Specific features of the EPR line shape of dimers due to spin-lattice relaxation

The magnetization relaxation in a coupled system of two spins has been shown to induce magnetization transfer between the observed transitions. In the degeneracy region of the transitions, the magnetization transfer becomes most effective and leads to the collapse of the magnetic resonance lines. In the electron paramagnetic resonance (EPR) spectra calculated for a polycrystal, this effect manifests itself in the form of additional peaks in the absorption line. The effect of anisotropy of the g factors of the dimer spins and misalignment of the axes of the g tensor and the interaction tensor on the appearance of additional lines in the EPR spectra has been analyzed.     

Exchange interaction at the supramolecular level. EPR investigation of two copper (II) compounds: [Cu2(acac)2(phen)2(bpe)](CIO4)2·(bpe)·CH3CN·H2O and [Cu2(acac)2(phen)2(bpp)](CIO4)2·6H2O (bpe=trans-1,2-bis(4-pyridyl)ethylene, bpp=bis(4-pyridyl)propane)

Intra- and intermolecular exchange and dipole-dipole interactions in two supramolecular compounds [Cu₂(acac)₂(phen)₂(bpe)](CIO₄)₂·(bpe)·CH₃CN·H₂O (I) and [Cu₂(acac)₂(phen)₂(bpp)]× (CIO₄)₂·6H₂O (II), which are built up of binuclear fragments through π-π stacking interactions, are investigated. The electron paramagnetic resonance (EPR) spectra of the polycrystalline samples of I and II were measured in the X-band in the temperature range of 300–4.2 K, and in the Q-band atT=300 and 4.2 K. The EPR spectra were interpreted as being due to weakly interacting dimer fragments. Triplet and singlet states of dimer fragments arise from a larger interactionJS ₁ S ₂ between two nearest copper complexes of two neighboring binuclear fragments. The theoretical analysis of the EPR spectrum of the polycrystalline sample for weakly interacting triplet states is carried out. The influence of the weak interaction between triplet states with value ofJ′ is considered in the model of the frequency exchange. A special attention is focused on the presence of the additional signal due to the exchange merging in some orientations where theJ′ value exceeds the fine structure parameters of the spectrum. The analysis of the conditions for the detection of the additional signal and of the influence of this signal on the form of the EPR spectrum allows us to estimate the value of the exchange interactionJ′=o.025±0.005 cm^?1 for compounds I and II and anisotropic part of exchange interaction between two nearest copper complexes asJ _zz =?0.02 cm^?1,J _xx.yy =0.01 cm^?1 for compound I.     

Three-Component Reaction of 1,3,4,6-Tetraketones with Acetone and Amines

Russian Journal of Organic Chemistry - 1,6-Diarylhexane-1,3,4,6-tetraones reacted with 2-aminophenol and acetone according to previously unknown pathway leading to the formation of...     

EPR and SEM study of organo-mineral associations in Lower Permian evaporite dolomites

Lower Permian (280 to 300 Ma) evaporite dolomite rocks from the western part of the East European platform were studied by optical microscopy, scanning electron microscopy with microprobe analysis, and X-band electron paramagnetic resonance (EPR). Microscopic studies showed that many dolomite grains consist of an aggregation of submicron dolomite crystals (0.2–2 μm) as a spheroidal nucleus which is overgrown by a larger dolomite rhombohedron (5–20 μm). The EPR spectrum of a raw rock sample is mainly determined by thermally unstable radiation centers and Mn²⁺ ions substituted at Ca and Mg sites in the dolomite crystal structure. The presence of dispersed organic matter at low concentrations was revealed from the backscattered electron images with a microprobe analysis of carbon-enriched areas on cleaved surfaces and the registration of the carbon-centered free organic radical signal in EPR spectra of heat-treated samples. A model of two successive growing stages for dolomite grains is suggested: the dolomite (or dolomite precursor) nucleation and aggregation in the colloidal stage to form suspended organo-mineral particles before the gravitational settling, and early diagenetic overgrowth at lower temperature and more stable environment of the marine bottom to form a dolomite rhombohedron. The observation of both growing stages for dolomite grains indicates that there was no recrystallization in the later stages of the rock history.     

Widths of the Besov Classes B p,θ r(Td)

Mathematical Notes - In this paper we obtain estimates of the orders of Kolmogorov widths of the Besov classes B p,θ r(Td of periodic functions of several variables with dominant mixed...     

Diffraction of pulse shear waves in a tunnel cavity of curvilinear section in an anisotropic massif

The problem of diffraction of longitudinal shear waves in the form of periodic triangular pulses by a cylindrical tunnel cavity in a rectilinearly orthotropic unbounded massif is reduced to a number of problems on the diffraction of harmonic shear waves of different relative length. Each of the problems on stationary diffraction is solved in series in the basis solutions of shear vibrations equations by using an affine coordinate transformation of the original domain. It is proposed to use a point method of least squares to seek the coefficients of the series. The influence of the degree of anisotropy of the elastic properties of the massif on the shear stress concentration at the boundary of a circular section is analyzed for a different position of the incident triangular pulse front relative to center of the cavity.Translated from Teoreticheskaya i Prikladnaya Mekhanika, No. 20, pp. 70–76, 1989.