Magnetic Correlation Engineering in Spin-Sandwiched Layered Magnetic Frameworks

The insertion of “sandwiched spins” between magnetic layers could efficiently affect the interlayer magnetic correlations, but doing so increases the complexity in the interlayer spin alignment because of competition between the inserted spin-layer interaction J_NNI and the interlayer through-space interaction J_NNNI if the magnitude of J_NNI is of the same order as J_NNNI with reciprocal signs of the respective interactions. Herein, systematic tuning of the magnetic phase variations by J_NNI and J_NNNI in two kinds of metal-variable isostructural series of supramolecular pillared layer magnets [MCp*₂][{Ru₂^II,II(2,3,5,6-F₄CO₂)₄}₂(TCNQ)] ⋅ 2 DCE (M=Co, Fe, Cr; 2,3,5,6-F₄PhCO₂⁻=2,3,5,6-tetrafluorobenzoate; TCNQ=7,7,8,8-tetracyano-p-quinodimethane; DCE=1,2-dichloroethane) and their DCE-free series, in which [MCp*₂]⁺ (Cp*=η⁵-C₅Me₅) species with S=0, 1/2, and 3/2 for M=Co, Fe, Cr, respectively, are sandwiched between ferrimagnetic layers of [{Ru₂}₂(TCNQ)]⁻, is demonstrated. The results showed that the flexible magnetic natures of these magnets are changeable in dependence on J_NNI and J_NNNI, as well as on interlayer inserted spins M.     

A solid-state dye-sensitized photovoltaic cell with a poly(N-vinyl-carbazole) hole transporter mediated by an alkali iodide

A polymer-based dye-sensitized solar cell in dry solid state was constructed using poly(N-vinyl-carbazole)(PVK) as a hole-transporting layer; the cell attained the highest power efficiencies of 2.4% and 2.0% at 1/4 sun and 1 sun (AM1.5), respectively, by incorporation of a solid intermediate layer (LiI, KI) at the dye-PVK interface.     

Drawing of single-crystal mats of linear polyethylene

Drawing of single-crystal mats of linear polyethylene has been investigated. Drawing is possible at temperatures higher than about 90°C. The drawing is accompanied by distinct necking, with a large decrease in the thickness of the mat and a very high maximum draw ratio, sometimes over 30. The maximum draw ratio is approximately proportional to the thickness of the lamellae. This behavior strongly suggests the unfolding of chains during drawing. A change of orientation of crystal axes occurs before necking without change of lamellar orientation. The a axis orients in the drawing direction; the b axis orients perpendicular to the direction of drawing; and the chain axis tilts away from the thickness direction of the mat. The structure of films drawn from mats is characterized by a distinct double orientation of crystals. This biaxial orientation in the drawn films has a high degree of correlation with the orientation of crystal axes observed before necking, and suggests that necking takes place in such a way that the chain tilts gradually about the b axis and ultimately unfolds. The postulate of formation of transitory two-dimensional crystals in necking seems useful in explaining the double orientation in the drawn film. The orientation behavior of crystal axes observed before necking is not always similar to that observed in the deformation of a single crystal. The difference is thought to be due to the effect of forces induced by drawing that act in the direction normal to the lamellae within a mat.     

Photoelectrochemical Verification of Proton-Releasing Groups in Bacteriorhodopsin

Light-induced transient currents of bacteriorhodopsin (bR) and its mutants (D96N, D85N, E204Q and E194Q) were measured at the interface of an electrode and the aqueous solution in an electrochemical cell. The transient positive (cathodic) and negative (anodic) photocurrents generated upon the onsets of continuous illumination and of turning off light, respectively, were investigated at different electrolyte pH. The wild type exhibits both positive and negative responses, with the sign of the response inverted at pH lt 5. In D85N the response is entirely suppressed, while D96N lacks the negative response. Laser pulse excitation (532 nm) of bR and the mutants showed the response rise time of the positive transient to be uniformly about 100 μs, indicating that the response is linked to the L to M transition in the photocycle. According to these results the positive and negative signals originate from the proton release and uptake reactions, respectively. Photoexcitation of the mutants E204Q and E194Q that lack protonatable residues at position 204 and 194, respectively, produced a negative response at neutral pH, which indicates that in these proteins proton uptake precedes proton release. This result is consistent with our observations made earlier with pH indicator dyes and demonstrates that Glu-204 and Glu-194 constitute the terminal proton release complex in the extracellular region of bR.     

Mn2(saltmen)2Ni(pao)2(L)2](A)2 with L=pyridine, 4-picoline, 4-tert-butylpyridine, N-methylimidazole and A=ClO4-, BF4-, PF6-, ReO4-: a family of single-chain magnets

A series of single-chain magnets, [Mn2(saltmen)2Ni(pao)2(L)2](A)2 (saltmen(2-)=N,N'-(1,1,2,2-tetramethylethylene) bis(salicylideneiminate), pao-=pyridine-2-aldoximate; A-=ClO4- with L=4-picoline; 2, 4-tert-butylpyridine; 3, N-methylimidazole; 4, and L=pyridine with A-=BF4-; 5, PF6-; 6, ReO4-; 7), was prepared by reactions between MnIII dimer units, i.e., [Mn2(saltmen)2(H2O)2](A)2 (A-=ClO4-, BF4-, PF6-) or Mn2(saltmen)2(ReO4)2, and NiII monomeric units, i.e., Ni(pao)2(L)2, in methanol/water media. The crystal structures of 4, 6, and 7 were established by single-crystal X-ray crystallography. These three compounds are isostructural with [Mn2(saltmen)2Ni(pao)2(py)2](ClO4)2 (1) (Clérac, R.; Miyasaka, H.; Yamashita, M.; Coulon, C. J. Am. Chem. Soc. 2002, 124, 12837) and crystallize in monoclinic space group C2/c. The linear arrangement of MnIII dimer units and NiII building blocks leads to an alternating chain having a repeating unit, [-(O)2-Mn-ON-Ni-NO-Mn-]. The chains are well separated with the nearest interchain intermetallic distance of 10.36 A for 4, 10.51 A for 6, and 10.30 A for 7, and there is no significant pi-pi interchain interaction between ligands. The void space between the chains is occupied by counteranions, which control the three-dimensional organization of the chains. The X-ray diffraction analysis (XRD) on a powder sample was also performed for all compounds. The XRD patterns for 1, 2, and 4-7 are very similar, emphasizing the isostructural nature of these materials although they have individually slight different interchain distances. Inversely, the XRD pattern for 3 reveals a completely different shape being indicative of the peculiar crystal packing compared to the others. Nevertheless, the one-dimensional nature of the structure is also kept in 3 as indicated by magnetic measurements. The whole family of compounds exhibits quasi-identical magnetic behavior compared to that described for 1. Above 30 K, the heterometallic chain can be described as an assembly of antiferromagnetically coupled Mn...Ni....Mn trimers (via oximate bridge, -24.2 K相似文献   

Carrier doping effect into quasi-one-dimensional bromo-bridged Ni(III) complexes with strong electron-correlation by Cu(II) ions, [Ni1-xCux(chxn)2Br]Br2-x

This communication will describe the electron doping effect into Ni(III) complexes by Cu(II) ions, [Ni(1-x)Cu(x)(chxn)(2)Br]Br(2-x) (x = 0.038 and 0.101) by using an electrochemical oxidation method. A drastic increase of electrical conductivity as well as a new absorption band around 0.5 eV in single crystal reflectance spectra was observed by doping Cu(II) ions, indicating the electron doping was successfully made. An ESR result shows unpaired electrons locate in the d(x2-y2) orbitals of Cu(II) and have almost no interaction with those of other ions.     

“Umpulong” of reactivity at the C-6 position of uridine: a simple and general method for 6-substituted uridines

Lithiated 2′,3′-O-isopropylidine-5′-$\text{O}$-methoxymethyl-uridine was found to react with a variety of electrophilic reagents regiospecifically at the C-6 position. The protecting groups of the ribose moiety in the 6-functionalized products were concurrently removed under mild conditions with aqueous trifluoroacetic acid. Consequently, the present method permits simple and general syntheses of 6-substituted uridines.     

CO2-Induced Spin-State Switching at Room Temperature in a Monomeric Cobalt(II) Complex with the Porous Nature

CO₂-responsive spin-state conversion between high-spin (HS) and low-spin (LS) states at room temperature was achieved in a monomeric cobalt(II) complex. A neutral cobalt(II) complex, [Co^II(COO-terpy)₂]⋅4 H₂O ( 1⋅4 H₂O ), stably formed cavities generated via π–π stacking motifs and hydrogen bond networks, resulting in the accommodation of four water molecules. Crystalline 1⋅4 H₂O transformed to solvent-free 1 without loss of porosity by heating to 420 K. Compound 1 exhibited a selective CO₂ adsorption via a gate-open type of the structural modification. Furthermore, the HS/LS transition temperature (T_1/2) was able to be tuned by the CO₂ pressure over a wide temperature range. Unlike 1 exhibits the HS state at 290 K, the CO₂-accomodated form 1⊃CO₂ (P =110 kPa) was stabilized in the LS state at 290 K, probably caused by a chemical pressure effect by CO₂ accommodation, which provides reversible spin-state conversion by introducing/evacuating CO₂ gas into/from 1 .