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'Pseudo Jahn Teller Effect' in keywords
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1987 (2)
1Author    W. Alter, Abriel, Ernst-Jürgen, Z. EhnderRequires cookie*
 Title    Vibronische Kopplung und dynamisch verzerrte Strukturen in Hexahalogenotelluraten(IV): Ergebnisse aus Tieftemperatur-Röntgenbeugungsuntersuchungen (300—160 K) und aus FTIR-spektroskopischen Experimenten (300—5 K) [1] Vibronic Coupling and Dynamically D istorted Structures in Hexahalogenotellurates(IV): Low Tem peratur X-Ray Diffraction (300—160 K) and FTIR-Spectroscopic (300—5 K) Results [1]  
 Abstract    From theoretical considerations a dynamically distorted octahedron as a result of vibronic coupling between the ground state and the first excited state should exist for 14 electron AX6E systems like TeX62-. A high symmetry crystal field yielding at least a center of symmetry for the Te position stabilizes this fluctuating structure, otherwise statical distortion will be observed. From X-ray diffraction experiments on antifluorite type compounds A 2TeX6 (A = Rb, Cs; X = Cl, Br) the averaged structure (m 3m symmetry) of the anions was found even at very low temperatures. The thermal parameters are not significantly different from those of similar S n X ^ -compounds. Distortions therefore are very small and are evident from FTIR spectroscopic meas­ urements only. Here very broad T lu-deformation vibration bands are observed down to tempera­ tures <10 K without splitting: A statically distorted species could not be frozen out. In contrast to XeF6 for TeX62~ the energy gap between the threefold, fourfold or sixfold minima of the potential surface (according to the symmetry of one component of the T ,u-vibration) is very small and shifted to temperatures lower than reached with the devices used for these experiments. 
  Reference    Z. Naturforsch. 42b, 1273—1281 (1987); eingegangen am 24. Juni 1987 
  Published    1987 
  Keywords    Lone Pair Electrons, Vibronic Coupling, Pseudo Jahn-Teller-Effect, Tellurates 
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 TEI-XML for    default:Reihe_B/42/ZNB-1987-42b-1273.pdf 
 Identifier    ZNB-1987-42b-1273 
 Volume    42 
2Author    Walter AbrielRequires cookie*
 Title    On the Stereochemistry of the Lone-Pair Electrons in AX 6 E-Systems: Dynamically Distorted Anion in (NH 4 ) 2 SeBr 6 , Statically Distorted Anion in l,3-Propanediammonium-Hexabromoselenate(IV) (C 3 N 2 H 12 )SeBr 6  
 Abstract    Using 293 K diffractometer intensity data, the crystal structures of (NH 4) 2 SeBr 6 (1) and [H 3 N(CH 2) 3 NH 3 ]SeBr 6 (2) have been determined by single crystal X-ray technique and refined to a final R w of 0.049 and 0.040, respectively. The dark red crystals of 1 are cubic (space group Fm3m) with a = 10.478(2) Ä and Z = 4. This structure contains SeBe 6 2 ~ octahedra (point symmetry m3m, distance Se —Br: 2.577(2) Ä) in an antifluorite type arrangement of cations and anions. In contrast, the SeBr fi 2-ion in 2 is statically distorted (approximate point symmetry 3m, distance Se-Br min. 2,547(2), max. 2.595(2) Ä. The dark red crystals are orthorhombic (space group Pnma) with a = 17.795(3), b = 7.5037(6), c = 10.476(1) Ä and Z = 4. The results agree with the rules for the appearance of a static/dynamic stereochemical effect of the lone pair electrons given for TeX 6 2 " (X = Cl, Br, I) species (W. Abriel, Acta Crystallogr. B 42, 449 (1986)). Consequently these rules can be extended considering SeX 6 2-as well. Basic structural data for all compounds containing AX 6 2-ions (A = Se, Te; X = Cl, Br, I) known to date are given including the zl-values (R. D. Shannon, Acta Crystallogr. A 32, 751 (1976)) as a measure for the distortion of the octahedral anion. 
  Reference    Z. Naturforsch. 42b, 415—420 (1987); received November 24 1986/January 12 1987 
  Published    1987 
  Keywords    Lone Pair Electrons, Pseudo-Jahn-Teller Effect, Symmetry Rules, Selenates, Crystal Structure 
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 TEI-XML for    default:Reihe_B/42/ZNB-1987-42b-0415.pdf 
 Identifier    ZNB-1987-42b-0415 
 Volume    42