UV-vis, IR and 1H NMR spectroscopic studies of some Schiff bases derivatives of 4-aminoantipyrine

Article abstract of DOI:10.1016/j.saa.2005.01.026

Five Schiff bases derived from 4-aminoantipyrine and benzaldehyde derivatives (I) are prepared and their UV-vis, IR, ¹H NMR and fluorescence spectra are investigated and discussed. The electronic absorption spectra of the hydroxy 4-aminoantipyr

Full text of DOI:10.1016/j.saa.2005.01.026

Spectrochimica Acta Part A 62 (2005) 621–629
UV–vis, IR and 1H NMR spectroscopic studies of some Schiff
bases derivatives of 4-aminoantipyrine
Raafat M. Issa, Abdalla M. Khedr∗, Helen F. Rizk
Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt
Received 5 November 2004; received in revised form 31 January 2005; accepted 31 January 2005
Abstract
1
Five Schiff bases derived from 4-aminoantipyrine and benzaldehyde derivatives (I) are prepared and their UV–vis, IR, H NMR and
fluorescence spectra are investigated and discussed. The electronic absorption spectra of the hydroxy 4-aminoantipyrine Schiff bases Ib
and Ie as well as the fluorescence spectra of Ie are studied in the organic solvents of different polarity. The UV–vis absorption spectra of
4-aminoantipyrine Schiff bases Ib, Id and Ie are investigated in aqueous buffer solutions of varying pH and utilized for the determination
of pKa and ꢀG of the ionization process. The reactions of the hydroxy compounds Ib and Ie with Ni(II) and Cu(II) ions are also studied.
The results of spectral studies are supported by some molecular orbital calculations using an atom superposition and electron delocalization
molecular orbital theory for a compound Ib.
© 2005 Elsevier B.V. All rights reserved.
Keywords: 4-Aminoantipyrine; Schiff bases; Spectral studies; Metal chelates
1. Introduction
2. Experimental
A considerable number of articles have been published on
the spectral behavior of Schiff bases [1–4]. This originated
from the fact that the Schiff bases and their metal complexes
exhibit wide applications in biological systems [5,6] and in-
dustrial uses, especially in catalysis [7,8] and dying [9–11].
Although Schiff bases containing a heterocyclic nucleus
have efficient biological activities, yet spectral studies of
these compounds are comparatively minor [12–14].
All compounds used were pure grade chemicals from
BDH, Aldrich or Sigma. The solvents used for spectral mea-
surements were spectroscopic grade from Aldrich.
The Schiff bases were prepared by refluxing a mixture of
10 mmole of 4-aminoantipyrine and 10 mmole of aldehyde
in 25 ml of ethanol on a water bath for 2–5 h [15]. The Schiff
base, precipitated on cooling, was filtered off and purified by
repeated crystallization from the appropriate solvent (yield
70–80%).
1
In the present work, the UV–vis, IR, H NMR and flu-
orescence spectra of some Schiff bases obtained from 4-
aminoantipyrine and benzaldehyde derivatives (Scheme 1)
are investigated. The UV–vis absorption bands are assigned
to corresponding electronic transitions; the IR bands and the
1H NMR signals of diagnostic importance are considered and
discussed. The reactions of some compounds with Ni(II) and
Cu(II) ions are also investigated. The electronic absorption
spectral data for Schiff base Ib are supported by using the
molecular orbital calculations.
The UV–vis spectra were recorded at room temperature
in the range of 200–600 nm on a Perkin-Elmer Lambda 4B
using a 1.0 cm matched silica cells. The IR spectra were
recorded in the solid state as KBr discs on a Perkin-Elmer
1
1430 ratio recording infrared spectrometer. The H NMR
spectra were obtained on a Brooker DMX 750 (500 MHz)
using d6 DMSO as a solvent and TMS as an internal
standard. The fluorescence spectra were recorded on a
Schimadzu RF 510 spectrofluorometer. The fluorescence
quantum yield for the solutions having absorbances less than
0.1 at the excitation wavelength and refereed to fluorescene
in 0.1 N NaOH (φf = 0.93) [16]. The X-band ESR spectra of
∗
Corresponding author. Fax: +20 40 3350804.
E-mail address: abkhedr2001@yahoo.com (A.M. Khedr).
1386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2005.01.026

622
R.M. Issa et al. / Spectrochimica Acta Part A 62 (2005) 621–629
Scheme 2. Keto–enol tautomerism in Schiff base Ie.
ring as an origin to the C N group as a sink. This can be
confirmed by determining the energy of this charge transfer
band from λmax values using the relation:
Scheme 1. Structure of the Schiff bases under investigation in which
R: Ph (Ia), o-OH-Ph (Ib), p-OCH3-Ph (Ic), p-OH-Ph (Id), and 2-OH-1-
naphthaldhyde (Ie).
1241.6
ECT
=
(1)
CT
λ
the solid Cu(II)-complexes were recorded on a Joel-X-band
spectrometer equipped with an E-101 microwave bridge.
Molecular orbital calculations were carried out on compound
Ib using the atom superposition and electron delocalization
molecular orbital (ASED-MO) theory.
max
and comparing the values thus obtained with those calculated
from the Briegleb relation [17]:
ECT = IP − (EA + C)
(2)
in which IP is the ionization potential of the donor part, EA
is the electron affinity of the C N acceptor group (−1.3 eV)
and C is the coulombic force between the electron transferred
and the positive hole left behind (C = 5.2 or 5.6 eV) [17]. The
values obtained for ECT from Eq. (1) lie between the two
values calculated from Eq. (2) by using the two values of C
with maximum difference of 0.26 eV (Table 1).
Itisworthytomentionthatthechargetransferbandissplit-
ted into two bands in the spectrum of Ie at 381 and 396 nm.
For Ib the spectrum displays a shoulder on the longer wave-
length side. This behavior can be ascribed to the possible
existence of a tautomeric shift between the C N and o-OH
group according to the equilibrium in Scheme 2.
3. Results and discussion
3.1. The electronic absorption spectra
The electronic absorption spectra of Ia–Ie in ethanol
(Fig. 1) displays four main bands (Table 1). The first
(210–234 nm) and second (240–281 nm) bands (A and B)
*
are assigned to the ␲–␲ transitions of the aromatic rings.
*
The third band (C) at 301–334 nm involves ␲–␲ transition
of the C O and C N groups; this band appears splitted in
the spectra of Ib and Ie where the C N group is involved in
an intramolecular hydrogen bond which causes a decrease of
the ␲–␲* energy of the C N group relative to that of the C O
group. The longer wavelength band (D) at 325–396 nm can
be assigned to an intramolecular charge transfer interaction.
The charge transfer will originate from 4-aminoantipyrine
The absorption at shorter wavelength is assigned to the
enolic form (II) while that at longer wavelength is due to the
ketonic structure (III) [18].
The oscillator strength (f) of the CT band was also deter-
mined from the relation [19]:
−9
f = 4.6 × 10
ε
ꢀν1/2
(3)
max
in which ꢀν1/2 is the bandwidth at half absorbance value and
εmax is the maximum molar extinction coefficient.
In cases where the CT band overlaps with the band C, the
band envelope was completed by considering it to follow a
Gaussian curve. The f-values determined are given in Table 1.
The ionization potentials of the 4-aminoantipyrine Schiff
bases under study were determined from the electronic ab-
sorption spectra applying the relation:
IP = a + bν
(4)
in which a and b are constants having the values (4.93 and
0.857) [20], (5.156 and 0.778) [21] or (5.11 and 0.701) [22];
*
ν is the energy of the lowest ␲–␲ transition. The values
obtained together with the mean values determined from the
above three values are given in Table 1.
Fig. 1. Electronic absorption spectra of 4-aminoantipyrine Schiff bases in
ethanol.

R.M. Issa et al. / Spectrochimica Acta Part A 62 (2005) 621–629
623
Table 1
Data from UV–vis and fluorescence spectra of 4-aminoantipyrine Schiff bases in ethanol
Compound number
Assignment
Ia
Ib
Ic
Id
Ie
*
210, 234
1.58, 1.79
252
1.76
313
1.81
325
2.16
3.82
8.13
7.66
7.79
7.86 0.24
1.01
3.96
3.56
325
212, 234
1.88, 1.99
262
213, 230
1.64, 1.51
281
1.41
307
1.90
329
2.64
3.77
8.09
7.62
7.75
7.82 0.24
0.74
3.92
3.52
329
213
1.70
242
1.70
317
2.14
330
2.90
3.76
8.07
7.61
7.74
7.81 0.24
0.66
3.91
3.51
330
212
3.32
240
3.28
λmax
εmax
λmax
εmax
λmax
εmax
λmax
εmax
Band A (␲–␲ Ar)
*
Band B (␲–␲ Ar)
1.27
*
301, 317
1.24, 1.49
346,
2.24
3.59
7.95
7.47
7.63
7.68 0.24
0.51
321, 334
1.24, 1.36
381, 396
2.26, 1.86
3.26, 3.14
7.69, 7.50
7.18, 7.08
7.40, 7.31
7.42 0.26, 7.30 0.21
0.29, 0.21
3.52, 3.40
3.12, 3.00
381
Band C (␲–␲ of C O or C N)
Band D (CT)
ECT (eV) from Eq. (1)
IP1 (eV)
IP2 (eV)
IP3 (eV)
Mean IP (eV) values
f
3.78
3.38
346
ECT from Eq. (2) [C = 5.2 eV]
ECT from Eq. (2) [C = 5.6 eV]
exc
λ
max
emm
max
No fluorescence
434
No fluorescence
No fluorescence
480
λ
0.064
0.1131
φf
λmax in (nm), εmax (L mol−1 cm−1 × 10−4) and f is the oscillator strength.
Despite the fact that the position of the CT band is influ-
enced by the substituent on the phenyl ring being shifted to
longer wavelength with the increasing donor character of the
substituent, yet it is not possible to have a quantitative treat-
ment because the shift is of a small magnitude. However, the
hydrogen bond formation between the C N group and the o-
OH group on the phenyl or naphthyl ring shifts the CT band
obviously to longer wavelength. The magnitude of shift is
higher for the naphthyl derivative.
the higher stabilization of the excited state with increased
solvent polarity. The application of the dielectric relations
of Gati and Szalay [23] or Suppan [24] to the data of the
CT band did not lead to linear relationships. This reveals
that the dielectric constant of the solvent does not play an
max
CT
important role in the band shift. The plot of E
in dif-
ferent solvents as a function of the various microscopic
solvent parameters: α (acidity), β (basicity), π* (dipolar-
ity) [25], Z [26] as well as ET [27] showed nonlinear re-
lations indicating that these solvent parameters are not the
main factors affecting the CT band position. Accordingly, it
can be assumed that the shift of the CT band is the resul-
tant of the influence of all these parameters. These effects
may be additive, counteracting or even may cancel out each
other.
The spectra of Ib and Ie are measured in organic solvents
of different polarity and the values of εCλT and λmax are
max
listed in Table 2. The obtained results indicate that the posi-
tion of the bands due to the localized transitions is slightly
influenced by solvent polarity. The CT band displays a gen-
eral red shift with an increased solvent polarity denoting
Table 2
Data from UV–vis spectra of 4-aminoantipyrine Schiff bases Ib and Ie in organic solvents of different polarity
max
CT
max
CT
max
CT
max
CT
emm
Solvent
λ
of Ib
ε
of Ib
λ
of Ie
ε
of Ie
λ
of Ie
φf of Ie
max
Methanol
Ethanol
Acetone
DMF
DMSO
CHCl3
346
343
355
357
348
345
346
346
347
344
344
347
2.22
2.24
1.94
2.82
2.66
2.70
2.42
2.60
2.62
2.61
2.70
2.72
380, 395 (sh)
381, 396 (sh)
382, 398 (sh)
386
2.62, 2.12
2.26, 1.86
2.08, 1.90
2.74
467
480
477
484
–
0.1156
0.1131
0.0754
0.0762
–
388
2.70
382, 398 (sh)
381, 395 (sh)
380, 395 (sh)
383, 397 (sh)
381, 396 (sh)
380, 395 (sh)
380, 395 (sh)
2.68, 2.24
2.60, 2.14
2.68, 2.24
2.64, 2.18
2.60, 2.22
2.88, 2.36
2.76, 2.30
–
–
CCl4
476
475
482
475
–
0.1087
0.0792
0.0876
0.1105
–
CH2Cl–CH2Cl
CH2Cl2
Toluene
Benzene
Ethylacetate
–
–
εmax × 10−4 (l mol−1 cm−1), λmax (nm), φf is the fluorescence quantum yield.

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R.M. Issa et al. / Spectrochimica Acta Part A 62 (2005) 621–629
3.2. Electronic absorption spectra of 4-aminoantipyrine
Schiff bases Ib, Id and Ie in buffer solutions of varying
pH and spectrophotometric determination of their acid
dissociation constant (pKa)
The 4-aminoantipyrine Schiff bases Ib, Id and Ie are con-
sidered as monobasic acids and their dissociation can be rep-
resented by the following equilibrium:
Ka
HL ꢀ L− + H+
where Ka is the acid dissociation constant for the compound.
The absorption spectra of 4-aminoantipyrine Schiff bases
Ib, Id and Ie are studied in universal buffer solutions of vary-
ing pH values containing 5% (v/v) methanol in the UV–vis
region (200–600 nm). The spectra obtained indicate that
the absorbance values and position of the absorption bands
changes with the pH of the medium due to the following:
1. In case of Ib, in solution having pH <6, the absorption
spectra showed an absorption peak with λmax = 280 nm
corresponding to HL form, the extinction of this peak
increases with increasing pH values of solution until
pH 6 and begin to decrease with increasing pH value,
while another absorption peak appeared at pH ≥6 with
λmax = 350 nm corresponding to the L− form. The ab-
sorbance of this peak increases with increasing the pH
value of the solution until pH 10. This behavior indicates
that, in solution of pH <6, Ib exist essentially as undisso-
ciated molecules, whereas at pH >10 the L− form exist;
at pH 6–10 the undissociated and dissociated forms are
present in different ratios.
Fig. 2. Absorbance–pH curves of 4-aminoantipyrine Schiff base (Ib).
configuration except in the position of the OH group. This
can be attributed to the formation of hydrogen bond in case
of o-OH which retards the liberation of H+ proton relative
to p-OH substituent. The strength of the hydrogen bond can
be taken as equal to the difference in energy in both cases
(8.70 kJ mol−1).
3.3. IR spectra
2. The spectra of Id showed two different peaks with
λmax = 250 and 364 nm corresponding to HL and L−, re-
spectively. The extinction of the first peak due to the undis-
sociated form (HL) decreases with increasing pH of the
solution, while the absorbance of the second peak of the
dissociated form (L−) increases with increasing pH val-
ues.
3. The spectra of ligand Ie showed a peakwithλmax = 292 nm
and two broad peaks with λmax = 330 and 395 nm. The
extinctions of the three peaks increases with increasing
pH of the solution due to the change from undissociated
form to the dissociated one with increasing pH.
Selected bands of diagnostic importance are discussed in
this part (Table 4). The spectra of all compounds exhibit two
medium intensity bands at 3174–3038 and 3087–3036 cm−1
corresponding to asymmetric and symmetric stretching vi-
brations of the aromatic C H groups. All compounds dis-
play an intense band at 1648–1617 cm−1 corresponding to
ν(C O) of the antipyrine ring. The ν(C N) band is observed
at 1591–1576 cm−1 being shifted to lower wave numbers for
Ib and Ie due to the contribution of the C N in these two
compounds in an intramolecular hydrogen bond.
The aliphatic CH3-groups lead to two small bands at
2984–2917 cm−1 due to the stretching modes, while their de-
The pH-absorbance curves of 4-aminoantipyrine Schiff
bases Ib, Id and Ie at different wavelengths corresponding
to λmax are of typical Z- or S-shaped (Fig. 2). This behav-
ior is utilized for the determination of the acid dissociation
constant (pKa) of these compounds by applying the limiting
absorbance [28] and the half-height methods [29] (Table 3).
The values of pKa were used in calculating the free energy
change (ꢀG*) of the ionization process from the relationship
formation vibrations give strong bands at 1200–1160 cm−1
.
Table 3
The values of pKa for 4-aminoantipyrine Schiff bases Ib, Id and Ie
Schiff base
λ (nm)
pKa
ꢀG* (kJ mol−1
)
LAM
HHM
Av. V
Ib
Id
Ie
350
346
395
7.54
5.88
5.66
7.08
5.73
5.15
7.31
5.81
5.41
42.41
33.71
31.39
ꢀG∗ = −2.303RT log K (at 303 K)
(5)
The ꢀG* value (Table 3) of Ib (o-OH) is higher than ꢀG*
value of Id (p-OH), although they have the same molecular
HHM: half-height method; LAM: limiting absorbance method; Av. V: aver-
age value; ꢀG*: free energy change.

R.M. Issa et al. / Spectrochimica Acta Part A 62 (2005) 621–629
625
Table 4
hydrogen coupled with the N H hydrogen which resonates
as a doublet at 6.82 and 7.12 ppm for Ib and Ie, respectively.
This behavior supports the occurrence of the keto–enol tau-
tomerism given above (Scheme 2).
Some selected bands of diagnostic importance from the IR spectra of 4-
aminoantipyrine Schiff bases
Compound number
Ia Ib Id
Assignment
Ie
4-Aminoantipyrine
–
–
–
–
–
–
–
–
–
3424
3317
–
3174
3087
2984
2917
1641
–
1406
1310
–
1200
–
ν(NH2) as
ν(NH2) s
ν(OH)
ν(CH) as (Ar)
ν(CH) s (Ar)
ν(CH) as (CH3)
ν(CH) s (CH3)
3.5. Fluorescence spectra
3450
3087
3056
2928
2918
1648
1590
1410
1369
1304
1180
1115
1020
860
3630
3138
3060
2935
2916
1617
1576
1418
1305
1250
1160
1093
1024
865
3427
3080
3043
2926
2917
1634
1587
1417
1326
1312
1155
1087
1027
870
The fluorescence spectra of 4-aminoantipyrine Schiff
bases were investigated in ethanol as a solvent. The data are
collected in Table 1. The spectra were also obtained for Ie
in solvents of different polarity; the results are collected in
Table 2. These results indicate that the values of the emis-
sion λmax and fluorescence quantum yield (φf) depend on
the molecular structure and solvent used as a medium. Also,
compounds Ib and Ie give good fluorescence spectra and
satisfactory values for the fluorescence quantum yield (φf)
whereas compounds Ia, Ic and Id do not give the convincing
fluorescence spectra. This behavior may be attributed to the
formation of hydrogen bonding in case of Ib and Ie which in-
crease the stability of the molecule in the excited state, which
is not possible in case of the other Schiff bases Ia, Ic and Id
[30]. The fluorescence spectra of Ie were recorded in some
3087
3036
2935
2920
1644
1591
1417
1370
1305
1179
1070
1017
870
C
C
N
C
O
N
CH3
N
δ(OH)
δ(CH3)
ν(C OH)
γ(CH N)
γ(OH)
–
–
728
675
673
674
641
γ(CH) ring
The spectrum of Id exhibits the ν(OH) as a sharp medium
band at 3630 cm−1, while for Ib and Ie it appears as
a broad band at 3450 and 3427 cm−1, resp−ec1tively. The
OH deformation bands lie at 1326–1250 cm while the
ν(C OH) bands are observed at 1115–1070 cm−1 and γ(OH)
organic solvents of varying polarity (Fig. 3 and Table 2). The
emm
data reflect that both λ
and φf are solvent dependent.
max
emm
The plot of λ
as a function of macro- or microscopic
max
solvent parameters gave nonlinear relationships indicating
that the solvent effect on emission spectra, as in the case of
ground state spectra, is actually the resultant of the influence
of the various solvent parameters.
at 870–860 cm−1
The aromatic rings give a group of intense bands due to
skeletal and CH deformations at different positions charac-
teristic for the type of substitution.
.
3.6. Spectral studies on the metal complexes of Ib and Ie
with Ni2+ and Cu2+ ions
3.4. 1H NMR spectra
The 1H NMR spectra of the antipyrine Schiff bases
(Table 5) display two sharp signals at 2.35–2.5 and
3.10–3.19 ppm with an integration equivalent to three hydro-
gens corresponding to the N (CH)2 and C CH3 groups. The
aromatic rings give a group of multi signals at 6.82–7.92 ppm.
The CH N hydrogen for (Ia–Id) resonates at 9.49–9.84 ppm
as a sharp singlet. For Schiff bases Ib and Ie two doublets
are observed: the first at 9.48 and 8.27 due to the azomethine
The addition of Ni(II) or Cu(II) ions to a solution of Ib
or Ie leads to the appearance of a new absorption band with
λmax = 410 and 450 nm for Ib and Ie, respectively. The extinc-
tions of these bands increase with increasing the metal ion
concentration which is a good evidence for the specification
of these bands to the formed metal complexes in the solu-
tion. The stoichiometry of the formed metal complexes was
determined using the mole ratio [31] and continuous vari-
Table 5
1H NMR spectral data of 4-aminoantipyrine Schiff bases in CDCl3
Compound number
Assignment
Ia
Ib
Ic
Id
Ie
4-Aminoantipyrine
2.5
3.19
–
2.339
3.15
–
2.45
3.10
–
2.42
3.12
–
2.42
3.16
–
2.13
2.82
2.98
C
N
NH2
CH3
CH3
–
–
–
3.28
–
6.92–7.82
9.71
–
–
–
–
–
–
OCH3
NH(tout)
Ar H
6.82
7.26–7.52
9.48b
9.84b
7.17a
7.39–7.80
8.27a
10.85
7.25–7.92
9.78
–
6.84–7.68
9.49
9.94
7.20–7.50
–
–
CH
OH
N
a
Doublet.
b
N
CH overlapping with OH.

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R.M. Issa et al. / Spectrochimica Acta Part A 62 (2005) 621–629
Table 6
Electronic absorption spectral data of Ni(II) and Cu(II) chelates with 4-
aminoantipyrine Schiff bases Ib and Ie
Compound Metal ion λmax Stoichiometry
MRM CVM
log βn
−ꢀG*
Ib
Ni(II)
Cu(II)
Ni(II)
Cu(II)
410
1:1
1:2
1:1
–
12.78
19.16
17.72
26.56
1:1
1:2
1:1
1:2
12.38
24.38
17.16
33.80
Ie
450
1:1
1:2
1:1
1:2
9.94
18.79
13.78
26.05
1:1
–
1:1
1:2
10.16
20.62
14.09
28.59
log βn: log stability constant; −ꢀG*: free energy change (k cal mol−1).
denoting the contribution of these two groups with the metal
ion. The bands due to the various vibrations of the phenolic
OH-group disappeared from the spectra of the complexes
denoting displacement of the phenolic proton through the
metal ion. Thus, the SB-Ib and SB-Ie would act as monobasic
tridentate ligands towards the metal ion [34].
The copper(II) nitrate complex displayed a strong band
at 1290 cm−1 characteristic for monodentate coordinated ni-
trate anion while the spectra of the acetate complexes contain
two bands near 1575 and 1535 cm−1 corresponding to a mon-
odentate acetate anion [35].
The IR spectra of all complexes exhibit two bands at
500–480 and 445–425 cm−1 corresponding to ν(M O) and
ν(M N) stretching modes [36].
The magnetic moment values for the Cu(II)-complexes
amounted to 1.49 for (1), 1.99 for (2) and 1.54 BM for (4)
supporting the octahedral, square planar and tetrahedral ge-
ometries for Cu(II)-complexes 1, 2 and 4, respectively. The
Ni(II)-complexes had a magnetic moment of 2.8 BM which
is the normal value for octahedral nickel(II)-complexes; this
is quite close to the spin-only value for the two unpaired
electrons [37].
Fig. 3. Emission spectra of a 1 × 10−5 M solution of the compound (Ie) in
organic solvents of varying polarity.
ation methods [32]. Also, their stability constants and free
energy changes are calculated [33]. The results obtained are
collected in Table 6.
The electronic absorption spectra of the prepared solid
complexes were recorded in the range of 200–1000 nm as
nujol mull. The electronic absorption spectra of Cu(II)- and
Ni(II)-complexes compared with those of the free Schiff
bases exhibit new bands or shoulders at longer wave-
lengths around 700 nm for Cu(II)-complexes and at 639 nm
for Ni(II)-complex (Table 7). The position of λmax and
the shape of the new bands are relevant to an octahedral
structure of Cu(II)-complex (1), square planar geometry
for Cu(II)-complex (2), distorted tetrahedral geometry for
Cu(II)-complexes (3 and 4) and octahedral geometry for
Ni(II)-complex (5) [38].
In order to investigate the molecular structure of the
formed Cu(II)- and Ni(II)-complexes with 4-aminoantipyrine
Schiff bases Ib and Ie, some solid complexes were pre-
pared and characterized. The prepared solid complexes
were found to have the following molecular composi-
tions: [CuLAcO(H2O)2]·2H2O (1), [CuLAcO]·2H2O (2),
[CuLCl]·2H2O (3), [CuL(NO3)] (4) and [NiL2] (5) where
L refers to the deprotonated ligand Ib in case of complex (1)
and Ie for complexes (2–5).
The data of elemental analysis of the complexes are in
good agreement with the suggested formulae (Table 7).
The IR spectra of the metal complexes (Table 7) compared
with those of the ligands showed that the C O and C N
bands are shifted to lower wave numbers by 10–30 cm−1
The molar conductance values for 10−3 M solution of
Cu(II)-complexes in DMF were found to lie within the
10–15 ꢁ−1 which reflects the non-electrolyte nature of the
complexes. This indicates that the anions are involved in the
coordination sphere of the metal ion [39].

R.M. Issa et al. / Spectrochimica Acta Part A 62 (2005) 621–629
627
Table 7
Elemental analysis, IR spectra and UV–vis band of the solid complexes (1–5)
No. Empirical formula
(molecular formula)
Color (for. wt.) Microanalysis resultsa
IR spectra
UV–vis
band due
to d–d
%C
%H
%N
%M
νOH νCH
N
νC
O
νM
O
νM
N
transition
1
2
3
4
5
[CuL(AcO)(H2O)2]·
2H2O (C20H27CuN3O8)
[CuL(AcO)]·2H2O
(C24H25CuN3O6)
[CuLCl]·2H2O
Green (501.00) 47.6 (48.0) 5.9 (5.4) 8.7 (8.4)
Brown (515.02) 55.5 (56.0) 4.5 (4.9) 8.5 (8.2)
Brown (491.43) 53.5 (53.8) 4.2 (4.5) 8.4 (8.6)
13.0 (12.8) 3416 1576
12.0 (12.3) 3477 1555
13.2 (12.9) 3455 1573
1603 478
1618 452
1604 496
1602 498
1609 489
408
715
670
730
675
639
428
430
431
441
(C22H22ClCuN3O4)
[CuL(NO3)]
Green (513.95) 51.8 (51.4) 3.6 (3.5) 10.9 (10.9) 11.9 (12.4) 3445 1578
[NiL2] (C44H36NiN6O4) Green (771.50) 68.1 (68.5) 4.6 (4.7) 11.0 (10.9) 7.2 (7.6) 3436 1579
(C22H18CuN4O7)
The reaction yield was 80–85%.
a
%F (%C), all complexes (1–5) decompose without melting above 300 ◦C.
The results obtained from the X-band ESR spectra of the
solid Cu(II)-complexes (1, 2 and 4) at room temperature in-
dicate the following:
non-rigid or non-perfectly following (ρnpf) component. For
the example of a diatomic molecule (ab),
ρmol = ρa + ρb + ρnpf
(6)
1. The ESR spectrum of Cu(II)-complex (1) gives three
anisotropic signals (g = gx = 2.4295, g = gz = 2.7468
where ρa and ρb are atomic charge densities centered on nu-
clei (a) and (b), and ρnpf is an electron delocalization or bond
charge density. According to the electrostatic theorem, the
forces on the nucleus (a) has two nonzero components; a
repulsive one due to the nucleus and electronic charge dis-
⊥
||
and gy = 2.6186) and geff = 2.6015 which confirm the oc-
tahedral geometry around the Cu(II) ion.
2. The ESR spectrum of Cu(II)-complex (2) show one signal
with pattern with geff value (2.1569) indicating a square
planar geometry around the Cu(II) ion.
tribution of atom (b) and an attractive force due to ρnpf
.
These forces are integrated, yielding the potential energy
E(R), where R is the internuclear distance
3. The ESR spectrum of Cu(II)-complex (4) show
two sharp anisotropic signals (g = gx = 1.8488 and
⊥
g = gz = 1.8957). The observedESR patternand geff value
||
E(R) = Er(R) + Enpf(R)
(7)
(1.8724) indicate a tetrahedral geometry around the Cu(II)
ion [40].
Er(R) is the repulsive energy due to atom superposition and
Enpf(R) is the attractive energy due to electron delocalization.
Enpf is approximated as the change in the total one-electron
valence orbital energy that is due to bond formation
Based on the knowledge gained above for the metal com-
plexes, the bonding in the Cu(II)-complexes (2–4) can be
formulated as follows (Scheme 3).
∼
=
E
E + ꢀE
r
(8)
MO
3.7. Molecular orbital calculations
¨
ꢀEMO is determined by using a modified extended Huckel
Hamiltonian. When this approximation to Enpf is employed,
the more electronegative atom is used to provide the density
function for Er. This technique has already been applied
for predicting molecular structures, reaction mechanism,
and electronic and vibrational properties [43–48]. The
input data consist of ionization potentials [49] (VSIP)
and valence-state Slater orbital exponents [50] for the
constituent atoms. These parameters are sometimes altered,
particularly in treating ionic heteronuclear molecules to
ensure reasonably accurate calculations of ionicities and
bond lengths in the diatomic fragment molecules. In this
way electronic charge self-consistency is taken into account
[42]. Atomic parameters used in the calculations are given
in Table 8. Because of ionicity, the ionization potentials for
N 2s and 2p are decreased by 2.0 eV from the atomic values
[49]. The C 2s and 2p Slater exponents are increased by
0.20 from the atomic values of Clementi and Raimondi [50]
to get a reasonable bond length. In all reported resulted for
The atom superposition and electron delocalization
molecular orbital theory [41,42] is used. This is a semiempir-
ical theoretical approach based on partitioning the molecular
density function (ρmol) into rigid atomic components and a
Scheme 3. The bonding in the Cu(II)-complexes (2–4). X: AcO−, n = 2 (2);
Cl−, n = 2 (3); and NO3−, n = 0 (4).

628
R.M. Issa et al. / Spectrochimica Acta Part A 62 (2005) 621–629
Table 8
Atomic parameters used in the calculations: principle quantum numbers, n;
ionization potentials, IP (eV); orbital exponents, ζ (a.u.)
Atom
s
p
n
IP
ζ
n
IP
ζ
C
N
O
H
2
2
2
1
16.590
18.330
28.480
13.600
1.8580
1.9240
2.2459
1.2000
2
2
2
11.260
12.530
13.620
1.8180
1.9170
2.2266
equilibrium structures, the bond lengths are variationally
optimized to the nearest degree. In all calculations the C H
˚
bond lengths are kept constant at 1.10 A.
Quantum chemical calculations using ASED-MO theory
are used to investigate the geometry and electronic struc-
ture of the Schiff base Ib. The optimization of bond lengths,
bond angles and dihedral angles (Table 9) produces a stable
structure with a minimum energy. It is shown that the stable
structure of Ib is in the trans form as shown in Fig. 4. The
molecular orbital calculations shows that the phenyl moiety
is out of plane with respect to both diazole and OH-phenyl
rings. The distortion from planarity takes place through ro-
tation around C4 C7, C7 C8, C8 C9, C9
N12 and N12 C13
by 3, 32, 2, 1 and 20◦, respectively. The bond lengths (bond
orders) of C9 N12, N12 C13, and C13 C14 bonds are equal
Fig. 4. The molecular structure of Schiff bases Ib obtained from ASED-MO
theory.
˚
to 1.38 (0.8653), 1.32 (1.1007) and 1.49 A (0.7690), respec-
tively, and the double bond character of N12 C13 bond is a
good evidence for Schiff base formation. The C19
O20 bond
have resonance character between a double bond and a single
one. The calculations reveal the formation of strong hydrogen
bond, N12 H39, as assumed before with bond length (bond
˚
length (bond order) 1.27 A (0.8174) donates some double
bond character of this bond. The partial double bond charac-
ter of the C O bond confirms the proposed keto–enol tau-
tomerism represented in Scheme 2 since the bond would
˚
order) equal to 1.58 A (0.1745), and confirmed by the pres-
ence of the negative charge on N12 equal to 0.23388 e.
The calculation of the charge distribution over the
whole skeleton of the molecule indicates the pres-
ence of relatively high electron density on atoms C1
(−0.00964), C3 (−0.02482), C5 (−0.02624), C9 (−0.07978),
N12 (−0.23388), C14 (−0.07271), C16 (−0.10965), C18
(−0.13964) and the highest electron density is present on
O20 (−0.54970) and O21 (−1.20709). Whereas an electron
deficient are found on atoms C2 (0.03381), C4 (0.16864), C6
(0.03277), C7 (0.33902), C8 (0.56451), C10 (0.09393), N11
(0.33290), C13 (0.20748), C15 (0.03768), C17 (0.04199), C19
(0.47925), C22 (0.06759) and C23 atoms (0.16712).
Table 9
˚
The calculated bond lengths (A), bond order, bond angle and dihedral angles
of compound Ib obtained from ASED-MO theory
Bond
Bond length
Bond order
Bond angle
Dihedral angle
C1 C2
C2 C3
C3 C4
C4 C5
C5 C6
C4 N7
N7 C8
C8 C9
C9 C10
C10 N11
C9 N12
N12 C13
C13 C14
C14 C15
C15 C16
C16 C17
C17 C18
C18 C19
C19 O20
C8 O21
C10 C22
C11 C23
1.38
1.38
1.38
1.39
1.38
1.39
1.34
1.35
1.38
1.39
1.38
1.32
1.49
1.36
1.43
1.39
1.39
1.39
1.27
1.30
1.50
1.50
0.9806
0.9821
0.9735
0.9579
0.9872
0.8484
0.9725
0.9850
0.9516
0.9857
0.8653
1.1007
0.7690
1.1181
0.8476
0.9947
0.9579
0.9679
0.8174
0.7508
0.6950
0.6667
120
120
120
120
120
120
131
119
106
104
117
140
124
120
119
120
120
120
120
120
120
120
0
180
0
0
0
177
328
182
0
The calculated types of electronic transitions in the Schiff
base Ib revealed the following points:
0
181
340
180
181
180
0
0
0
180
2
179
181
1. The lowest energy electronic transition between
the HOMO (−12.9827 eV) and the LUMO levels
(−9.4163 eV) equals to 3.5664 eV corresponding to CT
electronic transition with greater coefficients on C14, C15,
C17, C18 and O21 atoms. The calculated wavelength of
this transition is equal to 347.41 nm, which is in a good
agreement with the experimental value (346 nm).
*
2. The second type of electronic transition is a ␲–␲ tran-
sition with low energy (4.1002 eV) and high coefficients
on C19, O20 and O21atoms, which is a new evidence for

R.M. Issa et al. / Spectrochimica Acta Part A 62 (2005) 621–629
629
the occurrence of the keto–enol tautomerism. The calcu-
lated and experimental wavelengths are equal to 302.18
and 301 nm, respectively.
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3. The third electronic transition is a ␲–␲*(Ar) transition
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with an energy and wavelength equal to 5.2266 eV and
237.06 nm, respectively (exp. value = 234 nm).
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another ␲–␲*(Ar) transition which could be described by
an electron excitation from the level at 15.2645 eV, signif-
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