The synthesis and characterisation of novel organotin biocides.

  • T. G. Purcell

Student thesis: Doctoral ThesisPhD


A series of novel organotin derivatives of various biologically active ligands have been synthesised and characterised by several spectroscopic techniques and in two cases by X-ray crystallography. Five of these compounds were tested for biocidal activity and were found to exhibit varying degrees of fungicidal, bactericidal and herbicidal activity. Tributyltin and trimethyltin derivatives of 3-Indolyl acetate and its N-methyl analogue were considered, from spectroscopic (i.r., 1H n.m.r., Mossbauer) evidence, to adopt five coordinate polymeric structures, with bridging ligand moieties. Tricyclohexyltin (3-indolyl acetate) was found by X-ray studies to adopt a distorted tetrahedral geometry arising from rehybridisation to increase percentage p-orbital contribution to the bond to electronegative oxygen. The lattice structure of this compound was found to contain H-bonds linking the N-H group of the Indole ring to the carbonyl group of a neighbouring atom. A similar molecular (though not lattice structure) is proposed for tricyclohexyltin (N-methyl, 3-indolyl acetate) on the basis of analogous spectroscopic behaviour. Tricyclohexyltin (2-mercaptobenzothiazole) was similarly found to adopt a distorted tetrahedral geometry but no intermolecular bonding was observed. Other triorganotin derivatives of this ligand were considered to adopt the same geometry with varying degrees of distortion towards cis-R3SnNS caused by a close approach of the ring nitrogen. Derivatives of 2-mercaptobenzoxazole are also considered to be four coordinate with the exception of Bu3Sn(mbo) which seems to form a five coordinate structure at low temperature, based upon 77K Mossbauer spectroscopic evidence. The tricyclohexyltin derivative of 2-mercaptobenzimidazole is thought to form a polymeric H-bonded lattice with pendant four coordinate Cy3Sn-. Spectroscopic studies on tri- and diorganotin derivatives of piperazine bis-di-thiocarbamate indicate bonding by the ligand in an anisobidentate fashion. The triorganotin derivatives form ditin complexes (supported by Mass Spectrometry) while the diorganotins form covalently bonded polymers. Triorganotin derivatives of N,N' diphenyIphosphorodiamidic acid and N,N,N',N', tetraethyIphosphorodiamidic acid were all considered to contain tin in a five coordinate trans-R3SnO2 configuration. For triphenyltin derivatives of these ligands a long chain polymeric structure is proposed but for the other derivatives, in particular the trimethyltin derivatives, evidence for cyclic structures is found. Inorganic and organometallic tin salts of paraquat and diquat were synthesised in which, with the exception of the tin (II) derivative, tin was in a six coordinate octahedral configuration. Voltammetric studies on aqueous solutions of paraquat in the presence of SnCl4 indicated that the first reduction step becomes more difficult and the second reduction step less difficult with increasing concentration of SnCl4. This was taken as evidence for a fall in activity of these herbicides on forming such complexes.
Date of Award1985
Original languageEnglish
Awarding Institution
  • University of Bath

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