Studies in aryltin chemistry: part 7. Spectroscopic and fungicidal studies of somep-substituted tri-aryltin acetates, oxides and hydroxides

The fungicidal activity of a series of aryltin compounds, (p-ZC6H4)3SnX (X=OAc, OH, or 1/2O), where Z=F, Cl, CH3, CH3O, C2H5 or (CH3)3C, and for which IR and NMR (119Sn) data are reported, has been assessed by radial growth assays on Aspergillus niger, Botrytis cinera, Mucor hiemalis, Fusarium solani and Penicillium chrysogenum, and the results compared with those for the Ph3SnOAc and Ph3SnOH archetypes. In most cases, para-substitution only slightly reduces biocidal activity, but with p-CH3O the aryltin is completely ineffective. This result correlates with the seemingly decreased ability of the ‘(p-CH3OC6H4)3Sn’ moiety to achieve a trigonal-bipyramidal five-coordinate geometry with oxygen atoms in the axial positions, all other Ar3SnOAc and Ar3SnOH having this geometry in the solid state. A model for fungicidal action is proposed based on the need for the organotin inhibitor to attain the above geometry in the active site that it occupies in the ATPase enzyme, being the required condition for its biological activity.