Complexes of L‐methionyl‐L‐histidine (H2MetHis) with R2Sn(IV) ions (R = Me, nBu, Ph) have been synthesized. The crystal and molecular structures of Me2SnMetHis·0.5MeOH have been determined by X‐ray diffraction. The title compound contains two crystallographically independent molecular units possessing the same trigonal‐bipyramidal geometry at tin, each dimethyltin(IV) moiety being coordinated by the terminal amino nitrogen, deprotonated peptide nitrogen and terminal carboxylate group, neither the imidazole nor thioether groups being involved in bonding. IR spectroscopy was used to probe the structure of the complexes in the solid state, and the structure in solution (CD3OD) was assessed by 1H and 13C NMR. Me2Sn(IV)dipeptide complexes appear to be undissociated and to retain a pentacoordinated structure. Rotamer population of C‐terminal histidine was determined by analysis of vicinal coupling constants and side‐chain orientations have been interpreted with a view to potential applications of the compounds as recognition agents. Biological activity was tested on Ascidian embryos of Ciona intestinalis at different stages of development. Copyright © 2000 John Wiley & Sons, Ltd.

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Suunwzary Oxygen is necessary for the rapid reactions of the tris-( l,lO-phenanthroline)iron(II) and of the tris-(2,2'-bipyridyl) iron( 11) cations in aqueous sodium hydroxide.