Spectral and photophysical properties of zinc(II) complexes with alkylsubstituted derivatives of dipyrrolylmethene and their resistance to protolytic dissociation and photochemical destruction

The spectral and photophysical properties of zinc(II) complexes with alkylsubstituted derivatives of dipyrrolylmethene, along with the kinetics of their protolytic dissociation and photochemical degradation in organic solvents of different natures, are studied by means of electronic absorption and fluorescence spectroscopy. It is found that protic solvents have the strongest effect on absorption spectra, while electron donors affect fluorescence spectra due to differences in the mechanisms of solvation for the ground and excited states of molecules. It is shown that the reaction product of the protolytic dissociation of complexes in benzene solutions of acetic acid is a protonated form of ligand. The observable and genuine rate constants of dissociation reactions are determined and activation parameters are calculated. A kinetic model of the process is proposed, and the regularities of the effect the nature of ligand has on the kinetics of dissociation are established. The photochemical degradation of compounds proceeds on monopyrrole products, the photolysis rate falls as the a degree of alkylation increases, and the nature of the substituent in the β-position of the ligand’s pyrrole ring has a greater effect on the stability of a compound.     

Energy of a gravitational-inertial field

Taking into account the attempts over many years to solve the problem of energy (and momentum) of the gravitational field, it should be recognized that there is no possibility of introducing, for the gravitational field, in the general case, a unique definition of energy (momentum) [1, 2]. This is not incorporated in the principles of the general theory of relativity (GTR). Starting from this, we point out the following considerations for further work on this problem.Translated from Izvestiya Vysshykh Uchebnykh Zavedenii, Fizika, No. 12, pp. 63–66, December, 1981.     

The thermodynamic characteristics of formation of mono-and binuclear biladiene Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) chelates in dimethylformamide solutions

The spectral and calorimetric data on complex formation between alkyl substituted a,c-biladiene and Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) acetates in dimethylformamide are discussed. The stability of mononuclear biladiene chelates was shown to be determined by steric factors characterizing the formation of coordination polyhedra with the tetradentate ligand. The thermodynamic characteristics of the differential polychelate effect caused by the replacement of the bidentate dipyrrolylmetene ligand with the tetradentate biladiene anion in mononuclear zinc(II) complexes were estimated. The results showed that the largest contribution to the polychelate effect was made by the enthalpy component of the Gibbs energy.     

Status of the front-end-electronics for the time-of-flight measurements at the MPD experiment

The preamplifier based on the ASIC NINO for the Time of Flight system (TOF) of MPD/NICA was developed and tested. The signal is read from both sides of the strip of the multi gap Resistive Plate Chamber (MRPC). In total there are around 14000 channels of electronics. To measure time of flight of secondary particles from collision of heavy ions on the collider NICA the Time over Threshold (ToT) method is used. According to the bench tests the preamplifier board showed stable work and good time resolution <10 ps for one channel. It was also tested at the test beam facility of the Nuclotron. The time resolution of the TOF detector which used the described preamplifier was reached ～42 ps.     

Composition and structure of pyrophoric nickel catalysts according to X-ray diffraction data

The properties of a nickel catalyst obtained by treatment of nickel–aluminum alloy with sodium hydroxide in the presence of H₂O₂ and additionally stabilized with increased pressure were studied. Additional stabilization decreased the catalyst activity by 25%, but gave a more distinct picture for an XRD analysis of the active catalyst surface and decreased the time of deactivation of the dehydrated catalyst with air oxygen. The catalyst stabilization was explained by the displacement of water, decrease in the pore size, and surface inhomogeneity.     

Quantum-chemical study of interaction of dipyrrolylmethenes with boron trifluoride and other lewis acids

The geometric parameters and energies of the products of donor-acceptor interaction of dipyrrolylmethenes with BF₃ and other inorganic Lewis acids were calculated by quantum-chemical methods. The bond nature and the energies of formation of the donor-acceptor complexes under consideration were analyzed. It was shown that the complexes with p-element fluorides are noticeably stabilized by hydrogen bonds involving the hydrogen atom of the NH group of dipyrrolylmethene and the nearest fluorine atom of a Lewis acid. Hydrogen bonding promotes further elimination of HF in the synthesis of boron fluoride complexes of dipyrrolylmethenes. The energy profile was calculated for the reaction of formation of the boron fluoride complex with dipyrrolylmethene through the intermediate donor-acceptor complex.     

Erratum to: Several Articles in JETP Letters

JETP Letters - An Erratum to this paper has been published: https://doi.org/10.1134/S0021364022350016