New di- and triorganotin(IV) derivatives of tyrosinylphenylalanine as models for metal–protein interactions: Synthesis and structural characterization. Crystal structure of Me2Sn(Tyr-Phe) · MeOH

New di- and triorganotin(IV) derivatives of tyrosinylphenylalanine (H2Tyr-Phe) with general formulae R2Sn(Tyr-Phe) where R = Me,n-Bu, n-Oct and Ph, and R3′Sn(HTyr-Phe) where R′ = Me and Ph have been synthesized. The bonding and coordination behaviour in these derivatives are discussed on the basis of FT-IR, multinuclear 1H, 13C and 119Sn NMR and 119Sn Mössbauer spectroscopic studies. These investigations suggest that dipeptide in R2Sn(Tyr-Phe) acts as dianionic tridentate coordinating through −C(O)O−, –NH2 and (–CO)N−peptide groups while in case of R′3Sn(HTyr-Phe) the ligand acts as monoanionic bidentate coordinating through –C(O)O− and –NH2, and the polyhedron around tin in R2Sn(Tyr-Phe) and R′3Sn(HTyr-Phe) is a distorted trigonal-bipyramidal. It is further confirmed by the single crystal X-ray structure of Me2Sn(Tyr-Phe) · MeOH which shows two methyl groups and peptide nitrogen (N−peptide) in the equatorial positions, while the two axial positions are occupied by the carboxylic oxygen (O−carboxyl) and the amino nitrogen (Namino) atom from the same ligand molecule. One methanol molecule is also present in the asymmetric unit.