Fluoride-bridged dinuclear dysprosium complex showing single-molecule magnetic behavior: supramolecular approach to isolate magnetic molecules

Using Na-encapsulated benzo[18]crown-6 (Na)(B18C6) as a counter cation, we successfully magnetically isolated a fluoride-bridging Dy dinuclear complex {[(PW₁₁O₃₉)Dy(H₂O)₂]₂F} (Dy₂POM) with lacunary Keggin ligands. (Na)(B18C6) formed two types of tetramers through C-H⋯O, π⋯π and C-H⋯π interactions, and each tetramer aligned in one dimension along the c-axis to form two types of channels. One channel was partially penetrated by a supramolecular cation from the ±a-axis direction, dividing the channel in the form of a "bamboo node". Dy₂POM was spatially divided by this "bamboo node," which magnetically isolated one portion from the other. The temperature dependence of the magnetic susceptibility indicated a weak ferromagnetic interaction between the Dy ions bridged by fluoride. Dy₂POM exhibited the magnetic relaxation characteristics of a single-molecule magnet, including the dependence of AC magnetic susceptibility on temperature and frequency. Magnetic relaxation can be described by the combination of thermally active Orbach and temperature-independent quantum tunneling processes. The application of a static magnetic field effectively suppressed the relaxation due to quantum tunneling.

Enhancement of electrocatalytic abilities toward CO2 reduction by tethering redox-active metal complexes to the active site

Tethering metal complexes, like [Ru(bpy)₂Cl₂] (bpy = 2,2'-bipyridine), which are redox-active at low reduction potentials and have the ability to transfer electrons to another complex, to a [Ni(cyclen)]²⁺ electrocatalyst enhanced the reduction of CO₂ to CO at low overpotentials. The [Ni(cyclen)]²⁺ electrocatalyst was modified by tethering redox-active metal complexes via 4-methylpyridyl linkers. The redox-active metal complexes were reduced after CO₂ bound to the active site. In controlled potential electrolysis (CPE) experiments in 95 : 5 (v/v) CH₃CN/H₂O, [{([Ru]pic)₄cyclen}NiCl]⁵⁺ ([Ru]⁺ = {Ru(bpy)₂Cl}⁺; pic = 4-methylpyridyl) could be used to reduce CO₂ into CO at a turnover frequency (TOF) of 708 s^-1 with a faradaic efficiency (FE) of 80% at an onset potential of -1.60 V vs. NHE. At the same time, this electrocatalyst was active at an onset potential of -1.25 V vs. NHE, which is the reduction potential of one of the bpy ligands of the [Ru]⁺ moieties, with FE = 84% and TOF = 178 s^-1. When the electrocatalysis was performed using [bn₄cyclenNiCl]Cl (bn = benzyl) without tethered redox-active metal complexes, the TOF value was determined to be 8 s^-1 with FE = 77% at an onset potential of -1.45 V vs. NHE. The results show that tethering redox-active metal complexes significantly improves the electrocatalytic activities by lowering the potential needed to reduce CO₂.

4f-π Molecular Hybrid Exhibiting Rich Conductive Phases and Slow Relaxation of Magnetization

Cooperation between single-molecule magnets and electrical conductivity holds promise for preparing high-density magnetic devices; however, there are only a few reports so far. Here we report a 4f-π-based molecular hybrid, k-(ET)₅Dy(NCS)₇(KCl)_0.5 (1) (ET = bis(ethylenedithio)tetrathiafulvalene, NCS^- = thiocyanate), which undergoes slow relaxation of the magnetization and electrical conductivity. Unlike common ET-based conductive salts, K⁺ ions were intercalated into ET layers and coordinated with ET radicals. We found that the ET charges were sensitive to temperature, resulting in rich conductive phases at 75-300 K. In particular, the upturn in conductivity with a clear hysteresis loop was explained by the formation of partially oxidized states with charges close to 0.5+, which accounts for a metallic state. From the results of electronic structure calculations, the hole concentration increased to 125 K, which is consistent with a partially oxidized state upon cooling. The weak antiferromagnetic interactions accompanied by a dual magnetic relaxation process below 4 K are closely associated with the weak 4f-π interactions.

Emergence of Metallic Conduction and Cobalt(II)-Based Single-Molecule Magnetism in the Same Temperature Range

Single-molecule magnets exhibit magnetic bistabililties at the molecular level, making them promising for molecule-based spintronics due to high magnetic densities. The incorporation of SMM behavior and electrical conductivity in one compound is rare because these two physical properties often do not operate in the same temperature range, which further hinders their use in practical applications. Here we present an organic-inorganic molecular hybrid, β″-(BEDO-TTF)₃[Co(pdms)₂]·(MeCN)(H₂O)₂ (BO3) (BEDO-TTF = bis(ethylenedioxy)tetrathiafulvalene and H₂pdms = 1,2-bis(methanesulfonamido)benzene), which manifests both metallic conduction (electrical conductivity up to 1000 S cm^-1 at 12 K under 2.0 gigapascal pressure) and SMM behavior in the temperature range 12-26 K for the first time.

Simultaneous manifestation of metallic conductivity and single-molecule magnetism in a layered molecule-based compound

Single-molecule magnets (SMMs) show superparamagnetic behaviour below blocking temperature at the molecular scale, so they exhibit large magnetic density compared to the conventional magnets. Combining SMMs and molecular conductors in one compound will bring about new physical phenomena, however, the synergetic effects between them still remain unexplored. Here we present a layered molecule-based compound, β′′-(BEDO-TTF)₄ [Co(pdms)₂]·3H₂O (BO4), (BEDO-TTF (BO) and H₂pdms are bis(ethylenedioxy)tetrathiafulvalene and 1,2-bis(methanesulfonamido)benzene, respectively), which was synthesized by using an electrochemical approach and studied by using crystal X-ray diffraction. This compound simultaneously exhibited metallic conductivity and SMM behaviour up to 11 K for the first time. The highest electrical conductivity was 400–650 S cm⁻¹ at 6.5 K, which is the highest among those reported so far for conducting SMM materials. Furthermore, antiferromagnetic ordering occurred below 6.5 K, along with a decrease in conductivity, and the angle-independent negative magnetoresistance suggested an effective electron correlation between the conducting BO and Co(pdms)₂ SMM layers (d–π interactions). The strong magnetic anisotropy and two-dimensional conducting plane play key roles in the low-temperature antiferromagnetic semiconducting state. BO4 is the first compound exhibiting antiferromagnetic ordering among SMMs mediated by π-electrons, demonstrating the synergetic effects between SMMs and molecular conductors.

A metallic single-molecule magnet was synthesised demonstrating simultaneous metallic conduction and excellent SMM properties at the same temperature range for the first time, with potential applications in molecule-based quantum spintronics.

Dysprosium Chlorocyanoanilate-Based 2D-Layered Coordination Polymers

A series of two-dimensional (2D)-layered coordination polymers (CPs) based on the heterosubstituted anilate ligand ClCNAn^2- derived from 3-chloro-6-cyano-2,5-dihydroxybenzoquinone and Dy^III are reported. By changes in the synthetic methods (layering technique, solvothermal or conventional one-pot reactions) and conditions (solvent, concentration, etc.), different types of 2D extended networks could be prepared and structurally characterized. Compounds 1 and 1', two polymorphs with the formula [Dy₂(ClCNAn)₃(DMSO)₆]_n·(H₂O)_x [x = 7 (1), 0 (1')], were prepared by a conventional one-pot reaction and recrystallized at different concentrations. Compound 2, formulated as [Dy₂(ClCNAn)₃(DMF)₆]_n, was prepared by a layering technique, while compound 3, formulated as {(Me₂NH₂)₂[Dy₂(ClCNAn)₄(H₂O)₂]·(DMF)₂·(H₂O)₅}_n, was obtained by a solvothermal method. Compounds 1 and 2 are neutral 2D CPs of the ClCNAn^2- ligand and Dy^III ions, while 3 presents 2D anionic layers of [Dy₂(ClCNAn)₄(H₂O)₂]^2- alternating with cationic layers of Me₂NH₂⁺ ions. These compounds show very diverse networks, with compound 1 forming 2D (8,3) and (4,3) topology with eight- and four-membered rings with square cavities, 1' and 2, respectively, a 2D (6,3) topology with six-membered rings (a rectangular cavity for 1' and a regular hexagonal cavity for 2), and 3 a 2D (4,4) topology with distorted square cavities. In this respect, 1 and 1' represent the first examples of polymorphism in the family of anilate-based CPs. Thermal analysis measurements (differential scanning calorimetry and thermogravimetry) show an exothermic polymorphic transformation from the kinetically stable 1' phase to the thermodynamically stable phase 1. The magnetic behavior of 1-3 very likely indicates depopulation of the m_J levels, while the presence of weak antiferromagnetic coupling between the Dy^III centers mediated by the anilate bridge cannot be excluded.

Ln-Pt electron polarization effects on the magnetic relaxation of heterometallic Ho- and Er-Pt complexes

Heterometallic Ln-Pt complexes, with the formula [Ln₂Pt₃(H₂O)₂(SAc)₁₂] (Ln = Ho(1), Er(2); SAc = thioacetate), were synthesized. From natural bond orbital (NBO) and local orbital locator (LOL) analyses and X-ray absorption fine structure (XAFS) measurements, it was clear that the Ln-Pt interactions or electron polarization occurred. Butterfly-type hysteresis was observed for both 1 and 2. 1 and 2 underwent field-induced slow magnetic relaxation up to 4 K. These magnetic properties were induced by Ln-Pt electron polarization.

Isostructural M(ii) complexes (M = Mn, Fe, Co) with field-induced slow magnetic relaxation for Mn and Co complexes

We herein report the synthetic, structural, theoretical, and magnetic studies on three isostructural complexes, [M(L)2(CH3OH)2] (M = Mn (Mn), Fe (Fe), and Co (Co); HL = 2,6-bis(pyrazole-1-yl)pyridine-4-carboxylic acid). From single crystal X-ray crystallography, it is found that the complexes crystallized in the same space group (C2/c) and had seven-coordinate pentagonal bipyramidal structures. From direct current (dc) and alternating current (ac) magnetic susceptibility measurements, Mn and Co were found to undergo field-induced slow magnetic relaxation with two relaxation pathways. To elucidate the origin of the slow magnetic relaxation phenomena of Mn, electron paramagnetic resonance (EPR) measurements and theoretical calculations were performed. The EPR measurements were performed on polycrystalline powder samples, and the following parameters were obtained by simulating the EPR data: giso = 2.00 and small zero field splitting parameter D = -0.13 cm-1. To the best of our knowledge, this is the first example of a seven-coordinate mononuclear Mn(ii) complex undergoing slow magnetic relaxation.

Scaling Up Electronic Spin Qubits into a Three-Dimensional Metal-Organic Framework

Practical implementation of highly coherent molecular spin qubits for challenging technological applications, such as quantum information processing or quantum sensing, requires precise organization of electronic qubit molecular components into extended frameworks. Realization of spatial control over qubit-qubit distances can be achieved by coordination chemistry approaches through an appropriate choice of the molecular building blocks. However, translating single qubit molecular building units into extended arrays does not guarantee a priori retention of long quantum coherence and spin-lattice relaxation times due to the introduced modifications over qubit-qubit reciprocal distances and molecular crystal lattice phonon structure. In this work, we report the preparation of a three-dimensional (3D) metal-organic framework (MOF) based on vanadyl qubits, [VO(TCPP-Zn₂-bpy)] (TCPP = tetracarboxylphenylporphyrinate; bpy = 4,4'-bipyridyl) (1), and the investigation of how such structural modifications influence qubits' performances. This has been done through a multitechnique approach where the structure and properties of a representative molecular building block of formula [VO(TPP)] (TPP = tetraphenylporphyrinate) (2) have been compared with those of the 3D MOF 1. Pulsed electron paramagnetic resonance measurements on magnetically diluted samples in titanyl isostructural analogues revealed that coherence times are retained almost unchanged for 1 with respect to 2 up to room temperature, while the temperature dependence of the spin-lattice relaxation time revealed insights into the role of low-energy vibrations, detected through terahertz spectroscopy, on the spin dynamics.

Enhancement of electrocatalytic abilities for reducing carbon dioxide: functionalization with a redox-active ligand-coordinated metal complex

A binary system consisting of a ditopic planar pseudo-pincer ligand (qlca = quinoline-2-carbaldehyde (pyridine-2-carbonyl) hydrazone) coordinated to two metal centres affording [{Ru(bpy)2}(μ-qlca)NiCl2]Cl·4H2O·CH3OH (2) (bpy = 2,2'-bipyridine) is reported. The Ni2+ moiety acts as the electrocatalytic active site for CO2 reduction to CO. The turnover frequency (TOF) increased from 0.83 s-1 for [Ni(qlca)Cl2] (3) to 120 s-1 for 2, and the overpotential is 350 mV less than that for 3 due to the electronic influence of the {Ru(bpy)2}2+ moiety on the catalytic active site.

Slow Magnetic Relaxation in a Palladium-Gadolinium Complex Induced by Electron Density Donation from the Palladium Ion

Incorporating palladium in the first coordination sphere of acetato-bridged lanthanoid complexes, [Pd₂ Ln₂ (H₂ O)₂ (AcO)₁₀ ]⋅2 AcOH (Ln=Gd (1), Y (2), Gd_0.4 Y_1.6 (3), Eu (4)), led to significant bonding interactions between the palladium and the lanthanoid ions, which were demonstrated by experimental and theoretical methods. We found that electron density was donated from the d⁸ Pd²⁺ ion to Gd³⁺ ion in 1 and 3, leading to the observed slow magnetic relaxation by using local orbital locator (LOL) and X-ray absorption near-edge structure (XANES) analysis. Field-induced dual slow magnetic relaxation was observed for 1 up to 20 K. Complex 3 and frozen aqueous and acetonitrile solutions of 1 showed only one relaxation peak, which confirms the role of intermolecular dipolar interactions in slowing the magnetic relaxation of 1. The slow magnetic relaxation occurred through a combination of Orbach and Direct processes with the highest pre-exponential factor (τ_o =0.06 s) reported so far for a gadolinium complex exhibiting slow magnetic relaxation. The results revealed that transition metal-lanthanoid (TM-Ln) axial interactions indeed could lead to new physical properties by affecting both the electronic and magnetic states of the compounds.

Conducting single-molecule magnet materials

Multifunctional molecular materials exhibiting electrical conductivity and single-molecule magnet (SMM) behaviour are particularly attractive for electronic devices and related applications owing to the interaction between electronic conduction and magnetization of unimolecular units.

Anion-driven structures and SMM behavior of dinuclear terbium and ytterbium complexes

SMM behavior is observed for [Ln₂(HL)₄(NO₃)₆] (Ln = Tb and Yb, HL = 8-hydroxyquinaldine) complexes having nine-coordinated lanthanide centres, whereas, [Ln₂(HL)₄Cl₆]·2EtOH complexes, having hexa-coordinated lanthanide centres do not show any SMM property.

Proton Control of the Lanthanoid Single-Ion Magnet Behavior of a Double-Decker Complex with an Indolenine-Substituted Annulene Ligand

Two double-decker complexes with annulene ligands functionalized with indolenine groups were synthesized and characterized. The position of the proton acting as a counterion on one of the four indolenine nitrogen atoms was determined by using DFT calculations. Deprotonation and protonation of the complex induced by adding a base and an acid, respectively, were monitored by using NMR spectroscopy. Moreover, a correlation among the degree of protonation of the complex, the opening of the hysteresis, and the slow relaxation time is discussed.

Weak DyIII-DyIII Interactions in DyIII-Phthalocyaninato Multiple-Decker Single-Molecule Magnets Effectively Suppress Magnetic Relaxation

The Dy^III quintuple-decker complex DyCdCdDy and hetero quadruple-decker complex DyCdY were synthesized, and their magnetic properties were compared with those of the quadruple-decker complex DyCdDy. Single-crystal X-ray analysis revealed that the coordination geometries around the Dy^III ions of DyCdCdDy, DyCdY, and DyCdDy were similar. dc (direct current) magnetic measurements indicated that DyCdCdDy had very weak ferromagnetic Dy^III-Dy^III interactions but DyCdY did not. From a comparison of the magnetic relaxation times (τ) of the three complexes, the τ values of DyCdCdDy and DyCdDy, which have weak Dy^III-Dy^III interactions, are longer than that of DyCdY. In other words, weak Dy^III-Dy^III interactions effectively suppress magnetic relaxation.

Remote control of SMM behaviour via DTE ligands

Herein the use of DTE ligands to remotely control the magnetic properties of single-molecule magnets is discussed.

Photo-control of the magnetic properties of Dy(iii) and Ho(iii) homometal coordination polymers bridged by a diarylethene ligand

Two-dimensional Dy(iii) and Ho(iii) homometal coordination polymers containing the DTE ligand were obtained, and the magnetic properties of the open and closed forms were investigated.