LIGAND ADDITION-REACTIONS AND THE ELECTRON-TRANSFER PROPERTIES OF SNCL2.2H2O AND SNCL4.5H2O - MOLECULAR-STRUCTURE OF BIS(ETHYLCYSTEINATO)TIN(II)

The synthesis and characterization of the tin(II) compounds Sn(ECD) and Sn(CEE)2 and the tin(IV) complex Sn(ECD)2, where H2ECD is N,N'-1,2-ethylenediylbis(L-cysteine) diethyl ester and HCEE is L-cysteine ethyl ester, are reported. H2ECD can be described in a general sense as a ligand with a N2S2 coordination site while the related complex HCEE has a NS coordination site following deprotonation of each thiol group on H2ECD or HCEE. The crystal structure of Sn(CEE)2 demonstrates that the N2S2 coordination scheme is adopted by tin(II) in these complexes. The crystal structure data for Sn(CEE)2[C10H20N2O4S2Sn] are as follows: orthorhombic, space group P2(1)2(1)2(1), a = 5.582 (i) angstrom, b = 9.870 (1) angstrom, c = 28.886 (3) angstrom, V = 1591.5 angstrom3, Z = 4, d(c) = 1.732 g.cm-3, mu-(Mo) = 18.72 cm-1, R = 0.027 (R(w) = 0.030) for 252 parameters and 2324 unique reflections with F(o2) > 3-sigma(F(o2)). The speciation of SnCl2.2H2O and SnCl4.5H2O in the presence of either H2ECD or HCEE was monitored by UV-visible and electrochemical methods, both of which demonstrate formation of a single product for tin(II) but multiple products for tin(IV). The electrochemical properties of SnCl2.2H2O and SnCl4.5H2O in water at a platinum electrode were measured and the effects of complexation by either H2ECD or HCEE on the electrochemical response were examined. An adaptation of the chronocoulometric experiment was developed to examine the potential for oxidation of tin(II) to tin(IV), and this method has general applicability to systems characterized by EC electron-transfer mechanisms. The electrochemical properties of Sn(ECD)Cl2 were also determined and compared with the electron-transfer properties of SnCl2.2H2O and SnCl4.5H2O in nonaqueous solvents.