Crystal and molecular structure of dimethyl(L-tryptophyl-L-alaninato)tin(IV)–methanol (1/1) and Mössbauer spectroscopy studies of lattice dynamics of diorganotin(IV) dipeptide complexes

Abstract

The crystal and molecular structure of dimethyl(L-tryptophyl-L-alaninato)tin(IV)–methanol (1/1) has been determined by X-ray crystallography. The tin atom, bonding to two methyl carbons [Sn–C(1) 2.107(6), Sn–C(2) 2.121(8)Å; C(1)–Sn–C(2) 123.8(3)°], terminal amino nitrogen [Sn–N_amino 2.272(5)Å], deprotonated peptide nitrogen [Sn–N_peptide 2.064(5)Å] and terminal carboxylate [Sn–O_carboxylate 2.174(5)Å], has a five-co-ordinated trigonal-bipyramidal environment. An extended hydrogen-bond network gives rise to one-dimensional polymeric chains. The molecular dynamics of three tryptophan-containing dipeptide complexes with R₂Sn^IV(dipeptide dianion = Trp-AlaO, R = Me or Ph; dipeptide dianion = TrpTyrO, R = Me) have been investigated by variable-temperature ¹¹⁹Sn Mössbauer spectroscopy. The complexes behaved as Debye solid and, in particular, the calculated mean-square displacements of the tin atom confirm the occurrence of monomeric structures in such complexes interconnected through hydrogen bonds, which appear to be much stronger in SnMe₂(Trp-AlaO) and SnMe₂(Trp-TyrO) than in SnPh₂(Trp-AlaO).