Tamotsu Inabe

Ferromagnetic coupling in a new phase of the p-nitrophenyl nitronyl nitroxide radical

Abstract The crystal structure of a new phase of the p -nitrophenyl nitronyl nitroxide radical compound is described. A study of its magnetic properties reveals the largest intermolecular ferromagnetic coupling reported so far among a series of polymorphs of this compound.

Highly conductive metallophthalocyanine assemblies. Structure, charge transport, and anisotropy in the metal-free molecular metal H2(Pc)I

Abstract That a metal ion is not required for high electrical conductivity is unequivocally demonstrated by structural, charge transport, optical, and magnetic characterization of the simplest phthalocyanine “molecular metal” H 2 (Pc)I. The crystal structure consists of staggered H 2 (Pc) +0.33 units stacked at 3.251(3) A intervals and parallel chains of I − 3 counterions. At 300 K, σ ‖ = 700 Ω −1 cm −1 and σ ‖ σ⊥ > 500 . At 15 K, σ ∼ reaches a maximum of ca. 4000 Ω −1 cm −1 and falls only to ca. 3500 Ω −1‖ cm −1 at 1.5 K. Analysis of single crystal polarized specular reflectance data (ir to uv) yields ω p = 6360(30) cm −1 and a tight-binding bandwidth of 1.3(1) eV. The magnetic susceptibility is Pauli-like ( X S = 2.21(5) × 10 −4 emu mol −1 ) except for a small, sample dependent Curie component.

Ferromagnetic intermolecular interaction and crystal structure of the p-pyridyl nitronyl nitroxide radical

Abstract X-ray crystal analysis and magnetic measurements reveal the ferromagnetic linear chain with J F / k B =0.27 K in an α-nitronyl nitroxide, 2-(4-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-N-oxide.

A highly conducting partially oxidized salt of axially substituted phthalocyanine. Structure and physical properties of TPP[Co(Pc)(CN)2]2 {TPP=tetraphenylphosphonium, [Co(Pc)(CN)2]=dicyano(phthalocyaninato)cobalt(III)}

A highly conducting partially oxidized salt of TPP[Co(Pc)(CN)2 ]2 can be obtained by electrocrystallization of TPP[Co(Pc)(CN)2 ]. The crystal is composed of one-dimensional TPP arrays surrounded by slipped-stacked one-dimensional [Co(Pc)(CN)2 ] chains. The electrical conductivity at room temperature is quite high, 120 Ω–1 cm–1 , though at low temperature it is weakly semiconducting. The band width for this stacking mode has been estimated from both thermoelectric power measurements and an extended Huckel calculation. The latter suggests that the band width value for the slipped-stacking mode is about 40% of the value for the face-to-face stacking mode. The width estimated from the metallic temperature dependence of the thermoelectric power is actually in excellent agreement with that estimated from the calculation.

Ferromagnetic and antiferromagnetic intermolecular interactions in the two-dimensional triangular lattice of the m-N-methylpyridinium nitronyl nitroxide cation radical

Abstract An α-nitronyl nitroxide cation radical, 2-(3-N-methylpyridinium)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-N-oxide, has been found to possess a unique structure and magnetic properties: the molecules are manifested as dimers with a very short intermolecular contact between the NO group and the pyridinium ring, and the dimer units form an organic 2D triangular lattice. It includes both ferromagnetic and antiferromagnetic intermolecular interactions.

Giant Negative Magnetoresistance Reflecting Molecular Symmetry in Dicyano(phthalocyaninato)iron Compounds

Materials containing Fe(Pc)(CN) 2 dicyano(phthalocyaninato)iron molecules show a giant negative magnetoresistance from the interaction between the conduction and the local moment. Under a magnetic field, the resistance becomes two orders of magnitude smaller than the zero-field resistance. The magnetic-field-angle dependence of the magnetoresistance reflects the symmetry of the Fe(Pc)(CN) 2 molecule. We discuss, according to the scaling relation, the correlation between the magnetoresistance and the molecular spin fluctuation.

Large second-harmonic generation coefficients of bis(benzylidine) cycloalkanones estimated by the second-harmonic wave generated with the evanescent wave technique

Abstract The second-harmonic generation (SHG) coefficients ( d ) in a series of novel organic materials, i.e. bis(benzylidene)cycloalkanones derivatives, were estimated by means of the second-harmonic wave generated with the evanescent wave (SHEW) technique. As a result, it is found that several compounds exhibit a large d coefficient, in pentanone (MBCP). An X-ray crystallographic study reveals that the symmetry of MBCP is orthorhombic mm2. Comparison between d coefficients estimated by the SHEW and the Kurtz technique is also made.

Coupled Protonic and Electronic Conduction in the Molecular Conductor [2-(2-1H-Benzimidazolyl)-1H-benzimidazolium]–TCNQ

A novel molecular based proton-electron mixed conductor, (H3BBIM(+))(TCNQ)(Cl(-))(0.5)(H(2)O) (1), where H3BBIM(+) is 2-(2-1H-benzimidazolyl)-1H-benzimidazolium and TCNQ is 7,7,8,8-tetracyano-p-quinodimethane, was synthesized. The salt exhibited peculiar phase transitions as a result of proton-electron coupling phenomena within the crystal. Salt 1 is composed of a closed-shell H3BBIM(+) cation and an open-shell TCNQ anion radical, and was obtained by electrocrystallization in a buffered CH(3)CN solution. Crystal 1 was constructed from the segregated uniform stacks of H3BBIM(+) and TCNQ. The regular stack of partially electron-transferred TCNQ(-0.5) provided a one-dimensional electron-conducting column. Between the regular H3BBIM(+) columns, a channel-like sequence of holes was formed at the side-by-side space that is filled with disordered Cl(-) ions and H(2)O molecules, and which offer a proton-conducting path. The electrical conductivity at room temperature (10 S cm(-1)) was greater by a magnitude of four than the protonic conductivity (1x10(-3) S cm(-1)). Electronic conduction changed from metallic (T>250 K) to semiconducting (250>T>100 K), then insulating (T<100 K). Protonic conductivity was observed above 200 K. The continuous metal-semiconductor transition at 250 K is caused by the formation of the Cl(-) superstructure, whereas the disappearance of protonic conductivity at 200 K is related to the rearrangement of the [Cl(-)-(H(2)O)(2)] sublattice within the channel. The magnetic susceptibility continuously shifted from Pauli paramagnetism (T>250 K) to the one-dimensional linear Heisenberg antiferromagnetic chain (T<250 K). Lattice dimerization in regular TCNQ columns was confirmed by the appearance of vibrational a(g) mode at low temperatures. The strong localization of conduction electrons on each TCNQ dimer caused a Mott transition at 100 K. The melting and freezing of the [Cl(-)-(H(2)O)(2)] sublattice within the channel was correlated to the conduction electrons on the TCNQ stack and the protonic conductivity.

Magneto-structural correlation in a series of iodide salts of p-N-alkylpyridinium nitronyl nitroxides: dependence of the iodide-pyridinium ring interaction on the length of the N-alkyl chain

Magnetic measurements and X-ray crystal analyses were carried out on iodide salts of p-N-alkylpyridinium α-nitronyl nitroxides [4-(4,4,5,5-tetramethyl-1-oxido-3-oxyl-4,5-dihydro-3H-imidazol-2′-yl)-1-R-pyridinium, with R = methyl (1+), ethyl (2+), n-propyl (3+) and n-butyl (4+)]. The strongly antiferromagnetic crystal of 1+·I– consists of a radical dimer and the iodide ion is out of the plane of the pyridinium ring. 2+·I–, which is weakly antiferromagnetic, includes two crystallographically independent molecules, 2A+ and 2B+, each of which forms a centrosymmetric dimer. In the pyridinium ring of 2A+ the iodides are ‘out-of-plane’ while for 2B+ they are ‘in-plane’. The ferromagnetic 3+·I– and 4+·I– have similar structures: the crystal consists of a two-dimensional (2D) layer formed by a contact between the pyridinium ring and in-plane iodides. In this series, the iodide ion changes position from out-of-plane to in-plane and the magnetism varies from antiferromagnetic to ferromagnetic. It is found that the nitronyl nitroxide with an out-of-plane iodide has a short intermolecular contact between the NO groups (type I), while that with an in-plane iodide forms a contact between the NO group and the pyridinium ring (type II). The observed magnetic behaviour can be interpreted in terms of an antiferromagnetic interaction for the type I contact and a ferromagnetic interaction for type II.

Directionally tunable and mechanically deformable ferroelectric crystals from rotating polar globular ionic molecules

Ferroelectrics are used in a wide range of applications, including memory elements, capacitors and sensors. Recently, molecular ferroelectric crystals have attracted interest as viable alternatives to conventional ceramic ferroelectrics because of their solution processability and lack of toxicity. Here we show that a class of molecular compounds-known as plastic crystals-can exhibit ferroelectricity if the constituents are judiciously chosen from polar ionic molecules. The intrinsic features of plastic crystals, for example, the rotational motion of molecules and phase transitions with lattice-symmetry changes, provide the crystals with unique ferroelectric properties relative to those of conventional molecular crystals. This allows a flexible alteration of the polarization axis direction in a grown crystal by applying an electric field. Owing to the tunable nature of the crystal orientation, together with mechanical deformability, this type of molecular crystal represents an attractive functional material that could find use in a diverse range of applications.