Twenty eight new compounds from five different series of mono-, di- and triorganotin carboxylates containing silicon and germanium have been synthesized. The first series having the general formula [R1GeCHR2CH2COO]2 Sn[CH2Si(CH2)2R3]2 where R1 = C6H5, N(CH2CH2O)3, R2 = C6H5, CH3, p-FC6H4 and R3 = C6H5 have been prepared. The second and third series of diorganotin dicarboxylate having general formula [R1GeCHR2CH2COO]2 Sn[R3]2 where R1 = C6H5, N(CH2CH2O)3, R2 = CH3, C6H5, p-CH3C6H4, p-FC6H4 and p-OCH3C6H4 and R3 = C2H5 (2nd series), R3 = C7H7, p-CH3C7H6 (3rd series) have been synthesized.
The fourth series of triorganotin carboxylates with general formula [R1 GeCHR2CH2COO]Sn[R3]3, where R1 = C6H5, N(CH2CH2O)3, R2 = CH3, C6H5, p-CH3C6H4, P-OCH3C6H4 and R3 = C7H7 have been prepared. The fifth series of monoorganotin carboxylates having general formula [R1 GeCHR2CH2COO]3Sn[R3] where R1 = C6H5, N(CH2CH2O)3, R2 = C6H5, P-CH3C6H4, P-OCH3C6H4, p-FC6sH4 and R3 = C6H5 have been synthesized.
Organotin carboxylates have been prepared by the reaction of mono-, di- and triorganotin halide with germatranyl or trigermyl propionic acid in the presence of triethylamine. All these compounds were characterized by m.p., IR, 1H, 13C, 119Sn NMR, mass spectrometry, Mossbauer spectroscopy and X-ray crystallography.
Crystal structure studies were deemed important as drastic changes in stereochemistry at tin are known to accompany minor changes in constitution and modification of ligand via introduction of substituents. The spectroscopic studies reveal that the geometry around the tin center changes as the coordination around the tin atom increases. These compounds were observed to have four coordinated (tetrahedral), five coordinated (trigonal bipyramidal) and hexa-coordinated (octahedral) geometry around the tin center. In the area of structural work, some recent crystallographic results are presented. Crystal structure of one of the precursor Cl3GeCH(Ph)CH2COOH, was determined and published. It was found to have tric1inic system with space group pl/2. Another very interesting crystal structure of one of the target compound, [(Ph)3GeCH(Ph)CH2COO]2Sn[CH2(CH3)2Si(Ph)]2 was determined and found to be a skew trapezoid with tetrahedral geometry distorting toward octahedral.
In order to study the kinetic parameters such as energy of activation (E*) and order of reaction (n) of some of the representative compounds, thermogravimetric technique (TG) was employed for evaluation of thermal stability. The thermal studies were carried out in the temperature range of 40-1000°C under an inert atmosphere. The results obtained were assessed by Horowitz and Coats methods for the determination of various kinetic parameters. The values obtained by both methods were in good agreement with each other.
Rather a new technique, called chemical vapour deposition (CVD) has been employed for making thin films of some of the representative target compounds. These compounds have been evaluated as precursors for the deposition of mixed oxide film using close space sublimation (CSS), the most innovative among various chemical vapour deposition methodology. The films obtained were characterized by resistivity measurements by four-probe technique, scanning electron microscopy and qualitative and quantitative EDAX (elemental analysis). It has been established that these compounds produce fine thin films which show good conductivity and their resistivity increases with the decrease in temperature and vice versa. It revealed that the obtained films behave as semiconductors and can be efficiently used as precursors for the deposition of thin films of tin and germanium oxides on a glass substrate. Micrographs were obtained which shows the crystal structure of the deposited thin film with peculiar topography.
Bioassay screenings play a very significant role in drug development and pharmacological evaluation of newly synthesized compounds. Various bioassay techniques such as cytotoxicity, antileishmanial and enzyme inhibition were employed to study the behaviour of organotin(IV) derivatives in vitro analysis. These compounds show cytotoxicity against pathogens with good efficacy. These compounds were evaluated for in vitro leishmanicidal activity against promistigotes of leishmania donovani. The screening tests displayed high order of leishmanicidal activity for majority of target compounds. The order of activity varies with nature and position of the substituents in the propionate skeleton of these derivatives. These compounds offer potent antileishmanial activity which is comparable to the standard drug pentamidine.
These compounds were evaluated as inhibitors for α-glucosidase. Inhibition studies indicate notably that these compounds are potent inhibitors of α-glucosidase with Ki values in the very low micromolar range. Inhibition of α-glucosidase is considered important in managing noninsulin-dependent diabetes.