Rare-Earth Molecular Cluster Aggregates with Sandglass-like Core Topology as Surrogates for Minor Actinides in Immobilization within Alkaline-Earth Manganites.

In this study, a series of rare-earth molecular cluster aggregates with the formula [M9RE(μ4-OH)2(μ3-OH)8(sal-R)16]X (MRE(III) = Y (1), Eu (2), Dy (3), Tm (4), Yb (5), Lu (6); X- = Cl- (1-2, 4-6), or DyCl4- (3); Hsal-R = alkyl salicylate with R = Me (2, 4-6), Et (3), or Me and Et (1)) were synthesized via the direct reaction of rare-earth chlorides (MRECl3) with in situ generated lithium or zinc methyl salicylate salts in a ROH/tetrahydrofuran (THF) solution (ROH = MeOH, EtOH) under controlled moisture conditions. Complexes 1-6 were investigated as surrogates for minor actinides, with the aim of immobilizing these species in alkaline-earth manganites. The manganites were obtained by thermal decomposition of mixtures comprising either [Ca(sal-Et)2]n (7) or [Ba(sal-Et)2(THF)]n (8) with [Mn2(μ-OMe)2(sal-Me)4] (9) at 850 or 1100 °C. Thermolysis of compounds 7 and 9 in the presence of 0.22 or 1.11 mol % 1-6 at 1100 °C yielded MRE-doped CaMnO3 as the major phase, with variable amounts of CaMn2O4. Under analogous conditions, decomposition of 8 and 9 produced BaMnO3:MRE(III); transmission electron microscopy (TEM) also identified nanorod-like crystallites of MREMnO3. Alkaline-earth manganites, prepared via the aryloxide route, effectively incorporate MRE(III) ions at the Ca(II)/Ba(II) sites.