A new diamine containing disiloxane moiety and some derived Schiff bases: Synthesis, structural characterisation and antimicrobial activity

Article abstract of DOI:10.1080/10610278.2013.794947

A new siloxane diamine, 1,3-bis(amino-phenylene-ester-methylene) tetramethyldisiloxane (1), was obtained by a two-step procedure and used to prepare a series of Schiff bases (2-5), by reaction with different carbonylic compounds: salicylaldehyde, 3,5-dibromosalicylaldehyde, 5-chlorosalicylaldehyde and 3,5-di-tert-butyl-2-hydroxybenzaldehyde. All compounds, separated in crystalline form, were characterised by spectral (FTIR, UV-vis and NMR) analysis as well as by single-crystal X-ray diffraction. In these structures, different packing motifs occur depending on the different association degree determined by intra-and intermolecular π-π stacking interactions. Antimicrobial activity of the compounds was evaluated against three fungi and two bacteria, where the Schiff bases derived from salicylaldehyde and in special 5-chlorosalicylaldehyde showed remarkable activity.

Full text of DOI:10.1080/10610278.2013.794947

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A new diamine containing disiloxane moiety and
some derived Schiff bases: synthesis, structural
characterisation and antimicrobial activity
Mirela-Fernanda Zaltariov a , Maria Cazacu a , Nicoleta Vornicu b , Sergiu Shova a , Carmen
Racles a , Mihaela Balan a & Constantin Turta a
a “Petru Poni” Institute of Macromolecular Chemistry , Aleea Gr. Ghica Voda 41A, 700487 ,
Iasi , Romania
b Metropolitan Center of Research T.A.B.O.R, The Metropolitanate of Moldavia and
Bukovina , Iasi , Romania
Published online: 07 Jun 2013.
To cite this article: Supramolecular Chemistry (2013): A new diamine containing disiloxane moiety and some derived
Schiff bases: synthesis, structural characterisation and antimicrobial activity, Supramolecular Chemistry, DOI:
10.1080/10610278.2013.794947
To link to this article: http://dx.doi.org/10.1080/10610278.2013.794947
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Supramolecular Chemistry, 2013
http://dx.doi.org/10.1080/10610278.2013.794947
A new diamine containing disiloxane moiety and some derived Schiff bases: synthesis, structural
characterisation and antimicrobial activity
Mirela-Fernanda Zaltariova, Maria Cazacua*, Nicoleta Vornicub, Sergiu Shovaa, Carmen Raclesa,
Mihaela Balana and Constantin Turtaa
b
a“Petru Poni” Institute of Macromolecular Chemistry, Aleea Gr. Ghica Voda 41A, 700487 Iasi, Romania; Metropolitan Center of
Research T.A.B.O.R, The Metropolitanate of Moldavia and Bukovina, Iasi, Romania
(Received 29 December 2012; final version received 8 April 2013)
A new siloxane diamine, 1,3-bis(amino-phenylene-ester-methylene)tetramethyldisiloxane (1), was obtained by a two-step
procedure and used to prepare a series of Schiff bases (2–5), by reaction with different carbonylic compounds:
salicylaldehyde, 3,5-dibromosalicylaldehyde, 5-chlorosalicylaldehyde and 3,5-di-tert-butyl-2-hydroxybenzaldehyde. All
compounds, separated in crystalline form, were characterised by spectral (FTIR, UV–vis and NMR) analysis as well as by
single-crystal X-ray diffraction. In these structures, different packing motifs occur depending on the different association
degree determined by intra- and intermolecular p–p stacking interactions. Antimicrobial activity of the compounds was
evaluated against three fungi and two bacteria, where the Schiff bases derived from salicylaldehyde and in special
5-chlorosalicylaldehyde showed remarkable activity.
Keywords: Schiff base; amine; siloxane; supramolecular structure; self-assembling
1. Introduction
in metalloproteins, is a key factor for the biomimetic
activity of these molecules (12). Therefore, although there
are an extremely large number of publications on Schiff
bases (13) and their metal complexes (14), there is still
intensive research in this area which mainly aims to
diversify the range of amines and aldehydes and exploit the
full potential offered by this class of compounds. In the last
decade, we have prepared small molecule or polymeric
azomethines based on different carbonylic derivatives and
a siloxane diamine, mainly 1,3-bis(3-aminopropyl)tetra-
methyldisiloxane (15–20). The presence of the tetra-
methyldisiloxane moiety with its large and flexible
SiZOZSi bond angle ranging between 1358 and 1808
might confer some special features such as, low glass and
melt transitions or self-assembling ability.
A large variety of carbonylic and amine compounds can be
used to prepare azomethines (1, 2). The synthetic flexibility
permits to design molecular structures with tunable
properties (chemical, optical, magnetic and electrical)
and numerous representative derivatives found a wide
variety of applications in many fields such as medicine (to
design medicinal compounds) (3), biology (as biochemical
and antimicrobial reagents due to similarities with natural
biological compounds) (4), analytical chemistry (reagents
or optical, electrochemical and chromatographic sensors)
(5, 6) and materials chemistry (catalysts and antimicrobial
reagents, light emitting diodes OLED, PLED) (7), or as
oxygen carriers (8). Schiff base compounds are among the
most used ligands playing an important role in the
development of coordination chemistry. The main reasons
for this position are their easy preparation and coordination
ability with a large variety of metals with different
oxidation states forming highly stable coordination
compounds (9–11). The lone electron pair in a sp2
hybridised orbital of nitrogen atom of the azomethinegroup
imparts excellent chelating ability especially when there
are one or more donor atoms close to the azomethine group
(10). Depending on the chosen amine, the salen-type metal
complexes can conformationally be more rigid or flexible,
the last being able to adopt a variety of geometries and to
generate various active-site environments for the different
oxidation reactions. This flexibility, similar to that observed
Although it might be of interest, this direction was
insufficiently explored until now. A relatively small
number of compounds of this type are reported in the
literature due to the difficulty in their characterisation
(21–23). Highly flexible siloxane bonds make them
difficult to investigate by single-crystal X-ray diffraction.
In this study, we have synthesised an original siloxane
diamine and four derived Schiff bases by its reaction with
salicylaldehyde, 3,5-dibromosalicylaldehyde, 5-chlorosa-
licylaldehyde and 3,5-di-tert-butyl-2-hydroxybenzalde-
hyde. The compounds were characterised by spectral
(FTIR, UVand NMR) analysis as well as by single-crystal
X-ray diffraction. Antimicrobial activity against several
species was also evaluated.
*Corresponding author. Email: mcazacu@icmpp.ro
q 2013 Taylor & Francis

2
M.-F. Zaltariov et al.
are shown in Figures S4–S6 of the Supplementary
Information, available online.
2. Results and discussion
A siloxane-containing diamine was prepared by a two-step
procedure consisting of synthesis and isolation of sodium
salt of p-aminobenzoic acid (Scheme 1(a)) followed by the
esterification with bifunctional halo-compound containing
siloxane moiety, 1,3-bis(chlormethyl)-1,1,3,3-tetramethyl-
disiloxane (Scheme 1(b)). The first step occurred in an
aqueous reaction medium, whereas the second step
occurred in DMF.
All syntheses of the Schiff base compounds were
performed under similar conditions by condensation of
diamine 1 with four differently substituted salicylaldehyde
derivatives in 1:2 molar ratio, according to Scheme 2.
Condensation of the aldehydes with primary amine
readily gave the corresponding imines, which were easily
1
identified by their IR and H NMR spectra. Thus, fourier
transform infrared (FT-IR) spectra of the imines show
characteristic absorption bands attributed to the azo-
methine bond (ZCHvNZ) at 1620 cm21 (2), 1616 cm21
(3) and 1618 cm21 (4 and 5), siloxane bond (ZSiZOZ
SiZ) at 1055–1072 cm21, SiZCH3 at 837–842 cm21 and
1249–1255 cm21, and (vCvO) in the ester group at
1706–1720 cm21 (Figure S7 of the Supplementary
The salt formation (Figure S1(a) of the Supplementary
Information, available online) was verified by FTIR
spectroscopy where the band at 1664 cm21 characteristic
for the carboxylic group of p-aminobenzoic acid
disappeared being replaced by a new strong band at
1537 cm21 assigned to the carboxylate group. In the FTIR
spectrum of the condensation product (Figure S1(b) of the
Supplementary Information, available online), there are
present the absorption bands characteristic of the primary
aromatic amine at 3433, 3352 and 3236 cm21, besides
those for ester group at 1697 cm21, and for dimethylsilox-
ane moiety at 1074 cm21 (SiZOZSi), 843 and 1257 cm21
(SiZCH3). In the 1H NMR spectrum of the diamine (Figure
S2 of the Supplementary Information, available online), the
signals of aromatic protons appear at 7.84 and 6.66 ppm,
whereas the peak corresponding to resonance of the amine
protons appear at 4.09 ppm. Other peaks are those at 0.21
and 3.94 ppm corresponding to the protons from SiZCH3
and SiZCH2, respectively. Their intensity ratios (Ar:
ZNH2: SiZCH3: SiZCH2 ¼ 2:1:3:1) correspond to the
presumed structure. In the 13C NMR spectrum (Figure S3
of the Supplementary Information, available online), the
ZCvO peak appears at 167.3 ppm, the aromatic carbons
appear between 113.8 and 150.7 ppm, the ZCH2ZSi peak
is present at 57.4 ppm and the CH3ZSi peak appears
at 20.8 ppm. The 2D NMR spectra used for the assignment
of the signals from the 1D NMR spectra of compound 1
1
Information, available online). The H NMR spectra of
all the Schiff bases indicate the formation of the
azomethine bond by the presence of the peak correspond-
ing to ZCHvNZ proton at 8.68 ppm (5), 8.57 ppm (4),
8.56 ppm (3) and 8.64 ppm (2), and specific aromatic
protons from diamine and aldehyde moieties with some
modifications compared with the starting compounds. The
peaks corresponding to proton resonance from tetra-
methyldisiloxane units appear at 0.30–0.25 ppm and that
assigned to ZCH2Z at 4 ppm in the intensity ratio
corresponding to the presumed structures. All the 1D and
2D NMR experiments used for the characterisation of
compounds 2–5 are shown in Figures S8–S27 of the
Supplementary Information, available online.
The imines prepared in this way were formed in good
yields and were of high purity, as single crystals. All
compounds are stable at room temperature in the solid state.
2.1 Crystal structure
Compound 1 has a molecular crystal structure composed
from neutral entities, as depicted in Figure 1. The main
crystal structure motif can be characterised as a two-
dimensional layer (Figure 2). The construction of these
layers occurs via a system of N1ZH· · ·O1 hydrogen
bonds, the formation of which is completely realised in the
crystal. The hydrogen bonds parameters are presented
in Table 1. The further extension of the supramolecular
architecture occurs through N2ZH· · ·O5(1 þ x, y, z)
hydrogen bond, so that the crystal structure results from
the packing of two-dimensional double layers, the view of
which is shown in Figure 3.
NaOH
NaOOC
HOOC
NH2
NH2
– H2O
a
O
H2N
COONa Cl
Cl NaOOC
NH2
Si
Si
refluxing DMF –2 NaCl
b
The X-ray molecular structure of compound 2 is
presented in Figure 4, whereas those for compounds 3 and 4
are providedin the supporting information (Figures S28 and
S29 of the Supplementary Information, available online).
The asymmetric part of the unit cell in the crystal
structure of 3 and 4 contains two discrete molecules
(denoted as A and B) as crystallographic independent
O
Si Si
C O
O
H2N
O C
O
NH2
(1)
Scheme 1. Two-step synthesis pathway leading to siloxane
diamine 1.

Supramolecular Chemistry
3
O
Si
Si
H2N
C O
O
O
C
O
NH2
R2
C
H
O
2
R1
OH
–2 H2O
R2
R2
R1
O
O
C
N
C
O
O
C
N
C
H
Si
Si
H
O
OH
HO
R1 = R2 = H (2); R1 = R2 = Br (3); R1 = H, R2 = CI (4); R1 = R2 = t-Bu (5)
Scheme 2. Reaction pathway for the synthesis of the Schiff bases, 2–5.
R1
Figure 1. X-ray molecular structure of compound 1. Thermal ellipsoids are drawn at 50% probability level.
Figure 2. The association of the molecules 1 through N–H· · ·O hydrogen bonds in the crystal.

4
M.-F. Zaltariov et al.
Table 1. H-bonds parameters.
˚
Distance (A)
DZH· · ·A
DZH
H· · ·A
D· · ·A
Angle DZH· · ·A (8)
Symmetry code
1
N1ZH· · ·O1
N1ZH· · ·N2
N2ZH· · ·O1
N2ZH· · ·O5
2
0.86
0.86
0.85
0.86
2.18
2.35
2.45
2.13
2.960(3)
3.187(3)
3.124(1)
2.938(3)
150.4
164.2
136.8
156.6
x 2 1, y, z
x 2 2, 1 þ y, z 2 1
1 2 x, 1 2 y, 1 2 z
1 þ x, y, z
O1ZH· · ·N1
O7ZH· · ·N2
3
0.82
0.82
2.21
1.93
2.617(8)
2.594(6)
149.5
137.6
x, y, z
x, y, z
O1AZH· · ·N1A
O7AZH· · ·N2A
O1BZH· · ·N1B
O7BZH· · ·N2B
4
0.82
0.82
0.82
0.82
1.88
1.85
1.88
1.85
2.600(5)
2.573(4)
2.586(4)
2.584(5)
146.1
147.2
142.9
147.8
x, y, z
x, y, z
x, y, z
x, y, z
O1AZH· · ·N1A
O7AZH· · ·N2A
O1BZH· · ·N1B
O7BZH· · ·N2B
5
0.90
0.91
0.90
0.92
1.79
1.79
1.81
1.82
2.631(5)
2.595(6)
2.614(6)
2.589(7)
154.7
145.6
147.2
140.2
x, y, z
x, y, z
x, y, z
x, y, z
O1ZH· · ·N1
O1XZH· · ·N1X
0.82
0.82
1.83
1.88
2.568(4)
2.57(2)
148.4
140.8
x, y, z
x, y, z
units, which exhibit similar geometric parameters.
Structural studies have revealed that in all studied
structures, the molecules are in cis conformation, the
aromatic rings being oriented on the same side with respect
to siloxane moiety. The hydroxyl groups act as donor in
H-bonding towards azomethine nitrogen as acceptor
(Table 1). The molecular conformation for 2, 3 and 4 is
determined by intramolecular p–p stacking interaction,
Figure 3. The view of two-dimensional supramolecular double layer in the crystal structure 1.

Supramolecular Chemistry
5
Figure 4. Molecular structure (40% probability ellipsoids) of compound 2.
which is evidenced by short interplanar spacing between
adjacent aromatic systems (Figures 4, S28 and S29 of
the Supplementary Information, available online, respect-
ively). The steric effect of t-butyl substitutes in 5 imposes
the changes in molecular conformation leading to the large
separation of the aromatic rings and the absence of the
p–p stacking interaction within the molecule (Figure 5).
At the same time, the intermolecular p–p stacking
interactions play the key role in the crystal structure
formation for compounds 2–5. Figures 6–9 show the
packing diagram for crystal structures 2–5. Compounds 2
(Figure 6) and 4 (Figure 8) have a similar crystal structure
motif, which results from the packing of the isolated
bi-molecular entities associated by intermolecular p–p
Figure 5. Molecular structure (50% probability ellipsoids) of compound 5 with special position for O4 atom on two-fold axis.

6
M.-F. Zaltariov et al.
Figure 6. View of the crystal structure 2. H-atoms are omitted for clarity. Centroid-to-centroid distances are in the range between 3.751
˚
and 3.868 A.
stacking interaction. On the contrary, the crystal structure
of compound 3 (Figure 7) is characterised by the parallel
packing of two-dimensional double layers, whereas
compound 5 (Figure 9) is packed as one-dimensional
supramolecular chains.
2.2 UV–vis spectroscopy
The absorption spectra of the amine and derived Schiff
bases recorded in DMF are presented in Figure 8. The UV
data are centralised in Table 3 where the extinction
coefficients at the maximum absorption peaks are also
presented.
The values of SiZOZSi angles and SiZO distances for
compounds 2–5 are in the range between 143.91–172.38
˚
and 1.526–1.638 A, respectively (Table 2).
As it can be seen, while the diamine spectrum exhibits
one absorption peak at 294 nm characteristic for p–p
*
Figure 7. Views of two-dimensional double layer in the crystal
structure 3. H-atoms are omitted for clarity. Centroid-to-centroid
˚
distances are in the range between 3.703 and 4.042 A.
Figure 8. p–p stacking association in crystal structure 4. H-
atoms are omitted for clarity. Centroid-to-centroid distances are
˚
in the range between 3.761 and 4.096 A.

Supramolecular Chemistry
7
from each other being probably influenced by the
substituent type at the aromatic ring. In the case of the
compound 3, a supplementary large band appears at 426 nm
which, according to the literature (24), should be assigned
to the intramolecular charge transfer involving the whole
molecule. As mentioned earlier, as compared with the other
Schiff bases compounds (2, 4 and 5), compound 3 forms,
beside the intramolecular, the most extensive intermole-
cular p–p interactions resulting into the formation of
two-dimensional double layers (Figure 7(a),(b)). This
could be why UV–vis spectrum is different (Figure 10(a)).
Moreover, the spectrum is influenced by the nature of
the solvent as can be seen in Figure 10(b). Thus, in a less
polar solvent such as CH2Cl2, where the intermolecular
interactions could be favoured, the maximum of this
absorption band slightly shifts to higher wavelength value
(433 nm) but significantly decreases in intensity, from
4700 M21 cm21 in DMF to 2113 M21 cm21 in CH2Cl2
(Table 3).
Figure 9. p–p stacking one-dimensional chain in the crystal
structure 5. H-atoms are omitted for clarity. Centroid-to-centroid
˚
distance is equal to 4.096 A.
transition in aromatic rings, the Schiff bases exhibit
two absorption peaks, attributed to p–p transitions in
*
aromatic ring (at 282–306 nm) and azomethine groups (at
340–362 nm). The position of these bands differs slightly
Table 2. SiZOZSi bond angles and bond distances for all the molecules.
3
4
Parameter
1
2
A
B
A
B
5
SiZO length
1.614(2);
1.608(2)
158.1(2)
1.624(2);
1.637(2)
147.4(1)
1.623(3);
1.628(3)
146.5(2)
1.625(3);
1.638(3)
143.9(2)
1.577(3);
1.600(3)
158.9(2)
1.603(3);
1.526(3)
172.0(3)
1.629(1)
SiZOZSi angle
153.8(3)
Table 3. UV–vis absorption data for the synthesised ligands.
Sample
Solvent
Molar concentrations (mol/L)
l
max, nm (1, M21 cm21
)
1
2
3
DMF
DMF
DMF
CH2Cl2
DMF
DMF
4 £ 1025
3 £ 1025
2 £ 1025
3.9 £ 1025
2 £ 1025
2 £ 1025
296 (39,030)
–
282 (22,800)
296 (47,400)
280 (24,460)
294 (39,010)
306 (25,400)
344 (18,730)
330sh (5395), 426 (4700)
335 (3693), 433 (2113)
350 (22,630)
4
5
362 (15,550)
(a) 1.6
(b)
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
280
296
DMF
CH2CI2
3
4
2
5
335
426
330
350
433
300
350
400
450
500
550
600
250
300
400
450
500
550
600
λ, nm
λ, nm
Figure 10. UV–vis spectra of the compounds registered in DMF solution – a; comparative UV–vis spectra of compound 3 registered in
DMF and CH2Cl2 – b.

8
M.-F. Zaltariov et al.
Table 4. Results of in vitro antimicrobial and antifungal activity testing of compounds 2, 3, 4 and 5.
MIC (mg/ml)a
Sample
A. niger
P. frequentans
A. alternata
P. aeruginosa
Bacillus sp.
2
3
4
0.8
.128
0.05
0.8
.128
0.05
0.9
.128
0.06
1
1
.128
0.1
.128
0.1
5
.128
.3
.128
.3
.128
.3
.128
.3
.128
.3
Control platesb
a Minimum inhibitory concentration.
b Based on solvent only.
2.3 Antimicrobial activity
this diamine with salicylaldehyde and its derivatives, 3,5-
dibromosalicylaldehyde, 5-chlorosalicylaldehyde and 3,5-
di-tert-butyl-2-hydroxybenzaldehyde, the corresponding
bis(2-hydroxyazomethine)s 2–5 have been obtained. All
the compounds were characterised by spectral methods
(FTIR and NMR spectroscopy) and their crystal structures
were studied by X-ray crystallography. All compounds
have a molecular crystal structure, but exhibit different
crystal packing motifs. Thus, compounds 2 and 4 show
intra- and intermolecular p–p interactions between
aromatic rings, which determined the formation of isolated
di-molecular associates in the crystal structure. In
compounds 3 and 5, both intramolecular and extended
intermolecular p–p interactions occur resulting in two-
dimensional double layers and one-dimensional chains,
respectively. The optical behaviour is influenced by the
electronic nature of the group appended to the aromatic ring
but also by the type of the interactions occurring within the
molecule and at intermolecular level, as was emphasised
by UV–vis spectra. The results of the antifungal and
antibacterial activities test recommend two of the new
azomethines synthesised as potential antimicrobial agents.
It has already been proved in numerous publications
(25–27) that the Schiff bases and their metal complexes
show a wide range of biological activities, such as
antitumoural (25), antiviral (26) or antimicrobial (27). The
azomethine group present in such compounds has been
shown to be essential for biological activity (28, 29). For
the new Schiff bases obtained in this paper, we assessed
antifungal and antibacterial activity in vitro using three
fungi species (Aspergillus niger, Penicillium frequentans
and Alternaria alternata) and two bacteria – Gram-
negative (Pseudomonas aeruginosa) and Gram-positive
bacteria (Bacillus). The experimental test results on
compounds were compared against DMF as the control
and are expressed by value of the minimum inhibitory
concentration (MIC, mg/ml) in Table 4.
According to these results, compounds 3 and 5 derived
from 3,5-dibromosalicylaldehyde and 3,5-di-tert-butyl-2-
hydroxybenzaldehyde, respectively, had no effect against
tested fungi and bacteria (MIC . 128 mg/ml). Instead,
Schiff base 4, derived from 5-chlorosalicylaldehyde,
proved to have the greatest potential for biological
activity. MIC values for this compound range from 0.05 to
0.1 mg/ml revealing high antimicrobial effect compared
with control plate. This could be attributed to the presence
of chlorine in position 5, which, due to its electron-
acceptor effect, polarises the azomethine groups more
than do other substituents (27a). The combination of our
diamine, 1,3-bis(amino-phenylene-ester-methylene)tetra-
methyldisiloxane, with salicylaldehyde as in compound 2,
has a lower inhibitory effect on micro-organisms than
compound 4. However, the found MIC values between 0.8
and 1 mg/ml reveals some antimicrobial effect of the
compound 2 in comparison with the control.
4. Experimental
4.1 Materials
p-Aminobenzoic acid (Aldrich), 1,3-bis(chlormethyl)-
1,1,3,3-tetramethyldisiloxane (Fluka, Chemie GmbH,
Steinheim, Germany), salicylaldehyde, 3,5-dibromosali-
cylaldehyde, 5-chlorosalicylaldehyde and 3,5-di-tert-
buthyl-2-hydroxybenzaldehyde (Sigma-Aldrich, Chemie
GmbH, Steinheim, Germany), methanol (Chimopar,
Bucuresti, Romania), chloroform (Chimopar), dimethyl-
formamide (Aldrich), diethyl ether (Aldrich) and aceto-
nitrile (Aldrich) were used as received.
Three fungi (A. niger ATCC 53346, P. frequentans
ATCC 10110, Alternaria alternata ATCC 8741) from pure
culture and two bacteria (Pseudomonas aeruginosa ATCC
27813 and Bacillus sp. ATCC 15970) species from
American Type Culture Collection (ATCC), USA, were
used for biological activity testing. Petri plates with agar
culture medium type –Sabouraud (Merck, Darmstadt,
Germany) were used for these measurements.
3. Conclusions
A new diamine containing disiloxane moiety, 1,3-
bis(amino-phenylene-ester-methylene)tetramethyldisilox-
ane, has been prepared and fully characterised. Structural
analysis by single-crystal X-ray diffraction revealed its
self-assembling in 3D structure through NZH· · ·O and
NZH· · ·N hydrogen bonds. By condensation reaction of

Supramolecular Chemistry
9
4.2 Spectral techniques
methods using SHELXS-97 (31), and refined by full-matrix
least-squares on Fo2 with SHELXL-97 (31). All atomic
displacements for non-hydrogen, non-disordered atoms
were refined using an anisotropic model. In structure 4,
disiloxane methyl groups and the atoms of both
salicylimine moieties in structure 2 presented too large
thermal ellipsoids, so that disordered models, in combi-
nation with the available tools (PART, DFIX and SADI) of
SHELXL97 were applied in order to better fit the electron
density. The combined anisotropic/isotropic refinement has
been used for these non-H atoms. All the asymmetric parts
of the unit cell in structure 5 were found to be statistically
disordered over two positions with 0.72 and 0.28 s.o.f.
Nevertheless, anisotropic approach could be applied for
both major and minor components. Hydrogen atoms have
been placed by Fourier Difference accounting for the
hybridisation of the supporting atoms and the possible
presence of hydrogen bonds in the case of donor atoms. The
main crystallographic data together with refinement details
are summarised in Table 5.
FT-IR spectra were recorded using a Bruker Vertex 70
FT-IR spectrometer. Registrations were performed in
the transmission mode in the range of 400–4000 cm21 at
room temperature with a resolution of 2 cm21 and
accumulation of 32 scans.
The NMR spectra were recorded on a Bruker Avance
DRX 400 MHz Spectrometer (Bruker, Rheinstetten,
Germany) equipped with a 5 mm QNP direct detection
probe and z-gradients. Spectra were recorded in CDCl3 at
room temperature. The chemical shifts are reported as d
values (ppm). The atom labelling for the NMR assign-
ments is that from XRD structures. The assignments of all
the signals in the 1D NMR spectra were done using 2D
NMR experiments such as H,H-COSY, H,C-HMQC and
H,C-HMBC.
UV–vis absorption spectra measurements were carried
out in DMF solution on a Specord 200 spectrophotometer
(Analytik Jena AG, Jena, Germany).
4.3 Antimicrobial activity
In vitro antimicrobial activity tests against the bacterial
species P. aeruginosa and Bacillus sp., and fungal species A.
niger, P. frequentans and A. alternata, were carried out
according to the standard procedures (SR-EN 1275:2006
and NCCLS:1993) on agar-type media by the disc diffusion
method. According to these procedures, the successive
dilutionshave been made toobtain the suspensionsof micro-
organisms. Final load of as prepared stock inoculum was
1 £ 1024 mg/ml. Culture was performed by using mixture
1:1 micro-organism suspension and solution of the
compound to be tested that were deposed on the disc and
solid medium. Solutions of 0.5, 1.0 and 1.5 wt% sample
concentration in DMF have been prepared for each
compound and soaked in filter paper disc of 5 cm diameter
and 1 mmthickness. Thediscswereplaced onthe previously
seeded plates and incubated at 328C. A blank sample was
also prepared in order to verify the influence of the solvent
on the biological activity. The diameter of inhibition zone
around each disc was measured after 48 h and after 7 days.
The antimicrobial activity was estimated by measuring the
diameter of the area inhibited by the tested compounds.
4.5 Procedure
4.5.1 Synthesis of p-aminobenzoic acid sodium salt
NaOH (1.2 g, 0.03 mol) was dissolved in 10 mL of distilled
water and then 4.11 g (0.03 mol) p-aminobenzoic acid was
added. After complete dissolution of the p-aminobenzoic
acid, the water was evaporated and the yellow powder
obtained was dried in oven at 808C for 2 h. The resulting
sodium salt (4.3 g, 90% yield) was first analysed by IR
spectroscopy.
4.5.2 Synthesis of the siloxane-containing diamine,
1,3-bis(amino-phenylene-ester-
methylene)tetramethyldisiloxane, 1
In a round-bottom flask equipped with reflux condenser
having attached a calcium chloride tube and magnetic
stirrer, 30 mL of dry dimethylformamide, 4.3 g
(0.027 mol) p-aminobenzoic acid sodium salt and 3.12 g
(2.2 mL, 0.0135 mol) of 1,3-bis(chloromethyl)-1,1,3,3
tetramethyldisiloxane were added. The reaction mixture
was stirred under argon atmosphere to reflux for 8 h. The
NaCl by-product was separated by filtration and the filtrate
was poured into 100 mL of distilled water, when a brown
solid as a resin separated on the glass bottom. After
removing liquid phase, the residue was washed with water,
dried and dissolved in chloroform. The organic solution
was extracted several times with water until this resulted
colourless. The organic phase was evaporated and dried to
afford a crude residue that was crystallised from
chloroform obtaining colourless crystals (3.88 g, 33%
yield).
4.4 Crystallography
Crystallographic measurements for compounds 1–5 were
carried out with an Oxford-Diffraction XCALIBUR E CCD
diffractometer (Oxford Diffraction Limited, Oxford, UK)
equipped with graphite-monochromated Mo Ka radiation.
The crystals were placed 40 mm from the CCD detector.
The unit cell determination and data integration were
carried out using the CrysAlis package of Oxford
Diffraction (30). All structures were solved by direct

10
M.-F. Zaltariov et al.
u
a
b
g
u

Supramolecular Chemistry
11
IR nmax (KBr), cm21: IR nmax (KBr), cm21: 3433 m,
3352 s, 3236 m, 2957 w, 2907 w, 1695 vs, 1643 s, 1599 vs,
1514 s, 1441 m, 1410 w, 1315 vs, 1302 vs, 1254 s, 1171 s,
1117 s, 1074 s, 955 w, 843 s, 798 s, 771 s, 729 w, 700 m,
635 w, 604 m, 505 m, 393 w. 1H NMR (CDCl3,
400.13 MHz, d, ppm): 7.86 (d,3JH,H ¼ 8.4 Hz, 4H,
H3,5,16,20), 6.66 (d,3JH,H ¼8.4Hz, 4H, H2,6,17,19), 4.09
711 m, 690 s, 634 w, 603 w, 553 w, 538 w, 503 vw, 486 vw,
459 vw, 399 w.
1H NMR (CDCl3, 400.13 MHz, d, ppm): 14.03 (s, 2H,
OH), 8.56 (s, 2H, H7,28), 8.10 (d,3JH,H ¼ 8.4 Hz, 4H,
4
H10,12,23,27), 7.80 (d, JH,H ¼ 2.4 Hz, 2H, H4,32), 7.52
(d, 4JH,H ¼ 2.4 Hz, 2H, H6,30), 7.30, (d, 4H, H9,13,24,26,
overlap with solvent residual peak), 4.04 (s, 4H, H15,20),
0.30 (s, 12H, H16-19). 13C NMR (CDCl3, 100.16 MHz,
d, ppm): 166.4 (C14,21), 161.6 (C7,28), 157.3 (C2,34),
150.4 (C8,25), 138.7 (C4,32), 133.7 (C6,30), 131.0
(C10,12,23,27), 129.5 (C11,22), 121.2 (C9,13,24,26),
120.4 (C1,29), 112.3 (C3,33), 110.5 (C5,31) 58.4
(C15,20), 20.8 (C16-19).
(s, 4H, NH2), 3.94 (s, 4H, H8,13), 0.21 (s, 12H, H9-12). 13
C
NMR (CDCl3, 100.16 MHz, d, ppm): 167.3 (C7,17), 150.67
(C1,18), 131.4 (C3,5,16,20), 120.0 (C4,15), 113.8
(C2,6,17,19), 57.4 (C7,14), 20.8 (C9-12).
4.5.3 Synthesis of Schiff bases
4.5.3.1 Synthesis of the imine 2 derived from the diamine
1 and salicylaldehyde. To a stirred solution of diamine, 1,
(0.432 g, 1 mmol) in methanol/chloroform (1:2, v/v),
freshly distilled salicylaldehyde (0.244 g, 0.21 mL,
2 mmol) was added and the mixture was stirred at room
temperature for 3 h. A yellow precipitate was formed. The
product was filtered, washed with diethyl ether and then
crystallised from acetonitrile (0.58 g, 90% yield). IR nmax
(KBr), cm21: 3415 vw, 3060 w, 2958 w, 2906 w, 2854 vw,
1720 vs, 1620 s, 1598 vs, 1571 s, 1523 w, 1506 w, 1492 m,
1454 m, 1415 m, 1384 w, 1361 m, 1319 vs, 1292 s, 1280 s,
1249 vs, 1186 m, 1172 s, 1149 s, 1110 s, 1056 vs, 1012 m,
968 w, 958 w, 910 w, 850 s, 837 s, 800 s, 771 s, 752 s,
731 m, 690 m, 663 w, 634 w, 597 w, 557 w, 516 m, 443 w,
397 m.
4.5.3.3 Synthesis of the imine 4 derived from diamine 1
and 5-chlorosalicylaldehyde. To a stirred solution of
diamine, 1, (0.432 g, 1 mmol) in methanol/chloroform
(1:2, v/v), 5-chlorosalicylaldehyde (0.313 g, 2 mmol) was
added and the mixture was stirred at room temperature for
3 h. A solid yellow precipitate was formed. The product
was filtered, washed with diethyl ether and then crystal-
lised from chloroform (0.66 g, 95% yield). IR spectrum
(KBr pellet), cm21: 3373 w, 3060 vw, 2958 w, 2904 w,
1706 vs, 1618 m, 1600 s, 1562 s, 1517 w, 1504 w, 1479 s,
1431 w, 1415 m, 1384 m, 1357 m, 1317 vs, 1278 s, 1255 vs,
1170 s, 1118 s, 1072 s, 1014 m, 991 w, 979 w, 968 w, 925 w,
842 s, 817 s, 798 s, 785 s, 769 s, 727 m, 696 m, 671 w,
649 m, 636 w, 536 w, 516 w, 443 vw, 399 w.
1H NMR (CDCl3, 400.13 MHz, d, ppm): 12.93 (s, 2H,
OH), 8.64 (s, 2H, H7,28), 8.11 (d,3JH,H ¼ 8.4 Hz, 4H,
H10,12,23,27), 7.45–7.41 (m, 4H, H4,6,32,34), 7.31
(d,3JH,H ¼ 8.4 Hz, 4H, H9,13,24,26), 7.06, (d,
H5,33), 4.05 (s, 4H, H15,20), 0.31 (s, 12H, H16-19). 13C
NMR (CDCl3, 100.16 MHz, d, ppm): 166.6 (C14,21),
164.0 (C7,28), 161.2 (C2,30), 152.3 (C8,25), 133.7
(C4,32), 132.6 (C6,34), 130.8 (C10,12,23,27), 128.5
(C11,22), 121.1 (C9,13,24,26), 119.2 (C5,33), 118.9
(C1,29), 117.3 (C3,31), 58.2 (C15,20), 20.8 (C16-19).
1H NMR (CDCl3, 400.13 MHz, d, ppm): 12.92 (s, 2H,
OH), 8.57 (s, 2H, H7,28), 8.11 (d,3JH,H ¼ 8.4 Hz, 4H,
4
H10,12,23,27), 7.40 (d, JH,H ¼ 2.4 Hz, 2H, H6,34), 7.38
(dd, 3JH,H ¼ 8.8 Hz, 4JH,H ¼ 2.4 Hz, 2H, H4,32), 7.30, (d,
4H, H9,13,24,26, overlap with solvent residual peak), 7.01
(d, 3JH,H ¼ 8.8 Hz, 2H, H3,31) 4.04 (s, 4H, H15,20), 0.30
(s, 12H, H16-19). 13C NMR (CDCl3, 100.16 MHz, d,
ppm): 166.5 (C14,21), 162.7 (C7,28), 159.7 (C2,30),
151.7 (C8,25), 133.5 (C4,32), 131.5 (C6,34), 130.9
(C10,12,23,27), 129.0 (C11,22), 123.9 (C1,29) 121.1
(C9,13,24,26), 119.6 (C5,33), 118.9 (C3,31), 58.3
(C15,20), 20.8 (C16-19).
3
3JH,H ¼ 8.4 Hz, 2H, H3,31), 6.98 (t, JH,H ¼ 7.4 Hz, 2H,
4.5.3.2 Synthesis of the imine 3 derived from the diamine
1 and 3,5-dibromosalicylaldehyde. To a stirred solution of
diamine, 1, (0.432 g, 1 mmol) in methanol/chloroform (1:2,
v/v), 3,5-dibromosalicylaldehyde (0.567 g, 2 mmol) was
added and the mixture was stirred at room temperature for
3 h. A red precipitate was formed. The product was filtered,
washed with diethyl ether and then crystallised from
chloroform (0.87 g, 91% yield). IR spectrum (KBr pellet),
cm21: 3402 w, 3066 w, 2958 w, 2906 w, 1710 vs, 1703 vs,
1616 m, 1591 vs, 1550 m, 1502 w, 1446 s, 1427 m, 1413 m,
1384 m, 1357 m, 1313 vs, 1251 s, 1199 m, 1164 vs, 1110 s,
1055 s, 1014 m, 989 w, 945 w, 839 s, 798 s, 773 s, 738 m,
4.5.3.4 Synthesis of the imine 5 derived from the diamine
1 and 3,5-di-tert-butyl-2-hydroxybenzaldehyde. To a
stirred solution of diamine, 1, (0.432 g, 1 mmol) in
methanol/chloroform (1:2, v/v), 3,5-di-tert-butyl-2-hydro-
xybenzaldehyde (0.468 g, 2 mmol) was added. The
mixture was refluxed for 4 h, then the solvent mixture
was slowly evaporated at room temperature, which
resulted in the formation of yellow crystals (0.72 g, 83%
yield). IR spectrum (KBr pellet), cm21: 3402 w, 2997 w,
2958 s, 2910 m, 2868 m, 1710 vs, 1649 m, 1618 s, 1602 s,
1577 vs, 1504 w, 1465 m, 1438 m, 1413 m, 1384 s, 1363 m,

12
M.-F. Zaltariov et al.
187; (c) Arulmurugan, S.; Kavitha, H.P.; Venkatraman,
B.R. Rasayan J. Chem. 2010, 3, 385–410.
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1311 s, 1299 s, 1249 s, 1199 m, 1166 vs, 1114 s, 1056 s,
1016 m, 997 w, 983 w, 964 w, 931 vw, 879 m, 852 s, 839 s,
798 s, 769 s, 715 m, 696 m, 642 w, 619 vw, 588 vw, 534 vw,
513 w, 397 w, 379 vw.
1H NMR (CDCl3, 400.13 MHz, d, ppm): 13.43 (s, 1H,
OH), 8.68 (s, 1H, H15), 8.12 (d,3JH,H ¼ 8.4 Hz, 2H,
4
H18,20), 7.53 (d, JH,H ¼ 2.4 Hz, 1H, H4), 7.34
(d, 3JH,H ¼ 8.4 Hz, 2H, H17,21), 7.28, (d, 4JH,H ¼ 2.4 Hz,
1H,H6),4.06(s,2H,H23),1.52(s,9H,H12-14),1.38(s,9H,
H12-14), 0.31 (s, 6H, H24,25). 13C NMR (CDCl3,
100.16 MHz, d, ppm): 166.8 (C22), 165.2 (C15), 158.4
(C2), 152.6 (C16), 140.8 (C5), 137.1 (C3), 130.9 (C18,20),
128.7 (C4), 128.2 (C19) 127.1 (C6), 121.1 (C17,21), 118.1
(C1), 58.2 (C23), 35.1 (C7), 34.2 (C11), 31.4 (C12-14), 29.4
(C8-10), 20.8 (C24,25).
´
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(3), CCDC-901928 (4) and CCDC-901924 (5) contain the
supplementary crystallographic data for this contribution.
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: (þ44) 1223-336-033; or
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Copies of FTIR, H NMR, 13C NMR, H,H-COSY, H,C-
HMQC, and H,C-HMBC spectra for all key intermediates
and final products; figures showing p–p stacking
association for the compounds 2–5 are also enclosed.
Acknowledgements
This research was financially supported by European Regional
Development Fund, Sectoral Operational Programme ‘Increase
of Economic Competitiveness’, Priority Axis 2 (SOP IEC-A2-
O2.1.2-2009-2, ID 570, COD SMIS-CSNR: 12473, Contract
129/2010-POLISILMET).
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14
M.-F. Zaltariov et al.
Mirela-Fernanda Zaltariov, Maria Cazacu,
Nicoleta Vornicu, Sergiu Shova, Carmen Racles,
Mihaela Balan and Constantin Turta
A new diamine containing disiloxane moiety and
some derived Schiff bases: synthesis, structural
characterisation and antimicrobial activity
1–14