Crystal structure of golyshevite

The crystal structure of golyshevite, a new calcium-and carbon-rich representative of the eudialyte group, was established by single-crystal X-ray diffraction analysis (sp. gr. R3m, a = 14.231(3) Å, c = 29.984(8) Å, R = 0.062, 1643 reflections with F > 3σ(F)). The idealized formula of golyshevite is (Na₁₀Ca₃)Ca₆Zr₃Fe₂SiNb[Si₃O₉]₂[Si₉O₂₇]₂(OH)₃(CO₃) · H₂O. This mineral is characterized by the presence of calcium atoms both in the octahedral positions of six-membered rings and in extraframework positions, where calcium prevails. CO₃ groups are present as the major additional anions. Carbon atoms randomly occupy two positions on the threefold z axis at a distance of 0.75 Å from each other and are coordinated by oxygen atoms arranged around the z axis.     

Crystal structures of two new low-symmetry calcium-deficient analogs of eudialyte

The crystal structures of two new low-symmetry (sp. gr. R3) representatives of the eudialyte group from Mont Saint-Hilaire (Quebec, Canada) and the Lovozero massif (Kola Peninsula, Russia) were studied by single-crystal X-ray diffraction analysis and refined to R = 0.068 and 0.054 using 2899 reflections with F > 5σ(F) and 2927 reflections with F > 3σ(F), respectively. The idealized formulas of these representatives are Na₁₃(Ca₃Mn₃)Zr₃(Fe, Mn)₃(□)(Si)[Si₃O₉]₂[Si₉O₂₇]₂(O, OH, Cl)₃ · 2H₂O and Na₁₅(Ca₃Mn₃)Zr₃(Fe, Zr)₃(Si)(Si) · [Si₃O₉]₂[Si₉O₂₇]₂O₂(OH, F, Cl)₂ · 2H₂O. Both minerals are analogs of oneillite and are characterized by a low Ca content. The distinguishing features of the mineral from Quebec are that the M(4) site is essentially vacant (>50%) and Ca atoms occupy one independent site in the six-membered ring, whereas another site is occupied by Mn along with a small impurity of Na. In the mineral from the Lovozero massif, both the M(3) and M(4) sites are occupied predominantly by silicon, while Ca atoms are distributed between both octahedral sites of the six-membered ring, one of these sites being occupied predominantly by Mn.     

Structural characteristics of a new cation-deficient representative of the labuntsovite group

The crystal structure of a new representative of the labuntsovite group from the Khibiny massif (the Kola Peninsula) has been refined. The unit-cell parameters are a = 14.298(7) Å, b = 13.816(7) Å, c = 7.792(3) Å, β = 116.85(5)°, V = 1373.3 ų, sp. gr. C2/m, R^aniso = 0.047, 1084 reflections with F > 4σ (F). The mineral differs from lemmleinite-Ba and other members of the group by the predominance of the vacancies in two key cationic positions—C position is occupied by Ba cations (37%) and D position is occupied mainly by Mn cations (47%).     

The features of cationic polymerization of lactones under the action of onium salts

Results on the kinetics of polymerization of ϵ -caprolactone (ϵ -CL) under the action of quaternary onium salts with complex counterions are reported. The structure and molecular weight distribution (MWD) of polymerization products, and of the catalysts and active propagating centers were studied by gel permeation and gas chromatography, IR and UV spectroscopy, chemical and X-ray analysis. The role of photochemical transformations at ϵ -CL polymerization in the presence of onium salts with counterion FeCl₄ was revealed. The mechanism of polymerization is discussed.     

Some aspects of the control of physico-mechanical properties of polymer compositions with elastomeric inclusions

The paper reviews the author's works on the regulation of physico-mechanical properties of polymer compositions with elastomeric inclusions. The factors, determining the modification efficiency of elastomeric inclusions in epoxy matrices, are analyzed. The regularities of the phase separation in curing system and the control of the interface interaction and morphology of epoxy polymers with elastomeric inclusions are considered.     

Photoinduced Structural Changes in Poly(4-Vinyl Pyridine): A Luminescence Study

In the present work we show a way of controlling photoluminescence (PL) properties through photoinduced quasi-crystal formation in a system based on poly(4-vinyl pyridine) (P4VPy). Under UV irradiation at 380 nm, concentrated solutions of P4VPy in pyridine turn into gel. This phase transition results in changes in the optical properties of this polymer. The position of the PL maximum can be changed continuously from 440 to 480 nm during irradiation. After several minutes of UV irradiation a new red-shifted PL at 492 nm appears upon excitation by light of a wavelength corresponding to that of the initial PL maximum, which is also red-shifted during irradiation. Solutions of P4VPy in pyrimidine show similar behavior, but those in pyridazine do not exhibit such behavior. We have found that the reason for the observed changes in the electronic properties is a photoinduced directional ordering of polymer molecules in a special quasi-crystal formation. The process originates from a structural change in the side chain of P4VPy, namely, protonation of the polymeric pyridine after solvation. During irradiation, the polymeric pyridinium ion interacts with neutral polymeric pyridine molecules. Interchain interaction through hydrogen bonds lead to an electronic property change. We observed that the process of photoinduced sol-gel transformation is reversible. Mechanical perturbation or heating can convert the gel back to a fluid solution. The red-shifted PL is not observed, and the initial PL is blue-shifted to 450 nm and stays there.     

Chirality of exo-heterosubstituted semiquinoid systems

Conclusions The observation of diastereotopism of the methoxy groups (at a distance of eight bonds from the asymmetric center) in the PMR spectra of 4,4-disubstituted l-(dimethylphosphorylmethylidene)-2,5-cyclohexadienes has been used to demonstrate the chirality of para-semiquinoid systems containing a heteroatom in the unsaturated exo-fragment of the molecule and two substituents distinguishable from each other in the geminal position.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2296–2299, October, 1986.     

Influence of the size-dependent surface tension of a liquid film on a capillary force in an atomic force microscope

An adsorbed water film always exists between the sample and the probing tip of an atomic force microscope operating at atmospheric conditions. A new expression for the capillary force that acts between the tip and the thin liquid film has been obtained taking into account the size dependence of the surface tension of the liquid described by an exact solution of the Gibbs-Tolman-Koenig-Buff equation. The calculation agrees fairly well with the experimental results.