ISSN:
0044-2313
Keywords:
Th4Ta18O53
;
U4Ta18O53
;
chemical transport
;
crystal structure
;
Jahnberg-structure-family
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Description / Table of Contents:
Synthesis and Structure of M4Ta18O53 (M = Th, U); the First Representatives with a New Structure Type à la JahnbergColorless {brownblack}, hexagonal crystals of Th4Ta18O53 {U4Ta18O53} were obtained by chemical transport. Several mixtures of powders were used as starting materials for chemical transport reactions. Cl2 or TaCl5/Cl2 were applied as transport agents in several temperature gradients. The lattice constants are a = 6.2554(5) Å {6.253(1) Å}, c = 27.709(5) Å {27.609(6) Å} and Z = 1. Structure determination in the space group P63/mcm (no. 193) let to R1 = 0.0269 (wR2 = 0.0629) {R1 = 0.0295 (wR2 = 0.0674)}. Thorium as well as Uran is surrounded by oxygen like an trans-bis-capped octahedron (CN = 8) and Tantalum1 and Tantalum2 like pentagonal-bipyramids (CN = 7). The formula (Th2O3)2(Ta3O8)6 corresponds to the principle of building for the ideal construction. Because of necessarity of valence compensation the number of O-atoms in the real structure is diminished by one.The Th—O- and U—O-coordination polyhedra are for themselves arranged to o-layers and the Ta1—O- and Ta2—O-bipyramids for each other to p-layers. These layers are edge linked along the c-axes with a sequence of p-p-p-o-p-p-p-o. In fact of this these compounds are the first examples of the new structure type p-p-p-o as a member of a structure-family first described by Jahnberg. The various members differ in the sequence of layers with octahedral (o) and pentagonal-bipyramids (p).
Notes:
Durch chemischen Transport mit Cl2 oder TaCl5/Cl2 als Transportmittel wurden ausgehend von entsprechenden Ausgangsbodenkörpern im Temperaturgefälle T2 → T1 (z. B. 1000 °C → 980 °C) farblose {braunschwarze}, hexagonale Einkristalle von Th4Ta18O53 {U4Ta18O53} mit den Gitterkonstanten a = 6,2554(5) Å {6,253(1) Å}, c = 27,709(5) Å {27,609(6) Å} und Z = 1 erhalten. Die Strukturaufklärung in der Raumgruppe P63/mcm (Nr. 193), die bei R1 = 0,0269 (wR2 = 0,0629) {R1 = 0,0295 (wR2 = 0,0674)} konvergierte, ergab für Th {U} CN = 8 sowie Ta1 und Ta2 CN = 7. Th {U} ist in Form eines trans-bis-bekappten Oktaeders, Ta1 und Ta2 pentagonal-bipyramidal von Sauerstoff umgeben. Dem Bauprinzip der Idealstruktur entspricht die Formulierung (Th2O3)2(Ta3O8)6, die für die Realstruktur aufgrund des Valenzausgleiches um ein O-Atom zu vermindern ist.Die Th—O-{U—O-} Koordinationspolyeder sind in o-Schichten, die Ta1—O- und Ta2—O-Bipyramiden jeweils für sich in p-Schichten so angeordnet, daß sich eine Schichtabfolge p-p-p-o-p-p-p-o in c-Richtung ergibt. Hiernach sind die beiden Verbindungen als erste Vertreter einer neuen Variante der von Jahnberg erstmals beschriebenen Strukturen anzusehen, für die verschiedene Schichtabfolgen aus oktaedrischen (o) und pentagonal-bipyramidalen (p) Baueinheiten charakteristisch sind.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/zaac.19966220412
