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2001 (1)
2000 (3)
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1Author    Z. Akdeniz, M. P. TosiRequires cookie*
 Title    A Refined Ionic Model for Clusters Relevant to Molten Chloroaluminates  
 Abstract    A model of ionic interactions in neutral and ionized aluminium trichloride clusters, which accounts for ionic deformability through (i) effective valences and (ii) electrostatic and overlap polarizabilities, is evaluated for applications to classical simulation studies of the pure melt and of molten alkali chloroaluminates. The disposable parameters in the model are determined from the measured values of the bond length in the (A1C1 4)~ molecular ion and of an Al-Cl bond length and a vibrational frequency in the A1 2 C1 6 molecular dimer. The model is tested against the remaining available data from experiment and from quantum chemical calculations on molecular bond lengths, bond angles and vibrational frequencies for A1 2 C1 6 , (A1C1 4)~ and (A1 2 C1 7)~ clusters. Structural and dynamical properties are also evaluated for the (A1 2 C1 5) + , A1C1 3 and (A1C1 2) + clusters. The results for the energetics of dissociation, ion transfer and isomer excitation reactions are compared with as yet unpublished data obtained by P. Ballone in first-principles calculations by a density functional method. The overall quality of the tests supports the approximate validity and transferability of the model. 
  Reference    Z. Naturforsch. 54a, 180—186 (1999); received February 17 1999 
  Published    1999 
  Keywords    Ionic Clusters, Liquid Structure, Molten Salts 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0180.pdf 
 Identifier    ZNA-1999-54a-0180 
 Volume    54 
2Author    Z. Akdeniz, M. P. TosiRequires cookie*
 Title    Structure and Vibrational Spectra of the Vapour Molecules Fe 2 Cl 6 and AlFeCl 6  
 Abstract    Melting of aluminium and iron trichloride crystals is accompanied by a structural transition from octa-hedral to tetrahedral coordination of the metal ions, and a widely accepted interpretation of their liquid structure is that it mainly consists of strongly correlated dimeric units. Such A1 2 C1 6 and Fe 2 Cl 6 mole-cules are stable in the vapour phase and coexist in gaseous mixtures together with AlFeCl 6 molecules. In this work we extend to Fe 2 Cl 6 and AlFeCl 6 our earlier study of the ionic interactions in A1 2 C1 6], using a model which accounts for ionic deformability through (i) effective valences and (ii) electrostatic and overlap polarizabilities. The main disposable parameters of the model are adjusted to the Fe-Cl bond length in FeCl 3 monomer molecule and to the Fe-Fe bond length and a bond-stretching frequency in the Fe 2 Cl 6 molecule. The results are used to evaluate the structure of the AlFeCl 6 molecule, which has so far only been inferred from the observed Raman spectrum in mixed vapours. Extensive comparisons with data on molecular vibration-al frequencies are also presented for Fe 2 Cl 6 and AlFeCl 6 . 
  Reference    Z. Naturforsch. 54a, 477—481 (1999); received August 3 1999 
  Published    1999 
  Keywords    Ionic Clusters, Molecular Vapours, Molten Salts 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0477.pdf 
 Identifier    ZNA-1999-54a-0477 
 Volume    54 
3Author    Z. Akdeniz, M. P. TosiRequires cookie*
 Title    Static and Dynamic Structure of AU 2 C1 6 , AUA1C1 6 and AuFeCl 6 Clusters  
 Abstract    Fourfold coordination of trivalent metal ions by chlorines in molecular dimers changes from tetrahedral in A1 2 C1 6 and Fe 2 Cl 6 to planar in Au 2 Cl 6 . Within an ionic model we interpret this transition in the stable molecular shape as due to the quadrupolar polarizability of the gold(III) ion. We also demonstrate within the same model that a mixed tetrahedral-planar coordination is stable in AUA1C1 6 and AuFeCl 6 clusters. Quantitative comparisons are presented for the calculated molecular structures and vibrational frequencies against the available experimental data from crystalline diffraction and from Raman spectra of the crystal and of vapours. 
  Reference    Z. Naturforsch. 55a, 495—198 (2000); received February 12 2000 
  Published    2000 
  Keywords    Ionic Clusters, Molecular Vapours, Molecular Crystals 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0495.pdf 
 Identifier    ZNA-2000-55a-0495 
 Volume    55 
4Author    Z. Akdeniz, M. Çaliskan, Z. Çiçek, M. P. TosiRequires cookie*
 Title    Polymerie Structures in Aluminium and Gallium Halides  
 Abstract    The anionic species (Al" X3 n+ iwith X = CI or Br and n > 1 have been recognized for a number of years to form in acidic liquid mixtures of aluminium chloride or bromide with the corresponding halides of alkali or organic cations, in relative proportions which vary with the composition of the mixture. In this work we evaluate the structure and the energetics of such polymeric series in a comparative study of Al and Ga compounds. To this end we first extend an earlier study of the ionic interactions in the A1 2 C1 6 molecule] to determine microscopic ionic models for Ga 2 Cl 6 , Al 2 Br 6 , and Ga 2 Br 6 . The models are then used (i) to evaluate the polymeric clusters for n < 4 in the two trivalent-metal chlorides, and (ii) to explore the potential-energy hypersurface of alkali counterions in the case n = 2. We present tests of the results against available data and an evaluation of the convergence of the energy of the polymeric series towards a value of about 0.5 eV per monomer. 
  Reference    Z. Naturforsch. 55a, 575—580 (2000); received February 18 2000 
  Published    2000 
  Keywords    Ionic Clusters, Molecular Vapours, Molten Salts 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0575.pdf 
 Identifier    ZNA-2000-55a-0575 
 Volume    55 
5Author    Z. Akdeniz, M. P. TosiRequires cookie*
 Title    Structure and Energetics of Clusters Relevant to Thorium Tetrachloride Melts  
 Abstract    We study within an ionic model the structure and energetics of neutral and charged molecular clusters which may be relevant to molten ThCl 4 and to its liquid mixtures with alkali chlorides, with reference to Raman scattering experiments by Photiadis and Papatheodorou. As stressed by these authors, the most striking facts for ThCl 4 in comparison to other tetrachloride compounds (and in particular to ZrCl 4) are the appreciable ionic conductivity of the pure melt and the continuous structural changes which occur in the melt mixtures with varying composition. After adjusting our model to data on the isolated ThCl 4 tetrahedral molecule, we evaluate (i) the Th 2 Cl 8 dimer and the singly charged species obtained from it by chlorine-ion transfer between two such neutral dimers; (ii) the ThCl 6 and ThCl 7 clusters both as charged anions and as alkali-compensated species; and (iii) various oligomers carrying positive or negative double charges. Our study shows that the characteristic structural properties of the ThCl 4 compound and of the alkali-Th chloride systems are the consequence of the relatively high ionic character of the binding, which is already evident in the isolated ThCl 4 monomer. 
  Reference    Z. Naturforsch. 55a, 772—778 (2000); received August 13 2000 
  Published    2000 
  Keywords    Ionic Clusters, Liquid Structure, Molten Salts 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0772.pdf 
 Identifier    ZNA-2000-55a-0772 
 Volume    55 
6Author    Z. Akdeniza, M. P. TosiaRequires cookie*
 Title    Structure and Binding of Ionic Clusters in Th and Zr Chloride Melts  
 Abstract    We discuss microscopic ionic models for the structure and the binding of small clusters which may exist as structural units in molten ThCl4 and ZrCl4 and in their mixtures with alkali halides according to Raman scattering studies of Photiadis and Papatheodorou. The models are adjusted to the two isolated tetrahedral molecules. Appreciably higher ionicity is found for ThCl4 than for ZrCl4, and this fact underlies the strikingly different behaviour of the two systems in the dense liquid state -in particular, a molecular-type structure for molten ZrCl4 against a structure including charged oligomers in molten ThCl4. 
  Reference    Z. Naturforsch. 56a, 717—720 (2001); received September 10 2001 
  Published    2001 
  Keywords    Ionic Clusters, Liquid Structure, Molten Salts 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0717.pdf 
 Identifier    ZNA-2001-56a-0717 
 Volume    56