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1. Evaluating electrochemical accessibility of 4f ⁿ 5d ¹ and 4f ⁿ⁺¹ Ln( ii ) ions in (C ₅ H ₄ SiMe ₃ ) ₃ Ln and (C ₅ Me ₄ H) ₃ Ln complexes

   https://doi.org/10.1039/D1DT02427B  

   Trinh, Michael T. ; Wedal, Justin C. ; Evans, William J. ( October 2021 , Dalton Transactions)

   The reduction potentials (reported vs. Fc + /Fc) for a series of Cp′ 3 Ln complexes (Cp′ = C 5 H 4 SiMe 3 , Ln = lanthanide) were determined via electrochemistry in THF with [ n Bu 4 N][BPh 4 ] as the supporting electrolyte. The Ln( iii )/Ln( ii ) reduction potentials for Ln = Eu, Yb, Sm, and Tm (−1.07 to −2.83 V) follow the expected trend for stability of 4f 7 , 4f 14 , 4f 6 , and 4f 13 Ln( ii ) ions, respectively. The reduction potentials for Ln = Pr, Nd, Gd, Tb, Dy, Ho, Er, and Lu, that form 4f n 5d 1 Ln( ii ) ions ( n = 2–14), fall in a narrow range of −2.95 V to −3.14 V. Only cathodic events were observed for La and Ce at −3.36 V and −3.43 V, respectively. The reduction potentials of the Ln( ii ) compounds [K(2.2.2-cryptand)][Cp′ 3 Ln] (Ln = Pr, Sm, Eu) match those of the Cp′ 3 Ln complexes. The reduction potentials of nine (C 5 Me 4 H) 3 Ln complexes were also studied and found to be 0.05–0.24 V more negative than those of the Cp′more »3 Ln compounds.« less
2. Peculiarities of crystal structures and photophysical properties of Ga ^III /Ln ^III metallacrowns with a non-planar [12-MC-4] core

   https://doi.org/10.1039/c9qi01647c  

   Nguyen, Tu N. ; Eliseeva, Svetlana V. ; Chow, Chun Y. ; Kampf, Jeff W. ; Petoud, Stéphane ; Pecoraro, Vincent L. ( March 2020 , Inorganic Chemistry Frontiers)

   A new series of gallium( iii )/lanthanide( iii ) metallacrown (MC) complexes ( Ln-1 ) was synthesized by the direct reaction of salicylhydroxamic acid (H 3 shi) with Ga III and Ln III nitrates in a CH 3 OH/pyridine mixture. X-ray single crystal analysis revealed two types of structures depending on whether the nitrate counterion coordinate or not to the Ln III : [LnGa 4 (shi) 4 (H 2 shi) 2 (py) 4 (NO 3 )](py) 2 (Ln = Gd III , Tb III , Dy III , Ho III ) and [LnGa 4 (shi) 4 (H 2 shi) 2 (py) 5 ](NO 3 )(py) (Ln = Er III , Tm III , Yb III ). The representative Tb-1 and Yb-1 MCs consist of a Tb/YbGa 4 core with four [Ga III –N–O] repeating units forming a non-planar ring that coordinates the central Ln III through the oxygen atoms of the four shi 3− groups. Two H 2 shi − groups bridge the Ln III to the Ga III ring ions. The Yb III in Yb-1 is eight-coordinated while the ligation of the nine-coordinated Tb III in Tb-1 is completed by one chelating nitrate ion. Ln-1 complexes in the solidmore »state showed characteristic sharp f–f transitions in the visible (Tb, Dy) and near-infrared (Dy, Ho, Er, Yb) spectral ranges upon excitation into the ligand-centered electronic levels at 350 nm. Observed luminescence lifetimes and absolute quantum yields were collected and discussed. For Yb-1 , luminescence data were also acquired in CH 3 OH and CD 3 OD solutions and a more extensive analysis of photophysical properties was performed. This work demonstrates that while obtaining highly luminescent lanthanide( iii ) MCs via a direct synthesis is feasible, many factors such as molar absorptivities, triplet state energies, non-radiative deactivations through vibronic coupling with overtones of O–H, N–H, and C–H oscillators and crystal packing will strongly contribute to the luminescent properties and should be carefully considered.« less
3. Trends in trigonal prismatic Ln-[1]ferrocenophane complexes and discovery of a Ho ³⁺ single-molecule magnet

   https://doi.org/10.1039/D0SC01197E  

   Latendresse, Trevor P. ; Vieru, Veacheslav ; Upadhyay, Apoorva ; Bhuvanesh, Nattamai S. ; Chibotaru, Liviu F. ; Nippe, Michael ( April 2020 , Chemical Science)

   Lanthanide metallocenophanes are an intriguing class of organometallic complexes that feature rare six-coordinate trigonal prismatic coordination environments of 4f elements with close intramolecular proximity to transition metal ions. Herein, we present a systematic study of the structural and magnetic properties of the ferrocenophanes, [LnFc 3 (THF) 2 Li 2 ] − , of the late trivalent lanthanide ions (Ln = Gd ( 1 ), Ho ( 2 ), Er ( 3 ), Tm ( 4 ), Yb ( 5 ), Lu ( 6 )). One major structural trend within this class of complexes is the increasing diferrocenyl (Fc 2− ) average twist angle with decreasing ionic radius ( r ion ) of the central Ln ion, resulting in the largest average Fc 2− twist angles for the Lu 3+ compound 6 . Such high sensitivity of the twist angle to changes in r ion is unique to the here presented ferrocenophane complexes and likely due to the large trigonal plane separation enforced by the ligand (>3.2 Å). This geometry also allows the non-Kramers ion Ho 3+ to exhibit slow magnetic relaxation in the absence of applied dc fields, rendering compound 2 a rare example of a Ho-based single-molecule magnet (SMM)more »with barriers to magnetization reversal ( U ) of 110–131 cm −1 . In contrast, compounds featuring Ln ions with prolate electron density ( 3–5 ) don't show slow magnetization dynamics under the same conditions. The observed trends in magnetic properties of 2–5 are supported by state-of-the-art ab initio calculations. Finally, the magneto-structural relationship of the trigonal prismatic Ho-[1]ferrocenophane motif was further investigated by axial ligand (THF in 2 ) exchange to yield [HoFc 3 (THF*) 2 Li 2 ] − ( 2-THF* ) and [HoFc 3 (py) 2 Li 2 ] − ( 2-py ) motifs. We find that larger average Fc 2− twist angles (in 2-THF* and 2-py as compared to in 2 ) result in faster magnetic relaxation times at a given temperature.« less
4. The importance of the counter-cation in reductive rare-earth metal chemistry: 18-crown-6 instead of 2,2,2-cryptand allows isolation of [Y ^II (NR ₂ ) ₃ ] ¹⁻ and ynediolate and enediolate complexes from CO reactions

   https://doi.org/10.1039/C9SC05794C  

   Ryan, Austin J. ; Ziller, Joseph W. ; Evans, William J. ( February 2020 , Chemical Science)

   The use of 18-crown-6 (18-c-6) in place of 2.2.2-cryptand (crypt) in rare earth amide reduction reactions involving potassium has proven to be crucial in the synthesis of Ln( ii ) complexes and isolation of their CO reduction products. The faster speed of crystallization with 18-c-6 appears to be important. Previous studies have shown that reduction of the trivalent amide complexes Ln(NR 2 ) 3 (R = SiMe 3 ) with potassium in the presence of 2.2.2-cryptand (crypt) forms the divalent [K(crypt)][Ln II (NR 2 ) 3 ] complexes for Ln = Gd, Tb, Dy, and Tm. However, for Ho and Er, the [Ln(NR 2 ) 3 ] 1− anions were only isolable with [Rb(crypt)] 1+ counter-cations and isolation of the [Y II (NR 2 ) 3 ] 1− anion was not possible under any of these conditions. We now report that by changing the potassium chelator from crypt to 18-crown-6 (18-c-6), the [Ln(NR 2 ) 3 ] 1− anions can be isolated not only for Ln = Gd, Tb, Dy, and Tm, but also for Ho, Er, and Y. Specifically, these anions are isolated as salts of a 1 : 2 potassium : crown sandwich cation, [K(18-c-6) 2 ] 1+ , i.e. [K(18-c-6) 2more »][Ln(NR 2 ) 3 ]. The [K(18-c-6) 2 ] 1+ counter-cation was superior not only in the synthesis, but it also allowed the isolation of crystallographically-characterizable products from reactions of CO with the [Ln(NR 2 ) 3 ] 1− anions that were not obtainable from the [K(crypt)] 1+ analogs. Reaction of CO with [K(18-c-6) 2 ][Ln(NR 2 ) 3 ], generated in situ , yielded crystals of the ynediolate products, {[(R 2 N) 3 Ln] 2 (μ-OCCO)} 2− , which crystallized with counter-cations possessing 2 : 3 potassium : crown ratios, i.e. {[K 2 (18-c-6) 3 ]} 2+ , for Gd, Dy, Ho. In contrast, reaction of CO with a solution of isolated [K(18-c-6) 2 ][Gd(NR 2 ) 3 ], produced crystals of an enediolate complex isolated with a counter-cation with a 2 : 2 potassium : crown ratio namely [K(18-c-6)] 2 2+ in the complex [K(18-c-6)] 2 {[(R 2 N) 2 Gd 2 (μ-OCHCHO) 2 ]}.« less
5. 21-Component compositionally complex ceramics: Discovery of ultrahigh-entropy weberite and fergusonite phases and a pyrochlore-weberite transition

   https://doi.org/10.1007/s40145-022-0575-5  

   Qin, Mingde ; Vega, Heidy ; Zhang, Dawei ; Adapa, Sarath ; Wright, Andrew J. ; Chen, Renkun ; Luo, Jian ( April 2022 , Journal of Advanced Ceramics)

   Abstract Two new high-entropy ceramics (HECs) in the weberite and fergusonite structures, along with the unexpected formation of ordered pyrochlore phases with ultrahigh-entropy compositions and an abrupt pyrochlore-weberite transition, are discovered in a 21-component oxide system. While the Gibbs phase rule allows 21 equilibrium phases, 9 out of the 13 compositions examined possess single HEC phases (with ultrahigh ideal configurational entropies: ∼2.7 k B per cation or higher on one sublattice in most cases). Notably, (15RE 1/15 )(Nb 1/2 Ta 1/2 )O 4 possess a single monoclinic fergusonite (C2/ c ) phase, and (15RE 1/15 ) 3 (Nb 1/2 Ta 1/2 ) 1 O 7 form a single orthorhombic (C222 1 ) weberite phase, where 15RE 1/15 represents Sc 1/15 Y 1/15 La 1/15 Pr 1/15 Nd 1/15 Sm 1/15 Eu 1/15 Gd 1/15 Tb 1/15 Dy 1/15 Ho 1/15 Er 1/15 Tm 1/15 Yb 1/15 Lu 1/15 . Moreover, a series of eight (15RE 1/15 ) 2+ x (Ti 1/4 Zr 1/4 Ce 1/4 H 1/4 ) 2−2 x (Nb 1/2 Ta 1/2 ) x O 7 specimens all exhibit single phases, where a pyrochlore-weberite transition occurs within 0.75 < x < 0.8125. This cubic-to-orthorhombic transition does not changemore »the temperature-dependent thermal conductivity appreciably, as the amorphous limit may have already been achieved in the ultrahigh-entropy 21-component oxides. These discoveries expand the diversity and complexity of HECs, towards many-component compositionally complex ceramics (CCCs) and ultrahigh-entropy ceramics.« less