ISSN:
0044-2313
Keywords:
Cr5B3 Type
;
Ca5Hg3
;
Sr5Cd3
;
Crystal Structure
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Description / Table of Contents:
Preparation and Crystal Structure of Ca5Hg3 and Sr5Cd3Both the incongruently melting compounds, Ca5Hg3 and Sr5Cd3, have been synthesized from stoichiometric amounts of the pure elements. They crystallize with the Cr5B3 type of structure: space group I4/mcm, Z = 4; Ca5Hg3 (Sr5Cd3): a = 818.9(1) (871.7(1)) pm, c = 1 470.1(3) (1 660.1(3)) pm, c/a = 1.80 (1.90), R = 2.33% (2.97%). The most remarkable fragments are dumbbells X2, which have interatomic distances only slightly longer than the sum of Pauling's covalent radii: Hg—Hg (Cd—Cd) = 306 (298) pm. The structure can be constructed by rhombic dodecahedra as the only constituent moieties. These rhombic dodecahedra are built up by eight Ca (Sr) atoms and six Hg (Cd) atoms and are furthermore centered by an additional Ca (Sr) atom. Along [001] the rhombic dodecahedra share common vertices, but along [110] they are interconnected via common triangular faces. This kind of face sharing is responsible for the short distances obtained between the polyhedra, which leads to the occurrence of the dumbbells mentioned above.
Notes:
Die inkongruent schmelzenden Verbindungen Ca5Hg3 und Sr5Cd3 werden aus stöchiometrischen Mengen der reinen Elemente hergestellt. Beide Verbindungen kristallisieren im Cr5B3-Typ: Raumgruppe I4/mcm, Z = 4; Ca5Hg3 (Sr5Cd3): a = 818,9(1) (871,7(1)) pm, c = 1 470,1(3) (1 660,1(3)) pm, c/a = 1,80 (1,90), R = 2,33% (2,97%). Das bemerkenswerteste Strukturmerkmal sind diatomare Hanteln der Minderheitskomponente mit Abständen Hg—Hg (Cd—Cd) von 306 (298) pm. Als strukturaufbauendes Polyeder kann man ein längs [001] gestrecktes Rhombendodekaeder aus acht Ca-(Sr-) und sechs Hg-(Cd-) Atomen wählen, das von einem zusätzlichen Ca- (Sr-) Atom zentriert wird. Die Rhombendodekaeder sind entlang [110] über einige ihrer Rhomben flächenverknüpft, wodurch sich zwei Rhombendodekaeder so nahe kommen, daß die erwähnten Hanteln ausgebildet werden können.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/zaac.19946201102
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