Rearrangement of 2-amino-1-aryl-1,4-dihydropyridines

Heating of 2-amino-1-aryl-1,4-dihydropyridines in acidic aqueous media gives 2-arylamino-1,4-dihydropyridines. The reaction formally involves the migration of the aryl substituent from the endo-to exocyclic N atom. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1259–1260, July, 2006.     

Shape-driving effect of the proton 1/2[541] band in 171Ta

High-spin states in ¹⁷¹Ta were populated through the heavy-ion fusion-evaporation reaction ¹⁵⁷Gd (¹⁹F, 5n)¹⁷¹Ta at 105MeV beam energy. Lifetimes of the levels of the πh_9/21/2[541] band have been measured by using the Doppler shift attenuation method. The transition quadrupole moments ( Q_t) and the quadrupole deformation (β₂) have been extracted. Both β₂ and Q_t values decrease slightly with increasing rotational frequency. The average β₂ value of 0.26 is 18% larger than that of the πh_11/2 9/2[514] band. Total Routhian Surface calculations have been performed with the non-axial deformed Woods-Saxon potential and the predicted values of the quadrupole deformation β₂ are in good agreement with that deduced from our lifetime measurement. The shape-driving effect is discussed.     

Lifetimes in the ground-state band and the structure of 118Te

Lifetimes of excited states in ¹¹⁸Te have been measured using the Doppler Shift Attenuation (DSA) and Recoil Distance (RD) methods in the ¹⁰⁹Ag(¹³C, p3n) reaction at a beam energy of 54 MeV. Lifetime values of the ground-state band levels with spins I ^π = 2⁺-16⁺ have been obtained. The excitation energies and B(E2) values are interpreted in the framework of a version of IBFM ( IBM + 2qp) with the maximum boson number exceeding its standard value. A satisfactory agreement with experimental level scheme and B(E2) values for the ground-state band is achieved. Received: 7 June 2001 / Accepted: 7 February 2002     

Mössbauer-effect investigation of the magnetic phases in the Mn1−xCrxSb system

The magnetic phases of the Mn_1?xCr_xSb system, at 4.2°K, have been investigated through the Mössbauer effect in Sb¹²¹. The ferromagnetic component of the magnetization induces an effective magnetic field at the Sb nuclei which is observed to decrease with increase in Cr concentration. Bulk magnetization and neutron diffraction data are given for comparison and the ‘double exchange’ interaction model is considered in the discussion of the results.     

Structure of resonances and formation of stationary points in symmetrical chains of bilinear oscillators

Dynamics of strongly nonlinear systems can in many cases be modelled by bilinear oscillators, which are the oscillators whose springs have different stiffnesses in compression and tension. This underpins the analysis of a wide range of phenomena, from oscillations of fragmented structures, connections and mooring lines to deformation of geological media. Single bilinear oscillators were studied previously and the presence of multiple resonances both super- and sub-harmonic was found. Less attention was paid to systems of multiple bilinear oscillators that describe many natural and engineering processes such as for example the behaviour of fragmented solids. Here we fill this gap concentrating on the simplest case – 1D symmetrical chains of bilinear oscillators. We show that the presence and structure of resonances in a symmetric chain of bilinear oscillators with fixed ends depends upon the number of oscillating masses. Two elementary chains act as the basic ones: a single mass bilinear chain (a mass connected to the fixed points by two bilinear springs) that behaves as a linear oscillator with a single resonance and a two mass chain that is a coupled bilinear oscillator (two masses connected by three bilinear springs). The latter has multiple resonances. We demonstrate that longer chains either do not have resonances or get decomposed, in the resonance, into either the single mass or two mass elementary chains with stationary masses in between. The resonance frequencies are inherited from the basic chains of decomposition. We show that if the number of masses is odd the chain can be decomposed into the single mass bilinear chains separated by stationary masses. It then inherits the resonances of the single mass bilinear chain. The chains with the number of masses minus 2 divisible by 3 can be decomposed into the two mass bilinear chains separated by stationary masses and inherit the resonances of the two mass chains. The chains whose lengths satisfy both criteria (such as chains with 5, 11, 17 … masses) allow both types of resonances.     

Effect of very high pressure on the magnetic state of transition metal compounds

By simultaneously combining the methods of X-ray diffraction for structural phase transitions and EOS measurements, ⁵⁷Fe Mössbauer spectroscopy as a site-sensitive probe, and resistivity measurements for studying insulating-metal transitions, we are able to study the effect of extreme pressures and at varying temperature on magnetic and electronic properties of transition metal compounds. Studies are carried out with specially tailored diamond anvils and diamond anvil cells, reaching pressures beyond 100?GPa. From our studies, we can investigate the most basic phenomenon of the quantum effect of magnetism in insulating antiferromagnets, the Mott insulators, such as high to low spin crossovers, quenching of the magnetic moments' orbital term, and the collapse of the Mott–Hubbard state. Examples of these phenomena will be given in cases of ferrous and ferric oxides, ferrous-halides and the rare-earth iron perovskites.     

Pressure-induced quenching of the Jahn-Teller distortion and insulator-to-metal transition in LaMnO(3)

LaMnO(3) was studied by synchrotron x-ray diffraction, optical spectroscopies, and transport measurements under pressures up to 40 GPa. The cooperative Jahn-Teller (JT) distortion is continuously reduced with increasing pressure. There is strong indication that the JT effect and the concomitant orbital order are completely suppressed above 18 GPa. The system, however, retains its insulating state to approximately 32 GPa, where it undergoes a bandwidth-driven insulator-metal transition. Delocalization of electron states, which suppresses the JT effect but is insufficient to make the system metallic, appears to be a key feature of LaMnO(3) at 20-30 GPa.     

Magnetic interactions in119Sn substituted for Cu in antiferromagnetic and superconducting lamellar cuprates

Mössbauer Spectroscopy (MS) studies of¹¹⁹Sn were carried out in antiferromagnetic La₂(Cu_0.99Sn_0.01)O₄ (214) and in superconducting GdBa₂(Cu_0.99Sn_0.01)₃O₇(123). Non-magnetic Sn⁴⁺ substitutes for Cu if the right procedure for diffusing¹¹⁹SnO₂ in CuO is carried out. Studies performed in 214 show a large quadrupole splitting (QS) down to 120 K followed by an onset of a magnetic interaction reaching a saturation internal field ofH _eff=8.7(5) kOe atT=30K. From the combined magnetic-quadrupole interaction the angle θ formed byq _zz andH _eff, the η-parameter, and the sign ofQS were deduced and information on the local spin structure is derived. Studies conducted with the 123 material (T _c=90 K) reveal a broad unsplit line at temperatures down to 60 K followed by an abrupt onset of a magnetic interaction corresponding toH _eff (Sn)=8.3(1) kOe. The hyperfine fielddecreases with decreasing temperature reaching 6.0(1) kOe at 16 K. The onset of the magnetic interaction at the¹¹⁹Sn nucleus is explained as due to a local depletion of holes following the Sn⁴⁺ doping and a consequent quenching of the magnetic fluctuations in its vicinity.     

Photochemical studies: Irradiation induced transformations of reversibly dissociating cyclopentadienone-dimers and their monomers

Irradiation of dissociating cyclopentadienone-dimers (2 b, c, e) results in formation of two types of cage-products (5 and 8) in very low quantum yields and good, but wavelength and phase dependent chemical yields. Both processes are intramolecular, for 2b this was shown using isotopic labeling and massspectrometric techniques. Sensitization and quenching experiments indicate that triplet states are involved The mechanistic pathways are discussed. The cyclopentadienones(1 b,c,e) were isolated for the first time and irradiation of 1b in the solid gave exclusively the symmetric cage (8b)