Exchange interaction and spin dynamics in pentanuclear clusters, Cu3Ln2(ClCH2COO)12(H2O)8 (Ln = Nd3+, Sm3+, Pr3+)

New compounds, [Cu₃Ln₂(ClCH₂COO)₁₂(H₂O)₈]·2H₂O with Ln = Nd³⁺ (I), Sm³⁺ (II), Pr³⁺ (III), built up of pentanuclear clusters were synthesized and studied by means of X-ray analysis and electron paramagnetic resonance (EPR). X-ray data show that all compounds are isostructural and the pentanuclear clusteres may be considered as a linear system with alternating Cu(II) and Ln(III) ions: Cu(2)-L¹-Ln-L²-Cu(1)-L²-Ln-L²-Cu(2) with L¹ and L² being bridging fragments and Cu(1) and Cu(2) being structurally nonequivalent copper complexes. EPR studies demonstrate that in the temperature range of 100–293 K the signals due to only one type of the copper complexes are observed in the spectra of I–III. AtT<100 K the spectral temperature dependence is nontrivial. AtT<30 K new signals are detected in the spectra of I and II. The temperature dependence of the EPR spectra is interpreted under the assumption that the parameter of the exchange interaction Cu(2)-Ln considerably exceeds the parameter of the interaction Cu(1)-Ln. EPR spectra are calculated for the fragments of five paramagnetic centers in the frames of the model taking into account the nonequivalence of two copper complexes, short longitudinal and transverse paramagnetic relaxation times of the rare-earth ions at room temperature and the change of the relaxation rates when the temperature decreases. The results of the calculations show that it is possible to obtain information about the interactions in the system on the basis of the analysis of the temperature dependence of the EPR spectra of the central copper complex. The parameter of the isotropic part of the exchange interaction between copper and neodymium ions (for the interaction Cu(2)-Nd) is estimated as about 15 cm⁻¹. A considerable rearrangement of the spin states when the temperature changes is found for all complexes.     

Microwave spectra ofs-cis-Glyoxal (CHO−CHO) molecules in excited vibrational states

The microwave spectra of s-cis-glyoxal molecules in the excited states of torsional (v_t=1,2) and bending (v_bend=1) vibrations have been studied. For the v_t=1 state, the rotational constants have been refined and the quartic constants of centrifugal distorition have been determined. For the excited v_t=2 and v_bend=1 states, the rotational constants have found. For the ground vibrational state, the rotational constants and the quartic constants of centrifugal distortion have been refined. The vibrational frequencies have been determined from the relative intensities of rotational transitions. Ufa Scientific Center of Russian Academy of Sciences, Physics Department. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 3, pp.418–423, May–June, 1995. Translated by I. Izvekova     

Comparative study of the activity of Al?Pd and Al?Pt catalysts in deep oxidation of hydrocarbons

Atomic catalytic activity of palladium has been revealed to be higher than that of platinum in deep oxidation of methane and lower in the case of butane. According to the experimental data and the quantum-chemical calculation, the observed effects are ascribed to the different bond strength of the surface oxygen due to different reaction conditions.

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, _{Pd Pt}, . _{Pd Pt} - , .

     

Manifestation of the anticrossing of energy levels in EPR spectra of spin clusters

The EPR spectra of a system of two coupled spins with strongly anisotropic g factors have been calculated. It has been shown that the spectra can exhibit an additional absorption line in the vicinity of the energy level anticrossing. The emergence of this line is caused by strengthening of the off-resonance absorption in the anticrossing region.     

A Bandpass Filter Based on Dielectric Layers with a Strip Conductor Subwavelength Grating at Their Interfaces

Doklady Physics - The design of a multilayer bandpass filter has been investigated, in which each of the half-wavelength resonators consists of two dielectric layers with outer strip conductor...     

Microwave spectrum,centrifugal perturbation,dipole moment,and conformation of 4-methyl-1,3-dioxane

The microwave spectrum of 4-methyl-1,3-dioxane is studied in a frequency range from 16 GHz to 40 GHz. The rotational transitions of a-, b-, and c-types with J ≤ 57 are identified. The rotational constants (MHz) A = 4802.335(2), B = 2376.163(1), C = 1738.852(1) and the quartic constants of the centrifugal distortion are found for the ground vibrational state of the molecule. The components of the dipole moment (D) μ _a = 0.73(1), μ_b = 1.32(1), μ_c = 1.36(1) and the total dipole moment μ = 2.03(1) are determined. The experimental data obtained correspond to the chair conformation of the molecule with the equatorial orientation of the methyl group.     

Membrane transport of metal ions with lipophilic aminomethylphosphine oxides

The processes of membrane transport of ions of scandium(III), samarium(III), gadolinium(III), neodymium(III), aluminum(III), and a number of alkali and alkaline earth metals through liquid membrane impregnated with aminophosphoryl carriers of different structures were studied. Selectivity of bis (dialkylphosphinyl)amines towards scandium was found to be significantly higher than the selectivity of diphosphinylpiperazine and monophosphinylamine in particular. The dependence of transfer efficiency on the concentration of substrates and carriers was revealed. Optimal conditions for transporting rare and trace metal ions through the membrane were found, and the mechanism of transmembrane transport was discussed.     

Homodimerization of bicyclo[2.2.1]-2-heptene in presence of complex nickel catalysts

Conclusions Norbornene is dimerized in the presence of a nickel-containing catalytic system to give exo-2-(4-methylenecyclohex-1-en-3-yl)norbornane in 67% yield.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 910–913, April, 1979.