Published papers

The outstanding properties of diamond make it a very attractive material for use in many potential applications. In particular, the superior electrochemical properties of highly boron-doped conductive diamond films, prepared by the chemical vapor deposition (CVD) process, have received attention from electrochemists. This paper reports several diversified applications of boron-doped diamond electrodes; highly sensitive and interference-free microfiber electrodes with over-oxidized polypyrrole modification, integrated electrochemical detector for microchip capillary electrophoresis (CE), and smoothing treatments of micro-polycrystalline surface. Studies have been made of the electrochemical properties of each system and their application in electroanalysis is discussed. © 2004 Elsevier Ltd. All rights reserved.

Hybrid films of Prussian blue (PB), clay nanosheets, and alkylammonium cations were prepared by a combined method of Langmuir-Blodgett and self-assembly techniques. The absorbance at 700 nm for the hybrid film increased quadratically up to the 20th layer, and over the 20th layer it increased linearly. This indicated that the hybrid layers were built up in a layer-by-layer way over the 20th layer. X-ray diffraction (XRD) patterns of the film showed that stable thin sheets of PB were formed in the film, and that the in-plane structure of the PB sheet was identical to that of polycrystalline PB. © 2002 Elsevier B.V. All rights reserved.

Four cyano-bridged 3d-4f hetero-bimetallic Ln(III)-Fe(III) assemblies, {[Ln(DMF)4(H2O)3(μ-CN)Fe(CN)5] · H2O)n (Ln = Ce (1), Nd (2), Sm (3) and Gd (4); DMF = N,N-dimethylformamide), have been synthesized. X-ray crystallographic analysis of both 3 and 4 reveals three-dimensional network structures resulting from hydrogen bonds in the crystals. With respect to the coordination number on Sm(III) atoms, 3 is different from previously reported structures. Structural comparison indicates that the differences in magnetic properties between 3 and 4 do not derive from structural factors. Mössbauer spectra at both 298 and 10 K reveal that the characteristic quadrupole splitting for low-spin Fe(III) ions (S = 1/2) remains unchanged, indicating that the spin state of Fe(III) ions in 1-4 is not affected by temperature. The magnetic anisotropy derived from the ground states of Ln(III) ions with odd 4fn electrons (n = 1, 3, 5 and 7), 2F5/2, 4I9/2, 6H5/2 and 8S7/2 for Ce(III), Nd(III), Sm(III) and Gd(III), respectively, dominates the exchange interaction in the Ln(III)-NC-Fe(III) systems.

The title compound, [Cu(C15H11N2O 2)2(C8H11N)2], has its metal atom in a square-planar trans-CuN4 coordination environment; the CuII atom lies on a center of symmetry. The 5,5- diphenylhydantoinate and 2-phenylethylamine ligands behave as monodentate ligands and bind through their N atoms. The crystal structure is stabilized by N-H⋯O=C intermolecular hydrogen bonds [N⋯O = 2.864 (3) Å]. © 2004 International Union of Crystallography Printed in Great Britain - all rights reserved.

Co-Fe Prussian blue thin films have been prepared by means of a modified Langmuir-Blodgett technique, in which the hybrid monolayer composed of amphiphiles and clay platelets plays a template role for the formation Co-Fe Prussian blue thin films. Photoinduced magnetization was observed in the thin films as observed in the bulk Co-Fe Prussian blue. To the best of our knowledge, this is the first example of successful formation of Co-Fe Prussian blue thin films, which possess the ordered structure and, in addition, exhibit photoinduced magnetization.

The title compound, [Cu(C10H11ClNO)2], has been structurally characterized in the low-temperature phase (brown form). It adopts a stepped conformation and affords a square-planar frans-[CuN 2O2] coordination geometry, in which the CuII ion lies on a center of symmetry. The Cu - N and Cu - O bond distances are 2.032 (3) and 1.891 (2) Å, respectively. © 2004 International Union of Crystallography Printed in Great Britain - all rights reserved.

The crystal structure of the bis(acetone-κO)bis(N,N′- dimethylethylenediamine-κ2N,N′)copper(II) diperchorate was investigated. It was found that an elongated octahedral trans-[CuN 4O2] coordination geometry was adopted by the complex compound. Two ligands, at the axial sites having O-M-O axial acetone bonds, were also observed in the crystal structure of the metal complex. The results show that the bond length for inplane Cu-N is 2.041(3) Å and that for axial Cu-O is 2.507 (5) Å.

A novel photocontrollable magnetic thin film consisting of amphiphilic azobenzene cations, a smectite clay, and Prussian Blue has been designed and prepared by using the Langmuir-Blodgett method and an ion-exchange reaction. This magnetic thin film possesses a well-organized nanoscale layered structure. Reversible photoisomerization of the azobenzene chromophore realized photoswitching of the magnetization. The changes in the magnetization values were estimated to be ca. 11%. This figure was much larger than our previous system, which contained azobenzene multi-bilayered vesicles in a poly(vinyl alcohol) matrix (J. Am. Chem. Soc. 1999, 121, 3745). These larger changes in the magnetization values are due to the highly ordered structure of the hybrid multilayered films.

Photoinduced magnetization of the cyano-bridged 3d-4f hetero-bimetallic assembly Nd (DMF)4(H2O)3(μ-CN)Fe(CN)5.H2O (1) (DMF = N,N-dimethylformamide) is described in this paper. The χMT values are enhanced by about 45% after UV light illumination in the temperature range of 5-50 K. We propose that UV light illumination induces a structural distortion in 1. This small structural change is propagated by molecular interactions in the inorganic network. Furthermore, the cooperativity resulting from the molecular interaction functions to increase the activation energy of the relaxation processes, which makes observation of the photoexcited state possible. The flexible network structure through the hydrogen bonds in 1 plays an essential role for the photoinduced phenomenon. This finding may open up a new domain for developing molecule-based magnetic materials. © 2004 Kluwer Academic Publishers.

In the title compound, [Cu(ClO4)2(C4H 12N2)2], the Cu atom is located at a center of symmetry. It adopts an elongated octahedral trans-[CuN4O2] coordination geometry, which is a typical feature of the pseudo-Jahn-Teller effect. The axial Cu-O bond length is 2.605 (4) Å, while the in-plane Cu-N bond lengths are 1.987 (2) and 2.098 (2) Å. © 2004 International Union of Crystallography Printed in Great Britain - all rights reserved.

Photo-controllable molecular systems, [M(en)2][Pt(en) 2Cl2](1)4 (M2+=Pt2+, Pd2+ and en=ethylenediamine), have been designed by the self-assembly of chloride-bridged platinum/palladium complexes and photochromic amphiphiles of the azobenzene derivative, 4-[4-(N-methyl-N-n-dodecylamino)phenylazo]benzene sulfonic acid (designated as compound 1). Reversible structural changes caused by cis-trans photoisomerization of azo groups in compound 1 were observed by alternating illumination of UV and visible light. Visible illumination resulted in the formation of the plate-like structures, whereas UV illumination resulted in fragmentation of the assembling structures. Reversible changes were observed in the electronic states of the chloride-bridged platinum/palladium complexes; the plate-like structures exhibited charge transfer absorption of chloride-bridged platinum complexes and delocalized Pt(II)/Pt(IV) states, while the fragments of the separated complexes exhibited no charge transfer bands. As a consequence, we have discovered that the reversible structural changes in this system could be controlled by photoillumination. © 2004 Elsevier B.V. All rights reserved.

We have systematically investigated the structural features, electronic properties, thermally-induced structural phase transitions and absorption spectra depending on the solvent for ten Cu(II) complexes with 3,5-halogen-substituted Schiff base ligands. Structural characterization of two new complexes, bis(N-R-1-phenylethyl- and N-R,S-2-butyl-5-bromosalicydenaminato- κ2N,O)copper(II), reveals that they afford a compressed tetrahedral trans-[CuN2O2] coordination geometry with trans-N-Cu-N = 159.4(2)° and trans-O-Cu-O = 151.7(3)° for the 1-phenylethyl complex and trans-N-Cu-N = 157.9(3)° and trans-O-Cu-O = 151.0(3)° for the 2-butyl one. All the complexes exhibit a structural phase transition by heating in the solid state regardless of their structures at room temperature. The absorption spectra of a series of ten complexes exhibit a slight shift of the d-d band at 16 000-20 000 cm-1 and remarkable shift of the π-π* band at 24 000-28 000 cm-1, which suggests that the dipole moment of the solvents presumably affects the conformation of the π-conjugated moieties of the ligands rather than the coordination environment. We have also attempted 'photochromic solute-induced solvatochromism' by a system of bis(N-R-1-phenylethyl-3,5- dichlorosalicydenaminato-κ2N,O)copper(II) and photochromic 4-hydroxyazobenzene in chloroform solution. We successfully observed a change of the d-d and π-π* bands of the complex in the absorption spectra caused by cis-trans photoisomerization of 4-hydroxyazobenzene. © 2005 Elsevier Ltd. All rights reserved.

Pt-modified diamond electrodes were fabricated for electroanalytical applications by implantation method at 750 keV Pt2+ with a dose of 5 × 1014 cm- 2. The electrochemical behavior has been studied for oxidation of hydrogen peroxide by using cyclic voltammetry and flow injection analysis in phosphate buffer solution (pH 7). The electrode exhibited high catalytic activity and excellent electrochemical stability with a very low background current in comparison to Pt metal electrode. Very low limit of detection, 30 nM (S / N = 3), were examined with RSD of 2.91% (n = 20). These results indicate that metal-implanted method could be a promising method for controlling the electrochemical properties of diamond electrodes. © 2005 Elsevier B.V. All rights reserved.

Thin films of cobalt-iron cyanide (Co-Fe Prussian blue) have been fabricated by means of the modified Langmuir-Blodgett (LB) method using a smectite clay mineral (montmorillonite). In this combined method, clay LB films play a template role in the formation of the Co-Fe Prussian blue thin layer. The films were revealed to possess a well-organized structure not only in perpendicular directions to the film surface but also in parallel directions to the film surface. The photoinduced electron transfer from the iron ion to the cobalt through the bridging cyanide in the films occurred at low temperature (8 K), similar to that in the bulk Co-Fe Prussian blue. The films clearly exhibited magnetic anisotropy with regards to the direction of the applied magnetic field. Moreover, the photoinduced magnetization effect in the films was also found to be anisotropic. © 2005 American Chemical Society.

Two new mononuclear nickel (II) complexes incorporating Schiff base ligands, bis(N-R-1-phenylethyl- or N-2-propyl-3,5-dichlorosalicydenaminato) nickel (II), have been synthesized and characterized. The former chiral brown paramagnetic complex adopts a compressed tetrahedral [NiN2O 2] coordination geometry of Λ(R,R) absolute configuration with the coordination bond angles of N-Ni-N = 116.3(2)°and O-Ni-O = 141.4(2)°. On the other hand, the latter green diamagnetic complex adopts a square planar trans-[NiN2O2] coordination geometry. It is revealed that flexible distortion of the [NiN2O2] coordination environment and the overall dipole moment of the complexes are affected by both electronic withdrawing Cl-substituents and steric factors of the ligands. A structural phase transition occurs by heating in the solid state for both complexes. Negative solvatochromism relating to d-d and π-π* transitions can be observed, depending on the polarity of the solvents in which these complexes are dissolved. Furthermore, we have attempted to design a supramolecular solvatochromism system induced by a photochromic solute, that is a CHCl3 solution of the chiral Ni(II) complex and polar 4-hydroxyazobenzene solute. After UV light irradiation, we have successfully observed slight spectral changes of the π-π* bands in absorption and CD spectra due to conformational change of the R-1-phenylethylamine moieties of the chiral ligands. © 2005 Elsevier Ltd. All rights reserved.

The Ni(dmit) 2 salt with an Fe(III) spin-crossover cation, Fe(qsal)2, was prepared and showed a cooperative spin transition based on π-π interactions between π-ligands. The light-induced excited spin state trapping effect on this complex was also observed. Copyright © 2005 The Chemical Society of Japan.

A novel type of photocontrollable Prussian blue (PB) magnetic nanoparticle has been designed and prepared by using the reverse micelle technique. These magnetic nanoparticles possess a well-organized nanoscale structure. Reversible photoisomerization of azobenzene chromophores realized photoswitching of the magnetization. The photoisomerization of the composite materials was accompanied by a geometrically confined structural change within the reverse micelles, as reflected by changes in the dipole moment and the electrostatic field. As a result, the magnetization values could be switched reversibly by using alternating UV and visible light illumination. © 2005 American Chemical Society.

Electrochemical behavior of gold-nanoparticle-dispersed diamond electrodes have been studied for the oxidation of oxalic acid in phosphate buffer solution. Comparison is made with gold, as-deposited diamond and gold-implanted diamond. The electrodes combine the high catalytic activity of gold and the low background current of diamond electrodes. Moreover, the electrodes can overcome the problem of stability as it is found when using other electrodes. Copyright © 2005 The Chemical Society of Japan.

Two kinds of cobalt-iron cyanides (Rb0.66Co1.25[Fe(CN)6]·4.3H2O and Co1.5[Fe(CN)6]·6H2O) with different electronic structures have been investigated to understand the photoinduced long-range magnetic ordering. Rb0.66Co1.25[Fe(CN)6]·4.3H2O produces a photomagnetic effect, whereas Co1.5[Fe(CN)6]·6H2O does not respond to light. FT-IR and Mossbauer studies revealed that their oxidation states are expressed as Rb0.66CoIII0.84CoII 0.41-[FeII(CN)6] and CoII1.5[FeIII(CN)6], respectively. The difference in the oxidation states of the metal atoms in these two compounds has been explained by the Co coordination with H2O or CN ligands. In the case of Rb0.66Co1.25[Fe(CN)6]·4.3H2O, more CN ligands are involved in coordination than expected in the case of Co1.5[Fe(CN)6]· 6H2O. A charge-transfer (CT) band from FeII to CoIII is observed at around 550 nm for Rb0.66Co1.25[Fe(CN)6]· 4.3H2O. The magnetism of Rb0.66Co1.25[Fe(CN)6]·4.3H2O changed from paramagnetic to ferrimagnetic due to the CT from FeII to CoIII when illuminated at low temperature. The Curie temperature after illumination was 22 K. This metastable state was stable for more than several days at 5 K. The metastable state was restored back to its original one when the sample was heated to 120 K. It is considered that the interconversion proceeded via a pronounced domain formation. © 1999 American Chemical Society.

The local structure of a trapped photoexcited state of a Fe-Co cyanide magnetic material, Na0.4Co1.3Fe(CN)6·5H2O, was investigated by Fe and Co K-edge x-ray-absorption fine-structure spectroscopy. The excited state was prepared by visible-light irradiation at 36 K. In order to obtain detailed structural information, temperature dependence of the local structure was also studied without light irradiation. The Fe-C distance shows almost no change by light irradiation (1.92 Å before and after irradiation), while the average Co-N/O distance is noticeably elongated (1.94 and 2.08 Å before and after irradiation, respectively). This phase transformation is caused by the charge transfer from the FeII(S=0)·CN-CoIII(S=0) configuration to FeIII(S =1/2)-CN-CoII(S=3/2). The local structure of the trapped photoexcited state was found to be identical with that of the high-temperature phase, although the high-temperature phase was created much more effectively by light irradiation than thermal activation. ©1999 The American Physical Society.