Infra red spectra and structures of bimetallic Cp2TiH2AlX(X′) · L complexes

Summary The i.r. spectra of the crystalline complexes, Cp₂TiH₂AlX(X) · L (X and X = H or Hal; L = Et₂O or NEt₃) have been studied. Crystallization from solutions containing monomers Cp₂TiH₂AlClH · Et₂O (prepared at –70°), Cp₂TiH₂AlHCl · NEt₃, and Cp₂TiH₂AlHBr · Et₂O results in splitting off of 0.5 L and formation of structures containing ordinary and double H bridges, terminal H atoms, and nonequivalent Ti and Al atoms. The Cp₂TiH₂AlClH · 0.5 Et₂O complex prepared at 20° is a dimer both in solution and in the crystalline state. It contains two types of H-bridges, Ti-H-Al and Ti-H₂-Al, and equivalent Ti and Al atoms. The Cp₂TiH₂AlCl₂ · Et₂O compound is, seemingly, a dimer containing ordinary H-bridges, whereas Cp₂TiH₂AlCl₂ · NEt₃ crystallizes as a monomer with double H-bridges owing to the higher basicity of triethylamine compared with ether.     

Er5Ni3Al3Ge4: a quaternary variant of the NbCoB type

Single crystals of penta­erbium trinickel trialuminium tetra­germanium were synthesized from the elements by arc‐melting. The novel compound crystallizes in the space group Pmmn, e⁶b²a, with all nine crystallographically unique atoms in special positions of site symmetries m.. and mm2. This compound represents a new ordered variant of the NbCoB type. Its two‐layer structure is described as an inter­growth of the Er₃NiAl₃Ge₂ (Y₃NiAl₃Ge₂ type) and ErNiGe (TiNiSi type) structures. The coordination polyhedra are distorted penta­gonal prisms around Er atoms, tetra­gonal prisms around Al and Ni atoms, and trigonal prisms around Ge and Ni atoms, capped with eight, four and three extra vertices, respectively.     

Numerical Solution of Three-Dimensional Stability Problems for Elastic Bodies

A solution in Cartesian coordinates to plane and spatial stability problems for composites is obtained within the framework of the second variant of the three-dimensional linearized theory of stability of deformable bodies. Two mechanical models are used: a homogeneous anisotropic medium with averaged mechanical characteristics and a piecewise-homogeneous medium with orthotropic linearly elastic components. To solve the problems, a mesh approach is applied. Discrete models are constructed using the concept of a base scheme. The calculated results are analyzed     

Why an ac magnetic field shifts the irreversibility line in type-II superconductors

We show that for a thin superconducting strip placed in a transverse dc magnetic field--the typical geometry of experiments with high-T(c) superconductors--the application of a weak ac magnetic field perpendicular to the dc field generates a dc voltage in the strip. This voltage leads to the decay of the critical currents circulating in the strip, and eventually the equilibrium state of the superconductor is established. This relaxation is not due to thermally activated flux creep but to the "walking" motion of vortices in the two-dimensional critical state of the strip with in-plane ac field. Our theory explains the shaking effect that was used for detecting phase transitions of the vortex lattice in superconductors.     

Radiation defects in Ar+-ion-implanted Hg1−xCdxTe crystals

A study has been made of defect formation in Hg_1–xCd_xTe crystals after implantation with argon ions possessing energies of 50 and 150 keV over a wide range of radiation doses. The spatial distributions of electrically active radiation defects, measured by electrophysical methods, are compared with extended lattice imperfections, determined from Rutherford backscattering spectra. The distribution of radiation donors has been found to be shifted deeper into the semiconductor beyond the region of the interstitial impurity distribution and radiation donors have been found to be neutralized by extended lattice imperfections. The paper discusses the principal factors in the formation of the profiles of the carrier concentration distribution in the implanted cadmium telluride-mercury layer.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 83–90, December, 1988.     

Intensity distribution in the rotational structure of the electron-vibrational bands of nitrogen

The intensity distribution was measured for the rotational lines of the N₂ molecule in the radiation of a glow discharge in the pure gas, at pressure 0.1–5 torr, or with argon, at a total pressure of 2 torr, at a current of 40 mA. The distribution found lags behind a Boltzmann distribution in the 0–3 band (corresponding to the C³-B³ transition; the second positive system) over the pressure range 0.1–2 torr and in the 1–4 band (the C³-B³ transition; second positive system) at a pressure of 0.1 torr. In the N₂ + Ar mixture there is selective amplification of the J=25, 26 rotational lines.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 17–21, September, 1970.     

Magnesium borohydride complexed by tetramethylethylenediamine

A complex of magnesium borohydride, Mg(BH4)2.Me2NC2H4NMe2, has been synthesized and structurally characterized. This monomer complex has a pseudotetrahedral geometry around the Mg atom with tridentate BH4 groups and short Mg...B distances.     

Synthesis and structural characterization of novel zinc(II) and cadmium(II) complexes with pyridine-phosphine chalcogenide ligands

New pyridine-phosphine chalcogenide ligands, tris[2-(2-pyridyl)ethyl]phosphine sulfide 1a and tris[2-(2-pyridyl)ethyl]phosphine selenide 1b, react with zinc(II) and cadmium(II) chlorides in EtOH at room temperature to afford complexes of compositions 2ZnCl₂·2L (2, L = 1a) and 3CdCl₂·2L (3a,b, L = 1a,b) in high yields. The solid-state structure of complexes 2, 3 has been proved by X-ray analysis data. Complex 2 is a centrosymmetric dimer, where two atoms of zinc are bonded by two bridging pyridine-phosphine sulfide ligands through N atoms. Complexes 3a,b exist as polymeric chains with each bridging ligand acting as a chelate N,S- or N,Se-donor to one cadmium(II) center and as a pyridine N-donor to the next cadmium(II) center.     

Rearrangements of the [2+2]-cycloadducts of DDQ and 2-ethynylpyrroles

The [2+2]-cycloadducts of DDQ and 2-ethynylpyrroles, upon ethanolysis (reflux, 15 min or room temperature, 24 h), rearrange from bicyclo[4.2.0]octadienediones to bicyclo[3.2.0]heptadienone- and cyclobutenyl-dihydrofuranone moieties in 55-83% yields, the former rearrangement being the major direction. Benzoquinone ring cleavage is regioselective to afford mostly bicyclo[3.2.0]heptadienone-pyrrole ensembles (85-90% selectivity) in 39-78% yields. The only exception is when the starting compounds contain an ethoxycarbonyl substituent and the pyrrole counterpart is a 4,5,6,7-tetrahydroindole fragment. In this case, the ratio of the rearrangement products is 1:1.2 in a total yield of 83%. An important feature of the dihydrofuranone pathway rearrangement is its 100% diastereoselectivity.