
. ()
Z

ρcalc / g cm−
.
.
μ/mm−
Temperature (K)
Reflections collected
Independent reflections
Goodness–of–fit on F
R indices [I > σ(I)]
.


.
R = ., wR = .
˚
Table . Some selected bond lengths [A] and angles [°] for complex 1.
Cu—O
. ()
. ()
. ()
. ()
Cu—N
. ()
. ()
. ()
Cu—Oii
Oi—Cu—N
Oii—Cu—N
O—Cu—N
Oii—Cu—O
Symmetry code: (i) −x + , −y + , −z + , (ii)  + x, y, z
Figure . ORTEPdrawingofcomplex1withatomlabelling. Thermalellipsoidshavebeendrawnat%prob-
ability level [Symmetry code: (i) −x + , −y + , −z + ].

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
5
Figure . A perspective view of one-dimensional chain structures, showing the intermolecular O−HꢀꢀꢀO
hydrogen bonds (dashed lines).
In the crystal structure of complex 1, the aliphatic –OH group of the Schiff base ligand
is not coordinated and points away from the metal coordination zone, and actively par-
ticipates in intermolecular bifurcated O−H···O hydrogen bonds which link the molecules
to form hydrogen-bonded linear chains (Fig. 2). The intermolecular CuII ··· CuII dis-
II
˚
tance is 12.541 A in this chain structure. Besides that, Cu atom is further linked into
a discrete monomeric unit by a pair of long weak Cu···O interactions which will con-
tribute a molecular stack along the a axis. The CuII ··· CuII distance within this stacking
˚
structure is 4.293 A. Besides that intermolecular C−H···π and π···π contacts also con-
nect the molecules in the crystal structure which form to 3D structures (Table 3). This
hydrogen bonded polymeric networks lie in the bc-plane and stacks along to the a-axis
(Fig. 3).
Figure . (a) The crystal packing view of the complex 1 in the bc plane (b) Showing the distance between
ring centroids for complex 1.

6
A. DONMEZ ET AL.
˚
˚
Table . Hydrogen bond geometry (A, °) and distance between ring centroids [A] for complex 1.
D−HꢀꢀꢀA∗
D−H
HꢀꢀꢀA
DꢀꢀꢀA
D−HꢀꢀꢀA
Symmetry
O−HꢀꢀꢀO
.()
.()
.()
.()
.()
.()
()
()
 + x,  + y, z
 + x,  + y, z
O−HꢀꢀꢀO
C–H···Cg(I)
C−HBꢀꢀꢀCg()
C−HBꢀꢀꢀCg()
.
.
Cg(I)···Cg(J)
.()
.()
.
.
Cg(I)_Perp
−.()
.()
.
.
Cg(J)_Perp
.()


 + x, y, z
 −x,  −y,  −z
Cg()···Cg()
 + x, y, z
Cg()···Cg()
−.()
− + x, y, z
∗D: Donor, A: Acceptor, Cg(I): Plane number I ( = ring number in () above), Cg(I)-Cg(J) = Distance between ring Centroids,
Cg(I)_Perp = Perpendicular distance of Cg(I) on ring J, CgJ_Perp = Perpendicular distance of Cg(J) on ring I, Cg(): Cu-O-C-
C-C-N, Cg(): C-C-C-C-C-C
3.2. X-ray powder diffraction pattern of 1
Before proceeding to the spectroscopic and photoluminescence characterization, we note that
experimental powder X-ray pattern for complex 1 are well in position with those of simulated
patterns on the basis of single crystal structure of complex 1 which is in agreement of their
single phase and purity (Fig. 4).
Figure . X-ray powder diffraction pattern of complex 1 (Black- simulated from CIFs, Blue Experimental).
3.3. IR and UV-Vis analysis
The IR and solid state UV-Vis spectra of complex 1 were shown in comparison with that of
its free ligand H2L which are in agreement with its single crystal structure analysis (Figs. 5
and 6).
As seen from Figure 5, the IR spectra of the free ligand and its complex 1 depicts peaks
in nearly similar region. However, some significant variations have been illustrated in the
spectra of the complex 1 and its free ligand H2L. The IR spectra of the free ligand H2L exhib-
ited the prominent broad band at 3274 cm−1 which could be attributed to (O-H) stretching
vibrations. This band is disappeared in complex 1 indicating deprotonation of the phenolic
hydroxyl group and coordination of phenolic oxygen to the metal ion [38]. The character-
–1
=
istic stretching vibrations for υ(C N) bond is shifted from 1659 cm (for ligand H2L) to
1626 cm–1 (for complex 1), which indicates the coordination of the imine nitrogen atom to

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
7
Figure . IR spectra of the free ligand H2L and its complex 1.
the Cu(II) center [39]. The symmetric and asymmetric stretching bands appeared at the range
of 1550–1405 cm−1 which attributed to the υ(C–NO2) for the free ligand and complex 1 [40].
As seen from Figure 6, the UV-Vis spectrum for the ligand H2L, a prominent broad absorp-
tion band appears at λmax = 374 nm which may be assigned to the π-π∗ transitions [41]. The
absorption spectra of the complex 1 displayed different absorption pattern as compared to
the ligand H2L. The absorption peak was observed with the maxima at 428 nm in the spec-
trum of complex 1, could be assigned to π-π∗ or n-π∗ transition of the its ligand H2L [42].
The shifting of absorption bands in the spectra of the complex 1 signifies the copper(II) ion
coordination with the ligand H2L [7].
Figure . The solid state UV-Visible spectra of the free ligand H2L and its complex 1.
3.4. Photoluminescence properties
Figure 7 depicts the solid-state photoluminescence emission spectra of the free ligand and its
complex 1 at ambient temperature in the visible regions. As seen from the Figure 7, the emis-
sion spectrum of the free ligand displayed a navy-blue emission peak at λmax = 480 nm which
may be assigned to the n→π∗ or π→π∗ electronic transition (ILCT) [38, 43, 44] whereas the
emission spectrum of complex 1 revealed intense blue emission peak at λmax = 433 nm upon
excitation at 349 nm. The observed blue shift of the emission maximum between the complex

8
A. DONMEZ ET AL.
Figure . Room temperature solid state photoluminescence spectrums of the free ligand H2L and complex
1 (Upper-left photo is photoluminescent image of complex 1 and upper-right photo is photoluminescent
image of ligand H2L, while excited at  nm.
1 and the free ligand H2L was considered to mainly originate from the influence of the coor-
dination of metal atom to the ligand. In addition, the increase of the luminescence intensity of
complex 1 as compared to its free ligand H2L, could be due to the fact that upon the formation
of metal complex, which effectively increases the “rigidity” of the ligand and thus reduces the
loss of energy via radiationless thermal vibrations [45–48].
4. Conclusions
The synthesis and structural characterization of a new Schiff base CuII complex, 1, has been
presented together with an investigation into its photoluminescence properties. Spectroscopic
techniques confirmed the metal ligand coordination and single x-ray results show that the
CuII atom is coordinated by two singly deprotonated Schiff base ligands (H2L) using ON
donors. The aliphatic –OH group of the ligand is not coordinated and points away from the
metal coordination zone. The intermolecular O−H···O hydrogen bonds link the molecules
which form 1D chains along b axis. And these chains are further interlinked via C−H···π and
π···π interactions resulting in 3D networks. Additionally, photoluminescence studies show
that under the excitation of UV light, intense navy-blue emission for complex 1 and blue emis-
sion for its free ligand H2L are exhibited in the visible regions. The luminescent performances
making this complex may be good candidates for potential luminescence materials.
Acknowledgements
The authors are grateful to Mugla Sitki Kocman University Research Projects Coordination Office
(BAP-2016/052) for the financial support. The authors also acknowledge to Balikesir University, Science
and Technology Application and Research Center (BUBTAM) for the use of the Photoluminescence
Spectrometer.
Supplementary data
Crystallographic data for the structure reported in this paper have been deposited with the Cam-
bridge Crystallographic Data Centre (The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK;

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
9
deposit@ccdc.cam.uk; www: http://www.ccdc.cam.ac.uk; and are available free of charge on request,
quoting the Deposition No. CCDC 1513023.
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