Computational DFT/CI spectroscopic structural studies of some complexes of benzalbarbituric acid

Article abstract of DOI:10.1016/j.molstruc.2010.12.030

Via Gaussian 98, calculations have been carried out as B3LYP/6-31G ^** basis sets and the predominant tautomers of benzalbarbituric acid (BenzalBA) have been defined taking in consideration the energy of the density functional theory. The electronic transition energies have been calculated for the possible tautomers by the configuration interaction between the ground configuration Eigenfunction and the excited configuration Eigenfunctions explaining the absence of the relative intensity change in the UV spectrum by the heat effect as a result of the coincidence of the transition energies of the possible tautomers. The electronic spectra (UV-visible) were scanned for BenzalBA in different solvents of different polarities to determine the Einstein transition probabilities, dipole strengths, oscillator strengths, lifetime of the excited states and extinction coefficients. The hydrogen bonding and the orientation energy of the polar solvent molecules toward BenzalBA molecule were determined from the spectral studies in mixtures of polar and non-polar solvents. Some complexes were prepared from BenzalBA with some divalent metal ions, i.e. Fe⁺⁺, Zn⁺⁺ or Cu⁺⁺. Their structures have been confirmed by elemental analysis, mass spectra, ¹H NMR spectra, atomic absorption spectra and UV-visible spectra. It has been concluded that the structures of the complexes have the C_2h point group symmetry in which two BenzalBA moieties are chelated to any one of the metal ions Fe⁺⁺, Zn⁺⁺ and Cu⁺⁺.

Full text of DOI:10.1016/j.molstruc.2010.12.030

Journal of Molecular Structure 987 (2011) 232–240
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Computational DFT/CI spectroscopic structural studies of some complexes
of benzalbarbituric acid
⇑
Anwar S. El-Shahawy
Chemistry Department, Faculty of Science, Assiut University, Assiut 71516, Egypt
a r t i c l e i n f o
a b s t r a c t
Via Gaussian 98, calculations have been carried out as B3LYP/6-31Gꢀꢀ basis sets and the predominant tau-
tomers of benzalbarbituric acid (BenzalBA) have been defined taking in consideration the energy of the
density functional theory. The electronic transition energies have been calculated for the possible tau-
tomers by the configuration interaction between the ground configuration Eigenfunction and the excited
configuration Eigenfunctions explaining the absence of the relative intensity change in the UV spectrum
by the heat effect as a result of the coincidence of the transition energies of the possible tautomers. The
electronic spectra (UV–visible) were scanned for BenzalBA in different solvents of different polarities to
determine the Einstein transition probabilities, dipole strengths, oscillator strengths, lifetime of the
excited states and extinction coefficients. The hydrogen bonding and the orientation energy of the polar
solvent molecules toward BenzalBA molecule were determined from the spectral studies in mixtures of
polar and non-polar solvents. Some complexes were prepared from BenzalBA with some divalent metal
Article history:
Received 29 September 2010
Received in revised form 9 December 2010
Accepted 10 December 2010
Available online 22 December 2010
Keywords:
Benzalbarbituric acid (BenzalBA) complexes
B3LYP/6-31Gꢀꢀ/CI
UV
1H NMR
Mass spectra
ions, i.e. Fe++, Zn++ or Cu++. Their structures have been confirmed by elemental analysis, mass spectra, 1
H
NMR spectra, atomic absorption spectra and UV–visible spectra. It has been concluded that the structures
of the complexes have the C2h point group symmetry in which two BenzalBA moieties are chelated to any
one of the metal ions Fe++, Zn++ and Cu++
.
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
Ab initio and density functional theory (DFT) methods were
used to study the tautomers of barbituric acid in the gas phase
and in a polar medium. In the gas phase, the tautomers were
optimized at HF/6-31G MP2/6-31Gꢀ and B3LYP/6-31Gꢀ, B3PW91/
6-31Gꢀ levels of the theory. The self-consistent reaction field
theory (SCRF) at HF/6-31Gꢀ level has been used to optimized the
tautomers in a polar medium [6].
Benzalbarbituric acid was prepared by condensation reaction
between barbituric acid and benzaldehyde; UV–visible spectra of
BenzalBA have been scanned in pure and mixed solvents to calcu-
late some parameters, and Gaussian 98 program had been used to
study the structure of BenzalBA via the DFT.
Some of BenzalBA complexes were prepared from using diva-
lent ions such as Fe++, Zn++ or Cu++ therefore the structures of these
complexes have been confirmed by some analyses such elemental
analysis, mass spectra, atomic absorption spectra and UV–visible
spectra.
The n-heterocyclic compounds containing amide linkages are
widely used in medicine, principally as hypnotic drugs and pro-
duce depressive effects on the central nervous system [1]. The bar-
biturates possess effects on the motor and sensory functions [2].
Barbituric acid displays keto–enol tautomerism, the most
important tautomer being the triketo-form and 4-hydroxy tauto-
mer obtained from the methylene hydrogen to the adjacent keto
oxygen [3].
The attention is directed to barbituric acid derivatives having
inhibitory activity for matrix maetalloproteases comprised of for-
mula (I): ##STR1## pharmaceutical compositions thereof, pro-
cesses for preparing the derivatives, and methods for treating
diseases associated with elevated or uncontrolled levels of matrix
metalloprotease activity, e.g., cancer, specifically tumor progres-
sion and tumor metastasis, inflammation, or as a method of contra-
ception. This invention has been reported in the literature [4].
A conformational study on barbituric acid and thiobarbituric
acid was studied at ab initio MP2/6-31G level on the molecular,
protonated, mono and di-anionic forms. More over the electronic
transitions were obtained through ZINDO approaches [5].
2. Experimental work
2.1. Materials
The solvents were purified according to literature [7,8]; Benzal-
BA was prepared according to literature [9] and its melting point
has been detected to be 258 °C. The materials that were used to
⇑
Tel.: +20 129590672.
E-mail address: anwarshahawy@yahoo.com
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.12.030

A.S. El-Shahawy / Journal of Molecular Structure 987 (2011) 232–240
233
prepare the complexes in addition to BenzalBA are copper acetate
monohydrate Cu (CH3COO)2ꢁH2O, ferrous sulphate heptahydrate
FeSO4ꢁ7H2O and zinc acetate dihydrate Zn (CH3COO)2ꢁ2H2O which
were obtained from Analar grade salts (BDH). All materials em-
ployed in the present preparations were chemically pure.
structures using the closed shell Hartree–Fock, Becke’s three
parameters density functional theory (DFT) [11] in combination
with the Lee, Yang and Parr correlation functional B3LYP [12] with
basis sets 6-31Gꢀꢀ. The differentiation between the different prob-
able structures of BenzalBA was based on the total energy differ-
ence which has been achieved by the total energy which has
been calculated via SCF using RHF for these types of molecules.
2.2. Preparation of BenzalBA
3.2. Spectroscopic parameters
Preparation of the BenzalBA was done by mixing of (1 mol) bar-
bituric acid (BA) and (1 mol) from benzaldehyde, in methanol then
the mixture was refluxed for about 3 h, cooling, then filtered off the
precipitate and recrystallized with appropriate solvent so the melt-
ing point of the prepared compound is 258 °C.
The Einstein transition probability coefficients of emission, Aif,
and absorption, Bif, between two initial (i) and final (f) electronic
states are given as follows:
64p
mꢂ3e2
Aif
Bif
¼
¼
Gf Dif
ð1Þ
ð2Þ
2.3. Preparation of complexes
3h
3e3
Preparation of complexes was done using pure solvents and the
materials which have been previously mentioned before. Prepara-
tion of complexes [10] between BenzalBA and Cu++, Fe++ or Zn++
had been done by refluxing them in ethanolic solution in ratio
2:1 ligand to metal ion (M++) for about 2 h then the complex was
precipitated and washed firstly by ethanol.
All Melting points of the studied complexes have been men-
tioned in Table 1 and were determined on a SMP 10 melting point
apparatus.
8
p
GjDif
3h2C
where e is the electron charge, h the Planck’s constant, c the light
velocity, 3 ꢃ 1010 cm sꢄ1
,
m
the frequency of radiation in cmꢄ1, Gf
~
the degeneracy of the final state, and Dif is the dipole strength.
Substituting the numerical values and assuming the singlet
degeneracy state, then:
ꢄ3
Aif ¼ 7:211 ꢃ 1010
m
D
ð3Þ
ð4Þ
if
2.4. Instrumentations
Bif ¼ 14:50 ꢃ 1024Dif
The quantity Bif can be related to the oscillator strength, fij,
which is the measure of the intensity.
The carbon, hydrogen and nitrogen contents were determined
using Elementer Analyses System (GmbH, Donaustr-7, D-63452)
Hanau, (Germany). Chemistry Department, Faculty of Science,
Assiut University.
The electronic absorption spectra had been scanned by UV-
2011 PC, UV–Vis Scanning Spectrophotometer (Shimadzu) using
1 cm matched silica cells, Chemistry Department, Faculty of
Science, Assiut University.
The mass spectra of studied compound were performed by JEOL
JMS 600 Spectrometer at ionizing potential of 70 eV using the
direct inlet system, at Central Lab. Assiut University, Assiut.
The Atomic Absorption Spectra of the complexes were studied
by using an Atomic Absorption (GBC Scientific Equipment Pityltd
Model GBC 906 AA), Soils Laboratory for Analyses and Technical
Consultation Department, Faculty of Agriculture, Assiut University.
1H NMR spectra were recorded in deutrated dimethylsulphox-
ide (DMSO) with a Varian Instrument Division 90 MHz EM 390
NMR Spectrometry. All chemical shifts (d) are given in ppm versus
tetra-methylsilinate (TMS), American Company, Chemistry Depart-
ment, Faculty of Science, Assiut University.
8p
2mC
3h
f mDif ¼ 1:096 ꢃ 1011
G
f mDif
ð5Þ
~
~
f ij
¼
G
Also the oscillator strength can be related to the absolute inten-
sity as follows:
!
Z
Z
mC2
Np
e2
ꢄ9
~
m
~
m
f ij ¼ 0:102
e
d
¼ 4:315 ꢃ 10
ed
ð6Þ
where m is the electron mass, N the Avogadro’s number, and
molar extinction coefficient.
e
is the
If a molecule is in an excited state then, in the absence of an
external electromagnetic field, on the average, after a time it will
is called the mean lifetime of the excited state.
s
emit a photon.
1
s
s
¼
ð7Þ
Aif
Generally Dif can be calculated numerically as follows:
ꢀh
Dif ¼ 4:23671 ꢃ 10ꢄ20
ꢃ
emax
:
ð8Þ
3. Method of calculations
m
where ꢀh is the half width of the absorption band in cmꢄ1. Hence, the
oscillator strength can be calculated directly as follows:
3.1. Computational studies
Computational calculations on the isolated molecules in the gas
phase were performed within GAUSSIAN 98 package. Minimum
energy structures have been achieved by AM1 semi-empirical
method. Calculations were performed on the minimum energy
fij ¼ 4:6 ꢃ 10ꢄ9emax ꢃ ꢀh
ð9Þ
4. Results and discussion
4.1. Structural studies of BenzalBA
Table 1
Melting points of the complexes.
From DFT calculations point of view as B3LYP/6-31Gꢀꢀ basis sets
using Gaussian 98 program to study the structure of BenzalBA, it
has been concluded that the tautomer I has the lowest energy
ꢄ759.0024 a.u. so it is considered the most predominant tautomer
but when the energy difference was applied with all tautomers
Compound
Melting point (°C)
(BenzalBA)2–Cu++
(BenzalBA)2–Fe++
(BenzalBA)2–Zn++
300
320
296

234
A.S. El-Shahawy / Journal of Molecular Structure 987 (2011) 232–240
Table 2
(Scheme 1) it has been found that the three tautomers (I–II) are
possible, Table 2. The energy difference between tautomers (I
and II) is 0.6380 eV and the energy difference between tautomers
(I and III) is 2.0468 eV. Also the energies difference between tau-
tomers I, IV and V are 1.0314 and 1.9642 eV respectively. Therefore
the high values of the energy difference between tautomer I with
tautomers III–V do not permit their presence in equilibrium with
tautomers I and II.
B3LYP/6-31Gꢀꢀ parameters of Possible minimum energy structures of BenzalBA
molecule.
Tautomer
E (a.u.)
Dipole moment (Debye)
I
II
III
IV
V
ꢄ759.0024
ꢄ758.9789
ꢄ758.2713
ꢄ758.9645
ꢄ758.9302
3.0954
7.1427
10.5433
8.4678
6.6454
The DFT(B3LYP/6-31Gꢀꢀ) energies and the dipole moments of
the possible tautomers of BenzalBA have been tabulated in Table
2 after minimization by AM1 valence electron system. It can be no-
ticed that the tautomer of the lowest energy has the minimum va-
lue of the dipole moment, 3.0954D. The second possible tautomer
has the higher value, 7.1427D, therefore the dipole moment value
of BenzalBA should be between them. The tautomer IV has a very
poor existence with respect to the first tautomer as it appears in
Table 3 and can be neglected. Hence its contribution to the dipole
moment of BenzalBA is very poor.
n/no is the ratio between the numbers of molecules of the high-
er energy tautomer, with respect to the number of the molecules of
the lowest energy tautomer, no. This ratio has been calculated tak-
ing in consideration the DFT (B3LYP/6-31Gꢀꢀ) energy differences
between the first tautomer of the lowest energy and the other tau-
tomers of the higher energies, Table 3. The number of molecules N,
of the tautomer of the higher energy per mole was calculated at
27 °C. All the other tautomers, III–V are absent due to the big en-
ergy differences in contrary to tautomer II which has more closer
energy to that of tautomer I therefore BenzalBA has two possible
tautomers of them in equilibrium with each other at 27 °C.
The configuration interaction between the ground configuration
Eigenfunction UO with the excited singlet configuration Eigenfunc-
tions U1
(
w
40?41), U2
39?45), U7
38?44), U12
(
w
(
39?41), U3
(
(
w
w
39?42), U4
39?49), U9
38?45), U13 38?47), U14
37?45), U18 36?41), U19
36?44), U22 36?45), U23 36?47),
35?42), U26 35?44), U27 35?45), U28
34?41), U30 34?42), U31 33?41), U32
33?44) has been calculated by ZINDO program taking
(
(w
w
39?43), U5
38?41), U10
37?41),
(
(
w
w
39?44), U6
38?42), U11
(
w
w
39?48),U8
(w
(w
(
w
(w
U15
36?42), U20
U24 35?41), U25
35?47), U29
and U33
(w
37?42), U16
(w
37?44), U17
(w
(w
(w
(
w
36?43), U21
(
w
(w
(w
(w
(w
(w
(w
(w
(w
(w
(
w
(w33?42)
(
w
in consideration the eight HOMO’s and eight LUMO’s of the valence
electron system molecular orbitals of the possible tautomers of
BenzalBA. The following Tables 4, 6, 8, 10 and 12 show the singlet
state Eigenfunctions of the five possible tautomers and the Tables
5, 7, 9, 11 and 13 show the singlet transition energies between the
Table 3
B3LYP/6-31Gꢀꢀ energy difference of BenzalBA tautomers.
Structures
D
E (eV)
n/no at 27 °C
N at 27 °C
I and II
I and III
I and IV
I and V
0.6380
2.0468
1.0314
1.9642
1.89764 ꢃ 10ꢄ11
4.0077 ꢃ 10ꢄ35
4.6452 ꢃ 10ꢄ18
9.7952 ꢃ 10ꢄ34
1.1424 ꢃ 1013
0.0000
2796415
0.0000
Table 4
Singlet state Eigenfunctions of tautomer I.
Wg = UO
Wex1 = ꢄ0.22904U18 ꢄ 0.23576U19 + 0.28432U21 + 0.14195U23 + 0.41450U9
ꢄ 0.29982U11 + 0.13241U12
Wex2 = ꢄ0.33518U18 + 0.22378U21 ꢄ 0.18271U22 ꢄ 0.24662U9 + 0.34583U10
ꢄ 0.25370U12 ꢄ 0.18765U13
Wex3 = 0.68803U1
Scheme 1. Minimized energy tautomers of BenzalBA.

A.S. El-Shahawy / Journal of Molecular Structure 987 (2011) 232–240
235
Table 5
Table 12
Singlet excitation energies of tautomer I.
Singlet state Eigenfunctions of tautomer V.
Transition
D
E (eV)
D
E (nm)
D
E (nm exp)
f
Wg = UO
Wex1 = ꢄ0.17126U14 + 0.11962U16 + 0.51843U2 ꢄ 0.30024U5 + 0.10569U6
ꢄ 0.14667U7 ꢄ 0.10107U1
Wg
Wg
Wg
?
?
?
Wex1
Wex2
Wex3
3.3209
3.5865
3.6731
373.34
345.70
337.55
0.0002
0.0006
1.0165
Wex2 = ꢄ0.10474U18 + 0.17378U2 + 0.63914U1
Wex3 = 0.10800U33 ꢄ 0.19826U24 + 0.45330U18 ꢄ 0.18517U19 ꢄ 0.10339U22
ꢄ 0.15270U2 + 0.12067U3 ꢄ 0.16030U5 + 0.15800U6 ꢄ 0.12094U7
+ 0.20398U1
329
Table 6
Singlet state Eigenfunctions of tautomer II.
Table 13
Singlet excitation energies of tautomer V.
Wg = UO
Wex1 = ꢄ0.22904U18 ꢄ 0.23576U19 + 0.28432U21 + 0.14195U23 + 0.41450U9
ꢄ 0.29982U11 + 0.13241U12
Transition E (eV) E (nm)
D
D
D
E (nm exp)
f
Wex2 = ꢄ0.33518U18 + 0.22378U21 ꢄ 0.18271U22 ꢄ 0.24662U9 + 0.34583U10
ꢄ 0.25370U12 ꢄ 0.18765U13
Wg
Wg
Wg
?
?
?
Wex1
Wex2
Wex3
2.9789
3.7091
3.9595
416.21
334.27
313.13
0.0004
0.4807
0.0474
Wex3 = 0.68803U1
Table 7
Singlet excitation energies of tautomer II.
in the relative intensities in the absorption band at k = 325 nm
indicating to the existence of tautomers I and II since the allowed
excitation energies Wg
Transition
D
E (eV)
D
E (nm)
D
E (nm exp)
f
? Wex3 (p ?
pꢀ) for them lie at the same
Wg
Wg
Wg
?
?
?
Wex1
Wex2
Wex3
3.3209
3.5865
3.6731
373.34
345.70
337.55
0.0002
0.0006
1.0165
value 3.6731 eV (337.55 nm), (Fig. 1) which is not far from the
experimental value, 329 nm in chloroform as much lower solvent.
Therefore there is not splitting at this band position 325 nm in eth-
anol, by the heat effect due to the presence of the two possible tau-
tomers I and II since they have the same value of the excitation
energies, 3.6731 Tables 5 and 7.
329
Table 8
Singlet state Eigenfunctions of tautomer III.
Wg = UO
Wex1 = 0.54599U2 ꢄ 0.23676U4 + 0.26954U6 + 0.11807U7 + 0.15687U8
4.2. UV-spectral studies in pure solvents
Wex2 = 0.10973U31 + 0.17418U18 + 0.11750U21 ꢄ 0.11135U14 + 0.11304U5
+ 0.59984U1
The UV-spectra of BenzalBA have been scanned in different sol-
vents of different polarities such as ethanol, methanol, isopropanol,
chloroform, dimethylformamide (DMF), and n-hexane, Fig. 2; it has
Wex3 = 0.17929U33 ꢄ 0.24383U24 + 0.43836U18 ꢄ 0.15255U20 + 0.11111U22
+ 0.14727U2 ꢄ 0.11974U6 ꢄ 0.12765U7 ꢄ 0.18498U8 ꢄ 0.23917U1
been noticed that the lifetime
s of the excitation has its maximum
value in case of n-hexane solvent, 34.20 ns and the electronic tran-
sition energies in electronic spectra of BenzalBA have been blue
shifted with increasing the solvent polarity from 329.1 nm in CHCl3
as a solvent to 322.0 nm in n-hexane as a solvent, Table 14. The
Einstein transition probabilities Aif (spontaneous transition proba-
bility) and Bif (induced transition probability) have their maximum
values in the case of CHCl3 as a solvent 2.2951 ꢃ 108 sꢄ1 and
Table 9
Singlet excitation energies of tautomer III.
Transition E (eV) E (nm)
D
D
D
E (nm exp)
f
Wg
Wg
Wg
?
?
?
Wex1
Wex2
Wex3
3.0939
3.7764
3.9516
400.74
328.31
313.76
0.0002
0.6414
0.1305
Table 10
Singlet state Eigenfunction of tautomer IV.
Wg = UO
Wex1 = 0.18159U24 + 0.14831U25 ꢄ 0.26353U26 ꢄ 0.11710U28 ꢄ 0.14147U21
+ 0.41280U9 ꢄ 0.24890U11 + 0.21239U12
Wex2 = 0.26288U24 ꢄ 0.15601U26 + 0.13655U27 + 0.17783U18 + 0.10660U22
+ 0.20381U14 ꢄ 0.10010U15 + 0.13611U17 ꢄ 0.18477U9 + 0.29085U10
ꢄ 0.13146U11 ꢄ 0.21831U12 ꢄ 0.20888U13
Wex3 = ꢄ0.16084U29 + 0.11034U30 + 0.64329U1
Table 11
Singlet excitation energies of tautomer IV.
Transition E (eV) E (nm)
D
D
D
E (nm exp)
f
Wg
Wg
Wg
?
Wex1
3.3834
3.5792
3.8413
366.45
346.40
322.76
0.0026
0.0089
0.5837
?
?
Wex2
Wex3
ground singlet state Eigenfunction, Wg and the other singlet ex-
cited states Eigenfunctions, Wex
.
From the heat effect on the UV spectrum [13] of BenzalBA in
ethanol as a solvent it has been noticed that there is not change
Fig. 1. The heat effect on the electronic spectra of BenzalBA molecule in EtOH
(conc. = 8 ꢃ 10ꢄ5 mol Lꢄ1). (1) at 10 °C; (2) at 20 °C; (3) at 30 °C; and (4) at 40 °C.

236
A.S. El-Shahawy / Journal of Molecular Structure 987 (2011) 232–240
363
Fig. 2. Electronic absorption spectra of BenzalBA in organic solvents (con-
c. = 8 ꢃ 10ꢄ5 mol Lꢄ1). (1) CHCl3; (2) Isopropanol; (3) EtOH; (4) DMF; (5) MeOH;
(6) n-hexane.
364
365
366
367
368
369
16.382 ꢃ 108 s gꢄ1, respectively as well as the dipole strength Dif
having its maximum value in the same solvent, 11.298 ꢃ 10ꢄ17, Ta-
ble 14.
4.3. UV-spectral studies in mixed solvents
K.J.mol-1
The data of mixed solvents studies [14] have been tabulated in
Table 15. The maximum wavelength kmax of BenzalBA in the UV-
spectra has been blue shifted with increasing the mole fraction
of the more polar solvent in the mixed solvents with respect to
the other of lower polarity (e.g. from 329 nm in case of 100% CHCl3
to 325.0 nm in case of 100% MeOH), Fig. 3. On plotting the excita-
0.0
0.2
0.4
0.6
0.8
1.0
Mole fraction of MeOH in (MeOH-CHCl3mixture)
tion energy
D
E in kJ molꢄ1, against the mole fraction of the MeOH
with respect to CHCl3 solvent, a broken line with three segments is
obtained, Fig. 3; the first segment indicates to the orientation en-
Fig. 3. Hydrogen bonding and orientation energies of BenzalBA in (MeOH–CHCl3)
mixtures.
Table 14
The Einstein transition probabilities (Aif and Bif), dipole strength (Dif), oscillator strength (fif), lifetime (s) and extinction coefficient (e) of the electronic transition bands of
BenzalBA in different solvents.
Solvent
kmax (nm)
e
ꢃ 10ꢄ4 (L Mꢄ1 cmꢄ1
)
Aif ꢃ 10ꢄ8 (sꢄ1
)
Bif ꢃ 10ꢄ8 (s gꢄ1
)
Dif ꢃ 1017
fif
s
(ns)
EtOH
MeOH
Isopropanol
CHCl3
D.M.F
325
325
327
329
324
322
1.0799
0.885
1.3356
1.3963
0.9652
0.1625
1.8001
1.6041
2.1339
2.2951
1.7381
0.2923
12.928
11.016
14.868
16.382
11.847
1.9551
8.9156
7.5974
10.254
11.298
8.1706
1.3483
0.298
0.254
0.341
0.373
0.274
0.045
5.319
6.234
4.686
4.357
5.753
n-Hexane
34.20
Table 15
Electronic spectral data of BenzalBA in (MeOH–CHCl3) mixtures at kmax = 329 nm.
MeOH (%)
kmax (nm)
Molarity
MeOH
Mole fraction
MeOH
D
E (kJ molꢄ1
)
CHCl3
CHCl3
100
79.6
69.6
49.6
29.6
9.6
325
326
327
328
329
329
329
23.4535
18.5159
16.0471
11.1096
6.17197
1.23439
0.00000
0.00000
2.49958
3.74937
6.24895
8.74853
11.2481
11.8730
1.00000
0.88106
0.81060
0.64001
0.41365
0.09888
0.00000
0.0000
0.1189
0.1894
0.3600
0.5863
0.9011
1.0000
368.31
367.52
366.17
364.60
363.72
363.72
363.72
0.0

A.S. El-Shahawy / Journal of Molecular Structure 987 (2011) 232–240
237
Table 16
Data of BenzalBA in mixed organic solvents.
System
Orientation energy (K J molꢄ1
)
H-bonding energy (K J molꢄ1
2
)
n
Kf
ꢄ
D
Ga (K J molꢄ1
5.88976
)
MeOH–CHCl3
1
2
10.7152
Kf is formation constant.
a
D
G is free energy.
Table 17
The nitrogen elemental analyses of the complexes.
excited states. The second segment corresponds to the hydrogen
bonding between MeOH molecules with BenzalBA molecule. The
hydrogen bonding energy in this case is equal to 2 kJ molꢄ1, Table
16. The third segment represents the steady state of energy at-
tained after complex formation of the MeOH–BenzalBA complex
Complex
% Theoretical
% Experimental
(BenzalBA)2–Cu++
(BenzalBA)2–Fe++
(BenzalBA)2–Zn++
11.34
11.52
11.3
11.296
11.57
11.6
which is equal to 3 kJ molꢄ1. The free energy change
DG
# of forma-
tion of MeOH–BenzalBA complex in case of MeOH/CHCl3 mixed
solvents equals to 5.8898 kJ molꢄ1, Table 16. A support of bond for-
mation between BenzalBA and solvent molecules may be obtained
by determining the stability formation constant of the complex, Kf.
The utilized method for determination of stability constant Kf of
solvent–BenzalBA complex depends on the fact that absorbance
variation when adding different proportions of the proton donor
and it is the measure of formation tendency of the solute–solvent
complex. The stability constant Kf of the solute–solvent complex
has its value in case MeOH/CHCl3 mixed solvents with BenzalBA
molecule, 10.7152 kJ molꢄ1, Table 16, as well as the free energy
Table 18
The atomic absorption spectral data of the complexes.
Complex
% Theoretical
% Experimental
(BenzalBA)2–Cu++
(BenzalBA)2–Fe++
(BenzalBA)2–Zn++
12.9
11.5
13.2
12.94
11.57
13.5
ergy which is equal to 1 kJ molꢄ1 with respect to the orientation of
MeOH molecules towards BenzalBA molecule in the ground and
change
D
G# of the formation of MeOH/BenzalBA complex having
the maximum value 5.889 kJ molꢄ1. Generally the number of
Fig. 4. 1H NMR spectrum of BenzalBA.
Fig. 5. 1H NMR spectrum of [(BenzalBA)2–Zn] complex.

238
A.S. El-Shahawy / Journal of Molecular Structure 987 (2011) 232–240
Fig. 6. Mass spectrum of BenzalBA ligand.
Fig. 7. Mass spectrum of [(BenzalBA)2–Fe] complex.
Fig. 8. Mass spectrum of [(BenzalBA)2–Cu] complex.
MeOH molecules oriented towards BenzalBA molecule being equal
to 2, Table 16.
the theoretical percentages of nitrogen element have good coinci-
dence with the experimental percentages of nitrogen element in
the studied complexes confirming the ratio 2:1 (BenzalBA) to
M(II) in the complex.
4.4. Structural spectral studies of complexes
Dealing with the atomic absorption spectra, Table 18, it has
been found that the theoretical percentage of the metal ions
e.g., Cu++ is nearly coincident with the experimental percentage
12.9 and 12.94, respectively. Generally, the theoretical percentage
of metal ion M++ in the atomic absorption spectra has a good
The complexes of BenzalBA with one of the cations Cu++, Fe++
and Zn++ have been prepared as has been mentioned previously
in the experimental work and their melting points have been men-
tioned in Table 1. From the nitrogen elemental analyses, Table 17,

A.S. El-Shahawy / Journal of Molecular Structure 987 (2011) 232–240
239
Fig. 9. Mass spectrum of [(BenzalBA)2–Zn] complex.
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1
1
2
2
3
3
4
4
300
400
500
600
700
300
350
400
450
500
550
600
650
700
Wavelength (nm)
Wavelength (nm)
Fig. 10. Electronic absorption spectra of EtOH solutions of 8 ꢃ 10ꢄ5 mol Lꢄ1 (1–4)
as (1) BenzalBA, (2) (BenzalBA)2–Cu, (3) (BenzalBA)2–Fe, and (4) (BenzalBA)2–Zn
complexes.
Fig. 11. Electronic absorption spectra of DMF (dimethylformamide) solutions of
8 ꢃ 10ꢄ5 mol Lꢄ1 (1–4) as (1) BenzalBA, (2) (BenzalBA)2–Zn, (3) (BenzalBA)2–Fe and
(4) (BenzalBA)2–Cu complexes.
have been replaced by N–M++–N bonds in the complex in the
two moieties of BenzalBA of the complex.
coincidence with the experimental metal ion percentage in accor-
dance with the ratio 2:1 (BenzalBA) to M++ in the complex. Gener-
ally from the elemental analyses of nitrogen element of the
complexes, Table 17, and from the data of the atomic absorption
spectra, Table 18, it can be conclude that the complex molecule
has been formed by the chelation of two molecules of BenzalBA
Therefore, the complexation between two molecules of Benzal-
BA with a metal ion M++ has been formed by the chelation of the
metal ion with the more negative carbonyl oxygen atoms and
one the amide nitrogen atoms consuming one of the amide hydro-
gen atoms to form the complex (BenzalBA)2–M(II) including the
nitrogen–metal bond.
The suggested complexes have been confirmed by EI–MS spec-
tra (Figs. 6–9). These MS spectra show the m/z which is corre-
sponding to the molecular weight of the complexes confirming
the ratio between the ligand and the cation is 2:1 respectively.
Therefore, the complexation between two molecules of BenzalBA
with a metal M has been formed by the chelation of the metal
ion with the more negative carbonyl oxygen atoms and one of
with a metal ion M++
.
The 1H NMR spectrum of BenzalBA (Fig. 4) has two signals at
11.71, 11.86 ppm, which are due to the protons of the two asym-
metric amide groups in the barbituric acid moiety. The disappear-
ance of one of the two signals of the amide hydrogen atoms in the
1H NMR spectrum of (BenzalBA)2–Zn(II) complex as an example,
Fig. 5, confirms the consumption of one of the amide hydrogen
atoms in the complexation between BenzalBA and metal ion
(M++), and the N–H bonds in the complex of BenzalBA molecule
Table 19
The Einstein transition probabilities (Aif and Bif), dipole strength (Dif), oscillator strength (fif) and lifetime (s) and extinction coefficient (e) of the electronic transition bands of
[(BenzalBA)2–M] complexes in EtOH solvent.
Compound
kmax (nm)
e
ꢃ 10ꢄ4 (L Mꢄ1 cmꢄ1
)
Aif ꢃ 10ꢄ8 (sꢄ1
14.289
0.020
0.025
)
Bif ꢃ 10ꢄ9 (s gꢄ1
9.116
0.042
0.019
)
Dif ꢃ 1016
6.287
0.029
0.131
fif
s
(ns)
1
[(BBA)2Fe]
[(BBA)2Cu]
[(BBA)2Zn]
317
467
336
0.613
0.044
0.089
2.153
0.007
0.043
489
40

240
A.S. El-Shahawy / Journal of Molecular Structure 987 (2011) 232–240
Table 20
The Einstein transition probabilities (Aif and Bif), dipole strength (Dif), oscillator strength (fif), life time (s) and extinction coefficient (e) of the electronic transition bands of
[(BenzalBA)2–M] complexes in DMF solvent.
Compound
kmax (nm)
e
ꢃ 10ꢄ4 (L Mꢄ1 cmꢄ1
)
Aif ꢃ 10ꢄ8 (sꢄ1
)
Bif ꢃ 10ꢄ9 (s gꢄ1
)
Dif ꢃ 1016
fif
s (ns)
[(BBA)2–Fe]
[(BBA)2–Cu]
410
324
471
318
0.0660
0.1117
0.0429
0.4750
0.0524
0.5651
0.0266
2.0222
0.0723
0.3849
0.0555
1.2963
0.0499
0.2654
0.0383
0.8939
0.0132
0.0889
0.0088
0.3056
191
18
376
5
[(BBA)2–Zn]
the amide nitrogen atom consuming one of the amide hydrogen
atom to form the complex (BenzalBA)2–M(II) including the nitro-
gen–metal bond and the complex structure which has been sug-
gested to be C2h point group symmetry, but the BenzalBA
molecule itself has the suggested Cs point group symmetry in
which the two amide group are not symmetric.
and Zn++ were prepared. The structures of these complexes may
have C2h point group symmetry which has been confirmed by spec-
tral studies.
Acknowledgement
The UV-spectra of BenzalBA complexes have been scanned in
ethanol as a solvent Fig. 10, and it has been noticed that the lifetime
I am grateful to Prof. Dr. Moustafa M. Kamal president of Assiut
University for his financial support and his encouragement for the
scientific research.
s
of the excitation has its maximum value in case of [(BenzalBA)2–
Cu] complex, 489 ns at kmax = 467 nm Table 19. The Einstein transi-
tion probabilities Aif (spontaneous transition probability) and Bif (in-
duced transition probability) have their maximum values in the case
References
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,
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in the same solvent, 6.2869 ꢃ 10ꢄ16, Table 19.
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DMF (dimethylformamide) solvent Fig. 11, and it has been noticed
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s of the excitation has its maximum value in case
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in the case of (BBA)2 Zn 2.0222 ꢃ 108 sꢄ1 and 1.2963 ꢃ 109 s gꢄ1
,
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The structure of BenzalBA molecule has been confirmed by
B3LYP/6-31Gꢀꢀ calculations and finally it has two conformers
whose calculated transition energies are the same. Some com-
plexes of BenzalBA with some divalent metal ions, i.e. Cu++, Fe++