Ni(II) and Zn(II) Complexes Containing Alkynyl Functionalized Salicylaldimine Ligand and Heterocyclic Coligand: Synthesis, Characterization and Luminescence Properties

Article abstract of DOI:10.1007/s10895-016-2020-z

Some nickel(II) and zinc(II) complexes of the type [Ni(L)(phen/bipy)]X (1a–6a) and [Zn(L) (phen/bipy)]X (1b–6b) (where L?=?2-{(E)-[(4-trimethylsilylethynylphenyl)imino]methyl}-4-(4-nitro phenylethynyl)phenol; phen?=?1, 10-phenanthroline, bipy?=?2, 2′-bipyridine; X?=?ClO₄ ^?, BF₄ ^?, PF₆ ^?) have been prepared and characterized on the basis of elemental analyses, FTIR, ¹H NMR and mass spectral studies. The molecular structure of L was determined by single crystal X-ray diffraction studies. The electrochemical behaviour of the Ni(II) complexes indicate that the phen complexes appears at more positive potential as compared to those for bipy complexes, as a consequence of its strong π-acidic character. TGA was carried out to study the thermal behavior of the complexes. Room temperature luminescence is observed for all complexes corresponds to π?→?π* ILCT transition. The size of the counter anion and heterocyclic coligands phen and bipy shows marked effect on emission properties of the complexes.

Full text of DOI:10.1007/s10895-016-2020-z

J Fluoresc
DOI 10.1007/s10895-016-2020-z
ORIGINAL ARTICLE
Ni(II) and Zn(II) Complexes Containing Alkynyl Functionalized
Salicylaldimine Ligand and Heterocyclic Coligand: Synthesis,
Characterization and Luminescence Properties
1
1
1
M. S. More & S. S. Devkule & S. S. Chavan
Received: 19 October 2016 /Accepted: 29 December 2016
Springer Science+Business Media New York 2017
#
Abstract Some nickel(II) and zinc(II) complexes of the type
have attracted considerable attention owing to their intriguing
architectures and topologies, as well as potential applications
in many fields. Much effort has been focused on the synthesis
and properties of transition metal complexes of hybrid ligands
because they can provide new materials with useful properties
such as magnetic exchange [1], electrical conductivity [2],
photoluminescence [3], nonlinear optical property [4] and an-
timicrobial activity [5]. Among the various ligands Schiff ba-
ses are very interesting compounds because of their facile
syntheses, easily tuneable steric, electronic properties and
good solubility in common solvents [6, 7]; and also these
are very important classes of organic compounds from both
practical and theoretical point of view. Salicylaldimine Schiff
base ligands containing N and O donor atoms in particular are
interesting due to their ability to possess unusual configura-
tion, structural lability and their sensitivity towards molecular
environments [8]. They exhibit multifunctional properties
such as non-linear optical (NLO) materials [9], supramolec-
ular nanostructures [10], fluorescent molecular probes [11],
molecular aggregates [12], optical probes for medical applica-
tions [13] and electron transporting materials [14]. In recent
years considerable research efforts have been focused on in-
corporation of additional functionalities into coordinating li-
gand which are reported to exhibit very interesting lumines-
cent and optical properties [15]. The incorporation of addition-
al functionality into coordinating ligand and their metal com-
plexes was found to destabilize non-radiative d-d transitions to
maintain the structural integrity and thus displaying reason-
able luminescence properties. In particular, addition of alkynyl
functionality with π-conjugation constitutes an important
class of compounds as a luminescent material due to their
advanced electronic and structural properties [16, 17]. An im-
portant feature of this system is the structural modification
which causes a large π-delocalization over the coordinated
ligands than that of the regular complexes. The linear
[
(
N i ( L ) ( p h e n / b i p y ) ] X ( 1 a – 6 a ) a n d [ Z n ( L )
phen/bipy)]X (1b–6b) (where L = 2-{(E)-[(4-
trimethylsilylethynylphenyl)imino]methyl}-4-(4-nitro
phenylethynyl)phenol; phen = 1, 10-phenanthroline, bipy = 2,
−
−
−
2
´-bipyridine; X = ClO , BF , PF ) have been prepared and
4 4 6
1
characterized on the basis of elemental analyses, FTIR, H
NMR and mass spectral studies. The molecular structure of
L was determined by single crystal X-ray diffraction studies.
The electrochemical behaviour of the Ni(II) complexes indi-
cate that the phen complexes appears at more positive poten-
tial as compared to those for bipy complexes, as a conse-
quence of its strong π-acidic character. TGA was carried
out to study the thermal behavior of the complexes. Room
temperature luminescence is observed for all complexes cor-
responds to π → π* ILCT transition. The size of the counter
anion and heterocyclic coligands phen and bipy shows
marked effect on emission properties of the complexes.
.
.
Keywords Schiff base Ni(II)/Zn(II) complexes
Photoluminescence
Introduction
The rational design and construction of inorganic–organic hy-
brid materials made up of nitrogen/oxygen-donor ligands
*
S. S. Chavan
sanjaycha2@rediffmail.com
1
Department of Chemistry, Shivaji University, Kolhapur, MS 416
0
04, India

J Fluoresc
geometry of the alkynyl unit and its π-unsaturated nature has
made them attractive for preparation of luminescent sensors,
light emitting and nonlinear optical materials [18]. Moreover,
rigidity of the structure and dipole moment of the complexes
may thus increase. 1, 10-phenanthroline and 2, 2′-bipyridine
chelators are also good nitrogen donors and the complexes
formed serve as building blocks for the synthesis of
metallodendrimers, supramolecular assemblies, in analytical
chemisy, catalysis, electrochemistry, ring-opening metathesis
and polymerization [19, 20]. They also act as potential antitu-
mor agents and show better antitumor activity if they form
neutral complexes with transition metal ions [21].
spectral range. Cyclic voltammetry measurements were per-
formed with CH-400A Electrochemical Analyzer. A standard
three electrodes system consisting of Pt disk working elec-
trode, Pt wire counter electrode and Ag/AgCl reference elec-
trode was used. All the potentials were converted to SCE
scale. Tetrabutylammonium perchlorate (TBAP) was used as
the supporting electrolyte and all measurements were carried
out in DMF solution at room temperature and scan rate
−1
100 mV s .
Synthesis
Influenced by these facts we report herein synthesis of some
mixed ligand Ni(II) and Zn(II) complexes by the reaction of
alkynyl functionalized salicylaldimine ligand 2-{(E)-[(4-
trimethylsilylethynylphenyl)imino]methyl}-4-(4-
nitrophenylethynyl)phenol (L) in presence of 1, 10
phenanthroline and 2, 2′-bipyridine as a coligand, All the com-
plexes were characterized by elemental analyses and spectro-
scopic techniques. The influence of π-conjugation, coligands
Synthesis of 5-(4-nitrophenyl)ethynylsalicylaldehyde
To a mixture of 1-iodo-4-nitrobenzene (1.310 g, 5.26 mmol),
Pd(PPh ) Cl (0.074 g, 0.105 mmol), CuI (0.080 g, 0.42 mmol)
3
2
2
in 30 ml of Et N, a 5 ml of 5-ethynylsalicylaldehyde (1.0 g,
3
6.84 mmol) in CH Cl was added. The mixture was stirred for
2
2
16 h at 80 °C under N atmosphere. The resulting mixture was
2
filtered off and the residue obtained was purified by column
chromatography on silica with CH Cl /Pet. ether (1:2) as an
−
−
−
(
phen, bipy) and size of the counter anion (ClO , BF , PF )
4 4 6
2
2
on photophysical properties of the complexes have been studied.
eluent. The yellow powder is afforded by removal of solvent
under vacuum, and the product was identified as 5-(4-
nitrophenyl)ethynylsalicylaldehyde.
Experimental
Yield: 82%; Anal. Calcd for C H NO : C, 67.42; H, 3.39;
1
5
9
4
1
5
.24. Found: C, 67.59; H, 3.47; N, 5.09; H NMR (CDCl ,
3
Materials and General Methods
300 MHz): δ 11.22 (s, 1H, OH), 9.93 (s, 1H, HC = O), 8.23 (d,
H, Ph), 7.82 (d, 1H, Ph), 7.71 (dd, 1H, Ph), 7.66 (dd, 2H, Ph),
7.04 (d, 1H, Ph); MS (EI): m/z 267 (M ).
1
+
Some manipulations were performed under nitrogen atmo-
sphere using a vacuum line and standard Schlenk techniques.
The CH Cl was distilled from calcium hydride and diethyl
Synthesis of Ligand (L)
2
2
ether and THF from Na-ketyl. All other solvents and reagents
were of reagent grade and used without further purification. 5-
ethynylsalicylaldehyde was prepared by following the proce-
dure reported in the literature [22]. Zn(BF ) and Zn(PF )
A solution of 4-(trimethylsilylethynyl)aniline (1 mmol,
0.189 g) in THF (10 ml) was added drop wise to a solution
of 5-(4-nitrophenyl)ethynylsalicylaldehyde (1 mmol, 0.267 g)
in THF (10 ml) with constant stirring. The resulting mixture
was refluxed at about 80 °C until the completion of reaction
(checked by TLC). The resulting solution was concentrated
and the precipitate obtained was filtered, washed with diethyl
ether and dried in vacuo.
4
2
6 2
were obtained by stirring Zn(NO ) .6H O with two equiva-
3
2
2
lents of NaBF and KPF in acetonitrile at room temperature.
4
6
The white solid (NaNO or KNO ) was filtered off, and the
3
3
filtrate was evaporated to dryness to give the Zn(II) starting
1
materials [23]. H NMR spectra were recorded on Bruker
3
00 MHz instrument using TMS[(CH ) Si] as an internal
Yield: 78%; Elemental analyses (C, H and N, wt%) Anal.
Calc. for C H N O Si: C, 68.63; H, 5.51; N, 6.96; Found:
C, 68.55; H, 5.39; N, 6.87; IR (KBr, cm ): 2203, υ(C ≡ C);
3
4
standard and were reported in units of δ with residual protons
in the solvent as standard (CDCl , δ 7.24, d -dimethyl sulfox-
2
6 22 2 3
−1
3
6
ide, δ 2.50). ESI mass spectra were recorded on JEOL SX-102
spectrometer. Elemental analyses (C, H and N) were per-
formed on a Thermo Finnigan FLASH EA-112 CHNS ana-
lyzer. Absorption spectra were recorded on a Shimadzu UV–
Vis–NIR-100 spectrophotometer. Luminescence properties
were measured using a Perkin Elmer Spectroflourometer LS-
2155, υ(C ≡ CSi); 1618, υ(C = N); UV-Vis (DMF) λ (nm)
(ε ×10 , M cm ): 231 (29.7.1), 265 (21.2), H NMR
max
3
−1
−1
1
(CDCl ) (300 MHz): δ 13.29 (s, 1H, OH), δ 8.61 (s, 1H,
3
HC = N), 7.98–6.65 (m, 11H, Ar-H), 0.27 (s, 9H, (CH ) Si);
3
3
MS (ESI): m/z 438 (M + Na).
5
5. Luminescence lifetime measurements were carried out by
Synthesis of Complex [Ni(L)(phen)]X (1a-3a)
using time correlated single photon counting from HORIBA
Jobin Yvon. Infrared spectra were recorded on a Perkin-Elmer
FT-IR spectrometer using KBr pellets in the 4000–400 cm
To a solution of the appropriate Ni(II) salt, ((0.456 mmol,
0.1668 g), Ni(ClO ) ·6H O; (0.456 mmol, 0.1552 g),
−1
4
2
2

J Fluoresc
.
Ni(BF ) ·6H O or (0.456 mmol, 0.1590 g), Ni(PF ) 6H O)
(s, 1H, HC = N), 8.67–7.07 (m, 19H, Ar-H), 0.29 (s, 9H,
4
2
2
6 2
2
+
in THF (10 ml), an equimolar solution of ligand (L)
0.456 mmol, 0.200 g) in CH Cl (20 ml) solution was added
while stirring. The mixture was stirred for 20 min at room
temperature. To this, a solution of one equivalent of 1, 10-
phenanthroline (0.456 mmol, 0.0904 g) in THF (10 ml) was
added with continuous stirring. The mixture was refluxed for
h. The precipitate obtained was filtered off, washed with
diethyl ether and dried under vacuum.
a: Yield: 78%; Elemental analyses (C, H and N, wt%) Anal.
Calc. for C H N O ClSiNi: C, 58.82; H, 3.77; N, 7.22;
Si(CH ) ), MS (ESI): m/z 652 (M-ClO ) ; 5a:Yield: 80%;
3
3
4
(
Elemental analyses (C, H and N, wt%) Anal. Calc. for
C H N O BF SiNi: C, 58.49; H, 3.95; N, 7.58; Found: C,
2
2
3
6
29
4
3
4
−1
58.41; H, 3.89; N, 7.65; IR (KBr, cm ): 2196, ν(C ≡ C);
2145, ν(C ≡ CSi); 1610, ν(C = N); 1073, ν(BF ); UV-Vis
4
3
−1
−1
(DMF) λmax (nm) (ε ×10 , M cm ): 243 (24.8), 278 (14.5),
366 (7.89), 535 (1.22); H NMR (d -DMSO) (300 MHz): δ 8.65
1
4
6
(s, 1H, HC = N), 8.69–7.15 (m, 19H, Ar-H), 0.28 (s, 9H,
+
1
Si(CH ) ); MS (ESI): m/z 652 (M-BF ) ; 6a: Yield: 84%;
3
3
4
Elemental analyses (C, H and N, wt%) Anal. Calc. for
C H N O PF SiNi: C, 54.23; H, 3.67; N, 7.03; Found: C,
3
8 29 4 7
−1
Found: C, 58.75; H, 3.70; N, 7.29; IR (KBr, cm ): 2196,
3
6
29
4
3
6
−1
ν(C ≡ C); 2147, ν(C ≡ CSi); 1609, ν(C = N); 1097, 623,
54.16; H, 3.60; N, 7.11; IR (KBr, cm ): 2194, ν(C ≡ C);
2147, ν(C ≡ CSi); 1608, ν(C = N); 843, 558, ν(P-F); UV-Vis
(DMF) λmax (nm) (ε ×10 , M cm ): 249 (24.1), 281 (14.8),
3
−1
−1
ν(ClO ); UV-Vis (DMF) λ
(
(nm) (ε ×10 , M cm ): 235
4
max
1
3
−1
−1
25.2), 274 (16.2), 373 (7.33), 525 (1.23); H NMR (d -DMSO)
300 MHz): δ 8.65 (s, 1H, HC = N), 8.68–7.01 (m, 19H, Ar-H),
6
1
(
0
372 (7.69), 527 (0.81); H NMR (d -DMSO) (300 MHz): δ 8.65
6
+
.29 (s, 9H, Si(CH ) ); MS (ESI): 652 m/z (M-ClO ) ; 2a:
(s, 1H, HC = N), 8.71–7.19 (m, 19H, Ar-H), 0.29 (s, 9H,
3
3
4
+
Yield: 81%; Elemental analyses (C, H and N, wt%) Anal.
Calc. for C H N O BF SiNi: C, 59.80; H, 3.83; N, 7.34;
Found: C, 59.72; H, 3.76; N, 7.41; IR (KBr, cm ): 2197,
Si(CH ) ); MS (ESI): m/z 652 (M-PF ) .
3
3
6
3
8
29
4
3
4
−1
Synthesis of Complex [Zn(L)(phen)]X (1b-3b)
ν(C ≡ C); 2146, ν(C ≡ CSi); 1607, ν(C = N); 1071, ν(BF );
4
3
−1
−1
UV-Vis (DMF) λmax (nm) (ε ×10 , M cm ): 244 (25.1), 276
To a solution of the appropriate Zn(II) salt, ((0.399 mmol,
0.1486 g), Zn(ClO ) ·6H O; (0.399 mmol, 0.0954 g),
1
(
15.2), 376 (8.48), 536 (1.67); H NMR (d -DMSO)
6
4 2
2
(
300 MHz): δ 8.64 (s, 1H, HC = N), 8.66–6.90 (m, 19H, Ar-
Zn(BF4)2 or (0.399 mmol, 0.1418 g), Zn(PF ) ) in
THF (10 ml), an equimolar solution of ligand (L)
6 2
+
H), 0.29 (s, 9H, Si(CH ) ); MS (ESI): m/z 652 (M-BF ) ; 3a:
3
3
4
Yield: 80%. Elemental analyses (C, H and N, wt%) Anal. Calc.
for C H N O PF SiNi: C, 55.56; H, 3.56; N, 6.82; Found: C,
(0.399 mmol, 0.175 g) in CH Cl (20 ml) solution was added
2
2
while stirring. The mixture was stirred for 20 min at room
temperature. To this, a solution of one equivalent of 1, 10-
phenanthroline (0.399 mmol, 0.0791 g) in THF (10 ml) was
added with continuous stirring. The mixture was refluxed for
4 h. The precipitate obtained was filtered off, washed with
diethyl ether and dried under vacuum.
38
29
4
3
6
−1
55.49; H, 3.48; N, 6.91; IR (KBr, cm ): 2194, ν(C ≡ C); 2144,
ν(C ≡ CSi); 1606, ν(C = N); 845, 558, ν(P-F); UV-Vis (DMF)
3
−1
−1
λmax (nm) (ε ×10 , M cm ): 245 (25.7), 277 (15.0), 370
1
(
7.52), 529 (1.08); H NMR (d -DMSO) (300 MHz): δ 8.65
6
(
s, 1H, HC = N), 8.64–7.09 (m, 19H, Ar-H), 0.28 (s, 9H,
+
Si(CH ) ); MS (ESI): m/z 652 (M-PF ) .
1b: Yield: 79%; Elemental analyses (C, H and N, wt%)
Anal. Calc. for C H N O ClSiZn: C, 58.32; H, 3.73; N,
3
3
6
3
8 29 4 7
−
1
Synthesis of Complex [Ni(L)(bipy)]X (4a-6a)
7.16; Found: C, 58.27; H, 3.66; N, 7.23; IR (KBr, cm ):
2
195, ν(C ≡ C); 2148, ν(C ≡ CSi); 1606, ν(C = N); 1096,
3
−1
−1
To a solution of the appropriate Ni(II) salt, ((0.490 mmol,
625, ν(ClO ); UV-Vis (DMF) λ (nm) (ε ×10 , M cm ):
4 max
239 (27.7), 291 (16.8), 408 (11.0); H NMR (d -DMSO)
1
0
.1793 g), Ni(ClO ) ·6H O; (0.490 mmol, 0.1669 g),
4
2
2
6
.
Ni(BF ) ·6H O or (0.490 mmol, 0.0874 g), Ni(PF ) 6
(300 MHz): δ 8.65 (s, 1H, HC = N), 8.71–7.04 (m, 19H, Ar-
4
2
2
6 2
+
H O) in THF (10 ml), an equimolar solution of ligand (L)
2
H), 0.28 (s, 9H, Si(CH ) ); MS (ESI): m/z 683 (M-ClO ) ;
3 3
4
(
0.490 mmol, 0.215 g) in CH Cl (20 ml) solution was added
2b:Yield:76%; Elemental analyses (C, H and N, wt%) Anal.
2
2
while stirring. The mixture was stirred for 20 min at room
temperature. To this, a solution of one equivalent of 2, 2´-
bipyridine (0.490 mmol, 0.0765 g) in THF (10 ml) was added
with continuous stirring. The mixture was refluxed for 4 h.
The precipitate obtained was filtered off, washed with diethyl
ether and dried under vacuum.
Calc. for C H N O BF SiZn: C, 59.28; H, 3.80; N, 7.28;
Found: C, 59.23; H, 3.74; N, 7.33; IR (KBr, cm ): 2196,
3
8
29
4
3
4
−1
ν(C ≡ C); 2146, ν(C ≡ CSi); 1608, ν(C = N); 1067, ν(BF );
4
3
−1
−1
UV-Vis (DMF) λmax (nm) (ε ×10 , M cm ): 238 (28.6),
294 (16.4), 420 (11.7); H NMR (d -DMSO) (300 MHz): δ
1
6
8.64 (s, 1H, HC = N), 8.68–7.10 (m, 19H, Ar-H), 0.29 (s, 9H,
+
4a: Yield: 77%;. Elemental analyses (C, H and N, wt%) Anal.
Si(CH ) ); MS (ESI): m/z 683 (M-BF ) ; 3b: Yield: 82%;
3
3
4
Calc. for C H N O ClSiNi: C, 57.51; H, 3.89; N, 7.45; Found:
Elemental analyses (C, H and N, wt%) Anal. Calc. for
C H N O PF SiZn: C, 55.11; H, 3.53; N, 6.77; Found: C,
36 29 4 7
−1
C, 57.46; H, 3.82; N, 7.53; IR (KBr, cm ): 2195, ν(C ≡ C);
146, ν(C ≡ CSi); 1609, ν(C = N); 1096, 624, ν(ClO ); UV-Vis
3
8
29
4
3
6
−1
2
55.07; H, 3.49; N, 6.81; IR (KBr, cm ): 2194, ν(C ≡ C);
2145, ν(C ≡ CSi); 1607, ν(C = N); 845, 558, ν(P-F); UV-
4
3
−1
−1
(DMF) λmax (nm) (ε ×10 , M cm ): 242 (24.2), 275 (15.5),
1
3
−1
−1
359 (8.23), 518 (0.99); H NMR (d -DMSO) (300 MHz): δ 8.64
Vis (DMF) λmax (nm) (ε ×10 , M cm ): 246 (27.9), 308
6

J Fluoresc
1
Table 1 Crystal data and structure refinement details for L
(
16.3), 416 (10.0); H NMR (d -DMSO) (300 MHz): δ 8.64
6
(
s, 1H, HC = N), 8.73–7.15 (m, 19H, Ar-H), 0.29 (s, 9H,
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
26 22 2 3
C H N O Si
+
Si(CH ) ); MS (ESI): m/z 683 (M-PF ) .
438.54
Monoclinic
P2
3
3
6
1
Synthesis of Complex [Zn(L)(bipy)]X (4b-6b)
6.0262(3)
7.3503 (4)
b (Å)
c (Å)
α (°)
β (°)
25.4608 (14)
90.00
91.266
90.00(3)
1127.49(10)
2
1.292
0.562
460
To a solution of the appropriate Zn(II) salt, ((0.421 mmol,
0
.1571 g), Zn(ClO ) ·6 H O; (0.421 mmol, 0.1008 g),
4 2 2
Zn(BF4)2 or (0.421 mmol, 0.1499 g), Zn(PF ) ) in
γ (°)
V (A )
6 2
3
THF (10 ml), an equimolar quantity of L (0.421 mmol,
Z
0
.185 g) in CH Cl (20 ml) was added while stirring. The mix-
3
2
2
Density (mg/m )
μ (M
F (000)
Data collection
Temperature (K)
θ mini.-maxi.(deg)
Data set [h, k, l]
Total, unique data, Rint
Observed data
Extinction coefficient
Refinement
No. of reflection collected
Data / restraints / parameters
1 1
R , R
wR2, wR2
Goodness-of-fit
1
ture was stirred for 20 min at room temperature. To this, a
solution of one equivalent of 2, 2´-bipyridine (0.421 mmol,
K
0 α
)(mm−
)
0.0659 g) in THF (10 ml) was added with continuous stirring.
293(2)
The mixture was refluxed for 4 h. The precipitate obtained was
filtered off, washed with diethyl ether and dried under vaccum.
2.400 to 25.992
-7/7,-9/9,-31/31
[R(int) = 0.0641]
>2σ(I)
4
b: Yield: 75%. Elemental analyses (C, H and N, wt%)
Anal. Calc. for C H N O ClSiZn: C, 57.00; H, 3.85; N,
3
6
29
4
7
n/a
−
1
2
7
2
6
2
.39; Found: C, 56.93; H, 3.79; N, 7.44; IR (KBr, cm ):
Full-matrix least-squares on F
24,414
4428 / 1 / 296
0.0513, 0.0876
0.1187, 0.1386
1.046
195, ν(C ≡ C); 2147, ν(C ≡ CSi); 1606, ν(C = N); 1095,
3
−1
−1
23, ν(ClO ); UV-Vis (DMF) λmax (nm) (ε ×10 , M cm ):
4
1
49 (27.3), 292 (16.5), 397 (11.3) ; H NMR (d -DMSO)
6
(
300 MHz): δ 8.65 (s, 1H, HC = N), 8.65–6.96 (m, 19H, Ar-
+
H), 0.29 (s, 9H, Si(CH ) ), MS (ESI): m/z 683 (M-ClO ) ; 5b:
3
3
4
Yield: 81%; Elemental analyses (C, H and N, wt%) Anal.
Calc. for C H N O BF SiZn: C, 57.97; H, 3.92; N, 7.51;
Found: C, 57.91; H, 3.87; N, 7.56; IR (KBr, cm ): 2194,
97 was used to solution of structure and full matrix least-squares
refinement on F2 [24]. Molecular and packing diagrams were
generated using ORTEP-3 and Mercury-3.
3
6
29
4
3
4
−1
ν(C ≡ C); 2148, ν(C ≡ CSi); 1609, ν(C = N); 1071, ν(BF );
4
3
−1
−1
UV-Vis (DMF) λmax (nm) (ε ×10 , M cm ): 254 (28.4),
12 16.0), 410 (11.2); H NMR (d -DMSO) (300 MHz): δ
1
3
6
8
.65 (s, 1H, HC = N), 8.69–6.98 (m, 19H, Ar-H), 0.28 (s, 9H,
Results and Discussion
+
Si(CH ) ); MS (ESI): m/z 683 (M-BF ) ; 6b: Yield: 79%;
3
3
4
Elemental analyses (C, H and N, wt%) Anal. Calc. for
C H N O PF SiZn: C, 53.77; H, 3.64; N, 6.97; Found: C,
The treatment of 5-ethynylsalicylaldehyde with 1-iodo-4-
nitrobenzene in presence of PdCl (PPh ) and CuI in
3
6
29
4
3
6
2
3 2
−1
5
2
3.69; H, 3.61; N, 7.05; IR (KBr, cm ): 2196, ν(C ≡ C);
145, ν(C ≡ CSi); 1610, ν(C = N); 844, 558, ν(P-F); UV-
C H C l / N E t
3
a t 8 0 ° C a f f o r d e d 5 - ( 4 -
2
2
nitrophenylethynyl)salicylaldehyde in good yield. Further re-
action of 5-(4-nitrophenylethynyl)salicylaldehyde with
4-(trimethylsilylethynyl)aniline in THF afforded correspond-
ing Schiff base ligand 2-{(E)-[(4-trimethylsilylethynylphenyl)
imino]methyl}-4-(4-nitrophenylethynyl)phenol (L) in excel-
lent yield (Scheme 1). A series of ternary complexes
[Ni(L)(phen/bipy)]X (1a-6a) and [Zn(L)(phen/bipy)]X
3
−1
−1
Vis (DMF) λmax (nm) (ε ×10 , M cm ): 255 (25.5), 317
1
(
16.1), 413 (10.6); H NMR (d -DMSO) (300 MHz): δ 8.64
6
(
s, 1H, HC = N), 8.75–7.11 (m, 19H, Ar-H), 0.28 (s, 9H,
+
Si(CH ) ); MS (ESI): m/z 683(M-PF ) .
3
3
6
X-Ray Crystallography
(1b-6b) were prepared by the reaction of L with metal(II) salt
Single crystal X-ray structural study of L was performed on
Bruker KAPPA APEX-II diffractometer. Data were collected
in omega and phi scan mode, MoKα =0.71073 Å at room
temperature with scan width of 0.3° at θ (0°, 90° and 180°) by
keeping the distance at 40 mm between sample to fixed detector
at 24°. The X-ray generator was operated at 50 kV and 30 mA.
The details of crystal data, data collection and the refinements
are given in Table 1. The X-ray data collection was monitored
by SMART program (Bruker, 2003). All the data were corrected
using SAINTand SADABS programs (Bruker, 2003). SHELX-
in presence of 1, 10-phenanthroline or 2, 2´-bipyridine in
THF:CH Cl (1:1) mixture (where; phen = 1, 10-
2
2
−
−
phenanthroline; bipy = 2, 2´-bipyridine; X = ClO , BF ,
PF ) (Fig. 1). The complexes prepared show a great thermal
4
4
−
6
stability and are moisture insensitive in solid state.
Composition and identity of all the complexes were deduced
1
from satisfactory elemental analysis, FT-IR, UV-Vis, H
NMR, and mass spectral studies. They are freely soluble in
DMF and DMSO but sparingly soluble in dichloromethane,
chloroform and methanol.

J Fluoresc
CHO
OH
CHO
OH
CHO
OH
KOH
HC CSi(CH3)3
Br
Si(CH3)3
H
PdCl (PPh ) , CuI, NEt
CH Cl , MeOH
2
3
2
3
2
2
Si(CH3)3
PdCl (PPh )
2
3
2
CuI
I
NO2
NEt3
CHO
OH
N
H N
Si(CH3)3
2
O N
O N
OH
2
2
THF
Scheme 1 Synthetic route to the preparation of L
X-Ray Structure of L
hydrogen bond. All bond lengths and angles in (C1-C6), (C9-
C14) and (C16-C21), benzene rings have normal values
1.376(6), 1.381(6) and 1.386(6) Å respectively. The enol form
is observed in the asymmetric unit as concluded from bond
lengths C15-N2 (1.273(5) Å) and C12-O3 (1.342(5) Å). The
two benzene rings along with HC = N displays the trans con-
figuration and torsion angles of N(2)-C(16)-C(17)-C(18) is
177.6(4)°, C(17)-C(16)-N(2)-C(15) is −166.8(4)° and N(2)-
C(16)-C(21)-C(20) is 177.3(4)°, these angles are reported in
the literature with values of −176.8(2)°, −146.7(2)° and
175.5(2)° [26]. The bond distance between C(7)-C(8) is
1.194(6) Å and C(22)-C(23) is 1.202(6) Å and Si(1)-C(23) is
1.848(4) Å are smaller due to the presence of C ≡ CSiMe3.
These results are comparable with those of the ligands reported
earlier containing the similar moiety [27]. The ligand L partic-
ipate in weak C(6)-H(6)-O(1) and C(2)-H(2)-O(2) hydrogen
bonds with oxygen atom from nearest nitro group in the crystal
lattice, at the same time it being an acceptor of such hydrogen
bond through its own (O1) and (O2) atom.
Single crystals of ligand L suitable for X-ray diffraction were
obtained by slow evaporation of saturated solution of L in
dichloromethane. The X-ray diffraction data was solved in
the monoclinic crystal system with space group P2 . The mo-
1
lecular structure of L along with atom numbering scheme is
illustrated in Fig. 2 and the selected bond lengths and bond
angles are summarized in Table 2.
The crystal and molecular structure of L reveals some inter-
esting findings. First the structure exhibits a strong intramolec-
ular (O3-H3A-N2) hydrogen bond between the nitrogen atom
C = N of Schiff base and hydrogen atom of the -OH group of the
salicylaldehyde ring with a distance of 147(5) Å which is in
good agreement with the values reported in the literature [25].
Individually, each benzene ring in the molecule is almost planar
in which the C3, C14 and C20 atom from each benzene ring has
best plane by 0.042(3), 0.036(2) and 0.037(2) Å. The molecular
packing of the structure is stabilized by C-H-O intermolecular
Si(CH3)3
Si(CH3)3
N
N
N
O
N
N
N
O
M
M
O N
O N
2
2
X
X
1
a-3a and 1b-3b
4a-6a and 4b-6b
-
-
-
M= Ni(II)(1a-6a), Zn(II) (1b-6b); X= ClO , BF , PF
4
4
6
Fig. 1 Proposed molecular structure of the complexes 1a-6a and 1b-6b

J Fluoresc
Fig. 2 Single crystal X-ray diffraction structure of L
1607 cm− for 1b-6b. This change in frequency indicating
1
Spectroscopic Properties
imine nitrogen coordination. The characteristic band appeared
−
1
The IR spectra of selected groups in the spectra of L and their
Ni(II) (1a-6a) and Zn(II) (1b-6b) complexes are given in sec-
tion 2. In the IR spectra of L, a broad band at 2995 cm
at 1287 cm in L attributed to the phenolic stretch. This band
−1
observed at lower wave number by ca 10–20 cm in the
spectra of 1a-6a and 1b-6b relative to L suggesting involve-
ment of the C-O moiety in coordination. In addition, bands at
−1
assigned to ν(OH) vibration associated intramolecularly with
the nitrogen atom of the CH = N group. This band disappeared
in 1a-6a and 1b-6b confirmed the coordination of phenolic
oxygen to the metal (II) centers [28]. The medium intensity
−1
ca 1500, 800 and 730 cm in the phenanthroline complexes
−1
and 760, 740 cm in the bipyridine complexes confirm the
coordination of these ligand in the complexes. The perchlorate
complexes 1a, 1b and 4a, 4b exhibit typical bands in expected
−1
band at 2203, 2155 cm in the spectra of L undergo smaller
deshielding in all Ni(II) and Zn(II) complexes. Along with this
band the ligand L and its 1a-6a and 1b-6b complexes exhibit
−1
regions; broad band at ~1096 cm (ν ) and strong band at
3
−
1
~624 cm (ν ) are due to stretching vibration of non-
4
−
1
−
vibrations of Me Si at around 1248 and 840 cm . Another
coordinated ClO ion [29]. A broad band at around
1069 cm in 2a and 5a and 1072 cm in 2b and 5b corre-
sponds to the presence of BF anion. However, existence of
PF6 ion is exhibited by intense and medium bands occurring
3
1
4
band at 1618 cm− observed in the spectra of L slightly shifted
towards lower frequency at 1608 cm for 1a-6a and
−1
−1
−
1
−
4
−
−1
at ~844 and ~558 cm , respectively confirming formation of
Table 2 Selected bond lengths (Ǻ) and bond angles (°) for L
complexes 3a, 3b, 6a and 6b [30].
Bond lengths (Ǻ)
Bond angles (°)
C(7)-C(8)
1.194(6)
1.202(6)
1.466(5)
1.212(5)
1.213(5)
1.342(5)
1.273(5)
1.429(5)
1.848(4)
1.847(7)
1.838(6)
1.851(6)
O(1)-N(1)-O(2)
O(1)-N(1)-C(1)
O(2)-N(1)-C(1)
C(15)-N(2)-C(16)
C(25)Si(1)-C(24)
C(25)Si(1)-C(23)
C(24)Si(1)-C(23)
C(25)Si(1)-C(26)
C(24)Si(1)-C(26)
C(23)Si(1)-C(26)
123.2(4)
118.0(4)
118.7(4)
120.7(4)
110.6(4)
106.8(3)
109.0(3)
111.4(3)
109.8(3)
109.1(3)
C(22)-C(23)
C(1)-N(1)
N(1)-O(1)
N(1)-O(2)
C(12)-O(3)
C(15)-N(2)
C(16)-N(2)
Si(1)-C(23)
Si(1)-C(24)
Si(1)-C(25)
Si(1)-C(26)
Fig. 3 Electronic Absorption Spectra of complexes 1a-6a

J Fluoresc
with phen or bipy the resonance for phenolic protons get
disappeared in the spectra of 1a-6a and 1b-6b indicating de-
protonation of L and coordination of phenolic oxygen to the
metal ion [32]. The imine proton shifted to downfield region
and observed at around δ 8.65 ppm in 1a-6a and δ 8.64 ppm in
1
b-6b confirm the coordination through imine nitrogen [33].
1
The H NMR spectra shows several coupled multiplets along
with additional peaks in the aromatic region at δ 6.90–
8.71 ppm for 1a-6a and δ 6.96–8.75 ppm for 1b-6b associated
with coordinated phen or bipy ligand along with ring protons
of L. However, a sharp singlet at δ 0.27 ppm in L due to
terminal SiMe remains unchanged in 1a–6a and 1b–6b.
3
Fig. 4 Electronic Absorption Spectra of complexes 1b-6b
Thermogravimetric Analysis
The UV-visible absorption spectra of L and its Ni(II) (1a-
The thermal behavior of Ni(II) (1a-6a) and Zn(II) (1b-6b)
complexes were studied by thermogravimetric (TG) analysis
in the range 25 to 800 °C under flowing nitrogen at a heating
6
a) and Zn(II) (1b-6b) complexes were measured in
−4
dimethylformamide solution (10 M) at room temperature
and data are summarized in section 2. The absorption spectra
of L exhibit two intense bands at 231 and 265 nm which may
associated with π → π* and n → π* intraligand transitions,
respectively. Analogous bands are also observed in the com-
plexes at 235–249 and 274–281 nm for Ni(II) (1a-6a) (Fig. 3)
and 238–255 and 291–317 nm for Zn(II) (1b-6b) (Fig. 4)
complexes. The observed bathochromic shift in these com-
plexes relative to L is in accordance with coordination of L
to the metal ion. The low energy transition located at 359–
−1
rate of 10 °C min . The perchlorate complexes 1a, 4a, 1b and
4b are potentially explosive and hence are not studied for
safety reason. All Ni(II) and Zn(II) complexes are stable up
to 180–225 °C, indicating that these complexes do not under-
go mass loss of water or other solvent molecule. The thermal
decomposition process of 2a-6a and 2b-6b involves two de-
composition stages. The TGA plot of complexes 2a, 3a, 2b
and 3b shows the first decomposition stage is assigned to the
decomposition of coordinated salicylidene ligand L and takes
place in the region 180–525 °C (2a), 198–519 °C (3a), 210–
538 °C (2b) and 218–532 °C (3b) corresponding to mass loss
of 56.99%, 52.93%, 56.61% and 52.49%, respectively (theo-
retical mass loss 57.32% (2a), 53.26% (3a), 56.82% (2b) and
52.83% (3b)). The second decomposition stage occurs be-
tween 525–728, 519–714, 538–740 and 532–735 °C cor-
responds to mass loss of 25.61% (2a), 23.88% (3a), 25.56%
(2b) and 23.67% (3b), respectively attributed to the decom-
position of coordinated 1, 10-phenanthroline leaving NiBF4,
NiPF and ZnBF , ZnPF as final residue (theoretical mass
3
76 nm in 1a-6a and 397–420 nm in 1b-6b are attributed to
the metal to ligand charge transfer (MLCT) transition. In ad-
dition to these bands a weak absorption at 525–536 nm in 1a-
3
a and 518–535 nm in 4a-6a presumably due to spin allowed
1
1
(
A1g → A ) d-d transition for Ni(II) in square planar geom-
2g
etry [31]. Low value of d-d transition observed in phen com-
plexes (1a-3a and 1b-3b) indicating that in these complexes
the basal planes are comparatively more distorted than bipy
complexes (4a-6a and 4b-6b).
1
The H NMR spectra of L showed two characteristics res-
6
4
6
onances, first at ~δ 13.29 ppm corresponding to the phenolic -
OH proton and another at ~δ 8.61 ppm assigned to the imine
loss 25.97% (2a), 24.13% (3a), 25.74% (2b) and 23.93%
(3b)). The complexes 5a, 6a, 5b and 6b show very similar
behavior to the above, once again the complexes undergo a
(
CH = N) proton. After coordination to Ni(II) and Zn(II) along
Table 3 Electrochemical data of
Ni(II) complexes (1a-6a) in
dimethylformamide (10− M)
Compound
Oxidation potentials
pa(V) pc(V)
Reduction potentials
4
E
E
p
E1/2(V) ΔE (mV)
Epa(V)
Epc(V)
p
E1/2(V) ΔE (mV)
1
2
3
4
5
6
a
a
a
a
a
a
1.298
1.391
1.265
1.193
1.227
1.164
1.123
1.135
1.104
1.021
0.989
0.957
1.211(175)
1.263(256)
1.184(161)
1.107(172)
1.108(238)
1.065(207)
-1.107
-1.152
-1.139
-1.184
-1.249
-1.221
-1.245
-1.369
-1.347
-1.292
-1.325
-1.274
-1.176(138)
-1.260(217)
-1.243(208)
-1.238(108)
-1.287(76)
-1.247(53)

J Fluoresc
Fig. 5 Cyclic voltammogram of 1a
Fig. 7 Emission spectra of complexes 1a-6a
significant weight loss of 58.89% (5a), 54.72% (6a), 58.52%
in Table 3 and cyclic voltammogram of representative com-
plexes 1a and 5a are shown in Figs. 5 and 6, respectively.
All the Ni(II) complexes exhibit both anodic and cathodic
redox potentials. In anodic potential region the reduction wave
(Epc, 0.957–1.135 V) corresponding to Ni(III)/Ni(II) reaction is
obtained. During the reverse scan the oxidation of Ni(II)/Ni(III)
occurs in the potential range (Epa, 1.164–1.391 V). In cathodic
potential region the reduction wave (Epc, −1.245 to −1.369 V)
corresponding to Ni(II)/Ni(I) reaction is obtained. During the
reverse scan the oxidation of Ni(I)/Ni(II) occurs in the potential
range (Epa, −1.107 to −1.249 V). However the values of the
limiting peak-to-peak separation (ΔEp) ranging from 53 to
256 mV reveal that this process can be quasireversible.
Further, the redox process among the mixed ligand Ni(II) com-
plexes of phen appears at more positive potential (1.184–
(
1
5b) and 54.31% (6b) in the temperature range 184–529 (5a),
93–515 (6a), 207–542 (5b) and 220–551 °C (6b) is assigned
to the decomposition of coordinated salicylidene ligand L
(
(
theoretical mass loss. 59.19% (5a), 54.87% (6a), 58.65%
5b) and 54.41% (6b) respectively), while the second decom-
position stage occurs in the temperature range 529–722 (5a),
15–726 (6a), 542–739 (5b) and 551–732 °C (6b), indicative
5
of gradual breakdown of coordinated 2, 2´-bipyridine (ob-
served weight loss of 21.01%, 19.49%, 20.87% and 19.36%;
theoretical mass loss of 21.12% (5a) and 19.59% (6a),
2
0.96% (5b) and 19.42% (6b)) leaving NiBF , NiPF ,
4 6
ZnBF and ZnPF as a final residue.
4
6
Electrochemical Studies
1.263 V) as compared to those for corresponding bipy com-
plexes (1.065–1.108 V). This trend may be due to good stabili-
zation of the phen complexes compared to the bipy complexes,
as a result of its strong π-acidic character. These results are in
close agreement with those reported in the literature [34].
The electrochemical behaviour of Ni(II) complexes (1a-6a)
were studied by cyclic voltammetry in dimethylformamide
solution (10− M) containing 0.05 M n-Bu NClO as
4
4
4
supporting electrolyte. The electrochemical data are presented
Fig. 6 Cyclic voltammogram of 5a
Fig. 8 Emission spectra of complexes 1b-6b

J Fluoresc
−
−
−
Emission Behavior
BF <ClO <PF . These results could be attributed to differ-
4 4 6
−
−
−
ence in coordinating ability of BF , ClO , and PF with
4
4
6
The emission spectra of the ligand L and its Ni(II) (1a-6a) and
Z n ( I I ) ( 1 b - 6b ) c om p l e x e s w er e e x p l or e d i n
metal ion as well as difference in solubility of the complexes
in solution [36].
−4
dimethylformamide solution (10 M). The emission spectra
of 1a-6a and 1b-6b are depicted in Figs. 7 and 8 and data are
collected in Table 4. The ligand L exhibit emission in the
green region centered at λmax = 488 nm with an excitation at
λmax = 330 nm attributed to emission due to ligand centered
π–π* electron transition. In contrast, all the Ni(II) and Zn(II)
complexes show steady state marked differences in emission
behaviour in DMF solution. The emission spectra of 1a-3a
and 4a-6a show broad emission spectra with emission maxi-
ma at 545–550 nm in 1a-3a and 535–541 nm in 4a-6a upon
excitation at 335–346 and 345–355 nm, respectively. The
emission spectra of 1b-3b and 4b-6b bathochromically shifted
at longer wavelength with high intensity and exhibit emission
at 558–565 and 548–555 nm upon excitation at 320–330 and
The fluorescence quantum yield (ϕ) of all complexes was
determined with reference to quinine sulphate (ϕ = 0.52) and
observed at 0.1845–0.2413 for 1a-6a and 0.4595–0.5381 for
1b-6b. The area of the emission spectrum was integrated using
the software available on the instrument and the quantum yields
were calculated according to the following equation.
Â
Ã
Â
Ã
2
φS
φR
½A Š
ðAbsÞ
ðAbsÞ
η
S
R
S
¼
X
Â
à X
2
½ARŠ
½η Š
S
R
Here ϕ and ϕ are the fluorescence quantum yield of
S
R
the sample and reference, respectively. A and A are the
S
R
areas under the fluorescence spectra of the sample and
reference, respectively, (Abs) and (Abs) are the respec-
3
40–350 nm, respectively. The emission observed in these
S
R
complexes reveals that the emission origin predominantly
due to π → π* intra-ligand. Compare to L the significant
bathochromic shift in the emission spectra of Ni(II) and
Zn(II) complexes confirm the chelation of L to metal(II) ion
which effectively increases the ligand conformational rigidity
and thus reducing the non-radiative loss [35]. It was observed
that the fluorescence efficiency of the phen complexes (1a–3a
and 1b-3b) appears at longer wavelength with enhanced in-
tensity as compared to bipy (4a-6a and 4b–6b) complexes
tive optical densities of the sample and the reference so-
lution at the wavelength of excitation and η and η are
s
R
the values of refractive index for the respective solvent
used for the sample and reference. The significant in-
crease in ϕ value is observed for 1a-3a and 1b-3b as
compared to 4a-6a and 4b-6b. These results might be
due to better coordination of ligands to Ni(II) and
Zn(II). The Life time data of all the compounds are taken
at 298 K in DMF solution when excited at 320 nm. The
observed decay of the complexes fit well with mono ex-
ponential nature of the complexes and found to be 2.58–
3.38 ns for 1a-6a and 3.38–4.32 ns for 1b-6b (Table 4).
Compare to 1a-6a the average lifetime of 1b-6b is longer
than those observed for 1a-6a. These results could be
attributed to red shifted emission and increased emission
intensity observed in 1b-6b compare to 1a-6a.
(
Table 4). This is might be due to non-radiative decay process
which is more effective in the bipy complexes as compared to
phen complexes. It was also observed that the emission ener-
gy of the Ni(II) and Zn(II) complexes is sensitive to size of the
counter anion (Table 4). When the size of the counter-anion
increases the emission wavelength of all the complexes de-
creases and emission energy follows the sequence
Table 4 Emission data of Nickel
−
1
9
−1
9
Complex
λex (nm)
λem (nm)
ϕ
τ (ns)
K
r
(s /10 )
Knr (s /10 )
(II) (1a-6a) and Zn(II) (1b-6b)
complexes in dimethylformamide
1
2
3
4
5
6
1
2
3
4
5
6
a
a
a
a
a
a
b
b
b
b
b
b
335
340
346
345
350
355
320
325
330
340
345
350
547
550
545
537
541
535
560
565
558
550
555
548
0.2362
0.2413
0.2081
0.1950
0.2174
0.1845
0.4976
0.5381
0.4835
0.4792
0.4923
0.4595
2.99
3.38
2.74
2.69
3.16
2.58
3.91
4.32
3.84
3.46
4.11
3.38
0.07899
0.07139
0.07595
0.07249
0.06879
0.07147
0.1272
0.1245
0.1259
0.1385
0.1197
0.2554
0.2244
0.2890
0.2992
0.2476
0.3161
0.1285
0.1069
0.1345
0.1505
0.1236
0.1599
0.1359

J Fluoresc
1
0. Oliveri IP, Failla S, Malandrinoa G, Bella SD (2011) New molecu-
lar architectures by aggregation of tailored zinc(II) Schiff-base com-
plexes. New J Chem 35:2826–2831
Conclusion
In present study some nickel(II) and zinc(II) complexes of the
11. Zhou L, Cai P, Feng Y, Cheng J, Xiang H, Liu J, Wu D, Zhou X
type [Ni(L)(phen/bipy)]X(1a–6a) and [Zn(L) (phen/bipy)]X
(2012) Synthesis and photophysical properties of water-soluble
sulfonato-salen-type Schiff bases and their applications of fluores-
(
1 b – 6 b ) ( w h e r e
L
=
2 - { ( E ) - [ ( 4 -
2
+
cence sensors for Cu in water and living cells. Anal Chim Acta
35:96–106
trimethylsilylethynylphenyl)imino]methyl}-4-(4-
7
nitrophenylethynyl)phenol; phen = 1, 10-phenanthroline,
1
1
1
1
2. Consiglio G, Failla S, Finocchiaro P, Oliveri IP, Bella SD (2012)
Aggregation properties of bis(salicylaldiminato)zinc(II) Schiff-base
complexes and their Lewis acidic character. Dalton Trans 41:387–395
3. Hai Y, Chen J-J, Zhao P, Lv H, Yu Y, Xu P, Zhang J-L (2011)
Luminescent zinc salen complexes as single and two-photon fluores-
cence subcellular imaging probes. Chem Commun 47:2435–2437
4. Sano T, Nishio Y, Hamada Y, Takahashi H, Usuki T, Shibata K
(2000) Design of conjugated molecular materials for optoelectron-
ics. J Mater Chem 10:157–161
5. Averseng F, Lacroix PG, Malfant I, Dahana F, Nakatani K (2000)
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 10:1013–1018
−
−
−
bipy = 2,2-bipyridine; X = ClO , BF , PF ) have been
4
4
6
prepared and characterized. All Ni(II) complexes exhibit both
positive and negative redox potential corresponding to Ni(II)/
Ni(III) and Ni(II)/Ni(I) process, respectively. Further, the re-
dox processes of Ni(II)-phenanthroline complexes appears at
more positive potential as compared to those for correspond-
ing bipyridine complexes. The room temperature lumines-
cence is observed for all complexes in DMF solution as a
result of π → π* ILCT transition. The size of the counter
anion and heterocyclic coligands phen and bipy shows pro-
nounced effect on emission properties of the complexes.
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1
Acknowledgements We gratefully acknowledge Head, Sophisticated
Analytical Instrument Facility Center, IIT, Madras, India for providing
single crystal X-ray facilities.
1
1
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