Multinuclear magnetic resonance and related studies of coordination compounds of organosilicon with mixed azines

Article abstract of DOI:10.1080/10426500701758421

New hexa-coordinated complexes of organosilicon (IV) have been synthesized by the reactions of diethoxydimethylsilane with the mixed azines. Their structures have been inferred based on elemental analysis, UV, IR, and multinuclear magnetic resonance spect

Full text of DOI:10.1080/10426500701758421

Phosphorus, Sulfur, and Silicon, 183:1843–1852, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500701758421
Multinuclear Magnetic Resonance and Related Studies
of Coordination Compounds of Organosilicon with
Mixed Azines
Manish Godara, R. Maheshwari, Bharti Khungar,
Arpita Verma, S. Varshney, and A. K. Varshney
Department of Chemistry, University of Rajasthan, Jaipur, India
New hexa-coordinated complexes of organosilicon (IV) have been synthesized by the
reactions of diethoxydimethylsilane with the mixed azines. Their structures have
been inferred based on elemental analysis, UV, IR, and multinuclear magnetic reso-
nance spectral studies. The monomeric and nonelectrolytic nature of these complexes
has been confirmed by molecular weight determinations and conductance measure-
ments. The mixed azines and their silicon complexes also have been screened for
their antimicrobial activities against several fungi and bacteria and were found to
be quite active in this respect.
Keywords Antimicrobial studies; mixed azines; organosilicon (IV) complexes; spectral
studies
INTRODUCTION
Silicon complexes containing Si-O-C, Si-N-C, and Si-C bonding play
an important role in vital processes and have specific effects on the
living organisms. They are also found useful in polymer and textile
chemistry, space exploration, and cosmetics. The studies on the physi-
cal, chemical and biological properties1of organosilicon derivatives of
amino alcohols have provided valuable information about the influ-
ence of the amino group on the strength and reactivity of the Si-O
bond in aminoalkoxysilanes and about the degree of intermolecular
interaction between the nitrogen atom of the aminoalkoxy group, and
Received 4 January 2006; accepted 3 September 2007.
The authors express thanks to Professor P. D. Sharma, Head, Department of Chem-
istry, University of Rajasthan, Jaipur, for providing laboratory facilities and for his con-
stant encouragement. One of us Reena Maheshwari is thankful to C.S.I.R., New Delhi
for Senior Research Fellowship. S. Varshney and A.K. Varshney are thankful to UGC,
Bhopal for financial assistance.
Address correspondence to A. K. Varshney, Department of Chemistry, University of
Rajasthan, Jaipur 302004, India. E-mail: anilakv123@rediffmail.com
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M. Godara et al.
FIGURE 1 Mixed azines used as ligands in this work.
the silicon atom leading to the formation of a strong donor acceptor
Si←N bond in these derivatives.2 Azines constitute an important class
of nitrogen donor ligands. Therefore, it was considered worthwhile to
synthesize the organosilicon derivatives of biologically active ligands of
mixed azines. The structures of the ligands are shown in Figure 1.
EXPERIMENTAL
Chemicals and solvents used were dried and purified by standard meth-
ods and moisture was excluded from the glass apparatus using CaCl2
drying tubes.
The analyses of carbon, hydrogen, nitrogen, sulfur, and silicon in
complexes were carried out as reported earlier.3−5 The IR spectra were
recorded on a Perkin-Elmer 577 IR spectrophotometer in the region
4000–4200 cm–1 using KBr optics. The electronic spectra (in methanol)
were taken with a Toshniwal Spectrophotometer. A Perkin-Elmer Mode
RB-12 Spectrometer was used to obtain the 1H NMR spectra, DMSO-d6
was used as the solvent. 13C NMR spectra were recorded on a 90 MHz
Jeol NMR spectrometer using dry DMSO as the solvent and TMS as
the internal standard. The 29Si NMR spectra were recorded at 17.75
MHz using DMSO as solvent. Molar conductance measurements were
made in anhydrous dimethylformamide at 36 1◦C using a Model-305
Systronics conductivity bridge. Molecular weight determinations were
carried out by the Rast camphor method.6

Organosilicon Compounds with Mixed Azines
1845
TABLE I Physical Properties and Analytical Data of Ligands
Elemental analysis (%)
C
H
N
S
Mol. wt.
found
M.p. found found found found
S. no. Ligand Color and state
(◦C) (calcd.) (calcd.) (calcd.) (calcd.) (calcd.)
1.
2.
3.
4.
5.
6.
7.
L1H Lemon yellow,
shiny crystal
152 74.82
(74.98) (5.39) (12.49)
163 75.66 5.82 11.66
(75.76) (5.92) (11.76)
166 62.44 4.24 12.04
(62.59) (4.38) (12.16) (13.92) (230.27)
172 63.82 4.79 11.32 13.02 236.32
(63.91) (4.95) (11.47) (13.12) (244.30)
5.24
12.32
—
—
216.88
(224.24)
224.76
(238.27)
218.11
L2H Yellow,
shiny crystal
L3H Greenish brown,
shiny crystal
13.76
L4H Brown,
solid
L5H Reddish brown,
needle like crystal
L6H Reddish brown,
solid
198 67.20
(67.28) (4.71) (13.08)
181 68.32 5.22 12.11
(68.41) (5.30) (12.27)
175 72.86 4.80 15.88
(72.99) (4.98) (15.96)
4.58
12.96
—
—
—
202.12
(214.20)
220.64
(228.23)
250.67
L7H Light red,
solid
(263.28)
Synthesis of Ligands
The ligands were synthesized by the condensation of salicylalde-
hyde and hydrazine with aldehydes/ketones viz. benzaldehyde, ace-
tophenone, thiophene- 2-aldehyde7, 2-furyl methyl ketone, indol-3-
carboxaldehyde, furfuraldehyde, and 2-acetyl thiophene in 1:1:1 molar
ratio using ethanol as the reaction medium. The solution was refluxed
on a water bath for 3-4 hours and then allowed to cool at room tem-
perature. The crystals that separated out were washed with ethanol,
recrystallizd from the same solvent and dried in vacuo. Their elemental
analysis and physical properties are given in Table I.
Synthesis of Organosilicon Complexes
The calculated amount of diethoxydimethylsilane was added to the
weighed amount of ligand in 1:2 molar ratios in benzene as the reaction
medium. The reactants were refluxed for about 5 hrs to complete the re-
action. The ethanol liberated in the reaction was removed azeotropically
with benzene. The resulting products were rendered free from solvent.
The products so formed were finally dried in vacuo at 40
5◦ for 2–
3 hours after repeated washing with dry cyclohexane. The compounds
were purified by recrystallization from benzene and washing with dry

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M. Godara et al.
cyclohexane. Their physical properties and analytical data are recorded
in Table II.
RESULTS AND DISCUSSION
The reactions of diethoxydimethylsilane with these ligands are as fol-
lows:
1:2
(CH3)2 Si (OC2H5)2 + 2LH −−−−→ (CH3)2 SiL2 + 2C2H5OH.
(1)
Benzene,
where LH represents the mixed azines shown in Figure 1. On refluxing
for about 5 h, the resulting complexes are obtained as colored solids
or semisolids. These complexes are sensitive to moisture. The molar
conductance value of 10–3M solutions of the complexes (10–15 ohm
–1
cm2 mol–1) in DMF showed them to be non-electrolytes. The monomeric
nature of these complexes was confirmed by their molecular weight
determinations.
Electronic Spectra
In the electronic spectra of ligands, a band at ∼ 216 nm is observed due
to the B band of the benzene ring, which is shifted to a higher wave
number side on complexation. The band observed at ∼ 340 nm in the
ligand is the secondary band of benzene and which gets red shifted due
to the presence of >C=N-N=C< grouping. However, this band appears
at ∼ 370 nm in the complexes possibly due to the polarization in >C=N-
bond caused by silicon ligand electron interaction.
Infrared Spectra
The IR spectra of ligands show a broad and strong absorption band in
the region 3150–2850 cm–1 attributable to v (OH) mode indicating that
the hydroxyl groups are strongly hydrogen bonded with the azomethine
nitrogen.8 It disappears in the spectra of the silicon complexes showing
thereby the deprotonation of this functional group. One strong band in
–1
all the ligands at ∼ 1620 cm due to v(C=N) gets split into two sharp
bands at ∼ 1630 cm and ∼ 1600 cm–1on complex formation. The
–1
band at ∼ 1630 cm–1in the metal complexes, indicates the coordination
of the azomethine nitrogen to the silicon atom,9 whereas the other one
is due to uncoordinated azomethine group. The phenolic v (C-O) and v
(N-N) respectively at ∼1260 and ∼970 cm–1are also shifted to higher
frequency region because of complex formation. The appearance of new
and strong medium intensity bands at ∼ 625 cm–1 assignable to v (Si-O)

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M. Godara et al.
TABLE III H NMR Spectral Data (δ ppm) of Ligands and the
Organosilicon (IV) Complexes
Ligand/complexes
−OH
H-C=N
−CH3
L1H
12.90
—
13.10
—
13.35
—
13.40
—
12.99
—
13.05
—
13.15
—
8.80
9.10
8.70
9.21.
8.86
9.11
8.85
9.13.
8.88
9.11
8.90
9.13
8.84
9.16
—
1.56
—
1.60
—
1.57
—
1.53
—
1.50
—
1.62
—
(CH3)2 Si(L1)2 (1)
L2H
(CH3)2 Si(L2)2 (2)
L3H
(CH3)2 Si(L3)2 (3)
L4H
(CH3)2 Si(L4)2 (4)
L5H
(CH3)2 Si(L5)2 (5)
L6H
(CH3)2 Si(L6)2 (6)
L7H
(CH3)2 Si(L7)2 (7)
1.59
frequencies11, at ∼ 568 cm–1assignable to v (Si←N) frequencies12−14
and at ∼ 1265 and 760 cm–1 due to the asymmetric deformation13 mode
of CH3-Si and stretching vibration of Si-C, respectively, in the spectra
of complexes further support the formation of coordination compounds.
1H NMR Spectra
The proton signal of the azomethine moiety (-HC=N) observed at
δ 8.70–8.90 ppm in the spectra of the ligand and it gets shifted down-
field in the spectra of silicon complexes, which is attributed to the do-
nation of the lone pair electrons by the azomethine nitrogen to the
silicon atom. The aromatic proton signal at δ 7.75–7.10 ppm remain
almost unchanged. A broad signal observed at δ 12.90–13.40 ppm due
to OH proton in the ligands are not observed in the spectra of the corre-
sponding silicon complexes showing thereby the chelation of the ligand
moiety through deprotonated phenolic oxygen. Further, new signals at
δ1.50–1.62 ppm in the complexes are due to the methyl protons of Me2
Si group (Table III).
13C NMR Spectra
The 13C NMR spectra of L1H, L2H and their corresponding silicon
complexes have been recorded in Table IV. The signals due to the
carbon atoms attached to the phenolic and the azomethine groups in

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M. Godara et al.
FIGURE 2 Suggested structures of the Si(IV) complexes.
the ligands appear at δ 155.1, δ 153.2 and δ 175.7, δ 173.5 ppm respec-
tively. However, in the spectra of the corresponding silicon complexes
these signals appear at δ 164.1, δ 161.2 and δ 165.2 and δ 167.4 ppm
respectively. The considerable shifts in the carbon atoms attached to
nitrogen and oxygen indicate the involvement of nitrogen and oxygen
atom in coordination with the silicon atom.
TABLE V 29Si NMR Spectral Data of Silicon Complexes
Compound number
δ ppm
(CH3)2 Si(L1)2 (1)
(CH3)2 Si(L2)2 (2)
(CH3)2 Si(L3)2 (3)
(CH3)2 Si(L4)2 (4)
(CH3)2 Si(L5)2 (5)
(CH3)2 Si(L6)2 (6)
(CH3)2 Si(L7)2 (7)
−157.63
−157.80
−158.35
−158.46
−157.98
−157.82
−158.50

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M. Godara et al.
29Si NMR Spectra
29Si NMR spectra of silicon complexes have been recorded and given in
Table V. A sharp signal at δ− 158.50 to δ− 157.63 ppm clearly indicates
the six-coordinated environment around the silicon.15
Based on the above spectral studies, the following octahedral geom-
etry has been suggested for the silicon (IV) complexes.
Antimicrobial Activity
The antimicrobial activity of a few ligands and their corresponding
complexes were tested by paper disc method16 for their antimicrobial
activities at a concentration of 1 mg/disc. Streptomycin and Micostatin
were used as the reference compounds for antibacterial and antifungal
activities, respectively. The data are presented in Table VI. They were
tested against S. aureus, E. coli (bacteria) and A. niger, A. flavus, R.
phaseoli (fungi). The results have been recorded in the form of inhibi-
tion zones (diameter in mm) and activity index.
Further, the silicon complexes are more active as compared to the
free ligands, indicating that complexation increases the activity, and
the preliminary results achieved have led us to conclude that this type
of complex should be studied in detail for their applications in diverse
areas.
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