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International Journal of PharmTech Research
CODEN( USA): IJPRIF
ISSN : 0974-4304
Vol.1, No.2, pp 304-309, April-June 2009
Synthesis and Computational Verification of New Nickel(ІІ)
Complexes
Nabil M. El-Halabi1*, Adel M. Awadallah1, Fakhr M Abu-Awwad1, Zaki S. Safi2
1,Department
of Chemistry, The Islamic University of Gaza, Gaza, Palestine.
2,Department
of Chemistry, Al Azhar University of Gaza , Gaza, Palestine.
E-mail*: [email protected]
Abstract: Nitrilimines 7 generated in situ from the respective hydrazonyl chlorides are found to react with benzhydrazide 8
at room temperature to give the corresponding 2,3,5,6-tetraza-4-hexen-1-one 9. The reaction of 9a with nickel(ІІ) acetate
tetrahydrate, in two to one mole ratio in ethanol at room temperature overnight, gave poor yield of square planar complex with
a five-membered rings 10a. The new compounds 9a, 9b and 10a were characterized and identified by IR, 1H NMR, 13C NMR
and MS spectra. Computational procedures at B3LYP/6-31G(d) level of theory were used to verify the suggested structure of
the complex 10a employing both thermodynamic properties and geometrical features of both reactants and products.
Keywords: nickel; tetraza-4-hexen-1-one; benzhydrazide; B3LYP; energy profile.
Introduction:
Recently, we have reported the synthesis of
square planar metal complexes with substituted 1,2,4triazoleoximes1 hydrazones2 and substituted 1,2,4,5
tetrazineoximes3 . In all these works, we have N,Nbidentate ligands that lead to the formation complexes
with five or six membered rings.
Quit recently, Some new metal(II) complexes, ML2 [M =
Mn,
Co,
Ni,
Cu
and
Zn]
of
2acetylpyridinebenzoylhydrazone
1
containing
trifunctional N, N, O-donor system have been
synthesized, and two of them were crystallographically
characterized4 .
R
N
R
N
H
N
M
O
N
O
N
Ar
N
O
N
1-3
R
4-6
Entry
1/4
2/5
3/6
N
Ar
R
CH3
Ar
N
H
NH2
H
N
Ar
Nabil M. El-Halabi et al /Int.J. PharmTech Res.2009,1(2)
305
Selected first-row transition metal complexes
with 2-pyridinecarbaldehyde isonicotinoylhydrazone 2
and
2-pyridinecarbaldehyde
(4'aminobenzaldehydehydrazone)
3
were
recently
synthesized by Bernhardt et al in an attempt to design and
synthesis of ligands that exhibit high Fe chelation
efficacy5 . It was found that, divalent first-row transition
metals (Mn, Fe, Co, Ni, Cu and Zn) readily form bis
(complexes) with the above ligands with each ligand
coordinated meridionally through its pyridine-N, imine-N
and carbonyl-O atoms, forming distorted octahedral cisMN4O2 complexes.
In this work, ligands containing nitrogen and
oxygen atoms 9 will be prepared from the reaction of
nitrilimines 7 with benzhydrazides 8. The complexation
behavior of these ligands will be investigated. Since those
ligands contain many possible coordinating sites, they
may react as N,N-bidentate ligands leading to square
planar complexes , or as N,N,O-tridentate ligands leading
to octahedral complexes similar to the above complexes
4-6. Theoretical calculations that support the suggested
structure will be presented.
Results and discussion:
The compounds 9a, b are readily accessible via
the reaction of the corresponding nitrilimines 7 with
benzhydrazides 8 overnight at room temperature. The
assignments of structure 9a, b are based on spectral data.
The IR spectrum of 9a in KBr revealed the
presence of two NH absorption peaks at 3298 and 3280,
and two C=O absorption peaks at 1681 for CH3C=O and
1640 for NH-NHC=O. The IR spectrum of 9b revealed
the presence of two C=O absorption peaks at 1716 for
CH3OC=O and 1646 for NH-NHC=O.
The electron impact mass spectra of 9a, b
display the correct molecular ions in accordance with the
suggested structures.
The 1H-NMR spectra of both compounds show three N-H
signals in addition to the signals of the methyl groups and
the aromatic protons.
Scheme 1:
R
R
N
Cl
H2N
+
NH
Ar
7a,b
H
N
Ph
N
H
N
Et3N
O
NH
Ar
H
N
Ph
O
9a,b
8
Ni(OAc)2.4H2O
R
Ph
O
R
NH
Ar
N
NH
N
Ar
N
Ni
N
NH
N
Ar
R
NH
NH
N
O
Ni
O
Ar
N Ar
NH
Ph
Ar
N
HN
O
O
Ni
N
O
N
R
R
R
10a
12a
11a
Entry
7a/9a/10a/11a
Cl
Ar
R
7b/9b/10b/11b
C(O)CH3
Cl
COOCH3
Ar
N
N
N
HN
Ph
N
N
Ph
N
Ar
Nabil M. El-Halabi et al /Int.J. PharmTech Res.2009,1(2)
13
C-NMR spectra display the characteristic signals of the
suggested structure. Two C=O signals appear in addition
to the methyl signals and the signals of the aromatic
carbons.
The reaction of 9a with nickel(ІІ) acetate tetrahydrate, in
two to one mole ratio in ethanol at room temperature
overnight, gave poor yield of a green complex. The
assignment of the complex structure was based on
spectral data.
The IR spectrum of the complex shows two C=O beaks at
almost the same positions of compound 9a, and one NH
peak disappeared. This is evident of N,N-complexation of
the ligands and excludes the tridentate N,N,O-octahedral
complex 12a.
The electron impact mass spectrum of the nickel(II)
complex display the correct molecular ion for an ML2
complex.
The electrical conductance of the complex in DMF is
almost negligible supporting its non-electrolytic nature.
The electronic spectrum of the Ni(II) complex display a
distinct band around 20408 cm-1 assigned to 1A1g → 1B1g
transition in planar field6 .
The complex was assigned structure 10a in which the
ligand acts as N,N-bidentate ligand forming a complex
with five membered rings. The assignment is based on
the fact that five-membered rings are more stable than the
six-membered rings7 , and no metallation occurs with the
hydrazidic NH. This structure assignment was further
supported by computational calculations. The detailed IR,
1H-NMR, 13C-NMR and MS data are presented in the
experimental part.
Computational Procedures and Results:
In this work, the density functional theory (DFT)
is used to investigate the reaction depicted in scheme (1).
The hybrid gradient corrected exchange functional
proposed by Becke 8 combined with the gradientcorrected correlation functional of Lee, Yang, and Parr9
(B3LYP) in Gaussian 03 software10 is employed along
with 6-31G(d) basis set. B3LYP has been extensively
employed in similar computational procedures and turned
out to be quite reliable for geometrical optimizations.
Structures 9a, 9b, 10a, and 11b in scheme (1)
were fully optimized to obtain structural, electronic and
energetic information. The harmonic vibrational
frequencies were also calculated at the same level of
theory to ensure that each stationary point corresponds to
a true local minimum on the potential energy surface
(PES), and to estimate the zero-point energy (ZPE)
corrections. Relative energies were computed by
subtracting the most stable energy after including the
corresponding ZPE corrections scaled by an empirical
factor of 0.9806. Also, Enthalpies and Gibbs energies
were calculated by considering the thermal corrections at
298.15 K and the values obtained for the entropy by
using the harmonic vibrational frequencies.
306
In order to obtain more reliable energies for the
local minima, final energies were evaluated by using the
same functional combined with the 6-31+G(d,p) basis set
for all atoms except for Ni2+, where the (14s9p5d/9s5p3d)
basis set of Wachters11
and Hay12
was used,
supplemented with a set of (1s2p1d) diffuse functions
and with two sets of f functions and one set of g
functions. It has been shown that this approach is well
suited for the study of this kind of systems, yielding
binding energies in good agreement with experimental
values.
The corresponding Ni2+ binding energies, D0, were
evaluated by subtracting from the energy of the complex
the energy of the neutral and that of Ni2+, after including
the corresponding ZPE corrections scaled by a factor of
0.9806 [13]. Enthalpies and Gibbs free energies have
been evaluated by considering the thermal corrections at
298.15 K and the values obtained for the entropy by
using the harmonic vibrational frequencies.
In this computational procedures, the structures
10a and 11a are expected equally as products from the
direct interaction of Ni(CH3COO)2.2H2O with the ligand
9a, (Scheme 1). Both structures are local minima of the
PES with all harmonic frequencies being real. A single
point calculation at B3LYP/6-31+G(d,p) level of theory
have been carried out, where it is repeatedly reported that
for similar huge structures, this level of theory presents a
good correlation with the attained experimental results.
The corresponding relative H, E and G are displayed in
Table 1. The corresponding total energies, zero point
energies corrections, ZPEC, thermal correction to
enthalpies, TCH, and entropies, S, are listed in Table S1
of the supplementary material. The optimized geometries
of 5a and 6a are given in Figure 1.
As revealed from data of the relative energy
calculations listed in table 1, an interaction of Ni2+ with
the nitrogen atoms (Ns) at positions 1 and 3 to form
complex 10a is of a big significance, when compared to
the case of 11a, in which the metal interacts with Ns at
positions 1 and 4. Obviously, complex 10a is much more
stable than its rival 11a by about 196.5 kJ/mol. This large
difference in the structures’ relative energies doubtlessly
conclude that under normal conditions of reaction in the
gas phase, complex 10a is predominant while complex
11a can't be initially formed.
Similarly, the geometrical parameters as may be
concluded from the optimized structures presented in
Figure 1 can assure and explain the further stability of
complex 10a over complex 11a. The former exhibits a
symmetric structure of two almost regular pentagons with
Ni atom in common, where the counterpart bond lengths
are closely equal and the sums of the interior angles are
539.2o and 539.5o, with only about 0.5o away from the
well defined pentagons. Meanwhile, structure 11a shows
irregular squeezed hexagonals with different counterpart
bond lengths and much smaller interior angles than
expected (672o, and 689.2o). Additionally, in 10a the Ni-
Nabil M. El-Halabi et al /Int.J. PharmTech Res.2009,1(2)
5a
307
6a
Figure 1: Optimized Geometries of Complex 10a and 11a
Nabil M. El-Halabi et al /Int.J. PharmTech Res.2009,1(2)
308
N bond lengths are shorter than their counterpart
bonds formed in complex 11a with.
Structure 10a was evident based on spectral data.
Computational
procedures
at
the
B3LYP/631+G(d,p)//B3LYP/6-31G(d) level of theory have
presented other several indications supporting the
experimental findings.
Conclusion:
Table 1: calculated energies (KJ/mol), HOMO, LUMO (au) at B3LYP/6-31G
species
ΔE
ΔH
ΔS
ΔG
10a
0.00
0.00
0.00
0.00
11a
169.51
169.61
0.02
169.64
Supplementary Information
S1: Calculated energies, corrections, and entropies at B3LYP/6-31G
E1
E2
ZPEC
TCH
S
10a
-4403.68745
-4403.836918
0.564554
0.609129
268.16
11a
-4403.62567
-4403.771701
0.563948
0.608562
268.14
E1 = B3LYP/6-31(d)
E2 = B3LYP/6-31+(d,p)
Experimental:
Melting points were determined on an
Electrothermal Melting Temperature apparatus and are
uncorrected. The infrared spectra were obtained using
Perkin-Elmer 237FT-IR spectrophotometer (KBr discs).
1H and 13C NMR spectra were recorded on a Brucker
300MHz instrument for solutions in DMSO or CDCl3 at
25oC, using TMS as an internal reference. The Mass
spectra were run on MTA 112 Mass spectrometer.
Reaction of hyrazonoyl chlorides with
benzhydrazide
Hydrazonoyl chlorides 7 (0.02 mol) and benzhydrazide 8
(3.2g, 0.024 mol) were dissolved in tetrahydrofuran (100
mL). Triethylamine (4 mL) was added and the mixture
was then stirred over night for 48 hours. The solvent was
then evaporated, and the residual solid was washed with
water to remove the triethylamine salt. The crude product
was recrystallized from ethanol (40 mL).
4-Acetyl-6-(4-chlorophenyl)-1-phenyl-2,3,5,6-tetraza4-hexen-1-one (9a)
The yield of pure product was indicated by TLC; yield
4.06g (61.43%), yellow, mp 1820C; IR (KBr) 3298.2 -(NH-Ar), 3280 (NH(C=O)ph), 1681 ((C=O)CH3), 1640
(NH-NH(C=O)ph), 1597 (C=N); 1HNMR δ 2.5 (s, 3H,
CH3(C=O)), 10.2 (s, 1H, -NH(C=O)ph), 9.7 (s, 1H, =NNH-C6H4Cl), 7.1-7.9 (10H, one of -NH-NH(C=O)ph
and 9 for aromatic protons); 13C NMR  24.4
(CH3(C=O)), 192.2 ((C=O)CH3), 166.4 (HN(C=O)ph),
114.8, 127.5, 129.4, 132.3, 132.4 (5 signals, 9CH for
aromatic carbons), 124.3, 128.9, 139.6 (3 signals, 3C for
aromatic carbons); MS, m/z (%) 330 (M+), 211 (M+C9H9N3OCl), 105 (ph(C=O)), 77 (ph), 43 (CH3(C=O)).
6-(4-chlorophenyl)-4-methoxycarbonyl-1- phenyl2,3,5,6-tetraza-4-hexen-1-one (9b)
The yield of pure product was indicated by TLC; yield
2.7g (78%), yellow, mp 1790C; IR (KBr) 3296.2 (-(NH-Ar), 3264.3 (NH(C=O)ph), 1715 ((C=O)OCH3),
1645 (NH-NH(C=O)ph), 1598 (C=N); 1HNMR δ 3.9 (s,
3H, CH3(OC=O)), 10.4 (s, 1H, -NH(C=O)ph), 8.1 (s, 1H,
=N-NH-C6H4Cl), 7.1-7.9 (10H, one of -NH-NH(C=O)ph
and 9 for aromatic protons); 13C NMR  53.4
(CH3O(C=O)), 170 ((C=O)OCH3), 165 (HN(C=O)ph),
115.8, 127.4, 129.3, 129.6, 133.0 (5 signals, 9CH for
aromatic carbons), 127.3, 127.6, 141.5 (3 signals, 3C for
aromatic carbons); MS, m/z (%) 346 (M+), 226 (M+C9H9N3O2Cl).
Synthesis of bis (4-acetyl-6-(4-chlorophenyl)-1-oxo-1phenylhexan-2, 3, 5, 6-tetraza-4-ene) Nickel(ІІ)
complex 10a
To a solution of 4-acetyl-6-(4-chlorophenyl)-1-oxo-1phenylhexan-2, 3, 5, 6-tetraza-4-ene 0.66g (2.0 mmol) in
(25 mL) ethanol was added a solution of nickel(ІІ)
acetate tetrahydrate 0.248g (1 mmol) in ethanol (25 mL).
The resulting reaction mixture was stirred overnight at
room temperature for 72 hours. The deep green solid
product was collected by suction filtration, washed with
cold ethanol (5 mL) and dried in vacuo. The yield of the
Nabil M. El-Halabi et al /Int.J. PharmTech Res.2009,1(2)
309
pure product was indicated by TLC, yield .150 mg (16.52
%), mp over 300; IR (KBr) 3326.3 (NHNH(C=O)ph),1680.8
((C=O)CH3),
1646.4
(NHNH(C=O)ph), 1599 (C=N); 1HNMR δ 2.3 (s, 6H,
2CH3(OC=O)), 8.9 (s, 2H, -2NH(C=O)ph), 7.3-8.9 (20H,
two of -NH-NH(C=O)ph and 18 for aromatic protons);
13
C NMR  29.8 (CH3(C=O)), 200.1 ((C=O)CH3), 165.8
(HN(C=O)ph), 122.4, 127.2, 129.5, 132.6, 132.8 (5
signals, 18 CH for aromatic carbons), 122.4, 130.0, 134.1
(3 signals, 6C for aromatic carbons);
MS, m/z (%) 719.20 (M+.-Ni(C16H14ClN4O2)2).
[8]
[9]
[10]
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