Thorium(IV) Molecular Clusters with a Hexanuclear Th Core

Abstract

Three polynuclear thorium(IV) molecular complexes have been synthesized under ambient conditions from reactions of an amorphous Th precipitate, obtained via hydrolysis, with carboxylate functionalized ligands. The structures of Th(6)(OH)(4)O(4)(H(2)O)(6)(HCO(2))(12)·nH(2)O (1), Th(6)(OH)(4)O(4)(H(2)O)(6)(CH(3)CO(2))(12)·nH(2)O (2), Th(6)(OH)(4)O(4)(H(2)O)(6)(ClCH(2)CO(2))(12)·4H(2)O (3) each consist of a hexanuclear Th core wherein six 9-coordinate Th(IV) cations are bridged by four μ(3)-hydroxo and four μ(3)-oxo groups. Each Th(IV) center is additionally coordinated to one bound "apical" water molecule and four oxygen atoms from bridging carboxylate functionalized organic acid units. "Decoration" of the cationic [Th(6)(μ(3)-O)(4)(μ(3)-OH)(4)](12+) cores by anionic shells of R-COO(-) ligands (R = H, CH(3), or CH(2)Cl) terminates the oligomers and results in the formation of discrete, neutral molecular clusters. Electronic structure calculations at the density functional theory level predicted that the most energetically favorable positions for the protons on the hexanuclear core result in the cluster with the highest symmetry with the protons separated as much as possible. The synthesis, structure, and characterization of the materials are reported.

Mixed sandwich thorium complexes incorporating bis(tri-isopropylsilyl)cyclooctatetraenyl and pentamethylcyclopentadienyl ligands: synthesis, structure and reactivity

“…Only two other crystallographically characterised Th(IV) formate complexes have been reported, both of which are hexanuclear: neutral Th 6 (OH) 4 38,39 In each structure, the formate moieties bridge between two Th centres, as in 8, but the Th atoms are also bound to either (μ 3 -O) or (μ 3 -OH) bridges, which dictate the overall geometry of …”

Effects of the background electrolyte on Th(IV) sorption to muscovite mica

“…hydrolysis, and subsequent oligomerization. These reactions and their thermodynamics have been studied in great detail (Baes et al, 1958;Brown et al, 1983;Ryan and Rai, 1987;Felmy et al, 1991;Ekberg et al, 2000;Neck et al, 2002;Wilson et al, 2007;Rand et al, 2008;Walther et al, 2008;Knope et al, 2011;Knope and Soderholm, 2012), and it has become increasingly clear that condensation reactions can significantly impact Th(IV) solution chemistry, even at relatively low pH and low Th concentration.…”

Sorption of tetravalent thorium on muscovite

“…These reactions and their products have been extensively studied in solution, with particular emphasis on the determination of thermodynamic stability constants for the hydrolysis products (Baes et al, 1958;Brown et al, 1983;Ryan and Rai, 1987;Felmy et al, 1991;Ekberg et al, 2000;Neck et al, 2002;Wilson et al, 2007b;Rand et al, 2008;Walther et al, 2008;Knope et al, 2011). Overall, it is clear that condensation of hydrolysed Th plays an important role in its solution chemistry, particularly with the observed presence of dissolved polynuclear species even at relatively low concentrations and acidic pH.…”

“…Overall, it is clear that condensation of hydrolysed Th plays an important role in its solution chemistry, particularly with the observed presence of dissolved polynuclear species even at relatively low concentrations and acidic pH. Complementary solid-state studies provide insight into the stable structures of Th hydroxo-bridged dimers (Johansson, 1968;Wilson et al, 2007b), tetramers (Harrowfield et al, 1991), and hexamers (Takao et al, 2009;Knope et al, 2011). This chemistry must be considered when describing the sorption behavior of Th(IV) onto surfaces in contact with these solutions.…”