The Composition of Arylstibonic Acids

Abstract

This thesis describes a detailed ESI-MS investigation into the arylstibonic acids, organo-antimony-containing compounds that are currently of interest as anticancer reagents. Four arylstibonic acids, of nominal formula RC6H4SbO3H2 [R = p-chloro-, p-tolyl-, p-nitro- and α-naphthyl-] were synthesised, and a further eight archival samples from the National Cancer Institute Repository were obtained for use in the project. Results indicate clearly that the acids exist as polyoxometalate aggregates [H8(RSb)12O28], rather than monomeric species, in both the solid state and in acetonitrile solution, thus resolving a century-old debate concerning the nature of their molecular composition. Variations in solvent, time in solution and pH have also defined the stability of these aggregates under different conditions. Synthesis of arylstibonic acids by traditional methods (pre-1940) has been shown to lead to products contaminated with cations present during their preparation. An improved method of synthesis has been devised, and the crystal structure of an intermediate in the synthesis of these acids, [C6NH6][p-O2NC6H4SbCl5], is reported. Salts of arylstibonic acids with a range of cations were investigated by ESI-MS and shown to form a diverse family of polyoxostibonates with nuclearities including Sb12, Sb14 and Sb16. Crystal structures containing some of these aggregates, verified through parallel studies with collaborators, are described. Preliminary study of mixed polyoxometalates (Sb/As) showed a strong tendency to form As4Sb2 species but these could not be fully characterised.