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  • 1
    Electronic Resource
    Electronic Resource
    Thermodynamic properties of the spin-Peierls transition in CuGeO3 (1995)
    Springer
    The European physical journal 98 (1995), S. 167-169 
    Details
    ISSN: 1434-6036
    Keywords: 65.50 + m ; 75.10.Jm ; 75.50.Ee
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present an investigation of the spin-Peierls transition atT SP=14.5 K in polycrystalline CuGeO3 through specific-heat and thermal-expansion measurements. Clear second-order phase-transition anomalies are found in both properties atT SP, although only a small entropy of S≈0.1 Rℓn2 is released at the transition. Most of the entropy is released atT SP〈T〈150 K, where the temperature dependence of the magnetic contribution to the specific heat as well as the thermal expansion exhibit extrema atT *≈40 K. These are caused by one-dimensional antiferromagnetic fluctuations along the Cu chains, possibly accompanied by structural fluctuations. Using Ehrenfest's relation, a hydrostatic pressure coefficient (∂T SP/∂p)p→0 ≈ (0.45±0.06) K/kbar is derived.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01324522
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  • 2
    Electronic Resource
    Electronic Resource
    New polymer coated anion-exchange HPLC-phases: Immobilization of poly (2-hydroxy, 3N-ethylenediamino) butadiene on silica and alumina (1987)
    Springer
    Chromatographia 23 (1987), S. 435-441 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Anion-exchange stationary phases ; Polymer coating ; Cross-linking
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary PHEB=POLY(2-hydroxy, 3N-ethylenediamino)butadiene has been synthesized. This unsaturated pre-polymer can be immobilized on different, preferably inorganic supports of suitable porosity such as silica or alumina by cross-linking. Weak anion-exchange phase are obtained. Such phases do not have the disadvantages of organic polymeric phases, regarding pressure stability and swelling by solvent influence. The ion-exchange capacity and the retentivity of IE-separations can deliberately be varied via the thickness of the cross-linked polymer layer. Alumina can also be coated with PHEB applying the same cross-linking procedure. Such phases exhibit an exceptional chemical stability even when operated with mobile phases at very high pH-values. Separations of excellent selectivity are achieved for inorganic anions, as well as with mixtures of aliphatic and aromatic free acids also including hydroxy- (mono- or poly)carboxylic acids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02311821
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  • 3
    Electronic Resource
    Electronic Resource
    HPLC-separation of enantiomers using quinine, covalently bonded to silica as stationary phase (1988)
    Springer
    Chromatographia 25 (1988), S. 265-271 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chiral phases ; Polymer coating ; Quinine substituted polysiloxanes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Stationary phases for chiral separations have been synthesized by chemical modification of porous small particle silica using new procedures of fixation of the chiral moiety. So called pre-polymers of the methylpolysiloxane polysiloxane type are immobilized on silica surfaces by different procedures. These pre-polymers are substituted by chiral groups. Their synthesis is done externally i.e. not in-situ on the support surface. The immobilization on the silica surface is achieved by crosslinking and/or by chemical bonding. Anchor groups within the pre-polymer (e.g. SiH) as well as on the silica surface (SiOH) give rise to the chemical bonding therewith. Chiral phases with quinine as the chiral moiety were obtained which show high separation efficiency as well as chemical stability, in addition to the enantiomeric selectivity required for the separation of certain types of aliphatic and aromatic alcohols.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02324699
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  • 4
    Electronic Resource
    Electronic Resource
    Characterization of some commercial poly (styrene-divinylbenzene) copolymers for reversed-phase HPLC1 (1987)
    Springer
    Chromatographia 23 (1987), S. 341-349 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Cross-linked polystyrene ; Characterization of surfaces
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The properties of the poly(styrene-divinylbenzene) copolymers PRP-1 and PLRP-S have been studied by infrared spectroscopy and chromatographic techniques. The following results were obtained: PRP-1 and PLRP-S are spectroscopically very similar. Their surfaces are chemically neither homogeneous nor stable during use. Retained nonpolar solutes should be eluted with a mobile phase containing tetrahydrofuran. Uncharged acids and anions can be chromatographed without difficulty. Cations of amines should be chromatographed only with a mobile phase of low pH. Uncharged amino-alcohols cannot be chromatographed without the addition of a competitor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02316180
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  • 5
    Electronic Resource
    Electronic Resource
    Poly(vinylpyrrolidone)-coated silica: A versatile, polar stationary phase for HPLC (1986)
    Springer
    Chromatographia 21 (1986), S. 573-582 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Polyvinylpyrrolidone-coated silica gel ; Separation of polar compounds ; Separation of proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Poly(vinylpyrrolidone) (PVP) is immobilized on both, small- and large-pore silicas by thermal treatment, γ-radiation, or peroxide initiated polymerization. The hydrolytic stability of such a highly polar stationary phase significantly exceeds that of a comparable phase prepared by the chemical reaction of silica with a pyrrolidone ethyl dimethylchlorosilane silanization reagent. The properties of the different PVP-silicas are evaluated by elemental analysis, spectroscopy, and chromatography. Columns of PVP-silica packings can be used in several modes: a) under normal-phase conditions as a polar bonded stationary phase, b) under reversed-phase conditions, for the separation of organic proton-donor and hydrogen-bonding compounds, c) for the aqueous size exclusion chromatography of proteins, and d) with salt gradients for the hydrophobic interaction chromatography of proteins. The minimum observable reduced plate-height of PVP-silica columns is about 3. Double-layer polymer coating experiments using PVP-silica covered with poly(methyloctadecylsiloxane) have been performed to study diffusion and shielding effects of different polymer layers in the stationary phase. Depending on separation conditions, one or the other polymer governs the retention process. A mixed selectivity was observed in a reversed phase mode with acidic eluents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02311839
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  • 6
    Electronic Resource
    Electronic Resource
    LiSmAlF6  -  das erste Fluoroaluminat mit zweiwertigem Samarium (1991)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 606 (1991), S. 169-176 
    Details
    ISSN: 0044-2313
    Keywords: Lithium samarium hexafluoroaluminate ; preparation ; crystal structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: LiSmAlF6  -  the First Fluoroaluminate with Divalent SamariumLiSmAlF6, the first quaternary fluoride with Sm2+ that has been obtained as red transparent single crystals, is formed while heating corresponding mixtures of the starting materials in niobium or tantalum crucibles under argon after 7-10 d at about 800°C. Orange-red, microcrystalline powder samples of LiSmAlF6 could be prepared at T ≤ 700°C after 1-2 d under the same conditions.LiSmAlF6, crystallizes as a new structure type in P6322 (Nr. 182) with a = 507.9(1), c = 1 040.5(1) pm and Z = 2 (CAD4, 2 512 Io, Rw = 2,3%). The crystal structure of LiSmAlF6 is related to the LiCaAlF6 structure type whereby the essential difference lies in the coordination of the M2+ ions. Ca2+, as well as Sr2+ in LiSrAlF6, exhibit octahedral coordination, whereas Sm2+ has, surprisingly, trigonal prismatic coordination to F-. The two triangles of the SmF6 prism are twisted by 8.3° with respect to each other.Measurements of the magnetic susceptibility show the temperature dependence typically found for Sm2+. The Madelung part of the lattice energy has been calculated and is discussed.
    Notes: LiSmAlF6, das erste in Form roter, transparenter Einkristalle erhaltene quaternäre Fluorid mit Sm2+, bildet sich beim Erhitzen geeigneter Ausgangsmenge in Niob- oder Tantaltiegln unter Ar nach 7-10 d bei ca. 800°C. Orangerote, mikrokristalline Pulverproben von LiSmAlF6 können bei T ≤ 700°C bereits nach 1-2 Tagen unter sonst gleichen Bedingungen dargestellt werden.LiSmAlF6 kristallisiert in einem neuen Strukturtyp in P6322 (Nr. 182) mit a = 507,9(1), c = 1 040,5(1) pm und Z = 2(CAD4, 2 512 Io, Rw = 2,3%). Die Kristallstruktur von LiSmAlF6 ist dem LiCaAlF6-Typ verwandt, zeigt aber den wesentlichen Unterschied in der Umgebung für M2+ : Ca2+, wie auch Sr2+ in LiSrAlF6, werden oktaedrisch, Sm2+ jedoch überraschenderweise trigonal-prismatisch von F- koordiniert. Die beiden Dreiecke des SmF6-Prismas sind um 8,3° gegeneinander verdreht.Messungen der magnetischen Suszeptibilität zeigen die für Sm2+ typische Temperaturabhängigkeit. Der Madelunganteil der Gitterenergie wurde berechnet und diskutiert.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19916060117
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  • 7
    Electronic Resource
    Electronic Resource
    Über das neue gemischtvalente Ge7F16: [GeF6]2--Oktaeder zwischen [Ge6F10]2+-Schichten - zur stereochemischen Aktivität freier Elektronenpaare (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 623 (1997), S. 596-602 
    Details
    ISSN: 0044-2313
    Keywords: Germanium fluoride ; stereochemical activity ; crystal structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: About the New Mixed Valent Ge7F16: [GeF6]2- Octahedra between [Ge6F10]2+ Sheets - a Contribution to the Stereochemical Activity of Lone PairsFor the first time Ge7F16 colourless transparent single crystals have been prepared by the reduction of GeF4 with Ge at 300°C. The extremely hygroscopic fluoride crystallizes in a new structure type in Cc with a = 1818.0(6) pm, b = 754.3(2) pm, c = 1030.4(3) pm, β = 90.33(3)° und Z = 4.Ge7F16 is a mixed valent fluoride according to 6GeF2 × GeF4. Characteristical building units of the new structure type are [Ge6F10]2+ sheets, which are connected via [GeF6]2- octahedra. The Ge2+ within the sheets are coordinated by three nearest F- with distances of 183-218 pm and together with these form distorted trigonal pyramids. The structure of Ge7F16 can be considered as a member of the homologues series Gem4+Gen2+F4m+2n with m = 1 and n = 6. Bond order summations, band structure calculations and calculations of the Madelung part of the lattice energy. MAPLE, have been used for the discussion of the bonding situation.
    Notes: Neu dargestellt wurden farblose transparente Einkristalle von Ge7F16 durch Reduktion von GeF4 mit Ge bei 300°C. Das äußerst hygroskopische Fluorid kristallisiert in einem neuen Strukturtyp in der Raumgruppe Cc (Nr. 9) mit a = 1818.0(6) pm, b = 754.3(2) pm, c = 1030.4(3) pm, β = 90.33(3)° und Z = 4.Ge7F16 ist gemäß 6GeF2 × GeF4 ein gemischtvalentes Fluorid. Charakteristische Baugruppen des neuen Strukturtyps sind [Ge6F10]2+-Schichten, die über [GeF6]2--Oktaeder verbrückt sind. Die Ge2+ innerhalb der Schichten sind von je drei nächsten F- im Abstand von 183-218 pm koordiniert und bilden mit diesen verzerrte trigonale Pyramiden. Die Struktur von Ge7F16 läßt sich als Glied der homologen Reihe Gem4+Gen2+F4m+2n mit m = 1 und n = 6 beschreiben. Die Bindungsverhältnisse werden anhand von Bindungsordnungssummationen, Bandstrukturrechnungen und Berechnungen des Madelunganteils der Gitterenergie, MAPLE. diskutiert.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19976230193
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  • 8
    Electronic Resource
    Electronic Resource
    SmAlF5  -  ein neues SmII-fluoroaluminat mit Al2F10-Oktaederdoppeln und [AlF2/2F4/1]-Ketten (1993)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 619 (1993), S. 181-188 
    Details
    ISSN: 0044-2313
    Keywords: Samarium(II) fluoroaluminate ; preparation ; crystal structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: SmAlF5  -  a New Samarium(II) Fluoroaluminate with Al2F10 Bioctahedra and [AlF2/2F4/1] Chains.SmAlF5 has been obtained as orange-red transparent single crystals while heating mixtures of SmF3, Sm-powder and AlF3 (2:1:3) in a niobium crucible under Ar after 7-10 d at about 750°C. SmAlF5 crystallises in I 4/m (Nr. 87) with a=1 414.4(4), c=722.2(3) pm and Z=8 (CAD4, 4 340 IO, Rw=1.7%).The crystal structure of SmAlF5 is isotypic to BaTiF5. Characteristic building units are linear chains of trans-corner sharing AlF6 octahedra, which are connected via corners to two further AlF6 octahedra. Isolated Al2F10 octahedra lie disordered between such chains. The Sm atoms connect the AlF6 octahedra to a three-dimensional network. Measurements of the magnetic susceptibility show the temperature dependence typically found for Sm2+. The Madelung part of the lattice energy has been calculated and is discussed.
    Notes: SmAlF5 wurde in Form orangeroter transparenter Einkristalle beim Erhitzen von SmF3, Sm-Pulver und AlF3 (2:1:3) im Niobtiegel unter Ar nach 7-10 d bei ca. 750°C erhalten. SmAlF5 kristallisiert in I4/m (Nr. 87) mit a=1 414,4(4), c=722,2(3) pm und Z=8 (CAD4, 4 340 IO, Rw=1,7%).Die Kristallstruktur von SmAlF5 ist isotyp zu BaTiF5. Charakteristische Baugruppen sind lineare Ketten trans-Spitzen verknüpfter AlF6-Oktaeder, die über Spitzen mit zwei weiteren AlF6-Oktaedern verknüpft sind. Isolierte Al2F10-Oktaederdoppel liegen fehlgeordnet zwischen solchen Ketten. Die Sm-Atome verknüpfen die AlF6-Oktaeder zum dreidimensionalen Gerüst. Messungen der magnetischen Suszeptibität zeigen die für Sm2+ typische Temperaturabhängigkeit. Der Madelunganteil der Gitterenergie wurde berechnet und diskutiert.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19936190130
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