Some New Coordination Compounds Of Organo Silicon (Iv) With Semicarbazones And Thiosemicarbazones

Some New Coordination Compounds Of Organo Silicon (Iv) With Semicarbazones And Thiosemicarbazones

Arpita Verma*, S. Varshney and A. K. Varshney Department of Chemistry, University of Rajasthan, Jaipur-302004, India

Abstract: The reactions of diethoxydimethylsilane have been carried out with semicarbazones and thiosemicarbazones prepared by condensation of aldehydes/ketones with semicarbazide hydrochloride / thiosemicarbazide in absolute alcohol. The mode of bonding of these compounds have been established with the help of different spectral studies (1H,13C NMR, infrared and electronic) and elemental analysis. The monomeric nature of these complexes have been confirmed by molecular weight determination. The ligands and

their silicon (IV) complexes have also been screened for their fungicidal as well as bactericidal activity and were found to be quite active in this respect.

Keywords: Silicon (IV) complexes, diethoxydimethylsilane, spectral studies, semicarbazones and thiosemicarbazones.

INTRODUCTION

Semicarbazones and thiosemicarbazones are the most important nitrogen and oxygen/sulfur donor ligands and have drawn special attention due to their activity against

smallpox, viral diseases and certain kinds of tumour1.The real impetus towards developing the coordination chemistry of these potential ligands was probably provided by the remarkable antitumour,

antiviral, antimicrobial, antimalarial and anticonvulsant activities2-10 observed for some of these derivatives which has since been shown to be related to their metal complexing ability11.The stereochemistry of these ligands is also interesting as only the – nitrogen coordinates to metal atom. Depending on reaction conditions, these compounds may act as ionic or neutral ligands.

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 useful in polymer and textile chemistry, space exploration and cosmetics. The interest of organosilicon(IV) compounds is due to their versatile applicability in pharmaceutical and chemical industries. Some work has been reported on the divalent metal complexes of transition metals with bidentate

Schiff bases12.

Extensive studies have been made and a careful survey of literature revealed that there is considerable scope for undertaking systematic studies including the synthesis and biochemical applications of complexes of non transition metals with various semicarbazones and thiosemicarbazones. In the present investigations, several silicon derivatives have been prepared by the reaction of diethoxydimethylsilane with semicarbazones and thiosemicarbazones which are given below:

1. 9-Anthraldehyde semicarbazone Analytical method and physical

   H C N NH C

   O

   NH2

   measurements

   Nitrogen and sulfur were estimated by Kjeldahls method and Messengers method,

2. 9-Anthraldehyde thiosemicarbazone

   respectively13,14. The IR spectra were

   H C N NH C

   S

   NH2

   recorded on FTIR spectrophotometer using a model A-8400 S, Shimadzu in KBr pellets. 1H and13C NMR spectra were recorded on

3. 4-Acetyl biphenyl semicarbazone

   JEOL AL-300 spectrometer in d6 DMSO or CDCl3 using TMS as internal standard at

   C N NH C

   NH2

   90MHz. Molecular weight determinations

   CH3 O

4. 4-Acetyl biphenyl thiosemicarbazone

   were carried out by the Rast Camphor Method. Molar conductance measurements

   C N NH C

   NH2

   were made in anhydrous dimethyl

   CH3 S

5. 4-Fluoroacetophenone semicarbazone

   formamide at 36±1°C using a model 305 systronics conductivity bridge. The purity of

   F C N NH C

   NH2

   the compounds were checked by thin layer

   CH3 O

6. 4-Fluoroacetophenone thiosemicarbazone

   chromatography.

   Synthesis of ligands

   F C N NH C

   NH2

   All the ligands were synthesized by the

   CH3 S

7. p-tolualdehyde semicarbazone

   condensation of aldehydes / ketones viz. 9- anthraldehyde, 4-acetylbiphenyl, 4-

   H3C

   C N NH C

   H O

   NH2

   fluoroacetophenone and p-tolualdehyde with

8. p-tolualdehyde thiosemicarbazone

semicarbazide/thiosemicarbazide in 1:1

H3C

EXPERIMENTAL

C N NH C H S

NH2

molar ratio using absolute alcohol as the reaction medium. The mixture was heated on

a water bath for about half an hour and then

All the glass apparatus fitted with quickfit interchangeable joints were used and all the reactions were carried out under strictly anhydrous conditions. Benzene was first refluxed over sodium wire for several hours and finally distilled azeotropically with ethanol.

allowed to cool at room temperature. The crystals that separated out were recrystallized from the same solvent. Their physical properties and analysis have been recorded in Table 1.

Synthesis of silicon (IV) complexes

Silicon (IV) complexes were synthesized by the reaction of diethoxydimethylsilane with semicarbazones and thiosemicarbazones in 1: 2 molar ratio in dry benzene as reaction medium. The mixture was refluxed on refluxing column for about 3-4 hours. The product was rendered free from the solvent under reduced pressure and dried in vacuo at 40-50°C. The physical properties and analysis have been recorded in Table 2.

RESULTS AND DISCUSSION

The reactions of diethoxydimethylsilane with above mentioned ligands are given as follows:

1 : 2

deserved at ~ 2550 cm1 due to tautomerization. In the complexes, vNH or vSH bands do not appear due to formation of silicon-oxygen, silicon-sulfur and silicon- nitrogen bands.

The vC=N frequency of the free azomethine is observed in the region 1588- 1608 cm1 and it is shifted to lower frequency by ~ 15 cm1 in the case of complexes, indicating the coordination of azomethine nitrogen to silicon atom.

In the literature, a shift of this frequency to the higher as well as lower wave number side has been reported and in some cases even no change has been noted. In the

complexes, several new bands in the region 580-570 cm1, 540 cm1 and 600-610 cm1

are due to vSiN15, vSiS16 and vSiO, respectively and which are absent in the

1. (CH3)2Si(OC2H5)2 + 2N OH

Benzene 1 : 2

(CH3)2Si(N O)2 + 2C2H5OH

spectra of the ligands. The infrared spectral data of the ligands and their complexes are

2. (CH3)2Si(OC2H5)2 + 2N SH

(CH3)2Si(N S)2 + 2C2H5OH

Benzene

given in Table 3.

(Where N OH

and

N SH

represent

the donor sets of ligands).

All the values of molar conductance (10- 15 ohm1 cm2 mol1) in dry DMF at room temperature indicate their non electrolytic nature.

Electronic spectra

The electronic spectra of ligands and its silicon derivatives have been recorded. Two medium intensity bands at ~380 nm and

~410 nm are observed. The band at ~380 nm due to *transition in the ligands remain as such in the spectrum of the silicon complex. The band around ~410 nm is due to n* transition of the azomethine group which shifts in the spectra of the complexes. This may be due to coordination of azomethine nitrogen to metal atom.

IR spectra

In the infrared spectra of the ligands, medium intensity bands appearing in the region 3100-2850 cm1 may be assigned to vNH vibrations. In the solution spectra of ligands, vNH does not appear and vSH is

S. No. Ligands Colour & Stte Melting point Analysis: Found (Calcd.) (%) Molecular

(°C)

C H N S

weight: Found

S. No. Silicon

Ligands Molar

Product and colour &

Melting

Analysis: Found (Calcd.) % Molecular

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1H NMR spectra

The proton magnetic resonance spectra of ligands and their corresponding complexes have been recorded in d6-DMSO or CDCl3 using TMS as the internal standard.

The broad signals due to NH protons at

10.15 ppm in the ligands disappear in the case of silicon complexes showing ligation of silicon with nitrogen, oxygen and sulfur. The azomethine proton signal

C=NH

appearing at 8.00 in the

azomethine nitrogen to silicon atom.The new proton signals at 1.52 and 1.45 ppm in the compounds are due to the methyl protons of the (CH3)2 Si group.

13C NMR spectra

The 13C NMR spectra of ligands and their corresponding silicon (IV) complexes have been recorded in Table 4. The signals due to carbon atoms attached to azomethine groups and sulfur atoms show considerable shifts which indicate the involvement of nitrogen in coordination with the silicon

atom.

H

ligand undergoes deshielding in complex which indicates coordination of the

.

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13 5

C Si CH

1 2 5 8 9

1 16

H3 3

12 10 8 6

11 9 7 S 3 4

H3C C N N C

7 6 H O

NH2

H C N NH C

NH2 17 32

8 9 H C

Si CH

H C N N C

NH2 1 2 5 3 3

14 15

13

2 3 4 S

5

30 31

29

18 19

20 H3C C

21

N NH C

NH2

12 13 O

10

7 6 H

O H C 11

14 17 N N 18 NH

12 6

10 8

11 9 7

28 26 24 22

27 25 23

3 C C 2

16 15 H

Fig. 1: L2H Fig. 2: Si.2L2H Fig. 3: L7H Fig. 4: Si.2L7H

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BIOLOGICAL ACTIVITY

The antimicrobial activity of ligands and their metal complexes with silicon are tested using paper disc diffusion method 17,18. The

ligands and their corresponding complexes are screened against F.oxysporum, A. flavus and R. phaseoli. All of the complexes are found to be most active against these fungi at all concentrations (10, 50, 100 and 200 ppm). Potato dextrose agar medium is prepared in the flasks and sterilized. For antifungal activity, radial growth method is used. Some representative complexes are also tested against gram positive bacteria (S.aureus) and gram negative bacteria (E.coli).The bacteria are cultured for 24 hours at 37°C in an incubator.

The fungicidal as well as bactericidal activity of the ligands and their metal complexes increase with increase in concentration of the compounds. The results are recorded in the form of inhibition zone (diameter in mm) and activity index. The results show that the silicon complexes are more potent in their inhibition properties than the free ligands.The data are presented in Table 5.

ACKNOWLEDGEMENT

A.K.V. and S.V. are thankful to the U.G.C.; Bhopal, for financial assistance.

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Microorganisms C16H13N3S SiC34H30N6S2 C15H15N3O SiC32H34N6O2

(AI)

(1.00)

(1.00)

(1.20)

(1.10)

(0.60)

(0.52)

(0.80)

(0.63)

IZ = Inhibition zone (diameter in mm); AI = Activity index (Inhibition zone of test compounds/Inhibition zone of standard)

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