Synthesis, spectroscopic characterization, and antifungal activity of some mixed ligand complexes of Zn(II), Cd(II), and Hg(II)

Article abstract of DOI:10.1080/10426500903127540

A series of new mixed ligand complexes of Zn(II), Cd(II), and Hg(II) with citronellal thiosemicarbazone [3,7-dimethyl-6-octene-1-a1 thiosemicarbazone (LH)] and N-phthaloyl amino acids (AH) have been synthesized by the reaction of metal(II) chloride with ligands citronellal thiosemicarbazone (DOTSC) and N-phthaloyl glycine [1,3-dihydro-1,3-dioxo-2H-isoindole-2-acetic acid (A1H)] or N-phthaloyl alanine [1,3-dihydro-1,3-dioxo-(methyl)-2H-isoindole-2-acetic acid (A2H)] in 1:1:1 molar ratio in dry refluxing ethanol. All the complexes have been characterized by elemental analyses, molar conductance measurement, molecular weight measurement, IR, and multinuclear NMR (1H and 13C{1H}) spectral studies. IR, 1H, and 13C{1H} NMR spectral studies suggest the involvement of azomethine-N, thiol-S atoms of the thiosemicarbazone moiety and both carboxylate-O of N-phthaloyl amino acid moiety in coordination with central metal(II) ion, and four coordinated geometries have been assigned to these complexes. The free ligands and metal complexes have been screened for their antifungal activity against two fungal strains, Fusarium moniliformae and Macrophomina phaseolina, using the the radial growth method. The results of antifungal activity show that metal complexes show enhanced higher activity than the free ligands. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426500903127540

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Synthesis, Spectroscopic
Characterization, and Antifungal Activity
of Some Mixed Ligand Complexes of
Zn(II), Cd(II), and Hg(II)
Renu Sharma a & Meena Nagar a
a Department of Chemistry , University of Rajasthan , Jaipur, India
Published online: 03 Jul 2010.
To cite this article: Renu Sharma & Meena Nagar (2010) Synthesis, Spectroscopic Characterization,
and Antifungal Activity of Some Mixed Ligand Complexes of Zn(II), Cd(II), and Hg(II), Phosphorus,
Sulfur, and Silicon and the Related Elements, 185:7, 1526-1535, DOI: 10.1080/10426500903127540
To link to this article: http://dx.doi.org/10.1080/10426500903127540
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Phosphorus, Sulfur, and Silicon, 185:1526–1535, 2010
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500903127540
SYNTHESIS, SPECTROSCOPIC CHARACTERIZATION,
AND ANTIFUNGAL ACTIVITY OF SOME MIXED LIGAND
COMPLEXES OF Zn(II), Cd(II), AND Hg(II)
Renu Sharma and Meena Nagar
Department of Chemistry, University of Rajasthan, Jaipur, India
A series of new mixed ligand complexes of Zn(II), Cd(II), and Hg(II) with citronellal
thiosemicarbazone [3,7-dimethyl-6-octene-1-a1 thiosemicarbazone (LH)] and N-phthaloyl
amino acids (AH) have been synthesized by the reaction of metal(II) chloride with ligands
citronellal thiosemicarbazone (DOTSC) and N-phthaloyl glycine [1,3-dihydro-1,3-dioxo-2H-
isoindole-2-acetic acid (A1H)] or N-phthaloyl alanine [1,3-dihydro-1,3-dioxo-α(methyl)-2H-
isoindole-2-acetic acid (A2H)] in 1:1:1 molar ratio in dry refluxing ethanol. All the complexes
have been characterized by elemental analyses, molar conductance measurement, molecular
1
weight measurement, IR, and multinuclear NMR (1H and 13C{ H}) spectral studies. IR, 1H,
1
and 13C{ H} NMR spectral studies suggest the involvement of azomethine-N, thiol-S atoms
of the thiosemicarbazone moiety and both carboxylate-O of N-phthaloyl amino acid moiety in
coordination with central metal(II) ion, and four coordinated geometries have been assigned
to these complexes. The free ligands and metal complexes have been screened for their
antifungal activity against two fungal strains, Fusarium moniliformae and Macrophomina
phaseolina, using the the radial growth method. The results of antifungal activity show that
metal complexes show enhanced higher activity than the free ligands.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental
file.
Keywords Antifungal activity; radial growth method; thiosemicarbazone
INTRODUCTION
The mixed ligand complexes of metal ions have been extensively studied following
the recognition that they play an important role in biological processes.1–3 Mixed ligand
complexes with a metal ion bound to two different and biochemically important ligands have
aroused interest as models for metalloenzymes-substrate complexes.4,5 The physiologically
interesting mixed ligand complexes of amino acids with heavy metal ions play an important
Received 2 March 2009; accepted 17 June 2009.
The authors are greatly indebted to Prof. A. K. Bhargava and Prof. A. K. Mathur, Department of Plant
Pathology, Agriculture Research Station, Durgapura, Jaipur, for the help in antifungal screening. One of the
authors (RS) is grateful to CSIR, New Delhi, for providing a Senior Research Fellowship to her. The authors are
also thankful to the CDRI, Lucknow, for recording elemental analysis.
Address correspondence to Meena Nagar, Department of Chemistry, University of Rajasthan, Jaipur- 302
004, India. E-mail: nagar meena@yahoo.com
1526

MIXED LIGAND COMPLEXES
1527
role in biological systems and have been a subject of great interest for research.6–10 It has
been reported that zinc group metal compounds showed anti–HIV-I activities,11 and this
has provided an impetus for further studies in this field.
N-protected amino acids and thiosemicarbazones are potential organic ligands that
have aroused much interest because of their interesting bonding patterns and potential
biological applications of their metal complexes.12,13 The biological activities of thiosemi-
carbazones ligands have been attributed to their trace metal complexing abilities, and their
metal compounds have been generally found to possess enhanced therapeutic properties.14
As an extension of the work described in our previous communication,15,16 it was considered
relevant to prepare mixed ligand complexes of zinc group metal with these potential organic
ligands. The present work has the objectives of seeking more information concerning the
nature of bonding and comparative ligating capability of these ligands towards metal (II)
ions.
RESULTS AND DICUSSION
A systematic study of the reactions of metal(II) chlorides with ligands DOTSC
(LH) and N-phthaloyl glycine (A1H) or N-phthaloyl alanine (A2H) in 1:1:1 molar ratio
in anhydrous EtOH in the presence of Et3N have been carried out. The reactions can be
represented by the following equation:
EtOH
MCl2 + LH + AH + 2 Et3N−−−−−−−→[M(L)(A)] + 2 Et3N.HCl
Reflux
{Where M = Zn(II), Cd(II) and Hg(II); LH = Citronellal thiosemicarbazone;
O
C
R = H, CH }
AH =
N
CH COOH;
R
3
C
O
The analytical data of the complexes together with their molar conductance are given
in Table I. The data are consistent with the proposed formulae for the complexes. All
the complexes are insoluble in water and slightly soluble in common organic solvents
but readily soluble in DMSO and DMF. The molecular weight measurement data of these
complexes are consistent with their monomeric nature. The molar conductance data suggest
the non-electrolytic nature of complexes. All the complexes are stable at room temperature
and decompose upon heating at ∼300◦C.
IR Spectra
A study and comparison of infrared spectra of thiosemicarbazone (DOTSC), N-
phthaloyl amino acids, and their mixed ligand complexes (Table S2, available online in
the Supplemental Materials) imply that both ligands behave as a monobasic bidentate
ligand. The ν (C N) shift of the DOTSC from 1595 cm−1 to lower frequency in the
spectra of the metal complexes indicates coordination of the azomethine nitrogen atom.17
The appearance of a new band in the 448–487 cm−1 region is assigned to ν (M N) and

1528

MIXED LIGAND COMPLEXES
1529
supports coordination of nitrogen of azomethine group.18 The band having considerable
ν(C S) character, shift from 820 cm−1 in the uncomplexed DOTSC to 735–752 cm−1 from
spectra of the complexes, indicates coordination of thione/thiolato sulfur atom.19 The ν
(M S) band has been assigned in the 342–372 cm−1 range and supports coordination of the
thione/thiolato sulfur atom.20 Upon loss of the N(3) hydrogen from the thiosemicarbazone
moiety in the complex, an additional carbon–nitrogen double bond, N(3) = C(2), is formed.
This new ν (C N) vibration band is observed in the 1532−1561cm−1 region.18
In the IR spectra of N-phthaloyl amino acids, the imido νCO(sym) + νCOO(asym) and
νCOO(sym) vibrations are observed at 1700–1715 cm−1 and 1395–1400 cm−1, respectively.
The broad band appearing around ∼1700 cm−1 due to νCO(sym) + νCOO(asym) in ligands
is splits into two after complexation.21 The sharp band at 1702–1708 cm−1 and a medium
intensity band at 1578–1595 cm−1 may be due to νCO(sym) and νCOO(asym) vibrations,
respectively. The lower shift of the order of 140–168 cm−1 in the νCOO(asym) frequency
[ꢁν = νCOO(asym)—νCOO(sym)] upon complexation indicates chelating nature of the
carboxylate group of N-phthaloyl amino acids.22 The band appearing in the region 413–439
cm−1 may be due to M O vibrations.
1H NMR Spectra
The 1H NMR spectra of the [M(L)(A)] type complexes have been recorded in CDCl3
1
and DMSO-d6 (Table II). The H NMR spectra display the expected signals of different
type of protons presented in the complexes, but a comparison of the spectra of the ligand
with those of the complexes can lead to the following conclusions:
(i) The free ligand DOTSC exhibits a signal at δ 10.59 ppm due to N(3) proton. The
absence of this signal in the spectra of the complexes suggests that the proton has
been lost via thioenolization and coordination of sulfur atom.
(ii) The aldehyde hydrogen (CH N) shifts downfield from δ 7.45 ppm in the ligand
DOTSC to δ 7.52–7.81 ppm in the spectra of complexes, consistent with the formation
of a coordination band between the azomethine nitrogen and metal ion.15
(iii) The free N-phthaloyl glycine (A1H) exhibits a signal at δ 4.51 ppm due to + H,
N
N-phthaloyl alanine (A2H) exhibits singlet at δ 9.26 ppm due to carboxylate proton
(COOH), and the absence of these signals in the spectra of complexes suggests the
deprotonation of COOH group of N-phthaloyl amino acids and coordination of COO
group to metal ion.
13C NMR Spectra
The 13C NMR spectra of ligands DOTSC (LH), N-phthaloyl amino acids (AH), and
their Zn(II), Cd(II), and Hg(II) complexes were recorded in CDCl3 and DMSO-d6 (Table
III). The 13C resonance signals have been assigned according to chemical shift theory. A
considerable upfield shift (∼2–3 ppm) takes place in the position of C S (177.7 ppm,
DOTSC) and C N (148.0 ppm, DOTSC), indicating coordination through the azomethine
nitrogen and the thiol group.15,23
The 13C NMR spectra of the complexes show a downfield shift of ∼4 ppm in the
position of carboxylic carbon signal as compared to its position in the parent N-phthaloyl
amino acid, revealing bidentate nature of COO group of the ligand.15,24

1530

1531

1532
R. SHARMA AND M. NAGAR
O
C
C
O
N
CH
C
R
O
O
M
S
HC
N
N
C
NH2
(where M = Zn(II), Cd(II) and Hg(II); R=H, CH3)
Figure 1 Proposed structure formula for the complexes [M(L)(A)].
On the basis of above spectral data, the four-coordinated geometry has been suggested
for these complexes (Figure 1).
Antifungal Activity
The antifungal activity results of the compounds were compared against DMSO as the
control and are expressed as percentage inhibition versus control (Supplemental Materials,
Table S1).
CONCLUSION
The mixed ligand metal(II) complexes isolated during the present study demonstrated
that the interaction of metal(II) chloride with citronellal thiosemicarbazone and N-phthaloyl
amino acids leads to complexes with 1:1:1 stoichiometry, and they are found to be mononu-
clear. The bidentate nature of both type of ligands have been suggested on the basis of
spectral evidences. All the complexes showed enhanced antifungal activity over the parent
ligands.
EXPERIMENTAL
All the reactants and solvents used were of analytical grade. Triethylamine was
distilled over KOH pellets. Solvents were dried by conventional methods and distilled prior
to use. Elemental analyses were carried out on Elemental Vario EL III Carlo Erba 1108
analyzer. The IR spectra were recorded with KBr pellets in the 4000–200 cm−1 range on
1
1
a Shimadzu FT-IR 8400 spectrometer. The H and 13C{ H} NMR spectra were collected
in CDCl3 and DMSO-d6 solution using TMS as internal standard on a JEOL FX 300
FT-NMR spectrometer at 300.40 and 75.45 MHz frequencies for H and 13C{ H} NMR,
1
1

MIXED LIGAND COMPLEXES
1533
respectively. Sulfur was estimated gravimetrically as BaSO4, and metal contents were
determined gravimetrically by a procedure in the literature25 after digesting the organic
matter with aquaregia and then with concentrated sulfuric acid and evaporating the residue
to dryness. The ligands DOTSC16 and N-phthaloyl amino acids26 used were synthesized
by reported methods. Molar conductances were measured in 10−3M DMF solution on a
conductivity meter model 1601/E. Molecular weights of these complexes were determined
by cryoscopic method by using Backmann’s thermometer. Melting points of solids were
determined in sealed capillaries, and the decomposition temperatures of sticky solids were
determined on a melting point block.
Synthesis of Ligands
Synthesis of citronellal thiosemicarbazone (LH). Thiosemicarbazide (2.55
g, 28 mmol) was dissolved in 5% aqueous glacial acetic acid (50 mL) on a boiling water
bath. The solution was slowly added, with stirring, to a freshly prepared ethanolic solution
(50 mL) of 3,7-dimethyl-6-octenal (5 mL, 28 mmol). The reaction mixture was refluxed
on a water bath for 2 h and then kept in ice for overnight. The resulting white solid was
filtered, recrystallized from water (25 mL)/ethanol (25L) mixture, and dried over P2O5.
Yield: 90% (5.72 g); mp 58◦C; IR (cm−1): 3408s, 3265s, br (NH2); 3162s, ν(NH); 1595s,
1
ν(C N); 928w, δ(C S); 820m, ν(CS); H NMR (CDCl3, δ ppm, J in Hz): 0.98 (d, 3H,
J = 6.6, CHCH3); 1.19–1.26 & 1.32–1.34 (2m, 2H, CH2 in C-4, Hα + Hβ); 1.37–1.39
(m, 1H, CHCH3); 1.60 &1.68 (2s, 6H, (CH3)2C CH); 1.74–1.80 (m, 1H, CH2 in C-2,
Hβ); 1.94–2.12 (m, 2H, CH2 in C-5); 2.18–2.28 (m, 1H, CH2 in C-2, Hα); 5.10 (t, 1H,
CH C(CH3)2); 6.92 & 7.12 (2br s, 2H, NH2); 7.45 (t, 1H, J = 5.8, CH N); 10.59 (s, 1H,
NHC S); 13C NMR (CDCl3, δ ppm): 17.6 (C-9); 19.5 (C-10); 25.2 (C-5); 25.6 (C-8); 30.6
(C-3); 36.6 (C-4); 40.3 (C-2); 124.2 (C-6); 131.2 (C-7); 148.0 (C-1); 177.7 (C S); Anal.
Found for C11H21N3S (227.37): C, 57.95; H, 9.25; N, 18.61; S, 14.21. Calcd. C, 58.11; H,
9.31; N, 18.48; S, 14.10%.
Synthesis of N-phthaloyl amino acids (AH). An intimate mixture of finely
ground phthalic anhydride (60 mmol) and respective amino acids (60 mmol, viz., DL-
glycine or L-alanine) was heated for 30 min with stirring in an oil bath at 140–160◦C. After
cooling, the solid material was dissolved in hot MeOH (40 mL), the filtered solution was
diluted with water (40 mL), and the product was allowed to crystallize slowly, The reaction
yields colorless needle shape crystals of N-phthaloyl amino acid.
N-Phthaloyl glycine (A1H). Yield: 85% (10.46 g); mp 191–192◦C; IR (cm−1):
3163, ν(NH); 1750s, ν(CO)asym; 1700br, ν(CO)sym+ν (COO)asym; 1400w, ν(COO)sym; 1H
NMR (CDCl3, δ ppm, J in Hz): 4.49 (s, 2H, NCH2); 4.51 (s, 1H, N+H); 7.76–7.82(dd, 2H,
J1 = 5.4 Hz, J2 = 3.0 Hz, Ar-H); 7.85–7.91(dd, 2H, J1 = 5.4 Hz, J2 = 3.0 Hz, Ar-H); 13
C
NMR (CDCl3, δ ppm): 40.3 (CH2); 125.2, 134.2, 136.0 (Co, Ci & Cm of C6H4); 167.2 (CO);
170.3 (COO); Anal. Found for C10H7NO4 (205.17): C, 58.61; H, 3.46; N, 6.80. Calcd. C,
58.55; H, 3.44; N, 6.83%.
N-Phthaloyl alanine (A2H). Yield: 79% (10.38 g); mp 161–162◦C; IR (cm−1):
3424br, ν(OH); 1744s,ν(CO)asym; 1715br, ν(CO)sym+ν (COO)asym; 1395 w, ν(COO)sym
;
1H NMR (CDCl3, δ ppm, J in Hz): 1.74 (d, 3H, J = 7.2, CH3); 5.08 (q, 1H, NCH) 7.85
(m, 4H, C6H4); 9.26 (s, 1H, COOH); 13C NMR (CDCl3, δ ppm): 14.9 (CH3); 47.1 (CH);
123.5, 131.5, 133.1 (Co, Ci & Cm of C6H4); 167.2 (CO); 174.7 (COO); Anal. Found for
C11H9NO4 (219.19): C, 60.30; H, 4.17; N, 6.34. Calcd. C, 60.28; H, 4.14; N, 6.39%.

1534
R. SHARMA AND M. NAGAR
Synthesis of Complexes
3,7-Dimethyl-6-octene-1-al thiosemicarbazone (DOTSC) (1.48 g, 6.5 mmol) was
mixed with a solution of CdCl2 (1.19 g, 6.5 mmol) in anhydrous ethanol (∼ 40 mL), followed
by addition of 1,3-dihydro-1,3-dioxo-2H-isoindole-2-acetic acid (N-phthgly) (1.33 g, 6.5
mmol). After shaking the reaction mixture, triethylamine (1.8 mL, 13 mmol) was added
dropwise with constant stirring and refluxed for ∼8 h. The precipitate was filtered and
washed several times with hot ethanol and diethyl ether and dried under reduced pressure
to give a yellow colored solid (yield 82%, 2.87 g).
All other complexes of this series have been synthesized using a similar method.
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