Oxidative Dissolution of Lanthanide Metals Ce and Ho in Molten GaCl₃

Abstract

Gallium trichloride (GaCl3) was used as a solvent for the oxidative dissolution of the lanthanide (Ln) metals cerium (Ce) and holmium (Ho). Reactions were performed at temperatures above 100 °C in sealed vessels to maintain the liquid phase for GaCl3 during the oxidizing reactions. The best results were obtained from reactions using 8 equiv of GaCl3 to metal where the inorganic complexes [Ga][Ln(GaCl4)4] [Ln = Ce (1), Ho (2)] could be isolated. Recrystallization of 1 and 2 employing fluorobenzene (C6H5F) produced [Ga(η6-C6H5F)2][Ln(GaCl4)4] [Ln = Ce (3), Ho (4)] where reversible η6 coordination of C6H5F to [Ga]+ was observed. All complexes were characterized through elemental analysis (F and Cl), IR and UV–vis–near-IR spectroscopies, and both solution and solid-state NMR techniques.

Supercritical Gallium Trichloride in Oxidative Metal Recycling: Ga2Cl6 Dimers vs GaCl3 Monomers and Rheological Behavior

“…The derived viscosity of supercritical GaCl 3 is 2 orders of magnitude lower than that of the normal liquid at 400 K. This substantial reduction facilitates the rapid diffusion of solvent molecules and subsequent interactions with metallic species. The relevant geometry of the chlorinated oxidizer consists of either GaCl 4 – tetrahedral entities − or pyramidal units GaCl 3 . In particular, the pyramidal entities interact with platinum, forming a Pt–Ga chemical bond with a length of 2.402 Å …”

“…GaCl 3 , either molten, dissolved in organic solvents, or supported on polymeric matrices, has been effectively used as a catalyst in the synthesis of different organic and organometallic compounds. − Gaseous and liquid gallium trichloride have been employed in the growth and gas-phase epitaxy of high-quality single-crystal, polycrystalline or nanocrystalline semiconductors, such as GaN, − Ga 2 Te 3 , Ga 2 Se 3 , and Ga 2 O 3 . Molten GaCl 3 is also known as an efficient solvent for the oxidative dissolution of metallic lanthanides (Ce, Ho) transuranium elements (U, Pu), platinum, pnictogens (Sb, Bi), − and chalcogens (Se, Te) . The oxidative dissolution of metals has become highly attractive for a circular economy in different fields, such as extraction of gold from gold-bearing ores, chemical etching in microelectronics, recycling of components in high-tech devices (rare-earth elements and platinum-group metals, etc.)…”

Gallium Trichloride Fluid: Dimer Dissociation Mechanism, Local Structure, and Atomic Dynamics

“…Molten gallium trichloride appears to be a promising oxidative solvent for the recycling of metals, including rare earth elements, platinum and transuranium group metals, and heavy pnictogens and chalcogens [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]. The use of supercritical fluid additionally yields a much lower viscosity in the reaction media, higher diffusion coefficients, and favorable kinetics.…”

“…The dual molecular form of gallium trichloride, existing as edge-sharing tetrahedral dimers ES-Ga 2 Cl 6 or flat trigonal GaCl 3 monomers, creates the possibility to adjust the chemical geometry to a particular metal species. This is achieved by choosing either a tetrahedral chlorinated agent [ 1 , 2 ] or a planar molecular shape with an easily accessible gallium counterpart, facilitating the creation of a metal–gallium bond [ 3 ]. The dimer dissociation, Ga 2 Cl 6 ⇌ 2GaCl 3 , basically depends on temperature and pressure [ 8 , 9 ].…”

Ligand–Metal Complementarity in Rare-Earth and Actinide Chemistry

“…The Eu II complex is luminescent and has been compared to related complexes [Eu­(C 5 Ph 4 H) 2 (DME)] and [Eu­(C 5 Ph 5 ) 2 ], revealing a complicated relationship between the degree of solvation, M···C 5 –centroid distance, and fluorescence emission maximum . In contrast to the tendency of samarium, europium, and ytterbium to form divalent compounds, the team of Anderson, Klamm, Mason, and Tondreau report the oxidative dissolution of cerium and holmium metals in molten GaCl 3 , which affords trivalent [Ga]­[RE­(GaCl 4 -κ 2 Cl ) 4 ] (RE = Ce, Ho) from the melt along with cocrystallized [Ga]­[GaCl 4 ], the former of which was purified by recrystallization from fluorobenzene to give [Ga­(η6-FC 6 H 5 ) 2 ]­[RE­(GaCl 4 -κ 2 Cl ) 4 ]. The oxidizing molten GaCl 3 solvent conditions offer a rare route to soluble trivalent rare-earth complexes under mild conditions that do not require hydrocarbon solvents, except in a final purification step.…”