The dipeptide complexes R2SnL listed below have been synthesized: (a) Me2SnL; H2L = glycylalanine (H2GlyAla), glycylvaline (H2GlyVal), glycylmethionine (H2GlyMet), glycyltryptophan (H2GlyTrp), glycyltyrosine (H2GlyTyr); (b) nBu2SnL; H2L = H2GlyAla, H2GlyVal; (c) nBu2SnL.H2O; H2L = glycylglycine (H2GlyGly), H2GlyAla; (d) tBu2SnL; H2L = H2GlyAla, H2GlyVal; (e) tBu2SnGlyGly. H2O; (f) Ph2SnL; H2L = H2GlyAla, H2GlyVal, H2GlyTyr, H2GlyTrp; (g) Ph2Sn(HGlyVal)2. The crystal and molecular structures of nBu2SnGl Val have been determined by single‐crystal X‐ray diffraction. The polyhedron around tin is a distorted trigonal bipyramid, analogous to that of Et2SnGlyTyr (see Vornefeld et al., Appl. Organomet. Chem., 1992, 6: 75). According to infrared and 119Sn (ΔE parameters) Mössbauer spectroscopic data the R2SnL derivatives can be classified by their solid‐state structure into two types which are distinguished by the nature of the axial carboxylate [(i) monodentate, as in nBu2SnGlyVal; (ii) bidentate]. Bonding in R2SnL.H2O and Ph2Sn(HGlyVal)2 has been discussed on the basis of vibrational data. Rationalization of the 119Sn Mössbauer parameters has been attempted by ‘literal’ point‐charge model, calculations of ΔE in the structural context described above. According to 13C NMR spectra, compounds Me2SnL are undissociated in methanol solutions, whilst dissociation is inferred for aqueous solutions, probably concerning the carboxyl and amino groups only. Five‐coordination in methanol and aqueous solutions has been assumed for Me2Snl from 119Sn NMR chemical shifts. Values of coupling constants |2J(119Sn, 1H)|, determined from 1H NMR spectra, gave estimates of CSnC angles in Me2SnL in the range 128–136° in methanol and aqueous solutions, which correspond to values from 119Sn Mössbauer ΔE parameters (129.6–133.8°). The structural relationship of R2SnL molecules in the solid state and in solution phase has been discussed.

No abstract

Bis(triphenyllead) compounds (Ph3Pb)2A [H2A = H2Ser (= L-serine), H2Tyr (= L-tyrosine), H2Phoser (= phosphorylserine)], R3PbAcSer (HAcSer = O-acetylserine; R = Ph, Me) and Ph3SnAcSer have been prepared from R3MOH and the appropriate amino acids. From IR data it is inferred that all compounds are polymeric, and that (Ph3Pb)2A (A = Ser, Tyr) and Me3PbAcSer contain unsymmetrically bridging carboxylate groups and coordinating NH2. For (Ph3Pb)2Phoser a structure with a monodentate carboxylate group and intermolecular coordination of Pb by an NH2- and a P=O-group is proposed. The molecules of Ph3MAcSer (M = Pb, Sn) containing monodentate carboxylate groups are bridged by acetyl-C=O groups.

No abstract