Syntheses, structural characterization, luminescence and optical studies of Ni(II) and Zn(II) complexes containing salophen ligand

Article abstract of DOI:10.1016/j.molstruc.2016.08.083

Some Ni(II) (1a-d) and Zn(II) (2a-d) salophen complexes were prepared by the treatment of 5-bromosalicylaldehyde, 5-(trimethylsilylethynyl)salicylaldehyde, 5-(4-nitrophenyl)ethynylsalicylaldehyde or 5-(4-methoxyphenyl)ethynylsalicylaldehyde with nickel acetate or zinc acetate followed by addition of 2,3-diamino-5-bromopyridine. All complexes were characterized by elemental analyses, IR, ¹H NMR and mass spectral studies. X-ray powder diffraction of representative complexes 1c and 2b and SEM studies of 1b and 2d are used to elucidate the crystal structure and morphology of the complexes. The electrochemical behavior reveals that the redox responses of Ni(II) complexes shifted to more negative potential in order to increase the π-conjugation in the complexes. Room temperature luminescence is observed for all complexes corresponding to π→π? ILCT transition with some MLCT character in DMF and is finely tuned by the degree of extended π-conjugation and variation of the substituent group with different electronic effects in the complexes. The second harmonic generation (SHG) efficiency of the complexes was screened by Kurtz-powder technique indicating that all complexes possesses promising potential for the application as a useful nonlinear optical material.

Full text of DOI:10.1016/j.molstruc.2016.08.083

Accepted Manuscript
Syntheses, structural characterization, luminescence and optical studies of Ni(II) and
Zn(II) complexes containing salophen ligand
M.S. More, S.B. Pawal, S.R. Lolage, S.S. Chavan
PII:
S0022-2860(16)30913-9
10.1016/j.molstruc.2016.08.083
MOLSTR 22909
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 13 May 2016
Revised Date: 31 August 2016
Accepted Date: 31 August 2016
Please cite this article as: M.S. More, S.B. Pawal, S.R. Lolage, S.S. Chavan, Syntheses, structural
characterization, luminescence and optical studies of Ni(II) and Zn(II) complexes containing salophen
ligand, Journal of Molecular Structure (2016), doi: 10.1016/j.molstruc.2016.08.083.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
Graphical Abstract:
Syntheses, structural characterization, luminescence and optical studies
of Ni(II) and Zn(II) complexes containing salophen ligand
M. S. More, S. B. Pawal, S. R. Lolage, S. S. Chavan*
Department of Chemistry, Shivaji University, Kolhapur (MS), India-416 004
Abstract
Some Ni(II) (1a-d) and Zn(II) (2a-d) salophen complexes have been prepared and characterized. X-ray
diffraction of 1c and 2b and SEM studies of 1b and 2d are used to elucidate the crystal structure and
morphology of the complexes. All complexes exhibit a distinct MLCT absorption band and shifted to
longer wavelength by increasing π-conjugation in the complexes. Room temperature luminescence is
observed for all complexes in DMF which is finely tuned by the degree of extended π-conjugation
and variation of the substituent group with different electronic effects in the complexes. The second
harmonic generation (SHG) efficiency of the complexes was screened by Kurtz-powder technique
indicating that all complexes possesses promising potential application as a useful NLO material.
Keywords: Ni(II)/Zn(II)-salophen complexes, photoluminescence, optical properties
Corresponding author: Tel.: +91 231 2609381; fax: +91 231 2691533.
E-mail: sanjaycha2@rediffmail.com

ACCEPTED MANUSCRIPT
Graphical Abstract: Pictogram
Br
Br
N
N
O
N
N
O
N
N
NI
Zn
R
O
R
R
O
R
(1a-d)
(2a-d)
R=Br, C≡CSi(CH
3
)
3
, C≡CC
H
6 4
2 6 4 3
NO , C≡CC H OCH

ACCEPTED MANUSCRIPT
Syntheses, structural characterization, luminescence and optical studies
of Ni(II) and Zn(II) complexes containing salophen ligand
M. S. More, S. B. Pawal, S. R. Lolage, S. S. Chavan*
Department of Chemistry, Shivaji University, Kolhapur (MS), India-416 004
Abstract
Some Ni(II) (1a-d) and Zn(II) (2a-d) salophen complexes were prepared by the treatment of 5-bromo
salicylaldehyde, 5-(trimethylsilylethynyl)salicylaldehyde, 5-(4-nitrophenyl)ethynylsalicylaldehyde or
5-(4-methoxyphenyl)ethynylsalicylaldehyde with nickel acetate or zinc acetate followed by addition
of 2,3-diamino-5-bromopyridine. All complexes were characterized by elemental analyses, IR,
1
H NMR and mass spectral studies. X-ray powder diffraction of representative complexes 1c and
2
b and SEM studies of 1b and 2d are used to elucidate the crystal structure and morphology of
the complexes. The electrochemical behavior reveals that the redox responses of Ni(II)
complexes shifted to more negative potential in order to increase the π-conjugation in the
complexes. Room temperature luminescence is observed for all complexes corresponding to
π→π* ILCT transition with some MLCT character in DMF and is finely tuned by the degree of
extended π-conjugation and variation of the substituent group with different electronic effects in
the complexes. The second harmonic generation (SHG) efficiency of the complexes was
screened by Kurtz-powder technique indicating that all complexes possesses promising potential
for the application as a useful nonlinear optical material.
Keywords: Ni(II)/Zn(II)-salophen complexes, photoluminescence, optical properties
Corresponding author: Tel.: +91 231 2609381; fax: +91 231 2691533.
E-mail: sanjaycha2@rediffmail.com
1

ACCEPTED MANUSCRIPT
1
. Introduction
Transition metal complexes with salophen type ligand have attracted enormous attention in
coordination chemistry due to their structural liability, unusual configuration and sensitivity towards
environment as a functional material [1-3]. The important feature of these system is that salophen
ligand offering a tetradentate chelating system to form a stable complexes and thus they have strong
π→π* intermolecular interactions. They are known to act as an efficient catalyst both in
homogeneous and heterogeneous reactions for asymmetric ring-opening of epoxides,
aziridination, cycloproponation, oxidation, reduction reaction of ketones, epoxidation of olefins,
formation of cyclic and linear polycarbonates, catalytic enantioselective and diasterioselective redox
reactions and Diels-Alder reactions [4-7]. They become an efficient entities to study the interactions
with DNA, leading to the development of sensitive chemical probes for DNA [8]. Applications of
transition metal-salophen complexes also have been explored in material sciences such as nonlinear
optical (NLO) properties due to their potential applications in optoelectronic devices of information
storage, telecommunications, signal processing etc. [9-11]. Moreover, they are known to act as an
excellent candidate as a luminescent material with possible utilization in solar energy conversion,
luminescent sensors, electroluminescent sensors and probes for biological systems [12-14]. The
source of their luminescence is due to the metal to ligand charge transfer (MLCT) excited state,
which is usually sensitive to molecular configuration and peripheral ligand. Owing to their wide
utility in various fields and its ability to act as polyfunctional ligand many studies on coordination
behavior of salophen ligand with transition metal ions have been carried out [15-17]. In recent years
considerable research efforts have been focused on incorporation of additional functionalities
into coordinating ligand which are reported to exhibit very interesting luminescent and optical
properties [18, 19]. The incorporation of additional functionality into coordinating ligand and
2

ACCEPTED MANUSCRIPT
their metal complexes was found to destabilize non-radiative d-d transitions to maintain the
structural integrity and thus displaying reasonable luminescence properties. Addition of alkynyl
functionality particularly, with a π-conjugation constitutes an important class of compounds as a
luminescent material due to their advanced electronic and structural properties [20]. An important
feature of these system is the structural modification which causes a larger π-delocalization over the
salophen ligand than that of the regular complexes. Moreover, rigidity of the structure and the dipole
moment of the complexes may thus increase.
Influenced by these facts and to study the effect of a π-conjugation and donor-acceptor
substituent's of salophen ligand, it was considered worthwhile to undertake synthesis of some
Ni(II) (1a-d) and Zn(II) (2a-d) salophen complexes by treatment of 5-bromosalicylaldehyde,
5
-(trimethylsilylethynyl)salicylaldehyde, 5-(4-nitrophenyl)ethynylsalicylaldehyde or 5-(4-methoxy
phenyl)ethynylsalicylaldehyde with nickel acetate or zinc acetate followed by addition of 2,3-diamino-
-bromopyridine. All the complexes have been characterized by elemental analysis and several
5
spectroscopic techniques. The photoluminescence, redox behavior and SHG efficiency of the
complexes have been reported.
2
. Experimental
2
.1. Materials and measurements
All chemicals used were of AR grade. Solvents used for synthesis were distilled over appropriate drying
reagents. 5-(trimethylsilylethynyl)salicylaldehyde, 5-(4-nitrophenyethynyl)salicylaldehyde and 5-(4-
methoxyphenyl)ethynylsalicylaldehyde were prepared by following the procedure reported in the
1
literature [21]. H NMR spectra were recorded on Bruker 300 MHz instrument using TMS [(CH ) Si] as
3
4
an internal standard and were reported with residual protons in the solvent as standard (d6-
methylsulfoxide, δ 2.50). ESI mass spectra were recorded on JEOL SX-102A spectrometer. Elemental
3

ACCEPTED MANUSCRIPT
analyses (C, H and N) were performed on a Thermo Finnigan FLASH EA-112 CHNS analyzer.
Absorption spectra were recorded on a Shimadzu UV–Vis–NIR-100 spectrophotometer. Infrared spectra
-1
were performed on a Perkin-Elmer FT-IR spectrometer using KBr pellets in the 4000-450 cm spectral
range. Thermal analysis of the complexes was carried out on a Perkin Elmer thermal analyzer in nitrogen
atmosphere at a heating rate of 10 °C/min. Luminescence properties were measured using a Perkin Elmer
fluorescence spectrometer LS-55. Luminescence lifetime measurements were carried out by using time-
correlated single photon counting from HORIBA Jobin Yvon. X-ray powder diffraction was carried out
by using D2 PHASER-X-ray powder diffractometer operated by using CuKα line at 1.54056 Å as the
radiation source. The surface morphology of prepared complexes were analyzed using scanning electron
microscope (SEM) in which the images were acquired by using the JEOL JSM-6360. Cyclic
voltammetry measurements were performed with a CH-400A electrochemical analyzer. A standard three
electrode system, consisting of Pt disk working electrode, Pt wire counter electrode and Ag/AgCl
reference electrode were used. All potentials were converted to SCE scale. Tetrabutyl ammonium
perchlorate (TBAP) was used as a supporting electrolyte and all measurements were carried out in DMF
-1
solution at room temperature with scan rate 100 mVs .
2
.2. Synthesis of Ni(II)-salophen complexes (1a-d)
5
-bromosalicylaldehyde (0.342 mmol, 0.0688 g), 5-(trimethylsilylethynyl)salicylaldehyde (0.342
mmol, 0.0747 g), 5-(4-nitrophenyl)ethynylsalicylaldehyde (0.342 mmol, 0.0915 g) or 5-(4-methoxy
phenyl)ethynylsalicylaldehyde (0.342 mmol, 0.0863 g) was first treated with Ni(OAc) . 4H O
2
2
(
0.171 mmol, 0.0426 g) and the mixture was stirred in CH Cl :THF (20 ml:10 ml) for 30 min. at room
2 2
temperature. 2,3-diamino-5-bromopyridine (0.171 mmol, 0.0322 g) in THF (10 ml) was added to
the resulting solution and the mixture was stirred overnight. The solvent was then removed by
vacuum and the solid complex precipitated was collected by filtration, washed with 1:1
ethanol:water mixture and dried under vacuum at room temperature.
4

ACCEPTED MANUSCRIPT
1
a: Yield: 78 %; elemental analyses (C, H and N, wt %) Anal. Calc. for C H N O Br Ni:
1
9
10
3
2
3
-1
C, 37.37; H, 1.65; N, 6.88 found: C, 37.18; H, 1.47; N, 6.93; IR (KBr, cm ): 1608, υ(HC=N);
1
1
293, υ(C-O); H NMR (d -DMSO, 300 MHz): δ 9.37 (s, 1H, HC=N), δ 9.16 (s, 1H, HC=N),
6
+
δ 6.65-8.67 (m, 8H, Ar-H); MS (ESI): m/z 633 (M+Na) . 1b: Yield: 82%; elemental analyses (C,
H and N, wt %) Anal. Calc. for C H N O BrSi Ni: C, 53.97; H, 4.37; N, 6.51; found: C, 53.79;
2
9
28
3
2
2
-1
1
H, 4.26; N, 6.58; IR (KBr, cm ): 2140, υ(C≡C); 1609, υ(HC=N); 1296, υ(C-O); H NMR (d -DMSO,
6
3
1
00 MHz):δ 9.35 (s, 1H, HC=N), δ 9.19 (s, 1H, HC=N), δ 6.67-8.29 (m, 8H, Ar-H), δ 0.26 (s,
+
8H, (CH ) Si); MS (ESI): m/z 668 (M+Na) . 1c: Yield: 79%; elemental analyses (C, H and N,
3
3
wt %) Anal. Calc. for C H N O BrNi: C, 56.57; H, 2.44; N, 9.42; found: C, 56.49; H, 2.37; N,
3
5
18
5
6
-1
1
9
.51; IR (KBr, cm ): 2201, υ(C≡C); 1615, υ(HC=N); 1334, υ(C-O); H NMR (d -DMSO, 300
6
MHz): δ 9.39 (s, 1H, HC=N), δ 9.14(s, 1H, HC=N), δ 6.75-8.69 (m, 16H, Ar-H); MS (ESI): m/z
+
7
66 (M+Na) . 1d: Yield: 77 %; elemental analyses (C, H and N, wt %) Anal. Calc. for
-1
C H N O BrNi: C, 62.31; H, 3.39; N, 5.89; found: C, 62.22; H, 3.27; N, 5.96; IR (KBr, cm ):
37
24
3
4
1
2
197, υ(C≡C); 1613, υ(HC=N); 1282, υ(C─O); H NMR (d -DMSO, 300 MHz): δ 9.38 (s, 1H,
6
HC=N), δ 9.13 (s, 1H, HC=N), δ 6.73-8.61 (m, 16H, Ar-H), δ 3.74 (s, 6H, OCH ); MS (ESI):
3
+
m/z 736 (M+Na) .
2
.3. Synthesis of Zn(II)-salophen complexes (2a-d)
5
-bromosalicylaldehyde (0.392 mmol, 0.0789 g), 5-(trimethylsilylethynyl)salicylaldehyde (0.392
mmol, 0.0856 g), 5-(4-nitrophenyl)ethynylsalicylaldehyde (0.392 mmol, 0.1049 g) or 5-(4-
methoxyphenyl)ethynylsalicylaldehyde (0.392 mmol, 0.0991 g) was first treated with Zn(OAc)2.
2
H O (0.196 mmol, 0.0431 g) and the mixture was stirred in CH Cl :THF (20 ml : 10 ml) for 30 min.
2
2
2
at room temperature. 2,3-diamino-5-bromopyridine (0.196 mmol, 0.0369 g) in THF (10 ml) was
added to the resulting solution and the mixture was stirred overnight. Then the solvent was
removed by vacuum and the solid complex precipitated was collected by filtration, washed with
1
:1 ethanol:water mixture and dried under vacuum at room temperature.
5

ACCEPTED MANUSCRIPT
2
a: Yield: 75 %; elemental analyses (C, H and N, wt %) Anal. Calc. for C H N O Br Zn:
1
9
10
3
2
3
-1
C, 36.96; H, 1.63; N, 6.81; found: C, 36.78; H, 1.57; N, 6.89; IR (KBr, cm ) : 1608, υ(HC=N);
1
1
279, υ(C-O); H NMR (d -DMSO, 300 MHz) : δ 9.36 (s, 1H, HC=N), δ 9.21 (s, 1H, HC=N),
6
+
δ 6.67-8.21 (m, 8H, Ar-H); MS (ESI): m/z 635 (M+Na) 2b: Yield: 69 %; elemental analyses (C,
.
H and N, wt %) Anal. Calc. for C H N O BrSi Zn: C, 53.42; H, 4.33; N, 6.44; found: C, 53.26;
2
9
28
3
2
2
-1
1
H, 4.24; N, 6.62; IR (KBr, cm ): 2149, υ(C≡C); 1606, υ(HC=N); 1278, υ(C-O); H NMR (d -
6
DMSO, 300 MHz) : δ 9.34 (s, 1H, HC=N), δ 9.29 (s, 1H, HC=N), δ 6.69-8.26 (m, 8H, Ar-H), δ 0.26
+
(
s, 18H, (CH ) Si); MS (ESI): m/z 675 (M+Na) . 2c: Yield: 79 %; elemental analyses (C, H and N,
3
3
wt %) Anal. Calc. for C H N O BrZn: C, 56.06; H, 2.42; N, 9.34; found: C, 55.91; H, 2.27; N,
35
18
5
6
-1
1
9
.54; IR (KBr, cm ): 2202, υ(C≡C); 1614, υ(HC=N); 1312, υ(C-O); H NMR (d -DMSO, 300
6
MHz): δ 9.39 (s, 1H, HC=N), δ 9.14 (s, 1H, HC=N), δ 6.75-8.69 (m, 16H, Ar-H); MS (ESI): m/z
+
7
73(M ). 2d:Yield: 77%; elemental analyses(C, H and N, wt %) Anal. calc. for C H N O BrZn:
3
7
24
3
4
-1
C, 61.73; H, 3.36; N, 5.84; found: C, 61.56; H, 3.28; N, 5.89; IR (KBr, cm ): 2199, υ (C≡C);
1
1
615, υ(HC=N); 1286, υ (C-O); H NMR (d -DMSO, 300 MHz): δ 9.37 (s, 1H, HC=N), δ 9.12 (s, 1H,
6
+
HC=N), δ 6.71-8.60 (m, 16H, Ar-H), δ 3.74 (s, 6H, OCH ); MS (ESI): m/z 743 (M ).
3
2
.4. Kurtz powder SHG measurements
The SHG efficiency of all the complexes was measured with respect to urea by powder
technique developed by Kurtz and Perry using Q switched Nd-YAG laser (Lab-170 spectra
physics) 10 ns laser with first harmonic output of 1064 nm at the pulse repeatation rate 10 Hz.
The homogeneous powder was mounted in the path of laser beam of pulse energy 2.2 mJ
obtained by split beam technique.
3
. Results and discussion
3
.1. Synthesis and spectroscopic characterization
The synthetic route to the Ni(II) and Zn(II)-salophen complexes is shown in scheme 1. Initially,
5
-(trimethylsilylethylene)salicylaldehyde was prepared by Sonogashira Pd(II)/Cu(I) catalyzed
6

ACCEPTED MANUSCRIPT
coupling reaction of 5-bromosalicylaldehyde with trimethylsilylacetylene by following the
procedure reported in literature [22]. Removal of trimethylsilyl group in 5-(trimethylsilyl
ethylene)salicylaldehyde was achieved by treatment of KOH in methanol to afford 5-ethynyl
salicylaldehyde in excellent yield. The compound 5-(4-nitrophenyl)ethynylsalicylaldehyde and
5
5
8
-(4-methoxyphenyl)ethynylsalicylaldehyde were synthesized by further coupling reactions of
-ethynylsalicylaldehyde with 1-iodo-4-nitrobenzene and 1-iodo-4-methoxybenzene in THF at
0°C. To explore the influence of π-conjugation and substituent's on phenyl ring of salophen
ligand, the complexes 1a, 2a, 1b and 2b were prepared by following the procedure reported
earlier [23] for ease of handling and purification with little modification for which, nickel acetate
or zinc acetate was first treated with 5-bromosalicylaldehyde and 5-(trimethylsilylethynyl)
salicylaldehyde in THF for 30 min. at room temperature. To the resulting solution was added
2
,3-diamino-5-bromopyridine afforded monomeric complexes 1a, 1b, 2a and 2b, respectively.
The complexes 1c, 1d, 2c and 2d with extended π-conjugation and donor/acceptor substituent's
were prepared by treating nickel acetate or zinc acetate with 5-(4-nitrophenyl)ethynyl
salicylaldehdye or 5-(4-methoxyphenyl)ethynyl salicylaldehdye then subsequently treated with
2
,3-diamino-5-bromopyridine by similar method described above. Complexes 1c and 2c with an
additional electron-withdrawing NO group whereas, complexes 1d and 2d with an electron-
2
donating OCH group on phenylene ring were obtained. The generalized equation for the
3
reaction leading to the formation of the complexes is shown as follows
M(OAc) .nH O + 2 Br-SAL + DABP
[M(Br-C H OHC=NC H BrN=CHOH C -Br)]
6 3 6 3 3 6
2
2
M(OAc) .nH O + 2 TMS-SAL + DABP
[M(TMS-C H OHC=NC H BrN=CHOH C -TMS)]
6 3 6 3 3 6
2
2
M(OAc) .nH O + 2 RC H C CC H (OH)(CHO) + DABP
[M(R-C H C CC H OHC=NC H BrN=CHOH C C CH C -R)]
6 4
6 3 6 3 3 6
4 6
2
2
6
4
6
3
(
where ; M=Ni, Zn ; n= 4 (Ni), 2 (Zn) ; Br-SAL= 5-Bromosalicylaldehyde ; TMS-SAL= 5-Trimethylsilylethynylsalicylaldehyde ;R= NO , OCH ;
DABP= 2,3-diamino-
2 3
5-bromopyridine)
All complexes were air stable, moisture insensitive and insoluble in common organic solvents
except DMF and DMSO. The results of elemental analyses (C, H and N) which are given in
section 2 confirm the assigned composition of the complexes.
7

ACCEPTED MANUSCRIPT
The IR spectra of 1a-d and 2a-d exhibit a medium intensity band due to internal triple bond
-1
-1
(
C≡C) observed at ∼ 2145 cm [24]. The band observed at ∼ 1610 cm in the spectra of 1a-d and
a-d indicate involvement of imine (HC=N) nitrogen in coordination with metal ion [25]. This view
was further supported by the appearance of a band corresponding to the metal-nitrogen stretching
2
–1
–1
vibration at ca 501-519 cm in 1a-d and ca 504-515 cm in 2a-d. Similarly, another medium
-1
-1
intensity band observed at ca 1282-1334 cm in 1a-d and ca 1278-1312 cm in 2a-d is due to
ν(C-O) stretching vibration indicating coordination of the oxygen atom of the phenol group [26].
Further proof for complexation of oxygen is obtained from the appearance of (M-O) band at ca 537–
-1
-1
5
69 cm 1a-d and 543-564 cm 2a-d. The spectra of 1b and 2b exhibit vibrations of Me Si at
3
-1
-1
around 1248 and 840 cm [27]. Compound 1c and 2c exhibit two bands at ∼ 1560 cm and ∼ 1400
-1
cm which can be attributed to ν
and νsym (NO ) modes, respectively [28]. The strong band at
asym
2
-1
-1
1
244 and 830 cm in 1b and 2b ascribed to Me Si vibration [29]. However, a band at 1167 cm in
3
-1
1
d and 1169 cm in 2d is due to OCH group in the complexes [30].
3
1
The H NMR spectra of 1a-d and 2a-d displayed two resonances for two non-equivalent imine
(HC=N) protons and appeared at approximately 9.37 and 9.10 ppm confirm the imine nitrogen
coordination [31]. The resonance of all aromatic as well as heteroaromatic protons are well resolved
and observed at 8.59-6.65 ppm in 1a-d and 8.48-6.69 ppm in 2a-d. In addition to these the resonance at
0
.27 ppm in 1b and 2b is due to two terminal Me SiC≡C protons. However, the complexes 1d and 2d
3
exhibit resonance at 3.74 ppm for OCH group in the complexes [32].
3
3.2. Thermo gravimetric analysis
To investigate the thermal stability of Ni(II) (1a-d) and Zn(II) (2a-d) complexes thermo gravimetric
analysis (TGA) were performed up to 800°C under nitrogen atmosphere at a heating rate of 10°C
-1
min . TGA plots suggest that the complexes 1a and 2a underwent a weight loss due to the
expulsion of water molecules (obsd. 6.11(1a), 6.13 (2a)%; cald. 5.93 (1a), 5.83 (2a)%) in the
temperature range between 30-175°C and 32 to 184°C, respectively. Both the complexes
8

ACCEPTED MANUSCRIPT
collapse due to second decomposition stage of coordinated salophen ligand per formula unit
which occurs in between 175-749°C and 184-744°C with a significant weight loss of 88.69 (1a)
and 87.10 (2a), respectively (cald. 88.35 (1a) 86.81 (2a) %). The decomposition sequence of 1b and
2b is similar to that of 1a and 2a, once again the loss of water molecule is observed and indicate the
decomposition follows the same stages. The first weight loss observed in between 31-183°C and
3
2-182°C which is presumably due to loss of water molecule (obsd. 5.83 (1b), 5.81 (2b) %; calcd.
.58 (1b), 5.52 (2b)%). The second stage of decomposition with weight loss from 183-753°C (1b)
5
and 182-750°C (2b) is attributed to the loss of coordinated ligand (obsd. 88.73 (1b), 87.80 (2b) %;
calcd. 88.42 (1b), 87.51 (2b)%) to give final residue of metal oxide. The TGA curve of 1c, 2c and
1
d, 2d shows similar behavior. In the temperature range 33-176°C and 36-179°C these complexes
underwent weight loss corresponds to water molecule (obsd. 5.09 (1c), 5.06 (2c), 5.32 (1d), 5.28
2d); calcd. 4.84 (1c), 4.80 (2c), 5.05 (1d), 5.01 (2d)%). All the complexes exhibit weight loss which
is assigned to the decomposition of coordinated salophen ligand observed in between 176-764°C (1c,
(
2c) and 179-766°C (1d, 2d) with an observed weight loss of 90.22 (1c), 89.44 (2c), 89.84 (1d) and
88.96 (2d), respectively (calcd. 89.94 (1c), 89.14 (2c), 89.53 (1d), 88,69 (2d)%).
3.3. X-ray powder diffraction and SEM studies
Single crystal X-ray diffraction investigation is the most precise source of information regarding
the structure of the complexes. However, the difficulties in obtaining crystalline complexes in
proper symmetric form has rendered us to perform the powder X-ray diffraction method for such
study. The XRPD pattern obtained for the metal complexes 1c and 2b revealed well defined
crystalline peaks indicating that the complexes 1c and 2b is crystalline in phase due to inherent
crystalline nature (Fig. 1). The diffractogram of 1c records thirteen reflections between 5-80°
(2θ) with maximum at 2θ=18.644° corresponding to value of d=4.755Å (Table 1). The
diffractogram of 2b consists of nine reflections with maxima at 2θ=18.16° corresponding to
value of d=4.879Å (Table 2). The main peaks of 1c and 2b have been indexed by using computer
9

ACCEPTED MANUSCRIPT
software by trial and error method [33, 34], keeping in mind characteristics of various symmetry
2
systems till good fit could be obtain between observed and calculated 2θ and sin
θ values. The
method also yielded hkl values. The relative intensities corresponding to the prominent peaks
have been indexed. It was observed that the indexing of the diffractogram of 1c and 2b are
identical. Based on this it can be proposed that these compounds belong to same structural class.
2
A comparison of values of 2θ and sin
θ
for 1c and 2b reveals that, there is a good agreement
2
between the calculated and observed values of 2θ and sin
θ on the basis of assumption of monoclinic
structure [35]. The structure of 1c yields values for lattice constant a=11.1427Å, b=8.0223Å, and
3
c= 8.9645Å; α=γ= 90° and β= 122.7°, unit cell volume V=674.30Å . However, the structure of
2b yields values for lattice constant a=13.8704 Å, b=9.7067 Å and c=7.9356 Å; α=γ=90° and β=
3
9
9.192°, unit cell volume V=1056.69 Å . In conjunction with these cell parameters the conditions such
as a ≠b ≠c and α=γ ≠β required for the samples to be monoclinic were tested and found to be
satisfactory. These results are in good agreement with those are reported in the literature [ 36, 37].
To explore the morphology and particle size of the prepared complexes the scanning electron
micrography (SEM) studies of 1b and 2d have been studied and are presented in Fig. 2. The SEM of
1
b seemed of rock like crystals with average size of ~26 ꢀm whereas; the SEM of 2d shows crystals
like nanorods with average size of ~0.9 ꢀm.
.4. Cyclic Voltammetry
3
The redox properties of Ni(II) complexes were investigated cyclic voltammetrically in DMF
solution containing 0.05 M n-Bu NClO as a supporting electrolyte. All measurements were
4
4
-4
carried out in 10 M solution at room temperature in the potential range +1.5 to -1.5 with scan rate
-1
1
00 mVs . The electrochemical data of the complexes 1a-d is summarized in Table 3 and
representative cyclic voltammogram of 1b and 1d are displayed in Fig. 3 and Fig. 4, respectively.
The Ni(II) complexes exhibit a one electron quasireversible oxidation and reduction process. The
cyclic voltammetry studies on Ni(II) complexes reveals that all complexes undergoes anodic
10

ACCEPTED MANUSCRIPT
processes which is attributed to quasireversible one electron oxidation of Ni(II) to Ni(III) process
in the range of 0.890 -0.980 V while cathodic process is attributed to quasireversible one electron
reduction Ni(II) to Ni(I) process in the range of -1.227 to -1.369 V, similar to that of observed in
other Ni(II)-salopen complexes reported in the literature [38]. The electrochemical data of all the
Ni(II) complexes also reveals that the redox responses of Ni(II) complexes shifted to more
negative potential in order to increase π-conjugation in the complexes.
3
.5.Absorption and emission properties
The UV-Vis absorption spectra of all Nickel(II) (1a-d) and Zn(II) (2a-d) complexes were
-4
measured in DMF solution (10 M) at room temperature and data are summarized in Table 4.
In DMF, the absorption spectra exhibit intense bands at ca 235, 285 nm for 1a and ca 245, 275 nm
for 2a which can be assigned to π→π* and n→π* intra-ligand transitions, respectively (Fig. 5).
However, a band at 390 nm in 1a and 440 nm in 2a assigned to metal to ligand charge transfer
(MLCT) transition. Complexes 1b and 2b exhibit bands at 236, 290 nm and 240, 295 nm are
likely assigned to π→π* and n→π* transition, respectively. Another band at 395 nm in 1b and 445
nm in 2b assigned to MLCT transition. In addition to these, a week absorption at 490 and 505 nm
1
1
in 1a and 1b is due to spin allowed ( A → A ) d-d transition having square planar geometry
1g
2g
around Ni(II). The observed bathochromic shift in 1b and 2b relative to 1a and 2a is associated
with use of addition of electron donating C≡CSi(CH ) moiety in salicylidene ligand resulted in a
3
3
destabilization of π* HOMO orbital and a stabilization of LUMO π* orbital which lead to a
smaller HOMO-LUMO energy gap in 1b and 2b [39]. The analogous bands are also observed in
1
c, 1d, 2c and 2d with further bathochromic shift. Complexes 1c, 1d, 2c and 2d exhibit a high
intensity band at 235, 245, 236 and 240 which can be assigned to π→π* transition. Another band at
2
85 in 1c, 295 in 1d, 290 in 2c and 295 nm in 2d attributed to n→π* transition. However, a band at
15 in 1c, 440 in 1d, 441 in 2c and 447 in 2d is due to MLCT transition. The spin allowed transition
4
11

ACCEPTED MANUSCRIPT
1
1
(
A → A ) at 525 in 1c and 530 nm in 1d indicate four coordinate square planer geometry around
1g 2g
Ni(II). The observed bathochromic shift in these complexes is associated with increase in π-conjugation
and addition of donor-acceptor substituent's in respective complexes
As shown in Fig. 6, the emission observed in 1a-d and 2a-d appears to follow the same trend as
absorption energy. The complexes 1a and 2a exhibit emission at 526 and 531 upon excitation at
3
36 and 328 nm with life time of 1.65 and 1.91 ns, respectively (Table 5). When bromine is
replaced by electron donating C≡CSi(CH ) forming 1b and 2b complexes, the emission are
3
3
found to be red shifted in comparison to those of 1a and 2a and observed at 532 and 538 with life
time of 1.67 and 1.94 ns, respectively. The complexes 1c and 2c shows green emission with
maxima at 548 and 564 nm upon excitation at 338 and 341 nm accompanied by life time of 1.69
and 1.96 ns, respectively. However, 1d and 2d exhibit emission maxima at 535 and 549 nm
excited upon 348 and 358 nm with life time of 1.99 and 1.98 ns, respectively. The emission
observed in these complexes confirm that emission origin predominantly not only due to π→π* intra-
ligand transition but also due to some metal to ligand charge transfer (MLCT) character [40].
Compared to 1a, 1b, 2a and 2b the emission maxima in 1c, 1d, 2c and 2d are red shifted with
increase in life time and such red shift can be related to increase in π-conjugation and donor-acceptor
properties of substituted group on coordinated Schiff base ligand. These results might be due to
decrease in HOMO-LUMO energy gap and extension of delocalization of the π-electron system
along the conjugated backbone in the complexes. With electron withdrawing nitro group on
complexes 1c and 2c offers an extra conjugated backbone resulting in bathochromic shift (14 nm) in
emission spectra relative to 1d and 2d. Further, fluorescent intensity is significantly quenched in 1c
and 2c due to presence of electron withdrawing nitro group in the complexes. These results are in
good agreement with those are reported in the literature [41]. The emission quantum yield (φ) of all
the complexes was determined with reference to quinine sulphate (φ= 0.52) and appeared at 0.194-
0
.495 for 1a-d and 0.506-0.537 for 2a-d. The luminescence decay curve of representative complexes
12

ACCEPTED MANUSCRIPT
1
a and 2d are depicted in Fig. 7. The observed decay of the complexes fit well with single exponential
decay. Compare to 1a, 1b, 2a and 2b the average lifetime of 1c, 1d, 2c and 2d is longer than those
observed in 1a, 1b, 2a and 2b (Table 2). These results could be attributed due to red shifted emission
and decreased emission intensity observed in 1c, 1d, 2c and 2d as compare to 1a, 1b, 2a and 2b.
The K values of 1a-d and 2a-d shows marked effect with increase in π-conjugation in the complexes.
r
Further, the highest value of K of 1c and 2c are results from the cooperative effect of increase in
r
π-conjugation and electron withdrawing NO group on coordinated alkynyl Schiff base ligand.
2
3
.5. SHG activity of the complexes
Nonlinear optical material exhibiting efficient second harmonic generation (SHG) at short
wavelengths are important in the field of high density optical recording, laser printing, optical
measurement system and for other applications [42, 43]. Among them, new NLO materials made
from metal-organic and coordination network have been a major point of focus in recent years to
evaluate its potential application as a second-order NLO material [44]. The SHG efficiency of
1
a-d and 2a-d were screened by the quasi-Kurtz powder technique and the SHG efficincies
relative to the reference (urea) are displayed in Table 6. The comparison of the area of the SGH
signal emitted by the sample with the standard urea in the same experimental condition showed
that the complexes 1a and 2a are 0.19 and 0.21 times that for urea. The complexes 1b and 2b are
0
.24 and 0.27 times than that of urea. However, 1c, 1d, 2c and 2d are 0.36, 0.31, 0.34 and 0.28
times that that of urea, respectively. The best values of SHG are found for compound possessing
R=NO group with increased π-conjugation in the coordinated Schiff base ligand that expected
2
on the basis of the electronic asymmetry arguments.
4
. Conclusions
This study demonstrates that all the complexes exhibit a distinct MLCT (metal to ligand charge
transfer) absorption band and shifted to longer wavelength by increasing π-conjugation in the
complexes. Room temperature luminescence is observed for all complexes corresponding to
13

ACCEPTED MANUSCRIPT
π→π* intra-ligand transition with some metal-ligand charge transfer (MLCT) character in DMF
and are finely tuned by the degree of extended π-conjugation and variation of the substituent
group with different electronic effects in the complexes. The electrochemical behavior of the
Ni(II) complexes reveals that the redox responses of all Ni(II) complexes shifted to more
negative potential in order to increase π-conjugation in the complexes. The second harmonic
generation (SHG) efficiency of the complexes was measured by Kurtz-powder technique
indicating that all complexes possesses promising potential for the application as a useful nonlinear
optical material. Moreover, significant increase in π-conjugation increases SHG efficiency of
these complexes.
14

ACCEPTED MANUSCRIPT
References:
1
2
3
4
5
6
7
8
9
. Z.-L. You, H.-L. Zhu, W.-S.Z. Liu, Solvolthermal Syntheses and Crystal Structures of Three
Linear Trinuclear Schiff Base Complexes of Zinc(II) and Cadmium(II), Anorg. Allg. Chem.
6
30 (2004) 1617.
. Z.-L. You, H.-L. Zhu, W.-S.Z. Liu, Syntheses, Crystal Structures, and Antibacterial
Activities of Four Schiff Base Complexes of Copper and Zinc, Anorg. Allg. Chem. 630
(2004) 2754.
. A. Golcu, M. Tumer, H. Demirelli, R.A. Wheatley, Cd(II) and Cu(II) complexes of
polydentate Schiff base ligands: synthesis, characterization, properties and biological
activity, Inorg. Chim. Acta. 358 (2005)1785.
. K. E. Splan, A. M. Massari,G. A. Morris, S.-S. Sun, E. Reina, S. T. Nguyen, J. T. Hupp,
Photophysical and Energy-Transfer Properties of (Salen)zinc Complexes and Supramolecular
Assemblies, Eur. J. Inorg. Chem. (2003) 2348.
. G. A. Morris, H. Zhou, C. L. Stern, S. T. Nguyen, A General High-Yield Route to
Bis(salicylaldimine) Zinc(II) Complexes: Application to the Synthesis of Pyridine-Modified
Salen-Type Zinc(II) Complexes, Inorg. Chem. 40(2001)3222.
. W.-K. Dong, Y.-X. Sun, Y.-P. Zhang, Li Li, Xue-Ni He, X.-L. Tong., Synthesis, crystal
II
II
II
structure, and properties of supramolecular Cu , Zn , and Cd complexes with Salen-type
bisoxime ligands, Inorg. Chim.Acta.362 (2009)117.
. M. Nielsen, N. B. Larsen, K. V. Gothelf, Electron Transfer Reactions of Self-Assembled
Monolayers of Thio(Phenylacetylene) -Substituted Chiral Metal-Salen Complexes,
n
Langmuir.18 (2002) 27959.
. S. Chakraborty, C. R. Bhattacharjee, P. Mondal, S. Krishna Prasad, D. S. Shankar Rao,
Synthesis and aggregation behaviour of luminescent mesomorphic zinc(II) complexes with
‘salen’ type asymmetric Schiff base ligands, Dalton Trans. 44 (2015)7477.
. N. Novoa,T. Roisnel, P. Hamon, S. Kahlal, C. Manzur,H. M. Ngo, I. Ledoux-Rak, J.-Y.
Saillard, D. Carrillo, J.-R. Hamon, Four-coordinate nickel(II) and copper(II) complex based
ONO tridentate Schiff base ligands: synthesis, molecular structure, electrochemical, linear
and nonlinear properties, and computational study, Dalton Trans. 44(2015)18019.
10. P. G. Lacroix, Second-Order Optical Nonlinearities in Coordination Chemistry: The Case of
Bis(salicylaldiminato)metal Schiff Base Complexes, Eur. J. Inorg. Chem. (2001) 339.
15

ACCEPTED MANUSCRIPT
1
1. F. Averseng, P. G. Lacroix, I. Malfant, F. Dahan and K. Nakatani, Synthesis, crystal structure
and solid state NLO properties of a new chiral bis(salicylaldiminato)nickel(II) Schiff-base
complex in a nearly optimized solid state environment, J. Mater. Chem. 10 (2000) 1013.
1
2. I. H. A. Badr, M. E. Meyerhoff, Highly Selective Optical Fluoride Ion Sensor with
Submicromolar Detection Limit Based on Aluminum(III) Octaethylporphyrin in Thin
Polymeric Film, J. Am. Chem. Soc.127 (2005) 5318.
1
3. V. Liuzzo, W. Oberhauser, A. Pucci, Synthesis of new red photoluminescent Zn(II)-
salicylaldiminato complex, Inorg. Chem Commun. 13(2010) 686.
1
4. T. Feng, H.M. Peng, Y.M. Yao, Y. Zhang, Q. Shen, Y.X. Cheng, Synthesis, characterization
and photoluminescence of aluminum N-aryloxo functionalized β-ketoiminate complexes,
Chin. Sci. Bull. 56 (2011)1471.
1
5. R. Brissos, D. Ramos, J. C. Lima, F. Y. Mihan, M. Borra`s, J. de Lapuente, A. Dalla Cort, L.
Rodrıguez, Luminescent zinc salophen derivatives: cytotoxicity assessment and action
mechanism studies, New J. Chem. 37(2013)1046.
1
6. S. Bhattacharjee,.K.-E. Jeong,. S.-Y. Jeongb, W.-S. Ahn, Synthesis of a sulfonato-salen-
nickel(II) complex immobilized in LDH for tetralin oxidation, New J. Chem. 34(2010)156.
7. A. Zulauf, X. Hong, Brisset, E. Schulz, M. Mellah, Electropolymerization of chiral
chromium–salen complexes:new materials for heterogeneous asymmetric catalysis, New J.
Chem. 36(2012)1399.
1
1
8. C. Schmitz, P. Posch, M. Thelakkat, H.-W. Schmidt, A. Montali, K. Felman, P. Smith,
C. Weder, Polymeric Light-Emitting Diodes Based on Poly(p-phenylene ethynylene),
Poly(triphenyldiamine), and Spiroquinoxaline, Adv. Funct. Mater. 11(2001) 41.
9. V. W.-W. Yam, K. K.-W. Lo and K. M.-C. Wong, Luminescent polynuclear metal
acetylides, J. Organomet. Chem. 578(1999) 3.
1
2
2
0. C. Ma, A. Lo, A. Abdol-Maleki, M. J. MacLachalm, Synthesis and Metalation of Novel
Fluorescent Conjugated Macrocycles, Org. Lett. 6 (2004), 3841.
1. K.-L. Kuo, C.-C. Huang, Y.-C. Lin, Synthesis and photophysical properties of multinuclear
zinc-salophen complexes: enhancement of fluorescence by fluorene termini, Dalton Trans.
(2008)3889.
2
2. K.-H. Chang, C.-C. Huang, Y.-H. Liu,Y.-H. Hu, P.-T. Chou, Y.-C. Lin, Synthesis of photo-
luminescent Zn(II) Schiff base complexes and its derivative containing Pd(II) moiety, Dalton
Trans. (2004)1731.
16

ACCEPTED MANUSCRIPT
2
3. H.-C. Lin, C.-C. Huang, C.-H. Shi, Y.-H. Liao, C.-C. Chen, Y.-C. Lin Y.-H. Liu, Synthesis
of alkynylated photo-luminescent Zn(II) and Mg(II) Schiff base Complexes, Dalton Trans.
(2007) 781.
2
4. A. W. C. Leung, M. J. MacLachlan, Poly(salphenyleneethynylene)s: soluble, conjugated
metallopolymers that exhibit unique supramolecular crosslinking behavior, J. Mater. Chem.
1
7 (2007) 1923.
2
5. M. Mohammadikish, Green synthesis of nanorod Ni(salen) coordination complexes using a
simple hydrothermal method, Cryst. Eng. Comm. 16 (2014) 8020.
2
6. A. Ourari, Y. Ouennoughi, D. Aggoun, M. S. Mubarak, E. M. Pasciak, D. G. Peters,
Synthesis, characterization, and electrochemical study of a new tetradentate nickel(II)-Schiff
base complex derived from ethylenediamineand 50-(N-methyl-N-phenylaminomethyl)-2’-
hydroxyacetophenone, Polyhedron. 67 (2014) 59.
2
2
2
7. M. Shebl, S.M.E. Khalil, S.A. Ahmed, H.A.A. Medien, Synthesis, spectroscopic characterizatio
and antimicrobial activity of mono-, bi- and tri-nuclear metal complexes of a new Schiff bas
ligand, J. Mol. Struct. 980 (2010) 39.
8. J. Cisterna, V. Dorcet, C. Manzur, I. L.-Rak, J.-R. Hamon, D. Carrillo, Synthesis, spectral,
electrochemical, crystal structures and nonlinear optical properties of unsymmetrical Ni(II)
and Cu(II) Schiff base complexes, Inorg. Chim. Acta. 430 (2015) 82.
9. H. Balcar, J. Sedlacek, J. Zednik, V. Blechta, P. Kubat, J. Vohlidal, Polymerization of isomeric N-(4-
substituted benzylidene)-4-ethynylanilines and 4-substituted N-(4-ethynylbenzylidene)anilines by
transition metal catalysts: preparation and characterization of new substituted polyacetylenes with
aromatic Schiff base type Pendant groups, Polymer. 42 (2001) 6709.
3
0. P. Gili , M.G.Martin Reyes, Martin Zarza, I. L. F. Machado, M.F.C. Guedes da Silva, M. A.
N. D. A. Lemos A.J. L. Pombeiro, Synthesis, spectroscopic, magnetic and electrochemical
properties of Cu(II) and Fe(III) complexes with the new ligand N,N'- [ 1,1'-dithiobis
(phenyl)] bis( 5'-methoxysalicylaldimine), Inorg. Chim. Acta 244 (1996) 25.
3
1. A. Ourari, K. Ouari, W. Moumeni, L. S. Gilles, M. Bouet, M. A. Khan, Unsymmetrical
tetradentate Schiff base complexes derived from 2,3-diaminophenol and salicylaldehyde or
5
-bromosalicylaldehyde, Trans. Met. Chem. 31 (2006) 169.
3
2. S. D. Bella, I. Fragala, A. Guerri, P. Dapporto, K. Nakatani, Synthesis, crystal structure, and
second-order nonlinear optical properties of [N, N’-bis(1H-pyrrol-2-ylmethylene)-1,2-
benzenediaminato]nickel(II) Schiff base complexes, Inorg. Chim. Acta 357(2004) 1161.
17

ACCEPTED MANUSCRIPT
3
3
3
3
3. D. Kivelson, R. Neiman, ESR Studies on the Bonding in Copper Complexes, J. Chem. Phys.
3
5(1961) 149.
4. A. Boultif, D. Louer, Powder pattern indexing with the dichotomy method, J. Appl. Cryst.
7(2004) 724.
3
5. C. R. Bhattacharjee, G. Das, P. Mondal, Photoluminescent Hemidisc-Shaped Liquid
Crystalline Nickel(II) Schiff-Base Complexes, Eur. J. Inorg. Chem. (2011) 5390.
6. C. R. Bhattacharjee, G. Das, P. Mondal, S. K. Prasad, D. S. Shankar Rao, Novel Green Light
Emitting Nondiscoid Liquid Crystalline Zinc(II) Schiff Base Complexes, Eur. J. Inorg.
Chem. (2011) 1418.
3
7. F. Morale, R. W. Date, D. Guillon, D. W. Bruce, R. L. Finn, C. Wilson, A. J. Blake, M.
Schroder, B. Donnio, Columnar Mesomorphism from Hemi-Disklike Metallomesogens
Derived from 2,6-Bis[3’,4’,5’- tri(alkoxy)phenyliminomethyl]pyridines (L): Crystal and
Molecular Structures of [M(L)Cl ](M= Mn, Ni, Zn), Chem. Eur. J. 9 (2003) 2484.
2
3
8. A. Anthonysamy, S. Balsubramaniam, Synthesis, spectral, thermal and electrochemical studies
of nickel (II) complexes with N O donor ligands, Inorg. Chem. Commun. 8(2005) 908.
2
2
3
9. W. Yang, W. Yang, W. Li, W. Qin, Study on the synthesis, characterization, photophysical
performance and oxygen-sensing behavior of a luminescent Cu(I) complex with large
conjugation plane, Spectrochim. Acta. Part A. 104(2013) 56.
4
0. N. J. Turro, Energy Transfer Processes, Pure Appl. Chem. 49(1977) 405.
1. R. D. Archer, H. Chen, L. C. Thompson, Synthesis, Characterization, and Luminescence of
Europium(III) Schiff Base Complexes, Inorg. Chem. 37(1998) 2089.
4
4
4
4
2. J. Zyss, I. Ledoux, Nonlinear Optics in Multipolar Media: Theory and Experiments, Chem.
Rev. 94(1994) 77.
3. T. Verbiest, S. Houbrechts, M. Kauranen, A. Persoons, Second-order nonlinear optical
materials: recent advances in chromophore design, J. Mater. Chem. 7(1997) 2175.
4. S. D. Bella, Second-order nonlinear optical properties of transition metal Complexes, Chem.
Soc. Rev. 30(2001) 355.
18

ACCEPTED MANUSCRIPT
Figure captions:
Scheme 1: Synthetic route to the complexes 1a-d and 2a-d
Fig. 1: X-ray diffractogram of (A) 1c and (B) 2b
Fig. 2: Scanning electron micrographs of (A) 1b and (B) 2d
Fig. 3: Cyclic voltammogram of 1b in DMF (A) reduction potential (B) oxidation potential
Fig. 4: Cyclic voltammogram of 1d in DMF (A) reduction potential (B) oxidation potential
Fig. 5: Electronic Absorption Spectra of complexes (A) 1a-d and (B) 2a-d
Fig. 6: Emission spectra of complexes (A) 1a-d and (B) 2a-d
Fig. 7: Luminescence decay of (A) 1c and (B) 2d
19

ACCEPTED MANUSCRIPT
Table 1: X-ray diffraction data of 1c
2
2
d (Å)
I/I0
sin θ Obs.
92.2
sin θ Calc.
hkl
010
110
011
101
-102
111
-112
-221
300
-222
-321
003
-223
2θ Obs.
11.02
14.52
16.11
18.64
20.13
21.82
22.93
27.35
28.44
30.57
33.13
35.70
45.45
2θ Calc.
11.02
14.52
16.11
18.64
20.06
21.71
22.94
27.42
28.53
30.53
33.04
35.68
45.48
8
.0223
.0956
.4955
.7551
.4066
.0695
.8754
.2586
.1359
.9217
.7016
.5131
.9940
31.38
12.33
13.18
100
92.2
159.7
196.5
262.4
303.3
354.6
395.4
561.7
607.4
693.2
808.5
938.4
1494.2
6
5
4
4
4
3
3
3
2
2
2
1
159.7
196.5
262.4
305.5
358.3
395.0
558.7
603.3
695.0
812.9
939.4
1492.1
28.74
14.51
17.45
49.11
29.64
13.8
14.6
10.36
4.98
Table 2: X-ray diffraction data of 2b
2
2
d (Å)
I/I0
sin θ Obs.
94.6
sin θ Calc.
hkl
110
2θ Obs.
11.16
12.08
13.88
15.76
18.16
18.57
20.66
24.42
26.73
2θ Calc.
11.16
12.08
13.88
15.76
18.23
18.51
20.66
24.38
26.68
7
.9187
.3223
.3747
.6189
.8799
.7748
.2961
.6424
.3327
42.64
23.05
11.31
39.82
88.21
77.47
21.58
18.29
100
94.6
7
6
5
4
4
4
3
3
110.7
146.0
187.9
249.1
260.2
321.5
447.2
534.2
110.7
146.0
187.9
250.9
258.6
321.6
446.0
532.3
-101
101
-201
-211
201
211
-112
-401

ACCEPTED MANUSCRIPT
Table 3: Electrochemical data of Ni(II) complexes (1a-d) in DMF
Compound
Oxidation Potentials
Reduction Potentials
Epa (V)
0.890
0.901
0.980
0.942
Epc (V) E (V) ∆E (mV)
Epa (V) Epc (V) E (V) ∆E (mV)
1/2
p
1/2
p
1
a
0.765
0.751
0.721
0.690
0.827(169)
0.826(150)
0.850(269)
0.816(252)
-1.353
-1.315
-1.277
-1.254
-1.227
-1.249
-1.340
-1.369
-1.290(126)
-1.282(66)
-1.308(63)
-1.311(115)
1
b
1
c
1
d
Table 4: UV-Visible data of 1a-d and 2a-d in DMF
4
-1
-1
Complex
λmax (nm)(ε x 10 , M cm )
1
a
235(28.9),285(21.1), 390(15.1), 490(9.2)
236(27.5), 290(19.8), 395(11.6), 505(7.5)
235(25.8), 285(18.1), 415 (9.2), 525(4.2)
245(25.2), 295(17.5), 440(8.7), 530(3.6)
245(34.5), 275(16.6), 440(16.7)
1
b
1
c
1
d
2
a
2
b
240(32.5), 295(23.5), 445(12.5)
2
c
236(27.6), 290(20.8), 441(16.1)
2
d
240(21.5), 295(18.8), 447(14.9)

ACCEPTED MANUSCRIPT
Table 5: Photoluminescence data of 1a-d and 2a-d in DMF
-1
7
-1
7
Complex
λex (nm)
λem (nm)
φ
τ (ns) K (s /10 ) K (s /10 )
r nr
1
a
336
526
0.194
1.65
1.67
1.69
1.99
1.91
1.94
1.96
1.98
0.117
0.178
0.254
0.248
0.265
0.268
0.272
0.271
0.488
1
b
340
338
348
328
338
341
358
532
548
535
531
538
564
549
0.298
0.430
0.495
0.506
0.520
0.535
0.537
0.420
0.338
0.254
0.258
0.247
0.242
0.234
1
c
1
d
2
a
2
b
2
c
2
d
Table 6: Measured SHG values of 1a-d and 2a-d
Complex
Efficiency (relative to urea)
1
a
0.19
0.24
0.36
0.31
0.21
0.27
0.34
0.28
1
b
1
c
1
d
2
a
2
b
2
c
2
d

ACCEPTED MANUSCRIPT
Scheme 1
Br
Br
N
N
O
N
NH2
CHO
OH
N
H N
M
2
+
M(OAc)2
Br
Br
O
Br
THF
1
a, 2a
PdCl (PPh )
3 2
CuI
Br
NEt3
2
N
N
O
Br
N
CHO
OH
N
M
H N
NH2
2
Si(CH3)3
+
M(OAc)
2
Si(CH3)3
O
Si(CH3)3
THF
1
b, 2b
KOH
MeOH
CH Cl2
2
CHO
OH
CHO
OH
PdCl (PPh )
2
3
2
H
+
I
R
R
CuI, NEt
3
+
M(OAc)2
Br
THF
N
H N
NH2
2
Br
M= Ni, Zn; R= NO , OCH
2
3
N
N
O
N
O
M
R
R
1
c, 1d, 2c, 2d
Fig. 1:
(
A)
(B)

ACCEPTED MANUSCRIPT
Fig. 2:
(
A)
(B)
Fig. 3:
(
A)
(B)

ACCEPTED MANUSCRIPT
Fig. 4:
(
A)
(B)
Fig. 5:
(
A)
(B)

ACCEPTED MANUSCRIPT
Fig. 6:
(
A)
(B)
Fig. 7:
(
A)
(B)

ACCEPTED MANUSCRIPT
Research Highlights:
ꢀ
ꢀ
ꢀ
ꢀ
Synthesis of Ni(II), Zn(II)-Salophen complexes
1
Characterization by elemental analyses, IR, H NMR and mass spectral studies
Room temperature luminescence is observed for all complexes
All complexes possess potential application as a useful NLO material.