Enhanced hydrogen uptake of dihydrogen complex via porous materials support.

This research focuses on enhancing H2 adsorption by using the [Mo(PCy3)2(CO)3] complex supported on porous materials such as silica gel and mesoporous carbon. The study reports a significant increase in hydrogen adsorption capacity, reaching up to 9.3 times that of the bulk complex. This improvement suggests that using mesoporous materials as supports for the [Mo(PCy3)2(CO)3] complex enhances the accessibility of H2 gas to its open-metal sites.

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.

Hexagonal crystalline Magnus' green salt analogues prepared from hydroxy-functionalised Pt and Pd complexes.

New Magnus' green salt (MGS) analogues, [M(dabdOH)2][MCl4]·2H2O (dabdOH = (2S,3S)-2,3-diaminobutane-1,4-diol; M = Pd (1) and M = Pt(2)), in which [M(dabdOH)2]2+ and [MCl4]2- are stacked alternately to form linear chains, were obtained as hexagonal plate crystals. The hexagonal shape and large crystal size are unprecedented features as MGS analogues. An unusual trigonal grade separation of chain complexes has been revealed by the structural analysis. 1 and 2 exhibited remarkable yellow and pink colours, respectively, which are derived from weak M⋯M interactions. The dabdOH ligand, which has an additional hydrogen donor group (hydroxy group), produces a multiple-hydrogen-bond network. The combination of intrachain and interchain hydrogen bonds gives a two-dimensional (2D) hydrogen-bond sheet, and each 2D sheet is indirectly connected by hydrogen bonds via lattice water molecules. The OH-functionalised ligand greatly increases the hydrophilicity of the MGS analogues and yields the largest single crystals of all MGS analogues reported so far. The trigonal grade-separated chain structure is likely due to the geometric matching between the periodicity of chains and the short axis width of the chain. This strategy opens up new insight for preparing large crystals of MGS analogues and for constructing trigonal grade-separated nanowires in molecular crystals.

Single-Crystal Structures of Benzenehexathiol and Its Disulfide Forms.

Oligothiols are useful as building blocks in the construction of disulfide-based macrocycles and polymers or as ligands for coordination polymers. Above all, benzenehexathiol (BHT) is a particularly important molecule, as it is used to construct conductive two-dimensional MOFs. Despite the desire to clarify its structure and isolate it to high purity, the chemical instability of BHT has hampered single-crystal X-ray structure analysis of intact BHT. In addition, the synthesis of discrete disulfide molecules of BHT has not been reported. Here, we succeed in obtaining the single crystals of intact BHT, which is analyzed by single crystal X-ray structure analysis. Furthermore, the structures of a group of molecules with intermolecular disulfide bonds (BHT·4im and BHT2·2TBA, im = imidazole, TBA = tetrabutylammonium cation) obtained by processing BHT in the presence of bases are determined.

Beyond the Conventional Limitation of Photocycloaddition Reaction in the Roomy Nanospace of a Metal-Organic Framework.

Topochemical reactions provide selective products based on the molecular position; however, they generally require molecules to be placed in strictly limited orientations and distances, making them less versatile. In this study, we found that by confining trans-4-styrylpyridine (4-spy) as a reactive substrate in a flexible metal-organic framework (MOF) nanospace, [2+2] cycloadducts can be selectively obtained, even when the distance between two C═C bonds of 4-spy in the crystal is 5.9 Å, which is much larger than the conventionally observed upper limit (4.2 Å). Such an unusual cyclization reaction is suggested to occur due to the transient proximity of the 4-spy due to the "swing" motion in the nanospace. The MOF nanospace, with its high degree of molecular structural freedom, can be applied to different platforms that do not require the fine constraints of reactive distances for solid-phase reactions.

Quinoid-Based Three-Dimensional Metal-Organic Framework Fe2(dhbq)3: Porosity, Electrical Conductivity, and Solid-State Redox Properties.

We report the synthesis, characterization, and electronic properties of the quinoid-based three-dimensional metal-organic framework [Fe2(dhbq)3]. The MOF was synthesized without using cations as a template, unlike other reported X2dhbq3-based coordination polymers, and the crystal structure was determined by using single-crystal X-ray diffraction. The crystal structure was entirely different from the other reported [Fe2(X2dhbq3)]2-; three independent 3D polymers were interpenetrated to give the overall structure. The absence of cations led to a microporous structure, investigated by N2 adsorption isotherms. Temperature dependence of electrical conductivity data revealed that it exhibited a relatively high electrical conductivity of 1.2 × 10-2 S cm-1 (Ea = 212 meV) due to extended d-π conjugation in a three-dimensional network. Thermoelectromotive force measurement revealed that it is an n-type semiconductor with electrons as the majority of charge carriers. Structural characterization and spectroscopic analyses, including SXRD, Mössbauer, UV-vis-NIR, IR, and XANES measurements, evidenced the occurrence of no mixed valency based on the metal and the ligand. [Fe2(dhbq)3] upon incorporating as a cathode material for lithium-ion batteries engendered an initial discharge capacity of 322 mAh/g.

Creation of single molecular conjugates of metal-organic cages and DNA.

Here we report the development of an equimolar conjugate of a metal-organic cage (MOC) and DNA (MOC-DNA). Several MOC-DNA conjugates were assembled into a programmed structure by coordinating with a template DNA having a complementary base sequence. Moreover, conjugation with the MOC drastically enhanced the permeability of DNA through the lipid bilayer, presenting great potential as a drug delivery system.

Deprotonation-Induced Color Modulation in N,N'-Dihydroxynaphthalenediimide-Based Organic Crystals.

N,N'-dihydroxy-1,4,5,8-naphthalenetetracarboxdiimide (NDI-(OH)2 ) has attracted much attention in recent years, because its doubly deprotonated state, (O-NDI-O)2- , has metal-coordination ability and characteristic electronic transition useful for designing electronic and optical functions. In contrast, a molecular crystal with the mono-deprotonated (HO-NDI-O)- ion remains unknown. We herein report an organic crystal containing non-disproportionated (HO-NDI-O)- ions, which are connected by very strong O-H-O hydrogen bonds. Its lowest energy absorption band (450 to 650 nm) is observed in between that of NDI-(OH)2 (380 nm) and isolated (O-NDI-O)2- (500 to 850 nm) species, consistent with the molecular orbital calculations. This absorption originates from the electronic transition from deprotonated imide-based orbitals to NDI-core orbitals, which can be influenced by the hydrogen bonds around imide group. Consequently, the optical properties of NDI-(OH)2 can be modulated by the stepwise deprotonation and hydrogen-bonding interactions.

Observation of slow magnetic relaxation phenomena in spatially isolated π-radical ions.

The use of molecular spins as quantum bits is fascinating because it offers a wide range of strategies through chemical modifications. In this regard, it is very interesting to search for organic radical ions that have small spin-orbit coupling values. On the other hand, the feature of the magnetic relaxation of π-organic radical ions is rarely exploited due to the difficulty of spin dilution, and π-stacking interaction. In this study, we focus on N,N',N''-tris(2,6-dimethylphenyl)benzenetriimide (BTI-xy), where three xylene moieties connected to the imide groups cover the π-plane of the BTI core. As a result, BTI-xy radical anions without π-stacking interaction were obtained. This led to the slow magnetization relaxation, which is reported for the first time in organic radicals. Furthermore, the relaxation times in a solution state revealed the importance of spin interaction.

Porous Mn2+ Magnet with a Pt-Cl Framework: Correlation between Water Vapor Adsorption/Desorption and Slow Magnetic Relaxation.

We report the water adsorption/desorption behavior and dynamic magnetic properties of the Pt-Cl chain complex [{[Pt(en)2 ][PtCl2 (en)2 ]}3 ][{(MnCl5 )Cl3 }2 ] ⋅ 12H2 O (1). Upon heating 1 in a vacuum, we obtained the dehydrated form [{[Pt(en)2 ][PtCl2 (en)2 ]}3 ][{(MnCl5 )Cl3 }2 ] (1DH). The framework structures of 1 and 1DH are identical, and both complexes underwent slow magnetic relaxation. However, the magnetic relaxation times for 1DH were shorter than those for 1, meaning that the dynamic magnetic properties were controlled upon water vapor adsorption/desorption. From detailed analyses of the dynamic magnetic behavior, a phonon-bottleneck effect contributes to the magnetic relaxation processes. We discuss the mechanism for the changes in the magnetic relaxation processes upon dehydration in terms of the heat capacity and thermal conductivity.

Hydrogen Bonding Propagated Phase Separation in Quasi-Epitaxial Single Crystals: A Pd-Br Molecular Insulator.

In condensed matter, phase separation is strongly related to ferroelasticity, ferroelectricity, ferromagnetism, electron correlation, and crystallography. These ferroics are important for nano-electronic devices such as non-volatile memory. However, the quantitative information regarding the lattice (atomic) structure at the border of phase separation is unclear in many cases. Thus, to design electronic devices at the molecular level, a quantitative electron-lattice relationship must be established. Herein, we elucidated a PdII-PdIV/PdIII-PdIII phase transition and phase separation mechanism for [Pd(cptn)2Br]Br2 (cptn = 1R,2R-diaminocyclopentane), propagated through a hydrogen-bonding network. Although the Pd···Pd distance was used to determine the electronic state, the differences in the Pd···Pd distance and the optical gap between Mott-Hubbard (MH) and charge-density-wave (CDW) states were only 0.012 Å and 0.17 eV, respectively. The N-H···Br···H-N hydrogen-bonding network functioned as a jack, adjusting the structural difference dynamically, and allowing visible ferroelastic phase transition/separation in a fluctuating N2 gas flow. Additionally, the effect of the phase separation on the spin susceptibility and electrical conductivity were clarified to represent the quasi-epitaxial crystals among CDW-MH states. These results indicate that the phase transitions and separations could be controlled via atomic and molecular level modifications, such as the addition of hydrogen bonding.

Syntheses, Structures, and Properties of Coordination Polymers with 2,5-Dihydroxy-1,4-Benzoquinone and 4,4'-Bipyridyl Synthesized by In Situ Hydrolysis Method.

The coordination polymers (CPs) with binary ligands, including 2,5-dihydroxy-1,4-benzoquinone (H2DHBQ) and 4,4'-bipyridyl (bpy), were synthesized using in situ hydrolysis of 2,5-dimethoxy-1,4-benzoquinone (DMBQ). Three kinds of CPs were obtained depending on the metal ions. For M = Mn and Zn, a 1D zigzag chain structure with cis conformation ( cis-1D-M) was obtained, whereas Co, Ni, and Cu compounds afforded a 2D net structure with trans conformation (trans -2D-M) with a 1D pore. A linear chain structure was also obtained for M = Cu. Magnetic susceptibility (χM T) at 300 K in cis -1D-Mn and trans -2D-Co was evaluated to be 4.421 and 2.950 cm3 K mol-1, respectively, indicating that both compounds are in the high-spin state. According to the N2 adsorption isotherms at 77 K, trans -2D-Ni showed microporosity with the BET surface area of 177 m2 g-1, whereas the isomorphic trans -2D-Co rarely adsorbed N2 at 77 K. This phenomenon was explained by the difference of diffusion kinetics of the adsorbent molecules, which was supported by the CO2 adsorption isotherms at 195 K. The optical band gaps of cis -1D-Mn, cis -1D-Zn, trans -2D-Co, and trans -2D-Ni were estimated to be 1.6, 1.8, 1.0, and 1.1 eV, respectively, by using UV-vis-NIR spectroscopy.

An electrically conductive metallocycle: densely packed molecular hexagons with π-stacked radicals.

Electrical conduction among metallocycles has been unexplored because of the difficulty in creating electronic transport pathways. In this work, we present an electrocrystallization strategy for synthesizing an intrinsically electron-conductive metallocycle, [Ni6(NDI-Hpz)6(dma)12(NO3)6]·5DMA·nH2O (PMC-hexagon) (NDI-Hpz = N,N'-di(1H-pyrazol-4-yl)-1,4,5,8-naphthalenetetracarboxdiimide). The hexagonal metallocycle units are assembled into a densely packed ABCABC… sequence (like the fcc geometry) to construct one-dimensional (1D) helical π-stacked columns and 1D pore channels, which were maintained under the liberation of H2O molecules. The NDI cores were partially reduced to form radicals as charge carriers, resulting in a room-temperature conductivity of (1.2-2.1) × 10-4 S cm-1 (pressed pellet), which is superior to that of most NDI-based conductors including metal-organic frameworks and organic crystals. These findings open up the use of metallocycles as building blocks for fabricating conductive porous molecular materials.

Benzenetriimide-Based Molecular Conductor with Antiferro- to Ferromagnetic Switching Induced by Structural Change of π-stacked Array.

Benzenetriimide (BTI) is a promising building block for materials chemistry due to its characteristic 3-fold symmetry and redox properties, whereas little is known about its conductive and magnetic properties. In this study, we synthesized three charge-transfer complexes based on N,N',N''-trimethylbenzenetriimide (BTI-Me). One of the complexes contains isolated dimers of BTI-Me radical anion (BTI-Me⋅- ), while the other two have the infinite π-stacked array of BTI-Me with the formal charge of -0.5. The latter two complexes did not show metallic behavior but showed semiconducting behavior probably due to the characteristic insulation in one-dimensional electron system, so-called charge ordering and dimer-Mott insulation. The magnetic susceptibility of the complex in dimer-Mott state exhibits an unusual transition from antiferromagnetic to ferromagnetic spin states with the hysteresis loop of 15 K derived from the structural phase transition around 130 K. These properties were also supported by DFT calculations.

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.

Thermally induced electron-hole dissociation dynamics in quasi-one-dimensional bromo-bridged palladium(III) Mott-insulator [Pd(en)2Br](Suc-Cn)2·H2O (Cn-Y = dialkylsulfosuccinate; n = 5 and 6).

Current-voltage characteristics and dielectric properties were studied in bromo-bridged one-dimensional compounds, [Pd(en)2Br](Suc-C5)2·H2O, exhibiting mixed-valence and averaged valence (MV-AV) phase transition. In the AV phase, clear nonlinear current-voltage characteristics were observed. This phenomenon was explained by the thermally induced electron-hole separation assisted by an electric field. This mechanism was supported by the dielectric properties of [Pd(en)2Br](Suc-Cn)2·H2O (n = 5 and 6).

Elucidating 2D Charge-Density-Wave Atomic Structure in an MX-Chain by the 3D-ΔPair Distribution Function Method.

The front cover artwork is provided by Prof. Masahiro Yamashita's group at Tohoku University and designed by Dr. Laurent Guérin at University of Rennes 1. The image illustrates that the atomic structure of a 2D charge density wave can be revealed although the planes associated to this local 2D order are randomly stacked preventing the use of conventional structure determination techniques. Read the full text of the Research Article at 10.1002/cphc.202100857.

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.

Bromine Vapor Induced Continuous p- to n-Type Conversion of a Semiconductive Metal-Organic Framework Cu[Cu(pdt)2].

Guest-promoted modulation of the electronic states in metal-organic frameworks (MOFs) has brought about a new field of interdisciplinary research, including host-guest chemistry and solid-state physics. Although there are dozens of studies on guest-promoted enhancement of the electrical conductivity properties, including stoichiometry, conductive carriers and structure-property relationships have been scarcely studied in detail. Herein, we studied the effects of continuous and controlled bromine vapor doping on structural, optical, thermoelectric, and semiconducting properties of Cu[Cu(pdt)2] (pdt = 2,3-pyrazinedithiolate) as a function of bromine stoichiometry. We demonstrated that the same material could act as both p- and n-type semiconductors by tuning the stoichiometry of Br doped in Brx@Cu[Cu(pdt)2], and a change in the charge-carrier type from holes in pristine MOF to electrons upon bromine vapor doping was observed. Bromine molecules acted as an oxidant, causing the selective oxidation of [CuII(pdt)2] in the host framework. In addition, a redox hopping pathway between the partially oxidized CuII/CuIII center contributed to the enhancement of the electrical conductivity of the MOF.

Elucidating 2D Charge-Density-Wave Atomic Structure in an MX-Chain by the 3D-ΔPair Distribution Function Method.

Many solids, particularly low-dimensional systems, exhibit charge density waves (CDWs). In one dimension, charge density waves are well understood, but in two dimensions, their structure and their origin are difficult to reveal. Herein, the 2D charge-density-wave atomic structure and stabilization mechanism in the bromide-bridged Pd compound [Pd(cptn)2 Br]Br2 (cptn=1R,2R-diaminocyclopentane) is investigated by means of single-crystal X-ray diffraction employing the 3D-Δpair distribution function (3D-ΔPDF) method. Analysis of the diffuse scattering using 3D-ΔPDF shows that a 2D-CDW is stabilized by a hydrogen-bonding network between Br- counteranion and the amine (NH2 ) group of the cptn in-plane ligand, and that 3D ordering is prevented due to a weak plane to plane correlation. We extract the effective displacements of the atoms describing the atomic structure quantitatively and discuss the stabilization mechanism of the 2D-CDW. Our study provides a method to identify and measure the key interaction responsible for the dimensionality and stability of the CDW that can help further progress of rational design.