Synthesis and Characterisation of Organosilicon and Organotin Complexes derived from DHA Ligand
Jai Devi*, Suman Devi, Jyoti Yadav, Som Sharma
Department of Chemistry, Guru Jambheshwar University of Science and Technology,
Hisar-125001, Haryana, India
*Corresponding Author E-mail: jaidevi_gju@yahoo.com
ABSTRACT:
Organosilicon(IV) and organotin(IV) complexes with dehydroacetic acid and amino ether Schiff base ligand have been described with the help of elemental analyses, electronic, infrared, multinuclear magnetic resonance spectroscopy. Analysis of data suggested that the Schiff base provides two bidentate NO domains and was coordinated to silicon and tin moiety through the imine nitrogen and hydroxyl oxygen atom forming penta coordinated and hexa coordinate complexes in 1:2 and 1:1 molar ratio. Thermal studies of the synthesized organotin compounds shows that they are stable and decomposition of the complexes occur in two steps with the formation of metal oxides as the end product.
KEYWORDS: Dehyroacetic acid, aminoether, bidentate, thermal studies.
The organotin and organosilicon chemistry have important chemical, industrial, and biological properties and achieved significant attention of researchers worldwide [1–5]. Schiff bases and their complexes have interesting biological and pharmacological activities like anticancer,[6–9] antimalarial,[10] anti-inflammatory,[11] anti-HIV, antifertility,[12] anticonvulsant,[13] antimicrobial activities,[14–17] etc. They can also be used as plant growth regulating agents. Schiff bases accommodate different metal centers involving various coordination modes, allowing for the successful synthesis of homo-and heterocomplexes with varied stereochemistry. This aspect is used for modeling active sites in biological systems, which bind with central atom through azomethine nitrogen and provide best models for metal–ligand binding [18].
In coordination chemistry, dehydroacetic acid is known to form a number of metal complexes having excellent chelating properties and possess various promising activities, such as fungicidal, bactericidal, herbicidal, and food preservative.[19]. Based on the above considerations, attempts have been made to synthesize five silicon and tin complexes with the Schiff base derived from condensation of dehydroacetic acid with amino ether and characterized using different spectroscopic techniques like UV–Vis, FT-IR, NMR (1H, 13C, 29 Si and 119Sn).
EXPERIMENTAL:
MATERIAL AND METHODS
All the reagents and chemicals used were of Analytical grade and used without any further purification. All these compounds were supplied by Sigma-Aldrich. Solvents such as ethyl acetate, petroleum ether, methanol, ethanol, acetone, dimethylsulfoxide and dimethylformamide were of analytical reagent grade and were dried before use [20]. The IR spectra of all the compounds were recorded using KBr pellets in the range of 400-4000 cm-1 on Shimadzu IR affinity-I 8000 FT-IR spectrometer. . In the current study 1H, 13C, 29Si and 119Sn NMR spectra were recorded for structure elucidation of the Schiff base ligands and their complexes. The 1H NMR and 13C NMR spectra were recorded on a Bruker Avance II 300 MHz and 400 MHz NMR Spectrometer and all chemical shifts (δ) were reported in parts per million (ppm) downfield from the internal standard tetramethylsilane (TMS) in CDCl3 and DMSO-d6. . The electronic spectra were recorded in methanol and DMF on a UV-Vis-NIR Varian Cary-5000 spectrometer. The molar conductance values of 10-3 M solution of complexes were measured at 30°C, using conductivity bridge type model-306 Systronics having cell constant equal to one in dry DMSO and DMF as solvent at room temperature. Thermal decomposition studies were carried out using a Perkin Elmer Diamond TG/DTA thermogravimetric analyzer at a heating rate of 10 °C/min under high purity nitrogen atmosphere at a flow rate of 20 mL/min. Elemental analyses (C, H and N) of the samples was carried out using Perkin Elmer 2400 instrument. The estimation of silicon, tin and chlorine were carried out by the reported methods[21,22].
Synthesis of Ligand
Schiff base ligand 3,3’-((1E, 1’E)-((oxybis(ethane-2,1-diyl))bis(azanylylidene))bis(ethan-1-yl-ylidene))bis(4-hydroxy-6-methyl-2H-pyran-2-one) H2L was prepared by dissolving 1.04 (10 mmol) 2-(2-aminoethoxy)ethylamine and 3.44 g (20 mmol) of dehydroacetic acid in 20 mL dry ethanol in 1:2 molar ratio (scheme 1). The solutions were then mixed together and stirred continuously for 4-5h . Off white colored precipitate was obtained after completion of reaction. The product was recrystallized from same solvent and dried in vacuum.
Organosilicon and organotin complexes were prepared by stirring 4.04 g of H2L(10 mmol) with sodium metal 0.45 g (20 mmol) in 30 mL dry methanol in 1:2 molar ratio. To the above prepared sodium salt of Schiff base, 1.29 g dichloro dimethyl silane / 1.08g trimethyl chlorosilane and 2.19 g dichloro dimethyl tin / 1.99g monochloro trimethyltin were added slowly in 1:1 molar ratio in dry methanol and reaction mixture was refluxed for 5h (Scheme 1). Precipitates of NaCl were filtered and solvent was evaporated on rotary evaporator under reduced pressure. The final product obtained was recrystallized from mixture of dry methanol and hexane and finally dried under reduced pressure. Same procedure is applied for the synthesis of 1:2 molar ratio compounds. Physicochemical and analytical data is given in Table 1.
Scheme – I: Synthesis of DHA Schiff base and its organosilicon and organotin complexes
Table 1: Physicochemical characterization and elemental analyses of organosilicon(IV) and organotin(IV) complexes with DHA Schiff bases
|
Comp. No. |
Compounds |
Molecular formula |
Molecular Weight |
Yield (%) |
Analysis (%) Found(Calcd.) |
||||
|
C |
H |
N |
Sn |
Si |
|||||
|
1 |
H2L |
C20H24N2O7 |
404.41 |
89 |
46.10 (46.13) |
11.60 (11.61) |
26.92 (26.90) |
- |
- |
|
2 |
Me2Sn(L) |
C22H28N2O7Sn |
551.18 |
75 |
47.97 (47.94) |
5.15 (5.12) |
5.10 (5.08) |
21.57 (21.54) |
- |
|
3 |
Me2Si(L) |
C22H28N2O7Si |
460.55 |
71 |
57.35 (57.37) |
6.10 (6.13) |
6.09 (6.08) |
- |
6.13(6.10) |
|
4 |
[Me3Sn]2(L) |
C26H40N2O7Sn2 |
730.02 |
76 |
42.80 (42.78) |
5.50 (5.52) |
3.87 (3.84) |
32.50 (32.52) |
- |
|
5 |
[Me3Si]2(L) |
C26H40N2O7Si2 |
548.78 |
72 |
56.88 (56.90) |
7.74 (7.35) |
5.14 (5.10) |
- |
10.26(10.24) |
RESULTS AND DISCUSSION:
The Schiff base ligands H2L were obtained through the reaction of DHA with 2-(2-aminoethoxy)ethylamine in ethanol as solvent (Scheme 1) as white solid in good yield and their silicon and tin complexes were synthesized by refluxing H2L with dichlorodimethylsilane/ chlorotrimethylsilane and dichlorodimethyltin/ chlorotrimethyltin in the presence of sodium metal in dry methanol. It resulted in formation of brownish and purple colored solid complexes in 1:1 and 1:2 molar ratios. Molar conductance values of the complexes were found to be less than 18 ohm-1 cm2 mol-1 suggesting their non-electrolytic nature [23] .The mode of bonding and the geometry of the complexes were established by spectroscopic techniques.
ELECTRONIC SPECTRA
The electronic spectra of ligand as well as their organosilicon(IV) and organotin(IV) complexes gives information regarding the arrangement of ligand around central atom. Schiff base ligand exhibited a maxima at ∼ 386-389 nm assigned to n-π* transition of azomethine (˃C=N) group, which shifted to a lower wavelength in the complexes. This shift in the n-π* band may be due to the donation of the lone pair of electrons by the nitrogen of the Schiff base ligand to the central metal atom. In the Schiff base ligand some medium intensity band appeared in the range 228-235 nm due to π- π* transition of lactone ring which remains almost unchanged in the electronic spectra of complexes.
IR SPECTRA
The IR spectra of the free ligand was compared with the spectra of the complexes in order to study the binding mode of ligand with central atom. Several significant changes with respect to the ligand was observed in the corresponding complexes. The IR spectrum of free ligand showed characteristic broad band at 3412-3420 cm-1 and 1609-1620 cm-1 which were assigned to v(O-H) and v(C=N) stretching modes respectively [24, 25]. In the spectra of complexes a broad band due to v(O-H) stretching was absent suggesting deprotonation of the hydroxyl group on complexation and subsequent coordination of this hydroxyl oxygen to the metal atom. On complexation, the v(C=N) band is shifted to lower frequency with respect to ligand, which signifies that the nitrogen of azomethine group is coordinated to the metal atom. The presence of lactonic carbonyl v(C=O) was confirmed by the appearance of a sharp band at 1703 cm-1 in the IR spectrum of H2L, which was unchanged in the spectra of complexes, indicating its non involvement in the coordination. The IR spectra of complexes showed some new bands due to v(M-N) and v(M-O) at 443-453cm-1 and 536-570 cm-1 respectively, which support the formation of silicon and tin complexes. The IR peaks were further recommended from 1H NMR studies.
MULTINUCLEAR NMR SPECTRA
1H NMR SPECTRA
In 1H NMR spectra of the free ligand, the signal observed at δ 13.67 can be assigned to the hydroxyl proton of Schiff base ligand H2L [26]. This signal disappeared in the complexes, which confirms the coordination of ligand to central atom through the deprotonated hydroxyl group (Table 2). Proton attached to the C5 carbon of DHA ring appeared as a sharp singlet at δ 5.80. Methyl protons attached to C6 carbon appeared as a singlet at δ 2.45 remained almost unchanged on complexation, whereas methyl protons attached to azomethine carbon (C7) appeared at δ 0.98 in the ligand and shifted downfield in the complexes, suggested participation of azomethine nitrogen in the bond formation. Aliphatic protons of ligand appeared at δ 3.73-2.60 and remain unaltered in the complexes, indicating their non involvement in bond formation. In addition, the formation of complexes was supported by appearance of new signals at δ 1.10-1.40due to methyl protons attached directly to the central atom.
Table 2: 1H NMR spectral characteristics (δ) in ppm for organosilicon(IV) and organotin(IV) complexes of DHA Schiff bases
|
Comp .No. |
Compounds |
-OH |
C7-CH3 |
C6-CH3 |
C5-H |
-Ha |
-Hb |
Sn-R |
Si-R |
|
1 |
H2L |
13.67 (s, 1H) |
0.98(s, 3H) |
2.45(s, 3H) |
5.80(s, 1H) |
2.60-2.64(t,2H) |
3.69-3.73(t, 2H) |
- |
- |
|
2 |
Me2Sn(L) |
- |
0.68(s, 3H) |
1.61(s, 3H) |
5.60(s, 1H) |
2.48-2.51(t,2H) |
3.45-3.49(t,2H) |
1.10(s, 6H) |
- |
|
3 |
Me2Si(L) |
- |
0.89(s, 3H) |
1.98(s, 3H) |
5.55(s, 1H) |
3.20-3.23(t,2H) |
3.66-3.70(t,2H) |
- |
1.40(s, 6H) |
|
4 |
[Me3Sn]2(L) |
- |
0.91(s, 3H) |
1.77(s, 3H) |
5.69(s, 1H) |
2.45-2.50(t,2H) |
3.32-3.40(t,2H) |
1.39(s, 9H) |
- |
|
5 |
[Me3Si]2(L) |
- |
0.89(s, 3H) |
1.63(s, 3H) |
5.68(s, 1H) |
2.50-2.57(t,2H) |
3.56-3.61(t,2H) |
- |
1.17(s, 9H) |
13C NMR SPECTRA
In the 13C NMR spectra of complexes a remarkable shift was observed in the position of carbons attached to the different participating groups (Table 3). The peak at δ 171.09 in the spectrum of ligand confirmed the presence of azomethine (C=N) carbon which shifted towards lower value in the complexes, suggesting the participation of azomethine carbon in bond formation with silicon and tin atom . The shift in the signal due to C4 carbon attached to the hydroxyl group appeared at δ 160-179.85 indicated its participation in the bond formation. The signal for methyl carbon attached to C6 appeared at δ 19.78-17.22 in the spectra of the ligand and remained almost same in the complexes, whereas methyl carbon attached to C7 exhibited signal at δ 9.88-9.53 and shifted in the complexes again suggesting the involvemet of azomethine nitrogen in bond formation. Aliphatic carbon of the ligand appeared at δ 19.70-21.10 and remains unaltered in the complexes. In the complexes, the signal due to the carbons of the methyl group attached to central atom appeared in the range of δ 7.78-9.21.
29Si and 119Sn NMR spectra
In order to corroborate the geometry of the complexes, 29Si and 119Sn NMR spectra were recorded in CDCl3 and DMSO-d6. Sharp signals at δ −15 to −19 and δ −105 to −110 are assigned to (R3Si)2L and R2SiL complexes, respectively, which have penta and hexa-coordinated states around the silicon atom [27, 28]. Similarly, in case of tin complexes, sharp signals at δ – 150 to −159 and δ −400 to −415 indicated penta and hexa-coordinated state around the tin atom for (R3Sn)2L and R2SnL type of complexes, respectively. Display of a sharp singlet for each complex in the spectra proves the formation of single compound.
Table 3: 13C NMR spectral characteristics (δ) in ppm for organosilicon(IV) and organotin(IV) complexes of DHA Schiff bases
|
Comp. No. |
Compounds |
C-OH |
C=N |
C=O |
C-3 |
C-5 |
C-6 |
Aliphatic |
C6-CH3 |
C7-CH3 |
Sn-R |
Si-R |
|
1 |
H2L |
179.85
|
171.09 |
149.20 |
102.41 |
135.98 |
139.34 |
19.70(C-a), 50.23(C-b) |
17.22 |
9.88 |
- |
- |
|
2 |
Me2Sn(L) |
168.32 |
158.66 |
138.23 |
105.34 |
128.97 |
134.67 |
20.33C-a), 70.01(C-b) |
20.88 |
9.53 |
7.78 |
- |
|
3 |
Me2Si(L) |
162.62 |
158.55 |
140.34 |
105.65 |
134.01 |
137.30 |
20.32(C-a), 70.00(C-b) |
19.78 |
10.11 |
- |
9.21 |
|
4 |
[Me3Sn]2(L) |
162.09 |
159.76 |
143.03 |
104.18 |
133.99 |
137.92 |
21.10(Ca), 71.21C-b) |
19.90 |
10.34 |
8.87 |
- |
|
5 |
[Me3Si]2(L) |
160.89 |
160.11 |
141.13 |
105.60 |
133.32 |
137.00 |
20.12(Ca), 69.99(C-b) |
20.18 |
10.20 |
- |
8.04 |
THERMAL ANALYSIS OF ORGANOTIN(IV) COMPLEXES
The thermal (TG) curves of organotin(IV) complexes were obtained in the inert atmosphere. The calculated percentage mass losses, temperature ranges and thermal effects associated with the changes in the coordination compounds on heating revealed that the decomposition of the complexes ended with formation of SnO2 [29]. The TG of tin complexes shows that they are thermally quite stable to a varying degree. The complexes show a gradual loss in weight due to decomposition by fragmentation with increasing temperature. All the complexes exhibit similar behavior in TG studies. The thermogram of dimethyltin complex [Me2SnL] shows two steps decomposition- first step corresponds to the loss of two methyl groups attached to tin in the temperature range 140-250◦C. The second step corresponds to the loss of ligand moiety .Decomposition ended with formation of SnO2 as final residue in the temperature range of 250-470◦C.
In the similar way thermogravimetric curve for trimethyltin complex [Me3Sn]2L exhibits two steps- The first step of decomposition corresponds to the loss due to the loss of three methyl groups attached to tin atom in the temperature range 105-200◦C. In the second step the weight loss is due to the decomposition of ligand moiety in the temperature range of 200-495◦C leaving SnO2 as end product.
CONCLUSION:
Organosilicon(IV) and organotin(IV) compounds were synthesized and characterized by spectral techniques (UV-Vis, IR, 1H NMR, 13C NMR, 29Si, 119Sn NMR) and elemental analyses. The spectroscopic data suggest that Schiff base provides bidentate nitrogen and oxygen donors and was coordinated to silicon and tin moiety through the imine nitrogen and hydroxyl oxygen atom forming penta and hexa coordinated complexes.
ACKNOWLEDGEMENT:
Ms. Jyoti Yadav and Mr. Som Sharma is highly thankful to the HSCST Panchkula and CSIR New Delhi for the financial support.
REFERENCES:
1. Villar M Z J D F, Ellena J A, Castellano E E, Inorg Chim Acta, 45, 2002, 328.
2. Levai A, Jeko J, Monatsh Chem, 137, 2006, 339.
3. Jain M, Singh V, Singh R V, J Iran Chem Soc, 1, 2004, 20.
4. Asadi Z, Intern J Chem Kine, 20552, 2011, 247.
5. Pellerito L, Nagy L, Coord Chem Rev, 224, 2002, 111.
6. Bharti S K, Patel S K, Nath G, Tilak R, Singh S K, Trans Met Chem, 35, 2010, 917.
7. Oztas N A, Yenisehirli G, Ancınc N, Oztas S G, Ozcand Y, Spectrochim Acta A, 72, 2009, 929.
8. Alsoud Y A, Al-Masoudi N A, Ferwanah, Bioorg Med Chem, 11, 2003, 1701.
9. Rehman S U, Shahid K, Ali S, Bhatti M H, Parvez M J, Organomet Chem, 690, 2005, 1396.
10. Chaudhary A, Phor A, Gaur S, Singh R V, Heterocycl Commun, 10, 2004, 181.
11. Devi J, Batra N, Malhotra R, Spectrochim Acta A, 97, 2012, 397-405
12. Parrilha G L, Vieira R P, Rebolledo A P, Mendes I C, Lima L M, Barreiro E J, Piro O, Castellano E E, Beraldo, H, Polyhedron, 30, 2011, 1891.
13. Devi J, Devi S, Kumar A., Med. Chem. Comm. Pharm. Res., 7(2), 2015, 183-189
14. Hearn M J, Cynamon M H, J Antimicrob Chemother, 53, 2004, 185.
15. Salam M A, Arafath M A, Hussein M A, Basri R, Pervin R, Phosphorus Sulfur Silicon Relat Elem, 191, 2016, 1101.
16. Casas J, Castineiras A, Condori F, Couce M D, Russo U, Sanchez A, Seoane R, Sordo J , Varela J M, Polyhedron, 22, 2003, 53.
17. Katsoulakou E, Tiliakos M, Papaefstathiou G, Terzis A, Raptopoulou C, Geromichalos G, Papazisis K, Papi R, Pantazaki A, Kyriakidis D, Cordopatis P, Manessi-Zoupa, E J Inorg Biochem, 102, 2008, 1397.
18. Cimerman Z, Miljanic S, Galic N, Croat Chem Acta, 73, 2000, 81.
19. Kabak M, Elmali A, Elerman Y J, J Mol Struct, 477, 2000, 151.
20. Vogel A I, Text book of Quantitative Chemical Analysis, 5th ed. Longmans, Edison-Wesley, London, 1999.
21. Bassett J, Denny R C, Jeffery G H, Mendham J A, A textbook of quantitative inorganic analysis (Longmans, Londons) 1978.
22. Vogel A I, A Text Book of Quantitative Inorganic Analysis, 3rd ed., Longmanns, London, 1961.
23. Nidhi, Sonika, Malhotra R, Phosphorus Sulfur Silicon Relat Elem, 186, 2011, 1449.
24. Jednacak T, Novak P, Uzarevic K, Bratos I, Markovic J, Cindric M, Croat Chem Acta, 84, 2011, 203.
25. Asiri A M, Khadija O B, Molecules, 12, 2007, 1796.
26. Yusnita J, Puvaneswary S, Ali H M, Robinson W T, Lin T K, Polyhedron, 28, 2009, 3050.
27. Donia A M, EL-Boraey A H, J Anal Appl Pyrolysis, 63, 2002, 69.
28. Singh K, Dharampal P, Phosphorus Sulfur Silicon Relat Elem. 183, 2008, 2784.
29. Chilwal A, Malhotra P, Narula A K, Phosphorus Sulfur Silicon Relat Elem, 189, 2014, 410.
Received on 24.09.2017 Modified on 08.10.2017
Accepted on 18.10.2017 © AJRC All right reserved
Asian J. Research Chem. 2017; 10(5): 687-691.
DOI: 10.5958/0974-4150.2017.00117.1