The influence of interatomic distances on magnetic ordering in RMnSi compounds (R=La, Y, Sm, and Gd)

Magnetic ordering in the RMnSi (R=La, Y, Sm, and Gd) compounds is investigated. It is found that the type of magnetic ordering depends on the d _Mn-Mn distance between manganese atoms inside the magnetic layers located in the planes perpendicular to the c axis. This inference is based on the results of studies performed with SmMnSi and GdMnSi compounds in which the distances between manganese atoms are close to the critical value d _Mn-Mn that corresponds to the crossover between ferromagnetic and antiferromagnetic ordering in RMnSi compounds. The introduction of lanthanum and yttrium atoms into the rare-earth sublattice leads to an increase and a decrease in the unit cell size, respectively, and brings about magnetic phase transitions in the compounds under investigation.     

Experimental and theoretical study of vibrational spectra and structure of dihalogermylene and dihalostannylene complexes with 1,4-dioxane and triphenylphosphine

Vibrational (Raman and IR) spectra of the 1:1 complexes of dihalogermylene and dihalostannylene with 1,4-dioxane and PPh₃ have been reported, the structures of the complexes Cl₂Ge·C₄H₈O₂ and Cl₂Ge·PPh₃ updated using high-resolution X-ray method. Quantum-chemistry calculations of the geometry and normal mode frequencies and eigenvectors were carried out for some of the complexes. The results show that in the structure of the polymeric solid complexes of X₂M with 1,4-dioxane, intermolecular coordination XM plays a prominent role, whereas the corresponding complexes with PPh₃ are monomeric. In the vibrational spectra of all the complexes, an inversion of symmetric and antisymmetric stretching νXM (X=Cl, Br; M=Ge, Sn) frequencies, found for ‘free’ X₂M^II particles, still persists, suggesting that the X₂M moieties preserve their specifity as carbene analogues also in the complexes.     

Inversion of ν(MHal) stretching frequencies in the spectra of dihalosilylenes, -germylenes, -stannylenes,and their complexes with Lewis bases

The vibrational spectra of tetravalent metal halides (M = Si, Ge, Sn) and the corresponding dihalocarbene analogs M^IIHal₂, obtained by the authors, and the relevant published data are compared. The spectra of the M^IIHal₂ species exhibit inversion of the M-Hal stretching frequencies (ν^s(M^IIHal) > ν ^as(M^IIHal)). This can be used for analytical purposes and allows one to distinguish between the spectra of the M^IV and M^II halides. The IR and Raman spectra of the complexes of dihalogermylenes and -stannylenes with triphenylphosphine and 1,4-dioxane also exhibit inversion of the ν(MHal) stretching frequencies. This confirms the conclusion drawn earlier based on the analysis of the geometric parameters and reactivities of the complexes in question that the divalent state of the M atom in these species is retained. Dedicated to Academician N. K. Kochetkov on the occasion of his 90th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1089–1092, May, 2005.     

Pregnane glycosides of Cynanchum sibiricum III. The structure of sibiricosides D and E

Summary The structures of two pregnane glycosides fromCynanchum sibiricum Willd. have been established. Sibiricoside D (II) is sibirigenin (cynanchogenin) 3-D-glucosido-D-cymarosido-D-cymarosido-D-cymarosido-D-oleandroside. Sibiricoside E (I) is sibirigenin (or cynanchogenin) 3-D-glucosido-D-glucosido-D-cymarosido-D-cymarosido-D-cymarosido-D-oleandroside.The hypothesis has been put forward that glycosides of isolinoleone are present in the native state which are isomerized into linoleone derivatives in the process of isolation and treatment with acid and alkaline agents.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 171–177, March–April, 1975.     

Withasteroids ofPhysalis. IV. 28-Hydrowithaphysanolide.13C NMR spectrum of 14-α-hydroxywithasteroids

A new withasteroid has been isolated fromPhysalis viscosa L. — 28-hydroxywithaphysanolide, with mp 234°C, composition C₂₈H₃₈O₈. The¹³C NMR spectra of a number of withasteroids have been investigated. For 28-hydroxywithaphysanolide we propose the structure 4,14,17,20R,28-pentahydroxy-l-oxo-22R-witha-2,5,24-trienolide. The corresponding corrections have been made in the structural formulas of withaphysanolide and physalactone.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 197–207, March–April, 1984.     

Withasteroids ofPhysalis. III. Physanolide and 4β-hydroxywithanolide E

Two withanolides have been isolated from the epigeal part ofPhysalis viscosa L. One of them with the compositions C₂₈H₃₈O₈ has been identified as 4-hydroxy-withanolide E, and for the second, which has been called physanolide, the structure of 14,17,20R-trihydroxy-1,4-dioxo-22R-witha-5,24-dienolide has been proposed on the basis of its UV, IR, PMR, and mass spectra, and also the results of a partial synthesis of 14-hydroxyandrost-5-ene-1,4,17-trione, obtained by its oxidation.Institute of the Chemistry of Plant Substances, Academy of Sciences of Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 187–192, March–April, 1981.     

New Types of Phosphocavitandes

Abstract

New types of phosphocavitandes differing in structure of phosphorus surroundings were synthesized and investigated.