Search

A series of Ce 3+ complexes with counter cations ranging from Li to Cs are presented. Cyclic voltammetry data indicate a significant dependence of the oxidation potential on the alkali metal identity. Analysis of the single-crystal X-ray diffraction data indicates that the degree of structural distortion of the secondary coordination sphere is linearly correlated with the measured oxidation potential. Solution electronic absorption spectroscopy confirms that the structural distortion is reflected in the solution structure. Computational studies further validate this analysis, deciphering the impact of alkali metal cations on the Ce atomic orbital contributions, differences in energies of Ce-dominant molecular orbitals, energy shift of the 4f-5d electronic transitions, and degree of structural distortions. In sum, the structural impact of the alkali metal cation is demonstrated to modulate the redox and electronic properties of the Ce 3+ complexes, and provides insight into the rational tuning of the Ce 3+ imidophosphorane complex oxidation potential through alkali metal identity., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

Lanthanides in the trivalent oxidation state are typically described using an ionic picture that leads to localized magnetic moments. The hierarchical energy scales associated with trivalent lanthanides produce desirable properties for e.g., molecular magnetism, quantum materials, and quantum transduction. Here, we show that this traditional ionic paradigm breaks down for praseodymium in the tetravalent oxidation state. Synthetic, spectroscopic, and theoretical tools deployed on several solid-state Pr 4+ -oxides uncover the unusual participation of 4f orbitals in bonding and the anomalous hybridization of the 4f 1 configuration with ligand valence electrons, analogous to transition metals. The competition between crystal-field and spin-orbit-coupling interactions fundamentally transforms the spin-orbital magnetism of Pr 4+ , which departs from the J eff  = 1/2 limit and resembles that of high-valent actinides. Our results show that Pr 4+ ions are in a class on their own, where the hierarchy of single-ion energy scales can be tailored to explore new correlated phenomena in quantum materials., (© 2023. The Author(s).)

The synthesis and magnetic properties of two pairs of isomeric, exchange-coupled complexes, [LnCl 6 (TiCp 2 ) 3 ] (Ln = Gd, Tb), are reported. In each isomeric pair, the central lanthanide ion adopts either a pseudo-octahedral (O-Ln) or trigonal prismatic geometry (TP-Ln) yielding complexes with C 1 or C 3h molecular symmetry, respectively. Ferromagnetic exchange coupling is observed in TP-Ln as indicated by the increases in χ m T below 30 K. For TP-Gd, a fit to the susceptibility reveals ferromagnetic coupling between the Gd 3+ ion and the Ti 3+ ions ( J = 2.90(1) cm -1 ). In contrast to O-Tb, which shows no single-molecule magnetic behavior, the TP-Tb complex presents slow magnetic relaxation with a 100s-blocking temperature of 2.3 K and remanent magnetization at zero field up to 3 K. The calculated electronic structures of both compounds imply that trigonal prismatic geometry of TP-Tb is critical to the observed magnetic behavior., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The ground-state of S = 1 kagome lattice antiferromagnets (KLAFs), in the presence of strong geometric frustration and the smallest integer spin, has the potential to host a range of non-trivial magnetic phases including a quantum spin liquid. The effect of local geometry and metal-ion electronic structure on the formation of these predicted phases remain unknown due to, in part, the lack of an ideal analyte. Herein, a kagome lattice compound, (CH 3 NH 3 ) 2 NaV 3 F 12 ( 1-V ), featuring a single distinct V 3+ (d 2 ) site in the R 3̄ m space group, was synthesized hydrothermally. In this S = 1, d 2 system, the trivalent vanadium ions are tetragonally compressed due to Jahn-Teller distortion. The interlayer methylammonium cations show static positional disorder with three possible orientations. The negative Curie-Weiss temperature and dominant antiferromagnetic interactions make 1-V a candidate to study S = 1 KLAF physics. The frequency-dependence of ac magnetic susceptibility and the heat capacity results suggest that 1-V has a spin glass ground state. This freezing of the spin dynamics may be due to competing exchange interactions, structural imperfection arising from the static disorder of the interlayer methylammonium cations or the presence of 'defect'-like spins., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A redox pair of Ce 4+ and Ce 3+ complexes has been prepared that is stabilized by the [(NP(1,2-bis- t Bu-diamidoethane)(NEt 2 ))] 1- ligand. Since these complexes are isostructural to the recently reported isovalent terbium analogs, a detailed structural and spectroscopic comparative analysis was pursued via Voronoi-Dirichlet polyhedra analysis, UV-vis-NIR, L 3 -edge X-ray absorption near edge spectroscopy (XANES), cyclic voltammetry, and natural transitions orbital (NTO) analysis and natural bond orbital (NBO) analysis. The electrochemical studies confirm previous theoretical studies of the redox properties of the related complex [K][Ce 3+ (NP(pip) 3 ) 4 ] (pip = piperidinyl), 1-Ce(PN) . Complex 1-Ce(PN*) presents the most negative E pc of -2.88 V vs. Fc/Fc + in THF of any cerium complex studied electrochemically. Likewise 1-Tb(PN*) has the most negative E pc for electrochemically interrogated terbium complexes at -1.79 V vs. Fc/Fc + in THF. Complexes 1-Ce(PN*) and 2-Ce(PN*) were also studied by L 3 -edge X-ray absorption near edges spectroscopy (XANES) and a comparison to previously reported spectra for 1-Tb(PN*) , 2-Tb(PN*) , 1-Ce(PN) , and, [Ce 4+ (NP(pip) 3 ) 4 ], 2-Ce(PN) , demonstrates similar n f values for all the tetravalent lanthanide complexes. According to the natural bond orbital analysis, a greater covalent character of the M-L bonds is found in 2-Ce(PN*) than in 1-Ce(PN*) , in agreement with the shorter Ce-N bonds in the tetravalent counterpart. The greater contribution of Ce orbitals in the Ce-N bonding and, specifically, the higher participation of 4f electrons accounts for the stronger covalent interactions in 2-Ce(PN*) as compared to 2-Tb(PN*) ., (This journal is © The Royal Society of Chemistry 2020.)

A new series of Ln 3+ and Ln 2+ complexes has been synthesized using the tris(aryloxide)arene ligand system, (( Ad,Me ArO) 3 mes) 3- , recently used to isolate a complex of U 2+ . The triphenol precursor, ( Ad,Me ArOH) 3 mes, reacts with the Ln 3+ amides, Ln(NR 2 ) 3 (R = SiMe 3 ), to form a series of [(( Ad,Me ArO) 3 mes)Ln] complexes, 1-Ln . Crystallographic characterization was achieved for Ln = Nd, Gd, Dy, and Er. The complexes 1-Ln can be reduced with potassium graphite in the presence of 2.2.2-cryptand (crypt) to form highly absorbing solutions with properties consistent with Ln 2+ complexes, [K(crypt)][(( Ad,Me ArO) 3 mes)Ln], 2-Ln . The synthesis of the Nd 2+ complex [K(crypt)][(( Ad,Me ArO) 3 mes)Nd], 2-Nd , was unambiguously confirmed by X-ray crystallography. In the case of the other lanthanides, crystals were found to contain mixtures of 2-Ln co-crystallized with either a Ln 3+ hydride complex, [K(crypt)][(( Ad,Me ArO) 3 mes)LnH], 3-Ln , for Ln = Gd, Dy, and Er, or a hydroxide complex, [K(crypt)][(( Ad,Me ArO) 3 mes)Ln(OH)], 4-Ln , for Ln = Dy. A Dy 2+ complex with 18-crown-6 as the potassium chelator, [K(18-crown-6)(THF) 2 ][(( Ad,Me ArO) 3 mes)Dy], 5-Dy , was isolated as a co-crystallized mixture with the Dy 3+ hydride complex, [K(18-crown-6)(THF) 2 ][(( Ad,Me ArO) 3 mes)DyH], 6-Dy . Structural comparisons of 1-Ln and 2-Ln are presented with respect to their uranium analogs and correlated with density functional theory calculations on their electronic structures.

Actinium-225 is a promising isotope for targeted-α therapy. Unfortunately, progress in developing chelators for medicinal applications has been hindered by a limited understanding of actinium chemistry. This knowledge gap is primarily associated with handling actinium, as it is highly radioactive and in short supply. Hence, Ac(III) reactivity is often inferred from the lanthanides and minor actinides (that is, Am, Cm), with limited success. Here we overcome these challenges and characterize actinium in HCl solutions using X-ray absorption spectroscopy and molecular dynamics density functional theory. The Ac-Cl and Ac-OH2O distances are measured to be 2.95(3) and 2.59(3) Å, respectively. The X-ray absorption spectroscopy comparisons between Ac(III) and Am(III) in HCl solutions indicate Ac(III) coordinates more inner-sphere Cl(1-) ligands (3.2±1.1) than Am(III) (0.8±0.3). These results imply diverse reactivity for the +3 actinides and highlight the unexpected and unique Ac(III) chemical behaviour.