Thorium nanochemistry: the solution structure of the Th(iv)–hydroxo pentamer

Abstract

Tetravalent thorium exhibits a strong tendency towards hydrolysis and subsequent polymerization. Polymeric species play a crucial role in understanding thorium solution chemistry, since their presence causes apparent solubility several orders of magnitude higher than predicted by thermodynamic data bases. Although electrospray mass spectrometry (ESI MS) identifies Th(IV) dimers and pentamers unequivocally as dominant species close to the solubility limit, the molecular structure of Th 5 (OH) y polymers was hitherto unknown. In the present study, X-ray absorption fine structure (XAFS) spectroscopy, high energy X-ray scattering (HEXS) measurements, and quantum chemical calculations are combined to solve the pentamer structure. The most favourable structure is represented by two Th(IV) dimers linked by a central Th(IV) cation through hydroxide bridges.

Synthesis of ThO2nanostructures through a hydrothermal approach: influence of hexamethylenetetramine (HMTA) and sodium dodecyl sulfate (SDS)

“…Some of them may exist as some polynuclear species of thorium (IV) 39,40 . These polynuclear species might be stable under the corresponding solution pH and the temperature.…”

Exploring Actinide Materials Through Synchrotron Radiation Techniques

“…Tetravalent thorium exhibits a strong tendency of hydrolysis and forms complicated hydroxo complexes in aqueous solution. Under this circumstance, Walther et al investigated the solution structure of Th(IV)‐hydroxo pentamer. Long ranged correlation (>6.7 Å) was detected from PDF curves with the increasing Th concentrations, indicating the presence of oligomers larger than the dimer of Th(IV)‐hydroxo.…”

The Application of HEXS and HERFD XANES for Accurate Structural Characterisation of Actinide Nanomaterials: The Case of ThO2

“…Th IV is the softest among the tetravalent actinide ions and its tendency to hydrolyse is lower than that of other An IV .T h IV in solution can form not only mononuclear hydrolysis complexes, but also an umber of polynuclear species. [18][19][20][21][22][23] The fluorite structure of ThO 2 is the ultimateproduct of Th IV hydrolysis, but its well-defineds tructure is often identified only after thermalt reatment or as ar esult of ageing processes.D espite attempts to characterise Th IV precipitates since the 1960s, [24] the information on the structure and consequently on ThO 2 formationm echanismsi ns olution remains scarce. In most cases, highly hydrolysed thorium salts form Th IV precipitates with ill-defined structures.…”

“…Th IV is the softest among the tetravalent actinide ions and its tendency to hydrolyse is lower than that of other An IV . Th IV in solution can form not only mononuclear hydrolysis complexes, but also a number of polynuclear species [18–23] . The fluorite structure of ThO 2 is the ultimate product of Th IV hydrolysis, but its well‐defined structure is often identified only after thermal treatment or as a result of ageing processes.…”