M. Novel magnetic behavior of multidimensional organic polymer synthesized by cycloaddition reaction

We report the magnetic properties of a novel organic polymer. The material gives the large saturation magnetization (0.15G/g) at room temperature. Electron spin resonance (ESR) revealed a ferrimagnetic character, i. e., the existence of "exchange resonance branch" with extremely large g-value. The new organic polymer with large saturation magnetization can be stoichiometrically and reproducibly synthesized under ambient conditions and expected to be useful for practical applications

Solid-state high-resolution NMR studies on spin density distribution of a ferromagnetic coordination polymer: Ni(NCS)2(Him)2

We determined hyperfine coupling constants (hfcc) of the imidazole ligand in a ferromagnetic coordination polymer, di-μ-thiocyanatobis(imidazole)nickel(II), using 1H-, 2H-, and 13C-MAS-NMR. Partially or fully deuterated sample was prepared to measure temperature dependence of the isotropic shifts of NMR signals. We obtained hfcc of AC = +0.57, +0.69, +1.88 MHz for 2-, 4-, 5-carbon and AH = +0.66, +0.37, +0.48, +0.53 MHz for 1-, 2-, 4-, 5-proton in the imidazole ligand, respectively, which indicates that unpaired electron in dx2*y2 orbital of Ni(II) ion delocalizes over the imidazole ligand. On the basis of the NMR and DFT results, we proposed an interchain superexchange pathway through N-H...S hydrogen bond.http://www.sciencedirect.com/science/journal/0277538

Reversible solid-state structural conversion between a three-dimensional network and a one-dimensional chain of Cu(II) triazole coordination polymers in acidic/basic-suspensions or vapors

New Cu(II) triazole coordination polymers with 3D network were synthesized and reversible structural conversion between 3D network and 1D chain with color change was realized by pH controlled acidic and basic-suspensions or vapors. For each conversion process of decreasing and increasing pH, conversion was accomplished with high yield, in which the crystal before conversion played a role of a solid state crystal template

Magnetic Interactions of (μ-Pyrazolato)-Bridged Copper(II) Complexes Determined by Solid-State MAS NMR

We investigated electron spin densities of pyrazolato-bridged complexes [Cu(pz)2]n 1 and [Cu2(pz)2(NO3)(H2O)(phen)2]NO3 2 (Hpz = pyrazole, phen = 1, 10-phenanthroline) using solid-state high-resolution NMR to elucidate the magnetic interaction paths with the help of molecular orbital theory. We prepared deuterated analogue of these complexes, 1-d6 and 2-d6, to measure temperature dependence of 2H- and 13C-NMR shifts between 190 K and 350 K. The hyperfine coupling constants (HFCCs) and electron spin densities were determined from the slopes of the shifts as a function of the magnetic susceptibilities. The derived spin densities were all positive, which indicates the dominant magnetic interaction paths of these complexes are not π but σ orbitals of the pyrazolate ligand. The NMR results reasonably agreed with those of density functional theory (DFT) calculations for molecular models of 1 and 2.http://www.sciencedirect.com/science/journal/0277538

Structure and growth behavior of centimeter-sized helical oleate assemblies formed with assistance of medium-length carboxylic acids

The nonequilibrium organization of self-assemblies from small building-block molecules offers an attractive and essential means to develop advanced functional materials and to understand the intrinsic nature of life systems. Fatty acids are well-known amphiphiles that form self-assemblies of several shapes. Here, we found that the lengths of helical structures of oleic acid formed in a buffered aqueous solution are dramatically different by the presence or absence of certain amphiphilic carboxylic acids. For example, under the coexistence of a small amount of N-decanoyl-L-alanine, we observed the formation of over 1 centimeter-long helical assemblies of oleate with a regular pitch and radius, whereas mainly less than 100 μm-long helices formed without this additive. Such long helical assemblies are unique in terms of their highly dimensional helical structure and growth dynamics. Results from the real-time observation of self-assembly formation, site-selective small-angle X-ray scattering, high-performance liquid chromatography analysis, and pH titration experiments suggested that the coexisting carboxylates assist in elongation by supplying oleate molecules to a scaffold for oleate helical assembly

Self-Propulsion of a Light-Powered Microscopic Crystalline Flapper in Water

A key goal in developing molecular microrobots that mimic real-world animal dynamic behavior is to understand better the self-continuous progressive motion resulting from collective molecular transformation. This study reports, for the first time, the experimental realization of directional swimming of a microcrystal that exhibits self-continuous reciprocating motion in a 2D water tank. Although the reciprocal flip motion of the crystals is like that of a fish wagging its tail fin, many of the crystals swam in the opposite direction to which a fish would swim. Here the directionality generation mechanism and physical features of the swimming behavior is explored by constructing a mathematical model for the crystalline flapper. The results show that a tiny crystal with a less-deformable part in its flip fin exhibits a pull-type stroke swimming, while a crystal with a fin that uniformly deforms exhibits push-type kicking motion

Light-Driven Flipping of Azobenzene Assemblies-Sparse Crystal Structures and Responsive Behaviour to Polarised Light

For creation of autonomous microrobots, which are able to move under conditions of a constant environment and a constant energy supply, a mechanism for maintenance of mechanical motion with a capacity for self-control is required. This requirement, known as self-organisation, represents the ability of a system to evade equilibrium through formation of a spatio-temporal pattern. Following our previous finding of a self-oscillatory flipping motion of an azobenzene-containing co-crystal, we present here regulation of the flipping motion by a light-receiving sensor molecule in relation to the alignment and role of azobenzene molecules in crystals. In the anisotropic structure, a specific azobenzene molecule acts as a reaction centre for the conversion of light to a mechanical function process, whereas the other molecules act as modulators for spatio-pattern regulation. The present results demonstrate that autonomously drivable molecular materials can exhibit information-responsive, self-sustainable motion by incorporating stimulus-responsive sensors