Quantum-chemical analysis of the features of the electronic structure of model bis(imidazole)iron porphyrins as compared to data from Mössbauer spectroscopy

A quantum-chemical analysis of the electronic structure of two low-spin complexes, viz., bis(imidazole)hemichrome [Fe(III)P]2Im (S = 1.2) and bis(imidazole)hemochrome [Fe(II)P]·2Im (S = 0), which simulate hemi- and hemoproteins (P denotes porphyrin, Im denotes imidazole, and S is the spin of the iron ion), has been carried out by the extended Hückel method with SCF convergence with respect to the charges of the atoms. The data on the electronic structure of the complexes have been used for calculations of the quadrupole splitting in the⁵⁷Fe Mössbauer spectra of these compounds. An analysis of the contributions of the valence electrons of the Fe atom and the ligands to the quadrupole splitting as a function of the structure of the iron ion, its electronic environment, and the parameters of the first coordination sphere has been carried out. Good agreement between the calculated and experimental values of the quadrupole splitting has been obtained. An analysis of the orbital interactions has been carried out, and data on the classification and composition of the MO's have been presented.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 2, pp. 146–153, March–April, 1985.     

Reactions of azirines with sulfur nucleophiles. 2. Reactions of 2H-azirine with β,γ-dihydroxy thiols and β-dithiols. a new route to the synthesis of cyclic sulfides

The reaction of 2H-azirine with a number of dihydroxy thiols and dithiols leads to aziridin-2-yl alkyl sulfides. The latter readily isomerize to cyclic sulfides the size of the ring of which is determined by the length of the alkyl sulfide chain.For Communication 1, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 623–627, May, 1985.     

An analysis of the possible causes of apparent compensation effects when investigating a substance under varying experimental conditions

The major causes leading to the apparent compensation effect (lgA=aE+b) at the thermal decomposition of one and the same substance in a series of experimental conditions (varying of the mass of the sample, of the heating rate, of disperseness, and at different distances from the equilibrium) were discussed. It was found that the appearance of a compensation effect at the study of the thermal decomposition of one and the same substance demonstrates the incorrect setup of the experiment, resulting in erroneous values calculated for the kinetic parameters.

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Zusammenfassung Die Hauptursachen, welche zum scheinbaren Kompensationseffekt (lgA=aE+b) der thermischen Zersetzung ein und derselben Substanz führen, wurden unter verschiedenen Versuchsbedingungen untersucht: unter Änderung der Probenmasse, der Aufheizgeschwindigkeit, der Dispersität und der Entfernung vom Gleichgewicht. Es wurde festgestellt, daß das Auftreten eines Kompensationseffekts bei der Untersuchung der thermischen Zersetzung ein und derselben Substanz auf die unrichtige Durchführung des Experiments hinweist, die zur Berechnung falscher Werte der kinetischen Parameter führt.

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Résumé On a étudié les causes principales de l'effet de compensation apparent (lgA=aE+ +b) lors de la décomposition thermique de la même substance dans différentes conditions expérimentales, en faisant varier notamment la masse du prélèvement, la vitesse du chauffage, la dispersion et l'écart à l'équilibre. On a trouvé que l'apparition d'un effet de compensation lors de l'étude de la décomposition thermique de la même substance résultait de l'exécution incorrecte de l'expérience qui mène à des valeurs fausses lors du calcul des paramètres cinétiques.

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, (lg A=aE+b) : , , , . , , .