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, ß″-(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.

Periodicity of Single-Molecule Magnet Behaviour of Heterotetranuclear Lanthanide Complexes across the Lanthanide Series: A Compendium.

Acetato-bridged palladium-lanthanide tetranuclear heterometallic complexes of the form [Pd2 Ln2 (H2 O)2 (CH3 COO)10 ]⋅2 CH3 COOH [Ln2 =Ce2 (1), Pr2 (2), Nd2 (3), Sm2 (4), Tb2 (5), Dy2 (6), Dy0.2 Y1.8 (6''), Ho2 (7), Er2 (8), Er0.24 Y1.7 (8''), Tm2 (9), Yb2 (10), Y2 (11)] were synthesised and characterised by experimental and theoretical techniques. All complexes containing Kramers lanthanide ions [Ln3+ =Ce (1), Nd (3), Sm (4), Dy (6), DyY (6''), Er (8), ErY (8''), Yb (10)] showed field-induced slow magnetic relaxation, characteristic of single-molecule magnetism and purely of molecular origin. In contrast, all non-Kramers lanthanide ions [Ln3+ =Pr (2), Tb (5), Ho (7), Tm (9), Y3+ (11) is diamagnetic and non-lanthanide] did not show any slow magnetic relaxation. The variation in the electronic structure and accompanying consequences across the complexes representing all Kramers and non-Kramers lanthanide ions were investigated. The origin of the magnetic properties and the extent to which the axial donor-acceptor interaction involving the lanthanide ions and an electron-deficient d z 2 orbital of palladium affects the observed magnetic and electronic properties across the lanthanide series are presented. Unique consistent electronic and magnetic properties of isostructural complexes spanning the lanthanide series with properties dependent on whether the ions are Kramers or non-Kramers are reported.

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, ß''-(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.

An Organic-Inorganic Hybrid Exhibiting Electrical Conduction and Single-Ion Magnetism.

The first three-dimensional (3D) conductive single-ion magnet (SIM), (TTF)2 [Co(pdms)2 ] (TTF=tetrathiafulvalene and H2 pdms=1,2-bis(methanesulfonamido)benzene), was electrochemically synthesised and investigated structurally, physically, and theoretically. The similar oxidation potentials of neutral TTF and the molecular precursor [HNEt3 ]2 [M(pdms)2 ] (M=Co, Zn) allow for multiple charge transfers (CTs) between the SIM donor [M(pdms)2 ]n- and the TTF.+ acceptor, as well as an intradonor CT from the pdms ligand to Co ion upon electrocrystallisation. Usually TTF functions as a donor, whereas in our system TTF is both a donor and an accepter because of the similar oxidation potentials. Furthermore, the [M(pdms)2 ]n- donor and TTF.+ acceptor are not segregated but strongly interact with each other, contrary to reported layered donor-acceptor electrical conductors. The strong intermolecular and intramolecular interactions, combined with CT, allow for relatively high electrical conductivity even down to very low temperatures. Furthermore, SIM behaviour with slow magnetic relaxation and opening of hysteresis loops was observed. (TTF)2 [Co(pdms)2 ] (2-Co) is an excellent building block for preparing new conductive SIMs.

Dysprosium Chlorocyanoanilate-Based 2D-Layered Coordination Polymers.

A series of two-dimensional (2D)-layered coordination polymers (CPs) based on the heterosubstituted anilate ligand ClCNAn2- derived from 3-chloro-6-cyano-2,5-dihydroxybenzoquinone and DyIII 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 ClCNAn2- ligand and DyIII 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 mJ levels, while the presence of weak antiferromagnetic coupling between the DyIII centers mediated by the anilate bridge cannot be excluded.

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.

Synthesis, Structures, and Magnetic Properties of Two Coordination Assemblies of Mn(III) Single Molecule Magnets Bridged via Photochromic Diarylethene Ligands.

Two new coordination assemblies were prepared by combining the open and close forms of 1,2-bis(5-carboxyl-2-methyl-3-thienyl)perfluorocyclopentene (H2dae) with [Mn2(saltmen)2(H2O)2](PF6)2, where H2saltmen = 2,2'-((1 E,1' E)-((2,3-dimethylbutane-2,3-diyl)bis(azaneylylidene)) bis(methaneylylidene))diphenol. From X-ray diffraction analyses, the complexes had the following formula: [Mn2(saltmen)2(dae-open)] (1open) and [Mn(saltmen)(dae-close)]·H2O·Et3N (1close). Both complexes crystallized in the C2/ c monoclinic space group. In 1open, dae-o2- behaves as a bidentate ligand attached to the outer Mn-saltmen monomer via the oxygen atom of carboxylato groups, whereas in 1close, the dae-c2- ligand behaves as a monodentate ligand attached to the external Mn-saltmen dimer by only one carboxylato group of the photochromic ligand. The complexes showed reversible photochromic responses to UV/vis light and showed single-molecule magnet-like behavior. The relaxation times and energy barriers of the metal complexes are clearly affected by UV/vis irradiation.

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.

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

The work in this present investigation reports the syntheses, crystal structures and magnetic properties of five dinuclear lanthanide complexes having compositions [Tb2(HL)4(NO3)6] (1), [Tb2(HL)4Cl6]·2EtOH (2), [Yb2(HL)4(NO3)6] (3), [Yb2(HL)4Cl6]·2EtOH (4) and [Y2(HL)4(NO3)6] (5) with HL = 8-hydroxyquinaldine. It is evident from the crystal structures that the coordination number of trivalent lanthanide ions in compounds 1, 3 and 5 is nine, whereas that for compounds 2 and 4 is six. A dynamic magnetic study shows that both compounds 1 and 3 exhibit single-molecule-magnet (SMM) behavior while compounds 2 and 4 do not have any SMM property.

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.

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. The preparation of such materials remains a challenge that has been pursued by a bi-component approach of combination of SMM cationic (or anionic) units with conducting networks made of partially oxidized (or reduced) donor (or acceptor) molecules. The present status of the research concerning the preparation of molecular materials exhibiting SMM behaviour and electrical conductivity is reviewed, describing the few molecular compounds where both SMM properties and electrical conductivity have been observed. The evolution of this research field through the years is discussed. The first reported compounds are semiconductors in spite being able to present relatively high electrical conductivity, and the SMM behaviour is observed at low temperatures where the electrical conductivity of the materials is similar to that of an insulator. During the recent years, a breakthrough has been achieved with the coexistence of high electrical conductivity and SMM behaviour in a molecular compound at the same temperature range, but so far without evidence of a synergy between these properties. The combination of high electrical conductivity with SMM behaviour requires not only SMM units but also the regular and as far as possible uniform packing of partially oxidized molecules, which are able to provide a conducting network.

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), Gd0.4 Y1.6 (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 (τo =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.

Multiple Magnetic Relaxation Pathways and Dual-Emission Modulated by a Heterometallic Tb-Pt Bonding Environment.

A heterometallic Tb-Pt complex, [Tb2 Pt3 (SAc)12 (H2 O)2 ] (SAc=thioacetate), was synthesized. Dual emission was modulated by the presence of a heterometallic Tb-Pt bonding environment. The heterometallic Tb-Pt bond lowers the symmetry of the Tb ion and enhanced the emission efficiency. In addition, the Tb-Pt complex shows field-induced multiple magnetic relaxation pathways. Furthermore, it served as an antenna for the observed dual emission. In other words, the heterometallic Tb-Pt bond has a significant effect on the luminescence and magnetic properties of the complex.

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.

Field-Induced Slow Magnetic Relaxation of GdIII Complex with a Pt-Gd Heterometallic Bond.

Heterometallic Gd-Pt complexes ([Gd2 Pt3 (H2 O)2 (SAc)12 ] (SAc=thioacetate), [Y1.4 Gd0.6 Pt3 (H2 O)2 (SAc)12 ], and [Gd2 Pt3 (H2 O)6 (SAc)12 ]⋅7 H2 O have been synthesized. The crystal structures and DFT calculations indicated a Gd-Pt heretometallic bond. Single-crystal ESR spectra determined the direction of magnetic anisotropy as direction of the Gd-Pt bond. In other words, the Gd-Pt bond dictates the direction of magnetic anisotropy. The heterometallic Gd-Pt bond lowers the symmetry of the Gd ion, splitting the Kramers doublet in a dc field. Thus, we observed clear field-induced slow magnetic relaxation of [Y1.4 Gd0.6 Pt3 (H2 O)2 (SAc)12 ] up to 36 K. The relaxation process was determined to be a direct process.

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

The DyIII 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 DyIII ions of DyCdCdDy, DyCdY, and DyCdDy were similar. dc (direct current) magnetic measurements indicated that DyCdCdDy had very weak ferromagnetic DyIII-DyIII 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 DyIII-DyIII interactions, are longer than that of DyCdY. In other words, weak DyIII-DyIII interactions effectively suppress magnetic relaxation.