Spin qubits of Cu(II) doped in Zn(II) metal-organic frameworks above microsecond phase memory time.

With the aim of creating Cu(II) spin qubits in a rigid metal-organic framework (MOF), this work demonstrates a doping of 5 %, 2 %, 1 %, and 0.1 % mol of Cu(II) ions into a perovskite-type MOF [CH6 N3 ][ZnII (HCOO)3 ]. The presence of dopant Cu(II) sites are confirmed with anisotropic g-factors (gx =2.07, gy =2.12, and gz =2.44) in the S=1/2 system by experimentally and theoretically. Magnetic dynamics indicate the occurrence of a slow magnetic relaxation via the direct and Raman processes under an applied field, with a relaxation time (τ) of 3.5 ms (5 % Cu), 9.2 ms (2 % Cu), and 15 ms (1 % Cu) at 1.8 K. Furthermore, pulse-ESR spectroscopy reveals spin qubit properties with a spin-spin relaxation (phase memory) time (T2 ) of 0.21 µs (2 %Cu), 0.39 µs (1 %Cu), and 3.0 µs (0.1 %Cu) at 10 K as well as Rabi oscillation between MS =±1/2 spin sublevels. T2 above microsecond is achieved for the first time in the Cu(II)-doped MOFs. It can be observed at submicrosecond around 50 K. These spin relaxations are very sensitive to the magnetic dipole interactions relating with cross-relaxation between the Cu(II) sites and can be tuned by adjusting the dopant concentration.

Chemical pressure-induced PtIII-I Mott-Hubbard nanowire, [Pt(en)2I](Asp-Cn)2·H2O (13 ≤ n), detected via polarized infrared spectroscopy.

The electronic states of iodo-bridged platinum nanowire complexes have been studied using polarized FT-IR spectroscopy. The N-H symmetrical stretching mode was found to be highly sensitive to the electronic states, distinguishing mixed-valence (MV) and averaged-valence (AV) states. The first Pt(III) nanowire complexes have been realized by the chemical pressures of the counter-anions.

Ultra-small Mo-Pt subnanoparticles enable CO2 hydrogenation at room temperature and atmospheric pressure.

We present a partially-oxidised bimetallic Mo-Pt subnanoparticle (Mo4Pt8Ox) enabling thermally-driven CO2 hydrogenation to CO at room temperature and atmospheric pressure. A mechanistic study explained the full catalytic cycle of the reaction from CO2 activation to catalyst reactivation. DFT calculations revealed that alloying with Mo lowers the activation barrier by weakening the CO adsorption. This finding could be a first step for low-energy CO2 conversion.

Slow magnetic relaxation in a ferromagnetic CuII chain complex, induced by a phonon bottleneck effect.

The first slow magnetic relaxation in a ferromagnetic Cu(II) chain compound, Cu(dipic)(OH2)2 (dipicH2 = pyridine-2,6-dicarboxylic acid), induced by a phonon bottleneck effect under a magnetic field of 0.6 T, with a relaxation time of 2.2 s at 2.8 K, was observed.

Spin dynamics in a Heisenberg weak antiferromagnetic chain of an iodide-bridged Cu(II) complex.

[CuII(chxn)2I]I (chxn = 1R,2R-diaminocyclohexane) has been synthesized, which is the first report of an iodide-bridged Cu(II) chain structure. This chain compound shows S = 1/2 Heisenberg weak antiferromagnetism (J = -0.3 cm-1) and magnetic relaxation (τ = 43 ms at 1.8 K) with a Raman process in a static field.

Creation of a Field-Induced Co(II) Single-Ion Magnet by Doping into a Zn(II) Diamagnetic Metal-Organic Framework.

The combination of single-ion magnets (SIMs) and metal-organic frameworks (MOFs) is expected to produce new quantum materials. The principal issue to be solved in this regard is the development of new strategies for the synthesis of SIM-MOFs. This work demonstrates a new simple strategy for the synthesis of SIM-MOFs where a diamagnetic MOF is used as the framework into which the SIM sites are doped. 1, 0.5, and 0.2 mol% of the Co(II) ions are doped into the Zn(II) sites of [CH6 N3 ][ZnII (HCOO)3 ]. The doped Co(II) sites in the MOFs perform as SIM with a positive D term of zero-field splitting. The longest magnetic relaxation time is 150 ms (0.2 mol% Co) at 1.8 K under a static field of 0.1 T. Temperature dependency of the relaxation time suggests suppressing magnetic relaxation by reduction of spin-spin interaction upon doping in the rigid framework. Thus, this work represents a proof of concept for the creation of a single-ion doped magnet in the MOF. This simple synthetic strategy will be widely applied for the creation of quantum magnetic materials.

Step-by-Step Electrocrystallization Processes to Make Multiblock Magnetic Molecular Heterostructures.

Assembling conductive or magnetic heterostructures by bulk inorganic materials is important for making functional electronic or spintronic devices, such as semiconductive p-doped and n-doped silicon for P-N junction diodes, alternating ferromagnetic and nonmagnetic conductive layers used in giant magnetoresistance (GMR). Nonetheless, there have been few demonstrations of conductive or magnetic heterostructures made by discrete molecules. It is of fundamental interest to prepare and investigate heterostructures based on molecular conductors or molecular magnets, such as single-molecule magnets (SMMs). Herein, we demonstrate the fabrication of a series of molecular heterostructures composed of (TTF)2M(pdms)2 (TTF = tetrathiafulvalene, M = Co(II), Zn(II), Ni(II), H2pdms = 1,2-bis(methanesulfonamido)benzene) multiple building blocks through a well-controlled step-by-step electrocrystallization growth process, where the Co(pdms)2, Ni(pdms)2, and Zn(pdms)2 anionic complex is a SMM, paramagnetic, and diamagnetic molecule, respectively. Magnetic and SMM properties of the heterostructures were characterized and compared to the parentage (TTF)2Co(pdms)2 complex. This study presents the first methodology for creating molecule-based magnetic heterostructural systems by electrocrystallization.

Switching of the redox centers of a tris-2-mercaptophenolato chromium(III) metalloligand by a guest metal ion.

This work reports that the redox-active metalloligand (ML) fac-[CrIII(mp)3]3- (mp: 2-mercaptophenolato) coordinates with a Co(III) ion to afford the trianionic complex [CoIII{fac-CrIII(mp)3}2]3-. The free ML shows ligand-centered redox processes, whereas the guest-metal-bound trinuclear structure exhibited a guest-metal-centered Co(II)/Co(III) redox couple, demonstrating redox switching through guest-metal binding to the MLs.

Intramolecular Ferromagnetism in Di-Nuclear 3 d-Transition-Metal Single-Molecule Magnets by Pseudo-Serial Arrangement.

Di-nuclear citrate complexes, [CH6 N3 ]2 [M2 (citH)2 (H2 O)4 ] ⋅ 2H2 O (citH4 =citric acid; M=FeII (Fe-2), CoII (Co-2), and NiII (Ni-2)), are synthesized. The ligand, citH3- , is deprotonated only at the three carboxy groups, which is different from the previously reported tetra-nuclear structures with cit4- ligands. Magnetic measurements reveal that these complexes have intramolecular ferromagnetism with J=∼0 cm-1 (Ni-2), 0.02 cm-1 (Co-2), and 0.04 cm-1 (Fe-2). Co-2 and Fe-2 show slow magnetic relaxation, and are field-induced SMMs with activation energy of spin-reversal Ueff =27 cm-1 (Co-2) and 4.2 cm-1 (Fe-2). Density functional theory calculations indicate that the uniaxial anisotropy along the z-axis of each metal ion center forms the pseudo-serial arrangement, leading to intramolecular ferromagnetism via the magnetic dipole interaction. This work demonstrates the creation of ferromagnetic SMMs by the magnetic dipole engineering of 3d di-nuclear metal ion centers.

Ni(III) Mott-Hubbard-like State Containing High-Spin Ni(II) in a Semiconductive Bromide-Bridged Ni-Chain Compound.

Halogen-bridged linear chain metal complexes (MX-Chains) are fascinating compounds that have a quasi-one-dimensional (1D) electronic system. In this study, we synthesized the first Ni-based MX-Chain compound having hydroxy groups, i.e., [Ni(dabdOH)2Br]Br2·[Ni(dabdOHx)2Br]0.5·(2-PrOH)0.25·(MeOH)0.25 (1·solvent, x = ∼0.6, dabdOH = (2S,3S)-2,3-diaminobutane-1,4-diol). Single-crystal X-ray diffraction revealed that the MX-Chains in 1·solvent formed sheets and single-chain structures in the superlattice. It suggested an MH-like state, whereas the polarized reflection and Raman spectra suggested a CDW-like state. Magnetic and electron spin resonance measurements revealed that both high-spin Ni(II) (∼15%) and low-spin Ni(III) (∼85%) sites are present in the chain structures, i.e., the metal sites show mixed valency. Therefore, we concluded that 1·solvent adopts an intermediate state between the MH and CDW states. Moreover, a single crystal of 1·solvent exhibited semiconductive characteristics along the chain direction. This finding represents a new structural and electronic state of 1D electronic systems as well as MX-Chains.

Synthesis and magnetic properties of sub-nanosized iron carbides on a carbon support.

Iron carbide clusters with near-sub-nanometer size have been synthesized by employing a tetraphenylmethane-cored phenylazomethine dendrimer generation 4 (TPM-DPAG4) as a molecular template. Magnetic measurements reveal that these iron carbide clusters exhibit a magnetization-field hysteresis loop at 300 K. The data indicate that these iron carbide clusters are ferromagnets at room temperature.

Comparison between DySc2N@C80 and Dy2ScN@C80 single-molecule magnetic metallofullerenes encapsulated in single-wall carbon nanotubes.

Encapsulation of a metallofullerene single-molecule magnet, Dy2ScN@C80, into single-wall carbon nanotubes (SWCNTs) accelerates magnetic relaxation processes. In contrast, encapsulation of DySc2N@C80 suppresses them. The effects of the encapsulation are discussed in terms of intermolecular magnetic interactions and charge transfer among metallofullerenes and SWCNTs.

Macro- and atomic-scale observations of a one-dimensional heterojunction in a nickel and palladium nanowire complex.

The creation of low-dimensional heterostructures for intelligent devices is a challenging research topic; however, macro- and atomic-scale connections in one-dimensional (1D) electronic systems have not been achieved yet. Herein, we synthesize a heterostructure comprising a 1D Mott insulator [Ni(chxn)2Br]Br2 (1; chxn = 1R-2R-diaminocyclohexane) and a 1D Peierls or charge-density-wave insulator [Pd(chxn)2Br]Br2 (2) using stepwise electrochemical growth. It can be considered as the first example of electrochemical liquid-phase epitaxy applied to molecular-based heterostructures with a macroscopic scale. Moreover, atomic-resolution scanning tunneling microscopy images reveal a modulation of the electronic state in the heterojunction region with a length of five metal atoms (~ 2.5 nm), that is a direct evidence for the atomic-scale connection of 1 and 2. This is the first time that the heterojunction in the 1D chains has been shown and examined experimentally at macro- and atomic-scale. This study thus serves as proof of concept for heterojunctions in 1D electronic systems.

Tunable Synchronicity of Molecular Valence Tautomerism with Macroscopic Solid-Liquid Transition by Molecular Lattice Engineering.

The combination of a cobalt-dioxolene core that exhibits valence tautomerism (VT) with pyridine-3,5-dicarboxylic acid functionalized with chains bearing two, four, or six oxyethylene units led to new complexes ConEGEspy (n = 2, 4, and 6). These complexes commonly form violet crystals of the low-spin (ls)-[CoIII (nEGEspy)2 (3,6-DTBSQ)(3,6-DTBCat)] (ls-[CoIII ], 3,6-DTBSQ = 3,6-di-tert-butyl semiquinonato, 3,6-DTBCat = 3,6-di-tert-butyl catecholato). Interestingly, violet crystals of Co2EGEspy in the ls-[CoIII ] transitioned into a green liquid, accompanied by an almost complete VT shift (94 %) to the high-spin (hs)-[CoII (nEGEspy)2 (3,6-DTBSQ)2 ] (hs-[CoII ]) upon melting. In contrast, violet crystals of Co4EGEspy and Co6EGEspy in the ls-[CoIII ] exhibited partial VT (33 %) and only a 9.3 % VT shift after melting, respectively. These data demonstrate the tunability of the synchronicity of the molecular VT and macroscopic solid-liquid transitions by optimizing the tethered chains, thus establishing a new strategy for coupling bistable molecules with the macroscopic world.

Surface Ohmic Conductivity on a Mott Insulator Based on a One-dimensional Bromide-bridged Nickel(III) Complex.

Ohmic contacts are of critical importance to improve the performance of semiconductor devices as well as those of low-dimensional materials. Halogen-bridged metal complexes (MX-Chains) are fascinating quasi-one-dimensional (1D) electronic materials. However, reports on the electrical characteristics of MX-Chains remain elusive. Herein, we report the electrical characteristics of single crystals of [Ni(chxn)2 Br]Br2 (chxn: (1R,2R)-(-)-1,2-cyclohexanediamine), which is a 1D Mott insulator, using different probe arrangements. [Ni(chxn)2 Br]Br2 was shown for the first time to exhibit Ohmic characteristics on the crystal surface, albeit that the conductivity behavior of the interior of the crystal is nonlinear due to the Joule heating effect. The current flow on the surface is shallow (a few micrometers in depth) despite the millimeter-scale crystal size; this phenomenon is strongly connected to its structural anisotropy. The Ohmic contact revealed in this work should be valuable for the application of MX-Chains as electronic devices in the near future.

Highly Dispersed Molybdenum Oxycarbide Clusters Supported on Multilayer Graphene for the Selective Reduction of Carbon Dioxide.

Molybdenum oxycarbide clusters are novel nanomaterials that exhibit attractive catalytic activity; however, the methods for their production are currently very restrictive. This work represents a new strategy for the creation of near-subnanometer size molybdenum oxycarbide clusters on multilayer graphene. To adsorb Mo-based polyoxometalates of the type [PMo12 O40 ]3- as a precursor for Mo oxycarbide clusters, the novel tripodal-phenyl cation N,N,N-tri(4-phenylbutyl)-N-methylammonium ([TPBMA]+ ) is synthesized. [TPBMA]+ exhibits superior adsorption on multilayer graphene compared to commercially available cations such as tetrabutylammonium ([nBu4 N]+ ) and tetraphenylphosphonium ([PPh4 ]+ ). Using [TPBMA]+ as an anchor, highly dispersed precursor clusters (diameter: 1.0 ± 0.2 nm) supported on multilayer graphene are obtained, as confirmed by high-resolution scanning transmission electron microscopy. Remarkably, this new material achieves the catalytic reduction of CO2 to selectively produce CO (≈99.9%) via the reverse water-gas-shift reaction, by applying carbothermal hydrogen reduction to generate Mo oxycarbide clusters in situ.

An unusual Pd(III) oxidation state in the Pd-Cl chain complex with high thermal stability and electrical conductivity.

The Pd(iii) oxidation state is unusual and unstable since it strongly tends to disproportionate. We synthesized the quasi-one-dimensional (1D) halogen-bridged Pd(iii)-Cl complex [Pd(dabdOH)2Cl]Cl2 (1-Cl; dabdOH = (2S,3S)-2,3-diaminobutane-1,4-diol) with multiple hydrogen bonds. From single-crystal X-ray diffraction, the bridging Cl- ions were located at the midpoint of the Pd-Cl-Pd moieties in the 1D chains, indicating that the Pd ions are in a Pd(iii) average valence (AV) state. Moreover, bright spots for the Pd(iii) dz2 orbitals in the upper Hubbard band above the Fermi level were observed every ∼5 Šusing scanning tunnelling microscopy. These results clearly indicate that the Pd ions are in a Pd(iii) AV state in 1-Cl. In addition, 1-Cl has the highest thermal stability (470 K) among the Pd(iii) complexes reported and the highest electrical conductivity (0.6 S cm-1 at 300 K) among the 1D Pd-Cl chains reported so far.

Metallic Tungsten Nanoparticles That Exhibit an Electronic State Like Carbides during the Carbothermal Reduction of WCl6 by Hydrogen.

Carbothermal hydrogen reduction (CHR) is a unique dry chemical process used to fabricate metals and carbides on carbon supports. In this study, a stepwise CHR of WCl6 on a graphite support is demonstrated for the first time. Powder X-ray diffraction studies revealed that, at 773 K, metallic tungsten nanoparticles are produced, whereas, at 1073 K, the metastable W2C phase is generated rather than the thermodynamically stable WC phase. X-ray photoelectron spectroscopy and X-ray absorption near edge structure studies showed that the chemical state of the W nanoparticles simultaneously exhibits metallic W(∼0) and carbide W(δ+) character. The obtained results suggest that, although electronic interactions exist between the metallic W atoms and the graphite support, the body-centered cubic structure of the metallic tungsten is maintained, confirmed by the extended X-ray absorption fine structure. In addition, high-resolution scanning transmission electron microscopy observations revealed that the W nanoparticles exhibit a thin flattened shape on the support. These results support the notion that the mechanism for the formation of the W nanoparticles during the CHR is influenced by the electronic interactions between the W nanoparticles and the graphite support. Our work thus suggests that the combination of early-transition-metal atoms and carbon-based supports would afford modulatable electronic systems though the electronic interactions.

Subnano-transformation of molybdenum carbide to oxycarbide.

Ultrasmall particles exhibit structures and/or properties that are different from those of the corresponding bulk materials; in this context especially ultrasmall precious-metal particles have been extensively investigated. In this study, we targeted the transition base-metal Mo and succeeded in systematically producing Mo oxycarbide/carbide particles with diameters of 1.7 ± 0.7, 1.4 ± 0.5, 1.3 ± 0.4, 1.2 ± 0.3, 1.0 ± 0.3, and 0.8 ± 0.2 nm on a carbon support using the carbothermal hydrogen reduction method at 773 K and a diphenylazomethine-type dendrimer as a template. The formation and properties of the particles were confirmed using X-ray photoelectron spectroscopy, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images, and X-ray absorption fine structure (XAFS) studies. We found that Mo particles with a diameter of 1.3 nm or greater formed carbides such as ß'-Mo2C, whereas smaller particles formed oxycarbides, indicating a size-dependent transformation in the phase or composition of the particles. Thus, this work demonstrated a new concept, subnano-transformation, which would be a new class of phase transformation based on the concept of the size dependence in such an ultrasmall scale. In addition, the movement of Mo atoms within a cluster and on the fringes of a nanoparticle was also demonstrated during continuous time-course high-resolution HAADF-STEM observation.