Synthesis,structure and biological activity of organotin derivatives with pyridylmethylthiobenzoic acid

Reaction of 2-(2-pyridylmethylthio)benzoic acid (1) with R₂SnO (R = Et or ⁿBu) in a 1:1 molar ratio gives the dimeric compounds {(2-PyCH₂SC₆H₄CO₂)SnR₂]₂O}₂. A similar reaction of 2-(4-pyridylmethylthio)benzoic acid (2) with Et₂SnO yields an analogous result. However, treatment of 2 with ⁿBu₂SnO in a 1:1 molar ratio only gives the diorganotin dicarboxylate (4-PyCH₂SC₆H₄CO₂)₂Sn(ⁿBu)₂. X-ray crystal structure analyses indicate that the pyridyl nitrogen atoms do not coordinate to the tin atoms in the dimer, whilst in the diorganotin dicarboxylate the tin atom has a seven-coordinate distorted pentagonal-bipyramidal geometry, and this compound forms a linkage coordination polymer through the interactions of the pyridyl nitrogen atoms with the adjacent tin atoms. In addition, treatment of 1 or 2 with (Ph₃Sn)₂O in a 2:1 molar ratio affords triphenyltin carboxylates, in which the tin atoms also show different coordination environments. In the solid state, triphenyltin 2-(2-pyridylmethylthio)benzoate is a monomer and the pyridyl nitrogen atom does not participate in coordination to the tin atom either, while the interactions between the pyridyl nitrogen atoms and the adjacent tin atoms link triphenyltin 2-(4-pyridylmethylthio)benzoate into a coordination polymer. Preliminary in vitro tests for fungicidal activity show that all these compounds display good activity to Physolospora piricola in a low concentration. Moreover, the triphenyltin carboxylates show a higher inhibition percentage than the diorganotin carboxylates.