Two new organotin(IV) complexes with dianionic dipeptides containing the alpha-aminoisobutyryl residue (Aib) as ligands are described. The solid complexes [(n-Bu)(2)Sn(H(-1)L(A))] x 2MeOH (1 x 2MeOH) (L(A)H=H-Aib-L-Leu-OH) and [(n-Bu)(2)Sn(H(-1)L(B))] x MeOH (2 x MeOH) (L(B)H=H-Aib-L-Ala-OH) have been isolated and characterized by single-crystal X-ray crystallography and spectroscopic techniques (H(-1)L(2-) is the dianionic form of the corresponding dipeptide). Complexes 1 x 2MeOH and 2 x MeOH are monomeric with similar molecular structures. The doubly deprotonated dipeptide behaves as a N(amino), N(peptide), O(carboxylate) ligand and binds to the Sn(IV) atom. The five-coordinate metal ion has a distorted trigonal bipyramidal geometry. A different network of intermolecular hydrogen bonds in each compound results in very dissimilar supramolecular features. The IR, far-IR, Raman and (119)Sn NMR data are discussed in terms of the nature of bonding and known structures. The antibacterial and antiproliferative activities as well as the effect of the new compounds on pDNA were examined. Complexes 1 and 2 are active against the gram-positive bacteria Bacillus subtilis and Bacillus cereus. The IC(50) values reveal that the two compounds express promising cytotoxic activity in vitro against a series of cell lines.