Synthesis, characterization and antimicrobial activity of isomeric pyridyl-tetrazole derivative ligands and their bivalent metal complexes

Article abstract of DOI:10.14233/ajchem.2015.19144

Nickel(II) and zinc(II) complexes were synthesized from bidentate isomeric pyridyl tetrazole ligands such as 2-(1-vinyl-1H-tetrazol-5-yl)pyridine (L¹), N,N-dimethyl-3-(5-(pyridin-2-yl)-1H-tetrazol-1-yl)propan-1-amine (L²), 2-(2-vinyl-2H-tetrazol-5-yl)pyridine (L³), N,Ndimethyl-3-(5-(pyridin-2-yl)-2H-tetrazol-2-yl)propan-1-amine (L⁴). All the complexes were characterized in the light of elemental analysis, FTIR, UV-visible and magnetic studies. The spectroscopic data suggested that, the ligands act as neutral and monobasic bidentate ligands and form octahedral complexes with general formula [M(L^1-4)₂Cl₂] (M = Ni(II) and Zn(II). The isomeric pyridyl-tetrazole derivative ligands and their Ni(II) and Zn(II) complexes have also been screened for their antibacterial (Bacillus subtilis, Staphylococcus aureus, Proteus vulgaris) and antifungal activities (Aspergillus Niger, Candida albicans) by MIC method.

Full text of DOI:10.14233/ajchem.2015.19144

Asian Journal of Chemistry; Vol. 27, No. 12 (2015), 4405-4410
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2015.19144
Synthesis, Characterization and Antimicrobial Activity of Isomeric
Pyridyl-Tetrazole Derivative Ligands and their Bivalent Metal Complexes
1
1
B. UMAMAHESWARA RAO , V. KRISHNA2,* and G. NAGESWARA RAO
1Department of Inorganic and Analytical Chemistry, Andhra University, Visakhapatnam-530 003, India
2Department of Chemistry, Malla Reddy Engineering College (Autonomous), Hyderabad-500 100, India
*Corresponding author: E-mail: krishnanitw2010@gmail.com; vaddadi_krishna@yahoo.com
Received: 2 March 2015;
Accepted: 21 April 2015;
Published online: 29 August 2015;
AJC-17481
Nickel(II) and zinc(II) complexes were synthesized from bidentate isomeric pyridyl tetrazole ligands such as 2-(1-vinyl-1H-tetrazol-5-
yl)pyridine (L1), N,N-dimethyl-3-(5-(pyridin-2-yl)-1H-tetrazol-1-yl)propan-1-amine (L2), 2-(2-vinyl-2H-tetrazol-5-yl)pyridine (L3), N,N-
dimethyl-3-(5-(pyridin-2-yl)-2H-tetrazol-2-yl)propan-1-amine (L4).All the complexes were characterized in the light of elemental analysis,
FTIR, UV-visible and magnetic studies. The spectroscopic data suggested that, the ligands act as neutral and monobasic bidentate ligands
and form octahedral complexes with general formula [M(L1-4)2Cl2] (M = Ni(II) and Zn(II). The isomeric pyridyl-tetrazole derivative
ligands and their Ni(II) and Zn(II) complexes have also been screened for their antibacterial (Bacillus subtilis, Staphylococcus aureus,
Proteus vulgaris) and antifungal activities (Aspergillus niger, Candida albicans) by MIC method.
Keywords: Isomeric pyridyl-tetrazole derivatives, Nickel and Zinc complexes, Antimicrobial activity.
INTRODUCTION
EXPERIMENTAL
Biologically active isomeric pyridyl tetrazole derivatives
have been under investigations as part of inorganic chemis-
try. Polyazole rings are versatile ligands1 for coordinating
transition metals, therefore synthesis of transition metal
complexes containing polyazole rings, particularly tetrazoles
and their derivatives have given enormous significance, due
to their practical applications2-4. There is an increasing inte-
rest of tetrazole derivatives for the development of ‘‘click’’
chemistry which was reported by Sharpless and co-workers5.
Conversely, tetrazole-based compounds have made known
special functionalities with interesting structures6. Tetrazole
derivatives have found applications in therapeutics as anti-
hypertensive agents7, antibiotics8 and drugs for AIDS treat-
ment9.
Even though many tetrazole containing derivatives are
available in the literature, there is always an increasing demand
for the development of novel and effective tetrazole containing
therapeutic agents. In continuation of our ongoing research
on DNA binding and cleavage activities of transition metal
complexes10, in this paper we presented the synthesis,
antimicrobial activities of Ni(II) and Zn(II) complexes which
are obtained by the reaction of pyridyl-tetrazole derivatives
which contain pendant arms like vinyl or propyl-N(CH3)2
group.
Chemicals were purchased from Sigma,Aldrich and metal
salts used in the preparation of the complexes are of reagent
grade. The solvents used in the synthesis of the ligands and
metal complexes were distilled before use. All other chemicals
were of AR grade and were used without further purification.
The elemental analysis of carbon, hydrogen and nitrogen,
contents was performed using Perkin Elmer CHNS analyzer.
The electronic absorption spectra of the complexes were
recorded on JASCOV-670 spectrophotometer in the wavelength
region of 250-1400 nm in the solid state. The FTIR spectra of
the complexes were recorded on Tensor 2 FTIR spectrophoto-
meter in the region of 4000-400 cm-1 using KBr disc. The
magnetic susceptibilities of Ni(II) complexes were measured
with a Sherwood scientific balance. Diamagnetic corrections
were calculated from Pascal’s constants. The magnetic moment
values were calculated using the relation µeff = 2.83 (χmT)1/2
B.M.
Synthesis of ligands: The preparation of L is carried as
per literature11 m.p. 221-223 °C. C, 48.98; H, 3.43; N, 47.60,
1H NMR (CD3OD): 8.56 (d, 1H, J = 7.9 Hz, pyr-H), 8.0 (d,
1H, J = 7.8 Hz, pyr-H), 7.79 (t, 1H, J = 7.8 Hz, pyr-H), 7.26 (t,
1H, J = 7.9 Hz, pyr-H), 7.1 (s, 1H, tetrazole-H) ppm.
N,N-Dimethyl-3-(5-(pyridin-2-yl)-1H-tetrazol-1-
yl)propan-1-amine(L2-L4): To the compound L (1 g, 6.8

4406 Rao et al.
Asian J. Chem.
mmol) dissolved in acetonitrile (30 mL) was added potassium
carbonate (4.6 g, 34 mmol). The resulting solution was refluxed
for 0.5 h and to hot solution was added 3-chloro-N,N-dimethyl-
propan-1-amine (3.1 g, 22 mmol). The reaction mixture was
then stirred at reflux temperature for a further 24 h.After cooling,
the solvent was removed under reduced pressure to afford a
white precipitate, which was purified by column chromato-
graphy on silica gel (ethyl acetate:hexane by the ratio of 20:80)
to give isomers L1 and L3.
λ
max (MeOH) 376 nm, ε = 40 M-1cm-1. Magnetic moment: 3.2
B.M.
[Ni(L3)2]Cl2: Pale green crystals (0.14 g, yield 32 %)Anal.
calcd. for C16H14N10NiCl2 (475.95): C, 40.38; H, 2.96; N, 29.43;
Found: C, 40.76; H, 2.98; N, 29.96 % IR (KBr, νmax, cm-1):
3245, 2945, 1648, 1594, 1496, 1196, 1147, 1023, 835, 785.
λ
B.M.
max (MeOH) 388 nm, ε = 38 M-1cm-1. Magnetic moment: 3.2
[Zn(L1)2]Cl2: Waxy cream solid (0.17 g, 56 %).
L2:White brown solid (0.55 g, yield 26 %). m.p. 72-76 °C.
Anal. calcd. for C11H16N6 (232.28): C, 56.88; H, 6.94; N, 36.18;
1H NMR (CDCl3, 300 MHz): δ 8.71 (d, 1H, J = 4.5 Hz, pyr-
H), 8.37 (d, 1H, J = 8.1 Hz, pyr-H), 7.91 (dt, 1H, J = 7.8, 1.8
Hz, pyr-H), 7.45 (dd, 1H, J = 7.5, 5.1 Hz, pyr-H), 5.12 (t, 2H,
J = 6.9 Hz, CH2N), 2.88 (t, 2H, J = 6.9 Hz, CH2), 2.42(p, 2H,
J = 6.9 Hz, CH2), 2.29 (s, 6H, N(CH3)2) ppm. 13C NMR (CDCl3,
60 MHz): δ 150.45 (CN4), 148.53, 144.66, 137.16, 123.15,
122.24, 48.24 (CH2N4), 43.56 (CH2N-(CH3)2), 26.82, ppm.
L4:White brown solid (0.55 g, yield 26 %). m.p. 66-68 °C.
Anal. calcd. for C11H16N6 (232.28): C, 56.88; H, 6.94; N, 36.18;
1H NMR (CDCl3, 300 MHz): δ 8.65 (d, 1H, J = 4.5 Hz, pyr-
H), 8.28 (d, 1H, J = 8.1 Hz, pyr-H), 7.87 (dt, 1H, J = 7.8, 1.8
Hz, pyr-H), 7.34 (t, 1H, J = 7.5, 5.1 Hz, pyr-H), 5.06 (t, 2H,
J = 6.9 Hz, CH2N), 2.82 (t, 2H, J = 6.9 Hz, CH2), 2.42(p, 2H,
J = 6.9 Hz, CH2), 2.27 (s, 6H, N(CH3)2) ppm. 13C NMR (CDCl3,
60 MHz): δ 151.35 (CN4), 149.44, 145.36, 138.08, 124.64,
122.12, 49.54 (CH2N4), 44.34 (CH2N-(CH3)2), 26.82, ppm.
Synthesis of 2-(1-vinyl-1H-tetrazol-5-yl)pyridine: The
above procedure is followed with 2-chlorovinyl (2.0 g, 24
mmol) to give L1 and L3.
C16H14N10ZnCl2 (482.64): Calc. C, 39.82; H, 2.92; N, 29.02;
Found: C, 26.92; H, 2.63; N, 17.06 %. IR (KBr, νmax, cm-1):
2945, 2823, 1610, 1565, 1548, 1453, 1058, 1015, 850, 770.
1H NMR (CDCl3): δ = 8.78 (m, 1H, pyr-H), 8.35 (m, 1H, pyr-
H), 7.95 (m, 1H, pyr-H), 7.45 (m, 1H, pyr-H), 3.49 (d, 2H, J =
6.2 Hz, vinyl CH2), 2.18 (t, 1H, J = 6.2 Hz vinyl CH) ppm. 13C
NMR (CDCl3): δ 152.15 (CN4), 149.73, 144.39, 138.14,
125.79, 124.35, 127.3 (HC, vinyl), 102.9 ppm (2H, vinyl).
[Zn(L3)2]Cl2: Waxy orange solid (0.19 g, 58 %).
C16H14N10ZnCl2 (482.64): Calc. C, 39.82; H, 2.92; N, 29.02;
Found: C, 26.92; H, 2.63; N, 17.06 %. IR (KBr, νmax, cm-1):
2965, 2833, 1612, 1568, 1548, 1453, 1058, 1015, 850, 780.
1H NMR (CDCl3): δ = 8.68 (m, 1H, pyr-H), 8.45 (m, 1H, pyr-
H), 7.95 (m, 1H, pyr-H), 7.45 (m, 1H, pyr-H), 3.49 (d, 2H, J =
6.2 Hz, vinyl CH2), 2.18 (t, 1H, J = 6.2 Hz vinyl CH) ppm. 13C
NMR (CDCl3): δ 153.15 (CN4), 149.73, 145.39, 138.14,
125.79, 124.35, 127.3 (HC,vinyl), 102.9 ppm (2H, vinyl).
[Ni(L2)2]Cl2: Pale green precipatate (0.12 g, yield 32 %)
Anal. calcd. for C22H32N12NiCl2 (594.17): C, 44.47; H, 5.43;
N, 28.29; Found: C, 44.36; H, 5.33; N, 28.96 % IR (KBr, νmax
,
cm-1): 3245, 2945, 1648, 1594, 1496, 1196, 1147, 1023, 835,
785. λmax (MeOH) 346 nm, ε = 86 M-1cm-1. Magnetic moment:
3.2 B.M.
L1: White brown needles, (0.35 g, yield 27 %). m.p. 57-
59 °C. Anal. calcd. for C8H7N5 (173.17): C, 55.48; H, 4.07; N,
40.44; 1H NMR (CDCl3, 300 MHz): δ = 8.70 (d, 1H, J = 4.8
Hz, pyr-H), 8.37 (d, 1H, J = 7.8 Hz, pyr-H), 7.86 (dt, 1H, J =
7.8, 1.5 Hz, pyr-H), 7.53 (dd, 1H, J = 6.9, 5.1 Hz, pyr-H),
5.32(t, 1H, J = 6.9, vinyl-H), 4.21-4.18 (d, 2H, J = 6.9, vinyl-
2H). 13C NMR (CDCl3, 60 MHz): δ 152.15 (CN4), 149.73,
144.39, 138.14, 125.79, 124.35, 127.3 (HC, vinyl), 102.9 ppm
(2H, vinyl).
[Ni(L4)2]Cl2: Pale green precipatate (0.13 g, yield 42 %)
Anal. calcd. for C22H32N12NiCl2 (594.17): C, 44.47; H, 5.43;
N, 28.29; Found: C, 44.34; H, 5.32; N, 28.86 % IR (KBr, νmax
,
cm-1): 3235, 2925, 1648, 1594, 1496, 1196, 1157, 1023, 835,
785. λmax (MeOH) 366 nm, ε = 52 M-1cm-1. Magnetic moment:
3.2 B.M.
[Zn(L2)2]Cl2: Waxy cream solid (0.17 g, 56 %).
C22H32N12ZnCl2 (600.86): calc. C, 43.98; H, 5.37; N, 27.97;
Found: C, 43.92; H, 5.33; N, 28.36 %. IR (KBr, νmax, cm-1):
2955, 2823, 1610, 1545, 1548, 1453, 1058, 1015, 850, 770.
1H NMR (CDCl3, 300 MHz): δ 8.71 (d, 1H, J = 4.5 Hz, pyr-
H), 8.37 (d, 1H, J = 8.1 Hz, pyr-H), 7.91 (dt, 1H, J = 7.8, 1.8
Hz, pyr-H), 7.45 (dd, 1H, J = 7.5, 5.1 Hz, pyr-H), 5.12 (t, 2H,
J = 6.9 Hz, CH2N), 2.88 (t, 2H, J = 6.9 Hz, CH2), 2.42(p, 2H,
J = 6.9 Hz, CH2), 2.29 (s, 6H, N(CH3)2) ppm. 13C NMR (CDCl3,
60 MHz): δ 150.45 (CN4), 148.53, 144.66, 137.16, 123.15,
122.24, 48.24 (CH2N4), 43.56 (CH2N-(CH3)2), 26.82, ppm.
[Zn(L4)2]Cl2: Cream solid (0.18 g, 46 %). C22H32N12ZnCl2
(600.86): Calc. C, 43.98; H, 5.37; N, 27.97; Found: C, 43.92;
H, 5.33; N, 28.36 %. IR (KBr, νmax, cm-1): 2965, 2833, 1610,
L3: White brown needles, (0.35 g, yield 27 %). m.p. 57-
58 °C. Anal. calcd. for C8H7N5 (173.17): C, 55.48; H, 4.07; N,
40.44; 1H NMR (CDCl3, 300 MHz): δ = 8.70 (d, 1H, J = 4.8
Hz, pyr-H), 8.37 (d, 1H, J = 7.8 Hz, pyr-H), 7.86 (dt, 1H, J =
7.8, 1.5 Hz, pyr-H), 7.53 (dd, 1H, J = 6.9, 5.1 Hz, pyr-H),
5.31(t, 1H, J = 6.9, vinyl-H), 4.21-4.18 (d, 2H, J = 6.9, vinyl-
2H). 13C NMR (CDCl3, 60 MHz): δ 151.15 (CN4), 149.73,
144.39, 138.14, 125.79, 124.35, 127.3 (HC, vinyl), 102.9 ppm
(2H, vinyl).
Synthesis of complexes: The appropriate ligand (L1-L4)
(1.36 mol) was dissolved in methanol (30 mol) and added to a
methanolic solution (10 mol) of MCl2·H2O (1.36 mol). The
resulting pale green to green coloured solutions were then
heated to reflux for 2-3 h. The solution was left over night at
room temperature and filtered to collect respective precipitate.
[Ni(L1)2]Cl2: Dark green solid (0.12 g, yield 28 %) Anal.
calcd. for C16H14N10NiCl2 (475.95): C, 40.38; H, 2.96; N, 29.43;
Found: C, 40.76; H, 2.98; N, 29.96 % IR (KBr, νmax, cm-1):
3245, 2945, 1648, 1594, 1496, 1196, 1147, 1023, 835, 785.
1
1545, 1548, 1453, 1058, 1015, 850, 770. H NMR (CDCl3,
300 MHz): δ 8.61 (d, 1H, J = 4.5 Hz, pyr-H), 8.37 (d, 1H, J =
8.1 Hz, pyr-H), 7.91 (dt, 1H, J = 7.8, 1.8 Hz, pyr-H), 7.45 (dd,
1H, J = 7.5, 5.1 Hz, pyr-H), 5.12 (t, 2H, J = 6.9 Hz, CH2N),
2.88 (t, 2H, J = 6.9 Hz, CH2), 2.42 (p, 2H, J = 6.9 Hz, CH2),
13
2.29 (s, 6H, N(CH3)2) ppm. C NMR (CDCl3, 60 MHz): δ

Vol. 27, No. 12 (2015)
Synthesis of Isomeric Pyridyl-Tetrazole Derivative Ligands and their Bivalent Metal Complexes 4407
151.45 (CN4), 148.53, 144.66, 137.16, 123.15, 122.24, 48.24
(CH2N4), 43.56 (CH2N-(CH3)2), 26.82, ppm.
dimethyl-[2-(5-pyridin-2-yl-tetrazol-1-yl)-ethyl]amine·HCl
and 2-chloroethanol in basic medium afford regio iosmers L1,
L2, L3 and L4 by alkylation at either the 1-N or 2-N positions
in Scheme-I. The structures for the isomers are readily assigned
Antimicrobial activity: in vitro antimicrobial activity
of the metal complexes towards the bacteria Proteus vulgaris,
Klebsiella pnuemoniae, Staphylococcus aureus and Bacillus
subtilis and fungi Candida albicans was carried out using disc
diffusion method. The antibiotics kanamycin and clotrimazole
are the standards for antibacterial and antifungal activity
studies. Standard inoculum, 1-2 × 107 cfu/mL 0.5 McFarland
bacterial growth (no turbidity) in comparison to control was
regarded as MIC.
13
1
by their C NMR and H NMR spectra. The chemical shift
values for the quaternary carbon of tetrazole ring appeared
in range about 150.1-154.7 ppm in the 1-N- and 2-N-isomers
respectively. The 1-N isomer gave the signal at 150.45 (L1)
and 152.15 (L2) ppm respectively; while the 2-N isomer gave
the signal at 151.35 (L3) and 154.77(L4) ppm respectively.
The 1H NMR spectra of L1-L4 showed separately four signals
corresponding to pyridyl protons and two triplets for the
methylene groups. A singlet is observed in the spectra of L1
and L3 at 2.29 and 2.27 ppm which indicated the presence of
six protons of -N(CH3)2 groups respectively. The methylene
protons of L1-L4 beside the tetrazole ring appeared at 5.12,
5.06, 5.08 and 4.87 ppm respectively. Presence of -N(CH3)2 in
L2 and L4 is confirmed by infrared spectra with broad peak at
1190-1058 cm-1.
RESULTS AND DISCUSSION
All the Ni(II) complexes were coloured, stable and non-
hygroscopic in nature. The complexes are insoluble in common
organic solvents but soluble in DMF and DMSO. The elemental
analysis showed that the complexes have 1: 2 stoichiometry
of the type [M(L1-4)2]·Cl2, where L stands for singly deproto-
nated ligands12.
Infrared spectra of ligands (L2 and L4) show a broad band
in range 1190-1058 cm-1 corresponding to - N(CH3)2 and peaks
at 1650-1500 cm-1. Two similar peaks around 1150-900 cm-1
corresponds to tetrazole group15. The formation of coordination
bonds between tetrazole ring and Ni(II), Zn(II) is confirmed
by observing the IR frequencies of tetrazole ring. The ligands
L1-L4 showed characteristic infrared absorption bands at 1630-
1570 cm-1 which are shifted to lower frequencies in all Ni(II)
and Zn(II) complexes. Additional peaks around 1340-1200
cm-1 and 800-600 cm-1 are appeared due to the coordination
of pyridine ring with Ni(II) and Zn(II) atom.
Determination of metal content of the complexes:
Known amount (0.150 g) of complexes was decomposed with
concentrated nitric acid. This process was repeated till the
organic part of the complexes got completely lost. The excess
nitric acid was expelled by evaporation with concentrated
sulphuric acid. The Ni(II) and Zn(II) contents of the complexes
were determined as per the procedure available in the lite-
rature13.
Spectral data
A signal at 154.9 ppm in the 13C NMR spectrum of com-
pound L indicated the formation of a 1,5-disubstituted tetrazole
and the presence of a signal at 2220 cm-1 in the IR spectrum
indicated an azide bond (N-N or N=N band)14. The 1H NMR
spectrum of L, showed the expected signals for the pyridine
ring, while the NH proton on the tetrazole has appeared as a
broad signal at 7.1 ppm. Ligand (L) on treatment with N,N-
The ligands (L1-L4) are treated with NiCl2·2H2O and
ZnCl2.2H2O salt, in methanol at reflux temperature under N2
atmosphere for 2-3 h. All reactions were carried out using a
1:2 metal: ligand stoichiometry ratio to give corresponding
complexes (1-4) in Scheme-II. Physical properties of nickel
and zinc are shown in the synthesis. Elemental analysis of the
H
N
i)
N
N
N
CN
Cl
N
N
L
ii)
CH
3
N
CH
Cl
N
3
CH
3
N
CH
N
N
N
3
+
N
N
CH
3
N
N
N
N
N
N
N
N
N
N
N
N
+
N
CH
3
N
N
L3
L1
L2
L4
Scheme-I: Synthetic route for ligands L1-L4, reaction conditions (i) NaN3, LiCl, NH4Cl, DMF, reflux 10 h; (ii) K2CO3, acetonitrile, reflux 24 h

4408 Rao et al.
Asian J. Chem.
N
N
N
N
N
L1 L3
or
MCl2, M = Ni(II), Zn(II)
Methanol
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Cl
N
Cl
N
Cl
N
Ni
Zn
N
Ni
N
N
N
Cl
Cl
+
Cl
N
N
N
Cl
N
N
N
N
Zn
N
N
N
N
N
Cl
N
N
N
N
N
[Zn(L1)2]Cl2
N
[Ni(L1)2]Cl2
N
[Ni(L3)2]Cl2
[Zn(L1)2]Cl2
CH3
N
N
N
CH3
N
N
N
CH3
CH3
N
H3C
L2 or L4
N
H3C
H3C
CH3
H3C
CH3
N
MCl2, M = Ni(II), Zn(II)
N
N
Methanol
N
N
N
N
N
N
N
N
N
Cl
N
N
N
Cl
Ni
N
N
N
N
Zn
Cl
N
N
N
Cl
N
Cl
N
N
Cl
N
Zn
N
+
N
Cl
Ni
N
N
N
N
N
N
Cl
N
N
N
CH3
N
CH3
N
N
N
N
N
N
CH3
CH3
CH3
N
CH3
[Ni(L2)2]Cl2
N
[Zn(L2)2]Cl2
H3C
[Ni(L4)2]Cl2
H3C
[Zn(L4)2]Cl2
Scheme-II: Synthesis of 1N and 2N-substituted nickel and zinc, pyridyl-tetrazole ligands tetrazole complexes (1-4)

Vol. 27, No. 12 (2015)
Synthesis of Isomeric Pyridyl-Tetrazole Derivative Ligands and their Bivalent Metal Complexes 4409
metal complexes showed that these (1-4) are in 1:2 composi-
tion. All nickel complexes have magnetic moments value
ranging 3.2 BM, slightly higher than the spin only values (2.82
µeff) expected for a d8 system with one unpaired electron16 in
Ni(II) complexes.
complexes showed two bands around 25000 and 30000 cm-1
and are attributed to the n → π* and π → π* transitions, respec-
tively. Zinc(II) complexes are in d10 configuration and diamag-
netic in nature and thus do not show any d-d transitions.
Antimicrobial activity: The minimum inhibitory concen-
trations (MIC) of the complexes compared with the ligands
and standard drugs are listed in Table-2. The results indicate
that the metal complexes displayed more antibacterial activity
compared to the parent ligands under similar experimental
conditions. The results indicate that the metal complexes
displayed more antibacterial activity compared to the parent
ligands under similar experimental conditions on same micro-
organisms except L1 and L3. However, while the remaining
ligands did not show any activity. All Ni(II) and Zn(II)
complexes showed antifungal activity. Among all the metal
complexes complex showed good activity against all bacteria
and fungi strains. Increase in the activity of the complexes
compared to that of ligands can be explained on the basis of
Overtone’s concept and Tweedy’s chelation theory. The theory
states that the polarity of the metal ion is reduced on comp-
lexation due to the partial sharing of its positive charge with
donor groups. Consequently, the positive charge is delocalized
over the whole ring, which causes the improved lipophilicity
of the compound through cell membrane of the pathogen19.
The negative results can be attributed either to the inability of
the complexes to diffuse into the bacteria cell membrane and
Electronic spectra and magnetic moments: The elec-
tronic absorption spectra of the isomeric pyridyl tetrazole metal
complexes in solid state were recorded at room temperature
and the band positions of the absorption maxima, band assign-
ments, ligand field parameters and magnetic moment values
are listed in Table-1. The electronic spectra of Ni(II) complexes
displayed three absorption bands in the range 8000-9000,
14000-16000 and 20000-24000 cm-1. Thus, these bands may
be assigned to the three spin allowed transitions 3A2g (F) →
3
3T2g (F) (ν1), 3A2g (F) → 3T1g (F) (ν2) and 3A2g (F) → T1g(P)
(ν3), respectively, characteristic of octahedral geometry. The
values of transition ratio [ν2/ν1] and β lie in the range of 1.70-
1.80 and 0.89-0.95, respectively, providing further evidence
for octahedral geometry of Ni(II) complexes17. The B values
for the complexes are lower than the free ion value, there by
indicating orbital overlap and delocalization of d-orbitals.The
β-values obtained are less than unity suggesting the covalent
character of the metal-ligand bonds. All Ni(II) complexes are
paramagnetic and the magnetic movement values at room
temperature are in the range of 3.2 B.M. which is well agreed
with the reported octahedral Ni(II) complexes18. All Zn(II)
TABLE-1
ELECTRONIC, MAGNETIC AND LIGAND FIELD PARAMETERS OF THE PYRIDYL-TETRAZOLE Ni(II) COMPLEXES
Magnetic
moment
(B.M.)
Absorption
10 Dq
(cm-1)
LFSE
Compound
[Ni(L1)2]Cl2
[Ni( L2)2]Cl2
[Ni(L3)2]Cl2
[Ni(L4)2]Cl2
Tentative assignments
B (cm-1)
966
ν2/ν1
1.78
1.82
1.76
1.89
β
maxima (cm-1)
(kJ mol-1)
3A2g(F) → 3T2g(F) (ν1)
3A2g(F) → 3T1g(F) (ν2)
3A2g(F) → 3T1g(P) (ν3)
3A2g(F) → 3T2g(F) (ν1)
3A2g(F) → 3T1g(F) (ν2)
3A2g(F) → 3T1g(P) (ν3)
3A2g(F) → 3T2g(F) (ν1)
3A2g(F) → 3T1g(F) (ν2)
3A2g(F) → 3T1g(P) (ν3)
3A2g(F) → 3T2g(F) (ν1)
3A2g(F) → 3T1g(F) (ν2)
3A2g(F) → 3T1g(P) (ν3)
8532
15200
24900
3.12
3.18
3.25
2.91
8532
8787
8313
8628
0.92
0.89
0.90
0.95
122.50
126.19
119.40
123.92
8787
16000
24390
935
8313
14705
24390
943
8628
16313
24570
999
TABLE-2
MIC VALUES OF ANTIMICROBIAL ACTIVITY OF LIGANDS AND THEIR METAL COMPLEXES (µg/mL)
Compound
L1
Bacillus subtilis
Staphylococcus aureus
Proteus vulgaris
Aspergillus niger
Candida albicans
15
12
18
10
41
35
43
35
38
33
39
33
3
14
12
16
12
46
39
46
38
40
33
40
32
–
12
12
17
12
43
36
45
36
40
39
41
38
–
13
12
18
11
49
43
48
42
45
40
43
40
2
16
-
19
-
67
52
68
50
62
55
62
54
–
L2
L3
L4
[Ni(L1)2]Cl2
[Ni(L2)2]Cl2
[Ni(L3)2]Cl2
[Ni(L4)2]Cl2
[Zn(L1)2]Cl2
[Zn(L2)2]Cl2
[Zn(L3)2]Cl2
[Zn(L4)2]Cl2
Kanamycin
Clotrimazole
5
11
7
10
–

4410 Rao et al.
Asian J. Chem.
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activity or they can diffuse and become inactivated by unknown
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Conclusion
Nickel(II) and zinc(II) complexes have been synthesized
using isomeric pyridyl-tetrazole derivative ligands and charac-
terized by various analytical and spectral data. Based on the
electronic spectra, magnetic moment and elemental analysis
data, octahedral geometry was proposed for Ni(II) and Zn(II)
complexes. The antimicrobial activity data has shown that all
complexes displayed higher activity among all other ligands.
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and U. Sheridan, Polyhedron, 33, 289 (2012); (b) A. Fleming, F.
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ACKNOWLEDGEMENTS
This work was supported by GRIET (A) for financial
assistance.
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