文摘
The complex formation of [Me2Sn]2+/[Me3Sn]+ with glucuronic [(HL-1)], mandelic [(HL-2)] and gallic [(HL-3)] acids has been studied potentiometrically in aqueous solution (I = 1.0 mol·dm−3 KNO3, 298 ± 0.1 K) and the speciation of various complex species has been evaluated as a function of pH. The results show that these hydroxycarboxylic acid ligands (HL) coordinate via the deprotonated oxygen atom of the carboxylate group resulting in the formation of mixed hydroxo species [Me2Sn(L)(OH)] (12.6–46.2 % in 1:1, 18.3–64.0 % in 1:2) along with [Me2Sn(L)]+ (9.2–18.0 % in 1:1, 14.8–27.8 % in 1:2) in Me2Sn(IV)–(HL) systems and single 1:1 species [Me3Sn(L)] (7.1–12.2 % in 1:1, 13.2–21.7 % in 1:2) in Me3Sn(IV)–(HL) systems at acidic pHs. At physiological pH ~7.0, the major species is [Me2Sn(OH)2] (96.0–97.5 % in 1:1, 92.4–97.2 % in 1:2) with minor amount of [Me2Sn(L)(OH)] (0.4–2.5 % in 1:1, 1.0–5.8 % in 1:2) in Me2Sn(IV)–(HL) systems. Similarly, in Me3Sn(IV)–(HL) systems the major species formed is [Me3Sn(OH)] (86.6–91.5 % in 1:1, 84.7–89.3 % in 1:2) with a very small amount of [Me3Sn(L)] (1.0–1.4 % in 1:1, 1.7–3.0 % in 1:2). At pH >8.0, only hydroxo species are formed, viz. [Me2Sn(OH)2], [Me2Sn(OH)3]− and [Me3Sn(OH)]. In all of the systems, no polymeric species were observed in the studied pH range. Multinuclear (1H, 13C and 119Sn) NMR studies, carried out at different pHs, confirmed the species formation and led us to propose their possible geometries in aqueous solution.