Silver(I) complexes with symmetrical Schiff bases: Synthesis, structural characterization, DFT studies and antimycobacterial assays

Article abstract of DOI:10.1016/j.poly.2013.06.031

Synthesis, structural and spectroscopic characterizations, molecular modeling and antimycobacterial assays of new silver(I) complexes with two Schiff bases - MBDA and MBDB - are reported. The complexes [Ag(MBDA) ₂]NO₃, or AgMBDA, and

Full text of DOI:10.1016/j.poly.2013.06.031

Polyhedron 62 (2013) 104–109
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Silver(I) complexes with symmetrical Schiff bases: Synthesis, structural
characterization, DFT studies and antimycobacterial assays
Isabela L. Paiva a, Gustavo S.G. de Carvalho a, Adilson D. da Silva a, Pedro P. Corbi b,
Fernando R.G. Bergamini b, André L.B. Formiga b, Renata Diniz a, Weberton R. do Carmo a,
Clarice Q.F. Leite c, Fernando R. Pavan c, Alexandre Cuin a,
⇑
a Departamento de Química, Instituto de Ciências Exatas, UFJF, 36036-900 Juiz de Fora, MG, Brazil
b Instituto de Química, Universidade de Campinas, UNICAMP, 13083-970 Campinas, SP, Brazil
c Departamento Ciências Biológicas, Faculdade de Ciências Farmacêuticas, UNESP, 14800-900 Araraquara, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Synthesis, structural and spectroscopic characterizations, molecular modeling and antimycobacterial
assays of new silver(I) complexes with two Schiff bases – MBDA and MBDB – are reported. The complexes
[Ag(MBDA)2]NO3, or AgMBDA, and [Ag(MBDB)NO3] or AgMBDB, were obtained by the reaction of the
respective ligands with silver(I) nitrate in methanol. The Schiff bases were previously obtained by mixing
ethylenediamine or 1,3-diaminopropane with p-anisaldehyde. The characterizations of the complexes
were based on elemental (C, H and N) and thermal (TG-DTA) analyses and 13C and 1H NMR and FT-IR
spectroscopic measurements, as well as X-ray structure determination for AgMBDA. Spectroscopic data
predicted by DFT calculations are in agreement with the experimental data for the AgMBDA complex.
The AgMBDA complex has a monomeric structure with a molar proportion 1:2 Ag/ligand, while AgMBDB
presents a 1:1 proportion. The complexes AgMBDA and AgMBDB showed to be more effective against
Mycobacterium tuberculosis than antibacterial agent silver sulfadiazine – SSD.
Received 11 April 2013
Accepted 21 June 2013
Available online 29 June 2013
Keywords:
Schiff bases
Anisaldehyde
Silver
Tuberculosis
Mycobacterium
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
diluted solutions of AgNO3 are employed to prevent bacterial infec-
tions and conjunctivitis in newborns [2–4].
Silver compounds have been used as antibacterial agents for a
long time as therapeutic compounds [1]. Several silver(I) com-
pounds have been prescribed due their topical antibacterial effects.
Silver sulfadiazine (SSD), for example, is still widely used in the
treatment of bacterial infections in burns and skin wounds, and
On the other hand, the use of metals and their salts as antimi-
crobial agents declined sharply in the middle of the last century
upon the introduction of organic antibiotics such as penicillin.
Since microorganisms still represent a risk to the public health,
and also due to the resurgence of multirresistant bacterial strains,
the development and optimization of new drugs are always of
great interest. Tuberculosis (TB) still remains as a public health is-
sue in the beginning of the 21st century, causing nearly 3 million
deaths worldwide annually. In the developing countries TB is a
leading cause of morbidity and mortality. Co-infections with hu-
man immunodeficiency virus (HIV) have been responsible for
changes in the TB epidemiologic situation leading to the appear-
ance of multi-drug resistant strains [5]. With the ever increasing
problem of microbe resistance to current antimicrobial agents,
there is an urgent demand for new classes of compounds that will
efficiently inhibit the growth of pathogenic microorganisms.
Due to this critical situation, an intense effort is being addressed
to the development of new drugs against microorganisms, particu-
larly against Mycobacterium tuberculosis. Currently, there is a
strong interest in silver(I) complexes with biological therapeutic
Abbreviations: NMR, Nuclear magnetic resonance; t, triplet; d, duplet; TG/DTA,
Thermogravimetric/differencial thermal analyses; UV–Vis, Ultraviolet–visible;
MBDA,
N,N0-bis[(4-methoxyphenyl)methlylidene]ethane-1,2-diamine;
MBDB,
N,N0-bis[(4-methoxyphenyl)methlylidene]propane-1,3-diamine; AgMBDA, silver
complex with MBDA; AgMBDB, silver complex with MBDB; SSD, Silver sulfadiazine;
MIC, Minimal inhibitory concentration; CFU, colony forming unit; ATCC, American
type collection cell; 7H9, broth used to growth mycobacterial species; THF,
Tetrahydrofuran; DMSO, dimethylsulfoxide; CDCl3, Chloroform-d; DFT, Density
functional theory; LANL2DZ, Los Alamos National Laboratory, 2nd version on
double zeta function; B3LYP, Becke 3-Lee Yang Parr functional; TD, Time dependent
method; CCDC, Cambridge Crystallographic Data Centre.
⇑
Corresponding author. Address: LQBin – Laboratório de Química BioInorgânica,
Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de
Juiz de Fora, 36036-900 Juiz de Fora, MG, Brazil. Tel.: +55 32 3229 3310.
E-mail addresses: alexandre.cuin@ufjf.edu.br, alexandre_cuin@yahoo.com (A.
Cuin).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.06.031

I.L. Paiva et al. / Polyhedron 62 (2013) 104–109
105
activities. Recently, silver(I) complexes with alfa-hydroxy-acids
[6], aminoacids [7], benzotiazoles [8] and mercaptopurine [9], syn-
thesized in our laboratories, have been shown to be more effective
than SSD against M. tuberculosis. The mechanisms of antibacterial
action of the Ag(I) complexes have been poorly described. How-
ever, there are three possibilities: (i) interference with electron
transport; (ii) inhibition of bacterial deoxyribonucleic acid (DNA)
replication caused by the Ag(I) ion, and (iii) modification of the
bacterial cell membrane [6].
with distilled water and ether, and stored in a desiccator under sil-
ica. When ethylenediamine was used, a white crystalline solid was
obtained (15.6 g, 52.7 mmol, 95.4% yield, MBDA). A pale yellow so-
lid was obtained using 1,3-diaminopropane as reagent (16.5 g,
53.2 mmol, 96.2% yield, MBDB).
Elemental Anal. Calc. for MBDA (C18H20N2O2): C, 72.9; H, 6.80;
N, 9.45. Found: C, 73.2; H, 6.93; N, 9.90%. Elemental Anal. Calc.
for MBDB (C19H22N2O2): C, 73.5; H, 7.14; N, 9.03. Found: C, 73.2;
H, 6.90; N, 9.15%.
Schiff bases are typically obtained by condensation of amine
compounds and active carboxyl groups (aldehyde and ketone)
leading to –CH@N– groups [10]. Schiff base compounds have re-
ceived special attention due to their simple methods of preparation
and to their versatility of applications, especially in biological field
[11].
Here, we describe the synthesis, structural characterization, DFT
studies and biological assays of two Schiff bases named MBDA and
MBDB (see Fig. 1) and their silver(I) complexes, named AgMBDA
and AgMBDB, respectively. The crystal structure of AgMDBA is also
reported.
2.3. Synthesis of the Ag(I) complexes with MBDA and MBDB
2.3.1. AgMBDA complex
An ethanolic solution containing 0.592 g (2.0 mmol, 30 mL) of
MBDA was first prepared. Then, a silver nitrate solution (0.170 g,
1.0 mmol), prepared in a minimum of water (ꢁ1 mL) and diluted
with 10.0 mL of ethanol was added under vigorous stirring to the
MBDA solution. Immediately, a yellow solid was formed. The solu-
tion was filtered and the solid was washed three times with 5 mL
of cold ethanol. The solid was collected and dried in a desiccator
over P4O10. The filtrate was left to stand overnight and light-yellow
crystals suitable for X-rays studies were obtained. Yield ꢁ80%
(crystals plus powder). Elemental Anal. Calc. for [Ag(C18H20N2O2)2]-
NO3: C, 56.7; H, 5.29; N, 9.18; O, 14.7; Ag, 14.1. Found: C, 56.7; H,
5.38; N, 9.95; Ag, 14.3% (from the TG curve).
2. Experimental
2.1. Materials and measurements
The starting compounds p-anisaldehyde (98%), ethylenedia-
mine (>99.5%) and 1,3-diaminopropane (>99%) were purchased
from Sigma–Aldrich Laboratory Co., and silver nitrate (>99%) was
purchased from Acros Organics. All chemical reagents were used
without further purification. Elemental analyses of C, H and N were
performed on a CHNS-O EA 1110 Analyzer, CE Instruments. Ther-
mal analyses were performed on a DTG-60 Simultaneous DTA-TG
apparatus, Shimadzu, using the following conditions: synthetic
air, flow rate of 50 cm3 minꢀ1 and heating rate of 10 °C minꢀ1, from
25 to 700 °C for both complexes. The IR spectra were recorded on a
Spectrum 2000 FT-IR Perkin Elmer spectrophotometer in the range
2.3.2. AgMBDB complex
The synthesis of AgMBDB complex was performed by the reac-
tion of 0.310 g (1.0 mmol) of MBDB in 20 mL of THF, with a silver
nitrate solution previously prepared by adding 0.0849 g of AgNO3
to a mixture of water (less than 1.0 mL) and THF (10.0 mL). The sil-
ver nitrate solution was added to MBDB slowly and under stirring.
A white crystalline powder was obtained. The final solution was
left to stand for several days and elongated crystals were obtained.
However, the crystals were not suitable for single X-ray crystallo-
graphic studies. X-ray analysis using the powder diffraction meth-
odology are in progress. Yield ꢁ80%. Elemental Anal. Calc. for
[Ag(C19H22N2O2)NO3]ꢂ½H2O: C, 46.6; H, 4.74; N, 8.59; O, 18.0; Ag,
22.0. Found C, 46.5; H, 4.17; N, 8.69; Ag, 21.7% (from the TG curve).
4000–300 cmꢀ1. The samples were prepared as KBr pellets. The 13
C
and 1H NMR data for MBDA and AgMBDA were recorded on a Bru-
ker 500 MHz and for MBDB and AgMBDB samples were recorded
on a Bruker 250 MHz. Tetramethylsilane was used as the internal
standard. All NMR samples were prepared in deuterated dimethyl-
sulfoxide solutions – (CD3)2SO.
2.4. Structural characterization of the AgMBDA complex
Single-crystal data were collected using an Oxford GEMINI A-
Ultra CCD diffractometer with Mo K
a (k = 0.71073 Å) radiation at
2.2. Synthesis of Schiff bases
room temperature. The data collection, cell refinement and data
reduction were performed using the CRYSALISPRO software [12]. The
structure was solved by direct methods using SHELXS and refined
using SHELXL [13]. An empirical isotropic extinction parameter x
was refined according to the method described by Larson [14].
The C-bound H-atoms were included in calculated positions and
treated as riding atoms using SHELXL default parameters. The non-
H atoms were refined anisotropically, using weighted full-matrix
least-squares on F2. A semi-empirical absorption correction (mul-
ti-scan) was applied using CRYSALISPRO [12]. The structures were
drawn using ORTEP-3 for WINDOWS [15] and MERCURY [16].
To a 100 mL round bottom flask was added 55.3 mmol of ethy-
lenediamine (3.20 mL) or 1,3-diaminopropane (4.10 mL) in 50 mL
of absolute ethanol. Then, with continuous stirring, 15.1 mL
(110.8 mol) of p-anisaldehyde was slowly added. The reaction
was carried out under constant stirring at room temperature dur-
ing 4 h. The precipitates were then collected by filtration, washed
2.5. Antibacterial assays
The anti M. tuberculosis (anti-MTB) activities of the compounds
were determined by the Resazurin Microtiter Assay (REMA) [17].
Stock solutions of the test compounds were prepared in dimethyl
sulfoxide (DMSO) and diluted in Middlebrook 7H9 broth (Difco),
supplemented with oleic acid, albumin, dextrose and catalase
(OADC enrichment – BBL/Becton Dickinson, Sparks, MD, USA), to
obtain final drug concentration ranges from 0.15 to 250
lg/mL.
Fig. 1. Schematic structures for MBDA and MBDB.
The serial dilutions were realized in a Precision XS Microplate Sam-

106
I.L. Paiva et al. / Polyhedron 62 (2013) 104–109
ple Processor (Biotek™). Isoniazid was dissolved in distilled water,
as recommended by the manufacturer (Difco laboratories, Detroit,
MI, USA), and used as a standard drug. MTB H37Rv ATCC 27294 was
grown for 7–10 days in Middlebrook 7H9 broth supplemented
with OADC, plus 0.05% Tween 80 to avoid clumps. Cultures were
centrifuged for 15 min at 3150g, washed twice, and resuspended
in phosphate-buffered saline. Aliquots were frozen at ꢀ80 °C. After
2 days, an aliquot was thawed to determine viability and the col-
ony-forming unit (CFU) after freezing. MTB H37Rv (ATCC 27294)
was thawed and added to the test compounds, yielding a final test-
1609 cmꢀ1 for the ligand and the complex, respectively. The shift
of the absorption vibrational when the ligand and the complex
spectra are compared is an evidence that the MBDA coordinates
to silver(I) through the nitrogen atoms. It is also possible to ob-
serve in the MBDB and AgMBDB spectra the characteristic bands
due the symmetrical and asymmetrical vibrational modes of cou-
pling between C@N and C@C groups which occur at 1639 and
1606 cmꢀ1 in the MBDB spectrum and at 1641 and 1604 cmꢀ1 in
the AgMBDB spectrum. The presence of the nitrate ion in both
complexes were confirmed by the presence of a strong band at
1385 cmꢀ1, which is attributed to the stretching mode of NO3
and two bands of medium intensities at 853 cmꢀ1 (AgMBDA) and
835 cmꢀ1 (for AgMBD), which are assigned to out-of-plane defor-
mation of the same ion.
ing volume of 200
l
L with 2 ꢃ 104 CFU/mL. Microplates with serial
dilutions of each compound were incubated for 7 days at 37 °C,
after resazurin was added to test viability. Wells that turned from
blue to pink with the development of fluorescence indicated
growth of bacterial cells, while maintenance of the blue color indi-
cated bacterial inhibition. The fluorescence was read (530 nm exci-
tation filter and 590 nm emission filter) in a SPECTRAfluor Plus
(TecanÒ) microfluorimeter. The MIC value is defined as the lowest
concentration resulting in 90% inhibition of growth of MTB [18]. As
a standard test, the MIC value for isoniazid was determined on
each microplate. The acceptable MIC value for isoniazid is in the
3.2. 1H and 13C NMR analyses
The 1H and 13C NMR spectra were obtained in order to confirm
the coordination of the ligands to the metal ion by the nitrogen
atoms. The spectra of AgMBDA and AgMBDB were analyzed in
comparison to the NMR spectra of the free ligands. The 13C and
1H data are presented in Tables 1 and 2. Carbon and hydrogen
atoms were numbered as shown in Fig. 1. Small changes in the
13C NMR spectra were observed only for the carbon atoms of the
azomethine groups (–C@N–), which were shifted downfield, from
162 ppm for MBDA and MBDB, to 165.7 and 163.3 ppm for AgMB-
DA and AgMBDB complexes, respectively. These slight changes are
indicatives that the ligands are coordinated to Ag(I) ions through
the nitrogen atoms.
range 0.015–0.06 lg/mL. Each test was set up in triplicate and no
differences were found in MIC values for each compound. All re-
sults were the same.
2.6. Molecular modeling
Geometry optimizations were carried out using the GAMESS soft-
ware [19] convergence criterion of 10ꢀ4 a.u. in a conjugate gradient
algorithm. The LANL2DZ [20] effective core potential was used for
silver and the atomic 6-31G (d) basis set [21] for all other atoms.
Density functional theory (DFT) calculations were performed for
AgMBDA using the B3LYP [22] gradient-corrected hybrid func-
tional to solve the Kohn–Sham equations with a 10ꢀ5 convergence
criterion for the density charge. The molecular modeling data are
presented as Supplementary material.
3.3. Thermogravimetric (TG) and differential (DTA) thermal analyses
Thermal decomposition of AgMBDA was studied by TG and DTA
analyses in 25–700 °C range. The endothermic peak corresponding
to the melting point of complex is located at 182.7 °C. The AgMBDA
complex starts to decompose at 225 °C as well as two consecutive
mass losses were observed with exothermic peaks at 242 and
492 °C. The final product of thermal analysis was considered as
metallic silver. The total mass loss was 85.7%, while the expected
value was 85.9%.
3. Results and discussion
3.1. IR spectroscopy
For the AgMBDB complex, a slight mass loss is observed below
190 °C (1.82%), being attributed to the loss of hydration water (cal-
culated 1.8%). Other two consecutive mass losses are observed
(exothermic peaks at 240 and 410 °C). The endothermic peak ob-
The IR spectra are shown in Fig. 2. In the MDBA and AgMBDA
spectra the principal significant bands are due to coupling between
C@N and C@C groups on 1640–1646 cmꢀ1 and 1632 and
Fig. 2. Experimental FT-IR spectra for MBDA and MBDB, and their respective complexes AgMBDA and AgMBDB.

I.L. Paiva et al. / Polyhedron 62 (2013) 104–109
107
Table 1
1H NMR assignments, d and multiplicity for ligands and their Ag(I) complexes.
Table 3
Crystallographic data for AgMBDA.
Assignment
MBDA (d, ppm)
AgMBDA (d, ppm)
D
(d, ppm)
Compound
AgMBDA
Ag2C72H80N10O14
1525.2
monoclinic
C2/c
17.9282(4)
17.9479(3)
22.5421(5)
104.996(2)
7006.4(2)
4
Molecular formula
7
8.23s
7.64d
6.95d
3.80s
3.77s
8.63s
7.88d
6.97d
3.78s
3.94s
ꢀ0.41
ꢀ0.24
ꢀ0.02
0.02
ꢀ0.17
D
Formula weight (g molꢀ1
)
3 and 6
5 and 2
18
Crystal system
Space group
a (Å)
b (Å)
16
MBDB (d, ppm)
AgMBDB (d, ppm)
(d, ppm)
c (Å)
b (°)
7
8.22s
7.64d
6.95d
3.75s
2.48t
1.88m
8.35s
7.73d
6.93d
3.76s
2.48t
2.00m
ꢀ0.13
ꢀ0.09
0.02
V (Å3)
3 and 6
2 and 5
18
16
19
Z
Crystal size (mm)
0.49 ꢃ 0.46 ꢃ 0.05
ꢀ0.01
Dcalc (g cmꢀ3
)
1.446
0
l
(Mo K
a
) (cmꢀ1
)
0.631
ꢀ0.12
Transmission factors (min/max)
Reflections measured/unique
0.70193/1.00000
33070/8841
5556
s = Singlet; d = doublet, t = triplet and m = multiplet.
between the chemical shifts of the complex and the free ligand.
D
Represents the difference
Observed reflections [F2obs > 4 (F2obs)]
r
No. of parameters refined
472
R(F0)
WR (F0
0.0361
0.0941
2
)
S
0.993
0.052
Table 2
RMS (eꢀ Åꢀ3
)
13C NMR assignments, d for ligands and their Ag(I) complexes.
Assignment
MBDA (d, ppm)
AgMBDA (d, ppm)
D (d, ppm)
7
1
161.8
161.7
130.0
129.7
114.7
61.7
165.7
163.0
130.5
127.4
114.9
62.3
ꢀ3.9
ꢀ1.3
ꢀ0.5
2.3
ꢀ0.2
ꢀ0.6
ꢀ0.3
Table 4
Selected bonds and angles for AgMBDA compound.
3 and 6
4
2 and 5
18
Silver coordination sphere
Bond (Å)
Ag1 N1
Ag1 N2
2.297(2)
2.355(2)
Ag2 N3
Ag2 N4
2.317(2)
2.336(2)
16
55.9
56.2
MBDB (d, ppm)
AgMBDB (d, ppm)
D
(d, ppm)
Angle (°)
N1 Ag1 N2
N1 Ag1 N1
N1 Ag1 N2
N2 Ag1 N2
77.14(7)
N4 Ag2 N4
N3 Ag2 N3
N3 Ag2 N4
N3 Ag2 N4
77.01(7)
77.35(7)
137.70(7)
118.83(7)
7
1
161.6
160.8
129.9
129.3
114.5
58.6
163.3
162.1
132.3 and 130.0
128.2
114.6
59.7
55.8
32.6
ꢀ2.3
119.44(7)
137.98(7)
117.89(6)
ꢀ1.3
3 and 6
4
2 and 5
16
18
19
ꢀ2.4 and ꢀ0.1
1.1
ꢀ0.1
ꢀ1.1
55.7
32.4
ꢀ0.1
ꢀ0.2
served at 155.3 °C on the DTA curve is due to the melting of
AgMBDB. After 450 °C no mass losses were observed and the resi-
due fits to metallic silver. The experimental mass loss was 78.3%
and the expected one considering the molecular formula [Ag(C19-
H22N2O2)NO3]ꢂ½H2O was 77.6%.
3.4. Crystallographic studies for AgMBDA
The crystallographic parameters for AgMBDA are summarized
in Table 3, while selected bond distances and angles are given in
Table 4. The crystal structure of AgMBDA is shown in Fig. 3. Crys-
tals of AgMBDA contain two crystallographically independent half
molecules, see the Fig. 4. One of which shows the twofold axis
passing through the metal ion and the center of the two aliphatic
CH2–CH2 vectors, the other one possessing a complete MBDA li-
gand bound to a silver atom lying on the twofold axis. A single ni-
trate ion completes the asymmetric unit. However, being only
weakly bound to the rest of the structure, was found heavily disor-
dered, with electron density surrounding the central N atom being
described by a rather irregular polyhedron of six oxygen atoms of
partial occupancy.
Since the silver(I) ions are chelated by four nitrogen atoms from
two MBDA ligands the geometric parameter for four-coordinate
compounds, s, proposed by Alvarez and Avnir [23] was applied
to AgMBDA complex and both Ag1 and Ag2 fall in distorted tetra-
hedron geometry, since both torsion angles between chelate planes
are 70.1° and 70.7°.
Fig. 3. ORTEP representation of crystal structure of AgMBDA. The thermal ellipsoids
are drawn at 30% probability. Symmetry code: i(1 ꢀ x,y,1,5 ꢀ z) and
ii(1 ꢀ x,y,2,5 ꢀ z). The hydrogen atoms and nitrate ions were omitted for the
better visualization.
The Ag–N distances found fall 2.29–2.35 Å range and the dis-
tances are similar to the typical values found for other four-coordi-
nated Ag(I) complexes containing N-heterocyclic ligands [24]. The
main difference between these units is the angle between the aro-
matic rings of the ligands. For the block that contain Ag1 the angles
formed between the rings of the same ligand is around 28.6° and
the average is 72.4° for different ligands. For the Ag2 cationic block
the angles are 38.7° and 14.24° to the same ligand and an average
of 69.4° between different ligands. The cationic block charges are
neutralized by two nitrate anions present in the structure. In addi-

108
I.L. Paiva et al. / Polyhedron 62 (2013) 104–109
Table 5
MIC values of compounds, silver nitrate and SSD.
Compound MIC
g mLꢀ1
%
Molar mass
MIC
mol Lꢀ1
)
(l
)
Silver
(g molꢀ1
)
(
l
MBDB
AgMBDB
MBDA
AgMBDA
AgNO3
SSD
25
11.3
25
21.2
12.5
12.5
310.4
480.3
296.4
762.6
169.9
357.1
80.5
23.5
84.4
27.8
73.6
35.0
22.4
14.1
63.5
30.2
bond distance was 2.420 Å, while the N1–Ag–N2 and N1–Ag–N20
angles were 76.2° and 129.7°, respectively. Detailed bond dis-
tances, angles and dihedrals are provided as Supplementary
material.
3.6. Antibacterial assays
Fig. 4. The asymmetric unit of the AgMDBA crystal, showing two differently
oriented half complex cations (bisected by crystallographic twofold axes, see text)
and nitrate group viewed along the
c axis. The silver and nitrate atoms are
The minimum inhibitory concentrations (MIC) for the two
ligands and their silver(I) complexes, as well as the MIC values
for AgNO3, silver sulfadiazine – SSD and isoniazid, are presented
in Table 5. The MBDA and MBDB molecules show low activity
against M. tuberculosis. The silver(I) complexes were shown to be
more effective than the free ligands. The MIC values found for
numbered. The twofold axes are in green lines. Carbon, oxygen and hydrogen atoms
were colored as dark gray, red and light gray, respectively. The disordered atoms of
the nitrate ion are not shown. (Color online.)
tion, non conventional hydrogen bonds C–Hꢂ ꢂ ꢂO are responsible to
build two different 1D networks with different orientations. The
interaction of C18–H18Aꢂ ꢂ ꢂO2, and C19–H19Aꢂ ꢂ ꢂO3 gives rise to a
one-dimensional network viewed along the b- and a-axis, respec-
tively, see Fig. 5. Since AgMBDA is a monometallic complex, no
Ag–Ag interaction was observed.
AgMBDA and AgMBDB complexes were 27.8 and 23.5 l ,
mol Lꢀ1
respectively, are lower than two recently published Pt(II) com-
plexes with N-, S-donor ligand described in literature for the same
mycobacterium species [25]. The two Ag(I) complexes also possess
higher activity than free AgNO3. Furthermore, the AgMBDA and
AgMBDB complexes have 14.1% and 22.4% of silver in their compo-
sitions, while AgNO3 has 63.5%. These data suggest a synergism be-
tween Ag(I) ions and the free ligand. As described in Table 5, the
two complexes are more effective than the SSD complex.
3.5. Molecular modelling
The geometry of AgMBDA was optimized by theoretical calcula-
tions using density functional theory (DFT). The calculated Ag–N
Fig. 5. 1D representation network of AgMBDA. Viewed along (a) b-axis and (b) a-axis.

I.L. Paiva et al. / Polyhedron 62 (2013) 104–109
109
4. Conclusions
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The authors thank FAPEMIG/Brazil processes
– CEX-APQ-
00173/09; 02967/10 and 00256/11 CNPq/FAPESP/Brazil – 2012/
08230-2, 2009/06499-1 and 2011/11593-7, for financial support.
The authors are grateful to Professor Carol H. Collins for the English
revision of the manuscript.
Appendix A. Supplementary data
CCDC 897808 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: +44 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.poly.2013.06.031.