Structures, redox behavior, antibacterial activity and correlation with electronic structure of the complexes of nickel triad with 3-(2-(alkylthio) phenylazo)-2,4-pentanedione

Article abstract of DOI:10.1016/j.ica.2011.01.049

3-(2-(Alkylthio)phenylazo)-2,4-pentanedione (HL), an O, N, S donor ligand, is used for the synthesis of Ni(II), Pd(II) and Pt(II) complexes. The spectroscopic (IR, UV-Vis, and NMR) data determine the structure. The single crystal X-ray diffraction measurement of [Ni(L)₂] and [Pt(L)Cl] has confirmed the structures. Coulometric oxidation of [Ni(L)₂] and EPR spectra thereof show formation of Ni(III) state. DFT computation has calculated the electronic configuration and has explained the spectral and redox properties of the complexes. The compounds are screened for their in vitro anti-bacterial activity using Gram-positive and Gram-negative bacteria (Bacillus subtilis UC564, Escherichia coli TG1, Staphylococcus aureus Bang25, Pseudomonas aeruginosa C/1/7, Salmonella typhi NCTC62, Salmonella paratyphi NCTC A2, Shigella dysenteriae 8NCTC599/52, Streptococcus faecalis S2, Vibrio cholerae DN7 and Mricococcus luteus AGD1). The minimum inhibitory concentration is determined for the compounds. The effect of the structure of the investigated compounds on the antibacterial activity is discussed.

Full text of DOI:10.1016/j.ica.2011.01.049

Inorganica Chimica Acta 370 (2011) 175–186
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Structures, redox behavior, antibacterial activity and correlation with electronic
structure of the complexes of nickel triad with 3-(2-(alkylthio)phenylazo)-2,4-
pentanedione
Mrinal Kanti Paira a, Tapan Kumar Mondal a, Durbadal Ojha b, Alexandra M.Z. Slawin c, Edward R.T. Tiekink d,
Amalesh Samanta b, Chittaranjan Sinha a,
⇑
a Inorganic Chemistry Section, Department of Chemistry, Jadavpur University, Kolkata 700032, India
b Department of Pharmaceutical Technology, Jadavpur University, Kolkata 700032, India
c Department of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, UK
d Department of Chemistry, University of Malaya, Kuala Lumpur 50603, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 May 2010
Received in revised form 12 January 2011
Accepted 17 January 2011
Available online 31 January 2011
3-(2-(Alkylthio)phenylazo)-2,4-pentanedione (HL), an O, N, S donor ligand, is used for the synthesis of
Ni(II), Pd(II) and Pt(II) complexes. The spectroscopic (IR, UV–Vis, and NMR) data determine the structure.
The single crystal X-ray diffraction measurement of [Ni(L)2] and [Pt(L)Cl] has confirmed the structures.
Coulometric oxidation of [Ni(L)2] and EPR spectra thereof show formation of Ni(III) state. DFT computa-
tion has calculated the electronic configuration and has explained the spectral and redox properties of the
complexes. The compounds are screened for their in vitro anti-bacterial activity using Gram-positive and
Gram-negative bacteria (Bacillus subtilis UC564, Escherichia coli TG1, Staphylococcus aureus Bang25,
Pseudomonas aeruginosa C/1/7, Salmonella typhi NCTC62, Salmonella paratyphi NCTC A2, Shigella dysenteriae
8NCTC599/52, Streptococcus faecalis S2, Vibrio cholerae DN7 and Mricococcus luteus AGD1). The minimum
inhibitory concentration is determined for the compounds. The effect of the structure of the investigated
compounds on the antibacterial activity is discussed.
Keywords:
3-(2-(Alkylthio)phenylazo)-2,4-
pentanedione
Group 10 metals
Structure
Redox
Antibacterial activity
DFT computation
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
N@N–) is appended into acetylacetone to synthesize 3-(2-(alkyl-
thio)phenylazo)-2,4-pentanedione. We have also prepared Gr 10
The coordination behavior of transition metals with azo
(–N@N–) ligands is of interest for their -acidity, metal binding
(nickel(II), palladium(II), and platinum(II)) metal complexes with
this ligand. Two of these complexes ([Ni(L)2] and [Pt(L)Cl]) have
been structurally confirmed by X-ray diffraction studies. The struc-
ture of molecule plays significant role in determining their chem-
ical properties. DFT calculation using optimized geometry of the
molecules provides a competent method to correlate the electronic
structure and properties of the compounds. The electronic spectra
and redox properties of the complexes have been explained with
DFT computation results of the complexes. Antibacterial activity
of the ligands and the complexes has been studied against some
bacteria. The structure activity relation (SAR) of the compounds
has also been discussed in this work.
p
ability, dyes and pigmenting behavior, redox, photo-physical, cata-
lytic and biological properties [1–8]. Thus, the synthesis of ligands
incorporating –N@N– group is an important field of research. Nota-
ble examples of these ligands are arylazobenzene [9], arylazooxime
[10], arylazophenol [11], arylazopyridine [7,8,12], arylazoimidaz-
ole [13], arylazopyrimidine [14], and arylazoaniline [15]. The
ligands containing oxygen, nitrogen and sulfur donor centers have
been effectively used in modeling biomolecule, in exploring chem-
ical, electrochemical, catalytic activities and magnetic behaviors
[16–20]. In this work we report the synthesis of a ligand containing
O, N, and S donor centers with incorporation of the thioarylazo
group into acetylacetone. Acetylacetone and its derivatives have
many applications. They can be used for synthesizing metal com-
plexes either directly/functionalized molecules (condensation or
coupling with other molecules) [21–30]. Thioarylazo (R–S–C6H4–
2. Results and discussion
2.1. Synthesis and formulation
The ligands 3-(2-(alkylthio)-2-phenylazo)-2,4-pentanedione,
(alkyl (R) = Me, HL1; Et, HL2) are synthesized by coupling 2-(alkyl-
thio)phenyldiazonium chloride with acetylacetone in sodium
⇑
Corresponding author. Fax: +91 033 2413 7121.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.01.049

176
M.K. Paira et al. / Inorganica Chimica Acta 370 (2011) 175–186
R
S
-
Na+
S
SH
Metalic Na
Dry MeOH
RI
NH2
NH2
NH2
5
4
R
S
O
O
3
6
Me
Me
R
N
S
N
i) 1:1 HCl
ii) NaNO2
Me
11
in Na2CO3
+
Cl-
N
N
OH
O
Me10
HL
R = Me (HL1); Et (HL2)
O
R
N
N
R
S
S
R
Me
N
S
Ni
M
O
Me
Cl
N
O
N
O
Me
Me
N
Me
O
O
Me
M = Pd(II) (2), Pt(II) (3)
1
R = Me (a), Et (b)
Scheme 1. The ligands and the complexes.
carbonate solution. The precipitate so obtained is purified by re-
peated crystallization from aqueous ethanol (1:1, v/v) mixture
(Scheme 1). The purity of the products is checked by TLC and ele-
mental analysis.
transitions, respectively. The complexes show bands in the region
>400 nm along with intraligand charge transfer transitions
(Fig. 1). The Ni(II) complexes, [Ni(L)2] (1) show an intense (
e,
104 Mꢀ1 cmꢀ1) band at 422 nm and weak ( , 102–103 Mꢀ1 cmꢀ1
e
)
The reaction between Ni(OAc)2, 4H2O and HL is carried out in
1:2 mol ratio in methanol. Upon slow evaporation of the solution
affords shining dark green crystals of [Ni(L)2] (1). The reaction of
Pd(MeCN)2Cl2 or K2[PtCl4] with HL in 1:1 mol ratio in acetonitrile
solution has synthesised complexes, [M(L)Cl] (M = Pd(II), (2); Pt(II),
(3)). The composition of the complexes is supported by the micro-
analytical data. The complexes are soluble in chloroform, dichloro-
methane, acetonitrile, DMF, DMSO but insoluble in hexane,
benzene, toluene. Their solutions are non-conducting. At room
transitions at 520, 570 and 850 nm. The weak band at 850 nm is
attributed to symmetry forbidden d–d transition while the transi-
tions at 520 and 570 nm, are more intense than former which may
be due to metal-to-ligand charge transfer (MLCT) (vide DFT, TD-DFT
computation). Thioalkyl (–SR) group of the ligand is the reducing
temperature the effective magnetic moment (l
) of [Ni(L1)2] (1a)
and [Ni(L2)2] (1b) are 2.7 and 3.1 BM, respectively. This supports
d8 (t62ge2g ) electronic configuration of a mononuclear Ni(II) system
in octahedral symmetry. The complexes 2 and 3 are diamagnetic.
2.2. Spectral studies
Infrared spectra of the ligands (HL) exhibit a large number of
vibration and significant frequencies are
l(N@N) and l(C@O) at
1410 and 1670 cmꢀ1, respectively. In the complexes the bands
are shifted to lower frequency and bands at 1380–1400 and
1640–1650 cmꢀ1 are assigned to
l
(N@N) and
tively. The presence of stretching at 335–340 cmꢀ1 corresponds
to (M–Cl) and confirms the composition of [M(L)Cl] stoichiometry
l(C@O), respec-
l
in Pd(II) and Pt(II) complexes.
The electronic spectra of HL in chloroform show two significant
transitions at 250–255 and 370–380 nm with two shoulders at
2
2
Fig. 1. UV–Vis spectra of HL2
(
), [Ni(L )2] (1b) (—), [Pd(L )Cl] (2b) (
⎯⎯
⎯⎯
) and
2
⎯⎯
[Pt(L )Cl] (3b) (
) and. The inset picture shows the higher wavelength spectra of
275–280 and 390–400 nm which are assigned to
p–
p⁄ and n–p⁄
[Ni(L2)2] (1b) complex in CHCl3.

M.K. Paira et al. / Inorganica Chimica Acta 370 (2011) 175–186
177
Table 1
1H NMR data of HL and [M(L)Cl] in CDCl3.
Compounds
d (ppm) (J, Hz)
c
3-Ha
4-Hb
5-Hb
6-Ha
10-Hc
11-Hs
12-H
13-Hb
S-CH3
Enolic O-Hc
HL1
7.78 (8.1)
7.80 (8.2)
8.10 (8.4)
8.10 (8.4).
8.19 (8.3)
8.20 (8.3)
7.16 (7.2)
7.15 (7.5)
7.40 (7.4)
7.40 (7.3)
7.39 (7.5)
7.40 (7.5)
7.35 (7.7).
7.40 (7.7)
7.52 (7.7)
7.52 (7.6)
7.52 (7.6)
7.50 (7.5)
7.49 (7.2)
7.53 (7.6)
7.64 (7.9)
7.59 (7.6)
7.68 (7.4)
7.65 (7.2)
2.51
2.52
2.62
2.63
2.54
2.54
2.63
2.63
2.81
2.81
2.63
2.64
–
–
2.47
–
2.96
–
2.90
–
15.05
15.07
–
–
–
–
HL2
2.8d (14.6)
1.25 (7.3)
–
1.49 (7.2)
–
1.31 (7.0)
[Pd(L1)Cl] (2a)
[Pd(L2)Cl] (2b)
[Pt(L1)Cl] (3a)
[Pt(L2)Cl] (3b)
–
3.13e, 3.43e (55.0)
–
3.19e, 3.36e (57.0)
a
b
c
Doublet.
Triplet.
Singlet.
Quatret.
Sextet.
d
e
center which enhances the probability of charge transfer by MLCT
path [17]. The complexes [Pd(L)Cl] (2) show metal assisted transi-
tions at 420 and 445 nm while [Pt(L)Cl] (3) give absorption bands
at 443 and 464 nm.
gand HL2 acts as tridentate monoanionic O, N, S chelator (O, N and
S refer to enol-O, azo-N and thioether S–Et donor centers). The Ni–
N(azo) distance is comparable with reported data [32]. The Ni–S
distance is 2.4565(8) Å. The N@N distance is 1.290(3) Å. We do
not have free ligand bond length data to compare with the elec-
tronic delocalization in the complexes. However, on comparing
with free ligand data of 1-alkyl-2-(arylazo)imidazole (free ligand
data, 1.26 Å) [33] we believe that the N@N distance is significantly
The 1H NMR spectral data of the ligands, [Pd(L)Cl] (2) and
[Pt(L)Cl] (3), are given in Table 1 Free ligand, HL may exist in
keto-enol tautomeric form; a sharp resonance is observed at
15.05 ppm that is assigned to –OH frequency. On comparison with
intensity of proton signal the presence of only enolic, –(C@C–)–OH
is recommended. In the complexes, [Pd(L)Cl] (2) and [Pt(L)Cl] (3),
d(OH) is not observed which supports dissociation of the enolic
O–H and formation of the M–O bond; the –S–Me resonance is
downfield shifted by ꢁ0.5 ppm which accounts the coordination
of thioether, –S–Me, to Pd(II) (2) and Pt(II) (3). Similar observation
is also recorded for HL2. The –Me signals of acetylacetonato group
and aromatic protons of phenyl group are also downfield shifted.
This supports drifting of electron density from the metal ion (Pd(II)
and Pt(II)) upon coordination to the ligands [31].
long which may be due to charge delocalization from Ni(II) to
p-
acidic azo group. Inter- and intramolecular hydrogen bonds lead
to the formation of supramolecular chain structure (Fig. 2b). The
pendant –CO–(CH3) and azo-N (N(8)) are hydrogen bond acceptors
and coordinated –S–CH2–CH3 are hydrogen donors and they form a
hydrogen bonded 1-D chain.
2.3.2. [Pt(L2)Cl] (3b)
A view of the molecular structure of [Pt(L2)Cl] (3b) is shown in
Fig. 3a and the selected bond parameters are listed in Table 2. The
ligand forms two essentially planar five- and six-member chelate
rings with the bite angles 91.66(15)° and 87.77(12)° for N(1)–Pt–
O(2) and N(1)–Pt–S(1), respectively. The N@N bond length is
1.286(6) Å, which is shorter than in Ni(L2)2 (1.290(3)) (Fig. 2a,
2.3. Molecular structures
2.3.1. Bis-{3-(2-(ethylthio)phenylazo)-2,4-pentanedionato}nickel(II),
[Ni(L2)2] (1b)
Table 2). This implies weaker charge delocalization in d
p(Pt)–
p⁄(azo group) compared to d (Ni)–p⁄(azo group). This may be
p
The X-ray structure of [Ni(L2)2] (1b) is shown in Fig. 2a. Selected
bond lengths and bond angles are given in Table 2. The coordina-
tion environment around nickel is distorted octahedral, cis,cis-O;
trans,trans-N and cis,cis-S to NiN2O2S2 coordination sphere. The li-
due to a higher energy difference between interacting orbitals in
3b compared to 1b (see DFT–TD–DFT computation, discussed below).
The most prominent intermolecular interaction in the crystal
structure appears to be of the type C–HꢂꢂꢂCl [C(5)–
HꢂꢂꢂCl(1)i = 2.66 Å, C(5)ꢂꢂꢂCl(1)i = 3.579(6) Å with an angle at 164°
for symmetry operation i: x, ꢀ1 + y, z] which result the formation
of linear supramolecular chains (Fig. 3b) aligned along the b-axis.
2.4. Redox behavior of the complexes and electro-generation of Ni(III)
species
The complexes [Ni(L)2] (1) display a quasireversible (0.82 V (1a)
and 0.76 V (1b) and peak-to-peak separation >200 mV) one-elec-
tron redox response. Representative voltammogram is shown in
Fig. 4. The potential (E) values refer to one-electron stoichiometry
and are listed in Table 3 The redox behavior at positive to SCE is
metal centric and can be represented as in Eq. (1). DFT calculation
of [Ni(L2)2] (1b) shows that the higher energy singly occupied
molecular orbitals (SOMOs) are mainly dx2 ꢀ y2 and dz2 (138,
83%, dx2 ꢀ y2 and 139, 77%, dz2) of central metal ion, Ni(II)
(Fig. 5). Oxidation is electron extraction from highest level occu-
pied MO and thus, SOMO, 139 may participate in the redox
process.
½NiðLÞ2ꢃþ þ e ! ½NiðLÞ2ꢃ
ð1Þ
Fig. 2a. ORTEP view of Ni(L2)2 (1b) (40% probability ellipsoids).

178
M.K. Paira et al. / Inorganica Chimica Acta 370 (2011) 175–186
Table 2
Bond lengths and angles of [Ni(L2)2] (1b), [Pt(L2)Cl] (3b) and DFT generated data for 1b, [Pd(L2)Cl] (2b) and (3b).
[Ni(L2)2] (1b)
[Pt(L2)Cl] (3b)
[Pd(L2)Cl] (2b)
X-ray
DFT
X-ray
DFT
DFT
Ni(1)–N(7)
Ni(1)–O(10)
Ni(1)–S(1)
N(7)–N(8)
2.012(2)
2.021(19)
2.4565(8)
1.290(3)
90.60(8)
87.34(8)
90.60(8)
98.78(7)
83.38(7)
170.23(5)
93.26(6)
83.38(7)
98.78(7)
93.26(6)
170.23(5)
2.046
2.020
2.598
1.303
90.79
87.93
91.24
98.65
82.66
170.11
93.04
82.53
98.22
92.99
170.12
M–Cl(1)
M–S(1)
M–O(2)
M–N(1)
2.3019(15)
2.2258(13)
2.023(3)
1.960(4)
1.779(5)
1.206(7)
1.283(6)
1.286(6)
1.423(8)
2.354
2.273
2.029
2.004
1.790
1.224
1.269
1.282
1.449
93.46
88.81
179.3
177.6
87.03
90.67
2.333
2.281
2.029
2.007
1.789
1.224
1.261
1.280
1.455
92.29
90.55
179.3
177.1
87.03
90.11
N(7)i–Ni(1)–O(10)
N(7)–Ni(1)–O(10)
N(7)–Ni(1)–O(10)i
N(7)i–Ni(1)–S(1)
N(7)–Ni(1)–S(1)
O(10)–Ni(1)–S(1)
O(10)i–Ni(1)–S(1)
N(7)i–Ni(1)–S(1)i
N(7)–Ni(1)–S(1)i
O(10)–Ni(1)–S(1)i
O(10)i–Ni(1)–S(1)i
S(1)–C(1)
O(1)–C(8)
O(2)–C(9)
N(1)–N(2)
C(7)–C(9)
Cl(1)–M–S(1)
Cl(1)–M–O(2)
Cl(1)–M–N(1)
S(1)–M–O(2)
S(1)–M–N(1)
O(2)–M–N(1)
92.86(5)
87.69(11)
178.87(13)
178.91(12)
87.79(13)
91.65(16)
i
Symmetry: ꢀx, y, 1/2 ꢀ z.
Fig. 3b. H-bonded structure of C13H15ClN2O2PtS (3b) where the H-bond is C(10)–
H–Cl_b.
Fig. 2b. Inter and intra molecular H-bonding structure of Ni(L2)2 (1b).
Fig. 4. Cyclic voltammogram of [Ni(L2)2] in CH3CN–CH2Cl2 solution mixture using
Pt-working electrode, Pt-auxiliary electrode and SCE reference electrode in pres-
ence of [n-But4N](ClO4) as supporting electrolyte.
Fig. 3a. ORTEP structure of [Pt(L2)Cl] (3b) H atoms are omitted for clarity (30%
probability ellipsoids).
slow scan rate (20–100 mV sꢀ1
) DEP remains almost constant and
also the EPa and the EPc values. This observation suggests low het-
erogeneous electron-transfer rate constant which has been influ-
enced by the applied potential. This observation may reflect the
Ni(III)–Ni(II) reduction potential data are known for few com-
plexes involving thioether co-ordination [17]. The peak-to-peak
separation of the couple is largely dependent on scan rate and in-
creases from 130 mV at 50 mV sꢀ1 to 400 mV at 1000 mV sꢀ1. At

M.K. Paira et al. / Inorganica Chimica Acta 370 (2011) 175–186
179
Table 3
electronic properties of the molecules. The structures of 1b, 2b and
3b have been optimized by using DFT computation technique. The
calculated structures reproduce the experimental structures for 1b
and 3b (Table 3). The theoretical metric parameters (bond lengths
and angles) are slightly longer in the optimized structures com-
pared to the X-ray crystallographic structures. Most significant
bond length distortion is observed for Ni–S distance (elongated
by 0.14 Å compared to the X-ray structure of 1b). The N@N dis-
tance is elongated by 0.05 Å in 3b while it is 0.01 Å longer in 1b
in calculated structures than that of X-ray structures. The orbital
energies along with contributions from the ligands and metal are
given in Supplementary Materials (Tables S1–3). The features of
some selected occupied and unoccupied frontier orbitals are
shown in Fig. 6. Energy level correlations of M(O, N, S) motif is gi-
ven in Fig. 7. Two unpaired electrons of Ni(II) reside at two MOs
(abbreviated SOMO) 138 (83%, dx2 ꢀ y2; energy, ꢀ2.59 eV) and
139 (77%, dz2; energy, ꢀ2.17 eV) where orbital designation in
parenthesis represents the percentage contribution of d-function
and energy (Fig. 6). Thus these two functions are unusually nonde-
generate [34]. HOMO-2 (137) and HOMO-3 (136) are degenerate
(energy = ꢀ5.63 eV) and constituted by ligand functions (>95%).
Other filled MOs are also constituted by ligand contribution. The
LUMOs (orbitals 140, 141, etc.) are of ligand restricted functions
(contribution >95%). Mulliken spin densities around Ni(O, N, S) mo-
tif are Ni, 1.574; S, 0.145; O, 0.137; N@Nazo, 0.146e (Fig. 8). In 2b
and 3b the HOMO (energy: ꢀ6.21 eV for 2b and ꢀ6.16 eV for 3b)
is constituted by metal, chelated ligand and Cl. The contribution
of 2b: Pd, 18%; L2, 57%; Cl, 25% and 3b: Pt, 28%; L2, 37%, Cl, 35%.
The HOMO-1 (energy: ꢀ6.64 eV for 2b and ꢀ6.61 eV for 3b) also
carries both metal (12% in 2b and 18% in 3b) and ligand (2b: L2,
21%; Cl, 66% and 3b: L2, 10%, Cl, 72%). Other occupied MOs are
mainly composed of contribution from ligand (L2) and Cl except
HOMO-4 who carries >80% metal character. The LUMO (energy:
ꢀ2.67 eV (2b); ꢀ2.87 eV (3b)) has mainly ligand characteristics
(97%) of which 40% comes from azo (–N@N–) function. LUMO+1
has significant metal (>45%) and ligand contribution (L2, 40% and
Cl, 12%). Other unoccupied MOs carry mainly properties of L2.
The electronic absorption spectra have been assigned using the
time-dependent DFT method. Experimental absorption spectra of
the complexes are shown in Fig. 1 and calculated spectra are given
in Supplementary material (Figs. S1–3). The calculated excitation
wavelength and their assignment are given in Table 4. As seen,
TDDFT calculations well reproduce the absorption spectrum of
the complexes measured in chloroform.
Cyclic voltammetric data for the complexes.
Compound
Cyclic Voltammetry dataa
E (V), (DE, mV)
EM
EL
[Ni(L1)2] (1a)
[Ni(L2)2] (1b)
[Pd(L1)Cl] (2a)
[Pd(L2)Cl] (2b)
[Pt(L1)Cl] (3a)
[Pt(L2)Cl] (3b)
0.82 (220)
0.76 (230)
ꢀ0.38 (120)
ꢀ0.43 (110)
ꢀ0.52 (120)
ꢀ0.50 (120)
ꢀ0.38 (100)
ꢀ0.34 (150)
ꢀ0.76 (140)
ꢀ0.80 (160)
ꢀ1.28b
ꢀ1.28b
ꢀ1.22b
ꢀ1.20b
ꢀ1.28b
ꢀ1.35b
a
Solvent MeCN–CH2Cl2 (3:1, v/v), supporting electrolyte [Bu4N](ClO4), Pt-disk
milli working electrode, Pt-wire auxiliary electrode, Reference electrode SCE, at
298 K, EM = metal oxidation Ni(III)/Ni(II) couple, EL = ligand reductions [–N@N–]/
- -
- -
½—N —— N—ꢃꢀ and ½—N —— N—ꢃꢀ/[–N–N–] = E = 0.5 (Epa + Epc) where Epa is anodic
peak potential and Epc is cathodic peak potential,
D
Ep = |Epa ꢀ Epc|.
b
Epc.
Fig. 5. X-Band EPR of [Ni(L2)2]+ (1b+) (generated by coulometric oxidation) in
frozen acetonitrile-CH2Cl2 solution (G = 10ꢀ4 T).
change in geometry of the complex during redox transformation.
Ni(III), being a hard acid center, may develop strong covalent inter-
action with N(azo) and O(enolic) centers while Ni(II), a borderline
ion may interact with S(thioether). Thus, there will be a structural
distortion on going from [Ni(L)2] to [Ni(L)2]+ in the electrochemical
time scale. Reductive responses are observed at negative potential
to SCE; quasireversible couple at ꢀ0.3 to ꢀ0.5 V and ꢀ0.75 to
DFT and TD-DFT computation of optimized geometry of 1b has
calculated a weak transition at 758.2 nm (f, 0.0002) which is a d–
d band and in experiment the transition appears at 854 nm in
CHCl3. The calculated transition at 640.3 nm is the admixture of
- -
ꢀ0.90 V may be the description of [–N@N–]/½—N —— N—ꢃꢀ and an
- -
irreversible response at ꢀ1.3 V is assigned to ½—N —— N—ꢃꢀ/[–N–
MLCT, Ni(d
in experimental spectrum at 571 nm. Transition of 547.6 nm is
assigned to the mixture of Ni(d and L( ) ?
) ? N@N(p⁄
N@N(p⁄
which appears in the experimental spectrum at
p p) ? Ni(dp) which appears
) ? N@N(p⁄) and SMCT, S(
N–] (Table 3). Pd(II) (2) and Pt(II) (3) complexes only show reduc-
tive responses at negative to reference potential but no oxidative
response is observed.
p
)
p
Upon coulometric oxidation of [Ni(L)2] in acetonitrile-CH2Cl2
the solution turns to bluish violet due to the formation of Ni(III)
species. The tridentate nickel(III) complexes are thermally less sta-
ble and for these coulometry are performed at 258 K. Upon one-
electron reduction of the oxidized solutions Ni(II) species are
regenerated. However, we could not isolate Ni(III) complexes in
the solid state. Frozen solutions (77 K) of the Ni(III) complexes dis-
play axial EPR spectra with g\ ꢄ 2.10 and g|| ꢄ 2.02. A representa-
tive spectrum is shown in Fig. 5.
)
520 nm. A strong band is calculated at 425.5 nm while experi-
mental transition is observed at 422 nm. This is assigned to
L(
p
) ? Ni(d
p
) transition. Transitions calculated <400 nm are due
to ligand centerd transitions (
p
–
p⁄). In Pd(II), 2b and Pt(II), 3b
the transitions at longer wavelength (500–400 nm) may be con-
sidered as the combination of MLCT and XLCT [(X = Cl) ? p⁄(L)]
transitions (abbreviated in Table 4 as XLCT) along with a series
of M-to-ligand (MLCT), intraligand charge transfer (ILCT) transi-
tions, etc. They are predicted in the range between 500 and
300 nm. High intense absorption (f > 0.1) generally observes for
XLCT and ILCT transitions. In solution phase (CHCl3) the transition
energies are shifted to higher energy side which signifies prefer-
ential stabilization of occupied MOs than unoccupied MOs and
thus energy separation increases.
2.5. Theoretical calculation of electronic structure and correlation
electronic spectra, redox and magnetic properties of the complexes
Theoretical calculation using DFT computation technique is cur-
rently being used to define electronic configuration and to explain

180
M.K. Paira et al. / Inorganica Chimica Acta 370 (2011) 175–186
Fig. 6. Surface plots of some MOs of 1b, 2b and 3b along with their energy and composition.
Fig. 7. Energy correlation, composition and transition energies among MOs of 1b, 2b and 3b.
2.6. Antibacterial activity
disk diffusion method [35]. The complexes 2a and 2b are demon-
strated to be good in vitro inhibitory activity against 7 out of 10
bacterial strains used in this work. The results of the antimicrobial
activity of the compounds are shown in Table 5. Data reveal that
Antibacterial screening test of the ligands HL1/HL2 and their
metal chelates against the microorganisms initially employed the

M.K. Paira et al. / Inorganica Chimica Acta 370 (2011) 175–186
181
The results reveal that the drugs exhibit bacteriostatic but bacteri-
cidal at higher concentrations, probably due to interference by the
active principle(s) of the drugs.
The complexes 2a (12.8 ꢅ 10ꢀ8 mol) and 2b (24.7 ꢅ 10ꢀ8 mol)
exhibit separate zone of inhibition in different bacterial stains with
respect to concentration of streptomycin (50 lg/ml and 100 lg/ml)
and data are listed in Tables 6 and 7, respectively. In case of bacte-
rial stain S. paratyphi 2a does not show any zone of inhibition in
streptomycin but 2b exhibits different zone (in 50 and 100 lg/ml
exhibited 9 mm and 12 mm). The ligands do not show antibacterial
activity. The activity of metal complexes may be due to chelation of
the ligands with metal ions which reduce the polarity of the metal
ion mainly by partial sharing of positive charge with the donor
groups and possible p-electron delocalization over the whole che-
late ring enhancing the lipophilicity of the complexes. This in-
creased lipophilicity may lead to breakdown of the permeability
barrier of the cell and thus retards the normal cell processes
[36,37]. Antimicrobial activity of the complexes is compared with
standard data of Gentamicin (Table 5). Ni(II) complexes do not ex-
Fig. 8. Spin density plot in triplet state (isosurface cutoff value 0.003) of [Ni(L2)2].
Mulliken spin densities: Ni, 1.574; Sthio, 0.145; Oenolate, 0.137; N@Nazo, 0.146e.
the complex, 2a inhibits the growth of two organisms (Bacillus sub-
hibit any antimicrobial activity up to 500 lg/ml and some of the
tilis and Micrococcus luteus), as the MIC is 25
mol), and 2b inhibits the growth of three organisms (Shigella
l
g/ml (6.4 ꢅ 10ꢀ8
microbes become resistant to other complexes also. [Pd(L2)Cl]
exhibits promising activity againstS. dysenteriae, S. paratyphi, M. lu-
teus and MIC is 10 lg/ml (Tables 6 and 7). Pt(II) complexes are not
dysenteriae, Salmonella paratyphi and M. luteus), as MIC 10 lg/ml
(2.4 ꢅ 10ꢀ8 mol). We have tested 6% DMSO as control and no anti-
microbial activity has been found against these bacterial strains.
The studies on the action of 2a and 2b on two susceptible bac-
terial species (Figs. 9 and 10, respectively) at different concentra-
tions show that the growth of these organisms decreases with
increasing concentration of the complexes and are completely
inhibited at their MIC values. The minimum bactericidal concen-
tration (MBC) is found to be 4- to 8-times higher than MIC values.
promising towards antimicrobial activity. The structures and the
lability of M–Cl bond explain the trends. [Ni(L)2] is octahedral
(Figs. 2a and 2b) and does not have any vacant coordination site
to bind with bio-molecules of bacterial cell wall and requires high
energy to cleave any one of the Ni–O/N/S bonds. [M(L)Cl] are
square planar (Figs. 3a and 3b); two axial coordination sites are va-
cant and these complexes may interact with donor centers avail-
able in bio-molecules and are responsible for better anti-bacterial
Table 4
Calculated transitions obtained from TD-DFT computation of optimized geometry of [Ni(L2)2] (1b), [Pd(L2)Cl] (2b) and [Pt(L2)Cl] (3b).
Excited state
k (nm) (f ꢅ 103)
Energy (eV)
Transition
Character
Experimental (nm)
[Ni(L2)2] (1b)
1
3
758.7 (0.2)
640.3 (1.2)
1.634
1.936
(65%)125(b) ? 139(b)
(33%)122(b) ? 141(b)
(26%)123(b) ? 140(b)
Ni(d
Ni(d
Ni(d
Ni(d
p
p
p
p
) ? Ni(d
p
)
854
571
)/S(
p
p
) ? N@N(p⁄
)
)/S(
) ? Ni(d
p)
7
547.6 (1.0)
2.264
(42%)138(
(17%)137(
a
) ? 141(
a
a
)
)
) ? N@N(p⁄
)
520
a) ? 141(
L(p
L(p
L(p
L(p
) ? N@N(p⁄
)
11
17
22
425.3 (110)
388.4 (11.8)
364.5 (179.2)
2.915
3.192
3.402
(44%)135(b) ? 138(b)
(53%)136( ) ? 141(
(27%)136(b) ? 140(b)
(17%)137( ) ? 141(a)
) ? Ni(d
p
)
422
382
a
a
)
) ? N@N(p⁄
) ? N@N(p⁄
)
)
a
26
349.7 (189)
3.544
(50%)136(b) ? 140(b)
L(p
) ? N@N(p⁄
)
[Pd(L2)Cl] (2b)
1
2
3
496.5(0.0)
435.3(12.5)
418.1(58.4)
2.4968
2.8481
2.9651
(85%)HOMO ? LUMO+1
(60%)HOMO-1 ? LUMO+1
(33%)HOMO-4 ? LUMO+1
(29%)HOMO ? LUMO
(43%)HOMO-4 ? LUMO+1
(30%)HOMO ? LUMO
(43%)HOMO-3 ? LUMO
(23%)HOMO-2 ? LUMO+1
(23%)HOMO-6 ? LUMO
(23%)HOMO-5 ? LUMO+1
(40%)HOMO-7 ? LUMO
(39%)HOMO ? LUMO+3
L/Cl ? Pd/L(p⁄
Cl ? Pd/L(p⁄
d ? d, Pd ? L(p⁄
L(
) ? L(p⁄
d ? d, Pd ? L(p⁄
)
)
441
420
)
)
p
)
5
395.6(33.3)
336.6(145.7)
291.8(71.9)
3.1340
3.6833
4.2487
L(
Cl/L(
p
) ? L(p⁄
)
10
15
p
) ? L(p⁄
)
354
269
L(p
L(p
L(p
) ? Pd/L(p⁄
)
) ? L(p⁄
) ? Pd/L(p⁄
)/L(
) ? L(p⁄
)
)
18
23
275.2(38.4)
260.0(115.6)
4.5046
4.7681
Pd(d
L(
p
p
) ? L(p⁄
)
)
p
[Pt(L2)Cl] (3b)
1
2
6
462.0(63.9)
422.9(0.5)
348.9(46.5)
2.6834
2.9317
3.5540
(84%)HOMO ? LUMO
Pt(d
Cl ? L(p⁄) 443
Cl ? Pt/L(p⁄
Cl/L(
) ? L(p⁄
Cl ? Pt/L(p⁄
Cl/L(
) ? L(p⁄
d ? d, Pt(d
Pt(d )/Cl/L(
L(
) ? L(p⁄
p
)/Cl/L(
p
) ? L(p⁄
)
464
363
(80%)HOMO-1 ? LUMO
(42%)HOMO-1 ? LUMO+1
(41%)HOMO-3 ? LUMO
(43%)HOMO-1 ? LUMO+1
(26%)HOMO-3 ? LUMO
(73%)HOMO-4 ? LUMO+1
(87%)HOMO ? LUMO+3
(73%)HOMO-2 ? LUMO+1
)
p
)
)
7
343.2(52.8)
3.6116
)
p
9
14
18
330.0(35.5)
285.7(60.5)
270.9(49.3)
3.7570
4.3395
4.5763
p
p
)
) ? L(p⁄
)
p
) ? L(p⁄
)
278
p

182
M.K. Paira et al. / Inorganica Chimica Acta 370 (2011) 175–186
Table 5
Antibacterial activities of the compounds.*
Name of bacteria
Minimum inhibitory concentration (MIC) (lg/ml)
HL1
HL2
[Ni(L1)2] (1a)
[Ni(L2)2] (1b)
[Pd(L1)Cl] (2a)
[Pd(L2)Cl] (2b)
[Pt(L1)Cl] (3a)
[Pt(L2)Cl] (3b)
Gentamicin
Shigella dysenteriae
Escherichia coli
Salmonella typhi
Salmonella paratyphi
Bacillus subtilis
Pseudomonas aeruginosa
Streptococcus faecalis
Micrococcus luteus
Staphylococcus aureus
Vibrio cholerae
500
_
_
_
_
_
_
_
_
_
500
_
500
_
_
_
300
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
_
50
400
500
50
25
_
10
_
500
10
25
_
500
10
25
300
_
500
_
_
_
_
_
_
_
_
_
_
_
_
_
_
2
1
1
1
1
64
1
4
1
_
25
50
500
300
_
300
_
_
_
1
‘–’ Shows no antimicrobial activity upto 500
No inhibition was found even upto 6% DMSO that was used as control. While complex solution were prepared in 4% DMSO solution.
l
g/ml.
*
Fig. 9. Effect of 2a on two bacteria at different concentrations.
Table 6
Different concentration of drug 2a exhibit different zone of inhibition in different
bacterial strains with respect to streptomycin.*
Name of Organisms Diameter of zone of
inhibition (in mm) of
Diameter of zone of
inhibition (in mm) of
streptomycin in different
concentration
drug in different
concentration
50 (lg/ml) 100 (lg/ml) 50 (lg/ml) 100 (lg/ml)
Bacillus subtilis
Micrococcus luteus
11 0.33 13 0.16
14.5 0.28 16 0.33
18 0.33
21 0.66
20.5 0.28
26 0.33
*
Values are in terms of mean SEM of results done in triplicate.
3. Conclusion
3-(2-(Alkylthio)phenylazo)-2,4-pentanedione (HL) is used for
the synthesis of [Ni(L)2], [Pd(L)Cl] and [Pt(L)Cl]. The complexes
are characterized by spectroscopic techniques and single crystal
X-ray diffraction measurement in case of nickel(II) and plati-
Fig. 10. Effect of 2b on two bacteria at different concentrations.
num(II) complexes. Ni(II) complexes show
a high potential
activity. Both palladium(II) and platinum(II) ions strongly prefer
nitrogen and oxygen donor atoms [38] available in the bio mole-
cules. Due to very low reacting equilibrium constants for Pt(II)
complexes and their kinetic inertness compared to Pd(II) com-
plexes (105 times slow) [39], the interaction of Pt(II) complexes
is much slower than the isostructural Pd(II) complexes.
Ni(III)/Ni(II) redox couple. The electronic properties are explained
by DFT computation. Antibacterial properties of the ligands and
the complexes have been examined. The ligands are inactive and
[Pd(L)Cl] show the highest activity in the family of nickel triad.
The structural difference of octahedral [Ni(L)2] and square planar,
[M(L)Cl] account for the antibacterial efficiency of the compounds.

M.K. Paira et al. / Inorganica Chimica Acta 370 (2011) 175–186
183
Table 7
MeI (1.45 ml, 23 mmol) was added at cold condition and was stir-
red for another 30 min. The mixture was then refluxed for 2 h; the
color of the solution changed to red. The mixture was then poured
into large volume of water, a gummy mass separated and it was
extracted with benzene (15 ml ꢅ 3) and washed with water
(25 ml ꢅ 4). Benzene was then removed using a rotary evaporator.
The gummy mass was dissolved in 1:1 HCl (10 ml) and cold solu-
tion of NaNO2 (1.8 g in 10 ml water) was added in drops at 0 °C
(ice bath). The resulting mixture was then added in drops to the
solution of Na2CO3 (6 g in 30 ml water) and acetylacetone
(2.34 ml, 0.023 mol). A yellow-orange precipitate was obtained;
it was filtered and washed with cold water and dried over CaCl2.
Recrystallization from aqueous-ethanol solution (1:3 v/v) gave
the desired product 4.75 g (81.9%), m.p. 121 °C. Microanalytical
data: Anal. Calc. for C12H14N2O2S: C, 57.58; H, 5.64; N, 11.19.
Different concentration of drug 2b exhibit different zone of inhibition in different
bacterial strains with respect to streptomycin.*
Name of Organisms
Diameter of the
Diameter of the
inhibition zone (in mm)
of streptomycin in
inhibition zone (in mm)
of drug in different
concentration
different concentration
50 (l
g/
100 (
l
g/
50 (l
g/ml) 100 (
lg/
ml)
ml)
ml)
Shigella dysenteriae
Salmonella paratyphi
Micrococcus luteus
Bacillus subtilis
Staphylococcus
aureus
13 0.16
0.44
16 0.28
9.5 0.28
16 0.16
12 0.88
21 0.33
13 0.44
12 0.57
5
13.5 0.28
5
9
21 0.16
26
15.5 0.28 20 0.16
12 0.44 16
8
0.76
9
0.16
*
Values are in terms of mean SEM of results done in triplicate.
Found: C, 57.30; H, 5.67; N, 11.06%. IR data (KBr disk) (l
, cmꢀ1):
1671(s), 1626(m), 1506, 1357, 1319. kmax (nm,
e
ꢅ 10ꢀ3
,
molꢀ1 cmꢀ1): 397(18.3); 380(21.3); 275(8.82); 253(15.0).
The M–Cl bond lability, Pd–Cl ꢆ Pt–Cl, may explain the highest
antibacterial efficiency of [Pd(L)Cl]. Among the organisms tested
M. luteus is most susceptible to the drugs. Further pharmacological
and clinical studies are in progress to understand the mechanism
and the actual efficacy of these compounds in treating various
infections and skin diseases.
4.3.2. 3-(2-(Ethylthio)phenylazo)-2,4-pentanedione, HL2
HL2 was also prepared by the same procedure. Yield was 4.37 g
(85%), m.p. 101 °C. Microanalytical data: Anal. Calc. C13H16N2O2S:
C, 59.05; H, 6.10; N, 10.59. Found: C, 60.09; H, 6.08; N, 10.33%. IR
data (KBr disk) (l
, cmꢀ1): 1673(s), 1627(m), 1507, 1358, 1321. kmax
(
e
ꢅ 10ꢀ3
,
molꢀ1 cmꢀ1): 396(14.3); 374(17.6); 277(5.63);
4. Experimental section
253(12.6).
4.1. Materials
4.3.3. Preparation of bis-{3-(2-(methylthio)phenylazo)-2,4-
pentanedionato}nickel(II), [Ni(L1)2] (1a)
Acetylacetone (Hacac), 2-aminothiophenol, iodomethane (MeI),
iodoethane (EtI), Ni(OAc)2ꢂ4H2O were purchased from E. Merck, In-
dia. PdCl2 and K2[PtCl4] were purchased from Arrora Mathey, Kolk-
ata, India. All other chemicals used were of A.R. quality and were
used as received. The organic solvents were purified and dried by
standard methods [40]. 2-(Alkylthio)aniline was prepared by the
reported procedure [41].
To Ni(OAc)2,4H2O (0.060 g, 0.240 mmol) solution in methanol
(15 ml) the ligand, HL1 (0.120 g, 0.480 mmol) was added. Stirring
was continued for half an hour, the color changed to bluish green.
The solution was filtered and left undisturbed for a week; bluish
green crystals deposited at the bottom of the container. These were
collected by filtration, washed with MeOH–water (1:1 v/v) and fi-
nally with hexane. Yield, 0.085 g (63%). [Ni(L2)2] (1b) was prepared
by the same procedure. Yield, 0.088 g (59%).
4.2. Physical measurements
Microanalytical data: Anal. Calc. for C24H26N4O4S2Ni (1a): C,
51.32; H, 4.70; N, 10.05. Found: C, 51.42; H, 4.72; N, 9.94%. IR data
UV–Vis spectra were recorded using a Perkin–Elmer Lambda 25
, cmꢀ1): 1650, 1538, 1355, 1290. kmax
(
e
ꢅ 10ꢀ3
,
UV–Vis spectrophotometer and infrared spectra (4000–200 cmꢀ1
)
(KBr disk) (
l
molꢀ1 cmꢀ1): 852(0.038); 576(0.159); 519(0.295); 422(16.99);
382(14.33); 278(21.02). Anal. Calc. for C26H30N4O4S2Ni (1b): C,
53.55; H, 5.17; N, 9.57. Found: C, 53.60; H, 5.20; N, 9.50%. IR data
were obtained from a Perkin–Elmer Spectrum RX1 instrument.
Microanalyses were collected on a Perkin–Elmer 2400 CHN ele-
mental analyzer. 1H NMR spectra were recorded in a Bruker
300 MHz FT-NMR. Room temperature magnetic moment was mea-
sured using a Magnetic Susceptibility Balance, Sherwood Scientific
Cambridge, UK. The experimental susceptibilities were corrected
for the diamagnetism of the constituent atoms (Pascal tables). Mo-
lar conductance (KM) was measured in a Systronics conductivity
meter 304 model using ca. 10ꢀ3 M solutions in acetonitrile. Electro-
chemical measurements were performed using computer-con-
trolled PAR model 250 VersaStat electrochemical instruments
with Pt-disk electrodes. All measurements were carried out under
nitrogen environment at 298 K with reference to SCE in acetonitrile
using [nBu4N][ClO4] as supporting electrolyte. The reported poten-
tials are uncorrected for junction potential. EPR spectra were mea-
sured in MeCN–CH2Cl2 solution at room temperature (298 K) and
liquid nitrogen temperature (77 K) using a Bruker EPR spectrome-
ter model EMX 10/12, X-band ER 4119 HS cylindrical resonator.
(KBr disk) (
l
, cmꢀ1): 1649, 1540, 1358, 1294. kmax
(e
ꢅ 10ꢀ3
,
molꢀ1 cmꢀ1): 854(0.084); 571(0.367); 520(0.719); 422(33.84);
382(28.38); 285(34.78).
4.3.4. Preparation of chloro-{3-(2-(methylthio)phenylazo)-2,4-
pentanedionato}palladium(II), [Pd(L1)Cl] (2a)
PdCl2 (0.065 g, 0.368 mmol) was dissolved by refluxing in 20 ml
acetonitrile, an orange color solution resulted. To this solution HL1
(0.092 g, 0.370 mmol) in acetonitrile (10 ml) was added in drops
with stirring. The mixture was refluxed for 4 h. A silky yellow pre-
cipitate appeared on cooling. The solution was concentrated on a
rotary vacuum evaporator to 10 ml; the solid was filtered off,
washed with cold acetonitrile and then n-hexane and dried. Yield,
0.092 g (64%). The other complex was prepared by the same proce-
dure. The yield, 0.087 g (67%).
Microanalytical data: Anal. Calc. for C12H13N2O2SClPd (2a): C,
36.85; H, 3.35; N, 7.16. Found: C, 36.90; H, 3.42; N, 7.21%. IR data
4.3. Synthesis
(KBr disk) (l
, cmꢀ1): 1667, 1532, 1369, 1327, 1301, 334. kmax
4.3.1. 3-(2-(Methylthio)phenylazo)-2,4-pentanedione, HL1
To a cold solution of 2-aminothiophenol (2.9 g, 23 mmol) in
ethanol (50 ml) sodium (0.54 g, 23 mmol) was slowly added with
stirring for 1 h. The color changed to orange from yellow. Then
(
e
ꢅ 10ꢀ3
,
molꢀ1 cmꢀ1): 442(9.84); 420(12.45); 360(5.93);
269(22.90); 246(17.66). Microanalytical data: Anal. Calc. for
C
13H15N2O2SClPd (2b): C, 38.54; H, 3.73; N, 6.91. Found: C,
38.49; H, 3.80; N, 6.83%. IR data (KBr disk) (
l
, cmꢀ1): 1367, 1329,

184
M.K. Paira et al. / Inorganica Chimica Acta 370 (2011) 175–186
1301, 335. kmax
354(8.74); 269(34.08); 246(31.33).
(
e
ꢅ 10ꢀ3, molꢀ1 cmꢀ1): 441(14.97); 420(18.20);
Structure (Rigaku Corp., 2004). The structure was solved by the di-
rect-methods using SHELXS-97 [42] and successive difference Fourier
syntheses. Data processing and empirical absorption correction for
3b were accomplished with the programs CRYSTAL CLEAR [43] and AB-
SCOR [44], respectively. The structure was solved by heavy-atom
methods [45], the non-hydrogen atoms were refined with aniso-
tropic displacement parameters, and the hydrogen atoms were
fixed geometrically and refined using the riding model approxima-
tion. The molecular graphics were carried out using ORTEP-3 for
Windows [46] and PLATON-99 [47] programs. The residual electron
density is in the range 0.92 and ꢀ0.69 e Åꢀ3 for 1b and 1.40 to
ꢀ1.36 e Åꢀ3 for 3b.
4.3.5. Preparation of chloro-{3-(2-(methylthio)phenylazo)-2,4-
pentanedionato}platinum(II), [Pt(L1)Cl] (3a)
K2PtCl4 (0.11 g, 0.25 mmol) was dissolved in acetonitrile–water
(15 ml, 1:2, v/v) by refluxing, a light orange color developed. HL1
(0.066 g, 0.26 mmol) in acetonitrile (10 ml) was added to this solu-
tion and refluxed for another 8 h. The resultant yellow color solu-
tion was filtered and kept undisturbed. After a week, yellow
crystals suitable for X-ray diffraction were collected. Yield,
0.061 g (48%). The other complex was prepared by the same proce-
dure. Yield, 0.062 g (53%).
Microanalytical data: Anal. Calc. for C12H13N2O2SClPt (3a): C,
30.04; H, 2.73; N, 5.84. Found: C, 29.92; H, 2.84; N, 5.95%. IR data
4.5. Computation
(KBr disk) (
l
, cmꢀ1): 1668, 1324, 1295, 338. kmax
(
e
ꢅ 10ꢀ3
,
Full geometry optimizations of the complexes were carried out
using the density functional theory method at the B3LYP level [48].
All elements except Ni, Pd and Pt were assigned the 6-31G(d) basis
set. The SDD basis set with effective core potential was employed
for the Pd and Pt atoms [49] and LanL2DZ with effective core po-
tential for Ni atom. The vibration frequencies were calculated to
ensure that the optimized geometries represent the local minima
and there are only positive eigen values. All calculations were per-
formed with GAUSSIAN03 program package [50] with the aid of the
GAUSSVIEW visualization program [51]. Vertical electronic excitations
based on B3LYP optimized geometries were computed using
the time-dependent density functional theory (TD–DFT) formalism
[52] in chloroform using conductor-like polarizable continuum
model (CPCM) [53]. GAUSSSUM [54] was used to calculate the
fractional contributions of various groups to each molecular
orbital.
molꢀ1 cmꢀ1): 463(3.51); 443(3.99); 349(4.96); 272(6.54);
246(7.84). Microanalytical data: Anal. Calc. for C13H15N2O2SClPt
(3b): C, 31.62; H, 3.06; N, 5.67. Found: C, 31.58; H, 3.03; N,
5.73%. IR data (KBr disk) (l
, cmꢀ1): 1668, 1499, 1371, 1354,
1289, 340. kmax
363(13.65); 251(16.65).
(e
ꢅ 10ꢀ3, molꢀ1 cmꢀ1): 464(5.45); 443(6.09);
4.4. Crystal structure analysis of bis-{3-(2-(ethylthio)phenylazo)-2,4-
pentanedionato}nickel(II), [Ni(L2)2] (1b) and chloro-{3-(2-
(ethylthio)phenylazo)-2,4-pentanedionato}platinum(II), [Pt(L2)Cl]
(3b)
The crystals were grown by slow evaporation of the reaction
mixture over a week. Data were collected in 2h range, 6.4 to
50.7° with a Bruker CCD diffractometer using fine-focus sealed
graphite-monochromatized Mo K
a radiation (k = 0.70930 Å) at
125(2) K for
a
crystal of [Ni(L2)2] (1b) with dimensions
0.30 ꢅ 0.30 ꢅ 0.29 mm3. In case of [Pt(L2)Cl] (3b) intensity data
were measured in 2h range 5.4 to 53.0° at 153(2) K on a Rigaku
AFC12/Saturn724 CCD fitted with graphite-monochromatized Mo
4.6. Antibacterial assays
4.6.1. Microorganisms
The microorganisms used in this study included B. subtilis
UC564, Escherichia coli TG1, Staphylococcus aureus Bang25, Pseudo-
monas aeruginosa C/1/7, S. typhi NCTC62, S. paratyphi NCTC A2,
S. dysenteriae 8NCTC599/52, Streptococcus faecalis S2, Vibrio chol-
erae DN7 and M. luteus AGD1. They were obtained from Division
of Microbiology, Dept. of Pharmaceutical Technology, Jadavpur
University, Kolkata-700 032, and West Bengal, India. The bacterial
strains were grown in blood agar or MacConkey agar plates at 37 °C
and maintained on nutrient agar slants.
Ka radiation (k = 0.71070 Å) for an olive-green crystal with dimen-
sions 0.10 ꢅ 0.20 ꢅ 0.30 mm3. Crystallographic data and structure
refinement parameters are given in Table 8. Omega scans were
used for 3b. For 1b, data reduction was carried out using Crystal
Table 8
Crystallographic data for [Ni(L2)2] (1b) and [Pt(L2)Cl] (3b).
Crystal parameters
[Ni(L2)2] (1b)
[Pt(L2)Cl] (3b)
Empirical formula
Formula weight
Crystal system
Space group
Unit cell dimensions
a (Å)
C
26H30N4NiO4S2
C13H15ClN2O2PtS
493.87
monoclinic
C2/c
585.37
monoclinic
C2/c
4.6.2. Preparation of inoculums
Suspensions of organisms were prepared as per McFarland
Nephelometer standard [48]. A 24 h old culture was used for the
preparation of bacterial suspension in a sterile isotonic solution
of sodium chloride (0.9% w/v) and the concentration was
approximately 1.5 ꢅ 108 cells/ml. It was obtained by adjusting
the optical density of the bacterial suspension to that of a solution
of 0.05 ml of 1.175% of barium chloride and 9.95 ml of 1% sulfuric
acid.
24.355(2)
8.5168(8)
15.1757(14)
123.416(2)
2627.5(4)
4
19.367(5)
10.588(3)
14.753(3)
100.198(6)
2977.4(13)
8
b (Å)
c (Å)
b (°)
V (Å3)
Z
Dcalc (Mg/m3)
1.480
0.938
2.204
9.746
l
(Mo K
a
) (mmꢀ1
)
F(0 0 0)
1224
1872
T (K)
Total data
125(2)
11193
2410
171
0.045
153(2)
16123
3084
183
0.029
4.6.3. Drug solution
The compounds (10 mg) HL1 (0.04 mmol), HL2 (0.04 mmol),
[Ni(L1)2] (1a) (0.02 mmol), [Ni(L2)2] (1b) (0.02 mmol), [Pd(L1)Cl]
(2a) (0.027 mmol), [Pd(L2)Cl] (2b) (0.024 mmol), [Pt(L1)Cl] (3a)
(0.02 mmol), [Pt(L2)Cl] (3b) (0.02 mmol) were screened for their
antibacterial activity. All the drugs were dissolved in 4% of DMSO
to get the concentration of 1 mg/ml, which were used as stock
solution. Evaluation of the activity was carried out by agar dilution
technique using nutrient agar medium.
Unique data
Parameters
Ra
b
wR2
0.103
0.070
Goodness-of-fit (GOF)
1.11
1.20
a
R =
R
||Fo| ꢀ |Fc||/
R|Fo|.
w(F2o ꢀ F2c )2/
R
w(F2o )2]1/2
,
w = 1/[
r
2(Fo)2 + (0.049P)2 + 4.025P]
for
b
wR2 = [
R
[Ni(L2)2]; w = 1/[
r
2(Fo)2 + (0.022P)2 + 30.836P] for [Pt(L2)Cl]; where P = ((Fo2 þ 2F2c )/
3.

M.K. Paira et al. / Inorganica Chimica Acta 370 (2011) 175–186
185
4.6.4. Assay
Sensitivity tests were performed by disk diffusion method, as
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.ica.
2011.01.049.
per NCCLS [55] protocol. The Mueller Hinton agar plates, contain-
ing an inoculum size of 106 cfu/ml of bacteria were used. Prepared
drug solution impregnated disks at concentrations of 0–500 lg/ml
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