From a Piano Stool to a Sandwich: A Stepwise Route for Improving the Slow Magnetic Relaxation Properties of Thulium

Two mononuclear Tm^III complexes, [Tm­(COT)­I­(THF)₂] (<b>1-Tm</b>) and [K­(18-crown-6)­(THF)₂]­[Tm­(COT)₂] (<b>2-Tm</b>), display slow relaxation of the magnetization, making these compounds rare examples of non-Kramers Tm^III single-molecule magnets (SMMs). Utilizing a stepwise synthetic approach for the installation of cyclooctatetraenide (COT) ligands, we can observe the effect of symmetry optimization at the metal center. This method results in an 85% increase in the energy barrier to magnetization reversal (<i>U</i>_eff) for <b>2-Tm</b> (<i>U</i>_eff = 53.3 K) over <b>1-Tm</b> (<i>U</i>_eff = 7.93 K). The increased local symmetry of <b>2-Tm</b> reduces the need for large static fields, eliciting SMM behavior under a small field of 200 Oe. This illustrates the power of fine-tuning the ligand environment to enhance the magnetic relaxation properties of non-Kramers ions

Composition Control in Molecular Cluster-Aggregates: A Toolbox for Optical Output Tunability <i>via</i> Energy Transfer Pathways

Composition control is a powerful tool for obtaining high-performance lanthanide (Ln) luminescent materials with adjustable optical outputs. This strategy is well-established for hierarchically structured nanoparticles, but it is rarely applied to molecular compounds due to the limited number of metal centers within a single unit. In this work, we present a series of molecular cluster-aggregates (MCAs) with an icosanuclear core {Ln2Eu2Tb16} (Ln = Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Tm, and Yb) in which we explore composition control, akin to nanoparticles, to modulate the optical output. More specifically, we target to understand how the presence of a third LnIII doping ion would impact the well-known TbIII → EuIII energy transfer and the ratiometric optical thermometry performance based on the TbIII/EuIII pair. Photophysical properties at room and at varying temperatures were investigated. Based on experimental data and well-established intrinsic features, such as spin–orbit coupling strength and LnIII 4f energy levels’ structure, we discuss the possible luminescent processes present in each MCA and provide insight into qualitative trends that can be rationally correlated throughout the series

Slow Magnetic Relaxation Observed in Dysprosium Compounds Containing Unsupported Near-Linear Hydroxo- and Fluoro-Bridges

The encapsulating <i>N</i>1,<i>N</i>3-bis­(3-methoxysalicylidene)­diethylenetriamine (H₂valdien) ligand was employed to isolate two novel Dy^III compounds which contain rare bridging pathways for lanthanide systems. Compound <b>1</b>, [Na₂Dy^III₂(valdien)₂(μ-OH)­(dbm)₂(H₂O)₂]­[Na₂Dy^III₂(valdien)₂(μ-OH)­(NO₃)₂(dbm)₂], where dbm^– is dibenzoylmethanido, and compound <b>2</b>, [Na₃Dy^III₂(valdien)₂(μ-F)­(μ₃-F)₂­(Cl)₂(MeOH)₂]_<i>n</i>·0.5­(MeOH)·(H₂O), both exhibit linear lone hydroxo- and fluoro-bridges, respectively, between the metal centers. The unit cell of <b>1</b> comprises two discrete dinuclear molecules, which differ slightly, forming a cation–anion pair, while <b>2</b> forms a coordination polymer. The magnetic investigations indicate that both compounds display ferromagnetic coupling between the Dy^III ions. Magnetic susceptibility measurements in the temperature range 1.8–300 K reveal that the Dy^III ions in <b>1</b> are weakly coupled, resulting in a mononuclear single-molecule magnet-like behavior under an applied field. In the case of <b>2</b>, the stronger coupling arising from the fluoride-bridge, leads to zero-field single-molecule magnet (SMM) behavior with a non-negligible anisotropy barrier (<i>U</i>_eff) of 42 K

Isolation and Characterization of a Class II Mixed-Valence Chromium(I)/(II) Self-Activating Ethylene Trimerization Catalyst

Reduction of the tetranuclear {[(<i>t</i>-Bu)­NPPh₂]­Cr­[μ-(<i>t</i>-Bu)­NPPh₂]₂Cr}₂(μ-Cl)₂ (<b>1</b>) with either KC₈ or vinyl Grignard afforded the dinuclear, mixed-valence (Me₃P)­Cr­[μ-(<i>t</i>-Bu)­NPPh₂]₃Cr (<b>2</b>) with the two metals possessing distinctively different coordination environments. According to the formulation of <b>2</b> as Cr­(I)/Cr­(II) mixed-valence species, <b>2</b> acts as a self-activating catalyst, producing under pressure of ethylene a mixture of 1-butene and 1-hexene. Activation with three different activators selectively produced three different products, namely, 1-butene with TEAL, 1-hexene with DMAO/TEAL, and LAO-free highly linear HMWPE with DMAO. Mixtures of 1-hexene and 1-butene were also obtained upon activation with vinyl Grignard. In this case it was possible to isolate, albeit in very low yield, an intriguing butadiene/butadiene-diyl cluster, {[(η⁴-butadiene)Cr (μ,η⁴-butadienediyl)­(μ-NP)­Mg]₂(μ-Cl)₄Mg­(THF)₂}­{[(THF)₃Mg]₂(μ-Cl)₃}₂ (<b>3</b>), which is also a highly selective self-activating trimerization catalyst

Isolation and Characterization of a Class II Mixed-Valence Chromium(I)/(II) Self-Activating Ethylene Trimerization Catalyst

Reduction of the tetranuclear {[(<i>t</i>-Bu)­NPPh₂]­Cr­[μ-(<i>t</i>-Bu)­NPPh₂]₂Cr}₂(μ-Cl)₂ (<b>1</b>) with either KC₈ or vinyl Grignard afforded the dinuclear, mixed-valence (Me₃P)­Cr­[μ-(<i>t</i>-Bu)­NPPh₂]₃Cr (<b>2</b>) with the two metals possessing distinctively different coordination environments. According to the formulation of <b>2</b> as Cr­(I)/Cr­(II) mixed-valence species, <b>2</b> acts as a self-activating catalyst, producing under pressure of ethylene a mixture of 1-butene and 1-hexene. Activation with three different activators selectively produced three different products, namely, 1-butene with TEAL, 1-hexene with DMAO/TEAL, and LAO-free highly linear HMWPE with DMAO. Mixtures of 1-hexene and 1-butene were also obtained upon activation with vinyl Grignard. In this case it was possible to isolate, albeit in very low yield, an intriguing butadiene/butadiene-diyl cluster, {[(η⁴-butadiene)Cr (μ,η⁴-butadienediyl)­(μ-NP)­Mg]₂(μ-Cl)₄Mg­(THF)₂}­{[(THF)₃Mg]₂(μ-Cl)₃}₂ (<b>3</b>), which is also a highly selective self-activating trimerization catalyst

Isolation and Characterization of a Class II Mixed-Valence Chromium(I)/(II) Self-Activating Ethylene Trimerization Catalyst

Reduction of the tetranuclear {[(<i>t</i>-Bu)­NPPh₂]­Cr­[μ-(<i>t</i>-Bu)­NPPh₂]₂Cr}₂(μ-Cl)₂ (<b>1</b>) with either KC₈ or vinyl Grignard afforded the dinuclear, mixed-valence (Me₃P)­Cr­[μ-(<i>t</i>-Bu)­NPPh₂]₃Cr (<b>2</b>) with the two metals possessing distinctively different coordination environments. According to the formulation of <b>2</b> as Cr­(I)/Cr­(II) mixed-valence species, <b>2</b> acts as a self-activating catalyst, producing under pressure of ethylene a mixture of 1-butene and 1-hexene. Activation with three different activators selectively produced three different products, namely, 1-butene with TEAL, 1-hexene with DMAO/TEAL, and LAO-free highly linear HMWPE with DMAO. Mixtures of 1-hexene and 1-butene were also obtained upon activation with vinyl Grignard. In this case it was possible to isolate, albeit in very low yield, an intriguing butadiene/butadiene-diyl cluster, {[(η⁴-butadiene)Cr (μ,η⁴-butadienediyl)­(μ-NP)­Mg]₂(μ-Cl)₄Mg­(THF)₂}­{[(THF)₃Mg]₂(μ-Cl)₃}₂ (<b>3</b>), which is also a highly selective self-activating trimerization catalyst

Slow Magnetic Relaxation in Uranium(III) and Neodymium(III) Cyclooctatetraenyl Complexes

The synthesis, structure, and magnetic properties of a uranium­(III) sandwich complex, [Li­(DME)₃]­[U^III(COT″)₂] (COT″ = bis­(trimethylsilyl)­cyclooctatetraenyl dianion), and its coordinatively analogous tetravalent equivalent, [U^IV(COT″)₂], were investigated. Additionally, a full structural and magnetic comparison to the isostructural and isoelectronic lanthanide complex, [Li­(DME)₃]­[Nd^III(COT″)₂], is provided. DFT calculations reveal that the U^III complex leads to weaker ligand-to-metal donation as compared with the tetravalent equivalent complex. Alternating current magnetic susceptibility results reveal slow magnetic relaxation in both U^III and Nd^III complexes. The enhanced magnetic performance of the U^III congener further encourages the use of actinides in the design of single-molecule magnets

Unprecedented Octanuclear Dy^III Cluster Exhibiting Single-Molecule Magnet Behavior

An unprecedented Dy₈ cluster, [Dy₈(μ₄-O)­(μ₃-OH)₈(vht)₄(NO₃)₂(H₂O)₈]­(NO₃)₄, composed of two fused and distorted [Dy₄(μ₃-OH)₄]⁸⁺ cubane units is reported. The bridging of the two cubanes occurs through a planar μ₄-O (oxide) moiety, and leads to the largest reported distortion of the Dy-O-Dy angles within a [Dy₄(OH)₄] cubane core. In turn, this leads to clear zero-field slow relaxation of the magnetization, characteristic of single-molecule magnets (SMMs). Further magnetic analyses suggest that the relaxation may be largely dictated by quantum tunneling of the magnetization and Raman processes

Structural Rearrangement Through Lanthanide Contraction in Dinuclear Complexes

A new series of lanthanide complexes was synthesized, and the geometry and preliminary magnetic measurements of the complexes were explored. The specific ligand used (<i>N</i>′-(2-hydroxy-3-methoxybenzylidene)­benzhydrazide) (H₂hmb) was synthesized using a Schiff-base approach and was employed due to the presence of a coordination pocket that is able to accommodate magnetically selective lanthanide ions. The series can be divided into two groups that are categorized by a drastic structural rearrangement. The first group, Type I, contains six analogous complexes with the formula [M^III₂(Hhmb)₃­(NCS)₃]·2MeOH·py (M = Y <b>1</b>, Eu <b>2</b>, Gd <b>3</b>, Tb <b>4</b>, Dy <b>5</b>, Ho <b>6</b>), while the second group, Type II, contains two dinuclear complexes with formula [M^III₂(Hhmb)₂­(NCS)₄(MeOH)₂] (M = Er <b>7</b>, and Yb <b>8</b>). Single-crystal X-ray analysis revealed that all M^III ions in Type I exhibit monocapped distorted square antiprismatic geometries, while those of Type II exhibit distorted dodecahedron geometry. The direct current and alternating current magnetic measurements were carried out on all complexes, with <b>5</b>, <b>7</b>, and <b>8</b> exhibiting slow relaxation of the magnetization under an applied optimum dc field. Furthermore, complex <b>8</b> is the first example of a dinuclear Yb-based single-molecule magnet showing field-dependent multiple relaxation processes

High-Temperature Spin Crossover Behavior in a Nitrogen-Rich Fe^III-Based System

A nitrogen-rich ligand <i>bis</i>(1<i>H</i>-tetrazol-5-yl)­amine (H₃bta) was employed to isolate a new Fe^III complex, Na₂NH₄[Fe^III(Hbta)₃]·3DMF·2H₂O (<b>1</b>). Single crystal X-ray diffraction revealed that complex <b>1</b> consists of Fe^III ions in an octahedral environment where each metal ion is coordinated by three Hbta^2– ligands forming the [Fe^III(Hbta)₃]^3– core. Each unit is linked to two one-dimensional (1-D) Na⁺/solvent chains creating a two-dimensional (2-D) network. In addition, the presence of multiple hydrogen bonds in all directions between ammonium cation and ligands of different [Fe^III(Hbta)₃]^3– units generates a three-dimensional (3-D) network. Magnetic measurements confirmed that the Fe^III center undergoes a Spin Crossover (SCO) at high temperature (<i>T</i>_1/2 = 460(10) K)