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  • 1
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Semiempirical band structure calculations were performed on several skutterudite-type compounds by using the extended Hückel method. Starting with the molecular orbital calculations on isolated P4 and As4 rings, the reason for the band dispersions of the skutterudites was found to be the interactions between the nonmetal atoms. Both the intermolecular and the intramolecular interactions between the phosphorus atoms are stronger than those between the arsenic atoms. Hence, the dispersion of the bands in CoP3 is larger than that in CoAs3. The COOP (crystal orbital overlap population) integrals of the intramolecular P-P bonds reveal the relation between the valence electron count and the observed bond lengths. The P-P bonds in the skutterudite-type compounds like TP3 (T = Co, Rh, Ir) become stronger by reduction as in NiP3 and weaker by oxidation as in RT4X12 (X = P, As, Sb; R = alkaline earth or rare earth metals) because the bands near the Fermi level are bonding. The electronic reason for the geometric distortion of the Ge2Y2 (Y = S, Se) units of mixed skutterudites TGe1.5Y1.5 is caused by an electron pair gap on germanium, which corresponds to low electron density perpendicular to the ring plane on the germanium atoms.
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  • 2
    ISSN: 0044-2313
    Keywords: Dilithium magnesium tetrachloride ; dilithium vanadium tetrachloride ; dilithium cadmium tetrachloride ; crystal structures ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Crystal Structures of MgCrO4-type Li2VCl4 and Spinel-type Li2MgCl4 and Li2CdCl4The crystal structures of the ternary lithium chlorides Li2MCl4 (M = Mg, V, Cd) have been determined firstly by X-ray single-crystal experiments. Li2MgCl4 and Li2CdCl4 crystallize in an inverse spinel structure (space group Fd3m, Z = 8, a = 1 040.1(2) and 1 062.06(9) pm, structural parameters u = 0.25699(2) and 0.2550(1), R = 1.7 and 3.7% for 218 and 211 unique reflections). The Li—Cl distances of the tetrahedrally coordinated Li+ ions are significantly greater than calculated with Shannon's crystal radii ( 〉 238 ± 1 instead of 233 pm). Contrary to the results of X-ray powder data reported in the literature, Li2VCl4 crystallizes in the distorted spinel structure of MgCr2O4 type (space group F43m, Z = 8, a = 1 037.49(2) pm, R = 5.9% for 217 unique reflections). The decrease of the site symmetry of the octahedrally coordinated ions (V2+, Li+) from 3m to 3m resulting in contracted and widened tetrahedral M4 entities of the spinel structure is obviously caused by V—V metal - metal bonds (shortest V—V distance 366.2(7) pm).
    Notes: Die Kristallstrukturen der ternären Lithiumchloride Li2MCl4 (M = Mg, V, Cd) wurden mittels Röntgen-Einkristallmessungen bestimmt. Li2MgCl4 und Li2CdCl4 kristallisieren in einer inversen Spinell-Struktur (Raumgruppe Fd3m, Z = 8, a = 1 040,1(2) und 1 062,06(9) pm, Lageparameter u = 0,25699(2) bzw. 0,2550(1), R = 1,7 bzw. 3,7% bei 218 bzw. 211 symmetrieunabhängigen Reflexen). Die Li—Cl-Abstände der tetraedrisch koordinierten Li+-Ionen sind signifikant größer als erwartet ( 〉 238 ± 1 anstatt 233 pm). Li2VCl4 kristallisiert entgegen Literaturangaben in der verzerrten Spinell-Struktur des MgCrO4-Typs (Raumgruppe F43m, Z = 8, a = 1 037,49(2) pm, R = 5,9% bei 217 symmetrieunabhängigen Reflexen). Die Erniedrigung der Lage-Symmetrie der oktaedrisch koordinierten Ionen (V2+, Li+) von 3m nach 3m, die alternierend zu einer Kontraktion und einer Aufweitung der tetraedrischen M4-Baueinheiten der Spinell-Struktur führt, wird von V—V—Metall - Metall-Bindungen verursacht (kürzester V—V-Abstand 366,2(7) pm).
    Additional Material: 1 Ill.
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  • 3
    ISSN: 0044-2313
    Keywords: Dimanganese tin tetrasulfide ; crystal structure ; magnetism ; IR ; Raman ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Structure Redetermination and Magnetic Studies on Mn2SnS4The crystal structure of Mn2SnS4 was redetermined by single crystal and powder X-ray studies. It has a deficient NaCl superstructure crystallizing in the orthorhombic space group Cmmm proposed by Wintenberger and Jumas in 1980 (Z = 2, a = 740.7(1), b = 1047.5(1) and c = 366.7(2) pm, Rf = 1.4% for 266 unique reflections with I 〉 0σ1). Some additional reflections, which are not compatible with this cell, can be refined assuming formation of twinned trilling crystals. Mn2SnS4 undergoes antiferromagnetic ordering below 160 K. The effective magnetic moment μeff of Mn2+ is 5.92 B.M. The IR and Raman spectra display 5 and 3 bands in the range 150-320 cm-1, respectively.
    Notes: Die Kristallstruktur von Mn2SnS4 wurde mittels Röntgeneinkristall- und Röntgenpulver-Messungen nachbestimmt. Mn2SnS4 besitzt eine defiziente NaCl-Überstruktur und kristallisiert, wie von Wintenberger und Jumas [6] vorgeschlagen, in der orthorhombischen Raumgruppe Cmmm (Rf = 1,4% für 266 unabhängige Reflexe mit I 〉 0σ1). Die in dieser Zelle nicht indizierbaren Reflexe können unter der Annahme einer Mehrlingsbildung verfeinert werden. Das effektive magnetische Moment μeff von Mn2+ beträgt 5,92 B.M. Unterhalb 160 K liegt eine antiferromagnetische Ordnung vor. Die IR-und Raman-Spektren zeigen 5 bzw. 3 Banden im Bereich von 150-320 cm-1.
    Additional Material: 4 Ill.
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  • 4
    Publication Date: 1999-11-29
    Description: Semiempirical band structure calculations were performed on several skutterudite-type compounds by using the extended Hückel method. Starting with the molecular orbital calculations on isolated P4 and As4 rings, the reason for the band dispersions of the skutterudites was found to be the interactions between the nonmetal atoms. Both the intermolecular and the intramolecular interactions between the phosphorus atoms are stronger than those between the arsenic atoms. Hence, the dispersion of the bands in CoP3 is larger than that in CoAs3. The COOP (crystal orbital overlap population) integrals of the intramolecular P-P bonds reveal the relation between the valence electron count and the observed bond lengths. The P-P bonds in the skutterudite-type compounds like TP3 (T = Co, Rh, Ir) become stronger by reduction as in NiP3 and weaker by oxidation as in RT4X12 (X = P, As, Sb; R = alkaline earth or rare earth metals) because the bands near the Fermi level are bonding. The electronic reason for the geometric distortion of the Ge2Y2 (Y = S, Se) units of mixed skutterudites TGe1.5Y1.5 is caused by an electron pair gap on germanium, which corresponds to low electron density perpendicular to the ring plane on the germanium atoms. ©1999 Springer-Verlag Berlin Heidelberg
    Print ISSN: 0342-1791
    Electronic ISSN: 1432-2021
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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