Application of Protocols Devised to Study Bi(III) Complex Formation by Voltammetry: The Bi(III)–Picolinic Acid System

摘要

Bi(III) coordination chemistry has been largely neglected due to the difficulties faced when studyingthese systems even though Bi(III) is used in various medicinal applications. This study of the Bi(III)–picolinic acid system by voltammetry applies the rigorous methodologies already developed toenable the study of Bi(III) systems starting in very acidic solutions to prevent precipitation. Thisincludes calibrating the glass electrode accurately at these low pHs, compensating for the diffusionjunction potential below pH 2 and determining the reduction potential of uncomplexed Bi(III) whichcannot be directly measured. The importance of including nitrate from the background electrolyte asa competing species is highlighted, especially for data acquired below pH ∼ 2. From analysis of thevoltammetric data, it was not clear whether a ML3OH species formed in solution or whether it was acombination of ML4 and ML4OH. Information from crystal structures and electrospray ionizationmassspectrometry measurements was thus used to propose the most probable species model. Thelog β values determined were 7.77 ± 0.07 for ML, 13.89 ± 0.07 for ML2, 18.61 ± 0.01 for ML3, 22.7 ±0.2 for ML4, and 31.4 ± 0.2 for ML4OH. Application of these methodologies thus opens the door tobroaden our understanding of Bi(III) complexation.