Novel spin transition between S = 5/2 and S = 3/2 in highly saddled iron(III) porphyrin complexes at extremely low temperatures

A novel spin transition between S = 5/2 and S = 3/2 has been observed for the first time in five-coordinate, highly saddled iron(III) porphyrinates by EPR and SQUID measurements at extremely low temperatures.     

A directly fused tetrameric porphyrin sheet and its anomalous electronic properties that arise from the planar cyclooctatetraene core

Oxidation of a directly meso-meso linked cyclic porphyrin tetramer 2 gave a porphyrin sheet 3. The symmetric square structure of 3 is indicated by its simple 1H NMR spectrum that exhibits only two signals for the porphyrin beta-protons. The absorption spectrum of 3 displays characteristic Soret-like broad bands and weak Q-bands, and its magnetic circular dichroism (MCD) spectrum exhibits a negative Faraday A term at the 762 nm band as a rare case, indicating the absorption as a transition from a nondegenerate level to a degenerate level. A slightly longer S1-state (1.1 ps) and smaller TPA cross section (2750 GM) than a tetrameric linear porphyrin tape also indicate its unique electronic properties. The porphyrin sheet 3 forms stable 1:2 complexes with guest molecules G1 and G2, whose 1H NMR spectra exhibit remarkable downfield shifts for the guest protons that are located just above the cyclooctatetraene (COT) core of 3, whereas the imidazolyl protons bound to the zinc(II) porphyrin local cores are observed at slightly upfield positions. These results have been qualitatively accounted for in terms of the presence of a strong paratropic ring current around the COT core that propagates through the whole pi-electronic network of 3, hence competing with and cancelling the weak diatropic ring currents of the local zinc(II) porphyrins. This explanation was supported by DFT calculation performed at the GIAO-B3LYP/6-31G level, which indicated large positive NICS values within the COT core and small NICS values within the local zinc(II) porphyrins.     

Direct crystallographic observation of a coordinatively unsaturated transition-metal complex in situ generated within a self-assembled cage

In situ crystallographic observation of an extremely labile coordinatively unsaturated transition-metal complex, Cp'Mn(CO)2 (Cp' = methylcyclopentadienyl), was achieved by generating and trapping it within the confined cavity of a self-assembled cage in the crystalline state at a low temperature. The labile target Cp'Mn(CO)2 was formed by the photodissociation of the CO ligand from stable Cp'Mn(CO)3, which was accommodated within the cavity of the coordination cage. Being trapped in the cage at a low temperature, Cp'Mn(CO)2 showed sufficient stability to be analyzed by X-ray crystallography. The diffraction study revealed that the 16-electron unsaturated Mn complex adopted a pyramidal geometry rather than a planar geometry.     

Soft lithographic patterning of supported lipid bilayers onto a surface and inside microfluidic channels

We present simple soft lithographic methods for patterning supported lipid bilayer (SLB) membranes onto a surface and inside microfluidic channels. Micropatterns of polyethylene glycol (PEG)-based polymers were fabricated on glass substrates by microcontact printing or capillary moulding. The patterned PEG surfaces have shown 97 +/- 0.5% reduction in lipid adsorption onto two dimensional surfaces and 95 +/- 1.2% reduction inside microfluidic channels in comparison to glass control. Atomic force microscopy measurements indicated that the deposition of lipid vesicles led to the formation of SLB membranes by vesicle fusion due to hydrophilic interactions with the exposed substrate. Furthermore, the functionality of the patterned SLBs was tested by measuring the binding interactions between biotin (ligand)-labeled lipid bilayer and streptavidin (receptor). SLB arrays were fabricated with spatial resolution down to approximately 500 nm on flat substrate and approximately 1 microm inside microfluidic channels, respectively.     

Adsorption of pyrimidine molecules on Pd(110) observed by scanning tunneling microscopy

Adsorbed states of pyrimidine molecules on Pd(110) have been studied by a scanning tunneling microscope (STM). The pyrimidine molecules are preferentially adsorbed on terraces, not at steps. The isolated pyrimidine molecule shows a 0.6 nm × 0.6 nm rectangular shape with two parts of elongated protrusions. Two adsorption sites are observed: on-top site of the Pd[1 0] row and the midway between two [1 0] rows. Pyrimidine molecules show a strong tendency to form dimers even at a low coverage (0.01 ML), indicating that there is an attractive interaction between two adsorbed molecules.     

Solvent-driven association and dissociation of the hydrogen-bonded protonated decavanadates

Hydrogen-bond-assisted molecular aggregation of decavanadate anions, [H(n)V(10)O(28)]((6-n)-), in non-aqueous solutions was probed by systematic small-angle X-ray scattering and (1)H and (51)V NMR spectroscopic measurements in mixtures of acetone and 1,4-dioxane. Under acetone-rich conditions, the decavanadate anion prefers a self-associated hydrogen-bonded dimer of {[H(3)V(10)O(28)](2)}(6-), which dissociates into monomeric species as the proportion of 1,4-dioxane increases. The association/dissociation behaviors of the decavanadate anions were proven to be reversible and driven by the protophobic/protophilic nature of the solvent.     

Preparation and StructuralCharacterization of RuII‐DMSO and RuIII‐DMSO‐substituted α‐Keggin‐type Phosphotungstates, [PW11O39RuIIDMSO]5– and [PW11O39RuIIIDMSO]4–, and Catalytic Activity for Water Oxidation

Ru^II‐ and Ru^III‐substituted α‐Keggin‐type phosphotungstates with a dimethyl sulfoxide (DMSO) ligand, [PW₁₁O₃₉Ru^IIDMSO]^5– ( 1 ) and [PW₁₁O₃₉Ru^IIIDMSO]^4– ( 2 ), were synthesized. Compound 1 was prepared by reaction of [PW₁₁O₃₉]^7– with [Ru^II(DMSO)₄]Cl₂ in water at 125 °C under hydrothermal conditions and was isolated as a cesium salt. Compound 2 was prepared by reaction of 1 with bromine in water at 60 °C and was isolated as a cesium salt. The compounds were characterized by cyclic voltammetry, elemental analysis, UV/Vis, IR,³¹P NMR, ¹⁸³W NMR, ¹H NMR, and XANES (Ru K‐edge and L₃‐edge)spectroscopic methods. Single crystal structural analysis of 1 revealed that Ru^II is incorporated in the α‐Keggin framework and coordinated by DMSO through a Ru–S bond. Cyclic voltammetry of 1 indicated that the incorporated Ru^II‐DMSO is reversibly oxidizable to the Ru^III‐DMSO derivative 2 . Compound 1 showed catalytic activity for water oxidation in the presence of cerium ammonium nitrate as an oxidant.     

Spatial nonuniformity in resistive-switching memory effects of NiO

Electrically driven resistance change phenomenon in metal/NiO/metal junctions, so-called resistive switching (RS), is a candidate for next-generation universal nonvolatile memories. However, the knowledge as to RS mechanisms is unfortunately far from comprehensive, especially the spatial switching location, which is crucial information to design reliable devices. In this communication, we demonstrate the identification of the spatial switching location of bipolar RS by introducing asymmetrically passivated planar NiO nanowire junctions. We have successfully identified that the bipolar RS in NiO occurs near the cathode rather than the anode. This trend can be interpreted in terms of an electrochemical redox model based on ion migration and p-type conduction.