Spectral Studies and Bactericidal, Fungicidal, Insecticidal and Parasitological Activities of Organotin(IV) Complexes of Thio Schiff Bases Having no Donor Atoms

Twelve new organotin(IV) complexes of the type RnSnLm [where n = 3, m = 1, R = CH3 or C6H5; n = 2, m = 2, R = C6H5 or C4H9 ; L = anion of Schiff bases derived from the condensation of 2-amino-5-(o-anisyl)-l,3,4-thiadiazole with salicylaldehyde (HL-1), 2- hydroxynaphthaldehyde (HL-2) and 2-hydroxyacetophenone (HL-3)] have been synthesized and characterized by elemental analysis, molar conductances, electronic, infrared, far-infrared, 1H NMR and 119Sn Mössbauer spectral studies. Thermal studies of two complexes, viz., Ph3Sn (L-1) and Ph2Sn(L-2)2 have been carried out in the temperature range 25-1000∘C using TG, DTG and DTA techniques. All these complexes decompose gradually with the formation of SnO2 as an end product. In vitro antimicrobial activity of the Schiff bases and their complexes has also been determined against Streptococcus faecalis, Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus Penicillin resistance (2500 units), Candida albicans, Cryptococcus neoformans, Sporotrichum schenckii, Trichophyton mentagrophytes and Aspergillus fumigatus. The Schiff bases (HL-1), (HL-2) and the organotin(IV) compounds have also been tested against various important herbicidal, fungicidal, insecticidal species and also for parasitological activity against freeliving nematode.


INTRODUCTION
2,5-Disubstituted-l,3,4-thiadiazole moieties have been found to possess herbicidal, radioprotective, diuretic and bacteriostatic properties (1-3). However, very little work seems to have been done on the Schiff base complexes containing heterocyclic amines. Therefore, we report herein the synthesis and characterization of organotin(IV) complexes with the Schiff bases described in Fig.l, obtained by the condensation of 2-amino-5-(o-anisyl)-l,3,4-thiadiazole with aldehydes or ketones.

MATERIALS AND METHODS
All the reagents, viz., organotin halides (Fluka), salicylaldehyde, 2-hydroxynaphthaldehyde and 2hydroxyacetophenone (Fluka) were used as received. All the chemicals and solvents used were dried and purified by standard methods, and moisture was excluded from the glass apparatus using CaCI: drying tubes.
Carbon, hydrogen and tin content of th complexes were determined as previously rported (4). Molar conductance, electronic spectra, infrared, far-infrared, H NMR, gSn M6ssbauer and thermal measurements were carried out on the sam instruments as previously reported (5).
Antimicrobial activities of the Schiff bases and some of their organotin(IV) complexes were carried out at microbial section of the Central Drug Research Institute (CDRI), Lucknow using two fold serial dilution techniques. Herbicide, insecticide and fungicide efficacy as well as parasitological activity of a few compounds were evaluated by Cyanamid, U.S.A.
Synthesis of the Complexes The complexes were prepared by the replacement reactions of tri-and diorganotin(IV) chloride with the sodium salts of the Schiff bases in 1"1 and 1.'2 ratios, respectively, in absolute alcohol according to the folloxving method.
Sodium methoxide was prepared by the dissolution of sodium (0.16 g, 7.00 mmole) in absolute methanol (10 ml). To this solution was added 5.00 mmole of the Schiff base [(HL-I) to (HL-3)] in 25 ml of methanol and the mixture was first stirred for hr and then refluxed for 2 hrs. The sodium salt of the Schiff base so obtained in solution was added dropwise to the triorganotin chloride (5.00 mmole) or diorganotin dichloride (2.50 mmole) in absolute methanol (15 ml) with constant stirring. The resulting mixture was stirred for hr and then refluxed for 5-6 hrs. The contents were centrifuged to remove the sodium chloride and the unreacted sodio derivative of the Schiff base. The excess solvent was removed by distillation. The complex thus obtained was purified by recrystallization from petroleum ether (60-80C) and dried under vacuum. 1:2 1.1 Ph2SnCI2 / RaSnCI + NaL > Ph2SnL: / R3SnL + 2NaCI / NaCI Where R CH 3 or C6H L anion of Schiff bases (HL-I) to (HL-3), as indicated in Fig. 1.
Reactions of di-n-butyltin oxide with the Schiff bases have been carried out in 1:2 molar ratio in refluxing benzene. These reactions proceed with the liberation of water, which is removed azeotropically with benzene. The above reactions were found to be quite facile and could be completed in 8-10 hrs of refluxing. The resulting complexes are obtained in good yield in the form of coloured solids.
Results and Discussion Stoichiometry All the newly synthesized complexes are coloured solids and soluble in common organic solvents. The colours, yields, melting points, elemental analyses and molar conductances of the Schiff bases and their complexes are presented in Table 1. The analytical data are in good agreement with the proposed stoichiometry of the complexes. The low values of the molar conductance (6.28- 13.85 ohmcm 2 mole-) are in agreement with their non-electrolytic nature.

Electronic Spectra
In the electronic spectra of the Schiff bases and of their organotin(IV) complexes, two bands are observed (Table II) in the region 217 233 nm and 270 309 nm which may be as-  signed to 7t-rt* transition of the benzenoid and of the >C--N chromophore, respectively. A band in the region 355-538 nm in the spectra of the Schiff bases and complexes is likely to & Parasitological Activities of Organotin(IlO Complexes be the secondary band of the benzene ring coupled with the intramolecular charge transfer transition taking place within the ligand moiety. Furthermore, sharp bands were observed in the region 313-331 nm in the spectra of the complexes which could be assigned to the charge transfer transition from ligand to tin (7).

Infrared Spectra
The characteristic infrared frequencies of the Schiff bases and their organotin(IV) complexes are given in Table III. The infrared spectra of the Schiff bases exhibit a band at-2940 cmcharacteristic of hydrogen bonded phenolic vOH vibrations (8). It is absent in the spec-  The far-IR spectra of Ph3SnL and Ph2SnL2 show bands at 265 4-6 and 229 + 7 cm which may be assigned (7,11) to the v,,Sn-C and v, Sn-C, respectively, whereas the corresponding bands at 608 + 18 and 550 + 20 cmhave also been assigned (10) Table IV. A signal at 8.50 + 0.20 ppm due to the intramolecularly hydrogen bonded phenolic proton (8,9) of the Schiff bases disappear in the H NMR spectra of the organotin complexes indicating, thereby, the substitution of the phenolic proton by the organotin moiety. The signals due to the azomethine (-C(H)--N-) and methyl (-C(CH3)--N--) protons in the Schiff bases appear as a singlet at 7.05 and 1.60 ppm, respectively indicating that the azomethine nitrogen is hydrogen bonded (8,9). In the complexes, the signals shift downfield (2.10 ppm for the methyl and 8.20-8.50 ppm for the methine protons) as compared to their positions in the free Schiff bases owing to the coordination of the azomethine nitrogen to tin (8,9). The signals at 4.57 + 0.03 ppm in the Schiff bases has been assigned to the --OCHa protons which remains unaltered on complexation and thus clearly indicates the non-involvement of this group in complex formation. The complex pattern observed in the region 7.00-8.25 ppm in all the complexes is due to overlapping resonances of the phenyl groups bonded to tin and of the aromatic ligand protons. The butyl protons attached to the tin appear as a complex pattern (1.70 0.83 ppm) (12,13). The number of protons of various groups calculated from the integration curves and those calculated for the expected molecular formula agrees with each other.  Table V. The complexes viz., RaSnL (R CH or C6H5) and 1L2SnL2 (R CH_ or C4H9) are five-and six-coordinated, respectively, having monofimctional bidentate ligands with ON donor sites as indicated from the IR data. Trigonal bipyramidal R3SnL (L bidentate ligand) complexes have been reported (11,14) to have different Q.S. for the following three isomers (Q.S. 1.7-2.  (Table V) most active. The Schiff bases (HL-I) and (HL-2) were found to be active against fungal strains 6, 7, 8 and 10, and (HL-3) was active against fungal strain 7 only. As evident from Table VI, diphenyltin complexes are very active against all the bacteria and fungi used and show lower MIC values in comparison to the Schiff bases. The other complexes also show greater bactericidal and fungicidal activities as compared to their corresponding Schiff bases and show lower MIC values than those of the Schiff bases. The order of the activity is as follows: Ph2SnL2>Me3SnL>Ph3SnL>Bu2SnL2 Thus the results clearly indicate that the organotin(IV) complexes possess moderate bactericidal and fungicidal activities. The results of herbicidal, insecticidal, fungicidal and parasitological activities of (HL-1) and (HL-2), and the organotin complexes derived from them (see Table   VII) indicate that all the compounds tested except Ph3Sn(L-2 ) are completely inactive against the various species mentioned.   Thermal decomposition of two complexes, viz., Ph3Sn(L-I ) and Ph2Sn(L-2)z has been studied using TG, DTG and DTA tectmiques. Both complexes decompose gradually with the formation of SnO: as an end product.