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

## TL;DR

This paper describes the synthesis of rare-earth molecular clusters that can act as substitutes for minor actinides in alkaline-earth manganites, aiding in their immobilization.

## Contribution

The study introduces rare-earth molecular clusters with a sandglass-like core as novel surrogates for minor actinides in manganite immobilization.

## Key findings

- MRE-doped CaMnO3 was the major phase formed at 1100°C with variable amounts of CaMn2O4.
- BaMnO3:MRE(III) was produced under similar conditions with nanorod-like crystallites of MREMnO3 identified.
- Alkaline-earth manganites effectively incorporate MRE(III) ions at Ca(II)/Ba(II) sites.

## Abstract

In this study, a
series of rare-earth molecular cluster aggregates
with the formula [M9
RE(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.