Synthesis, characterization, reactivity, and antibacterial studies of triethylammonium-3-silatranylpropyldithiocarbamate, spectroscopic, and quantum mechanical studies of 3-(silatranyl)propylammonium chloride

Article abstract of DOI:10.1080/15533174.2011.618474

3-aminopropylsilatrane (1) was crystallized as its hydrochloride salt, 3-(silatranyl)propylammonium chloride (2), which was confirmed by spectroscopic and X-ray diffraction studies. Single-crystal X-ray data revealed orthorhombic crystal system (space group = P₂₁₂₁₂₁) with three molecules packed in an asymmetric unit cell. Herein, a special emphasis on the experimental and computational methods is given to study the geometric and spectroscopic parameters of 3-(silatranyl)propylammonium chloride (2). The scaled values of vibrational frequencies were obtained by using different basis sets. To study the reactivity of 1 toward nucleophilic addition reactions, it was treated with CS₂ in the presence of triethylamine, which resulted in a novel silatrane, triethylammonium-3-silatranylpropyldithiocarbamate (4). Due to its ability to act as bidentate ligand (L), reactivity of 4 was studied by reacting it with Cu(II), Co(II), Ni(II), and Pd(II) metal salts. The composition, nature of bonding, and geometry of complexes have been deduced from elemental analysis, and infrared and electronic spectral studies. The electronic and vibrational absorption spectra of these complexes indicated the formation of Cu(II), Ni(II), and Pd(II) complexes in 1: 2 ratio but 1:3 ratio (M:L) in Co(II) complex. Compound 4 is found to be moderately active against some bacteria such as Esherichia coli, Bacillus subtillus, and Staphylococcus aureus.

Full text of DOI:10.1080/15533174.2011.618474

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 42:823–832, 2012
Copyright ꢀ Taylor & Francis Group, LLC
C
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2011.618474
Synthesis, Characterization, Reactivity, and Antibacterial
Studies of Triethylammonium-3-
silatranylpropyldithiocarbamate, Spectroscopic, and
Quantum Mechanical Studies of
3-(Silatranyl)propylammonium Chloride
Raghubir Singh,1 Jugal Kishore Puri,2 Varinder Kaur Chahal,2 Raj Pal Sharma,2
Sabeta Kohli,3 Rajni Kant,3 and Baljinder Singh Gill4
1Department of Applied Sciences, Sachdeva Engineering College for Girls, Gharuan, Mohali, India
2Department of Chemistry, Panjab University, Chandigarh, India
3Department of Physics, University of Jammu, Jammu Tawi, India
4Department of Biotechnology, Panjab University, Chandigarh, India
INTRODUCTION
3-aminopropylsilatrane (1) was crystallized as its hydrochlo-
ride salt, 3-(silatranyl)propylammonium chloride (2), which was
confirmed by spectroscopic and X-ray diffraction studies. Single-
crystal X-ray data revealed orthorhombic crystal system (space
group = P212121) with three molecules packed in an asymmet-
ric unit cell. Herein, a special emphasis on the experimental and
Silatranes have captured extensive interest of scientists due
to their unusual structure, biological properties and applica-
tions in the field of material sciences.[1–4] A variety of deriva-
tives of 3-aminopropylsilatrane have been prepared in the past
due to reactivity of –NH2 group with various reagents such as
computational methods is given to study the geometric and spectro- alkyl halides, aryl halides, phosphoramide-tegafur derivatives,
phosphoryl halides, and dicyclohexylcarbodiimide.[4,5] It is
well known that silatranes derived from 3-aminopropylsilatrane
scopic parameters of 3-(silatranyl)propylammonium chloride (2).
The scaled values of vibrational frequencies were obtained by using
different basis sets. To study the reactivity of 1 toward nucleophilic
addition reactions, it was treated with CS2 in the presence of tri-
such as 1-arylaminopropylsilatranes (aryl = chlorophenyl
and nitrophenyl) and 1-arylsulfonylaminopropylsilatranes
ethylamine, which resulted in a novel silatrane, triethylammonium-
3-silatranylpropyldithiocarbamate (4). Due to its ability to act as exhibit significant antimicrobial activity against gram-
negative and gram-positive bacteria.[6,7] In addition, 3-
formylchromoniminopropylsilatrane and its metal complexes
bidentate ligand (L), reactivity of 4 was studied by reacting it with
Cu(II), Co(II), Ni(II), and Pd(II) metal salts. The composition, na-
ture of bonding, and geometry of complexes have been deduced
from elemental analysis, and infrared and electronic spectral stud-
showed antibacterial activity against K. pneumoniae, S. aureus,
E. coli, and B. subtilis.[8]
ies. The electronic and vibrational absorption spectra of these
complexes indicated the formation of Cu(II), Ni(II), and Pd(II)
complexes in 1: 2 ratio but 1:3 ratio (M:L) in Co(II) complex.
Compound 4 is found to be moderately active against some bacte-
ria such as Esherichia coli, Bacillus subtillus, and Staphylococcus
aureus.
Prompted by favorable research work and our interest in
the field of organosilicon complexes,[9–11] we worked on 1 in
order to explore its reactivity. In the present contribution, the
molecular structure of 3-(silatranyl)propylammonium chloride
(2), established by X-ray crystallography and its comparison
with theoretical studies, is reported. The optimization of struc-
ture was done by using computational studies such as Density
Functional Theory (DFT) and Hartree-Fock theory with differ-
ent basis sets.
Keywords 3-aminopropylsilatrane, dithiocarbamate, DFT, HF,
metal complexes, Triethylammonium-3-silatranylpropyl-
dithiocarbamate
Previously, we reported one-pot synthesis of 3-
isothiocyanatopropylsilatrane in which CS2 was reacted with
Received 4 January 2011; accepted 21 August 2011.
Raghubir Singh is thankful to UGC, New Delhi for providing finan- 1 to form its dithiocarbamic acid, followed by addition of dicy-
clohexylcarbodiimide.[5] In the presented work, dithiocarbamate
cial support [F-4–1/2006 (BSR)]. Rajni Kant is thankful to Ministry
of Science and Technology, Govt. of India for funding under major
research [project No. SR/S2/CMP-47].
Address correspondence to Jugal Kishore Puri, Department of
Chemistry, Panjab University, Chandigarh 160 014, India. E-mail:
prof jkpuri@yahoo.com
of 1 (derivatives of dithiocarbamic acid) was synthesized by ad-
dition of carbon disulphide in the presence of triethylamine,
which resulted in the formation of [3-(2,8,9-trioxa-5-aza-1-sila-
bicyclo[3.3.3]undec-1-yl)-propyl]-dithiocarbamic acid (3). As
823

824
R. SINGH ET AL.
TABLE 1
the compound was insoluble in common organic solvents, its
triethylammonium salt (4) was prepared for characterization.
Since dithiocarbamates are known to be very good chelating
agents and can stabilize a wide range of oxidation states of dif-
ferent metal ions due to their unique property to remain intact
under a variety of reaction conditions.[12,13] Therefore, differ-
ent metal complexes (5–8) have been prepared to study the
reactivity of 4 as coordinating ligand. Compound 4 also shows
antibacterial activity against Esherichia coli, Bacillus subtillus,
and Staphylococcus aureus.
X-ray crystal data and structure refinement of 2
Empirical formula
Formula weight
Temperature
(C9H21ClN2O3Si)3
806.45
293(2) K
Diffractometer used
X’calibur Single crystal
diffractometer
Radiation used,
wavelength
Crystal system, space
group
MoKα, 0.71073 Å
Orthorhombic, P212121
Unit cell dimensions (Å) a = 11.3331(7), b = 17.9935(10), c
= 19.7443(9); α = 90◦, β = 90◦,
γ = 90◦
EXPERIMENTAL
Materials and Methods
Volume
4026.3(4) Å3
12 (three molecules in a unit cell)
1.330 Mg/m3
All the syntheses were carried out under a dry nitrogen atmo-
sphere using vacuum glassline. Organic solvents used were dried
and purified according to standard procedures and stored under
nitrogen. 3-aminopropyl(triethoxy)silane (Aldrich, St. Louis,
USA), triethanolamine (Merck, India), and carbon disulphide
(Qualigens, India) were used as such without any further pu-
rification. Triethylamine (Qualigens, India) was kept over KOH
for several days and distilled prior to use. Infrared spectra were
routinely obtained as Nujol thin films or KBr pellets on a Perkin-
Elmer RX-I FT IR spectrophotometer (USA). Mass spectral
measurements (ESI source with capillary voltage, 2500 V) were
carried out on a VG Analytical (70-S) spectrometer. C, H, and N
analyses were obtained on a Perkin-Elmer Model 2400 CHN el-
emental analyzer (USA). S and Si were estimated by gravimetric
methods. The solution NMR spectra were recorded at 25◦C on
Jeol FT NMR (AL 300 M Hz) and Bruker Avance II FT NMR
(AL 400 MHz) spectrometers (USA) (1H, 13C) using CDCl3 as
the solvent. Chemical shifts in ppm were determined relative to
internal CDCl3 and external tetramethylsilane (TMS).
Z
Density (calculated)
F(000)
1728
Crystal size
Theta range for data
collection
0.30 × 0.22 × 0.20 mm
3.07 to 32.39◦
Index ranges
–16 ≤ h ≤ 13, –26 ≤ k ≤ 19, –28 ≤
l ≤ 29
Reflections collected
Independent reflections
Refinement method
Data / restraints /
17158
11291 [R(int) = 0.0306]
Full matrix least squares on F2
11291/ 0 / 470
parameters
Goodness-of-fit on F2
Final R indices, 1631
reflections [I > 2σ(I)]
R indices (all data)
Absorption corrections
0.957
R1 = 0.0548, wR2 = 0.1194
R1 = 0.0942, wR2 = 0.1306
None
X-Ray Crystallography
Three-dimensional intensity data were collected by using
X’calibur single-crystal X-ray diffractometer with CCD cam-
era using MoKα radiation (λ = 0.71073 Å). CrysAlisPro soft-
ware was employed for data collection, data reduction, and
space group determination.[14] The structure was solved by
direct methods using SHELXS86 software (England). Full-
matrix least-squares refinement of the non-hydrogen atoms with
isotropic temperature factors was carried out using SHELXL97
(England). Subsequent cycles of refinement yielded final R-
factor of 0.0548. All principle crystallographic parameters and
X-ray diffraction characteristics are summarized in Table 1.
(B3LYP) with 3–21G∗(d), 6–31+G∗(d), and 6–311+G∗(d) ba-
sis sets.
Assessment of Antibacterial Activity
Disc diffusion method
Antimicrobial activity was determined by disk diffusion
method. In this technique, the filter paper (Whatman no. 1)
sterile disc of 5 mm diameter impregnated with test compounds
(2 mg/mL of DMSO) were placed in nutrient agar plate at 37◦C
for 12 h. The inhibition zones around the dried impregnated
disks were measured after 12 h.
Theoretical Studies
Test microorganism
Quantum mechanical calculations were carried out by us-
ing GAUSSIAN 03 series of programs (USA). Geometries
Test isolates were taken from the MTCC (Microbial Type
were fully optimized at both the Restricted Hartree-Fock (RHF) Culture Collection) at the Institute of Microbial Technology
and DFT level, using Becke’s three-parameter hybrid exchange (IMTECH), Chandigarh, India, and included Escherichia coli,
functional and the correlation functional of Lee, Yang, and Parr Bacillus subtillus, and Staphylococcus aureus.

3-(SILATRANYL)PROPYLAMMONIUM CHLORIDE
825
Found: C, 35.99; H, 5.60; N, 8.05; Si, 8.02; IR: cm−1, 1509
vs ν (C-N), 1010 vs ν (C-S), 581 w ν (Si-N), 477 s ν (Co-S);
UV-Vis: nm, 655, 322, 245.
Synthesis of 3-aminopropylsilatrane (1)
The starting material 1 was synthesized according to
the method reported in literature.[15] 3-aminopropyl(triethoxy)
silane (5.00 g, 22.5 mmol) was added at room temperature to tri-
ethanolamine (3.36 g, 22.5 mmol) in a two-necked flask which
was fitted with a Dean Stark trap. The resulting mixture was re-
fluxed to remove ethanol formed during the reaction. After the
complete removal of ethanol, the reaction mixture was kept in
refrigerator for 5 h, when white solid was obtained. Dry hexane
was added, and contents were stirred for 30 min, filtered, and
dried under vacuum.
Synthesis of Cu Complex (6)
To a well-stirred solution of 4 (0.5 g, 1.22 mmol) dissolved in
acetonitrile, anhydrous CuCl2 (0.08 g, 0.61 mmol) was added.
The contents were stirred for 5 h at room temperature. A brown-
colored solution was obtained, which indicated complexation of
copper with 3. The solution was filtered under vacuum, solvent
was evaporated near to dryness, and hexane was added. The
contents were stirred for 30 min, filtered, and brown solid was
dried under vacuum. Anal. Calcd. for C20H40CuN4O6S4Si2: C,
35.30; H, 5.92; N, 8.23; Si, 8.25; Found: C, 32.83; H, 5.08; N,
8.13; Si, 7.67; IR: cm−1, 1528 vs ν (C-N), 1011 vs ν (C-S), 581
w ν (Si-N), 459 s ν (Cu-S); UV-Vis: nm, 431, 370.
Synthesis of
Triethylammonium-3-silatranylpropyldithiocarbamate (4)
3-aminopropylsilatrane (2 g, 8.62 mmol) in dry THF (50 mL)
was taken in a 100 mL two-necked round bottom flask and
to this solution 2 mL of CS2 was added dropwise with con-
stant stirring. The reaction mixture was cooled in an ice salt
mixture. A light yellow solid separated out immediately. The
contents were stirred for 30 min. Then, triethylamine (1 mL,
8.62 mmol) was added dropwise with constant stirring. Ini-
tially, yellow solid was dissolved but reappeared after 10 min.
The reaction mixture was stirred for 5 h at room temperature.
The crude product was filtered, washed with THF (2 × 10 mL),
and dried under vacuum. M.Pt: 142–145◦C. Yield: 3.13 g, 90%.
Anal. Calcd. for C16H35N3O3S2Si (%): C, 46.91; H, 8.61; N,
10.26; S, 15.65; Si, 6.86. Found: C, 46.70; H, 7.98; N, 10.01;
S, 14.78; Si, 6.02. IR (KBr pellet, cm−1): 3356, 3181 s ν (N-
H), 2926, 2871 vs, ν (C-H), 1630 m, ν (C = S), 1471 vs,
ν (C-N), 1360 m, 1325 m, ω (CH2N), 1278 m, ω (CH2O),
1185 m, τ (CH2O), 1121 s, 1096 s, 987 s, 938 s, ν (Si-O-
C-C), 760 s, δas (SiO3), 716 vs, 613 m, δ (C = S), 645 m,
Synthesis of Ni Complex (7)
In dry acetonitrile, 4 (0.5 g, 1.22 mmol) was taken in a round-
bottomed flask and nickel chloride (0.08 g, 0.61 mmol) was
added. Light green color appeared and the contents were stirred
for 5 h at room temperature. The precipitated solid was filtered
and solvent was evaporated when green solid was obtained.
Hexane was added, stirred for 30 min, filtered, and dried under
vacuum. Anal. Calcd. for C20H40N4NiO6S4Si2: C, 35.55; H,
5.97; N, 8.29; Si, 8.31; Found: C, 34.50; H, 5.10; N, 7.94; Si,
7.98; IR: cm−1, 1543 vs ν (C-N), 1012 vs ν (C-S), 581 w ν
(Si-N), 455 s ν (Ni-S); UV-Vis: nm, 380, 324.
Synthesis of Pd Complex (8)
To the stirred solution of 4 (0.5 g, 1.22 mmol) in dry
acetonitrile, palladium chloride (0.12 g, 0.61 mmol) was added.
The mixture turned brown upon stirring for 5 h. The contents
were filtered and reduced under vacuum. Hexane was added to
obtain a brown solid, which was filtered, washed with 15 mL of
hexane. The solid was dried under vacuum and analyzed with
spectroscopic methods. Anal. Calcd. for C20H40N4O6PdS4Si2:
C, 33.21; H, 5.57; N, 7.74; Si, 7.76; Found: C, 33.01; H, 5.33;
N, 7.01; Si, 7.02; IR: cm−1, 1547 vs ν (C-N), 1012 vs ν (C-S),
581 w ν (Si-N), 446 s ν (Pd-S); UV-Vis: nm, 296.
1
δs (SiO3), νs (Si-C), 584 m ν (Si←N), 472 m, δ (NCS). H
NMR (400 MHz, CDCl3, ppm): δ 3.75–3.78 (t, 6H, OCH2),
2.80–2.83 (t, 6H, NCH2), 0.431–0.455 (t, 2H, CH2Si), 1.66–1.70
(m, 2H, CCH2C), 3.50–3.51 (t, 2H, CH2NCS2), 1.35–1.39 (t,
9H, CCH3), 3.22–3.27 (q, 6H, NHCH2), 8.00 (s, 1H, NH), 8.59
(s, 1H, NH). 13C NMR (100.62 MHz, CDCl3, ppm): δ 209.41
(NCS2), 55.33 (OCH2), 49.37 (CH2NC), 48.99 (NCH2), 43.75
(NHCH2), 21.78 (CCH2C), 11.51 (SiCH2), 6.91 (CH3). EI-MS:
m/z (relative abundance,%): 233.5 (23.01), 192.5 (29.51), 174.5
(14.68), 150.5 (1.65), 102.5 (100).
RESULTS AND DISCUSSION
Synthesis
Synthesis of Co Complex (5)
Investigation of spectroscopic data and crystallographic de-
tails of crystals evidenced the formation of 1·HCl. It was con-
cluded from literature survey that 1 undergoes a photochemi-
cal reaction in dichloromethane to form its ammonium salt. In
the past, Balsells et al.[16] discussed photochemical behavior of
aliphatic amines in dichloromethane and suggested the forma-
tion of hydrochlorides of different primary amines in amine-
dichloromethane mixture. A proposed mechanism for the for-
mation of 2 from mixture of 1 in dichloromethane is given in
Scheme 1.
To a well-stirred solution of 4 (0.5 g, 1.22 mmol) dissolved
in acetonitrile, anhydrous CoCl2 (0.053 g, 0.41 mmol) was
added. Green coloration appeared immediately. The contents
were stirred for 5 h at room temperature. The solution became
dark green during the course of reaction, which indicated com-
plexation of cobalt with 3. The contents were filtered under
vacuum and solvent was evaporated near to dryness. Hexane
was added and the contents were stirred for 30 min. Green
solid was filtered under vacuum and dried. Anal. Calcd. for
C30H60CoN6O9S6Si3: C, 36.60; H, 6.14; N, 8.54; Si, 8.56;

826
R. SINGH ET AL.
SCH. 1.
The previously mentioned mechanism involves the photoex- dichloromethane-hexane mixture. ORTEP view of asymmetric
citation of 1 in which it is elevated to higher energy excited unit along with atomic labeling (thermal ellipsoids are drawn
state (S1). The reaction proceeds via n-σ∗ transition generating at 50% probability) is shown in Figure 1. The bridging ele-
diradical or zwitterionic state. This excited molecule then ab- ments in rings are labeled as Ring R1 (N1, Si, O3, C6, C5),
stracts hydrogen from the solvent, resulting in the formation of Ring R2 (N1, Si, O1, C1, C2), and Ring R3 (N1, Si, O2, C3,
ammonium ion, which facilitates the transfer of Cl− ion with C4). The corresponding atoms in molecule I and III have been
ꢁ ꢁꢁ
simultaneous generation of carbene.
represented by and , respectively. The molecules I, II, and
The participation of aminopropylsilatrane (1) in nucleophilic III comprise three five-membered rings with Si-N as a com-
addition reactions was confirmed by treating it with CS2 (1:1) mon (fused) bond. Si-N bond distances in case of all the three
followed by addition of triethylamine, which resulted in the asymmetric molecules (2.113(2) Å, 2.190(3) Å, and 2.116(3)
formation of 4 (Scheme 2). From the previous reports, it Å) are in agreement with the structural trends found for sila-
was found that Si-N bond undergoes cleavage on addition tranes. Selected bond lengths and angles for 2 are summarized in
of electrophiles resulting in the quaternization of N atom.[17] Table 2.
Herein, it is observed that addition of CS2 results in the for-
In the asymmetric unit, there exist three independent
mation of new silatrane without affecting transannular Si-N molecules. The molecules I and II a+dopt anticlinal confor-
bond. The presence of S atoms makes 4 very interesting, as mation A in which CH2CH2CH2NH3 moiety is oriented in
it can display variable coordination modes. Different metal a zig-zag fashion (Figure 2). W+hereas molecule III acquired
ions such as Cu, Co, Ni, and Pd form different metal com- conformation B in which NH3 group of chain is present
plexes with 4. Among these metal ions, Cu(II), Pd(II), and on same side of CH2(α) (i.e., the chain is not in a zig-
Ni(II) form 1:2 complexes, whereas Co(II) forms a 1:3 (M:L) zag fashion). The molecule III stays in this conformation
complex.
TABLE 2
X-Ray Crystal Structure
Selected bond lengths (Å) and angles (◦) of I, II, and III
Crystals of 2 were obtained by slow evaporation of sol-
vent from saturated solution of 1 in dichloromethane and
Bond length, Bond
angles
Molecule I Molecule II Molecule III
O(1)-Si (av)
Si-C(7)
Si-N(1)
N(1)-C(4) (av)
C(8)-C(7)
C(8)-C(9)
1.670 (2)
1.888 (3)
2.113 (2)
1.461 (5)
1.520 (4)
1.522 (4)
1.481 (5)
118.66 (1)
96.53 (1)
179.08 (1)
113.5 (3)
113.6 (2)
114.2 (2)
109.9 (3)
1.653 (3)
1.873 (3)
2.190 (3)
1.463 (5)
1.521 (5)
1.509 (4)
1.484 (4)
117.30 (2)
97.55 (1)
179.29 (2)
113.0 (3)
112.3 (3)
112.2 (2)
109.7 (3)
1.671 (2)
1.868 (3)
2.116 (3)
1.393 (6)
1.517 (4)
1.514 (5)
1.496 (5)
119.35 (1)
96.63 (1)
178.41 (1)
112.3 (7)
113.3 (3)
117.0 (2)
112.2 (3)
N(2)-C(9)
O(2)-Si-O(3) (av)
O(2)-Si-C(7) (av)
C(7)-Si-N(1)
C(4)-N(1)-C(5)
C(7)-C(8)-C(9)
C(8)-C(7)-Si
N(2)-C(9)-C(8)
SCH. 2.

3-(SILATRANYL)PROPYLAMMONIUM CHLORIDE
827
FIG. 1. Perspective view of asymmetric unit cell with atomic numbering scheme (thermal ellipsoids drawn at 50% probability) (color figure available online).
presumably due to extra stabilization caused by N2ꢁꢁ-
it is difficult to depict hydrogen-bonded network with clarity.
However, the plot (Figure 3) clearly displays network of few
intra- and intermolecular hydrogen bonds of the type C-H. . .O,
C-H. . .Cl, N-H. . .Cl and N-H. . .O.
H10G. . .Cl−ꢁꢁ interaction, which forced CH2-NH3 bond to
+
rotate toward Cl−. The molecular arrangement of this kind
is quite favorable in the formation of a trifurcated Cl− ion
interaction.
Unit cell packing revealed the arrangement of molecules in
a zig-zag fashion along the b-direction in the bc-plane. The lat-
tice is further stabilized by some additional hydrogen bonded
interactions (between oxygen atoms of silatrane moiety and
hydrogen atom of NH3+ as well as CH2(γ )). In view of the mul-
tiple molecule phenomena as exhibited by the asymmetric unit,
The carbon atoms C5, C2ꢁꢁ, and C5ꢁꢁ, which are linked to
nitrogen (N1, N1a˝), have large thermal amplitude and hence are
found disordered. Asymmetry parameter calculations as pro-
posed by Duax and Norton for molecule I are: ring R1 (ꢀC2
= 14.498, ꢀCs = 5.4712), ring R2 (ꢀC2 = 11.981, ꢀCs =
5.0601), and ring R3 (ꢀC2 = 11.865, ꢀCs = 6.196). Corre-
sponding values for molecules II and III are: ring R1 (ꢀC2 =
2.5075, ꢀCs = 5.4712; ꢀC2 = 3.637, ꢀCs = 1.5578), for ring
R2 (ꢀC2 = 2.2000, ꢀCs = 13.5889; ꢀC2 = 6.5800, ꢀCs =
0.9398), and for ring R3 (ꢀC2 = 2.1066, ꢀCs = 15.424; ꢀC2
= 6.823, ꢀCs = 0.4716), respectively[18,19]
Theoretical Studies
The geometry of 2 was optimized and values for vari-
ous bond lengths and bond angles optimized by DFT/B3LYP
and HF methods with different basis sets such as 3–21G∗(d),
6–31+G∗(d), and 6–311+G∗(d) are given in Table 3. In the-
oretical calculations, the molecule is considered in gaseous
state; therefore, crystal effects are found to be absent. Some
bond lengths and angles such as the Si-C bond length computed
with DFT/3–21G∗(d) were almost similar with X-ray crystallo-
graphic data but Si-N, Si-O (av.), and N-C bond lengths deviate
from the experimental values. The changes observed in bond
lengths might be because of crystal packing forces in the solid
state.
FIG. 2. Conformation of independent molecules; A belongs to I and II, B
belongs to molecule III (color figure available online).

828
R. SINGH ET AL.
FIG. 3. Unit cell molecular packing diagram showing hydrogen-bonding network along b direction in bc plane (color figure available online).
in the range 833–967 cm−1 obtained from theoretical calcu-
lations. Two bands observed at 1124 cm−1 and 971.5 cm−1
for symmetric and asymmetric stretching of NC3 fragment of
silatrane ring are displayed in the range of 1055–1160 cm−1
and 976–972 cm−1, respectively, by theoretical studies. In ad-
dition, Si–N stretching frequency is of great interest as it in-
dicates hypervalency of silicon. Theoretically, this absorption
band along with silatranyl skeletal vibrations is obtained in
the region 570–600 cm−1 that is in accordance with experi-
mental data (i.e., at 583.4 cm−1). In the present studies, Si-O
asymmetric and symmetric stretching is observed in the re-
gion of 1110–1170 cm−1 and 740–760 cm−1, respectively. In
addition, investigation of silatranes for structural fragment of
Si-O-C-C was characterized by typical frequencies appearing
in the region of 1480–575 cm−1. Therefore, experimental data
of this molecule are found to be consistent with theoretical
data.
Spectroscopic Studies
IR spectroscopy
Theoretical values for fundamental vibrational frequencies
optimized by HF and DFT/B3LYP using 6–31+G∗(d) basis
sets are given in Table 4 and are compared with experimen-
tal IR frequencies. Comparison of frequencies calculated at the
DFT method using different basis sets with experimental val-
ues revealed that B3LYP method is in good agreement with
experimental observation. The HF and DFT methods showed
symmetric and asymmetric stretching for methylene groups in
the region of 2900–3000 cm−1, which are supported by ex-
perimental results. Theoretically, C-H stretching frequency for
O-CH2 is found to be higher than N-CH2, which is observed
experimentally at 2934.6 and 2875.9 cm−1
Generally, ν (C–N) absorption in silatranes is observed in
the range of 800–900 cm−1. In this molecule, position of the
ν (C–N) absorption is also observed at 863 cm−1, which lies
.

3-(SILATRANYL)PROPYLAMMONIUM CHLORIDE
829
TABLE 3
Selected bond lengths, bond angles, and other parameters optimized by DFT and HF studies of 2
HF
DFT
Parameters
3–21G∗(d)
6–31+G∗(d)
6–311+G∗(d)
3–21G∗(d)
6–31+G∗(d)
6–311+G∗(d)
Total energy; a.u
N(1)→Si
−1427.936
2.615
−1435.074
−1435.263
−1433.479
2.398
−1440.625
−1440.832
2.594
2.616
2.503
2.534
Si-C(7)
1.866
1.876
1.871
1.879
1.883
1.877
Si-O av.
1.649
1.646
1.641
1.692
1.679
1.674
N(1)-C(2,4,6) av.
N(2)-C(9)
1.468
1.518
2.936
1.448
1.487
2.939
1.448
1.486
2.936
1.490
1.519
2.875
1.462
1.492
2.868
1.460
1.491
2.872
NH3+-Cl−
N(2)-C(9)-C(8)
C(9)-C(8)-C(7)
C(8)-C(7)-Si
O(1)-Si(1)-O(2)
O(2)-Si(1)-O(3)
O(3)-Si(1)-O(1)
C(2)-N(1)-C(4)
C(4)-N(1)-C(6)
C(6)-N(1)-C(2)
111.75
113.78
112.33
113.69
113.15
112.70
117.46
117.45
117.39
112.59
114.50
114.51
114.31
113.81
113.48
117.83
117.79
117.79
112.72
114.51
114.60
113.94
113.43
113.15
118.01
117.98
117.97
112.70
113.90
113.05
117.05
116.69
116.12
115.38
115.37
115.31
113.71
114.57
114.93
116.12
115.51
115.38
116.88
116.86
116.85
113.69
114.53
114.88
115.71
115.08
114.91
117.17
117.15
117.14
1400–1150 cm−1 are assigned to asymmetric and symmetric
deformations of CH2 group, respectively. Si–O stretching vi-
bration is assigned to the bands present in 1100–1080 cm−1
region. A weak band observed in the region 480–450 cm−1 is
attributed to stretching vibrations of the M–S.
IR spectra of 4 exhibit absorption bands characteristic of
the dithiocarbamate and silatranyl moiety. These bands were
assigned by comparison with the spectra of starting materials
and literature data.[20–22] Strong bands present in the regions
C–S stretching frequencies are of great interest, as these can
be used to differentiate between mono- and bidentate modes of
binding of dithiocarbamate ligands. The absorption frequen-
cies for C-S and C = S can be observed in the region of
1350–1250 cm−1 and 1680–1470 cm−1, respectively. In these
studies, C = S stretching was observed at 1653 cm−1 in 4, which
is absent in metal complexes, indicating the absence of double
bond. In metal complexes (5–8), presence of only one band in
the region of 1061–980 cm−1 for ν(CSS) mode, suggests a sym-
metrical bonding of bidentate dithiocarbamate moiety. In the
free dithiocarbamate (4), C-N band was observed at 1471 cm−1
,
which was shifted in the range of 1550–1509 cm−1 after coordi-
nation with metals indicating the presence of partial double bond
character in C-N bond. Vibrational bands for silatrane moiety
remained unaffected after complexation. All the bands observed
for silatranyl moiety are consistent with literature in addition to
Si-N bond observed in the region 584–576 cm−1
.
NMR spectroscopy
1H and 13C NMR chemical shifts studied for molecular struc-
ture were obtained by HF and DFT (B3LYP) and compared with
experimental NMR data. GIAO 1H and 13C chemical shifts val-
ues (with respect to TMS) were obtained at HF/3–21G∗(d),
HF/6–31+G(d), B3LYP/3–21G∗(d), and B3LYP/6–31+G(d)
FIG. 4. Expected structures of complexes 5–8.

830
R. SINGH ET AL.
TABLE 4
Comparison of observed FT-IR and calculated frequencies of 2 In vitro antibacterial activity of compound 4 bacterial strain of
(HF and DFT methods) along with their probable assignments Bacillus subtillus using microbroth dilution assay
TABLE 6
>HF
DFT
Exp. Value
Assignments
MIC50
(mg/mL)
MIC90
(mg/mL)
MIC range
(mg/mL)
6–31+G (d)
3383
6–31+G (d)
Compound 4
Ampicillin
1.8
0.00004
3.9
0.0001
0.8–3.94
0.00002–0.0001
3407
3330
3378 s (b)
νas (N-H)
νs (N-H)
3314
2929–2910
2986–2965
νas (NCH2)
and νas
levels of theory for the optimized geometries. 13C chemical shift
values obtained with HF/3–21G∗(d) were found to be different
from the values obtained from other studies: HF/6–31+G∗(d),
B3LYP/3–21G∗(d), and B3LYP/6–31+G∗(d), which are found
to be consistent with experimental values. Comparing 1H NMR
spectra of 2 with those of 1, a downfield shift was observed
for CH2(β) and CH2(γ ). It may be attributed to the presence
of electron withdrawing Cl− adjacent to CH2(γ ). In addition, a
singlet observed at 1.9 ppm due to NH2 in 1 disappeared and a
singlet at 7.2 ppm for NH3+ protons appeared in 2 indicated the
formation of ammonium salt.
(OCH2)
2903
2872–2869
2839–2835
2973
2909–2906
2889–2886
νas (CCH2C)
νs (OCH2)
νs (NCH2)
2934.6 vs
2875.9 vs
1630.5 m
1620
1616
1534
1469
1458
1428
1367
1361
1290
1142
1119
1055
1016
976
1611
—
ρ (N-H)
ρ (N-H)
ω (NH3)
1506
1464
1458
1423
1369
1352
1275
1110
1088
1160
1068
972
1008
967
747
760
578
1532.1 s
1471.5 vs
δ (H3NCH2)
δ (CCH2C)
δ (SiCH2)
ω (OCH2)
ω (CH2CH2C)
t (CCH2C)
νas (Si-O)
ν (C-O)
νas (NC3)
ν (C-C) chain
νs (NC3)
ν (C-C) ring
ν (C-N) ring
νs (Si-O)
1414.6 w
1378.0 s
1326.6 s
1279.3 vs
1192.6 m
1124.0 vs
1096.8 vs
1016.7 s
971.5 w
938.8 s
1H NMR spectra of 4 shows a downfield shift for OCH2
(3.75–3.78 ppm) and NCH2 (2.80–2.83 ppm) protons of
Si(OCH2CH2)3N moiety as compared with precursor 1. Cor-
respondingly, triplet due to -CH2NCS2 protons is also shifted
downfield as compared to –CH2NH2. Comparison of NMR
data with previously reported 3-isothiocyanatopropylsilatrane
showed that peaks due to -CH2NCS2 and -CCH2C- are shifted
downfield, whereas there is no significant change in the posi-
tions of other peaks. This indicates that silatranyl moiety is not
affected by the presence of different groups on C3 (NCS or
NCS2) due to the presence of bridge formed by -CH2CH2CH2-
chain. In the 13C NMR, δ NCS2 appeared at 209.41 ppm, which
is shifted downfield as compared with δ NCS (177.05 ppm) in 3-
isothiocyanatopropylsilatrane. The peaks appearing at 55.0 and
48.0 ppm due to δ OCH2 and NCH2 are observed at the same
position as in 1.
958
833
768
706
909.3 s
762.8 vs
721.1 vs
583.4 s
ν (Si-C)
ν (Si-N)
595
Note. s = strong; m = medium; w = weak; νas = asymmetric
stretching; νs = symmetric stretching; δ = in–plane bending; ω =
out–of–plane bending; ρ = scissoring; t = twisting.
UV-vis spectra
UV-vis absorption spectra, recorded in chloroform for all
compounds (4–8), confirm the formation of metal complexes.
Absorption spectra for 4 showed maxima at 254 and 287 nm,
TABLE 5
Antibacterial screening data for 4 (inhibition zone diameter
after 12 h)
TABLE 7
In vitro antibacterial activity of compound 4 bacterial strain of
Escherichia coli using microbroth dilution assay
Inhibition zone diameter (mm)
Bacillus
subtillus
Staphylococcus
aureus
Compound
E. coli
MIC50
(mg/mL)
MIC90
(mg/mL)
MIC range
(mg/mL)
Compound 4
Ampicillin
(10 µg/mL)
9
9
10
46
52
52
Compound 4
Ampicillin
1.7
0.00004
3.6
0.0001
0.765–3.62
0.00002–0.0001

3-(SILATRANYL)PROPYLAMMONIUM CHLORIDE
831
SCH. 3.
whereas all metal complexes were colored and showed maxima moderately active (10–14 mm), slightly active (6–10 mm), and
in visible region due to d-d transitions. The expected structures less than 5 mm is taken as inactive. Data of antibacterial activity
for these metal complexes are shown in Figure 4, which are in are shown in Table 5.
accordance with the literature.[21,22]
The minimum inhibitory concentrations (MIC) of compound
4 were determined by using microbroth dilution method. In
the broth dilution MIC method, various concentrations of a
compound were inoculated with a standard suspension of test
bacteria. Following an overnight incubation at 35◦C, MIC was
determined by observing lowest concentration of the compound
that will inhibit visible growth of the test bacteria. Growth was
determined photometrically by measuring A600. Percentage of
growth was calculated by using the following formula:
Mass spectra
Mass spectral data of 4 shows characteristic fragmentation
pattern of silatrane moiety. A base peak due to (C2H5)3NH+ was
observed at m/e = 102. The presence of a peak due to silatranyl
cation at 174 is a very common feature in the mass spectrum
of silatranes, which is formed by the homolytic cleavage of Si-
CH2 bond. The stability of silatranyl cation has been discussed
on the basis of theoretical studies.[23] A peak observed at m/e
233 is assigned to fragment formed by the removal of CS2 and
triethylammonium ion from 4. In addition, silatranyl moiety
undergoes fragmentation and shows peaks at m/e value 150 and
192 as shown in Scheme 3.
OD of organism grown with sample
Percentage of growth =
OD of control
MIC data against bacterial culture of Bacillus subtillus, Es-
cherichia coli, and Staphylococcus aureus is summarized in Ta-
bles 6, 7, and 8, respectively. MIC50 (defined as minimum con-
centration at which 50% of the isolates were inhibited) of com-
pound 4 against Bacillus subtillus was 0.0382 mg/mL, whereas
MIC90 (defined as minimum concentration at which 90% of the
isolates were inhibited) was 0.0689 mg/mL.
Biological Activity
To find out antibacterial activity, compound 4 was dissolved
in DMSO and the sample was tested in triplicate. DMSO alone
was taken as control and results were compared with control.
Antibacterial activity is classified as highly active (>14 mm),
TABLE 8
In vitro antibacterial activity of compound 4 bacterial strain of
Staphylococcus aureus using microbroth dilution assay
CONCLUSION
The present work summarizes crystallographic, theoretical,
and spectroscopic data of 3-(silatranyl)propylammonium chlo-
ride. The formation of 2 is attributed to photochemical reaction
of 1 in dichloromethane. X-ray crystal structure parameters are
in accordance with theoretical studies. It is also concluded that
3-aminopropylsilatrane undergoes 1:1 addition reaction with
CS2 to form 3-siltranylpropyldithiocarbamic acid, which can
MIC50
(mg/mL)
MIC90
(mg/mL)
MIC range
(mg/mL)
Compound 4
Ampicillin
1.5
0.00005
3.2
0.625–3.21
0.00015 0.00003–0.0001
Note. Ampicillin has been used as standard drug.

832
R. SINGH ET AL.
yield triethylammonium-3-silatranylpropyldithiocarbamate on
treatment with triethylamine. The product was obtained in very
good yield and spectroscopic data have shown characteristics of
dithiocarbamate as well as silatranyl moiety. Dithiocarbamate
moiety shows chelation with different transition metal ions due
to the presence of S atoms. Spectral results support proposed
structures of the metal complexes. In addition, antimicrobial
activity of newly synthesized compound 4 was also evaluated
against bacterial culture of Bacillus subtillus, Escherichia coli,
and Staphylococcus aureus. The results obtained clearly indi-
cate that compound 4 discussed here is active toward growth
inhibition of bacteria under this investigation.
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CCDC 738531 contains the supplementary crystallographic
data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
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