International Journal of ChemTech Research

CODEN( USA): IJCRGG ISSN : 0974-4290

Vol.5, No.4, pp 1750-1755, April-June 2013

Synthesis, Characterization and Antimicrobial Activity

of Schiff Base Ligand Complexes of Sm(III), Gd(III) and
Dy(III) ions
S.Santhi1* and C.G. Radhakrishnan Namboori2
1
N.S.S College, Pandalam, Pathanamthitta, Kerala,India.
2
Mahatma Gandhi College, Thiruvananthapuram-695004, Kerala,India

*Corres. author: santhiprasad46@gmail.com

Phone:9447030780

Abstract: The Gd(III), Dy(III) and Sm(III) complexes of Schiff base derived from acetoacetanilide and 1,3-
diaminopropane,[MX3(LH2)], where X= Cl-, NO3-, NCS -, have been synthesized in alcohol and characterized
by elemental analysis, electrical conductance in non-aqueous solvents, spectral as well as magnetic
susceptibility measurements. In these complexes, ligand LH2 acts as a tetradentate ligand coordinating through
the two azomethine nitrogen atoms and the two enolizable carbonyl group of acetoacetanilide moiety. The molar
conductance of the complexes in DMF and DMSO are in the range of non-electrolytes. The antimicrobial
activities of the ligand and their metal complexes were screened by agar diffusion method and found that the
metal complexes have higher antimicrobial activity than the free ligand.
Key Words: Acetoacetanilide, 1,3-diaminopropane, Schiff base.

Introduction
A Schiff base ligand represents one of the most widely utilized classes of ligands in metal coordination
chemistry. Synthesis of tetradentate Schiff base ligands by reaction between diamines and a corresponding
salicylaldehyde derivative is an important reaction in organic chemistry, due to the great number of molecules
that can be generated and well-known ability of these tetradentate ligands to form stable complexes with
different cations. The literature reveals that Schiff base ligands are excellent coordinating ligands because of
the high stability of the coordination compounds, their good solubility in common solvents and the flexibility in
varying the chemical environment about the C=N group. The π system in a Schiff base often imposes a
geometrical constriction and affects the electronic structure as well [1] . The present work is the study of
Gd(III), Dy(III) and Sm(III) metal complexes of the Schiff base derived from acetoacetanilide and 1,3-
diaminopropane. Synthesis, Characterization and antimicrobial activities of above metal complexes are reported
here.

Experimental
Metal salts, acetoacetanilide, 1,3-diaminopropane and other reagents were AR grade. Solvents such as
ethanol, methanol and acetone were purified by standard procedures [2]. C,H and N were estimated by using
elemental analyser, elementar Vario EL III. The metal estimations were carried out by oxalate-oxide method [3].
The IR spectra of the Schiff base and its metal complexes were recorded on a FTIR Shimadzu
spectrophotometer in the 4000-400 cm-1 region in KBr powder. The electronic spectra of the complexes were
S.Santhi et al /Int.J.ChemTech Res.2013,5(4) 1751

recorded in HPLC grade DMF and DMSO on a Shimadzu spectrophotometer in the region of 800-200 nm.
Molar conductivity measurements were recorded on systronic conductivity meter type 304. Magnetic
measurements of the complexes were performed on a Magway MSB Mk 1 susceptibility balance at room
temperature. Thermal decomposition studies were recorded in a static nitrogen atmosphere with a heating rate of
100C/min, using diamond TG/DTA thermogravimetric/ differential thermal analyzer.
Synthesis of the ligand
The Ligand(LH2) was prepared by the condensation of acetoacetanilide and 1,3-diaminopropane in 2:1 molar
ratio by refluxing in acetone [4].
Preparation of metal complexes
The lanthanide(III) chlorides, nitrates and thiocyanates were synthesized by following the general
method. To a hot methanolic solution of the ligand LH2 (0.001 mol), a methanolic solution of the Ln(III) salt
(0.001 mol) was added dropwise with constant stirring. The pH of the mixture was adjusted to 7- 8 by adding
10% alcoholic ammonia solution and again refluxed the mixture for 10- 12 hours more. The resulting solution
was concentrated to one third and kept overnight. The precipitated metal complex was filtered, washed with
methanol and finally dried in a vacuum desiccator over calcium chloride.

Results and Discussion

All the complexes are stable at room temperature and non-hygroscopic. They are insoluble in common
organic solvents like ether, acetone, benzene, carbon tetrachloride and nitrobenzene but are freely soluble in
DMF and DMSO. Lanthanum(III) complexes are purple or reddish in colour. The analytical data and empirical
formulae of the complexes are presented in Table 1. The data indicates 1:1 molar ratio of the metal and the
ligand and the complexes can be represented as[ Ln(LH2) X3] where Ln = Sm, Gd or Dy and X = Cl-,NO3 -,
NCS -.

Table 1: Elemental and other physico- chemical data of LH2 and its complexes
M.P Found(Calcd.)%
Compound 0 Colour µeff(BM)
C M C H N Cl/S
286 Greenish 23.48 42.76 4. 44 8.38 16.35
[Sm(LH2)(Cl)3] 1.54
white (23.16) (42.55) (4.35) (8.63) (16.38)
288 Dirty 20.68 36.83 3.57 13.52
[Sm(LH2)(NO3)3] -- 1.63
white (20.63) (37.90) (3.87) (13.45
279 Dirty 21.23 43.29 4.12 13.38 12.90
[Sm(LH2)(NCS)3] 1.66
white (20.97) (43.55) (3.94) (13.67 (13.41)
294 Reddish 24.34 42.22 4.52 8.37 16.14
[Gd(LH2)(Cl)3] 7.78
yellow (23.97) (42.10) (4.30) (8.54) (16.21)
295 Reddish 21.65 37.85 3.66 13.42
[Gd(LH2) (NO3)3] -- 7.85
yellow (21.37) (37.55) (3.84) (13.33
286 Reddish 22.02 43.72 3.65 13.38 12.89
[Gd(LH2)(NCS)3] 7.14
yellow (21.72) (43.13) (3.90) (13.54 (13.29)
292 Reddish 23.96 41.43 4.65 8.71 16.42
[Dy(LH2)Cl3] 10.53
brown (24.57) (41.77) (4.27) (8.47) (16.08)
290 Light 22.06 36.98 3.63 13.25
[Dy(LH2)(NO3)3] -- 10.67
brown (21.93) (37.28) (3.81) (13.23
290 Light 22.15 42.68 3.24 13.76 13.83
[Dy(LH2)(NCS)3] 10.55
brown (22.28 ) (42.82) (3.66) (13.45 (13.19)
S.Santhi et al /Int.J.ChemTech Res.2013,5(4) 1752

Electrical conductance
The molar conductance values of 10-3M solutions of the complexes of gadolinium, dysprosium and
samarium in two non aqueous solvents, DMF and DMSO are respectively in the range of 12.8- 15.6 and 7.6-9.8
ohm-1cm2mol-1. These observed values of the metal complexes indicate the non-electrolytic nature [5].
Magnetic behaviour
The magnetic moment values of the complexes are presented in Table 1. All the lanthanide complexes
synthesized were paramagnetic and the observed magnetic moment values of Gd(III) (7.14-7.85 BM) and
Dy(III) (10.53-10.67 BM) complexes except that of Sm(III) showed only very little deviation from the
calculated values of the lanthanide ions. This indicates that the 4f electrons are not much disturbed by the
ligand field produced by the Schiff bases. The deviation of the magnetic moment values of Sm(III) complexes
(1.54-1.66 BM) could be attributed to low J-J separation, which leads to the thermal population of higher energy
levels [6,7].
Infrared spectra
The characteristic IR frequencies of the ligand LH2 and its complexes along with their assignments are
listed in Table 2. Bands due to –OH and –C=N are distinguishable and provide evidence regarding the structure
of the ligand and its bonding with metal. A band at 1591 cm-1 in the ligand is attributed to −C=N stretching
vibration. On coordination, this band is shifted to
lower frequency by 7-22 cm-1. The negative shift of this band is a clear indication of the participation of the
azomethine nitrogen atoms in complex formation[8,9,10].

Table 2: Important IR spectral bands of LH2 and its lanthanide(III) complexes

Compound ν(C=N)cm-1 ν(C- O)cm-1 ν(M-O)cm-1 ν(M-N)cm-1
LH2 1591 1251 - -
[Sm(LH2)(Cl3)] 1575 1259 414 535
[Sm(LH2)(NO3)3] 1578 1261 416 536
[Sm(LH2)(NCS)3] 1569 1262 420 524
[Gd(LH2)Cl3] 1584 1260 425 510
[Gd(LH2) (NO3)3] 1583 1258 421 510
[Gd(LH2)(NCS)3] 1576 1262 418 512
[Dy(LH2)Cl3] 1581 1261 420 524
[Dy(LH2)(NO3)3] 1582 1264 421 525
[Dy(LH2)(NCS)3] 1577 1259 416 520

This is supported by the appearance of band at 510-536 cm-1 corresponding to the stretching vibration of M–N
bond. Bands at 414-425 cm-1 correspond to M–O stretching vibrations. Band at 3305 cm-1 observed in the ligand
is due to stretching vibrations of free –OH. In the complexes, this frequency is downshifted to 3240–3280 cm-1
indicating a weakening of –OH bond due to coordination through enolic –OH. The coordination by enolic OH
group is in a different manner. The enolic oxygen was coordinated to the metal ion without deprotonation. The
stretching vibration of enolic C-O observed at 1251 cm-1 in the ligand shows a positive shift by 8-13 cm-1 in
complexes indicate bond formation[11]. The nitrate complexes of samarium(III), gadolinium(III) and
dysprosium(III) show characteristic vibrational frequencies of the coordinated nitrate ions. The infrared spectra of
nitrate complexes revealed two additional strong bands around 1430 cm-1 and 1310 cm-1 which were not present in the
ligand. These could be attributed to ν4 and ν1 vibrations, respectively, of the coordinated nitrate ion. The
magnitude of separation of these bands is around 110 cm-1, which indicates that the nitrate ion is coordinated to
the metal ion in a monodentate fashion [11]. The combination frequency observed in the region 1700-1800 cm-1
of the infrared spectrum corresponds to (ν1+ ν4) for a monodentate coordination and are in good agreement with
the suggested value of Lever et al [12]. The medium band around 1073 cm-1 due to the ν2 vibrations of the nitrate is
an additional evidence for the presence of coordinated nitrate ion [13]. In the chloride complexes the chloride
ions are also coordinated to the metal ion as evidenced by the non electrolytic nature of the complexes.
S.Santhi et al /Int.J.ChemTech Res.2013,5(4) 1753

The lanthanide thiocyanate complexes show strong IR bands around 2060-2070 cm-1 attributed to
the (C-N) stretching frequency. The position and intensity of these bands suggests the N-bonded nature of the
thiocyanate group. This lies on the boarder line for distinguishing between sulphur and nitrogen bonding in the
thiocyanate. The (C-S) bond identified in the region 780-840 cm-1 attests the above inference. The δ (NCS) is
also identified in the region 470-480 cm-1 [14].
Electronic spectra
The f orbitals in Ln3+ species are deep inside the metal; therefore, the crystal field effects are very
much smaller in the lanthanide complexes compared to those in the d series of metals[4]. The electronic spectra
of the complexes in DMSO exhibit the two spectral bands in the regions at 250-257 nm (40000-38911 cm-1) and
352-359 nm (28409-27855 cm-1), which are very close to those observed in the spectrum of the ligand.
Compared with the electronic spectrum of the ligand, there is a shift to lower frequency, which further confirms
the formation of complexes.
Thermogravimetric analysis
All complexes were studied by thermodynamic analysis from ambient temperature to 7000C in nitrogen
atmosphere. Thermal curves obtained for most of the compounds were similar in character. All complexes
decompose in a single stage and all of them start to lose mass only at around 240 °C, indicating the thermal
stability of the complex. The stability is due to the strong coordination of the tetradentate ligand with Ln(III) salt
resulting in the formation of complex. The TG/DTG plot for the thermal decomposition in air is shown in
figure. Single stage decomposition corresponds to the loss of three coordinated ions and ligand molecule
resulting in the formation of metal oxide. The final mass data obtained from TG measurement and the
theoretical value confirms the final residue as Ln2O3.
Antimicrobial activity
The ligand LH2 and some of their corresponding metal complexes were screened in vitro for their antibacterial
activity against two Gram-negative (Escherichia coli and Salmonella typhimurium) and two Gram-positive
(Bacillus subtilis and Staphylococcus aureus) bacterial strains using agarwell diffusion method using Imipenem
as standard. The antifungal activity of the ligands LH2 and some of their complexes were evaluated by agar
diffusion method against the fungi Candida Albicans and F.Oxysporium using Flucanozole as standard. The
results of antibacterial and antifungal studies are presented in Table 4 and 5. A comparative study of the ligand and
their metal complexes indicates that most of the metal complexes exhibit higher antimicrobial activity than that of
the free ligand and the control. Hence complexation increases antimicrobial activity [10,14]. The enhanced
activity of the complexes can be explained on the basis of Overtone’s concept [15] and Tweedy’s Chelation theory
[16].

Table.3 : Results of antibacterial assay (concentration used 1mg/mL of DMSO).

<10: weak, Between 10 and 16: Moderate, >16: Significant
Gram-bacteria Gram-positive
Compound
E.coli S.typhi B.subtilis S.aureus
LH2 11 14 13 12
[Gd(LH2)(NO3)3] 18 16 08 13
[Dy(LH2)(NO3)3] 14 18 17 17
[Sm(LH2)(NO3)3] 20 19 18 20
[Gd(LH2)(NCS)3] 22 21 19 19
[Dy(LH2)(NCS)3] 12 18 17 15
[Sm(LH2)(NCS)3] 25 24 21 22
SD* 32 28 31 33

*SD: standard drug-Imipenem

S.Santhi et al /Int.J.ChemTech Res.2013,5(4) 1754

Table .4: Results of antifungal assay (concentration used 1mg/mL of DMSO). <10: weak,
Between 10 and 16: Moderate, >16: Significant
Compound C.albicans F. oxysporium
LH2 16 10
[Gd(LH2)(NO3)3] 19 18
[Dy(LH2)(NO3)3] 24 20
[Sm(LH2)(NO3)3] 18 20
[Gd(LH2)(NCS)3] 16 19
[Dy(LH2)(NCS)3] 22 25
[Sm(LH2)(NCS)3] 20 18
SD* 28 32
SD*: Standard Flucanozole

Conclusion
Analytical data show that all the complexes have the composition [M(LH2)(X)3], where M = Sm(III),
Gd(III), Dy(III) and X = Cl-, NO3- and NCS-. The molar conductance values in DMF and DMSO and the
infrared spectral values show that all the complexes are non-electrolytes. Hence all the three ionic groups are
present inside the coordination sphere. In the nitrato and thiocyanato complexes the anion is coordinated
through nitrogen atom. The thermogravimetric studies reveal the absence of coordinated water molecules.
Infrared spectra of complexes reveal that LH2 behaves as a neutral tetradentate ligand coordinating through two
azomethine nitrogen and two enolic oxygen atoms. The infrared spectrum of the nitrate complexes further
attests the monodentate coordination of the nitrate group. The magnetic moment values suggest the complexes
are paramagnetic. The XRD pattern displayed only a few reflections which cannot be indexed to any crystal
system. This indicates the amorphous nature of the metal complexes. A coordination number of seven may be
assigned to the metal ion in all the complexes. The tentative structure of the complexes is represented in the
Figure 1.
X

HN NH
C N N C

H C X M X C H

C OH HO C

H3C CH3

X = Cl  , NO 3 , NCS
M= Sm(III), Gd(III), Dy(III)
Figure1. Proposed structure for the complexes

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