By combining bulk properties, neutron diffraction and non-resonant X-ray diffraction measurements, we demonstrate that the new multiferroic Cu3Nb2O8 becomes polar simultaneously with the appearance of generalised helicoidal magnetic ordering. The electrical polarization is oriented perpendicularly to the common plane of rotation of the spins -an observation that cannot be reconciled with the "conventional" theory developed for cycloidal multiferroics. Our results are consistent with coupling between a macroscopic structural rotation, which is allowed in the paramagnetic group, and magnetically-induced structural chirality. [5] are cycloidal multiferroics, so called because their magnetic structures can be described as incommensurate circular (or elliptical) modulations with the wavevectors in the plane of rotation of the spins. In cycloidal multiferroics, the non-collinear magnetic configuration itself is established by the competition between nearest and next-nearest neighbor interactions. The coupling to the crystal structure occurs through the spin-orbit interaction, making it energetically favorable to develop local Dzyaloshinskii-Moriya (DM) vectors, associated with a local polarization. In simple, high-symmetry cases, the electrical polarization is perpendicular both to the magnetic propagation vector and to the normal to the plane of rotation of the spins, since the following formula holds [6]: P = λk m × (s 1 × s 2 ), where s 1 and s 2 are two adjacent spins along the propagation direction k m and λ is a coupling constant. In more complex, lower symmetry cases, the electrical polarization need not be perpendicular to the propagation vector, which, in turn, need not be contained in the plane of rotation of the spins (generic helicoidal structures). However, it is a strong prediction of the cycloidal multiferroics model that if all the spins rotate in a common plane, then the electrical polarization must be strictly contained within that plane.In this letter, we present a new multiferroic, with chemical formula Cu 3 Nb 2 O 8 and centrosymmetric triclinic symmetry (space group P1) in the paramagnetic phase. Using magnetic neutron powder diffraction, magnetic susceptibility, heat capacity, electrical polarization and non-resonant X-ray magnetic scattering measurements, we show that Cu 3 Nb 2 O 8 orders magnetically at T N ∼ 26 K, and develops an electrical polarization below a second magnetic transition at T 2 ∼ 24 K. In the polar phase below T 2 , a coplanar helicoidal magnetic structure is stabilized with propagation vector k m = (0.4876, 0.2813, 0.2029) in a general direction in reciprocal space. Strikingly, the electrical polarization in Cu 3 Nb 2 O 8 (with a magnitude of 17.8 µCm −2 ) is almost exactly perpendicular to the plane of rotation of the spins, in clear contradiction with the predictions of the cycloidal multiferroics model. We conclude that the electrical polarization in Cu 3 Nb 2 O 8 must arise through coupling of the chiral component of the magnetic structure with the crystal structure, ra...

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Redox-active pyrrole (Py) monomers were intercalated into 1D nanochannels of [Cd(NDC)0.5(PCA)]·Gx (H2NDC = 2,6-napthalenedicarboxylic acid, HPCA = 4-pyridinecarboxylic acid, G = guest molecules) (1) - a fluorescent 3D MOF (λem = 385 nm). Subsequent activation of 1⊃Py upon immersing into iodine (I2) solution resulted in an increment of the bulk electrical conductivity by ∼9 orders of magnitude. The unusual increase in conductivity was attributed to the formation of highly oriented and conducting polypyrrole (PPy) chains inside 1D nanochannels and specific host-guest interaction in 1⊃PPy thereof. The Hall-effect measurements suggested 1⊃PPy to be an n-type semiconductor material with remarkably high-carrier density (η) of ∼1.5 × 10(17) cm(-3) and mobility (μ) of ∼8.15 cm(2) V(-1) s(-1). The fluorescence property of 1 was almost retained in 1⊃PPy with concomitant exciplex-type emission at higher wavelength (λem = 520 nm). The here-presented results on [MOF⊃Conducting Polymer] systems in general will serve as a prototype experiment toward rational design for the development of highly conductive yet fluorescent MOF-based materials for various optoelectronic applications.

We present eight epochs of 43‐GHz, dual‐polarization VLBA observations of the gravitational lens system PKS 1830‐211, made over fourteen weeks. A bright, compact ‘core’ and a faint extended ‘jet’ are clearly seen in maps of both lensed images at all eight epochs. The relative separation of the radio centroid of the cores (as measured on the sky) changes by up to 87 μ as between subsequent epochs. A comparison with the previous 43‐GHz VLBA observations made 8 months earlier shows even larger deviations in the separation of up to 201 μas. The measured changes are most likely produced by changes in the brightness distribution of the background source, enhanced by the magnification of the lens. A relative magnification matrix that is applicable on the milliarcsecond scale has been determined by relating two vectors (the ‘core–jet’ separations and the offsets of the polarized and total intensity emission) in the two lensed images. The determinant of this matrix, −1.13 ( ± 0.61), is in good agreement with the measured flux density ratio of the two images. The matrix predicts that the 10‐mas‐long jet, which is clearly seen in previous 15‐ and 8.4‐GHz VLBA observations, should correspond to a 4‐mas‐long jet trailing to the south‐east of the south‐western image. The clear non‐detection of this trailing jet is a strong evidence for substructure in the lens and may require more realistic lens models to be invoked, such as that of Nair & Garrett.

Ordered nanoporosity in covalent organic framework (COF) offers excellent opportunity for property development. Loading nanoparticles (nPs) onto them is one approach to introducing tailor-made properties into a COF. Here, a COF-Co/Co(OH) composite containing about 16 wt% of <6 nm sized Co/Co(OH) nPs is prepared on a N-rich COF support that catalyzes the release of theoretical equivalence of H from readily available, safe, and cheap NaBH . Furthermore, the released H is utilized for the hydrogenation of nitrile and nitro compounds to amines under ambient conditions in a facile one-pot reaction. The COF "by choice" is built from "methoxy" functionalized dialdehydes which is crucial in enabling the complete retention of the COF structure under the conditions of the catalysis, where the regular Schiff bonds would have hydrolyzed. The N-rich binding pockets in the COF ensure strong nP-COF interactions, which provides stability and enables catalyst recycling. Modeling studies reveal the crucial role played by the COF in exposing the active facets and thereby in controlling the activation of the reducing agent. Additionally, via density functional theory, we provide a rational explanation for how these COFs can stabilize nanoparticles which grow beyond the limiting pore size of the COF and yet result in a truly stable heterogeneous catalyst - a ubiquitous observation. The study underscores the versatility of COF as a heterogeneous support for developing cheap and highly active nonnoble metal catalysts.