Synthetic, structural and thermal decomposition studies of heterobimetallic bismuth-based coordination complexes

Abstract

The reaction between triphenyl bismuth and salicylic acid in refluxing toluene proceeds via an acid hydrolysis pathway to produce a yellow complex analyzing as bismuth (III) salicylate---[Bi(Hsal)3]n---in quantitative yield. The composition of the complex is critically affected by the ratio of bismuth to salicylic acid that is employed in the reaction mixture. The material produced from a 1:3 ratio of bismuth to salicylic acid being essentially insoluble, while the product of a 1:20 ratio of bismuth:salicylic acid is soluble in a wide range of solvents including hot toluene. Bismuth (III) salicylate is a useful synthon for the formation of heterobimetallic coordination complexes. The material reacts readily with the transition metal alkoxides Ti(OiPr)4, Nb(OEt)5 and Ta(OEt)5 to produce bimetallic compounds by an alcohol exchange pathway. The reactivity of the bismuth salicylate is mediated by the acidity of the phenolic oxygen on the salicylate ligand. The composition of the complexes produced in this manner are affected by the stoichiometry of the reagents, the concentration of water in the reaction mixture, the solvent polarity and the pH of the system and, most importantly, the identity of the transition metal species. Heterobimetallic complexes can also be produced by direct Lewis acid-base adduct formation between bismuth (III) salicylate and metal complexes. The complexes produced in this manner have lower nuclearity than the compounds derived from the alkoxide-based routes, but better control over the ultimate stoichiometry of the system is obtained. The heterobimetallic complexes produced through both reaction pathways smoothly decompose to produce crystalline binary oxide materials. In general, the conditions required to achieve decomposition and crystallization of the molecular precursors are significantly reduced compared to traditional solid-state syntheses. The properties of the oxides produced from the molecular precursors including crystallinity, morphology and phases present are strongly influenced by the conditions of decomposition.