Crystal structure of holtite II

The crystal structure of the As-containing mineral holtite II was refined by the Rietveld method. The orthorhombic unit-cell parameters are a = 4.6893(1) Å, b = 11.881(1) Å, c = 20.394(1) Å, sp. gr. Pnma, Z = 4. Holtite II has an octahedral framework structure composed of two types of nonequivalent columns of Al octahedra, which was found in the structures of dumortierite-group minerals and holtite I. The differences in the structures of holtite II and holtite I were revealed. These differences are associated with the differences in the composition and configuration of the columns of Al(1) polyhedra, which are located inside the framework and are linked to SiO₄ tetrahedra, as well as with the arrangement of pyramidal SbO₃ groups.     

1,3-Diaza[3]ferrocenophanes functionalized with a nitronyl nitroxide group

An aza-Wittig reaction of 1,1′-bis(triphenylphosphoranylidenamino)-ferrocene with 4-iodo-, 2,5-difluoro-4-iodo-, pentafluoro-, or 4-methoxycarbonylphenylisocyanates is described here. Intermediate betaines, which are products of a nucleophilic attack of the nitrogen atom of the remaining iminophosphorane moiety on the carbon atom of the carbodiimide functional group, were isolated; their structures were proved by monocrystal X-ray diffraction. Hydrolysis of the betaines under mild conditions gave corresponding arylamino-1,3-diaza[3]ferrocenophanes. On the other hand, as demonstrated, under more rigid conditions, the betaines could be converted into ferrocenophanes with the 1,3-diazetidine-2,4-diimine coupler. The iodo- or diiodo-derivatives of 1,3-diaza[3]ferrocenophanes were cross-coupled with a nitronyl nitroxide-2-ide gold(I) complex to obtain corresponding metallocenophanes functionalized with the nitronyl nitroxide group(s). The molecular and crystal structures of the halogenated and spin-labeled ferrocenophanes were solved by X-ray analysis. In arylamino-1,3-diaza[3]ferrocenophanes, according to cyclic voltammetry, the position of the quasi-reversible oxidation peak associated with the Fe(II)/Fe(III) redox couple deviates within 0.09?V depending on substituents in the arylamino group.     

Structural and magnetic state of a lightly doped Zn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te crystal

The specific features of the structure and the spin system of a lightly doped Zn_{1 − x} V _x Te (x = 0.0002) crystal have been investigated for the first time using thermal neutron diffraction and magnetic measurements. The results of these experiments have been discussed in a close connection with the previously obtained information on neutron diffraction and magnetism in Zn_{1 − x} V _x Se (x = 0.0018) and Zn_{1 − x} Cr _x Se (x = 0.0029, x = 0.0450) single crystals.     

Enhancement of the Local Electromagnetic Field over Planar “Particles” Formed on the Surface of a Polar Crystal

Small “particles” of an open surface were formed on a SiC polar crystal with openings in the opaque metal mask covering the sample. The dimensions of the holes were about surface phonon polariton wavelength. Such a sample was irradiated with an electromagnetic wave ( λ = 10.68μm) at a frequency close to the lattice resonance of SiC. A significant enhancement in the field amplitude of surface phonon polariton waves was detected over such “particles” compared to the amplitude over an infinite open surface of SiC. Such a phenomenon, observed by us in the IR band, is similar to plasmon resonance on small metal particles in the visible band, but the lateral resolution of the ASNOM used (no worse than 30 nm at 10 μm) makes the obtained field distribution more detailed. The maps of the local field amplitude and phase obtained on SiC surface with ASNOM are in a good quantitative agreement with simulations using the Green’s function.