Synthetic and structural comparisons of bismuth(iii) carboxylates synthesised under solvent-free and reflux conditions

Abstract

Two synthetic approaches to the formation of bismuth(III) carboxylates have been explored and compared. Ph₃Bi was reacted with a series of carboxylic acids (RCO₂H) of varying pK_a and functionality (R = PhCHCH, o-MeOC₆H₄, m-MeOC₆H₄, o-H₂NC₆H_,, o-O₂NC₆H₄, p-O₂NC₆H₄, 2-(C₅H₄N)) under reflux conditions in toluene and solvent-free. The thermochemical profiles of the solvent-free reactions were also studied by DSC-TGA. All reactions produced the tri-substituted bismuth carboxylates in comparable yields and purity with the exceptions of picolinic acid and p-nitrobenzoic acid. 2-Picolinic acid exclusively formed the di-substituted complex, [PhBi(2-(C₅H₄N)CO₂)₂]₄, by both methods, while p-nitrobenzoic acid gave the tri-substituted complex through reflux and the di-substituted complex under solvent-free conditions. Two of the complexes were structurally authenticated by single crystal X-ray diffraction: [PhBi(2-(C₅H₄N)CO₂)₂]₄ is tetrameric formed through five membered chelate rings involving the pyridyl N and O(-C) rather than the less stable carboxylate (-CO₂) chelates, while [Bi(o-MeOC₆H₄CO₂)₃]_∞, is a polymer in which dimeric units, constructed around two chelating and one unsymmetrical bridging carboxylate on each Bi centre, are then joined together through longer intermolecular Bi–O bridging bonds.