Synthesis and spectroscopic studies of binuclear metal complexes of a tetradentate N2O2 Schiff base ligand derived from 4,6-diacetylresorcinol and benzylamine

Article abstract of DOI:10.1016/j.saa.2007.09.035

A tetradentate N₂O₂ donor Schiff base ligand, H₂L, was synthesized by the condensation of 4,6-diacetylresorcinol with benzylamine. The structure of the ligand was elucidated by elemental analyses, IR, ¹H NMR, electronic and mass spectra. Reaction of the Schiff base ligand with nickel(II), cobalt(II), iron(III), cerium(III), vanadyl(IV) and uranyl(VI) ions in 1:2 molar ratio afforded binuclear metal complexes. Also, reaction of the ligand with several copper(II) salts, including Cl^-, NO₃^-, AcO^-, ClO₄^- and SO₄^2- afforded different metal complexes that reflect the non-coordinating or weakly coordinating power of the ClO₄^- anion as compared to the strongly coordinating power of SO₄^2- and Cl^- anions. Characterization and structure elucidation of the prepared complexes were achieved by elemental and thermal analyses, IR, ¹H NMR, electronic, mass and ESR spectra as well as magnetic susceptibility measurements. The metal complexes exhibited different geometrical arrangements such as square planar, octahedral, square pyramidal and pentagonal bipyramidal arrangements. The variety in the geometrical arrangements depends on the nature of both the anion and the metal ion.

Full text of DOI:10.1016/j.saa.2007.09.035

Available online at www.sciencedirect.com
Spectrochimica Acta Part A 70 (2008) 850–859
Synthesis and spectroscopic studies of binuclear metal complexes of a
tetradentate N2O2 Schiff base ligand derived from
4,6-diacetylresorcinol and benzylamine
Magdy Shebl
Department of Chemistry, Faculty of Education, Ain Shams University, Roxy, Cairo, Egypt
Received 25 July 2007; received in revised form 19 September 2007; accepted 20 September 2007
Abstract
A tetradentate N2O2 donor Schiff base ligand, H2L, was synthesized by the condensation of 4,6-diacetylresorcinol with benzylamine. The
structure of the ligand was elucidated by elemental analyses, IR, 1H NMR, electronic and mass spectra. Reaction of the Schiff base ligand with
nickel(II), cobalt(II), iron(III), cerium(III), vanadyl(IV) and uranyl(VI) ions in 1−:2 molar ratio afforded binuclear metal complexes. Also, reaction
2−
of the ligand with several copper(II) salts, including Cl−, N−O3−, AcO−, ClO4 and SO4 afforded different metal complexes that reflect the
non-coordinating or weakly coordinating power of the ClO4 anion as compared to the strongly coordinating power of SO4 and Cl− anions.
2−
Characterization and structure elucidation of the prepared complexes were achieved by elemental and thermal analyses, IR, 1H NMR, electronic,
mass and ESR spectra as well as magnetic susceptibility measurements. The metal complexes exhibited different geometrical arrangements such
as square planar, octahedral, square pyramidal and pentagonal bipyramidal arrangements. The variety in the geometrical arrangements depends on
the nature of both the anion and the metal ion.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Schiff base ligand; Binuclear complexes; 4,6-Diacetylresorcinol; Benzylamine
1. Introduction
4,6-Diacetylresorcinol serves as a starting material for the
generation of multidentate symmetrical Schiff bases [13–15].
Thepresentstudy, isextensiontoourwork[16–18]wherethelig-
and was prepared by the condensation of 4,6-diacetylresorcinol,
as starting material, with benzylamine to give the new Schiff
base, H2L, ligand, Fig. 1. The Schiff base ligand was
allowed to react with copper(II), nickel(II), cobalt(II), iron(III),
vanadyl(IV), uranyl(VI) and cerium(III) ions, in the molar ratio
(1:2; ligand:metal ion). The structures of the ligand and its metal
complexes were characterized by elemental and thermal analy-
ses, IR, 1H NMR, electronic, ESR and mass spectra as well as
magnetic susceptibility measurements at room temperature.
Schiff bases offer a versatile and flexible series of ligands
capable to bind with transition, non-transition, lanthanide and
actinide metal ions to give complexes with suitable properties
for theoretical studies and/or practical applications [1–3]. A
large number of Schiff bases and their metal complexes have
been studied because of their interesting and important prop-
erties such as their ability to reversibly bind oxygen [4] and
their use in catalyses for: oxygenation and oxidation reactions of
organic compounds [5], redox systems in biological processes
[6], Aldol reactions [7], degradation of dyes through decom-
position of hydrogen peroxide and other reagents, in textile
industries [8], reduction of thionyl chloride [9] and oxidation
of DNA [10]. Also, Schiff bases can be used in degradation of
organic compounds [11] and in radiopharmaceuticals [12].
2. Experimental
2.1. Materials
Metalsalts, resorcinol, aceticanhydride, benzylamine, EDTA
and nitric acid were either Aldrich, BDH or Merck products.
Organic solvents were reagent grade chemicals.
E-mail address: magdy shebl@hotmail.com.
1386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.09.035

M. Shebl / Spectrochimica Acta Part A 70 (2008) 850–859
851
Fig. 1. The optimized structure of the Schiff base ligand, H2L.
(χMT)1/2 B.M., where χM is the molar susceptibility corrected
using Pascal’s constants for the diamagnetism of all atoms in
the compounds [19]. Microanalyses of carbon, hydrogen, nitro-
gen, sulfur and chlorine were carried out at the Microanalytical
Center, Cairo University, Giza, Egypt. Analyses of the metals
followed the dissolution of the solid complex in concentrated
HNO3, neutralizing the diluted aqueous solutions with ammo-
nia and titrating the metal solutions with EDTA. ESR spectra
of the complexes were recorded at a Elexsys, E500, Bruker
company, National Research Centre, Dokki, Cairo, Egypt. TGA-
measurements were carried out on a Shimadzu-50 thermal
analyzer. Melting points of the complexes were determined
using a Stuart melting point instrument.
2.2. Measurements
FT-IR spectra were recorded on a Perkin-Elmer 1650 spec-
trometer (4000–400 cm−1) in KBr pellets. Electronic spectra
were recorded at room temperature on a Jasco model V-550
UV–Vis spectrophotometer as nujol mulls and/or solutions in
DMF. The 1H NMR spectra of the ligand and the UO2(VI) com-
plex, as a solution in DMSO-d6, were recorded on a Bruker WP
200SYspectrometer atroomtemperatureusing TMS asaninter-
nal standard. Mass spectra were recorded at 290 ◦C and 70 eV
on a Hewlett-Packard mass spectrometer model MS-5988. The
pH values were measured by a WTW-D-8120 digital pH-meter
fitted with a combined glass electrode. Magnetic susceptibil-
ities of the complexes were measured by the Gouy method
at room temperature using a Johnson Matthey, Alfa Products,
Model MKI magnetic susceptibility balance. The effective mag-
netic moments were calculated from the expression μeff. = 2.828
2.3. Synthesis of the Schiff base ligand, H2L
The Schiff base ligand was prepared in two steps. The first
step was the formation of 4,6-diacetylresorcinol (DAR) by
acetylation of resorcinol. The method of preparation of DAR
was as cited in the literature [13]. The second step was the con-
densation of 4,6-diacetylresorcinol (DAR) stoichiometrically in
a molar ratio 1:2 with benzylamine to give the Schiff base ligand
as follows:
Fig. 2. Mass spectrum of the ligand.
Scheme 1. Synthesis of the Schiff base, H2L, ligand.

Table 1
Analytical and physical data for H2L ligand and its metal complexes
No.
Reactions
Complexes
M.F. [F. Wt]
Color
pH of the
mixture
Yield
(%)
mp
(◦C)
Elemental analysis,
(%) found/(calc.)
C
H
N
S/Cl
M
H2L
C
24H24N2O2 [372.47]
Yellow
Green
–
2.1
85
60
181
>300
77.00 (77.39)
39.38 (39.51)
6.31 (6.49)
4.74 (4.70)
7.70 (7.52)
–
–
–
(1)
(2)
(3)
(4)
H2L + Cu(NO3)2·2.5H2O [(L)Cu2(NO3)2(H2O)6]
7.90 (7.68)
6.10 (6.32)
5.50 (5.25)
3.70 (3.54)
17.20 (17.42)
C24 34N4O14Cu2 [729.65]
H
H2L + Cu(OAc)2·H2O
H2L + CuCl2·2H2O
[(L)2Cu2]·H2O
Brown
3.5
4.8
2.1
50
80
50
273
161
65.08 (65.07)
53.89 (53.99)
38.20 (37.94)
5.53 (5.23)
4.94 (5.10)
3.91 (4.20)
–
14.10 (14.34)
C48H46N4O5Cu2 [886.02]
[(H2L)2Cu2Cl4]·3H2O
Pale brown
13.45 (13.28) 11.70 (11.90)
C48H54N4O7Cl4Cu2 [1067.89]
H2L + Cu(ClO4)2·6H2O
[(L)Cu2(H2O)4](ClO4)2·0.5EtOH Green
>300
8.71 (8.96)
15.80 (16.06)
(C25H33N2O14.5Cl2Cu2)
[791.54]
(5)
(6)
(7)
H2L + CuSO4·5H2O
H2L + Ni(NO3)2·6H2O
H2L + Co(NO3)2·6H2O
[(H2L)Cu2(H2O)4(SO4)2]·2H2O Green
4.9
3.0
2.4
85
48
52
282
>300
>300
35.82 (36.04)
42.17 (42.15)
40.38 (40.39)
4.12 (4.54)
4.83 (4.42)
4.93 (5.02)
3.84 (3.50)
7.85 (8.19)
7.75 (7.54)
8.44 (8.02)
15.65 (15.89)
16.90 (17.17)
15.70 (15.85)
(C24H36N2O16S2Cu2) [799.78]
[(L)Ni2(NO3)2(H2O)4]
(C24H30N4O12Ni2) [683.95]
[(L)Co2(NO3)2(H2O)6]·0.5
EtOH (C25H37N4O14.5Co2)
[743.46]
Pale green
Yellowish brown
–
–
(8)
H2L + Fe(NO3)3·9H2O
[(H2L)Fe2(NO3)6(H2O)2]·6H2O Brownish red
4.5
60
80
47
55
>300
>300
>300
268
28.50 (28.82)
32.96 (32.98)
36.64 (36.56)
49.90 (49.66)
4.00 (4.03)
3.36 (3.32)
4.35 (4.35)
4.02 (4.33)
11.45 (11.20)
3.00 (2.56)
3.20 (3.55)
6.61 (6.95)
–
10.85 (11.17)
a (43.57)
C
24H40N8O28Fe2 [1000.32]
(9)
H2L + UO2(OAc)2·2H2O [(L)(UO2)2(OAc)2(MeOH)2]
Yellowish orange 2.4
–
(C30 36N2O12U2) [1092.69]
H
(10) H2L + VOSO4·H2O
(11) H2L + Ce(NO3)3·6H2O
[(H2L)(VO)2(SO4)2]·5H2O
(C24H34N2O17S2V2) [788.55]
[(L)2Ce2(NO3)2(MeOH)2]
(C50H52N6O12Ce2) [1209.24]
Green
5.5
2.0
8.30 (8.13)
–
a (12.92)
Yellow
a (23.17)
a: not determined.

M. Shebl / Spectrochimica Acta Part A 70 (2008) 850–859
853
Table 2
Characteristic IR spectral data of the ligand H2L and its metal complexes
No.
Complexes
IR Spectra (cm−1
)
ν(OH)H2O/EtOH,
ν(C N)
ν(C–O)
Other bands
MeOH/phenolic
H2L
3445
3420
3424
3447
3425
3484
3390
3447
3405
3422
1610
1594
1589
1600
1587
1586
1600
1586
1586
1591
1247
1250
1260
1268
1261
1250
1257
1250
1267
1259
1
2
3
4
5
6
7
8
9
[(L)Cu2(NO3)2(H2O)6]
[(L)2Cu2]·H2O
1341, 1263; ν(NO3−) (monodentate)
[(H2L)2Cu2Cl4]·3H2O
[(L)Cu2(H2O)4](ClO4)2·0.5EtOH
[(H2L)Cu2(H2O)4(SO4)2]·2H2O
[(L)Ni2(NO3)2(H2O)4]
[(L)Co2(NO3)2(H2O)6]·0.5EtOH
[(H2L)Fe2(NO3)6(H2O)2]·6H2O
[(L)(UO2)2(OAc)2(MeOH)2]
1057, 629; ν(ClO4−) (ionic)
1263, 1107; ν3(SO42−) (bidentate)
1441, 1381, 1326, 820; ν(NO3−) (bidentate)
1367, 1262; ν(NO3−) (monodentate)
1381, 1259; ν(NO3−) (monodentate)
1528; νas(COO−),1455; νs(COO−) (bidentate)
917; ν3(UO2)
10
11
[(H2L)(VO)2(SO4)2]·5H2O
3419
3425
1582
1583
1250
1250
1262, 1090; ν3(SO42−) (bidentate) 967;
ν(V O)
1453, 1351, 1302, 817; ν(NO3−) (bidentate)
[(L)2Ce2(NO3)2(MeOH)2]
Amixtureof4,6-diacetylresorcinol(2 g, 10.3 mmol)andben-
and finally air-dried. All of the complexes prepared are stable at
room temperature, non-hygroscopic and insoluble in water and
common organic solvents. The following detailed preparation
is given as an example and the other complexes were obtained
similarly.
zylamine (2.21 g, 20.6 mmol) in ethanol was refluxed for 5 h
then cooled, after cooling a yellow product was precipitated.
The precipitate was filtered off, washed with ethanol, air-dried
and recrystallized from benzene. The crystals were dried in a
desiccator over anhydrous calcium chloride. The analytical and
physical data for H2L ligand and its metal complexes are listed
in Table 1. Scheme 1 illustrates the synthesis of the Schiff base,
H2L, ligand.
2.4.1. Synthesis of the [(L)Cu2(NO3)2(H2O)6], complex (1)
An ethanolic solution (30 mL) of Cu(NO3)2·2.5H2O
(0.562 g, 2.42 mmol) was added gradually to an ethanolic solu-
tion (40 mL) of the ligand (0.45 g, 1.21 mmol). The solution was
stirred for 8 h and a green precipitate was formed. The precipitate
was filtered, washed with ethanol then diethylether and finally
air-dried. The yield was 0.529 g (60%).
2.4. Synthesis of the metal complexes
The metal salt and the ligand, both dissolved in ethanol, were
mixed in the molar ratio 1:2 (L:M) and stirred for 8 h. In case
of VO(IV) complex, water was added to ensure the complete
dissolution of VOSO4·H2O. The uranyl(VI) and cerium(III)
complexes were prepared in methanol. The resulting precipi-
tates were filtered, washed with ethanol or methanol then ether
2.4.2. Unsuccessful trials
Trials to prepare Zn(II), Cd(II) and Th(IV) complexes of the
Schiff base, H2L, ligand were unsuccessful where oily products
were obtained which can not be isolated in pure forms.
Table 3
Electronic spectra and magnetic moments data of the ligand and its metal complexes
Electronic spectral bandsa (nm)
μeff. B.M.
μcompl. B.M.
b
c
No.
Complexes
H2L
(272, 350, 382)d
567, 675
573
570, 660
537
523, 635
420, 570
560
444, 540
470
–
–
1
2
3
4
5
6
7
8
[(L)Cu2(NO3)2(H2O)6]
[(L)2Cu2]·H2O
1.83
1.99
1.96
1.85
2.00
3.08
5.05
5.84
Diam.
2.15
2.11
2.38
2.53
2.50
2.56
2.75
4.25
7.15
8.18
Diam.
2.95
2.80
[(H2L)2Cu2Cl4]·3H2O
[(L)Cu2(H2O)4](ClO4)2·0.5EtOH
[(H2L)Cu2(H2O)4(SO4)2]·2H2O
[(L)Ni2(NO3)2(H2O)4]
[(L)Co2(NO3)2(H2O)6]·0.5EtOH
[(H2L)Fe2(NO3)6(H2O)2]·6H2O
[(L)(UO2)2(OAc)2(MeOH)2]
[(H2L)(VO)2(SO4)2]·5H2O
[(L)2Ce2(NO3)2(MeOH)2]
9
10
11
619
460
a
b
c
d
Nujol mull.
μeff. is the magnetic moment of one cationic species in the complex.
μcompl. is the total magnetic moments of all cations in the complex.
Solutions in DMF (×10−3 M).

854
M. Shebl / Spectrochimica Acta Part A 70 (2008) 850–859
Table 4
The 1H NMR data of the free ligand H2L and its UO2(VI) complex (9)
δH (ppm)
Ha
Hb
Hcaromatic
Hd
He
Hf
Hg
Hh
H2L
2.50(6H) 3.7 (4H)
2.50(6H) 3.9 (4H)
7.15–7.65 (10H)
7.1–7.6 (10H)
5.88 (1H)
6.15 (1H)
8.23 (1H)
8.50 (1H)
–
–
–
[(L)(UO2)2(OAc)2(MeOH)2] (9)
3.0 (6H)
3.2 (6H)
4.85 (2H)
band at 1610 cm−1 attributed to ν(C N) and a strong band at
1247 cm−1 assigned to the stretching frequency of the phenolic
C–O bond; ν(C–O). The electronic spectrum of the ligand in
DMF (Table 3) showed three bands at 272, 350 and 382 nm.
3. Results and discussion
3.1. Characterization of the ligand
*
The structure of the ligand was elucidated by elemental anal-
yses, electronic, IR, 1H NMR and mass spectra. The results of
the elemental analyses (Table 1) are in good agreement with
the proposed formula. The IR spectrum of the ligand (Table 2)
showed a broad band at 3445 cm−1 assigned to ν(OH), strong
The higher energy band is assigned to ␲–␲ transitions of
the azomethine linkage and the aromatic benzene ring. The
*
medium energy band is assigned to n–␲ transitions while the
lower energy band is attributed to charge transfer (CT) tran-
sitions within the molecule. 1H NMR spectral data (δ ppm)
Scheme 2. Mass fragmentation pattern of the ligand.

M. Shebl / Spectrochimica Acta Part A 70 (2008) 850–859
855
(M:L); M = Cu(II), Ni(II), Co(II), Fe(III), Ce(III), UO2(VI)
or VO(IV). Also, the ligand was allowed to−react with sev-
eral Cu(II) salts of Cl−, NO3−, AcO−, ClO4 and SO42−, in
order to determine the effect of the counterions on the prod-
ucts. All complexes are binuclear complexes (2:1; M:L) while
in complexes 2, 3 and 11, two ligand molecules are coordi-
nated to two metal ions (2:2; M:L). Measurements of the pH
values of the reaction mixtures showed the release of the phe-
nolic proton in some cases (complexes 1, 2, 4, 6, 7, 9 and 11)
where the pH is in the range (2–3.5). However, the pH is in
the range (4.5–5.5) in complexes 3, 5, 8 and 10 which may
indicate that the ligand acts as a neutral ligand. This is sup-
ported through characterization of the metal complexes. Also,
the obtained copper(II) complexes reflect the−non-coordinating
or weakly coordinating power of the ClO4 anion as com-
2−
pared to the strongly coordinating power of SO4 and Cl−
anions.
Fig. 3. X-band ESR spectra of the complexes 1: [(L)Cu2(H2O)4]
(ClO4)2·0.5EtOH (4), 2: [(H2L)Cu2(H2O)4(SO4)2]·2H2O (5) and 3:
[(H2L)(VO)2(SO4)2]·5H2O (10).
of the ligand relative to TMS (0 ppm) in DMSO-d6, Table 4,
give further support of the suggested structure of the ligand.
The signal due to the phenolic OH group was not observed
which may be due to the formation of hydrogen bonds with
the azomethine nitrogen atom. The mass spectrum of the ligand
(Fig. 2) showed the molecular ion peak at 372 a.m.u., confirm-
ing its formula weight (F.W. 372.47). The mass fragmentation
pattern, shown in Scheme 2, supported the suggested struc-
ture of the ligand. Furthermore, the proposed structure of the
free ligand was optimized (Fig. 1) and structural parameters
were evaluated by means of a semi-empirical molecular orbital
calculations at the PM3 level provided by the ALCHEMY
3
˚
2000 program. These data are found to be, V (A ) = 352.72,
2
˚
S (A ) = 417.39, EHOMO(eV) = −8.64, ELUMO(eV) = −0.25 and
dipole moment μ (D) = 4.61. These data show the same trend
3
˚
of 4,6-diacetylresorcinol (DAR) that showed V (A ) = 167.9,
2
˚
S (A ) = 205.7, EHOMO(eV) = −9.55, ELUMO(eV) = −0.73 and
dipole moment μ (D) = 4.29 [15].
3.2. Characterization of the metal complexes
The Schiff base ligand has two NO donor sites; there-
fore, it could react with all metal ions in the molar ratio 2:1
Fig. 4. The proposed structures of Cu(II) complexes.

856
M. Shebl / Spectrochimica Acta Part A 70 (2008) 850–859
−
odentate nature of the coordinated NO3 group [24]. In case
of copper(II) complexes (complexes 1–5), the modes of coordi-
nation of the anion with the Cu(II) ion were deduced from the
IR data which indicated that coordination of the donor anion
molecules (X) leads to lengthening of the (Cu–N) bond which
leads to shortening in the (C N) bond as observed from the fre-
quencies of C N for copper(II) complexes containing different
anions i.e., as the strength of Cu–X bond increases, the Cu–N
bond decreases so that ν(C N) increases. This is illustrated from
ꢀν values [ꢀν = ν(C N)free ligand − ν(C N)complex] which have
the following order:
Fig. 5. The proposed structure of the Ni(II) complex (6).
Anion
ꢀν
−
ClO4−
NO3
Cl−
23
16
10
3.2.1. IR spectra of the metal complexes
The IR spectral data are listed in Table 2. Comparison of
the IR spectra of the metal complexes with that of the free lig-
and revealed that all complexes showed a broad band in the
range 3484–3390 cm−1 assignable to ν(OH) of the coordinated
oruncoordinatedwaterand/oralcoholmoleculesassociatedwith
the complexes which are confirmed by elemental and thermal
analyses. Also, the band at 1610 cm−1 assigned to ν(C N) in the
free ligand was shifted to lower wave number in all of the com-
plexes, indicating the participation of the azomethine nitrogen
in chelation. The band at 1247 cm−1 assigned to ν(C–O) in the
free ligand was shifted to 1250–1268 cm−1 in the complexes and
the intensity of the band has decreased showing the involvement
of the phenolic oxygen in coordination. In complex 4, the broad
band around 1057 cm−1 assigned to ν3(Cl–O) indicates the non-
coordinated (ionic) nature of the ClO4− ion [20] (Td symmetry).
The ionic nature is further supported by the appearance of a band
at 629 cm−1 [15]. In addition, in complexes 5 and 10, the chelat-
This is consistent with the donor ab−ility of the anion
(DNX = 6.36, 19 and 34.1 for ClO4−, NO3 and Cl−; respec-
tively) [25], this is in a good agreement with Gutmann bonds
rules [26]. The results indicate that the ligand is flexible for
the charge redistribution over the whole system and hence for
the execution of the system organization [27,28]. The unique
feature of this system is that the electron density at the coordi-
nation centre remains nearly constant. Also, complex 9 showed
strong absorption band at 917 cm−1, which is assigned to the
antisymmetric ν3(O U O) vibration [21]. Also, the character-
istic band of the ν(V O) is observed in the IR spectrum of
the vanadyl complex (10) at 967 cm−1 [29]. Support for the
above interpretation is the appearance of the non-ligand bands
at 517–578 and 411–483 cm−1 assigned to ν(M–O) and ν(M–N)
[30], respectively.
2−
ing bidentate SO4 group was indicated by the appearance of
ν3(S–O) bands at 1263 and 1107 for the former complex and
at 1262 and 1090 cm−1 for the latter complex, which are char-
acteristic for the high symmetry Td (tetrahedral) point group
[21]. In complex 9, the chelating bidentate CH3COO− group
was supported by bands located at 1528 and 1455 cm−1. These
two bands are due to νas(COO−) and νs(COO−), respectively.
The separation of the two bands, ꢀν = νas − νs = 73 cm−1, is
comparable to the values cited for the bidentate character of
the acetate group [22]; ꢀν = 75–80 cm−1. Complexes 6 and 11
showed four bands at 1441, 1381, 1326 and 820 cm−1 for the
former complex and at 1453, 1351, 1302 and 817 cm−1 for the
latter complex assigned to the bidentate chelating NO3− groups
[23]. On the other hand, complexes 1, 7 and 8 showed bands
at 1381–1341 and 1263–1259 cm−1 which confirmed the mon-
3.2.2. Electronic and ESR spectra, magnetic measurements
and thermal analyses
3.2.2.1. Coppercomplexes. TheSchiffbaseligandwasallowed
to re−act with several Cu(II) salts of Cl−, NO3−, AcO−,
ClO4 and SO42−, in order to investigate the effect of the
counterions on the structure of the products. These reactions
afforded different complexes with different modes of bond-
ing. All the obtained complexes are binuclear complexes (2:1;
M:L) except complexes 2 and 3 which could be considered as
2:2 (M:L) complexes where two ligand molecules are coor-
dinated to two metal ions. All the complexes are octahedral
except complexes 2 and 4 which have square planar geome-
try. The effective magnetic moment of all copper complexes
is in the range (1.83–2.00) B.M. which is consistent with the
presence of one unpaired electron. The electronic spectra of
the complexes (1, 3 and 5) show two absorption bands at
675–635 and 570–523 nm which indicate octahedral geometry
[31]. However, complexes (2 and 4) show one band at 573 and
537 nm, respectively, indicating square planar geometry [32].
X-band ESR spectra of [(L)Cu2(H2O)4](ClO4)2·0.5EtOH (4)
and [(H2L)Cu2(H2O)4(SO4)2]·2H2O (5), Fig. 3, were recorded
in the solid state at 25 ◦C. The spectrum of the former com-
plex exhibits one broad band with g = 1.95. The shape of the
spectrum is consistent with the square-planar geometry around
Fig. 6. The proposed structure of the Co(II) complex (7).

M. Shebl / Spectrochimica Acta Part A 70 (2008) 850–859
857
Fig. 7. The proposed structure of the Fe(III) complex (8).
Fig. 9. The proposed structure of the VO(IV) complex (10).
each Cu(II) center in the complex [33,34]. The spectrum of the
falls in the 4.7–5.2 B.M. range expected for octahedral cobalt(II)
complexes [38]. The presence of half ethanol molecule and six
coordinated water molecules was supported by TGA.
latter complex exhibits two signals at g = 2.05 and g = 2.22,
⊥
ꢀ
gaver. = 1/3(g + 2g ) = 2.11. The shape of the spectrum is con-
ꢀ
⊥
sistent with the octahedral geometry around each Cu(II) center
in the complex. The positive contribution in the geff value than
the value of a free electron (2.0023) indicates an increase in the
covalency of the bonding between the Cu(II) ion and the ligand
molecule [35]. Thermal analysis of the prepared complexes con-
firmed the presence of uncoordinated, coordinated water and/or
ethanol molecules. On the basis of the above characterization,
the tentative structures of the Cu(II) complexes are shown in
Fig. 4.
3.2.2.4. The Fe(III) complex. The Fe(III) complex, [(H2L)
Fe2(NO3)6(H2O)2]·6H2O (Fig. 7), was obtained from the reac-
tion of the ligand with Fe(NO3)3·9H2O. The electronic spectrum
of the Fe(III) complex showed two absorption bands at 444 and
540 nm. The first band is assigned to a charge transfer band
4
and the second band could be assigned to 6A1 → T2 electronic
transition [29], suggesting an octahedral arrangement around the
Fe(III) ion. The value of the magnetic moment of the complex
(8) is 5.84 B.M., Table 3, which is consistent with the presence of
five unpaired electrons in the Fe(III) ion in an octahedral geome-
try [39]. The thermogram of the complex showed a weight loss at
94 ◦C which corresponds to six hydrated water molecules. How-
ever, the two coordinated water molecules were lost in another
decomposition stage with the decomposition of the complex.
3.2.2.2. The Ni(II) complex. Based on the electronic spectral
and magnetic data, nickel(II) complex, Fig. 5, has the octa-
hedral geometry with its characteristic features. The electronic
spectrum of the complex as nujol mulls (Table 3) showed two
bands, the first band occurs at 420 nm which is corresponding to
3
the 3A2g → T1g(P) transition. The other band occurs at 570 nm
3
which is corresponding to the 3A2g → T2g electronic transition.
3.2.2.5. The UO2(VI) complex. The reaction of UO2(OAc)2
·2H2O with the ligand yielded a binuclear UO2(VI) complex
(Fig. 8). The electronic spectrum of the complex showed one
absorption band at 470 nm, which is attributed to an electronic
transition from the apical oxygens to f orbitals of the ura-
nium(VI) ion or due to a charge transfer transition from the
Thetwotransitionsareconsistentwithanoctahedralgeometryof
the complex [36]. The magnetic moment of the complex is 3.08
B.M. which indicates the presence of two unpaired electrons
per the Ni(II) ion, also confirming its octahedral geometry [37].
The thermogram of the complex confirmed its structure where
it showed a weight loss corresponding to four coordinated water
molecules at 120 ◦C.
1
ligand to uranium(VI) ion [40]. The H NMR spectral data of
the UO2(VI) complex in DMSO-d6 solutions along with its
assignment are included in Table 4. New signals appeared in
the spectrum of the complex corresponding to methanol and
acetate group indicating the involvement of them in the coordi-
nation. The UO2(VI) complex showed a weight loss at 105 ◦C
corresponding to the elimination of two coordinated methanol
molecules.
3.2.2.3. The Co(II) complex. The reaction of Co(NO3)2·6H2O
with the ligand yielded a binuclear Co(II) complex (Fig. 6). The
electronic spectrum of the obtained complex showed a band at
560 nm corresponding to T1g(F) → A2g(F) transition which
is consistent with the octahedral geometry of the complex. The
effective magnetic moment of the complex is 5.05 B.M. which
4
4
Fig. 8. The proposed structure of the UO2(VI) complex (9).
Fig. 10. The proposed structure of the Ce(III) complex (11).

858
M. Shebl / Spectrochimica Acta Part A 70 (2008) 850–859
(10) at room temperature, Fig. 3, showed a broad band centered
on g = 2.00, without resolved hyperfine structure. In particular,
the hyperfine coupling with the nearby 51V (I = 7/2) nucleus
is not observed. The absence of vanadium hyperfine coupling
is common in solid state samples [42] and is attributed to the
simultaneous flipping of neighbouring electron spins [43,44]
or due to strong exchange interactions, which average out the
interaction with the nuclei. The thermogram of the complex
showed a weight loss at 85 ◦C which corresponds to the loss of
five hydrated water molecules.
3.2.2.7. The
Ce(III)
complex. The
reaction
of
Ce(NO3)3·6H2O with the ligand yielded a binuclear complex,
[(L)2Ce2(NO3)2(MeOH)2], (Fig. 10). The electronic spectrum
of the Ce(III) complex showed a new absorption band at 460 nm
which may be related to metal-ligand charge transfer excitation
[45]. The magnetic moment of the complex is 2.11 B.M. which
is close to the experimental range of 2.14–2.46 B.M. [46,47].
The thermogram of the complex showed a weight loss at 130 ◦C
which corresponds to the loss of two coordinated methanol
molecules.
3.2.3. Mass spectra of the metal complexes
The mass spectra of the complexes provide good evidence
for the molecular formulas of these complexes. The com-
plexes 1 and 6, [(L)Cu2(NO3)2(H2O)6] (F.W. 729.65) and
[(L)Ni2(NO3)2(H2O)4] (F.W. 683.95) as representative com-
plexes, are depicted in Fig. 11. The mass spectra of these
complexes showed the highest mass peak with m/e 733 and
685, respectively which agree with the formula weights of the
complexes.
4. Conclusion
The condensation reaction of 4,6-diacetylresorcinol with
benzylamine afforded the tetradentate Schiff base, H2L, lig-
and. The reactions of the Schiff base ligand with copper(II),
nickel(II), cobalt(II), iron(III), vanadyl(IV), uranyl(VI) and
cerium(III) ions, in molar ratio (1:2; ligand:metal ion) were
studied. Also, the ligand was allowed to react with different
copper(II) salts containing different anions such as Cl−, AcO−,
ClO4− and SO42−, in order to determine the effect of the coun-
terions on the products. All complexes are binuclear (2:1; M:L)
while in complexes 2, 3 and 11, two ligand molecules are coor-
dinated to two metal ions (2:2; M:L). The spectroscopic data
showed that, the Schiff base ligand acts in all metal complexes as
neutral or dianionic tetradentate ligand through the two azome-
thine nitrogen atoms and the two oxygen atoms of the two
phenolic groups. The metal complexes exhibited different geo-
metrical arrangements such as square planar, octahedral, square
pyramidal and pentagonal bipyramidal arrangements.
Fig. 11. Mass spectra of the complexes A: [(L)Cu2(NO3)2(H2O)6] (1) and B:
[(L)Ni2(NO3)2(H2O)4] (5).
3.2.2.6. The VO(IV) complex. The VO(IV) complex,
[(H2L)(VO)2(SO4)2]·5H2O (Fig. 9), was obtained from
the reaction of the ligand with VOSO4·H2O. The electronic
spectrum of the complex showed a d–d transition band at
619 nm and its IR spectrum showed ν(V O) at 967 cm−1
.
These data indicate that the geometry around VO(IV) cation is
square-pyramidal [40]. The magnetic moment of the complex
is 2.15 B.M. which is higher than expected for d1-system;
suggesting an orbital contribution [41]. The X-band ESR
spectrum of a powdered sample of [(H2L)(VO)2(SO4)2]·5H2O
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