Thermal analysis of new dimethyl/dibutyl tin(IV) compounds with amino acids

Six diorganotin(IV) compounds with amino acids of general formula (CH₃)₂SnAACl]₂ and (CH₃CH₂CH₂CH₂)₂SnAACl]₂ (where AA = l-methioninate, l-cysteinate, and l-tryptophanate) were synthesized by reacting dimethyltin(IV) dichloride (M) and dibutyltin(IV) dichloride (B) with l-methionine (M₁) or l-cysteine (C) or l-tryptophan (T) using acetonitrile as solvent and designated as MM₁, MC, MT, BM₁, BC, and BT. The structural characterization of dimethyltin(IV) and dibutyltin(IV) compounds were done using elemental analysis, FT-IR, ¹H-NMR, ¹³C-NMR, and ¹¹⁹Sn-NMR spectroscopy. The thermal properties of the synthesized compounds were studied by thermogravimetric analysis and differential scanning calorimetry techniques in a dynamic atmosphere of nitrogen. The thermal decomposition mechanisms were similar for compounds MM₁, BM₁, MC, BC, and occurred in one step, while in compounds MT and BT it occurred in two consecutive steps. The TG curves of the MT and BT compounds suggest the loss of the ligand (AA) in the first step, with probable formation of a tin oxide R₂SnO intermediate. At the end of the second step free tin is obtained similar to the MM₁, BM₁, MC, BC in accordance with the stoichiometry of the related compounds.