A series of transition and non-transition metal complexes from a N 4O2 hexadentate Schiff base ligand: Synthesis, spectroscopic characterization and efficient antimicrobial activities

Article abstract of DOI:10.1016/j.saa.2010.06.041

Some transition and non-transition metal complexes of the hexadentate N₄O₂ donor Schiff base ligand 1,8-N-bis(3-carboxy) disalicylidene-3,6-diazaoctane-1,8-diamine, abbreviated to H ₄fsatrien, have been synthesized. All th

Full text of DOI:10.1016/j.saa.2010.06.041

Spectrochimica Acta Part A 77 (2010) 740–748
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
A series of transition and non-transition metal complexes from a N4O2
hexadentate Schiff base ligand: Synthesis, spectroscopic characterization and
efficient antimicrobial activities
Saikat Sarkara, Kamalendu Deyb,∗,1
a Department of Chemistry, Santipur College, Santipur 741404, West Bengal, India
b Department of Chemistry, University of Kalyani, Kalyani 741235, West Bengal, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 April 2010
Received in revised form 19 June 2010
Accepted 28 June 2010
Some transition and non-transition metal complexes of the hexadentate N4O2 donor Schiff base ligand
1,8-N-bis(3-carboxy)disalicylidene-3,6-diazaoctane-1,8-diamine, abbreviated to H4fsatrien, have been
synthesized. All the 14 metal complexes have been fully characterized with the help of elemental analyses,
molecular weights, molar conductance values, magnetic moments and spectroscopic (UV–Vis, IR, NMR,
ESR) data. The analytical data helped to elucidate the structures of the metal complexes. The Schiff base,
H4fsatrien, is found to act as a dibasic hexadentate ligand using N2N2O2 donor set of atoms (leaving the
COOH group uncoordinated) leading to an octahedral geometry for the complexes around all the metal
ions except VO2+ and UO22+. However, surprisingly the same ligand functions as a neutral hexadentate
Keywords:
Schiff base
Hexadentate
IR
Electronic spectra
Antimicrobial
2+
and neutral tetradentate one towards UO2 and VO2+, respectively. In case of divalent metal complexes
they have the general formula [M(H2fsatrien)] (where M stands for Cu, Co, Hg and Zn); for trivalent metal
complexes it is [M(H2fsatrien)]X·nH2O (where M stands for Cr, Mn, Fe, Co and X stands for CH3COO,
Cl, NO3, ClO4) and for the complexes of VO2+ and UO22+, [M(H4fsatrien)]Y (where M = VO and Y = SO4;
M = UO2 and Y = 2 NO3). The Schiff base ligand and most of the complexes have been screened in vitro to
judge their antibacterial (Escherichia coli and Staphylococcus aureus) and antifungal (Aspergillus niger and
Pencillium chrysogenum) activities.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
Besides, very little is known about the coordination behaviour
of the trivalent metal ions towards such polydentate compart-
Polydentate Schiff base ligands are of great interest because
their binding selectivity can be altered subtly by having the ligand
enforce a specific spatial arrangement of donor atoms (i.e. preorga-
nization of the donor atoms) or incorporate a set of donor atoms tai-
lored to the metal of interest. In addition, polydentate ligands have
the potential to form complexes of high stability and slow ligand
exchange kinetics. This is important in preventing rapid demetalla-
tion or complex decomposition if the ligand is to direct the radionu-
clide to the target organ or if the ligand is to be used as an effective
chelating agent for the treatment of metal overload [1]. More-
over, the metal complexes derived from such ligand systems have
immense importance in different fields like biochemistry, cataly-
sis, magnetochemistry, materials sciences, etc. [2]. These ligands
are generally consisting of N3O3, N4O3, N2O4, etc. donor atoms [2].
mental ligands [3–6]. There is currently considerable interest in
the coordination chemistry of the trivalent group 13 metal ions,
the biomedical interest originates from the association of Al(III)
with neurological disorders such as Alzheimer’s disease [7] and
from the incorporation of Ga(III) and In(III) radionuclides (67Ga,
68Ga and 111In) into diagnostic radio pharmaceuticals [8]. Besides,
siderophores are interesting chelating agents for Fe(III), which are
involved in the transport of iron in biological systems [9]. These
complexes usually have six oxygens in an octahedral sphere around
the Fe(III) with the most important classes containing hydroxamic
acid (e.g. ferrichrome, ferrioxamine) or catechol groups (e.g. enter-
obactin). These neutral siderophores, and synthetic analogues have
been extensively studied with respect to their use in iron overload
treatment [10]. Only a few Fe(III) complexes have been isolated so
far, where the Fe(III) is shown to enter either of the compartments,
by the isolation of pure N2O2/N2N2O2 and O2O2 isomers [3–6].
In few of our recent works, a series of polydentate ligands with
well characterized properties and suitably designed metal com-
plexes including organoderivatives have been reported [11–18].
In this context and in continuation of our very recent work [19],
∗
Corresponding author. Tel.: +91 9433664151.
E-mail addresses: saikat s@rediffmail.com (S. Sarkar),
kdey chem@rediffmail.com (K. Dey).
1
Former Professor of Chemistry and UGC Emeritus Fellow.
1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.06.041

S. Sarkar, K. Dey / Spectrochimica Acta Part A 77 (2010) 740–748
741
we report here the synthesis and characterization of some transi-
tion and non-transition metal complexes of the hexadentate Schiff
base ligand, H4fsatrien. Efficient antimicrobial activities have also
been excavated with most of these metal complexes which in-turn
gives the illustration of these series to be environmentally benign
materials.
kept under reflux for 1–2 h. Instantaneous precipitation occurred
in the case of Co(II), Hg(II) and Zn(II).
The Cu(II) acetate gave a clear greenish-blue solution from
which the complex separated out only after evaporation to half
of the initial volume and on cooling to ice temperature. Yield 50%.
The precipitated complexes were filtered, washed thoroughly
with methanol and diethyl ether and dried in vacuum over anhy-
drous CaCl2. The reaction of Co(II) acetate was carried out under an
atmosphere of dinitrogen to avoid aerial oxidation. All the com-
pounds are soluble in DMF and DMSO. The yields were around
70–85%.
2. Experimental
2.1. Materials and general methods
Triethylenetetramine was purchased from Aldrich and used as
such. 3-Formylsalicylic acid was synthesized according to Duff and
Bills [20]. Spectrograde solvents were used for physical measure-
ments. All the other reagents and solvents were purchased from
commercial sources, purified and dried by standard procedures
[21].
2.4.1.1. [VO(H4fsatrien)]SO4 (5). Similarly a methanolic solution of
H4fsatrien was prepared using H2fsa (1.66 g, 10 mmol) and trien
(0.73 g, 5 mmol) in which few drops of glacial acetic acid were
added. To this ligand solution was then added a methanolic solu-
tion of VOSO4·2H2O (0.995 g, 5 mmol) followed by a methanolic
solution of NaOAc (0.82 g, 10 mmol) and the whole mixture was
heated under gentle reflux on a water bath for 1 h. During reflux a
greenish-yellow compound was separated out, which was filtered
off, washed with ethanol and dried in vacuo. It is soluble in DMF
and DMSO. Yield 85%.
2.2. Physical measurements
The elemental analyses were carried out on Elementar Vario
EL III, Carlo Erba 1108 elemental analyzers at the Sophisticated
Analytical Instrument Facility (SAIF), Central Drug Research Insti-
tute, Lucknow. The electronic spectra (in DMSO and other media
as indicated in the text) were recorded on a Shimadzu UV-2401PC
spectrophotometer and infrared spectra (KBr) on a Perkin-Elmer
L120-000A spectrophotometer. The ESR spectrum was measured
in an ESR spectrometer at SAIF, Kolkata. The molar conductance
(10−3 M in DMSO) was measured using an Elico conductivity bridge
and the magnetic data were measured on a Guoy Balance.
2.4.1.2. [UO(H4fsatrien)](NO3)2 (6). This yellow compound was
prepared by a method similar to that employed for the prepara-
tion of vanadyl complex except using of UO2(NO3)2·6H2O(2.51 g,
5 mmol) in place of vanadyl sulphate. It was filtered off, washed
with ethanol and dried in vacuo. It is soluble in DMF and DMSO.
Yield 80%.
2.4.2. Preparation of mononuclear complexes of H4fsatrien with
trivalent metal ions
2.3. Preparation of the ligand,
1,8-N-bis(3-carboxy)disalicylidene-3,6-diazaoctane-1,8-diamine,
H4fsatrien
2.4.2.1. [Cr(H2fsatrien)]CH3COO·2H2O (7). Similarly the reaction
of the solution of H4fsatrien (5 mmol) with the solution of
Cr(CH3COO)3·6H2O (1.69 g, 5 mmol) in methanol–water mixture
(20 mL, 50:50, v/v) afforded this greenish powdery compound. It
was filtered off, washed with ethanol and dried in vacuo. The com-
pound is soluble in hot methanol, DMF and DMSO. Yield 70%.
The hexadentate Schiff base ligand was prepared following
our earlier method [19] as follows. 3-Formylsalicylic acid (H2fsa)
(1.66 g, 10 mmol) was dissolved in methanol (25 mL) to which tri-
ethylenetetramine (trien) (0.73 g, 5 mmol) taken in methanol was
added (20 mL) dropwise with stirring. Immediately a yellow solu-
tion was obtained. Glacial acetic acid (3/4 drops) was then added to
it with stirring to facilitate completion of the condensation reaction
and stirring continued for 6 h at −10 ◦C. Then the temperature was
allowed to rise to room temperature with the separation of a yellow
powdery compound. It was filtered off, washed with methanol and
ether and dried in vacuo over fused CaCl2. The compound is soluble
in DMSO and DMF. Yield 25%.
2.4.2.2. [Cr(H2fsatrien)]Cl·2H2O (8). This greenish-yellow com-
pound was prepared by following the same method used for its
acetate analogue using CrCl3·6H2O (1.33 g, 5 mmol) instead of
Cr(CH3COO)3·2H2O. It was filtered off, washed with ethanol and
dried in vacuo. It is also soluble in DMF and DMSO. Yield 60%.
2.4.2.3. [Mn(H2fsatrien)]CH3COO (9). A solution of H4fsatrien
(5 mmol) was prepared as described above. To this was added
Mn(CH3COO)3·2H2O (1.34 g, 5 mmol) dissolved in 15 mL of
methanol with stirring. The mixture was heated under reflux for
1/2 h, while air was drawn through it. The brown solution, thus
produced, gave yellowish-brown powdery compound on concen-
tration and cooling. It was filtered off, washed with methanol and
dried in vacuo. This compound is soluble in DMF and DMSO. Yield
60%.
Due to poor yield of the ligand, we used the in situ reaction
procedure for the synthesis of the metal complexes.
2.4. Preparation of the metal complexes
2.4.1. Preparation of mononuclear complexes of H4fsatrien with
some divalent, VO2+ and UO2 metal ions
2+
The mononuclear divalent metal complexes [Cu(H2fsatrien)]
(1), [Co(H2fsatrien)] (2), [Hg(H2fsatrien)] (3) and [Zn(H2fsatrien)]
(4) were isolated as follows:
2.4.2.4. [Fe(H2fsatrien)]NO3·H2O
(10). The
solution
of
Fe(NO)3·9H2O (2.02 g, 5 mmol) in dry methanol was added to
the preformed Schiff base (H4fsatrien) solution (5 mmol) in dry
methanol dropwise with stirring. The solution, which immediately
turned dark brown, was refluxed gently for 1/2 h and the methanol
was evaporated slowly on a water bath. On cooling, the deep
chocolate coloured compound, which separated out, was filtered,
washed with diethyl ether and dried in air. This complex is soluble
in water, hot methanol, DMF and DMSO. Yield 60%.
3-Formylsalicylic acid (H2fsa) (1.66 g, 10 mmol) was dissolved in
methanol (25 mL) to which was added triethylenetetramine (trien)
(0.73 g, 5 mmol) in methanol (20 mL) dropwise with stirring and
a yellow solution was obtained. Few drops glacial acetic acid was
then added to it. The mixture was then heated under gentle reflux
for 1/2 h on water bath. Metal(II) acetate (5 mmol) dissolved in
minimum volume of methanol (15 mL) was added dropwise to the
Schiff base (H4fsatrien) solution with stirring and the mixture was

742
S. Sarkar, K. Dey / Spectrochimica Acta Part A 77 (2010) 740–748
Scheme 1.
2.4.2.5. [Fe(H2fsatrien)]Cl·2H2O (11). This reddish-brown com-
pound was synthesized by a method similar to that used for (10)
using FeCl3·6H2O (1.35 g, 5 mmol) in place of Fe(NO)3·9H2O. Solu-
bility is same as for compound (10). Yield 60%.
into long methylene chain may or may not coordinate to the metal.
This can be confirmed by comparing the spectral and magnetic
properties of the complexes with that of the simple complexes
derived from salicylaldimines.
So, the Schiff base ligand H4fsatrien, in principle, can function in
the following fashions to afford mononuclear complexes with di-
and trivalent metal ions:
2.4.2.6. [Co(H2fsatrien)]Cl (12). To
a
solution of H4fsatrien
(5 mmol), CoCl2·6H2O (1.19 g, 5 mmol) in methanol was added
dropwise and air was drawn through the solution for 4 h. The
solution was filtered and evaporated on water bath till the solid
started separated out from the solution. The mixture was filtered,
washed with methanol, acetone and finally with diethyl ether and
air-dried. This Co(II) complex is soluble in DMF and DMSO. Yield
60%.
(i) dibasic hexadentate, utilizing two phenolic oxygen (after
deprotonation), two azomethine nitrogens and two secondary
amine nitrogens, and
(ii) dibasic tetradentate, utilizing two phenolic oxygen (after
deprotonation) and two azomethine nitrogens.
2.4.2.7. [Co(H2fsatrien)]NO3 (13). This deep-brown compound was
prepared by the same method used for the preparation of
[Co(H2fsatrien)]Cl using Co(NO3)2·6H2O (1.45 g, 5 mmol). The mix-
ture was filtered, washed with methanol, acetone and finally with
diethyl ether and air-dried. Solubility remains same as (12). Yield
60%.
However, spectral and magnetic data obtained on all the mono
nuclear complexes of the hexadentate ligand H4fsatrien indicate
that the metal ion enters the inner compartment occupying the
N2N2O2 sites. But, H4fsatrien is being observed to act as a neutral
2+
tetradentate and neutral hexadentate ligand towards UO2 and
VO2+, respectively.
The present paper reports the results of the interaction of
H4fsatrien with CoCl2·6H2O, Co(NO3)2·6H2O, Co(CH3COO)2·4H2O,
2.4.2.8. [Co(H2fsatrien)]ClO4 (14). The above-mentioned Co(III)
complex, [Co(H2fsatrien)]NO3 (13), was dissolved in minimum
amount of water and aqueous NaClO4 was added in excess. This
dark reddish-brown perchlorate complex separated out of the solu-
tion immediately. The product was digested for 15 m on water bath,
filtered and washed thoroughly with acetone and diethyl ether and
dried in air. It is partially soluble in water but fully soluble in DMF
and DMSO. Yield 80%.
Cu(CH3COO)2·H2O,
Cr(CH3COO)3·6H2O,
Zn(CH3COO)2·2H2O,
VOSO4·2H2O,
Mn(CH3COO)3·2H2O,
CrCl3·6H2O,
Fe(NO3)3·9H2O, FeCl3·6H2O and UO2(NO3)2·6H2O under varied
reaction conditions leading to the isolation of new mononuclear
complexes of these metal ions. The chemical composition of the
isolated complexes depends to some extent on the metal template
effect, solvents, temperature and pH of the solution. Elemental
analyses and other characterization data are shown in Table 1,
which support their formulations. The molecular weights are also
in good agreement with the theoretical values. The spectra of
some representative complexes are given in Supplementary files.
Unfortunately no single crystal could be grown in spite of our best
efforts.
[For all the above-mentioned preparative reactions the pH of
the mother liquor was found to lie between 4 and 6.]
3. Results and discussion
3.1. Syntheses
The formation of the metal complexes may be expressed by the
chemical equations (Scheme 2):
The
ligand
1,8-N-bis(3-carboxy)disalicylidene-3,6-
diazaoctane-1,8-diamine, H4fsatrien, was prepared by the reaction
of 3-formylsalicylic acid with triethylenetetramine (2:1 molar
ratio) in methanol at room temperature. The results of the ele-
mental analysis, molecular weight, infrared, 1H and 13C NMR data
are consistent with the formula shown in Scheme 1.
3.2. The 1H and 13C NMR spectra
The 1H NMR spectra of the ligand H4fsatrien has been measured
in DMSO-d6 with TMS as internal reference. The data is depicted in
Table 2. A sharp singlet at 8.94 ppm and a broad one at 6.2 ppm are
assigned to the azomethine and N–H protons, respectively. Bridg-
ing methylene protons give rise to broad signals at 2.50–2.79 and
3.00–3.83 ppm assignable to –X–(CH2)n–X– and N–CH2, respec-
tively [18,22,23]. The broad signal at 10.8 and at 12.28 ppm may be
considered as phenolic OH, carboxylic COOH protons, respectively.
Multiplets of aromatic protons appear in the region 7.98–6.60 ppm.
The 13C NMR spectrum of the ligand exhibits 11 signals. The sig-
nals at 167.1, 139.1, 136.6, 130.3, 116.93 and 114.09 ppm are due to
aromatic carbons. The carboxylic carbon and imine carbon appear
at 172 and 161.5 ppm, respectively. The methylene carbons are
observed at 51.2, 50.2 and 49.15 ppm. These data support the for-
mulation of the isolated Schiff base, H4fsatrien.
In the case of the present ligand, H4fsatrien, the characteris-
tics of mononuclear complexes where the metal is occupying in
the inner coordination site (N2N2O2) may be compared to that
of the simple ligand derived form salicylaldehyde and the respec-
tive diamines. In the case of mononuclear complexes derived from
similar type hexadentate ligands, if the metal occupies the inner
compartment, it yields one of the positional isomeric forms MN2N2,
MN2O2 or MN2N2O2. Simple ligands derived from salicylaldehyde
and tetradentate ␣,␻-polyamines react with metal ions to form
neutral complexes where the phenolic protons are displaced by
the metal ion. It is presumed that similar situation exists with the
present ligand, H4fsatrien and the possibility of the positional iso-
mer MN2N2 mightbe excluded. Thenwewillbeleftwith the MN2O2
and MN2N2O2 isomers, where the extra donor sites incorporated

S. Sarkar, K. Dey / Spectrochimica Acta Part A 77 (2010) 740–748
743
The 1H NMR spectra of the diamagnetic complexes
[Hg(H2fsatrien)] (3), [Zn(H2fsatrien)] (4), [Co(H2fsatrien)]Cl
(12), [Co(H2fsatrien)]NO3 (13) and [Co(H2fsatrien)]ClO4 (14) were
measured in TFA and DMSO-d6, respectively with TMS as internal
standard and the data are recorded in Table 2. The 1H NMR spectra
of the complexes are almost similar to that of the ligand H4fsatrien,
with slight shift to higher fields. The broad signal for the hydrogen
for phenolic OH at about ı 10.8 ppm is absent in all the complexes.
This indicates deprotonation and coordination of the phenolic OH.
The imino protons appear as doublets in this complex indicating
the non-equivalence of the two imino groups of the molecule
which would result from distorted octahedral geometry around
the metal ion. All the observed resonances are assigned based on
similar assignments for simple salicylaldehyde or acetylacetone
derived ligands and their similar complexes. The broad signal for
the secondary NH appeared at almost the same location as found
for the free ligand position. Slightly lower frequency shifts are
also observed for the aromatic protons when compared with the
free ligand. All these suggest coordination of the ligand H4fsatrien
as a dibasic hexadentate N2N2O2 donor in the complexes. It may
be inferred that the ligand H4fsatrien behaves similarly in other
complexes reported in Table 1.
3.3. Infrared spectra
The inferences drawn from the 1H and 13C NMR spectral data
of the ligand are substantiated by the appearance of infrared bands
at ∼3412 cm−1 (br) for OH, at 3290 cm−1 (br) for NH, at 2930 cm−1
for CH, at 1690 cm−1 for COOH and 1657 cm−1 for >C N, respec-
tively.
The general trend of the infrared spectra of the present metal
complexes is comparable with those published previously with
similar type of ligands [18,19]. All the metal complexes show
broad to medium bands in the region 3600–3000 cm−1, which are
assignable to OH stretching vibrations due to the presence of free
COOH groups and/or due to the presence of water molecule(s)
(see Table 1). The NH stretching frequencies of the complexes
are observed at around 20–50 cm−1 lower compared to the free
ligand value. These lower values compared to the free ligand sug-
gest coordination of the nitrogen atom of the secondary amine
(NH) to the metal. The ꢃ(C N) frequency in the complexes is
observed around 1648–1621 cm−1 (which is 9–36 cm−1 lower
than that observed in the free ligand) and lends support to the
coordination of the imine nitrogen. The infrared spectra of the
complexes (1)–(14) showed the vibration of the free carboxyl
group ꢃas(COOH) around 1700 cm−1, suggesting a mononuclear
formulation of the complexes. The phenolic ꢃ(C–O) frequency gen-
erally appeared at around 1500 cm−1 in the free Schiff base and
at 1540 cm−1 when attached to a single metal (non-bridging). On
the other hand, the bridging phenolic ꢃ(C–O) frequency appears
at 1560 cm−1. Hence the higher-energy shift of the band has
been used for a diagnosis of the formation of a phenolic oxy-
gen bridge. On the basis of this and also on the basis of the data
available [24,25], we can safely say that the complexes (1)–(14)
are mononuclear in nature with free COOH groups. Characteristic
bands for water of crystallization in the complexes (7), (8), (10)
and (11) are observed at 3120–3450 cm−1 (br) assignable to ꢃ(OH)
[26].
Band assignments in the region 3100–3400 cm−1 and around
1600 cm−1 are complicated by the presence of secondary amine
and C N chromophoric groups in the present complexes. Besides,
absorption of water molecule also appears in the 3100–3500 cm−1
range. All these complicate the proper interpretation of the bands
in the region.

744
S. Sarkar, K. Dey / Spectrochimica Acta Part A 77 (2010) 740–748
Scheme 2.
Infrared spectrum of the VO2+ complex shows bands almost
appearance of a very strong band at 1170 cm−1 in the perchlorate
complex, [Co(H2fsatrien)]ClO4 (14), can be assigned to the ꢃ3 mode
of vibrations (in Td symmetry) [28]. The ꢃ(M–N) and ꢃ(M–O) fre-
quencies for all the complexes appear around 496–596 (w/m) cm−1
and 382–486 (w/m) cm−1, respectively.
comparable to that of the free ligand H4fsatrien excepting the low-
ering of azomethine (C N) band by about 34 cm−1 in the complex.
The ꢃ3 and ꢃ4 modes of vibration of sulphate are observed at 1015
and 622 cm−1, respectively, which confirms that sulphate remains
as free ion. These observations suggest that the ligand functions
as a neutral tetradentate ligand bonding through two-azomethine
nitrogen and two phenolic OH groups. Unfortunately, we could
not grow any suitable crystal for X-ray crystal structure analysis.
The ꢃ(V O) of the complex observed at 960 cm−1, supporting in all
probability the presence of monomeric V O unit in the complex
[27,28].
Based on the above discussion, the following structures
(Figs. 1 and 2) may be proposed for the isolated complexes (1)–(14).
3.4. Molar conductance values
The molar conductance values of the complexes (1)–(4) in DMSO
solution are found in the range ꢁM = 9.6–17.9 ohm−1 cm2 mol−1
,
The infrared spectrum of the complex (6) shows an intense
absorption bands at 890 cm−1 attributable to ꢃas(UO2) mode
[27,28]. However, the ꢃsym(UO2) vibration in the complex could not
be detected unequivocally since the ligand absorbs in this region.
Appearance of a strong sharp band at 1380 cm−1 demonstrates the
indicating non-electrolyte nature of the complexes in the solu-
tion of DMSO [29]. On the other hand, (5) and (7)–(14) show ꢁM
values in the range 48.1–53.2 ohm−1 cm2 mol−1, suggesting 1:1
electrolyte nature [29]. The molar conductance value of the com-
plex (6) is 62.1 ohm−1 cm2 mol−1 indicating that the complex is a
1:2 electrolyte [29].
presence of ionic nitrate (NO3−). It is thus plausible that the UO2
2+
ion in the complex (6) may attain eight coordination [27,28] (Fig. 1).
The other infrared bands of the complex may be discussed as in
the case of [VO(H4fsatrien)]SO4 (5), supporting neutral hexaden-
tate nature of the ligand. The infrared bands observed at about
820–830(m), 1380–1390(s) and 750–760(s) cm−1 regions in the
nitrate salts, [UO2(H4fsatrien)](NO3)2 (6), [Fe(H2fsatrien)]NO3·H2O
(10) and [Co(H2fsatrien)]NO3 (14) may be assigned to the ꢃ1, ꢃ2, ꢃ3
modes of vibrations (in D3h symmetry) [28]. On the other hand, the
3.5. Magnetic moments, electronic and ESR spectra
The magnetic susceptibility of all the newly synthesized com-
plexes were measured in the solid state at room temperature
and the calculated magnetic moment values are recorded in
Table 1. The complexes [Cu(H2fsatrien)] (1), [Co(H2fsatrien)]
(2), [VO(H4fsatrien)]SO4 (5), [Cr(H2fsatrien)](CH3COO)·2H2O
Table 2
1H NMR spectral data of ligand and some complexes.
Ligand/complex
NH
COOH
OH
H–C
N
C–H
–X–(CH2)n–X
N–CH2
H4fsatrien
6.2 (2H, br)
6.11 (2H, br)
6.04 (2H, br)
6.12 (2H, br)
6.08 (2H, br)
6.18 (2H, br)
12.28 (2H, br)
12.36 (2H, br)
12.3 (2H, br)
12.27 (2H, br)
12.31 (2H, br)
12.39 (2H, br)
10.8 (2H, br) 8.86 (2H, d)
7.98–6.6 (6H,3m.5)1 (8H, br)
6.89–6.65 (6H3,.m47) (8H, br)
6.85–6.65 (6H3,.m40) (8H, br)
6.80–6.56 (6H3,.m48) (8H, br)
6.92–6.73 (6H3,.m5 )(8H, br)
6.82–6.61 (6H3,.m43) (8H, br)
4.3 (4H, br)
4.2 (4H, br)
4.1 (4H, br)
4.21 (4H, br)
4.2 (4H, br)
4.16 (4H, br)
[Hg(H2fsatrien)] (3)
[Zn(H2fsatrien)] (4)
[Co(H2fsatrien)]Cl (12)
[Co(H2fsatrien)]NO3 (13)
[Co(H2fsatrien)]ClO4 (14)
–
–
–
–
–
8.53 (2H, d)
8.45 (2H, d)
8.49 (2H, d)
8.58 (2H, d)
8.50 (2H, d)

S. Sarkar, K. Dey / Spectrochimica Acta Part A 77 (2010) 740–748
745
2+
Fig. 1. Proposed structures of the divalent, VO2+ and UO2 metal complexes.
Table 3
(7), [Mn(H2fsatrien)](CH3COO) (9), [Fe(H2fsatrien)]NO3·H2O
(10), (11) are paramagnetic,
while the complexes [Hg(H2fsatrien)] (3), [Zn(H2fsatrien)]
(4), [UO2(H4fsatrien)](NO3)2 (6), [Co(H2fsatrien)]Cl (12),
[Co(H2fsatrien)]NO3 (13) and [Co(H2fsatrien)]ClO4 (14) are all
diamagnetic.
ESR spectral data of [Cu(H2fsatrien)] (2) at room temperature in the solid state.
[Fe(H2fsatrien)]Cl·2H2O
g
||
g
go
G
⊥
2.201
2.056
2.104
3.6
The UV–Vis band observed for H4fsatrien around 265 nm
is assigned to ␲ → ␲* transition. Another band around 360 nm
appears as a shoulder may be assigned to n → ␲* transition of phe-
nolic moiety. A prominent band in the region around 400 nm may
tentatively be assigned to the enaminone form of the ligand present
in equilibrium with the phenol-imino tautomer [30,31]. However,
all these bands have appreciably changed in the metal complexes
suggesting involvement of the ligand in complex formation. The
magnetic moment, electronic and ESR spectra of the metal com-
plexes are discussed individually.
six-coordinate complexes with Ni(II), Co(III) and Fe(III). It is there-
fore plausible that in the present Cu(II) complex, [Cu(H2fsatrien)]
(1), the ligand attains pseudo-octahedral geometry around Cu(II)
as found in the Ni(II) complex [19].
The powder ESR spectrum at room temperature (Table 3)
exhibits characteristic axial spectrum with g > g for the Cu(II)
||
⊥
complex, [Cu(H2fsatrien)] (1) indicating tetragonal symmetry with
dx ground state. The G value is less than four, which indicates
2
2
−y
that the tetragonal axes are misaligned [34–36].
3.5.1.1. Copper(II) complex, [Cu(H2fsatrien)] (1)
3.5.1.2. Cobalt(II) complex, [Co(H2fsatrien)] (2)
The mononuclear Cu(II) complex (1) exhibits very broad band
in the region 690–610 nm in DMF solution. The solid complex also
yields similar spectrum indicating similarity in the geometry in
solid and in the solution. The observed magnetic moment of the
complex (1.96 B.M.) corresponds to one unpaired electron. It is
known that Cu(II) square planar complexes derived from Schiff base
ligands absorb above 590 nm and tetrahedral complexes below
830 nm. The observed absorption of the present Cu(II) complex
in the region 690–610 nm can, therefore, be assigned to the six-
coordinate geometry around Cu(II) ion. It has been demonstrated
earlier [32,33] that the Schiff bases derived by the condensation of
triethylenetetramine with salicylaldehyde or acetylacetone form
The Co(II) complex exhibits low intensity bands at around 875
and 650 nm, characteristic of octahedral Co(II) species. The sim-
ilarity of the spectra in the solid state and in solution indicates
the similarity of the species in both the states. The details of the
magnetic moment values of Co(II) complexes in different geome-
tries have been discussed elsewhere [18]. The observed magnetic
moment value of 4.38 B.M. for the present Co(II) complex corre-
sponds to the presence of three unpaired electrons. As found in
Cu(II) complex, described above, this Co(II) complex is also six-
coordinated occupying the inner N2N2O2 compartment with all the
donor atoms coordinating to the metal ion.
Fig. 2. Proposed structures of the trivalent metal complexes.

746
S. Sarkar, K. Dey / Spectrochimica Acta Part A 77 (2010) 740–748
3.5.1.3. Mercury(II) complex, [Hg(H2fsatrien)] (3), zinc(II)
complex, [Zn(H2fsatrien)] (4)
were observed for bands in this region in the Cr(III) complexes of
similar Schiff base ligands.
The electronic spectra of Hg(II) and Zn(II) complexes do not
differ much from those of ligand spectrum. No d–d transition is
expected for Hg(II) and Zn(II) complexes due to d10 configuration.
They can show both L → M and M → L charge-transfer bands. But
in this case bands at 270 nm and 350 nm are observed and may be
assigned to the ␲ → ␲* and n → ␲* transitions of the ligand system
in the complexes. The physico-chemical data also support pseudo-
octahedral geometry for these two metal complexes where the
Schiff base, H4fsatrien functions as a dibasic hexadentate N2N2O2
donor ligand.
Considering the data available a pseudo-octahedral structure
may be proposed for these complexes in which the ligand func-
tions as a dibasic hexadentate fashion utilizing its N2N2O2 inner
compartment. The two COOH groups being remained free.
3.5.1.6. Manganese(III) complex, [Mn(H2fsatrien)]CH3COO (9)
The Mn(III) complex (9) is paramagnetic and shows magnetic
moment value 4.78 B.M. at room temperature (Table 1) indicat-
ing the presence of trivalent manganese. This value suggests the
absence of exchange or super exchange interactions.
High-spin Mn(III) complexes with octahedral geometry are
3.5.1.4. Oxovanadium(IV) complex, [VO(H4fsatrien)]SO4 (5)
The VO2+ complex (5) is paramagnetic, the ꢀeff value being
1.73 B.M., which is quite close to spin-only value for one unpaired
electron as is expected for VO2+ chelates. This normal magnetic
moment value indicates that there is no significant interaction
between neighbouring V(IV) ions [27].
The electronic spectrum of the complex (5) in nujol mull shows
one prominent maximum at about 670 nm. In addition; a few shoul-
ders (or broad/weak bands) appeared in the spectrum at about 770,
635 and 550 nm.
expected to give one charge-transfer band around 400 nm
5
(log ε = 3.5) and a spin-allowed d–d transition band, 5Eg → T2g
,
around 500 nm (log ε = 2.5). The electronic spectrum of the present
Mn(III) complex (9) measured (DMSO) in the region 250–385 nm,
considering several intense bands and shoulders. The positions of
the bands can be roughly divided into two areas, between 710–670
and 625–385 nm. The bands at high wave number are shown
as shoulder on intense charge-transfer absorptions. The absorp-
tion in the visible region at 625–385 nm can be assigned to the
5
5Eg → T2g transition, though there is the possibility that the bands
Although the electronic spectra of VO2+ complexes have been
discussed in many places [27], yet assignments of absorption bands
have been a matter of controversy. However, most of the discus-
sions are made in terms of C4v symmetry. In this symmetry three
electronic transitions are expected for the d1 VO2+ ion [37]. The
lowering of the symmetry from C4v to C2v or Cs has the effect of
removing the degeneracy in the d orbitals and thus four transitions
are predicted.
at 400 nm may be charge-transfer in origin. The splitting of the
bands is most likely due to the Jahn–Teller distortion as observed
in many complexes of Mn(III) [11]. High-spin Mn(III) complexes
always show at least one absorption in the region 800–770 nm.
The relationship of this band to the structure of the complexes
has not been clarified. We also observed a band at 675 nm and
according to Levason and McAuliffe [39] and Lever [40] such band
may be assigned to low-energy charge-transfer transition in such
chelates.
It has been observed in the present investigation that all the
bands are not well resolved into their components. The broad band
As discussed above, a pseudo-octahedral structure may be
proposed for this Mn(III) complex (9) considering all the physico-
chemical data collected. In the chelate, Mn(III) occupies the inner
N2N2O2 compartment.
at 635 nm is easily identified and may be attributed to 2B2 → B1 in
2
2
C
4v symmetry [37]. Theshoulderat 550 nmmaybedueto 2B2 → A1
transition (in C4v). The high intensity of this band may be due
to influence of some charge-transfer or intra-ligand transitions
[27]. The low-energy band observed at 770 nm may be assigned
3.5.1.7. Iron(III) complexes [Fe(H2fsatrien)]NO3·H2O (10) and
[Fe(H2fsatrien)]Cl·H2O (11)
to 2B2 → E transition. If the present VO2+ complex (5) of the lig-
2
and H4fsatrien is square pyramidal in structure like those of VO2+
complexes of ␤-diketones, they should then readily add a donor lig-
and to the metal at the vacant axial coordination site and thereby
produce a marked shift the d–d transition bands. However, the
electronic spectrum of the present VO2+ complex is found to be
solvent independent. This may be due to steric hindrance of the
ligand. Alternatively, it may so happen that in the complex the sec-
ondary amine (–NH) functionality might form a weak bond with
the vanadium atom and thus prevent the incoming donor ligand
from forming a bond.
The complex obtained from Fe(NO3)3·9H2O and H4fsatrien is
[Fe(H2fsatrien)]NO3·H2O (10) showing room temperature mag-
netic moment of 4.90 B.M. corresponding to high-spin Fe(III). On
the other hand, the reaction of FeCl3·6H2O and H4fsatrien afforded
a complex [Fe(H2fsatrien)]Cl·2H2O (11) having magnetic moment
5.23 B.M. This difference in magnetic moment values may be
due to anionic effect [41–44]. These magnetic moment values
are higher than low-spin (S = 1/2, 2T2) and lower than high-spin
(S = 5/2, 6A1) values. Similar observations were made earlier with
[Fe(sal)2trien]+ and [Fe(acac)2trien]+ and discussed [41–44]. The
electronic spectra of the complexes show bands in the regions
475–500 and 590–610 nm which may be assigned to an octahedral
environment around Fe(III). The DMSO solution of the complexes
behaves as a 1:1 electrolyte with a molar conductance of 52.1 and
49.8 ꢂ−1 cm2 mol−1, respectively for (10) and (11). The X-ray crys-
tal structure of a similar Fe(III) complex, [Fe(sal)2trien]+ is known
[41–44], which reveals an octahedral environment around Fe(III)
with all the N2N2O2 donors coordinating to the Fe(III) ion. Simi-
larly we tentatively propose an octahedral structure for the present
Fe(III) complexes [Fe(H2fsatrien)]+ (10) and (11) with Fe(III) in
the inner compartment N2N2O2 leaving the O2O2 compartment
vacant. Sinn et al. [41] have shown that the Fe(III) complexes with
hexadentate ligands derived from triethylenetetramine (trien) and
salicylaldehyde/acetylacetone (sal/acac) exhibit spin equilibrium
in solution. The band at around 500 nm was assigned to the high-
spin isomer and the ∼625 nm band due to low-spin isomer. The
appearance of these bands in the present complexes is an indication
3.5.1.5. Chromium(III) complexes, [Cr(H2fsatrien)]CH3COO·2H2O
(7) and [Cr(H2fsatrien)]Cl·2H2O (8)
The magnetic moment values, 3.82 and 3.88 B.M. found at room
temperature for the Cr(III) complexes (7) and (8) are slightly lower
(Table 1) than the spin-only values for a d3 and has been discussed
earlier [38].
The electronic spectra of the Cr(III) complexes (7) and (8) in solu-
tion (DMSO) show three absorption bands in the range 555–475 nm
(sh), 475–435 nm (ε ∼ 3500) and 400–370 nm (ε ∼ 4000–5000).
These chelates when measured in nujol mulls give almost identi-
cal spectra, especially in the range 555–385 nm. This suggests that
the environment of Cr(III) in these chelates is almost the same in
the solid as well as in the solution state. The bands observed in
the range 555–385 nm may be considered as the split components
4
4
of the T2g (Oh) and T1g(F) (Oh) terms, despite their high molar
extinction coefficients. Similar high molar extinction coefficients

S. Sarkar, K. Dey / Spectrochimica Acta Part A 77 (2010) 740–748
747
Table 4
Antimicrobial activity of the ligand and metal complexes.
Complex
Growth inhibition zone diameter (in mm)
1 (mg/mL)
1 (mg/mL)
Escherichia coli
Staphylococcus aureus
Aspergillus niger
Pencillium chrysogenum
Control DMSO
Ligand (H4fsatrien)
[Cu(H2fsatrien)] (1)
[Co(H2fsatrien)] (2)
0.0a
5a
0.0a
7a
0.0a
5a
0.0a
5a
11a
9a
10a
8a
8a
12b
14b
16b
10a
21c
12b
12b
17c
17c
10a
8a
10a
11a
[Zn(H2fsatrien)] (4)
12b
16b
8a
13b
13b
7a
12b
18c
7a
[VO(H4fsatrien)]SO4 (5)
[Cr(H2fsatrien)]CH3COO·2H2O (7)
[Cr(H2fsatrien)]Cl·2H2O (8)
[Mn(H2fsatrien)]CH3COO (9)
[Fe(H2fsatrien)]NO3·H2O (10)
[Fe(H2fsatrien)]Cl·2H2O (11)
[Co(H2fsatrien)]Cl (12)
[Co(H2fsatrien)]NO3 (13)
[Co(H2fsatrien)]ClO4 (14)
14b
11a
15b
21c
16b
12b
10a
15b
10a
14b
19c
12b
11a
9a
17c
8a
15b
20c
17c
11a
12b
a
Inactive.
Fairly active.
Decidedly active.
b
c
for the presence of spin equilibrium in [Fe(H2fsatrien)]NO3·H2O
(13) and [Fe(H2fsatrien)]Cl·2H2O (11).
Nutrient agar (NA) (peptone, beef extract, NaCl and Agar–Agar)
has been used for both bacterial and fungal media. The ligand
and the complexes have been dissolved in DMSO to make a con-
centration of 10 mg/mL in order to obtain final concentration of
1 mg/mL by proper dilution. Now to determine the antimicrobial
activities holes made on agar medium were incorporated with
0.05 mL of test solution of particular concentration and kept for
3 h at room temperature for diffusion of the ligand and its com-
plexes. Then the bacterial and fungal cultures have been incubated
at suitable temperature (37 ◦C) for 48 h. After the proper incubation,
the zones of inhibition were measured and the results are given in
Table 4.
The complexes are found more active than the corresponding
Schiff base ligand and it may be attributed to chelation theory [47].
Within the chelated metal complexes the polarity of the metal ions
are greatly reduced due to overlapping with the ligand orbitals and
the delocalization of the ␲ electrons over the whole complex is
also observed as well. These two factors are responsible for the
enhanced penetration of the metal complexes into the lipid mem-
branes as well as it blocks the metal binding sites in the enzymes
of microorganisms. Thus, by blocking the synthesis of the proteins,
the complexes actually inhibit the growth of the microorganisms
[48].
3.5.1.8. Cobalt(III) complexes, [Co(H2fsatrien)]Cl (12),
[Co(H2fsatrien)]NO3 (13) and [Co(H2fsatrien)]ClO4 (14)
All the Co(III) complexes are diamagnetic at room temperature
indicating that Co(III) is in the low-spin state. The diamagnetism
of these chelates serves as a check for the absence of any para-
magnetic Co(II) ion as impurity, and it is also indicative of their
octahedral geometry, a preferred stereochemistry for Co(III) ion.
Electronic spectral data also support this view.
All the complexes exhibit very strong absorption in the UV-
region and medium intensity absorption in the visible region. The
absorptions fall in the range 610–575, 500–495, 380–370, 305–300
and 275–270 nm. The two highest energy bands may be due to
internal ligand transitions or the charge-transfer transitions from
the ligand to metal ion. The two bands in the range 610–575
and 500–495 nm, tentatively, may be assigned as the split com-
1
ponents of the 1A1g → T1g transitions [40]. The high-energy bands
at 380–370 nm is probably due to the 1A1g → T2g transition mixed
1
with metal to ligand (t2g → ␲*) transitions [40]. All these physico-
chemical data suggest a pseudo-octahedral structure for the Co(III)
complexes (12), (13) and (14).
Linear hexadentate ligands are known to form six-coordinated
Co(III) complexes with a variety of donor atoms (viz. O/N/S). Dwyer
et al. [45] have established the six-coordinate behaviour of these
ligands towards Co(III) ion. In all the complexes two azomethine
nitrogen atoms, two secondary amine nitrogen atoms are cis- to
each other. Similar structural propositions may be extended for
the trivalent metal complexes [Cr(H2fsatrien)]+, [Mn(H2fsatrien)]+
and [Co(H2fsatrien)]+ (Fig. 2). The observed physico-chemical data
justify these formulations that the metal(III) is in N2N2O2 compart-
ment with all the donor atoms coordinating. The 1H NMR spectra of
[Co(H2fsatrien)]+ exhibited resonances similar to [Zn(H2fsatrien)]
complex, which also support this tentative structural proposi-
tion.
5. Conclusion
Some mononuclear complexes of divalent and trivalent metal
ions with a hexadentate N4O2 Schiff base ligand have been syn-
thesized and properly characterized. The ligand shows dibasic
nature offering two imine nitrogens, two amine nitrogens and
two phenolic oxygen towards the metal ions leading to octahe-
dral geometry except for UO2 and VO2+ where the same ligand
functions as neutral hexadentate and neutral tetradentate sys-
tem. The complexes are also shown to act as active antimicrobial
agents.
2+
Acknowledgements
4. Antimicrobial activities
S.S. is thankful to UGC, ERO, Kolkata for providing financial
assistance (No. F. PSW-107/09-10 (ERO) dt. 08-10-09.) and K.D.
is thankful to the UGC, New Delhi for awarding Emeritus Fellow-
ship and Financial grants to carry out this work. We are grateful to
Sophisticated Analytical Instrument Facility, Central Drug Research
Institute, Lucknow, SAIF and IICB, Kolkata for elemental analy-
The antimicrobial activities of the Schiff base ligand and its
complexes have been tested following previously published meth-
ods [46] against Staphylococcus aureus as Gram-positive bacteria,
Escherichia coli as Gram-negative bacteria and antifungal activ-
ity against the fungi Aspergillus niger and Pencillium chrysogenum.

748
S. Sarkar, K. Dey / Spectrochimica Acta Part A 77 (2010) 740–748
ses and some spectroscopic measurements. Facilities provided by
the Department of Science and Technology, Govt. of India, New
Delhi under Funds for Improvement in Science and Technology pro-
gramme are also gratefully acknowledged. We are also thankful to
Dr. P. Chaudhuri, Department of Environmental Science, University
of Calcutta for some helpful discussion. We are also grateful to the
reviewers for their valuable comments.
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