STUDIES ON SOME ORGANOTIN(IV) COMPLEXES OF THIO SCHIFF BASES

Abstract

Organotin chemistry is among the very strongest areas in the interdis ciplinary organometallic field, since 1940 an enormous activity has been going on in the field of organometallic and coordination chemistry. The first organotin compound was made in 1849 but large-scale applications have developed only recently; indeed, world production figures for organotin compounds have in creased more than 600-fold since 1950. Basic studies in organotin chemistry are stimulated by the success with which a powerful array of various modem physical techniques can be applied to organotin compounds. Organotins have become a leading commercial organometallic first through their use m Poly(vinyl chloride) stabilization, and now as biocides, where their suc cess is based upon their extremely high performance/unit weight ratio and their deg radation by chemical action into non-toxic inorganic tin compounds. Today organotins are used widely as agricultural fungicides and miticides, industrial bio cides and surface disinfectants, and as anthelminthics and marine antifouling agents. Organotins also find extensive uses as catalysts in the manufacture of flexible polyurethane foams, and as beneficial additives for lubricating oils and ballistic addi tives for solid rocket engine fuels. Recently, some diorganotin compounds have been reported to possess antitumor and antileukemia activity and to act as antiviral agents for AID-therapy. Schiff bases are the most important nitrogen donors and are used as ligands towards a wide variety of metal ions. The chemistry of Schiff bases has attracted a considerable attention of chemists during last two decades as many of these have been used as anticancer, antitumor, antitubercular and as analytical agents. o II The enhancement of biological activity and suppression of toxicity by carry ing out the complexion of biologically act.ve compounds with metals is the ma jor factor for the recent growing importance of Schiff base metal complexes, since several of these have been found to show a remarkable anticancers, antitumor, antitubercular, antipyretic, bactericidal and fungicidal activities. The properties of Schiff bases can be greatly modified by introducing organic substituents into the ligand molecule, thereby, inducing different stereochemistries in the resultant metal complexes. Looking into the wide applications of Schiff base metal complexes and of organotin compounds, it was thought worthwhile to synthesize and characterize new organotin(IV) complexes of biologically important thio Schiff bases. These complexes may have a great biological importance. For the sake of convenience the work embodied in the thesis is presented in the following chapters. The first chapter of the thesis : 'INTRODUCTION' describes the important applications of organotins and of Schiff bases, and a critical review of the avail able literature on organotin(IV) complexes of the Schiff bases Second chapter incorporates the details of make, purity and other specifica tions of materials and equipments used in the present study. Third chapter concerns with the preparation and characterization of organotin(IV) complexes of the general formulae R,SnCl4.n.L and RnSnL'm (where n = 3, R= CH3 or C6H5 and m= 1; n =2, R- C6H? and m= 2; Land L'H are the Schiff bases derived from the condensation of 2-amino-4-phenylthiazole with benzaldehyde, 4-methoxybenzaldehyde, furfu. aldehyde, salicylaldehyde and 2-hydroxy- 1 -naphthaldehyde. Ill The possible structures of the complexes have been proposed on the basis of physico-chemical studies, viz., elemental analyses, molar conductance, molecu lar weight determination and electronic, infrared, far-infrared, 'H NMR, 13C NMR and !19Sn Mossbauer spectral studies. The five-coordinated di- and triorganotin(IV) complexes of the types RnSnCl4.n.L (where n = 3, R = C6H5 or CH3 and n = 2, R = C6H5; L - monodentate ligand) and R,SnL' (where R = CH3 or C6H5 and L'H = bidentate ligand) have been proposed to exhibit a distorted trigonal bipyramidal geometry around tin atom as supported from their spectral studies. Whereas, a dis torted octahedral structure has been proposed for the six-coordinated I^SnL' type of complexes, in which ligands are bidentate and coordinate through both the azomethme nitrogen and phenolic oxygen atom. Thermal studies of a few complexes have been earned out in the tempera ture range 25-1000°C using TG, DTG and DTA techniques. Mass loss consider ation at main decomposition stages indicates the conversion of the complex to tin(IV) oxide. In vitro antimicrobial activity of the ligands and some of their complexes has also been determined against a gram-negative bacterium (Escherichia coli), grampositive bacteria (Salmonalla typhi and Bacillus subtilis) and pathogenic fungi (As pergillus terms and Collectrotrichuni falcatum Went). The activity has been found to increase on complexation. Fourth chapter describes the synthesis and the results of spectroscopic in vestigations of organotin(IV) complexes of general formulae RnSnCl4 n.L and R„SnL'm [where n = 3, R = C6H5 or CH3 ; n = 2, R = C6H5 ; n = 3, m- 1, R = CH3 or C6H5 ; n = 2, m = 1 or 2, R = C6H5 or C4H9; L = Schiff bases derived from the condensation of thiosemicarbazide with acetophenone (L-l), 4-nitrobenzaldehyde (L- 2), cyclohexanone (L-3), 5-chlorosalicylaldehyde (L-4), glyoxal (L-5), 2-hydroxy- 1-naphthaldehyde (L-6), 2-methoxybenzaldehyde (L-7), 4-methoxybenzaldehyde (LIV 8), fuifuraldehyde (L-9), salicylaldehyde (L-10) and benzylmethyl ketone (L-ll), and L' = anion of Schiff bases (L-l) to (L-4)]. The possible structures of the complexes have been proposed on the basis of physico-chemical and spectral studies as used in third chapter. Adistorted octa hedral structure has been proposed for all the six-coordinated complexes of the gen eral formula RSnCl4n.L, in which ligands are bidentate and coordinating through the azomethine nitrogen and sulphur atoms. The complexes of the types R^nL* [where R=C6H, or CH3 for L' =anion of (L-l); R=CfiH5 for L' =anion of (L-2)] and R^SnL' [where R= C6H, or C4H9 tor L' - anion of (L-4)] are fivecoordinated having distorted trigonal bipyramidal geometry. While the complexes of the type R^SnL', [R =C4H9 for L' =anion of (L-l) and (L-3); R=C6H5 for L' = anion of (L-2)] are six-coordinated having distorted octahedral geometry around tin atom. Tin(IV) oxide or Tin(II) sulphide has been obtained as an end product in the thermal decomposition of afew complexes as revealed by the per centage weight loss and powder X-ray determination of the residue. The ligands and their com plexes have also been tested against pathogenic bacteria [Streptococcus faecalis, Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus Penicillin resistance (2500 units)] and fungi (Candida albicans, Cryptococcus neoformans, Sporotrichum schenckii, Trichophyton mentagrophytes, Aspergillus fumigatus). The complexes have shown considerable activity in comparison to the ligands. Fifth chapter of the thesis deals with synthesis and structural features of organotin(IV) complexes of the general formulae RSnCl, .L and RSnL' rwhere n =3, R=CH3 or C6H5 ; n=2, R=C6H, ; n=3, m= 1, R=CH or CJL ; n = ' 6 5' 2, m= 2, R= C6H5 or C4H9 ; L= Schiff bases derived from the condensation of V 2-amino-5-(o-anisyl)-l,3,4-thiadiazole with salicylaldehyde (L-l), 2-hydroxy-lnaphthaldehyde (L-2), 2-hydroxyacetophenone (L-3), benzylmethyl ketone (L-4), acetyl acetone (L-5) and furfuraldehyde (L-6), and L' = anion of the Schiff bases (L-l) to (L-3)]. The possible structures of the complexes have been proposed on the basis of physico-chemical and spectral studies as used in third chapter. The six-coordi nated di- and triorganotin(IV) complexes of the types RnSnCl4n.L [where R=CH or CH3 , n = 3; R= CgH5 , n = 2; L. =bidentate ligand coordinates through the azomethine nitrogen and thiadiazole ring sulphur) and R^SnL^ (where R=C6H or C4H9 ; L' = anions of (L-l) to (L-3), which are bidentate and coordinate through the azomethine nitrogen and phenolic oxygen] have been proposed to possess dis torted octahedral arrangement around tin atom. While the distorted trigonal bipyramidal structure has been proposed for the five-coordinated R3SnL' (where R = CH3 or C6H5 ; L' = anion of (L-l) to (L-3), which are bidentate) type of com plexes. Thermal decomposition of a few complexes suggests the formation of tin(IV) oxide as an end product. The ligands and their complexes have also been tested against the pathogenic bacteria and fungi as mentioned in fourth chapter. Greater activity has been shown by the complexes in comparison to the ligands. The results of herbicidal, insecticidal, fungicidal and parasitological activi ties of a few selected compounds, which have been carried out by Cyanamid, U.S.A., are also included.