Synthesis and spectroscopic properties of Ni(II) complexes of some aroyl hydrazone ligands with 2,6-diacetyl pyridine monooxime: X-ray crystal structure of the salicyloylhydrazone Ni(II) complex

Article abstract of DOI:10.1016/j.ica.2010.05.009

Five Ni(II) complexes of aroyl hydrazone ligands with 2,6-diacetyl pyridine monooxime are reported. X-ray crystal structure of the Ni(II) salicyloylhydrazone complex is also reported. In these complexes Ni(II) is in a distorted octahedral N₄O₂ coordination environment, with each of the two ligands coordinating through the pyridine nitrogen, imino-hydrazone nitrogen and the deprotonated oxygen of the hydrazone moiety. The iminooxime group remain uncoordinated in both the ligands and the planes containing the CH₃-CN-OH groups are orthogonal to the adjacent pyridine rings. On excitation at 375 nm, the ligands as well as the Ni(II) complexes, show luminescence. However, the Ni(II) complexes have much lower quantum yield of emission than the free ligands.

Full text of DOI:10.1016/j.ica.2010.05.009

Inorganica Chimica Acta 363 (2010) 3641–3646
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Inorganica Chimica Acta
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Synthesis and spectroscopic properties of Ni(II) complexes of some aroyl
hydrazone ligands with 2,6-diacetyl pyridine monooxime: X-ray crystal structure
of the salicyloylhydrazone Ni(II) complex
Subhendu Naskar a,c, Sumita Naskar a, Ray J. Butcher b, Shyamal Kumar Chattopadhyay a,
*
a Department of Chemistry, Bengal Engineering and Science University, Shibpur, Howrah 711 103, India
b Department of Chemistry, Howard University, 525 College Street, NW, Washington, DC 20059, USA
c Department of Applied Chemistry, Birla Institute of Technology, Mesra, Ranchi- 835215, Jharkhand, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Five Ni(II) complexes of aroyl hydrazone ligands with 2,6-diacetyl pyridine monooxime are reported. X-
ray crystal structure of the Ni(II) salicyloylhydrazone complex is also reported. In these complexes Ni(II)
is in a distorted octahedral N4O2 coordination environment, with each of the two ligands coordinating
through the pyridine nitrogen, imino-hydrazone nitrogen and the deprotonated oxygen of the hydrazone
moiety. The iminooxime group remain uncoordinated in both the ligands and the planes containing the
CH3–C@N–OH groups are orthogonal to the adjacent pyridine rings. On excitation at 375 nm, the ligands
as well as the Ni(II) complexes, show luminescence. However, the Ni(II) complexes have much lower
quantum yield of emission than the free ligands.
Received 16 November 2009
Received in revised form 27 March 2010
Accepted 5 May 2010
Available online 12 May 2010
Keywords:
Ni(II) complexes
2,6-Diacetyl pyridine monooxime Schiff’s
base
Ó 2010 Elsevier B.V. All rights reserved.
X-ray crystal structure
Luminescence
1. Introduction
zones, formed by condensing aroyl hydrazides with diacetyl pyr-
idine monooxime (Fig. 1).
Metal complexes of aroyl hydrazone ligands have remained an
attractive area of research for coordination chemists and struc-
tural chemists because of their versatile coordination chemistry
and capability to generate varied molecular architecture and coor-
dination geometry [1–9]. Aroyl hydrazone themselves are known
to have a variety of applications such as hole transporting agents
[10–12] in organic layer photo conductors, and in pharmaceutical
industry [13–16] as drugs for treatment of cancer, schizophrenia,
leprosy, etc. It has also been suggested that nucleophilic substitu-
tion [4] of hydrazone ligands may be an important route to
assemble nanoscale molecular clusters. Recently we have re-
ported Ni(II) and Zn(II) complexes of aroyl hydrazones formed
by condensation of aroyl hydrazides and diacetyl monooxime
and observed that they possess interesting supramolecular struc-
ture [17]. Though there are several reports dealing with the coor-
dination chemistry of diacetyl pyridine dioximes [18–24], the
coordination behavior of diacetyl pyridine monooxime and its
Schiff’s bases have not been adequately explored so far [25,26].
In this paper we report Ni(II) complexes of several aroyl hydra-
2. Experimental
2.1. Materials and methods
2,6-Diacetyl pyridine, hydroxylamine hydrochloride, methyl
picolinate, ethyl isonicotinate and methyl anthranilate were pur-
chased from Aldrich. All other chemicals and solvents were of re-
agent grade and used as such. Solvents for spectroscopic and
cyclic voltammetry experiments were of HPLC grade, obtained from
Merck. Elemental analyses were performed on a Perkin–Elmer 240
C, H, N analyzer. Infrared spectra were recorded as KBr pellets on a
JASCO FT-IR-460 spectrophotometer. UV–Vis spectra were recorded
in DMF (HPLC grade) solution (10À3–10À5 (M)) of the complexes
using a JASCO V-530 or Ocean-Optics USB2000 spectrophotometer.
Fluorescence spectra of the DMF solution of the complexes, at room
temperature, were recorded using a PTI made modular spectrofluo-
rometer, consisting of Xe-arc lamp, and model 814 photomultiplier
detection system. Cyclic voltammograms were recorded in DMF
solutions, containing 0.1 (M) TEAP as supporting electrolyte, using
a PAR 273 potentiostat, with Pt disc working electrode, Pt wire
as counter electrode and Ag, AgCl/saturated NaCl as reference
* Corresponding author. Fax: +91 033 2668 2916.
E-mail address: shch20@hotmail.com (S.K. Chattopadhyay).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.05.009

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S. Naskar et al. / Inorganica Chimica Acta 363 (2010) 3641–3646
2.2.4. Ligand L4H2
A mixture of anthraniloyl hydrazide (0.755 g, 5 mmol) and 2,6-
diacetyl pyridine monooxime (0.890 g, 5 mmol) was refluxed in
220 ml MeOH for 5 h. Reduction of volume and subsequent filtra-
tion, followed by washing with diethyl ether gives light yellow col-
or solid. Yield: 0.813 g, 52.3%. M.P.: 204 °C. Anal. Calc. for
N
*
N
N
O
*
HO
NH
z
C
16H17N5O2: C, 61.73; H, 5.46; N, 22.50. Found: C, 61.66; H, 5.59;
N, 22.37%. Selected IR bands (cmÀ1): 3242 br (
O–H), 1656 (amide
N–O). ESI-MS: 312 (MH+),
*
m
X
Y
I), 1617 (mC=N), 1570 (amide II), 1019 (m
334 (M+Na+).
X
Y
Z
2.2.5. Ligand L5H2
L1H2
CH
CH
N
CH
CH
CH
CH
N
OH
H
Isonicotinoyl hydrazide (0.685 g, 5 mmol) and 2,6-diacetyl pyr-
idine monooxime (0.890 g, 5 mmol) was refluxed in 250 ml MeOH
for 7 h. The volume was reduced and pale yellow colored solid was
filtered, washed with (5 ml  2) MeOH and (10 ml  3) diethyl
ether. Yield 0.674 g, 45.7%. M.P.: 188 °C. Anal. Calc. for
L2H2
L3H2
L4H2
L5H2
H
C
15H15N5O2: C, 60.60; H, 5.05; N, 23.56. Found: C, 60.52; H, 5.23;
N, 23.35%. Selected IR bands (cmÀ1): 3231 br (
O–H), 1666 (amide
N–O). ESI-MS: 298 (MH+),
CH
CH
NH2
H
m
I), 1603 (mC=N), 1556 (amide II), 1020 (m
320 (M+Na+).
Fig. 1. Schematic diagram of the ligands.
2.3. Synthesis of the complexes
electrode. The ferrocene/ferrocenium couple was observed at
E0(
Ep) = 0.48V (100 mV) under our experimental condition.
All the complexes were prepared following a similar method. A
typical example is described below.
D
2.3.1. Ni(L1H)2 (1)
2.2. Synthesis of the ligands
One mmol of L1H2 (0.312 g) was dissolved in 35 ml MeOH, to
which 1 mmol of triethylamine (0.101 g) was added, when a clear
solution was obtained. Addition of 0.5 mmol Ni(ClO4)2Á6H2O
(0.182 g) results in a reddish brown color solution, which was stir-
red at 70 °C for half an hour, when reddish brown colored solid
separated out. The stirring was continued for additional 2 h. The
solid was filtered under vacuum, washed successively with 2 ml
of MeOH, and 10 ml diethyl ether. Yield: 0.155 g (45.6%). X-ray
quality single crystals, containing the solvated 1 (1ÁDMFÁ0.5H2O)
were obtained by diffusion of diethyl ether into a DMF solution
of the compound. Analysis of 1: Anal. Calc. for C32H30N8O6Ni: C,
56.41; H, 4.40; N, 16.45. Found: C, 56.33; H, 4.71; N, 16.18%. Elec-
2,6-Diacetyl pyridine monooxime and aroyl hydrazides were
prepared by published procedures [27,8,9]. All the ligands were
prepared following a similar procedure.
2.2.1. Ligand L1H2
A
mixture of 2,6-diacetyl pyridine monooxime (0.890 g,
5 mmol) and salicyloylhydrazide (0.760 g, 5 mmol) was refluxed
in 100 ml methanol for 4.5 h. The solvent was reduced to ꢀ20 ml
on a rotary evaporator and the solution was filtered. The light yel-
low solid obtained was washed with methanol (2 ml  3), followed
by diethyl ether (5 ml  2) and then dried in vacuum. Yield: 1.05 g,
67.6%. M.P.: 200 °C. Anal. Calc. for C16H16N4O3: C, 61.53; H, 5.12; N,
17.94. Found: C, 61.32; H, 5.24; N, 17.63%. Selected IR bands
tronic spectrum in MeOH solution k/nm (
(15603), 374 (29876), 393sh (25118). Selected IR bands (cmÀ1):
3406 br ( O–H), 1595 (Amide I + C=N), 1562 (amide II), 1023 ( N–O).
e
/dm3 molÀ1 cmÀ1): 293
m
m
m
(cmÀ1): 3254 br (
II), 1024 (
N–O). ESI-MS: 313 (MH+), 335 (M+Na+).
mO–H), 1645 (amide I), 1605 (mC=N), 1556 (amide
m
2.3.2. Ni(L2H)2 (2)
Yield: 0.179 g (55.1%). Anal. Calcd. for C32H30N8O4Ni: C, 59.19;
2.2.2. Ligand L2H2
H, 4.62; N, 17.26. Found: C, 59.29; H, 4.40; N, 17.15%. Electronic
Benzoyl hydrazide (0.680 g, 5 mmol) was refluxed with 2,6-dia-
cetyl pyridine monooxime (0.890 g, 5 mmol) in 180 ml MeOH for
4.5 h. The solid was isolated following the same procedure as
L1H2. Yield: 0.953 g, 64.4%. M.P.: 142 °C. Anal. Calc. for
spectrum in MeOH solution: k/nm
(25644), 330 (23539), 411sh (5584). Selected IR bands (cmÀ1):
3434 br ( O–H), 1589 (amide I + C=N), 1549 (amide II), 1051 ( N–O).
(e
/dm3 molÀ1 cmÀ1): 304
m
m
m
2.3.3. Ni(L3H)2 (3)
Yield: 0.139 g (42.7%). Anal. Calc. for C30H28N10O4Ni: C, 55.32; H,
4.30; N, 21.51. Found: C, 55.11; H, 4.40; N, 21.39%. Electronic spec-
C
16H16N4O2: C, 64.86; H, 5.40; N, 18.91. Found: C, 64.56; H, 5.36;
N, 18.88%. Selected IR bands (cmÀ1): 3217 br (
O–H), 1658 (amide
N–O). ESI-MS: 297 (MH+),
m
I), 1616 (mC=N), 1571 (amide II), 1016 (m
319 (M+Na+).
trum in MeOH solution: k/nm (
334sh (11017), 375sh (5508). Selected IR bands (cmÀ1): 3407 br
O–H), 1630 (amide I), 1595 ( C=N), 1558 (amide II), 1038 ( N–O).
e
/dm3 molÀ1 cmÀ1): 298 (17537),
2.2.3. Ligand L3H2
(m
m
m
Picolyl hydrazide (0.685 g, 5 mmol) and 2,6-diacetyl pyridine
monooxime (0.890 g, 5 mmol) were refluxed for 3 h in 200 ml
MeOH. Solid compounds were isolated as described above. Yield:
0.716 g, 48.6%. M.P.: 174 °C. Anal. Calc. for C15H15N5O2: C, 60.60;
H, 5.05; N, 23.56. Found: C, 60.53; H, 5.27; N, 23.45%. Selected IR
2.3.4. Ni(L4H)2 (4)
Yield: 0.198 g (58.3%). Anal. Calc. for C32H32N10O4Ni: C, 56.57; H,
4.71; N, 20.62. Found: C, 58.29; H, 4.40; N, 18.95%. Electronic spec-
trum in MeOH solution: k/nm (
397sh (5396). Selected IR bands (cmÀ1): 3423 br (
(amide I), 1594 ( C=N), 1575 (amide II), 1024 ( N–O).
e
/dm3 molÀ1 cmÀ1): 297(9524),
bands (cmÀ1): 3361 br (
(amide II), 1009 (
N–O). ESI-MS: 298 (MH+), 320 (M+Na+).
m
O–H), 1665 (amide I), 1591 (
mC=N), 1572
mO–H), 1605
m
m
m

S. Naskar et al. / Inorganica Chimica Acta 363 (2010) 3641–3646
3643
Table 1
on a Bruker smart CCD area detector diffractometer at 103(2) K,
using a graphite-monochromated Mo K radiation. The data were
Crystal data and structure refinement for 1ÁDMFÁ0.5H2O.
a
solved by direct method and refined by least square program using
SHELX 97 [28]. The non-hydrogen atoms were refined with aniso-
tropic displacement parameters. All hydrogen atoms were placed
at calculated positions and refined as riding atoms using isotropic
displacement parameters. The hydrogen atoms of water were re-
fined isotropically, but the O–H distance was restrained to 0.82 Å
and the H–O–H angle restrained to 104.5°. Thermal parameter
was set to be 1.5 times that of the O to which they were attached.
Corrections for Lorentz polarization effect and semi-empirical
absorption were applied. The refinement converged with residuals
summarized in Table 1.
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C35H38N9NiO7.5
763.45
103(2)
0.71073
triclinic
ꢀ
P1
10.8707(12)
15.7487(13)
20.7149(19)
90.176(2)
91.474(2)
98.096(2)
3509.8(6)
1.445, 4
b (Å)
c (Å)
a
(°)
b (°).
c
(°)
Volume (Å3)
Density (calculated) (g cmÀ3), Z
Absorption coefficient (mmÀ1
)
0.617
3. Results and discussion
Reflections collected: total, unique
Observed reflections [I > 2r(I)]
20 897, 20 897
17 875
The hydrazone Schiff’s bases were obtained cleanly by refluxing
a methanolic solution of the 2,6-diacetyl pyridine monooxime with
the corresponding aroyl hydrazides. The Ni(II) complexes were ob-
tained in moderately good yield by reaction of the hydrazone
Schiff’s bases with Ni(ClO4)2Á6H2O in methanol at around 60–
70 °C. The elemental analyses, i.r. and UV–Vis spectroscopic data
are consistent with their formulation as bis-hydrazone complexes
of Ni(II).
Absorption correction
semi-empirical from equivalents
0.8560 and 0.7277
20 897/3/973
1.061
R1 = 0.0424, wR2 = 0.1139
R1 = 0.0517, wR2 = 0.1182
0.739 and À0.649 e ÅÀ3
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
r(I)]
R indices (all data)
Largest differences in peak and hole
2.3.5. Ni(L5H)2 (5)
3.1. Description of the crystal structure
Yield: 0.129 g (39.8%). Anal. Calc. for C32H30N8O4Ni: C, 59.19; H,
4.62; N, 17.26. Found: C, 59.29; H, 4.40; N, 17.15%. Electronic spec-
The ORTEP diagram and atomic numbering scheme for molecule 1
of 1ÁDMFÁ0.5H2O is given in Fig. 2 (for molecule 2, the ORTEP diagram
is given in Supplementary Fig. 1) while the important bond angles
and distances are collected in Table 2. In the lattice of Ni(L1H)2
there are two crystallographically distinct molecules whose Ni
atoms are designated as Ni1 and Ni2, respectively. In both these
molecules Ni(II) is in a distorted octahedral N4O2 coordination
environment, with each of the two ligands coordinating through
the pyridine nitrogen, imino-hydrazone nitrogen and the deproto-
trum in MeOH solution: k/nm (
335sh (24356), 398sh (9657). Selected IR bands (cmÀ1): 3434 br
O–H), 1593 (amide I + C=N), 1512 (amide II), 1024 ( N–O).
e
/dm3 molÀ1 cmÀ1): 301(45654),
(m
m
m
2.4. Crystal structure determination
On crystallization from DMF-diethyl ether mixture, 1 crystal-
lizes as 1.DMF.0.5H2O. Data on one of the crystal were collected
Fig. 2. ORTEP diagram (30% probability level) for molecule 1 of 1ÁDMFÁ0.5H2O.

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S. Naskar et al. / Inorganica Chimica Acta 363 (2010) 3641–3646
Table 2
In molecule 2, the inter-chelate angles vary in the range 2.5 (2)–3.7
(2) and 86.0 (2)–89.5 (2), for chelate rings involving same ligand
and different ligands, respectively. The best square plane in this
case is formed by Ni2, O(2C), N(2D), N(3C), N(2C).
Selected bond distances (Å) and angles (°) for 1ÁDMFÁ0.5H2O.
Ni(1)–N(2B)
Ni(1)–N(2A)
Ni(1)–O(2B)
Ni(1)–O(2A)
Ni(1)–N(3A)
Ni(1)–N(3B)
Ni(2)–N(2D)
Ni(2)–N(2C)
Ni(2)–O(2C)
Ni(2)–O(2D)
Ni(2)–N(3D)
Ni(2)–N(3C)
1.968(2)
1.974(2)
2.0929(16)
2.0985(16)
2.1534(19)
2.196(2)
1.9822(19)
1.988(2)
2.0990(16)
2.1189(16)
2.1808(19)
2.1963(19)
Each of O–H group of the salicyloyl moiety is intra-molecularly
hydrogen bonded to the corresponding N1 atom of the hydrazone
moiety forming a five-membered chelate ring. There are two DMF
and one water molecules in the unit cell and all of them participate
in H-bonding. The water molecule acts as one hydrogen bond
acceptor and two hydrogen bond donor. It accepts H-bond from
O(3B)–H(3B) oxime moiety and donate H-bonds to oxime nitro-
gens N(4B) #2 and N(4A)#2 (symmetry code for #2 is Àx + 1, Ày,
Àz; Table 3). Two molecules of 1, which are related to each other
by symmetry transformation #2, form hydrogen bonded dimer
by complementary hydrogen bonding between their related water
molecules (Fig. 3). The two DMF molecules also enter into hydro-
gen bonding interactions. The DMF oxygen O2S is hydrogen
bonded to oxime hydroxyl group O(3A)–H(3A), while the O(1S)
of the second DMF molecule is hydrogen bonded to the oxime hy-
droxyl O(3D)–H(3DB)#1 of a neighboring molecule (symmetry
code for #1 is x À 1, y, z). The later hydrogen bond interaction along
with C11S–H11EÁÁÁO2D and C11S–H11EÁÁÁC7D hydrogen bonds re-
sult in formation of a one dimensional chain of molecules 2 along
N(2B)–Ni(1)–N(2A)
N(2B)–Ni(1)–O(2B)
N(2A)–Ni(1)–O(2B)
N(2B)–Ni(1)–O(2A)
N(2A)–Ni(1)–O(2A)
O(2B)–Ni(1)–O(2A)
N(2B)–Ni(1)–N(3A)
N(2A)–Ni(1)–N(3A)
O(2B)–Ni(1)–N(3A)
O(2A)–Ni(1)–N(3A)
N(2B)–Ni(1)–N(3B)
N(2A)–Ni(1)–N(3B)
O(2B)–Ni(1)–N(3B)
O(2A)–Ni(1)–N(3B)
N(3A)–Ni(1)–N(3B)
N(2D)–Ni(2)–N(2C)
N(2D)–Ni(2)–O(2C)
N(2C)–Ni(2)–O(2C)
N(2D)–Ni(2)–O(2D)
N(2C)–Ni(2)–O(2D)
O(2C)–Ni(2)–O(2D)
N(2D)–Ni(2)–N(3D)
N(2C)–Ni(2)–N(3D)
O(2C)–Ni(2)–N(3D)
O(2D)–Ni(2)–N(3D)
N(2D)–Ni(2)–N(3C)
N(2C)–Ni(2)–N(3C)
O(2C)–Ni(2)–N(3C)
O(2D)–Ni(2)–N(3C)
N(3D)–Ni(2)–N(3C)
170.08(8)
77.76(7)
100.12(7)
92.81(7)
77.50(7)
91.49(6)
111.54(8)
77.90(8)
88.08(7)
154.93(7)
77.34(8)
105.06(8)
154.82(7)
93.40(7)
97.59(7)
170.66(8)
97.84(7)
77.19(7)
76.71(7)
95.38(7)
91.55(6)
76.68(8)
111.34(8)
94.45(7)
153.28(7)
108.71(8)
76.60(7)
153.44(7)
95.08(7)
91.10(7)
Table 3
Hydrogen bonds for 1ÁDMFÁ0.5H2O (Å and °).
D–HÁÁÁA
d(D–H)
d(HÁÁÁA)
d(DÁÁÁA)
\(DHA)
O(1A)–H(1A)ÁÁÁN(1A)
O(3A)–H(3A)ÁÁÁO(2S)
O(1B)–H(1B)ÁÁÁN(1B)
O(3B)–H(3B)ÁÁÁO(1W)
O(1C)–H(1C)ÁÁÁN(1C)
O(1D)–H(1D)ÁÁÁN(1D)
O(3D)–H(3DB)ÁÁÁO(1S)#1
O(1W)–H(1W1)ÁÁÁN(4B)#2
O(1W)–H(1W2)ÁÁÁN(4A)#2
0.84
0.84
0.84
0.84
0.84
0.84
0.84
0.823(17)
0.834(17)
1.84
1.81
1.81
1.83
1.80
1.82
1.91
2.122(19)
1.98(2)
2.556(3)
2.626(3)
2.549(3)
2.660(3)
2.543(3)
2.550(3)
2.699(3)
2.934(3)
2.793(3)
141.7
164.7
145.7
170.8
146.7
143.7
156.5
169(4)
164(3)
Symmetry transformations used to generate equivalent atoms: #1 x À 1, y, z; #2
Àx + 1, Ày, Àz.
nated oxygen of the hydrazone moiety. The iminooxime groups re-
main uncoordinated in both the molecules and the planes contain-
ing the CH3–C@N–OH groups are orthogonal to the adjacent
pyridine rings.
The Ni–Npy, Ni–Nhydrazone, and Ni–O distances are very similar in
both the molecules and all of them are unexceptional. The bond
lengths follow the order Ni–Nhydrazone < Ni–O < Ni–Npy. In molecule
1 (containing Ni1 and its coordination sphere) trans angles vary be-
tween 155° and 170°, while in molecule 2 the same varies between
153° and 171°. Similarly the cis angles vary between 78° and 122°,
and 77° and 111° in molecules 1 and 2, respectively. The large devi-
ation of the cis and trans angles from the ideal octahedral value
may be attributed to the bite angle constraint of the tridentate li-
gand. However, molecular modeling using MM+ and PM3 programs
show [29,30] that while the CH3–C@N–OH groups are orthogonal
to the adjacent pyridine rings in the optimized structures, similar
to that observed in the X-ray crystal structure, the trans angles
should lie between 170° and 173°, while the cis angles lie between
86° and 96°. Thus the large distortion of the bond angles observed
in the crystal structure may be the result of crystal packing forces,
such as the hydrogen bonding observed in the structure, rather
than due to inherent geometrical constraint of the ligand. In mol-
ecule 1, the five-membered chelate rings formed by the two li-
gands are grossly planar, with the inter-chelate angles between
the same ligand lying in the range 4.3 (2)–4.9 (3)°, while those be-
tween two different ligands are in the range 84.3 (2) –89.2 (2)°. The
best square plane is formed by Ni1, O(2A), N(2A), N(3A) and N(2B).
Fig. 3. Formation of H-bonded dimer of molecule 1.

S. Naskar et al. / Inorganica Chimica Acta 363 (2010) 3641–3646
3645
‘a’ axis. The dimers of molecule 1 also form similar one dimen-
L4H
2
sional chain along ‘a’ axis by C9A–H9ABÁÁÁO2B#3 and C11–
H11AÁÁÁO2B#3 interactions (symmetry code for #3 is Àx, Ày, Àz).
Adjacent chains of molecule 1 and molecule 2 are connected to
each other by a weak C16C–H16HÁÁÁO1B interaction forming a
three dimensional network (Supplementary Fig. 2).
L1H
400000
350000
300000
250000
200000
150000
100000
50000
0
2
L3H
2
L5H
2
4
3
1
2
5
3.2. Infrared spectra
L2H
The bands due to the amide I at ꢀ1650 cmÀ1, the mC=N band at
ꢀ1610 cmÀ1 and amide II at ꢀ1550 cmÀ1 undergo shift towards
lower energy in the complexes. This behavior is compatible with
the participation of the imine nitrogen and deprotonated amide
oxygen atom of both the ligands in coordination to the metal, in
agreement with previous results [8,9]. There is an increase in the
mO–H frequency on complexation; this may indicate a change in
conformation of the oxime moiety after complexation, which low-
ers its hydrogen bonding ability. It has been noted that the mO–H
band is very sensitive to molecular configuration [31].
2
350
400
450
500
550
600
Wavelength (nm)
Fig. 5. Luminescence spectra of the ligands and the complexes (ligands 5 Â 10À6 M,
complexes 3 Â 10À6 M).
3.3. Electronic spectra
All the ligands show a relatively weak band at 380–420 nm re-
*
p transition. There is a strong band
sion both in the free as well as in the complexed state. This obser-
vation is inconsistent with the well known quenching effect of
ligand fluorescence in Ni(II) octahedral complexes, which is often
called as chelation enhanced quenching (CHEQ) [32–34]. Quantum
yield measurement shows that the anthraniloyl, salicyloyl and
benzoyl hydrazone ligands have Uemission values of ꢀ0.2, while
the picolyl and isonicotinoyl hydrazone ligands have Uemission val-
ues of ꢀ0.6. In the complexes the Uemission values are ꢀ0.1, except
in the picolylhydrazone complex where the value is ꢀ0.4. This
shows, the quantum yield of emission has indeed decreased on
complexation with Ni(II). However, as the Ni(II) complexes have
higher absorbance at 375 nm compared to those of the free ligands,
so their luminescence intensity are higher, at comparable
concentrations.
gion, which is assigned to n ?
*
at 290–300 nm, due to
p ? p transition. Besides, there is another
band/shoulder at 320–360 nm region, which is also assigned to
*
p
? p transition. In the Ni(II) complexes there is a broad band/
shoulder at 390–410 nm due to LMCT transition (Fig. 4). The band
*
due to n ?
p
transition is probably buried under the more intense
*
LMCT transition. The
p ? p transition observed at 290–300 nm
for the ligands is also present in the complexes. In the complexes
2, 3 and 5 there is an additional peak/shoulder at ꢀ330 nm, where
as in case of complex 1 a strong peak at 375 nm is observed. They
*
are also assigned to
p
?
p
transitions.
3.4. Luminescence spectra
On exciting at 375 nm, the hydrazone ligands show lumines-
*
p ex-
cence at 410 nm, which is probably due to emission from 1n
3.5. Cyclic voltammetry
cited state. On complexation the luminescence intensity is
enhanced by almost three times (Fig. 5), the emission undergoes
slight shift towards lower energy, and it is now observed at 420–
430 nm. The anthraniloyl hydrazone ligand shows strongest emis-
All the complexes show an irreversible oxidation at 1.2 V, which
is assigned to ligand based oxidation. The complexes also show a
quasi-reversible reduction, between À0.7 and À1.0 V, with
DEp
values lying between 250 and 300 mV. This reduction is tentatively
assigned to Ni(II)/Ni(I) couple. A second reduction wave at À1.2 to
2.0
À1.4 V with
DEp lying between 60 and 150 mV is assigned to li-
gand based reduction (see Supplementary Figs. 3–8).
4. Conclusions
1.5
1.0
0.5
0.0
Ni(L4H)2
Ni(L2H)2
Ni(L5H)2
Ni(L3H)2
Ni(L1H)2
Five new aroyl hydrazone ligands with 2,6-diacetyl pyridine
monooxime are reported. The ligands are highly luminescent.
Though the ligands are potentially tetra-dentate, with Ni(II), they
behave as tridentate donors, the hydrazone moiety and the pyri-
dine nitrogen of each ligand participates in coordination, while
the oxime moiety remains uncoordinated. The Ni(II) complexes
are also fluorescent, but their fluorescence quantum yields are
much smaller than the parent ligands.
Acknowledgements
300
400
500
600
700
800
SKC and Sumita acknowledge CSIR for funding. We also
acknowledge DST, AICTE, UGC and MHRD for funding instrumental
facilities in our department.
wavelength (nm)
Fig. 4. Electronic spectra of the Ni(II) complexes.

3646
S. Naskar et al. / Inorganica Chimica Acta 363 (2010) 3641–3646
[15] A. Bacchi, A. Bonardi, M. Carcelli, P. Mazza, P. Pelagatti, C. Pelizzi, G. Pelizzi, C.
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for 1ÁDMFÁ0.5H2O. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif. Supplementary data associated with this
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