Synthesis, characterization, molecular modeling and antibacterial activity of N1′, N2′-bis[1-(pyridin-2-yl)ethylidene] oxalohydrazide and its metal complexes

Article abstract of DOI:10.1016/j.molstruc.2011.04.043

New complexes of N^1′,N^2′-bis[1-(pyridin- 2-yl)ethylidene]oxalohydrazide (H₂L) with Cr³⁺, Mn ²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu ²⁺, Cd²⁺, VO²⁺ and Ag⁺ have been prepared and characterized. The ligand has 10-12 buffering range and pK's of 4.62, 7.78 and 9.45. The IR spectra showed the neutral, (mono- or dibasic) bidentate, tridentate or tetradentate of H₂L. The molar conductance values, in DMSO, are in the range of nonelectrolytes. An octahedral geometry is proposed for the Cr³⁺, Mn²⁺, Fe³⁺, Ni ²⁺; VO²⁺ complexes and square-planar for the Co ²⁺ and Cu²⁺ complexes. The ESR spectra support the mononuclear species for [VO(H₂L)SO_4-(H₂O) ₂]·H₂O and [Cu(H₂L)(OAc) ₂]·H₂O. The molecular parameters have been calculated to confirm the geometry of the ligand and its complexes. The ligand and some complexes were screened against Bacillus thuringiensis (Bt) as Gram positive and Pseudomonas aeuroginosa (Pa) as Gram negative bacteria using the inhibitory zone diameter. The data showed no effect for the complexes on Pa bacteria growth except [Ag(H₂L)(NO₃)]H₂O which had a high activity. Cu²⁺, VO²⁺ and Ag⁺ complexes exhibit activity against BT; Cu²⁺complex is the highest one.

Full text of DOI:10.1016/j.molstruc.2011.04.043

Journal of Molecular Structure 998 (2011) 20–29
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
0
Synthesis, characterization, molecular modeling and antibacterial activity of N1 ,
0
N2 -bis[1-(pyridin-2-yl)ethylidene]oxalohydrazide and its metal complexes
⇑
O.A. El-Gammal, R.M. El-Shazly, F.E. El-Morsy, A.A. El-Asmy
Department of Chemistry, Faculty of Science, Mansoura University, Mansoura, Egypt
a r t i c l e i n f o
a b s t r a c t
0
0
New complexes of N1 ,N2 -bis[1-(pyridin-2-yl)ethylidene]oxalohydrazide (H2L) with Cr3+, Mn2+, Fe3+, Co2+
,
Article history:
Ni2+, Cu2+, Cd2+, VO2+ and Ag+ have been prepared and characterized. The ligand has 10–12 buffering
range and pK’s of 4.62, 7.78 and 9.45. The IR spectra showed the neutral, (mono- or dibasic) bidentate,
tridentate or tetradentate of H2L. The molar conductance values, in DMSO, are in the range of
nonelectrolytes. An octahedral geometry is proposed for the Cr3+, Mn2+, Fe3+, Ni2+; VO2+ complexes and
square–planar for the Co2+ and Cu2+ complexes. The ESR spectra support the mononuclear species for
[VO(H2L)SO4ꢀ(H2O)2]ꢁH2O and [Cu(H2L)(OAc)2]ꢁH2O. The molecular parameters have been calculated to
confirm the geometry of the ligand and its complexes. The ligand and some complexes were screened
against Bacillus thuringiensis (Bt) as Gram positive and Pseudomonas aeuroginosa (Pa) as Gram negative
bacteria using the inhibitory zone diameter. The data showed no effect for the complexes on Pa bacteria
growth except [Ag(H2L)(NO3)]H2O which had a high activity. Cu2+, VO2+ and Ag+ complexes exhibit
activity against BT; Cu2+complex is the highest one.
Received 26 February 2011
Received in revised form 28 April 2011
Accepted 28 April 2011
Available online 5 May 2011
Keywords:
Hydrazide
Spectra
Molecular modeling
Antimicrobial activity
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Hydrazide derivatives constitute very important class of NO do-
nors due to their capability and structural flexibility which provide
rigidity to the skeletal framework of the prepared multinuclear
complexes. Systematic investigation of the transition metal
complexes of these compounds revealed interesting electrical,
magnetic properties and pharmacological activities [1,2]. The
hydrazone complexes exhibit some intriguing structural features
owing to the potency of the ligand to act in a planar pentadentate
fashion [3–6] along with the tridentate character [6,7–10]. More-
over, the ligands exhibit keto-enol tautomerism and can coordi-
nate as neutral [5], monoanionic [11], dianionic [3,12,13] or
tetraanionic [14] bearing unusual coordination numbers [3,15] in
some mononuclear or binuclear species depending on the metal
ion concentration, the medium pH and the nature of hydrazone.
Continuation to our previous work [16,17], the present work
2.1. Materials
VOSO4ꢁH2O, Cr3(OAc)7(OH)2, MnCl2ꢁ4H2O, CoCl2ꢁ6H2O, Co(OAc)2
ꢁ4H2O, NiCl2ꢁ6H2O, Ni(OAc)2ꢁ4H2O, CuCl2ꢁ2H2O Cu(OAc)2ꢁH2O and
Cd(OAc)2ꢁ2H2O were Aldrich or Fluka products and used without
further purification.
10 20
2.2. Synthesis of 2,2-N ,N -bis(1-(pyridin-2-yl)ethylidene)
oxalohydrazide (H2L)
It was prepared by heating 1:2 M ratio of oxalohydrazide
(1.18 g, 0.01 mol) and 2-acetylpyridine (2.24 ml, 0.02 mol) in
30 ml hot ethanol. The reaction mixture was boiled under reflux
for 3 h, evaporated and after cooling, white crystals of H2L (Struc-
ture 1) were formed. The precipitate was filtered off, recrystallized
from ethanol and finally dried in a vacuum desiccator over anhy-
drous CaCl2. The purity was checked by TLC. The melting point is
261 °C (yield is 78%).
0
0
aims to prepare and characterize N1 ,N2 -bis[1-(pyridin-2-yl)ethyl-
idene]oxalohydrazide and its complexes. Thermal behavior of the
isolated complexes was discussed. The pH and solvent effects on
the ligand was studied. Finally, the antibacterial activity of the
ligand and its complexes was tested.
2.3. Synthesis of the metal complexes
A hot ethanol or aqueous-ethanol solution of metal acetate
[Co(II), Ni(II), Cd(II)] or CrCl3, MnCl2, FeCl3, AgNO3 (1.0 mmol)
and VOSO4 (2.0 mmol), was added to a hot ethanol of H2L
(0.324 g, 1.0 mmol). The resultant mixture was heated under reflux
⇑
Corresponding author. Tel.: +020101645966.
E-mail address: aelasmy@yahoo.com (A.A. El-Asmy).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.04.043

O.A. El-Gammal et al. / Journal of Molecular Structure 998 (2011) 20–29
21
O
C
for 2–3 h. The formed precipitates were filtered off, washed with
ethanol followed by diethyl ether and dried. The complexes,
[Cu(H2L)(OAc)2]ꢁH2O and [Cu2(L)(OAc)2(H2O)2]ꢁ3H2O were isolated
by mixing of Cu(OAc)2 and ligand solutions in molar ratio 1:1 and
3:1 (M:L), respectively, with yield of 70–93%. The physical and ana-
lytical data of the isolated complexes are listed in Table 1. The
complexes have high melting points (>300 °C), insoluble in com-
mon organic solvents and soluble in DMSO and DMF except for
the Co(II) and Ni(II) complexes which are partially soluble. Molar
conductance values indicate a non-electrolytic nature of the com-
plexes [18]; the relative high value measured for [Fe(H2L)Cl3]ꢁH2O
(46.36 L molꢀ1 cmꢀ1) may be due to solvolysis.
HN
N
C
O
NH
N
C
C
(54.088)54.000
N
N
N
(324.337)324.000
(78.093)78.000
2.4. Analysis and Instrumentation
Elemental analyses (C, H, N) were performed with a Perkin–
Elmer 2400 series II analyzer. Molar conductance values
(10ꢀ3 mol Lꢀ1) of the complexes, in DMSO, were measured using
a Tacussel conductivity bridge model CD6NG. IR spectra (4000–
400 cmꢀ1) were recorded on a Mattson 5000 FTIR spectrophotom-
eter. Electronic spectra were recorded on a Unicam UV–Vis
spectrophotometer UV2. 1H NMR measurements in d6-DMSO at
room temperature were carried out on a Varian Gemini WM-
200 MHz spectrometer at the Microanalytical Unit, Cairo Univer-
sity. The ESR spectra of Cu2+ and VO2+ complexes were recorded
on a Bruker EMX spectrometer working in the X-band (9.78 GHz)
with 100 kHz modulation frequency. The microwave power and
modulation amplitudes were set at 1 mW and 4 Gauss, respec-
tively. The low field signal was obtained after four scans with 10
folds increase in the receiver again. A powder spectrum was ob-
tained in a 2 mm quartz capillary at room temperature. Magnetic
susceptibilities were measured with a Sherwood scientific mag-
netic susceptibility balance at 298 K. Thermogravimetric measure-
O
C
HN
N
C
O
NH
N
C
NH
N
C
C
H
N
(119.145)121.000
(246.245)247.000
O
O
HN
CH
HN
C
C
NH2
C
N
ments (TGA, DTA, 20–1000 °C) were recorded on
Shimadzu thermogravimetric analyzer at a heating rate of 10 °C/
min and nitrogen flow rate of 20 ml/min.
a DTG-50
C
N
O
N
N
(162.169)162.000
2.5. Molecular modeling
(205.193)205.000
Scheme 1. Fragmentation pattern for H2L.
An attempt to gain a better insight on the molecular structure of
the ligand and its complexes, geometric optimization and confor-
mational analysis has been performed by the use of MM+ force
field as implemented in hyperchem 8.0 [20]. Semi empirical meth-
od PM3 is then used for optimizing the full geometry of the system
using Polak–Ribiere (conjugate gradient) algorithm and Unre-
stricted Hartee–Fock (UHF) is employed keeping RMS gradient of
0.01 kcal/Å mol.
2.6. Antibacterial activity
The in vitro antibacterial activity of H2L and its complexes was
evaluated against Bacillus thuringiensis (Bt) as Gram positive
bacterium and Pseudomonas aeuroginosa (Pa) as Gram negative
bacterium using streptomycin as a control. The hole plate diffusion
method [19] was adopted for the activity measurements. The bac-
terial strains were grown in nutrient agar slants. A suspension of
the studied compounds (0.2 ml of each (10 lg/ml) was incubated
at 36 °C for 36 h for the bacterial culture. After inoculation, the
diameter (in mm) of the clear inhibition zone surrounding
the sample is taken as a measure of the inhibition power against
the particular organisms. The experiments were repeated three
times and the values recorded are the mean average.
Structure 1. Molecular modeling of H2L.

22
O.A. El-Gammal et al. / Journal of Molecular Structure 998 (2011) 20–29
Table 1
Analytical and physical data of H2L and its metal complexes.
Compound empirical formula
Yield (%) Color
M.P. (°C) % Found (Calcd.)
Ko in DMSO
C
H
M
–
Cl
H2L C16H16N6O2
93
80
White
Brownish green >300
261
59.88 (59.25) 5.36 (4.97)
–
–
–
–
–
–
2..51
–
–
–
[Cu(H2L)(OAc)2]ꢁH2O CuC20H24N6O7
45.75 (45.84) 5.09 (5.00) 12.02 (12.12)
36.50 (36.53) 5.04 (4.59) 19.39 (19.32)
39.59 (39.28) 4.54 (4.28) 18.80 (19.26)
50.77 (50.61) 4.40 (4.77) 8.02 (7.73)
[Cu2(L)(OAc)2(H2O)2]ꢁ3H2O Cu2 C20H30N6O11 70
Dark green
Dark Brown
Reddish brown
Brown
Pale green
Orange
Pale Green
Yellow
Gray
>300
>300
>300
Ch. 270
>300
>300
>300
>300
[Co2L(OAc)2(H2O)2]ꢁH2O Co2C20H26N6O9
[Ni(HL)2(H2O)2]ꢁH2O NiC32H36N12O7
[Fe(H2L)Cl3]ꢁH2O FeC16H18N6O3Cl3
81
80
88
86
82
85
75
78
38.20 (38.08) 3.61 (3.59) 11.42 (11.06) 21.30 (21.07) 46.36
37.47 (37.05) 4.00 (3.88) 10.00 (10.02) 20.14 (20.50) 16.03
39.77 (39.52) 4.47 (4.14) 11.60 (11.29) 15.00 (14.58) 35.64
[Cr(H2L)Cl3]ꢁ2H2O CrC16H20N6O4Cl3
[Mn(H2L)Cl2(H2O)]ꢁH2O MnC16H22N6O4Cl2
[VO(H2L)SO4(H2O)]ꢁ2H2O VOC16H22N6O5SO4
[Cd(HL)(OAc)(EtOH)]EtOH CdC22H30N6O6
[Ag(H2L)NO3]ꢁH2O AgC16H18N7O6
35.46 (35.49) 4.02 (4.09)
45.64 (45.02) 3.67 (5.15) 18.77 (19.15)
–
–
–
–
19.85
1.00
27.32
265–270 37.40 (37.51) 4.70 (3.54) 21.27 (21.05)
3.2. IR and 1H NMR spectra
3. Results and discussion
The most important IR bands of H2L (Structure 1) and its com-
plexes are given in Table 2. The ligand has multi coordination sites
which gave variable coordination modes. Its spectrum shows two
The data of elemental analysis together with some physical
properties of the complexes are summarized in Table 1.
bands at 1593 and 1575 cmꢀ1 assignable to
m
(C@N)azomethine and
m
(C@N)pyridine [25] while the strong band at 1693 cmꢀ1 is attrib-
uted to
m
m
(C@O). The medium band at 3342 cmꢀ1 is attributed to
3.1. Molecular modeling
(NH) [21] while the band at 1060 cmꢀ1 is due to
m(NAN) [26].
The absence of bands at 1800–1960 and 2300–2400 cmꢀ1 proves
no intramolecular hydrogen bonding (NAHꢁ ꢁ ꢁO) [27].
The molecular modeling of H2L and its metal complexes drawn
in structures (1–11) showed the following: (i) a large variation in
the N8AN9 bond length on coordination via Nazomethine and CAO;
N1AC6 length becomes more shorter in [Cu2(L)(OAc)2ꢀ(H2O)2]ꢁ
3H2O [21]. (ii) The C10AO11 and C12AO13 distances in all complexes
become shorter except for [Co2L(OAc)2]ꢁ3H2O and [Cu2L(OAc)2
(H2O)2]ꢁ3H2O in which the bond is enlongated referring to the
formation of MAO [22]. (iii) The distance remains unaltered in
[Ag(H2L)(NO3)]ꢁH2O and [Cu(H2L)(OAc)2]ꢁH2O. (iv) The bond angles
of hydrazone moiety are altered somewhat upon coordination. (v)
The 1H NMR spectrum of H2L, in d6-DMSO solution (Fig. 1) sug-
gests the existence of the ligand in the enol form as evidenced by
the appearance of signals at d = 15.8, 11.8 and 11.6 ppm assignable
to the protons of OH (due to the enolization of one carbonyl group)
and NH. The signal attributed to the methyl protons (6H) is ap-
peared at 2.32 ppm while those of pyridine rings (8H) are observed
as multiple peaks at 7.34 [t, 2H (HAC5; HAC18)], 7.72 [d, 2H
(HAC4; HAC19)], 7.77 [d, 2H (HAC3; HAC20)] and 8.52 ppm [d,
2H (HAC6; HAC17)] [28]; the numbering of the atoms in the ligand
is shown as follows:
The large change affects the N8AN9AC10
, N9AC10AO11 and
O11AC10AC12 angles [21]. (vi) The N8AN9AC10 angle changes from
119.5° to (108.7–121.9°) in all complexes due to the formation of
N8AMAO11 ring [22]. (vii) The bond angles in [Cr(H2L)Cl3]ꢁ2H2O,
[Mn(H2L)(H2O)Cl2]ꢁH2O and [Fe(H2L)(H2O)Cl3]ꢁH2O, [Ni(HL)2ꢀ
(H2O)2]ꢁH2O and [VO(H2L)(SO4)(H2O)]ꢁ2H2O are quite near an
octahedral geometry. (viii) The bond angles in [Cu(H2L)(OAc)2]ꢁH2O
and [Co2L(OAc)2]ꢁ3H2O lie in the range reported for a square–
planar geometry; the lower HOMO values showed that the
molecules donating electron ability are weak. (ix) The high HOMO
energy implies that the molecules are good electron donors; LUMO
energy presents the ability of a molecule to receive electron [23].
(x) The bond angle within the hydrazone backbone did not change
significantly but the angle around the metal undergoes appreciable
variations upon changing the metal center [24].
H2L behaves in [Ag(H2L)(NO3)]ꢁH2O (Structure 2) as a neutral
monodentate coordinating via C@Nazoethine as indicated by the shift
of its band to higher wavenumber [24–26]. The spectrum shows
two bands at 1433 and 1385 cmꢀ1 assignable to
m5(NO3) and
Table 2
Important IR spectral bands of H2L and its metal complexes.
Compound
m(NH)
m(C@O)
m
(C@N)azo
m(C@N)py
m
(C@Nꢂ)
m(CAO)
m
(NAN)
m(MAO)
m
(MAN)
m
(OAH)ꢂ
H2L
3342
–
–
1693
1696
–
1593
1598
1603
1602
1598
1622
1612
1614
1623
1569
1614
1575
1569
1569
1563
1565
1571
1563
1571
1593
1542
1580
–
–
1630
1635
1621
–
–
–
–
–
–
1265
1259
1321
–
–
–
–
1060
1061
1097
1073
1086
1065
1047
1068
1043
1057
1096
–
–
–
[Cu(H2L)(OAc)2]ꢁH2O
[Cu2(L)(OAc)2(H2O)2]ꢁ3H2O
[Co2L(OAc)2(H2O)2]ꢁH2O
[Ni(HL)2(H2O)2]ꢁH2O
[Fe(H2L)Cl3]ꢁH2O
568
564
580
580
550
551
555
553
591
–
456
457
460
450
465
484
460
464
464
477
3421
3427
3411
3420
3418
3438
3420
3420
–
–
–
2975
3296
3282
3282
3262
3399
3344
1700
1695
1691
1676
1691
1657
1705
[Cr(H2L)Cl3]ꢁ2H2O
[Mn(H2L)Cl2(H2O)]ꢁH2O
[VO(H2L)SO4(H2O)]ꢁ2H2O
[Cd(HL)(AcO)EtOH]EtOH
[Ag(H2L)NO3]ꢁH2O
1617
–
1264
–
3434
m
(OAH)ꢂ of H2O.

O.A. El-Gammal et al. / Journal of Molecular Structure 998 (2011) 20–29
23
Fig. 1. 1H NMR spectra of: (i) H2L and (ii) [Ag(H2L)NO3]ꢁH2O.
In [Fe(H2L)(H2O)Cl3]ꢁH2O, [Cr(H2L)Cl3]ꢁ2H2O and [Mn(H2L)Cl2ꢀ
(H2O)]ꢁH2O (Structures 3–5) H2L behaves as neutral NNO
tridentate via C@Nazomethine, C@Npy and C@O. This mode is revealed
by the weakness of the (C@O) band suggesting that one C@O is
involved in coordination. The shifts of (C@N)py and (NAN) to
higher wavenumbers and that of (C@N)azomethine to lower wave-
a
m
m
m
m
number indicate the involvement of their nitrogens in bonding.
In [Cu(H2L)(OAc)2]ꢁH2O and [VO(H2L)(SO4)(H2O)]ꢁ2H2O (Struc-
tures 6 and 7), the ligand coordinates through C@Nazomethine and
one of the C@O groups. This mode is confirmed by the shifts of
m
(C@N)azomethine and
respectively. The broad bands at 1542 and 1374 cmꢀ1 assignable
to as(OCO) and s(OCO) with difference )
= 168 cmꢀ1
m(C@O) to higher and lower wavenumbers,
m
m
(
D
m
confirming the monodentate nature of the acetate group [30]. In
[VO(H2L)SO4(H2O)]ꢁ2H2O, the bands at 1228, 1043, 989 and
464 cmꢀ1 are due to m3
, m1, m4 and m2 of sulfate suggesting its biden-
tate nature [31] while the band at 989 cmꢀ1 is characteristic for
Structure 2. Molecular modeling of [Ag(H2L)(NO3)]ꢁH2O.
m(V@O) [32] which overlapped with m2 of sulfate.
The IR spectra of [Cu2(L)(OAc)2(H2O)2]ꢁ3H2O and [Co2L(OA-
m
1(NO3) with difference (
D
m
= 48 cmꢀ1) in agreement with the
c)2(H2O)2]ꢁH2O (Structures 8 and 9) show that H2L behaves as a
dibasic NNONNO coordinating via the two C@Nazomethine, the two
C@Npy and the two enolized carbonyl groups. This behavior is sup-
monodentate nature of NO3 [29]. The neutral behavior of H2L in
[Ag(H2L)(NO3)]ꢁH2O is supported by its 1H NMR spectrum, in d6-
DMSO solution (Fig. 2) which shows the NH signals at 11.71 and
11.57 ppm.
ported by the disappearance of
m(C@O) with the appearance of
m
(CAO) at 1259 cmꢀ1 and the shifts of C@Nazomethine to higher

24
O.A. El-Gammal et al. / Journal of Molecular Structure 998 (2011) 20–29
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
(a)
300
400
500
600
700
800
900
Wavelength (nm)
Structure 3. Molecular modeling of [Fe(H2L)(H2O)Cl3]ꢁH2O.
3.0
2.5
2.0
1.5
1.0
0.5
0.0
(b)
400
500
600
700
800
900
Wavelength (nm)
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
Structure 4. Molecular modeling of [Cr(H2L)Cl3]ꢁ2H2O.
(c)
300
400
500
600
700
800
900
Wavelength (nm)
Fig. 2. Electronic spectra of: (a) [Co2(L)(OAc)2(H2O)2]ꢁH2O, in DMF; (b) [VO(H2L)-
SO4(H2O)]ꢁ2H2O, in DMF and (c) Mn(H2L)Cl2(H2O)]ꢁH2O in Nujol.
wavenumber and C@Npy to lower wavenumber. Moreover, the new
band at ca. 1630 cmꢀ1 attributed to
m
(Nꢂ@C@C@Nꢂ) is an additional
Structure 5. Molecular modeling of [Mn(H2L)Cl2(H2O)]ꢁH2O.
evidence for ꢀth1e enolization. The acetate group has bands at 1385
and 1265 cm assignable to as(OCO) and s(OCO) with difference
= 120 cmꢀ1) [30] in a bidentate nature.
In [Ni(HL)2(H2O)2]ꢁH2O (Structure 10), H2L coordinates via
@CAOA and NH groups acting as a monobasic bidentate support-
ing by the weakness and the shift of the bands due to (C@O) and
(NH) to higher and lower wavenumbers, respectively. The IR spec-
tate by the appearance of 1542 and 1434 cmꢀ1 bands with
m
m
Dm
= 108 cmꢀ1 [30]. New bands are observed in all complexes at
(Dm
580–591 and 450–484 cmꢀ1 assigned to
m(MAO) and m(MAN)
[33,34]. The broad bands at ꢃ3411–3438, 868–850, and
ꢃ567 cmꢀ1 in the IR spectra of complexes are referred to
m(H2O),
m
q
r(H2O) and qw (H2O) for the coordinated water while the broad
m
band centered at ꢃ3500 cmꢀ1 may be due to the hydrated water.
trum of [Cd(HL)(OAc)(EtOH)]EtOH (Structure 11) indicates that
H2L coordinates in a mononegative bidentate through the two car-
bonyl groups (in keto and enol forms). This mode is supported by
3.3. Electronic spectra and magnetic measurements
the shift of
pearance of
1264 cmꢀ1 due to
m
m
(C@O) (weak band) to lower wavenumber; the disap-
(NH) and the appearance of new bands at 1617 and
(C@Nꢂ) and
(CAO). The acetate group is biden-
The electronic spectra of H2L and its complexes were recorded
in DMF and Nujol and the assignments of their bands, magnetic
m
m

O.A. El-Gammal et al. / Journal of Molecular Structure 998 (2011) 20–29
25
Structure 9. Molecular modeling of [Co2(L)(OAc)2(H2O)2]ꢁH2O.
Structure 6. Molecular modeling of [Cu(H2L)(OAc)2]ꢁH2O.
Structure 7. Molecular modeling of [VO(H2L)(SO4)(H2O)]ꢁ2H2O.
Structure 10. Molecular modeling of [Ni(HL)2(H2O)2]ꢁH2O.
Structure 8. Molecular modeling of [Cu2L(OAc)2(H2O)2]ꢁ3H2O.
Structure 11. Molecular modeling of [Cd(HL)(OAc)(EtOH)]EtOH.
moments, molar absorptivity and the ligand field parameters are
given in Table 3. The ligand spectrum showed
a band at
The electronic spectrum of [Cu(H2L)(OAc)2]ꢁH2O shows a broad
band at 14 925 cmꢀ1 due to 2B1g ? 2A1g in a square–planar geom-
etry [35–37]. The bands at 24 272 and 23 585 cmꢀ1 may be due to
LMCT [38]. The magnetic moment value (2.29 BM) is found higher
40 323 cmꢀ1 assigned to
p ?
pꢂ and two strong bands at 34 722
and 26 596 cmꢀ1 due to n ? pꢂ of C@O and C@N. Large change is
observed in the spectra of the complexes with a new n ? pꢂ band
at 36 496–33 557 cmꢀ1 and n ? pꢂ band at 26 316–27 933 cmꢀ1
.

26
O.A. El-Gammal et al. / Journal of Molecular Structure 998 (2011) 20–29
6
4
2
0
-2
-4
-6
2600
2800
3000
3200
3400
[G]
3600
3800
4000
4200
6
4
2
0
-2
-4
-6
2600
2800
3000
3200
3400
3600
3800
4000
[G]
Fig. 3. ESR spectra of: (i) [VO(H2L)SO4(H2O)]ꢁ2H2O and (ii) [Cu(H2L)(OAc)2]ꢁH2O.
than the spin only value of the Cu(II) complexes referring to the
spin–orbital coupling [39]. On the other hand, the electronic spec-
trum of [Cu2(L)(OAc)2(H2O)2]ꢁ3H2O, in Nujol, shows bands at
16 722 and 14 044 cmꢀ1 due to the d–d transition attributing to
the six coordinate geometry [40].
The spectrum of [Co2(L)(OAc)2(H2O)2]. H2O (Fig. 2a) shows a
band at 17 391 cmꢀ1 in DMF (18 549 cmꢀ1 in Nujol) due to
2B2g ? 2A1g and 1A1g ? 2A2g in a square–planar Co(II) complex
[41]. The magnetic moment value (2.57 BM) may suggest the exis-
tence of mixed stereochemistry confirming by two bands at 13 477
and 17 391 cmꢀ1. The second band is assigned to 4A2 ? 4T1(F) (m3
)
in a tetrahedral geometry while the band at 23 364 cmꢀ1 is due to a
square–planar geometry [42].
The electronic spectrum of [Ni(HL)2(H2O)2]ꢁH2O exhibits two
bands at 17 544 and 23 041 cmꢀ1 in DMF assignable to
3A2g ? 3T1g (F) and 3A2g ? 3T1g (P), respectively, in an octahedral
structure [35,42]. The calculated values [Dq,
B
and
b = 788.47 cmꢀ1, 829.97 cmꢀ1 and 0.79] as well as the magnetic
moment value are in accordance with the octahedral geometry.
The spectrum of the [Fe(H2L)(H2O)Cl3]ꢁH2O exhibits bands at
15 244, 18 868 and 24 630 cmꢀ1 attributed to 6A1g ? 4T1g(G),
6A1g ? 4T2g (G) and 6A1g ? 4Eg (G), respectively, in an octahedral
configuration [43]. The magnetic moment value (6.77 BM.) is a fur-
ther support for the suggested geometry.

O.A. El-Gammal et al. / Journal of Molecular Structure 998 (2011) 20–29
27
Table 4
Decomposition steps with the temperature range and weight loss for H2L complexes.
Complex
Temp. range, °C
Removed species
Wt. loss
Found%
Calcd.%
[Cu(H2L)(OAc)2]ꢁH2O
39–154
ꢀ(H2O)
3.576
37.410
43.151
15.863
3.838
37.439
43.543
15.180
208–339
440–684
685–800
ꢀ(2OAC + C5H4N)
ꢀ(C5H4N + CONH + CNH + 2CNCH3)
(CuO) (residue)
[Cu2(L)(OAc)2(H2O)2]ꢁ3H2O
[Co2L(OAc)2(H2O)2]ꢁH2O
[Ni(HL)2(H2O)2]ꢁH2O
[Fe(H2L)Cl3]ꢁH2O
41–121
ꢀ2(H2O)
5.316
2.745
35.756
32.018
24.165
5.478
2.739
35.312
32.275
24.193
122–177
178–356
357–464
464–800
ꢀ(H2O)
ꢀ(2OAC + C5H4N + 2H2O)
ꢀ(C5H4N + 2CNCH3 + 2CN)
2(CuO) (residue)
38–130
ꢀ(3H2O)
8.461
29.055
29.055
8.471
8.833
29.102
29.102
8.490
315–496
4967–616
617–678
679–800
ꢀ(C5H4N + OAC + CNCH3)
ꢀ(C5H4N + OAC + CNCH3)
ꢀ(2CN)
2CoO (residue)
24.463
24.473
25–76
ꢀ(2H2O)
4.910
18.544
29.991
36.705
9.850
4.744
18.061
30.851
8.36.509
9.835
77–230
231–400
401–564
565–800
ꢀ(C5H4N + H2O + CNCH3)
ꢀ(3C5H4N)
(3CNCH3 + 2CONH + CNO + CN)
NiO (residue)
44–150
ꢀ(H2O)
3.847
30.312
44.051
8.471
3.570
29.542
44.727
8.335
151–301
302–477
478–590
591–800
ꢀ(C5H4N + 2Cl)
ꢀ(C5H4N + Cl + CNCH3 + NH + 2CO)
ꢀ(NH + CCH3)
FeN (residue)
13.319
13.844
[Cr(H2L)Cl3]ꢁ2H2O
43–136
ꢀ(2H2O)
6.572
35.043
45.665
12.720
6.946
35.561
44.768
12.724
251–385
386–500
501–800
ꢀ(C5H4N + 3Cl)
ꢀC5H4N + CCH3 + CNCH3 + 2CONH)
CrN (residue)
[Mn(H2L)Cl2(H2O)]ꢁH2O
51–138
ꢀ(H2O)
3.979
9.872
23.286
17.665
30.588
14.610
3.705
10.996
23.352
17.291
30.062
14.589
139–280
281–385
386–463
463–578
579–800
ꢀ(H2O + Cl)
ꢀ(C5H4N + Cl)
ꢀ(CNCH3 + CONH)
ꢀ(C5H4N + CNCH3 + CNH)
MnO (residue)
[VO(H2L)SO4(H2O)]ꢁ2H2O
Cd(HL)(OAc)EtOH]EtOH
[Ag(H2L)NO3]ꢁH2O
74–122
ꢀ2(H2O)
6.846
48.035
29.323
15.796
6.656
47.709
30.316
15.319
237–482
483–695
696–800
ꢀ(2C5H4N + CNCH3 + CONH + 2H20)
ꢀ(CNCH3 + CNH + SO4)
VO2 (residue)
40–143
ꢀ(EtOH)
7.187
31.533
39.608
21.672
7.849
31.220
39.053
21.878
281–421
646–791
792–800
ꢀ(EtOH + C5H4N + OAC)
ꢀ(C5H4N + 2 CNCH3 + CONH + CN)
(CdO)(residue)
237–306
557–696
697–800
ꢀ(2C5H4N + CNCH3 + CONH + H2O
ꢀ(NO3)
50.304
12.156
37.540
50.422
12.104
37.472
(AgCNCH3CONH)(residue)
The electronic spectrum of [Cr(H2L)Cl3]ꢁ2H2O shows bands at
17 544 and 24 155 cmꢀ1 assignable to 4A2g ? 4T2g(F) (
1) and
4A2g ? 4T1g(F) (
2), respectively in an octahedral geometry [44].
The 4A2g ? 4T1g(P) ( 3) band is expected to be at 32 470 cmꢀ1, gen-
erally overlapped with the charge transfer band. The B value is cal-
culated by: B = (2m21 ꢀ 3m1 m2 22)/(15m2 ꢀ 27
1) [45] and the value
b is computed as: b = B/Bs (Bs = 918 cmꢀ1). The calculated Dq, B, b
and m2 m1 values as well as the magnetic moment (4.56 BM) con-
The spectrum of [Ag(H2L)NO3]ꢁH2O exhibits two bands at
36 496 and 31 654 cmꢀ1 attributed to intraligand and charge trans-
fer transitions. The shift of 26 596 cmꢀ1 in the ligand spectrum to
29 411 cmꢀ1 is an evidence for the participation of C@N in coordi-
nation [17].
m
m
m
+
m
m
3.4. Electron spin resonance
/
firm an octahedral environment.
The solid state ESR spectra of [Cu(H2L)(OAc)2]ꢁH2O and
[VO(H2L)SO4(H2O)2]ꢁH2O complexes (Fig. 3) showed only an in-
tense and broad signal without hyperfine splitting with giso of
2.12 and 1.987, respectively. In case of Cu(II) complex, the shape
of the spectrum is consistent with a square–planar environment
and its higher g value comparing to that of the free electron
(g = 2.0023) revealing an appreciable covalency of the metal ligand
bonding with dx2 ꢀ y2 as the ground-state [48] characteristic of
square planar or square pyramidal or octahedral stereochemistry
[49]. From structurally copper complexes of thiosemicarbazides
The magnetic moment (2.11 B.M.) and the electronic spectrum
of [VO(H2L)SO4(H2O)2]–H2O (Fig. 2b) is typical for octahedral VO2+
complexes as illustrated by the two bands at 22 831 and
19 011 cmꢀ1 assignable to 2B2 ? 2E and 2B2g ? 2B1 [45,46].
The spectrum of [Mn(H2L)(H2O)Cl2]ꢁH2O (Fig. 2c) exhibits bands
at 17 300 and 20 830 cmꢀ1 in Nujol due to 6A1g ? 4T1g (G) and
6A1g ? 4T2g (G), respectively in an octahedral geometry [47]. Also,
the magnetic moment (7.12 BM) is consistent with that reported
for a high spin d5 system.

28
O.A. El-Gammal et al. / Journal of Molecular Structure 998 (2011) 20–29
Table 5
at 300 and 322 nm. The pK’s of the ligand were calculated by the
half-height method (absorbance–pH curves) giving different pK
values. In DMSO, the pK’s obtained were 4.16, 7.00, 9.03 and 5.7,
9.6 at 300 and 322 nm, respectively due to the two amide protons.
In MeOH, the values are 7.16 and (4.60, 9.00) at 3 0 0 and (3 2 2)
nm while in H2O; one value (7.16) is obtained at the chosen wave-
lengths. The data are consistent with those obtained previously
[16]. One can observe that in different solvents a different number
of pK’s are determined and the value at Ca. 7.00 is commonly cal-
culated in the different solvents.
Effect of water and some organic solvents on the ligand.
Solvent
Bands (nm)
Concentration,
M
Molar absorpitivity
(e)
molꢀ1 L ꢄ 104
Water
222, 240, 292, 300,
(318)
–
–
Methanol 218, 280, 314, (330)
3 ꢄ 10ꢀ4
0.80, 0.90, 0.82, 0.63
Ethanol
Benzene
DMF
224, 296, 318, (332)
288, 302, 318, (342)
276, 286, 318, 340,
(350)
–
–
–
–
–
–
DMSO
240, 298, 318, (344)
1.5 ꢄ 10ꢀ4
0.73, 0.12, 0.15, 0.14
3.8. Effect of solvents on the ligand
e
Value is calculated for the band between brackets.
The effect of H2O, EtOH, MeOH, benzene, DMF and DMSO on the
spectrum of H2L is illustrated in Table 3. In H2O, five bands are ob-
served at 222, 240, 292, 300 and 318 nm. The spectrum in benzene
shows bands at 288, 302, 318 and 342 nm. The change of the spec-
trum from H2O to benzene may be attributed to the formation of
hydrogen bonding with H2O or solvent polarity effect. The hydro-
gen bond strength is calculated from the difference between 318
and 342 nm (24 nm = 41 666 cmꢀ1) [17]. The molar absorptivity
in MeOH and DMSO are shown in Table 5. The last band
may arrange the solvents as: H2O < CH3OH < C2H5OH < C6H6 <
DMSO < DMF according to the polarity of the solvents.
Table 6
Antibacterial activities in terms of inhibition zone diameter (mm) of H2L and its metal
complexes.
Compound
Zone of inhibition of bacterial growth (mm)
Bt (Gram-positive)
Pseudomonas
(Gram-negative)
H2L
0
12
0
0
18
0
[Ag(H2L)NO3]ꢁH2O
[Cr(H2L)Cl3]ꢁ2H2O
[Cu (H2L)(OAc)2]ꢁH2O
[VO(H2L)SO4ꢁH2O]ꢁ2H2O
20
7
0
0
3.9. Antimicrobial activity
The biological activity of H2L and its Cu2+, Cr3+, VO2+, Ag+ com-
plexes against B. thuringiensis (Bt) and P. aeuroginosa (Pa) is sum-
marized in Table. Examining the values for Gram’s positive
bacteria in Table 6, one can arrange the compounds as: [Cu(H2L)
(OAc)2]ꢁH2O > [Ag(H2L)NO3]ꢁH2O > [VO(H2L)SO4(H2O)]ꢁ2H2O and
only [Ag(H2L)NO3]ꢁH2O complex exhibited an inhibition effect
against Pa organism. It is known that, the coordination number,
solubility and the hydrophobicity of the complex governs the anti-
microbial activity. In the present case, the activity is strongly
denendent on the central metal ion and its ability to diffuse into
the cell membrane of the organism.
[50], it has been observed that the increase in g|| value with con-
Cu
comitant decrease in
A component leads to an increase in the
||
tetrahedral distortion. The degree of distortion, f(a) = g||/A|| for
the complex (119 cmꢀ1) lies within the range expected for a square
planar geometry [51]. The ESR spectrum of the VO2+ complex is
isotropic with giso lower than the free-electron value (2.0023) as
expected for the d1-system with an octahedral arrangement re-
lated to the spin–orbit interaction of the ground state with a
low-lying excited state. This decrease in the free-electron value re-
veals a strong ligand field strength [52].
3.5. Mass spectra
4. Conclusion
0
0
N1 ,N2 -bis[1-(pyridin-2-yl)ethylidene]oxalo hydrazide (H2L)
and its complexes with Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Cd2+
The successive fragmentation of H2L is illustrated in Scheme 1.
The molecular ion peak (3 2 4) is typical with the calculated molec-
ular weight (324.337). The end fragment (5 4 0) may be corre-
sponding to C4H6.
,
VO2+ and Ag+ have been characterized. The ligand pK’s are 4.62,
7.78 and 9.45. The ligand behaves as neutral (mono- or dibasic)
bidentate, tridentate or tetradentate. Cr3+, Mn2+, Fe3+, Ni2+ and
VO2+ form octahedral complexes while Co2+ and Cu2+ form
square–planar. [VO(H2L)SO4ꢀ(H2O)2]ꢁH2O and [Cu(H2L)(OAc)2]ꢁ
H2O are mononuclear species. No effect was observed for the com-
plexes on Pa bacteria growth except for [Ag(H2L)(NO3)]H2O which
had a high activity; Cu2+ exhibits a high activity against BT.
3.6. Thermogravimetric studies
The stages of decomposition, temperature range, decomposition
product as well as the weight loss percentages of some complexes
are given in Table 5. Fig. 3 shows the TGA curve of [Cu(H2L)
(OAc)2]ꢁH2O as a representative example. The thermogram displays
three degradation steps at 39–154, 208–339 and 440–684 °C with
weight losses of 3.57 (Calcd. 3.84%), 37.41 (Calcd. 37.41%) and 43.1
(Calcd. 43.5%) corresponding to the loss of H2O, 2OAC + C5H4N and
C5H4N + CONH + CNH + 2CNCH3 species. The residual part is CuO
(Found 15.9; Calcd. 15.2%).
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2011.04.043.
An inspection of the data represented in Table 4 indicates that
the TG thermogram displayed a high residual part for the studied
complexes revealing high stability of the formed chelates.
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