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.

Single-Crystal-to-Single-Crystal Installation of Ln4 (OH)4 Cubanes in an Anionic Metallosupramolecular Framework.

Postsynthetic installation of lanthanide cubanes into a metallosupramolecular framework via a single-crystal-to-single-crystal (SCSC) transformation is presented. Soaking single crystals of K6 [Rh4 Zn4 O(l-cys)12 ] (K6 [1]; l-H2 cys=l-cysteine) in a water/ethanol solution containing Ln(OAc)3 (Ln3+ =lanthanide ion) results in the exchange of K+ by Ln3+ with retention of the single crystallinity, producing Ln2 [1] (2Ln ) and Ln0.33 [Ln4 (OH)4 (OAc)3 (H2 O)7 ][1] (3Ln ) for early and late lanthanides, respectively. While the Ln3+ ions in 2Ln exist as disordered aqua species, those in 3Ln form ordered hydroxide-bridged cubane clusters that connect [1]6- anions in a 3D metal-organic framework through coordination bonds with carboxylate groups. This study shows the utility of an anionic metallosupramolecular framework with carboxylate groups for the creation of a series of metal cubanes that have great potential for various applications, such as magnetic materials and heterogeneous catalysts.

2D Molecular Superconductor to Insulator Transition in the ß''-(BEDT-TTF)2[(H2O)(NH4)2M(C2O4)3]·18-crown-6 Series (M = Rh, Cr, Ru, Ir).

The series of salts ß''-(BEDT-TTF)2[(H2O)(NH4)2M(C2O4)3]·18-crown-6 show ambient-pressure superconductivity when M = Cr, Rh. Evidence indicates that the previously reported Cr and Rh salts show a bulk Berezinski-Kosterlitz-Thouless superconducting transition. The isostructural ruthenium and iridium salts are reported here. The Ir salt represents the first radical-cation salt to contain a 5d tris(oxalato)metalate anion. The Ru and Ir salts do not show superconductivity but instead undergo a broad chemically induced metal to insulator transition at 155 K for ruthenium and at 100 K for iridium. The c axes of the Ru and Ir salts are much shorter than those of the Rh and Cr salts. Thus, the more stable metallic state of the Cr and Rh salts is associated with the more strongly 2D electronic systems. The different low-temperature behavior of the Ru and Ir salts, which exhibit a smaller interlayer spacing, could originate from a structural change in the anionic layer which thus can be easily transmitted to the donor layers and generate a localized state. However, another possibility is that it originates from Berezinski-Kosterlitz-Thouless effects.

Control of the Spin Dynamics of Single-Molecule Magnets by using a Quasi One-Dimensional Arrangement.

Magnetic dipole interactions are dominate in quasi one-dimensional (1D) molecular magnetic materials, in which TbNcPc units (Tb3+ =terbium(III) ion, Nc2- =naphthalocyaninato, Pc2- =phthalocyaninato) adopt a structure similar to TbPc2 single-molecule magnets (SMMs). The magnetic properties of the [TbNcPc]0/+ (neutral 1 and cationic 2) with 1D structures are significantly different from those of a magnetically diluted sample (3). In particular, the magnetic relaxation time (τ) of 2 in the low-temperature region is five orders of magnitude slower than that of 3. Furthermore, the coercivity (HC ) of 2 remained up to about 20 K. The single-ion anisotropy of Tb3+ ions in a 1D structure and the magnetic dipole interactions acting among molecules determines the direction of the magnetic properties. These results show that the spin dynamics can be improved by manipulating the arrangement of SMMs in the solid state.

Bulk Kosterlitz-Thouless Type Molecular Superconductor ß″-(BEDT-TTF)2[(H2O)(NH4)2Cr(C2O4)3]·18-crown-6.

A new molecular superconductor, ß″-(BEDT-TTF)2[(H2O)(NH4)2Cr(C2O4)3]·18-crown-6, has been synthesized from the organic donor molecule BEDT-TTF with the anion Cr(C2O4)33-. The crystal structure consists of conducting organic layers of BEDT-TTF molecules which adopt the ß″ packing motif (layer A), layers of NH4+ and Λ-Cr(C2O4)33- (layer B), layers of (H2O)(NH4)18-crown-6 (layer C), and layers of NH4+ and Δ-Cr(C2O4)33- (layer D) which produce a superstructure with a repeating pattern of ABCDABCDA. As a result of this packing arrangement, this is the 2D superconductor with the widest gap between conducting layers where only a single donor packing motif is present (ß″). Superconducting critical temperatures at ambient pressure observed by electrical transport and magnetic measurements are 4.0-4.9 and 2.5 K, respectively. The strong 2D nature of this system, the broad transition to Tzero at 1.8K, and the transition of α of V ∝ Iα from 1 to 3 on I-V curves strongly suggest that the superconducting transition is very close to a Kosterlitz-Thouless transition. The magnetic field dependence of the superconducting critical temperature parallel to the conducting plane gives an upper critical field µ0Hc2∥ > 8 T, which is over the calculated Pauli-Clogston limit for this material.

Ambient-pressure molecular superconductor with a superlattice containing layers of tris(oxalato)rhodate enantiomers and 18-crown-6.

We report a novel multilayered organic-inorganic hybrid material, ß″-(BEDT-TTF)2[(H2O)(NH4)2Rh(C2O4)3]·18-crown-6. This is the first molecular superconductor to have a superlattice with layers of both BEDT-TTF and 18-crown-6 and also the first with the anion tris(oxalato)rhodate. This is the 2D superconductor with the widest gap between conducting layers, where only a single donor packing motif is observed (ß″). The strong 2D nature of this system strongly suggests that the superconducting transition is a Kosterlitz-Thouless transition. A superconducting Tc of 2.7 K at ambient pressure was found by transport measurements and 2.5 K by magnetic susceptibility measurements.

BEDT-TTF radical-cation salts with tris(oxalato)chromate and guest additives.

The family of radical-cation salts ß''-(BEDT-TTF)4[(A)M3+(C2O4)3]·guest (M = Fe, Cr, Ga, Al, Co, Mn, Rh, Ru; A = K+, H3O+, NH4 +) has produced superconductors, metals, semiconductors, and metal-insulators through introduction of different guest molecules into the structure. We present three new additions to the family ß''-(BEDT-TTF)4[(A)Cr(C2O4)3]·guest with the guest molecules toluene, phenol, or salicylaldehyde. These new guests are liquid or solid additives within the electrocrystallisation medium. All three salts show metallic behaviour from room temperature down to <10 K and do not show a superconducting transition.

Correlation-driven organic 3D topological insulator with relativistic fermions.

Exploring new topological phenomena and functionalities induced by strong electron correlation has been a central issue in modern condensed-matter physics. One example is a topological insulator (TI) state and its functionality driven by the Coulomb repulsion rather than a spin-orbit coupling. Here, we report a 'correlation-driven' TI state realized in an organic zero-gap system α-(BETS)2I3. The topological surface state and chiral anomaly are observed in temperature and field dependences of resistance, indicating a three-dimensional TI state at low temperatures. Moreover, we observe a topological phase switching between the TI state and non-equilibrium Dirac semimetal state by a dc current, which is a unique functionality of a correlation-driven TI state. Our findings demonstrate that correlation-driven TIs are promising candidates not only for practical electronic devices but also as a field for discovering new topological phenomena and phases.

Enantiopure and racemic radical-cation salts of B(mandelate)2- and B(2-chloromandelate)2- anions with BEDT-TTF.

We report the first examples of radical-cation salts of BEDT-TTF with spiroborate anions [B(mandelate)2]- and [B(2-chloromandelate)2]-, synthesized from either enantiopure or racemic bidentate mandelate or chloromandelate ligands. In the salts prepared using enantiopure ligands only one of two diastereoisomers of the spiroborate anion is incorporated, with the boron centre having the same stereochemistry as the enantiopure ligand. For the racemic salts one racemic pair of spiroborate anions containing an R and an S mandelate ligand is incorporated. In certain solvents helical crystals were obtained when using spiroborate anions with enantiopure ligands. Electrical and magnetic properties, and band structure calculations are reported.

Melamine-induced synthesis of a structurally perfect kagomé antiferromagnet.

We report here a structurally perfect kagomé lattice {[Cu3(bpy)6](SiF6)3(melamine)8}n (1), where bpy is 4,4'-bipyridine and [SiF6]2- is a hexafluorosilicate anion. In comparison to general 1D linear, 2D layered and 3D cubic metal-organic frameworks, by using Cu2+ nodes and bpy ligands, a perfect kagomé lattice was synthesized by introducing C3 symmetrical melamine molecules. Magnetic susceptibility and low-temperature heat capacity measurements indicated weak antiferromagnetic interactions between the spins and no long-range magnetic ordering to 0.7 K. Using C3 symmetrical melamine molecules can be considered as a challenging synthetic strategy to afford new topological materials.

Electronic state of a conducting single molecule magnet based on Mn-salen type and Ni-dithiolene complexes.

The electrochemical oxidation of an acetone solution containing [Mn(III) (5-MeOsaltmen)(H(2)O)](2)(PF(6))(2) (5-MeOsaltmen(2-) = N,N'-(1,1,2,2-tetramethylethylene)bis(5-methoxysalicylideneiminate)) and (NBu(4))[Ni(dmit)(2)] (dmit(2-) = 2-thioxo-1,3-dithiole-4,5-dithiolate) afforded a hybrid material, [Mn(5-MeOsaltmen)(acetone)](2)[Ni(dmit)(2)](6) (1), in which [Mn(2)](2+) single-molecule magnets (SMMs) with an S(T) = 4 ground state and [Ni(dmit)(2)](n-) molecules in a charge-ordered state (n = 0 or 1) are assembled in a layer-by-layer structure. Compound 1 crystallizes in the triclinic space group P1 with an inversion center at the midpoint of the Mn···Mn dimer. The [Mn(2)](2+) unit has a typical nonplanar Mn(III) dimeric core and is structurally consistent with previously reported [Mn(2)] SMMs. The six [Ni(dmit)(2)](n-) (n = 0 or 1) units have a square-planar coordination geometry, and the charge ordering among them was assigned on the basis of ν(C═C) in IR reflectance spectra (1386, 1356, 1327, and 1296 cm(-1)). The [Mn(2)](2+) SMM and [Ni(dmit)(2)](n-) units aggregate independently to form hybrid frames. Electronic conductivity measurements revealed that 1 behaved as a semiconductor (ρ(rt) = 2.1 × 10(-1) Ω·cm(-1), E(a) = 97 meV) at ambient pressure and as an insulator at 1.7 GPa (ρ(1.7GPa) = 4.5 Ω·cm(-1), E(a) = 76 meV). Magnetic measurements indicated that the [Mn(2)](2+) units in 1 behaved as S(T) = 4 SMMs at low temperatures.

Electric dipole induced bulk ferromagnetism in dimer Mott molecular compounds.

Magnetic properties of Mott-Hubbard systems are generally dominated by strong antiferromagnetic interactions produced by the Coulomb repulsion of electrons. Although theoretical possibility of a ferromagnetic ground state has been suggested by Nagaoka and Penn as single-hole doping in a Mott insulator, experimental realization has not been reported more than half century. We report the first experimental possibility of such ferromagnetism in a molecular Mott insulator with an extremely light and homogeneous hole-doping in π-electron layers induced by net polarization of counterions. A series of Ni(dmit)2 anion radical salts with organic cations, where dmit is 1,3-dithiole-2-thione-4,5-dithiolate can form bi-layer structure with polarized cation layers. Heat capacity, magnetization, and ESR measurements substantiated the formation of a bulk ferromagnetic state around 1.0 K with quite soft magnetization versus magnetic field (M-H) characteristics in (Et-4BrT)[Ni(dmit)2]2 where Et-4BrT is ethyl-4-bromothiazolium. The variation of the magnitude of net polarizations by using the difference of counter cations revealed the systematic change of the ground state from antiferromagnetic one to ferromagnetic one. We also report emergence of metallic states through further doping and applying external pressures for this doping induced ferromagnetic state. The realization of ferromagnetic state in Nagaoka-Penn mechanism can paves a way for designing new molecules-based ferromagnets in future.

Chiral metal down to 4.2 K - a BDH-TTP radical-cation salt with spiroboronate anion B(2-chloromandelate)2.

We report the first example of a chiral BDH-TTP radical-cation salt. Chirality is induced in the structure via the use of a chiral spiroboronate anion where three stereocentres are present, one on each chiral ligand and one on the boron centre. Despite starting from a labile racemic mixture of BS and BR enantiomers, only one enantiomer is present in the crystal lattice. The anions pack in a novel double anion layer which is the thickest anion layer found in a BDH-TTP salt. This material is chiral and shows metallic behaviour down to at least 4.2 K.

Single-chain magnets constructed by using the strict orthogonality of easy-planes: use of structural flexibility to control the magnetic properties.

A family of single-chain magnets (SCMs), of which the SCM character originated from the spatial arrangement of high spin Fe(II) ions with easy-plane anisotropy, was synthesized, and their magnetic properties were investigated. The chain complexes including alternating high-spin Fe(II) ions and low-spin Fe(III) ions, catena-[Fe(II)(ClO(4))(2){Fe(III)(bpca)(2)}]ClO(4)·3MeNO(2) (1·3MeNO(2)), catena-[Fe(II)(ClO(4))(H(2)O){Fe(III)((Me)L)(2)}](ClO(4))(2)·2MeNO(2)·H(2)O (2·2MeNO(2)·H(2)O), catena-[Fe(II)(ClO(4))(H(2)O){Fe(III)((Bu)L)(2)}](ClO(4))(2)·3.5MeNO(2) (3·3.5MeNO(2)), and catena-[{Fe(II)(ClO(4))(H(2)O)Fe(II)(H(2)O)(2)}(0.5){Fe(III)((Ph)L)(2)}](ClO(4))(2.5)·4EtNO(2) (4·4EtNO(2)), were synthesized with the use of bridging ligand Hbpca (bis-(2-pyridylcarbonyl)amine)) and its derivatives of H(Me)L, H(Bu)L, and H(Ph)L each incorporating methyl, tert-butyl, or phenyl group on the 4-position of pyridyl ring. These complexes showed a typical ferrimagnetic behavior on direct current (dc) susceptibility data, and from an alternating current (ac) susceptibility measurements, SCM or superparamagnetic behaviors were confirmed with the Δ/k(B) values of 22.5(4), 21.8(18), and 28.8(3) K for 1·3MeNO(2), 2·2MeNO(2)·H(2)O, and 3·3.5MeNO(2), of which the easy-axis anisotropy was originated from the orthogonal arrangement of easy-planes of Fe(II) ions. In the crystal structures, cylindrical voids were formed along the chain axis being surrounded by four chains in 1·3MeNO(2), 2·2MeNO(2)·H(2)O, and 4·4EtNO(2) and two chains in 3·3.5MeNO(2), and solvent molecules as well as coordination-free perchlorate anions occupied these voids in a slightly different fashion depending on the complexes. 2·2MeNO(2)·H(2)O maintains its chemical composition in a dried condition, whereas 1·3MeNO(2), 3·3.5MeNO(2), and 4·4EtNO(2) easily release solvent molecules to give 1, 3, and 4, respectively. 1 and 3 maintain the crystalline character showing slightly different X-ray diffraction (XRD) patterns from those of 1·3MeNO(2) and 3·3.5MeNO(2), and an enhancement of SCM character after release of the solvent molecules was observed for both. 4 lost crystalline character to become amorphous, and it lost the SCM character at the same time.

Chiral molecular conductor with an insulator-metal transition close to room temperature.

Materials exhibiting both chirality and conductivity do not exist in nature and very few examples have been synthesised. We report here the synthesis of a chiral molecular metal which remains metallic down to at least 4.2 K. This material also exhibits room-temperature switching capabilities with a transition upon cooling below 10 °C.

Mobility of hydrated alkali metal ions in metallosupramolecular ionic crystals.

The design and creation of ionic crystals that show high mobility of ionic species in the solid state has long been a research topic of considerable attention not only due to the practical applications of these materials but also due to the correlation of such ionic species with ion-transport biological systems. In this work, we report the mobility of alkali metal ions (M = Li+, Na+, K+) in the ionic crystals M6[Rh4Zn4O (l-cysteinate)12]·nH2O (M6[1]·nH2O). In M6[1]·nH2O, alkali metal ions are distributed in a disordered manner, together with a number of water molecules, within a rigid hydrogen-bonded framework of anionic clusters of [1]6-. The alternating current conductivities of M6[1]·nH2O in the solid state increase in the order of Li6[1]·nH2O < Na6[1]·nH2O < K6[1]·nH2O, which is opposite to the order of the naked ionic radii. The conductivities reach the superionic level of σ = 1.3 × 10-2 S cm-1 at 300 K for a single crystal of K6[1]·nH2O. These results reflect the high mobility of hydrated alkali metal ions in the crystal lattice of M6[1]·nH2O, which is supported by solid-state NMR spectroscopy, together with ion diffusion experiments in the solid state. The high mobility leads to quick exchange of K+ ions in K6[1]·nH2O with Li+ and Na+ ions with retention of single crystallinity.

Electron Transport in Carbon Nanotubes with Adsorbed Chromium Impurities.

We employ Green's function method for describing multiband models with magnetic impurities and apply the formalism to the problem of chromium impurities adsorbed onto a carbon nanotube. Density functional theory is used to determine the bandstructure, which is then fit to a tight-binding model to allow for the subsequent Green's function description. Electron⁻electron interactions, electron⁻phonon coupling, and disorder scattering are all taken into account (perturbatively) with a theory that involves a cluster extension of the coherent potential approximation. We show how increasing the cluster size produces more accurate results and how the final calculations converge as a function of the cluster size. We examine the spin-polarized electrical current on the nanotube generated by the magnetic impurities adsorbed onto the nanotube surface. The spin polarization increases with both increasing concentration of chromium impurities and with increasing magnetic field. Its origin arises from the strong electron correlations generated by the Cr impurities.

Construction of a low-temperature thermodynamic measurement system for single crystal of molecular compounds under pressures.

An apparatus to obtain low-temperature thermodynamic information under high pressures for a tiny single crystal of molecular compounds was developed based on the ac technique. To detect small temperature oscillation of a sample inside the cramp-type pressure cell, we have used a small ruthenium oxide chip sensor as a thermometer. The adoption of the four-terminal method by the ac resistance bridge has made high-resolution detection of thermal anomaly possible in the low-temperature region. The constructed high-pressure thermodynamic system was mounted on a 3He refrigerator and we have succeeded to detect the thermal anomaly in relevant to magnetic order of single crystal sample of Mn4-cluster complex up to 1.05 GPa. A distinct peak of the heat capacity and its upward shift with increasing pressures was observed using a tiny crystal of about 100 microg. The high-pressure behavior of the discontinuity of heat capacity at the superconductive transition of 6 mg of metal indium has also been detected by this apparatus. The details and performance of the technique are reported.

Dielectric Jump and Negative Electrostriction in Metallosupramolecular Ionic Crystals.

In natural ionic solids, cationic and anionic species are alternately arranged to minimize electrostatic energy. Aggregation of identical ionic species is commonly prohibited due to the repulsive, long-range nature of Coulombic interactions. Recently, we synthesized unique ionic solids, [AuI4CoIII2(dppe)2(D-pen)4]X2·nH2O (dppe = 1,2-bis(diphenylphosphino)ethane, D-pen = D-penicillaminate), in which complex cations are self-assembled into a cationic supramolecular octahedron, while monovalent or divalent inorganic anions are aggregated into an anomalous anionic cluster accommodating several water molecules. This quite unusual aggregation manner originates from various molecular-level non-Coulombic interactions such as hydrogen bonds and CH-π interactions; thus, this class of ionic solids is referred to as non-Coulombic ionic solids, abbreviated as NCISs. Herein, we report that the NCISs with a peculiar charge-separated (CS) structure in a cubic lattice show a negative, isotropic electrostriction phenomenon that has never been found in any ionic solids, as well as an anomalously large relaxer-like dielectric jump phenomenon reaching to an application level of ε'/ε0 ~ 105. The appearance of these phenomena was explained by the cooperative dynamics of inorganic anions and dipolar water molecules in the pliable anionic clusters that are surrounded by a rather robust cationic metallosupramolecular framework with a meso-scopic scale.