Fundamental Aspects of Bismuth Chemistry and Methods of Characterization

Bismuth is mined as either bismuth oxide (Bi2O3, 'bismite') or bismuth sulfide (Bi2S3, 'bismuthinite'). Bismuth(III) carbonate, Bi2(CO3)3 is formed from the treatment of Bi2O3 with excess CO2, or from Bi(NO3)3 with excess Na2CO3 or K2CO3. The composition of Bi2(CO3)3 is sensitive to reaction conditions, which lead to the 'light' and 'heavy' terminology for 'bismuth subcarbonate' in the early pharmaceutical and medical literature.14 BiCl3 and Bi(NO3)3 are prepared from Bi2O3 by reaction with the corresponding mineral acids. In weakly acidic to basic conditions, these bismuth salts are 'hydrolyzed' to the oxides BiOCl and BiONO3, respectively, which have lower solubility. They contain the bismuthyl ion (BiO+) and are commonly referred to as 'basic', 'oxy-' or 'sub-' salts.

The inherently low solubility of bismuth compounds in both aqueous and organic solvents precludes the application of many characterization techniques. Most bismuth compounds have been identified by isolation of crystalline

ranitidine

O SH OH SH

British cysteine (cys) anti-Lewisite

O SH

O H HN. glutathione (GSH) O

thiosalicylic acid (tsal)

Figure 27.1 Molecular drawings and common abbreviations for compounds whose interaction with bismuth is recognized to be biologically relevant material and determination of the solid-state structure by X-ray crystallography. As a result, numerous complexes of bismuth are unique examples involving a particular ligand, and series of related compounds are rare. Moreover, the isolated samples represent the most readily crystallized compounds and are not necessarily broadly indicative of bismuth chemistry. Therefore, few general synthetic procedures have been established to obtain series of compounds for systematic assessment of physical and chemical properties. Although compositions of solutions and stability constants have been assessed for some systems using bismuth-ion-selective electrodes, potentiometry, polarography or oscillo-polarography, and ligands on bismuth may be evaluated by NMR spectroscopy (1H and 13C), these data do not provide definitive formulae or allow for structural assignments. Electrospray ionization mass spectrometry (ESI-MS) has been employed to investigate reaction mixtures containing complexes of bismuth,15 and offers a sensitive and versatile technique to determine the formulae of ionic species in the gas-phase.

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