Raman scattering investigation of ferroelastic Sb5O7I crystals

Sb₅O₇I undergoes a displacive phase transition at 481 K where the symmetry is changed fromC _6h ² toC _2h ⁵ . In the low temperature monoclinic phase the crystal is ferroelastic. The polarized Raman spectra of Sb₅O₇I have been measured at various temperatures below and above the phase transition. The frequencies and symmetries of most of the theoretically expected Raman active phonons in the ferroelastic phase have been determined. The observation of a soft mode in the ferroelastic phase which disappears above the phase transition together with the fact that the unit cell of the ferroelastic phase is twice as large as that of the paraelastic structure permits the conclusion that the phase transition results from a phonon instability at the Brillouin zone boundaryM-point of the hexagonal phase. The temperature dependent splittings and intensity changes of several Raman lines are discussed with respect to the ferroelastic property of the crystal and the phase transition.     

Investigations of the selective population of hydrogen subsurface sites on Pd(110) using He diffraction and thermal-desorption spectroscopy

Surface-structure models for the 2×1 and 1×2 hydrogen chemisorption phases formed on Pd(110) at 100 K have been derived from He-diffraction data. The respective coverages correspond to 1 and 1.5 monolayers (ML). Upon heating to 200 K, the 1×2 saturation phase transforms back into the 2×1, and 0.5 ML hydrogen moves subsurface. Based on structural arguments, we suggest that only the first available subsurface sites, i.e., the octahedral interstitials between topmost and second layers are populated by thermal activation. The subsurface movement is eased since H-chemisorption sites on top of the second Pd layer can be occupied in the 1×2 owing to substrate reconstruction. Structural considerations also explain that exactly 1 ML H can be accommodated subsurface by thermal cycling. New TDS measurements corroborate these notions: only the ₂ desorption state, probably associated with Hin subsurface sites between first and second Pdlayers, is selectively filled by the thermal-cycling processes. The ₁ state remains empty upon thermal cycling, and is very likely connected with hydrogen deeper in the bulk.     

Dramatic selectivity changes on carrier gas flow change in a series-coupled GC capillary tandem

We describe the polarity of selectivity of a GC separation system in terms of Retention Index data. In a series-coupled capillary system having stationary phases of differing polarity even slight (independent!) carrier gas flow changes in one part of the capillary series result in a dramatic change of selectivity. “Dramatic” is a relative term! Using a simple electronically controlled flow changing device we found retention index changes of several hundred units for polar test compounds such as phenols on a SE30/Carbowax tandem. This means: The classical theoretical model for understanding retention (and selectivity) in chromatography must be corrected. We propose a very simple approach involving addition of the expression RESIDENCE TIME to the chromatographic vocabulary. Instead of using flow resistors, one can just add a pressure regulator to the coupling point. A powerful analytical concept is now in easy reach.     

Configurationally and conformationally homogeneous cyclicN-aryl sulfimides. I. Synthesis and mechanism of formation

Reactions of thianes andcis-andtrans-1-thiadecalins with 4-chloroaniline andN-chlorsuccinimide ortert-butylhypochlorite gave configurationally homogeneous cyclicN-4-chlorophenyl sulfimides. With appropriately substituted sulfides conformationally homogeneous thiane-and cis-1-thiadecalin-1-imides were obtained. Formation of sulfimides with axially oriented S–N bond is strongly disfavoured. Reactions with conformationally rigid ring systems yielded only sulfimides with equatorial S–N bond; two isomeric sulfimides, both with equatorial S–N bond, were obtained with the mobilecis-1-thiadecalin. Sulfimides with axial S–N bond were prepared from conformationally rigid sulfoxides with equatorial S–O bond. It is assumed that formation of sulfimides with rigid ring systems proceeds viaN-chloroanilines, while reactions of conformationally mobile systems withN-chlorosuccinimide may also occur via intermediate succinimidyl sulfonium ions.

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Konfigurativ und konformationell einheitliche cyclische N-Aryl-sulfimide.I. Synthese und Bildungsmechanismus

Zusammenfassung Durch Umsetzung von Thianen und voncis- undtrans-1-Thiadekalinen mit 4-Chloranilin undN-Chlorsuccinimid odertert-Butylhypochlorit wurden konfigurativ einheitliche cyclischeN-4-Chlorphenylsulfimide dargestellt. Bei geeigneter Substitution am Heteroring wurden konformativ einheitliche Thianundcis-1-Thiadekalin-1-imide erhalten. Die Bildung von Sulfimiden mit axial orientieter S–N-Bindung ist stark benachteiligt. Konformativ starre Ringsysteme führen praktisch ausschließlich zu den Sulfimiden mit äquatorialer S–N-Bindung; aus dem konformativ beweglichencis-1-Thiadekalin werden bei der Umsetzung mittert-Butylhypochlorit zwei isomere Sulfimide, beide mit äquatorialer S–N-Bindung, erhalten. Sulfimide mit axialer S–N-Bindung wurden aus konformativ starren Sulfoxiden mit äquatorialer S–O-Bindung erhalten. Es wird angenommen, daß die Sulfimidbildung bei konformativ starren Ringsystemen weitgehend überN-Chloraniline, bei Umsetzung von beweglichen Ringsystemen mitN-Chlorsuccinimid auch über Succinimidylsulfoniumionen verläuft.

     

Preparation,characterization, and binding profile of imprinted semi-IPN cryogel composite for aluminum

Human body is greatly exposed to aluminum due to its high abundance in the environment. This nonessential metal is a threat to the patients of chronic renal disorders, as it is easily retained in their plasma and quickly accumulates in different tissues. Thus, there is great need to remove it from the aqueous environment. In this study, Al³⁺ imprinted semiinterpenetrating polymer network (semi-IPN)-based cryogel composite was prepared and applied for the purification of environmental and drinking water samples from aluminum. Poly (2-hydroxyethyl methacrylate) (pHEMA) discs were produced via cryogenic treatment and imprinted semi-IPN was introduced to the 3-(trimethoxysilyl) propyl acrylatemodified macroporous cryogel discs. The adsorption properties and selectivity of the aluminum (III) imprinted semi-IPN cryogel composite were studied in detail. The imprinted semi-IPN cryogel composite showed good selectivity towards aluminum (III) ions with the imprinting factor (IF) of 76.4 in the presence of competing copper (II), nickle (II), and iron (III) ions. The maximum adsorption capacity of 271 μmol g^-1 was obtained for aluminum (III) at pH 7.0 within 10 min using imprinted semi-IPN cryogel composite. The good selectivity and reusability of aluminum (III)-imprinted semi-IPN cryogel composite makes this material an eligible candidate for the purification of drinking water from aluminum (III) leaving important minerals remained in the water.