Orbital-selective Mott-insulator transition in Ca 2 - x Sr x RuO 4

The electronic structures of the metallic and insulating phases of the alloy series Ca_2-xSr_xRuO₄ ( 0 ? x ? 2) are calculated using LDA, LDA+U and Dynamical Mean-Field Approximation methods. In the end members the groundstate respectively is an orbitally non-degenerate antiferromagnetic insulator (x = 0) and a good metal (x = 2). For x > 0.5 the observed Curie-Weiss paramagnetic metallic state which possesses a local moment with the unexpected spin S = 1/2, is explained by the coexistence of localized and itinerant Ru-4d-orbitals. For 0.2 < x < 0.5 we propose a state with partial orbital and spin ordering. An effective model for the localized orbital and spin degrees of freedom is discussed. The metal-insulator transition at x = 0.2 is attributed to a switch in the orbital occupation associated with a structural change of the crystal. Received 27 July 2001     

Metastable ion study of substituted cyclopentadienylmanganese cations in the gas phase

The behavior of some substituted cyclopentadienylmanganese ions has been studied by tandem mass spectrometry. This metastable ion study showed that only C₅H₅Mn⁺ and (C₅H₄CN)Mn⁺ ions retain their nido-cluster structure (1), which is characterized by a simple metal-ligand bond cleavage. Other substituted ions, RXC₅H₄Mn⁺, rearrange to a different extent, depending on the nature of the substituent. The first rearrangement step is R radical migration to the central metal atom, leading to RMnC₅H₄X⁺-type ions (2). These ions decompose by elimination of X (for X=CO) or with formation of RMnX⁺, but further rearrangements can also occur. These are the reverse migration of R from the metal atom to the π-ligand (for R=H, Ph) and cyclopentadienyl ring expansion (for X=CH₂). Collisional activation mass spectra contained an Mn⁺ ion peak, which can indicate the existence of stable type 1 structures for most cyclopentadienylmanganese ions. Carboxyl and hydroxymethyl derivatives exist, presumably as ions of type 2. The neutralization-reionization mass spectra of RXC₅H₄Mn⁺ ions are also discussed.     

Reactivity of some “ladder” type complexes under conditions of metallation

The behavior of binuclear “ladder” type complexes FpL, where Fp=Cp(CO)₂Fe, L=p-MeC₆H₄Cr(CO)₃ (4), CH₂C₆H₅Cr(CO)₃ (5), andp-FpC₆H₄Cr(CO)₃ (6), under conditions of metallation was studied. Unlike compounds5 and6, the σ-bound ligand L in compound4 migrates from the iron atom to the cyclopentadienyl ring to give complexes Me(CO)₂FeC₅H₄−C₆H₄(p-Me)Cr(CO)₃. The electrochemical reduction potentials of the complexes4–6 and the rearrangement products were measured. The migration activity of L is determined by the ease of reductive cleavage of the Fe−L bond and the susceptibility of the system to undergo intramolecular electron transfer from the Cp ligand to the aromatic ring. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1832–1835, September, 1998.     

Mass spectrometric study of μ4-oxohexa-μ-acetatotetrazinc,Zn4O(CH3CO2)6

The electron impact mass spectrum of Zn₄O(CH₃CO₂)₆ isostructural to Be₄O(CH₃CO₂)₆ studied earlier is reported. The principal fragmentation paths of both compounds involve the elimination of M(CH₃CO₂)₂ where M is Zn, Be, or (CH₃CO)₂O. Further fragmentations proceed by the losses of CH₂CO and H₂O. The spectrum of Zn₄O(CH₃CO₂)₆ contains intense doubly charged ions. The results obtained are interpreted in terms of stereochemical considerations.     

Mass spectrometry of π-complexes of transition metals XVIII. Products of addition of hydrogen and deuteroexchange in mass spectra of some π-complexes of transition metals

In the mass spectra of some π-complexes of transition metals, obtained by their simultaneous evaporation with organic molecules and deuteroanalogues, protonated (deuterated) molecular and fragment ions have been discovered. They are formed as a result of ion—molecule reactions in the ionization chamber of the mass spectrometer at pressures of 10^?510^?4mmHg as well as during the interactions of neutral molecules.     

On the Theory of Heat Conductivity, Electrical Conductivity, and Hydraulic Conductivity of Polydisperse Polyhedral Foams and Highly Concentrated Emulsions

Rigorous formulas for the heat conductivity, electrical conductivity, and hydraulic conductivity of polydisperse polyhedral foams and highly concentrated emulsions are derived on the basis of the ideas recently formulated by one of the authors, with the structure of Plateau borders and films represented in the form of hierarchic series.     

Mass spectrometry of π-complexes of transition metals : XII. Ferrocenyl and cymantrenyl derivatives of chalcones

The main processes of the electron-impact induced fragmentation of the ferrocenyl and cymantrenyl analogues of chalcones RCOCH=CHR′ (R, R′ = C₅H₄FeC₅H₅, C₅H₄Mn(CO)₃, or aryl) involve a cleavage of the metalligand bond. A “chalcone” mode of fragmentation is weakly pronounced, due to the fact that the positive charge is localized preferably on the metal atom.     

Synthesis and chemical transformations of mono- and disubstituted cyanamides

The review briefly discusses the known methods for the preparation of substituted cyanamides, their typical transformations, and some aspects of practical applications of these compounds in medicine, various branches of industry, and agriculture.Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 10, 2004, pp. 1439–1454.Original Russian Text Copyright © 2004 by Nekrasov.Dedicated to the memory of Prof. Yu.S. Andreichikov