Removal of di- and tri-alkyltin(IV) compounds by polyphosphonate ligand: A speciation perspective

The potential of employing diethylenetriamine-N,N,N′,N″,N″-pentakis(methylenephosphonic acid), DTPMP, to remove (CH3)3Sn+, (C2H5)3Sn+, (C3H7)3Sn+, (CH3)2Sn2+, (C2H5)2Sn2+ cations from aqueous solution was evaluated on the basis of speciation modeling. For this purpose, the interactions of DTPMP towards alkyltin(IV) cations in NaCl at I = 0.1 mol L− 1 (for (CH3)2Sn2 +, also in the ionic strength range 0.1 ≤ I ≤ 1 mol L−1) was studied. Potentiometric measurements evidenced the formation of MLHj species, with 0 ≤ j ≤ 5, and stability constant values that follow the trend (CH3)3Sn+ > (C2H5)3Sn+ > (C3H7)3Sn+, for trialkyltin(IV) cations and (CH3)2Sn2 + > (C2H5)2Sn2+, for dialkyl ones. 1H NMR investigations in solution allowed to confirm all the models proposed on the basis of potentiometric findings and, in some cases, to gain information about the coordination arrangement around the tin. Once assessed the most reliable speciation models, the sequestering ability of the polyphosphonic ligand was evaluated by pL0.5 empiric parameter (ligand concentration required to sequester 50% of the metal cation present in traces).