Frustrated Magnetism and Spin Anisotropy in a Buckled Square Net YbTaO.

The interplay between quantum effects from magnetic frustration, low-dimensionality, spin-orbit coupling, and crystal electric field in rare-earth materials leads to nontrivial ground states with unusual magnetic excitations. Here, we investigate YbTaO, which hosts a buckled square net of Yb ions with = 1/2 moments. The observed Curie-Weiss temperature is about -1 K, implying an antiferromagnetic coupling between the Yb moments.

Exploring Charge Redistribution at the Cu/CoSe Interface.

This study investigates the electronic interactions and charge redistribution at the dopant-support interface using a Cu/CoSe cluster construct. Specifically, the redox cluster series [CuCoSeL] ([-Cu]; = 0, -1, -2, -3; L = PhPNTol, Ph = phenyl, Tol = -tolyl) spanning four distinct oxidation states is synthesized and characterized using a multitude of techniques, including multinuclear NMR, UV-vis, XANES, and X-ray crystallography. Structural investigations indicate that the clusters are isostructural and chiral, adopting a pseudo- symmetry.

Proton-Coupled Electron Transfer at the Pu Couple.

The synthesis and solution and solid-state characterization of [Pu(NPC)], , (NPC = [NPBu(pyrr)]; Bu = C(CH); pyrr = pyrrolidinyl) and [Pu(NPC)][K(2.2.2.

A Four-Coordinate Pr Imidophosphorane Complex.

The imidophosphorane ligand, [NPBu] (Bu=tert-butyl), enables isolation of a pseudo-tetrahedral, tetravalent praseodymium complex, [Pr(NPBu)] (1-Pr), which is characterized by a suite of physical characterization methods including single-crystal X-ray diffraction, electron paramagnetic resonance, and L-edge X-ray near-edge spectroscopies. Variable-temperature direct-current magnetic susceptibility data, supported by multiconfigurational quantum chemical calculations, demonstrate that the electronic structure diverges from the isoelectronic Ce analogue, driven by increased crystal field. The four-coordinate environment around Pr in 1-Pr, which is unparalleled in reported extended solid systems, provides a unique opportunity to study the interplay between crystal field splitting and spin-orbit coupling in a molecular tetravalent lanthanide within a pseudo-tetrahedral coordination geometry.

A tetrahedral neptunium(V) complex.

Neptunium is an actinide element sourced from anthropogenic production, and, unlike naturally abundant uranium, its coordination chemistry is not well developed in all accessible oxidation states. High-valent neptunium generally requires stabilization from at least one metal-ligand multiple bond, and departing from this structural motif poses a considerable challenge. Here we report a tetrahedral molecular neptunium(V) complex ([Np(NPC)][B(ArF)], 1-Np) (NPC = [NPBu(pyrr)]; Bu = C(CH); pyrr = pyrrolidinyl (N(CH)); B(ArF) = tetrakis(2,3,4,5,6-pentafluourophenyl)borate).

Overdestabilization vs Overstabilization in the Theoretical Analysis of f-Orbital Covalency.

The complex nature of the f-orbital electronic structures and their interaction with the chemical environment pose significant computational challenges. Advanced computational techniques that variationally include scalar relativities and spin-orbit coupling directly at the molecular orbital level have been developed to address this complexity. Among these, variational relativistic multiconfigurational multireference methods stand out for their high accuracy and systematic improvement in studies of f-block complexes.

Tetravalent Cerium Alkyl and Benzyl Complexes.

High-valent cerium complexes of alkyl and benzyl ligands are unprecedented due to the incompatibility of the typically highly oxidizing Ce ion and the reducing alkyl or benzyl ligand. Herein we report the synthesis and isolation of the first tetravalent cerium alkyl and benzyl complexes supported by the tri--butyl imidophosphorane ligand, [NP(Bu)]. The Ce monoiodide complex, [CeI(NP(-butyl))] (), serves as a precursor to the alkyl and benzyl complexes, [Ce(Npt)(NP(-butyl))] () (Npt = neopentyl, CHC(CH)) and [Ce(Bn)(NP(-butyl))] () (Bn = benzyl, CHPh).

Coordination Modes and Binding Patterns in Lanthanum Phosphoramide Complexes.

A monoanionic phosphoramide ligand is introduced, which forms a series of lanthanum complexes with the ligand in both anionic and neutral forms. Stoichiometric control alone provides monometallic complexes with either two or three phosphoramide ligands. Alternatively, a combination of anionic and neutral proteo ligands featuring intramolecular hydrogen bonding can be obtained.

Intervalence Charge Transfer in Nonbonding, Mixed-Valence, Homobimetallic Ytterbium Complexes.

There are several reports of compounds containing lanthanide ions in two different formal oxidation states; however, there are strikingly few examples of intervalence charge transfer (IVCT) transitions observed for these complexes, with those few occurrences limited to extended solids rather than molecular species. Herein, we report the synthesis, characterization, and computational analysis for a series of ytterbium complexes including a mixed-valence Yb complex featuring a remarkably short Yb···Yb distance of 2.9507(8) Å.

Structural distortion by alkali metal cations modulates the redox and electronic properties of Ce imidophosphorane complexes.

A series of Ce 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.

Increased Crystal Field Drives Intermediate Coupling and Minimizes Decoherence in Tetravalent Praseodymium Qubits.

Crystal field (CF) control of rare-earth (RE) ions has been employed to minimize decoherence in qubits and to enhance the effective barrier of single-molecule magnets. The CF approach has been focused on the effects of symmetry on dynamic magnetic properties. Herein, the magnitude of the CF is increased via control of the RE oxidation state.

Tetrathiafulvalene-2,3,6,7-tetrathiolate linker redox-state elucidation S K-edge X-ray absorption spectroscopy.

Sulfur K-edge XAS data provide a unique tool to examine oxidation states and covalency in electronically complex S-based ligands. We present sulfur K-edge X-ray absorption spectroscopy on a discrete redox-series of Ni-based tetrathiafulvalene tetrathiolate (TTFtt) complexes as well as on a 1D coordination polymer (CP), NiTTFtt. Experiment and theory suggest that Ni-S covalency decreases with oxidation which has implications for charge transport pathways.

Divergent Stabilities of Tetravalent Cerium, Uranium, and Neptunium Imidophosphorane Complexes.

The study of the redox chemistry of mid-actinides (U-Pu) has historically relied on cerium as a model, due to the accessibility of trivalent and tetravalent oxidation states for these ions. Recently, dramatic shifts of lanthanide 4+/3+ non-aqueous redox couples have been established within a homoleptic imidophosphorane ligand framework. Herein we extend the chemistry of the imidophosphorane ligand (NPC=[N=P Bu(pyrr) ] ; pyrr=pyrrolidinyl) to tetrahomoleptic NPC complexes of neptunium and cerium (1-M, 2-M, M=Np, Ce) and present comparative structural, electrochemical, and theoretical studies of these complexes.

Chemical design of electronic and magnetic energy scales of tetravalent praseodymium materials.

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.

Tuning symmetry and magnetic blocking of an exchange-coupled lanthanide ion in isomeric, tetrametallic complexes: [LnCl(TiCp)].

The synthesis and magnetic properties of two pairs of isomeric, exchange-coupled complexes, [LnCl(TiCp)] (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 or molecular symmetry, respectively. Ferromagnetic exchange coupling is observed in TP-Ln as indicated by the increases in below 30 K.

Ligand Control of Oxidation and Crystallographic Disorder in the Isolation of Hexavalent Uranium Mono-Oxo Complexes.

The development of high-valent transuranic chemistry requires robust methodologies to access and fully characterize reactive species. We have recently demonstrated that the reducing nature of imidophosphorane ligands supports the two-electron oxidation of U to U and established the use of this ligand to evaluate the inverse-trans-influence (ITI) in actinide metal-ligand multiple bond (MLMB) complexes. To extend this methodology and analysis to transuranic complexes, new small-scale synthetic strategies and lower-symmetry ligand derivatives are necessary to improve crystallinity and reduce crystallographic disorder.

Ground-State Spin Dynamics in Kagome-Lattice Titanium Fluorides.

Many quantum magnetic materials suffer from structural imperfections. The effects of structural disorder on bulk properties are difficult to assess systematically from a chemical perspective due to the complexities of chemical synthesis. The recently reported S = 1/2 kagome lattice antiferromagnet, (CHNH)NaTiF, , with highly symmetric kagome layers and disordered interlayer methylammonium cations, shows no magnetic ordering down to 0.

Elemental chalcogen reactions of a tetravalent uranium imidophosphorane complex: cleavage of dioxygen.

Herein we report the first example of a mononuclear uranium complex, [U(NP(pip))] (1-U), that selectively reduces dioxygen to produce a terminal oxo complex, [UO(NP(pip))] (2-U; [NP(pip)] is tris(piperidinyl)imidophosphorane). Reactions between 1-U and the heavier elemental chalcogens, S or Se, result in six-coordinate U(VI) complexes, [U(κ-E)(NP(pip))] (E = S (3-U) or Se (4-U)).

Spectroscopic and electrochemical characterization of a Pr imidophosphorane complex and the redox chemistry of Nd and Dy complexes.

The molecular tetravalent oxidation state for praseodymium is observed in solution oxidation of the anionic trivalent precursor [K][Pr(NP(1,2-bis-Bu-diamidoethane)(NEt))] (1-Pr(NP*)) with AgI at -35 °C. The Pr complex is characterized in solution cyclic voltammetry, UV-vis-NIR electronic absorption spectroscopy, and EPR spectroscopy. Electrochemical analyses of [K][Ln(NP(1,2-bis-Bu-diamidoethane)(NEt))] (Ln = Nd and Dy) by cyclic voltammetry are reported and, in conjunction with theoretical modeling of electronic structure and oxidation potential, are indicative of principal ligand oxidations in contrast to the metal-centered oxidation observed for 1-Pr(NP*).

Photoluminescence of Pentavalent Uranyl Amide Complexes.

Pentavalent uranyl species are crucial intermediates in transformations that play a key role for the nuclear industry and have recently been demonstrated to persist in reducing biotic and abiotic aqueous environments. However, due to the inherent instability of pentavalent uranyl, little is known about its electronic structure. Herein, we report the synthesis and characterization of a series of monomeric and dimeric, pentavalent uranyl amide complexes.

Chalcogen-atom abstraction reactions of a Di-iron imidophosphorane complex.

Reaction of the complexes [Fe2(μ2-NP(pip)3)2(NP(pip)3)2] (1-Fe) and [Co2(μ2-NP(pip)3)2(NP(pip)3)2] (1-Co), where [NP(pip)3]1- is tris(piperidinyl)imidophosphorane, with nitrous oxide, S8, or Se0 results in divergent reactivity. With nitrous oxide, 1-Fe forms [Fe2(μ2-O)(μ2-NP(pip)3)2(NP(pip)3)2] (2-Fe), with a very short Fe3+-Fe3+ distance. Reactions of 1-Fe with S8 or Se0 result in the bridging, side-on coordination (μ-κ1:κ1-E22-) of the heavy chalcogens in complexes [Fe2(μ-κ1:κ1-E2)(μ2-NP(pip)3)2(NP(pip)3)2] (E = S, 3-Fe, or Se, 4-Fe).

Synthesis of a d kagome lattice antiferromagnet, (CHNH)NaVF.

The ground-state of = 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, (CHNH)NaVF (), featuring a single distinct V (d) site in the 3̄ space group, was synthesized hydrothermally.

High-Frequency and -Field Electron Paramagnetic Resonance Spectroscopic Analysis of Metal-Ligand Covalency in a 4f Valence Series (Eu, Gd, and Tb).

The recent isolation of molecular tetravalent lanthanide complexes has enabled renewed exploration of the effect of oxidation state on the single-ion properties of the lanthanide ions. Despite the isotropic nature of the S ground state in a tetravalent terbium complex, [Tb(NP(1,2-bis-Bu-diamidoethane)(NEt))], preliminary X-band electron paramagnetic resonance (EPR) measurements on tetravalent terbium complexes show rich spectra with broad resonances. The complexity of these spectra highlights the limits of conventional X-band EPR for even qualitative determination of zero-field splitting (ZFS) in these complexes.

In-Plane Cation Ordering and Sodium Displacements in Layered Honeycomb Oxides with Tetravalent Lanthanides: NaLnO (Ln = Ce, Pr, and Tb).

The detailed structural characterization of "213" honeycomb systems is a key concern in a wide range of fundamental areas, such as frustrated magnetism, and technical applications, such as cathode materials, catalysts, and thermoelectric materials. NaLnO (Ln = Ce, Pr, and Tb) are an intriguing series of "213" honeycomb systems because they host tetravalent lanthanides. "213" honeycomb materials have been reported to adopt either a cation-disordered 3̅ subcell, a cation-ordered trigonal (312), or monoclinic (2/ or 2/) supercell.