Monomeric and Trimeric Thorium Chlorides Isolated from Acidic Aqueous Solution.

Area of Science:

• Inorganic Chemistry
• Materials Science
• Geochemistry

Background:

• Thorium(IV) chemistry in aqueous solutions and solid-state is not fully understood.
• Novel structural motifs in thorium compounds are crucial for advancing materials science and geochemistry.

Purpose of the Study:

• To synthesize and characterize new thorium(IV) compounds.
• To investigate the structural diversity and stability of thorium species in solution.
• To explore the potential applications of these compounds in geochemistry and materials design.

Main Methods:

• Synthesis of thorium(IV) compounds from acidic aqueous solution at room temperature.
• Characterization using single crystal X-ray diffraction, Raman, and IR spectroscopies.
• Computational analysis including Density Functional Theory (DFT) and correlated molecular theory.
• Small-angle X-ray scattering (SAXS) for solution-state analysis.

Main Results:

• Isolation and characterization of two thorium(IV) compounds: [Th(H2O)4Cl4]·2(HPy·Cl) (1) and (HPy)3[Th3(H2O)2Cl10(OH)5]·4(HPy·Cl) (2).
• Compound 1 features discrete mononuclear Th(H2O)4Cl4 units, while compound 2 exhibits a novel hydroxo-bridged trimeric [Th3(OH)5]7+ core.
• Extensive hydrogen bonding and π-π stacking interactions stabilize the structures.
• DFT calculations predicted vibrational frequencies and relative stability.
• SAXS confirmed the intactness of the [Th3(OH)5]7+ trimeric unit in water.

Conclusions:

• The isolation of the novel trimeric [Th3(OH)5]7+ core provides new insights into thorium solution and solid-state chemistry.
• Outer coordination sphere interactions play a significant role in stabilizing these thorium structures.
• The trimeric thorium unit is stable in aqueous solution and relevant for geochemical modeling and thorium-based material design.