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1. 2.2.2-Cryptand as a bidentate ligand in rare-earth metal chemistry

   https://doi.org/10.1039/d0qi00746c  

   Chung, Amanda B.; Huh, Daniel N.; Ziller, Joseph W.; Evans, William J. (November 2020, Inorganic Chemistry Frontiers)

   null (Ed.)

   The 2.2.2-cryptand ligand (crypt) that is heavily used in reductions of rare-earth metal complexes to encapsulate alkali metals has been found to function as a bidentate ligand to rare-earth metal ions in some cases. The X-ray crystal structures of the reduced dinitrogen metal complex, [{(R 2 N) 2 Ce(crypt-κ 2 -O,O′)} 2 (μ–η 2 :η 2 -N 2 )] (R = SiMe 3 ), and the ytterbium metallocene, (C 5 Me 5 ) 2 Yb(crypt-κ 2 -O,O′), are presented to demonstrate this binding mode. The implications of this available binding mode in rare-earth metal cryptand chemistry are discussed. 

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2. A rare earth metallocene containing a 2,2′-azopyridyl radical anion

   https://doi.org/10.1039/d1sc04285h  

   Delano IV, Francis; Castellanos, Ernesto; McCracken, John; Demir, Selvan (December 2021, Chemical Science)

   Introducing spin onto organic ligands that are coordinated to rare earth metal ions allows direct exchange with metal spin centres. This is particularly relevant for the deeply buried 4f-orbitals of the lanthanide ions that can give rise to unparalleled magnetic properties. For efficacy of exchange coupling, the donor atoms of the radical ligand require high-spin density. Such molecules are extremely rare owing to their reactive nature that renders isolation and purification difficult. Here, we demonstrate that a 2,2′-azopyridyl (abpy) radical ( S = 1/2) bound to the rare earth metal yttrium can be realized. This molecule represents the first rare earth metal complex containing an abpy radical and is unambigously characterized by X-ray crystallography, NMR, UV-Vis-NIR, and IR spectroscopy. In addition, the most stable isotope 89 Y with a natural abundance of 100% and a nuclear spin of ½ allows an in-depth analysis of the yttrium–radical complex via EPR and HYSCORE spectroscopy. Further insight into the electronic ground state of the radical azobispyridine-coordinated metal complex was realized through unrestricted DFT calculations, which suggests that the unpaired spin density of the SOMO is heavily localized on the azo and pyridyl nitrogen atoms. The experimental results are supported by NBO calculations and give a comprehensive picture of the spin density of the azopyridyl ancillary ligand. This unexplored azopyridyl radical anion in heavy element chemistry bears crucial implications for the design of molecule-based magnets particularly comprising anisotropic lanthanide ions. 

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3. Selective Crystallization of Rare‐Earth Ions into Cationic Metal‐Organic Frameworks for Rare‐Earth Separation

   https://doi.org/10.1002/anie.202017042  

   Yang, Huajun; Peng, Fang; Schier, Danielle E.; Markotic, Stipe A.; Zhao, Xiang; Hong, Anh N.; Wang, Yanxiang; Feng, Pingyun; Bu, Xianhui (April 2021, Angewandte Chemie International Edition)

   Abstract For rare‐earth separation, selective crystallization into metal‐organic frameworks (MOFs) offers new opportunities. Especially important is the development of MOF platforms with high selectivity toward target ions. Here we report a MOF platform (CPM‐66) with low‐coordination‐number environment for rare‐earth ions. This platform is highly responsive to the size variation of rare‐earth ions and shows exceptional ion‐size selectivity during crystallization. CPM‐66 family are based on M₃O trimers (M=6‐coordinated Sc, In, Er‐Lu) that are rare for lanthanides. We show that the size matching between urea‐type solvents and metal ions is crucial for their successful synthesis. We further show that CPM‐66 enables a dramatic multi‐fold increase in separation efficiency over CPM‐29 with 7‐coordinated ions. This work provides some insights into methods to prepare low‐coordinate MOFs from large ions and such MOFs could serve as high‐efficiency platforms for lanthanide separation, as well as other applications. 

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4. Implementation of 2,2′-azobispyridine radical mono- and dianions in dinuclear rare earth metal complexes

   https://doi.org/10.1039/D4CC03222E  

   Delano_IV, Francis; Demir, Selvan (October 2024, Chemical Communications)

   An unprecedented dinuclear rare earth metal complex with a bridging 2,2'-azobispyridyl radical anion was isolated from the one-electron oxidation of the parent neutral complex. Both were characterized through crystallography, spectroscopy, and DFT. 

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5. Direct Hydrogenolysis of Cellulose to Methane Utilizing Rare‐Earth Promoted Nickel Catalysts

   https://doi.org/10.1002/ijch.202200119  

   Koch, Christopher J.; Alagaratnam, Anushan; Goeppert, Alain; Surya Prakash, G. K. (January 2023, Israel Journal of Chemistry)

   Abstract Cellulose is one of the main components of plant matter, which makes it a viable target for biomass conversion to fuels. The direct conversion of cellulose to methane utilizing nickel‐based catalysts often has challenges associated with it. Carbon agglomeration creating nickel‐carbon nanoparticles deactivating catalytic hydrogenation of cellulose has been well reported. Utilizing rare‐earth metals as promoters increases the conversion of cellulose to methane, albeit with deactivation of the catalyst in the form of nickel‐rare‐earth‐carbon nanoparticles. Adding an additional zinc metal promoter eliminates the carbon agglomeration and allows for increased methane yields. Herein, we report an 81 % methane yield from cellulose in 48 hours utilizing a Ni/Zn/Y/Al₂O₃catalyst at 225 °C and under 50 bar H₂pressure. 

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