Molecular structure of a benzoic acid adduct of zinc benzoate dihydrate — [Zn(C6H5COO)2·2H2O]2C6H5COOH

Institute of Inorganic and Physical Chemistry, Azerbaijan Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 6, pp. 203–207, November–December, 1992.     

Insights into the structure and reactivity of acylperoxo complexes in the Kochi-Jacobsen-Katsuki catalytic system. A density functional study

Structural properties of the acylperoxo complexes [(Salen)Mn(III)RCO(3)] (2) and [(Salen)Mn(IV)RCO(3)] (3), the critical intermediates in the Kochi-Jacobsen-Katsuki reaction utilizing organic peracids or O(2)/aldehydes as oxygen source, have been studied with the density functional theory. Four distinct isomers, cis(O,N), cis(N,O), cis(N,N), and trans, of these complexes have been located. The isomer 2-cis(O,N) in its quintet ground state, and nearly degenerate isomers 3-cis(O,N) and 3-cis(N,O) in their quartet ground states are found to be the lowest in energy among the other isomers. The O-O bond cleavage in the cis(O,N), cis(N,O), and trans isomers of 2 and 3 has been elucidated. In complex 3, the O-O bond is inert. On the contrary, in complex 2, the O-O bond cleaves via two distinct pathways. The first pathway occurs exclusively on the quintet potential energy surface (PES) and corresponds to heterolytic O-O bond scission coupled with insertion of an oxygen atom into an Mn-N(Salen) bond to form 2-N-oxo species; this pathway has the lowest barrier of 14.9 kcal/mol and is 15.6 kcal/mol exothermic. The second pathway is tentatively a spin crossover pathway. In particular, for 2-cis(O,N) and 2-cis(N,O) the second pathway proceeds through a crucial minimum on the seam of crossing (MSX) between the quintet and triplet PESs followed by heterolytic O-O cleavage on the triplet PES, and produces unusual triplet 2-cis(O,N)- and 2-cis(N,O)-oxo ([(Salen)Mn(V)(O)RCO(2)]) species; this pathway requires 12.8 kcal/mol and is 1.4 kcal/mol endothermic. In contrast, for the 2-trans isomer, spin crossing is less crucial and the O-O cleavage proceeds homolytically to generate 2-trans-oxo [(Salen)Mn(IV)(O)] species with RCO(2) radical; this pathway, however, cannot compete with that in 2-cis because it needs 21.9 kcal/mol for activation and is 15.3 kcal/mol endothermic. In summary, the O-O cleavage occurs predominantly in the 2-cis complexes, and may proceed either through pure high spin or spin crossover heterolytic pathway to produce 2-cis-oxo and 2-N-oxo species.     

Cooperative pull and push effects on the O-O bond cleavage in acylperoxo complexes of [(Salen)MnIIIL]: ensuring formation of manganese(V) oxo species

The acidity (pull) and the axial ligand (push) effects on the O-O bond cleavage in the [(Salen)Mn(III)(RCO(3))L] acylperoxo complexes, with model L = none, NH(3), and HCO(2)(-) (1), have been studied with B3LYP density functional calculations. The acidic conditions have been mimicked by explicit protonation of 1 to afford a variety of [(Salen)Mn(III)(RCO(3)H)L] (2) and [(SalenH)Mn(III)(RCO(3))L] (3) complexes in ground quintet states. The protonation assists the O-O bond heterolysis, thus primarily forming highly reactive Mn(V)(O) species, and consequently suppresses formation of the less reactive Mn(IV)(O) species through homolytic channel described earlier in 1 [Khavrutskii, I. V.; Rahim, R. R.; Musaev, D. G.; Morokuma, K. J. Phys. Chem. B 2004, 108, 3845-3854]. In addition to the qualitative change of the O-O bond cleavage mode, the protonation affects the rate of the O-O bond cleavage. Therefore, varying the acidity of the reaction media helps control the O-O bond cleavage mode and rate.     

ESR studies of Mo?Ti oxide catalysts

According to ESR studies on mixed⁹⁵Mo-enriched Mo–Ti oxide systems, different types of Mo⁵⁺ ions and their formation conditions in these systems have been established.

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Mo–Ti , ⁹⁵Mo. Mo⁵⁺ .

     

Preparation of new amino derivatives of the lactone tanachin and their antimicrobial activity

Several amino derivatives have been obtained from the sesquiterpene lactone tanachin by means of the Michael reaction, and their structures have been confirmed by spectral methods. The antimicrobial activities of the compounds synthesized relative to some strains of microorganisms are considered.Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 24–28, January–February, 1996. Original article submitted October 21, 1994.     

Theoretical study of the structure and stability of dimers (LiBO)2, (LiAlO)2, (LiBS)2, and (LiAlS)2

Institute of New Chemical Problems, Russian Academy of Sciences, Chernogolovka. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 1, pp. 10–17, January–February, 1992.     

Heat capacity of a Cr2O3 antiferromagnet near the critical temperature

The heat capacity of a Cr₂O₃ antiferromagnet near the critical temperature is precisely measured by ac calorimetry. The critical behavior of the heat capacity is examined. The regularities of variations in the universal critical parameters near the critical point are determined, and their values are calculated. A crossover from the Heisenberg (n=3) to the Ising (n=1) critical behavior is revealed.     

New nonlinear intensity Kerr effect in the polar geometry

The problem of the electromagnetic wave reflection on the second optical harmonic from a semi-infinite optically isotropic magnetic medium is considered for the uniform magnetization direction corresponding to the polar Kerr effect. In the first approximation in magnetization, the method of Green’s tensor functions is used to derive expressions for the complex amplitudes of the wave fields for the incidence of s-and p-polarized waves (as well as of their superposition) on the medium. It is shown that, in the latter case, the nonlinear polar Kerr effect is of the intensity type. The dependences of the intensity effect on the angle of incidence of the inducing wave and on the angle of its polarization, which were obtained in numerical experiments, are presented. A comparative analysis of the linear and nonlinear intensity Kerr effects is carried out.     

Gel based on microcrystalline cellulose and azidin

The structure of a gel based on microcrystalline cellulose (MCC) and the antiprotozoic preparation azidin is studied. Intense ultrasonic irradiation produces a physicochemical reaction in the MCC:azidin system that lengthens the effective lifetime of the drug. Institute of Chemistry and Physics of Polymers, Academy of Sciences of the Republic of Uzbekistan, Mirzo Ulugbek Tashkent State University, Tashkent, fax (3712) 44 26 61; 46 08 97. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 577–580, September–October, 1999.