Systematic control of the molar ratio between thorium hydroxides and selenic acid and their reaction temperature under hydrothermal conditions results in four novel thorium-based selenate complexes, namely, [ThO(OH)(SeO)(HO)]·(SeO)·13HO (Th-1), [ThO(OH)(SeO)(HO)]·7HO (Th-2), Th(OH)(SeO)HO (Th-3), and Th(SeO)(HO)·2.5HO (Th-4), as well as the thorium mixed selenite selenate compound Th(SeO)(SeO) (Th-5). Smaller [HSeO]/[Th(IV)] ratio or lower temperature give rise to the formation of octameric [Th(μ-O)(μ-OH)] cores in Th-1/Th-2 and infinite [Th(μ-OH)HO] chains in Th-3, respectively. Increasing the [HSeO]/[Th(IV)] ratio or elevating the temperature generates a microporous (11.3 Å voids) open-framework Th-4, a monomeric thorium species without oxo/hydroxyl ligands, and a three-dimensional thorium structure Th-5. Formation of these compounds suggests that variables including acidity and temperature play a critical role in the hydrolysis and oligomerization of Th ions. Increasing acidity limits the deprotonation of water molecules and formation of nucleophilic hydroxo/oxo-aquo Th species, and high temperature appears to suppress the olation/oxolation hydrolysis reactions, which in both ways limit the formation of the thorium oligomers.

Periodate is a strong oxidant and is often reduced to IO or I under hydrothermal conditions. Here, we present a rare case of a mixed-valent iodate(V)/periodate(VII) compound, Th(HO)(IO)[IVO(OH)], prepared with a hydrothermal method starting from periodic acid. Crystallographic results demonstrate that heptavalent iodine adopts IO distorted octahedral geometries, which are stabilized on the crystallographically compatible crystal lattice sites of VO octahedra through an aliovalent substitutional disorder mechanism. X-ray photoelectron and synchrotron radiation X-ray absorption spectroscopes both quantitatively confirm the presence of mixed valent iodine oxoanions with a molar ratio (I/I) of 4:1, consistent with the single crystal X-ray analysis. The crystallization of mixed-valent products with compatible lattice site can be fancily utilized for stabilizing the uncommon oxidation states of other elements in general.