The formation constants of the species formed in the systems H + + dimethyltin(IV) + 5 -IMP and 5 -UMP, H + + 5 -IMP and H + + 5 -UMP have been determined in aqueous solution in the pH range 1.5-9.5 at constant temperature (25• C) and constant ionic strength (0.1 mol dm −3 NaClO 4 ), using spectrophotometric and potentiometric techniques. 1 H and 31 P NMR investigations in aqueous solution confirmed the species formation. The precipitated complexes of IMP and UMP by Me 2 Sn(IV) 2+ at low pH values were characterized by elemental analysis and FTIR spectroscopy methods, the bonding sites of the ligands were determined and ruled out purine and pyrimidine moieties (N-7 and N-1 in IMP and N-3 in UMP, respectively) while a bidentated coordination of the phosphate group is concluded in both cases. Finally, the experiments revealed the existence of complexes with trigonal bipyramidal structures that is in agreement with similar systems resulted previously.