Physics:Square antiprismatic molecular geometry

From HandWiki
Square antiprismatic molecular geometry
ExamplesXeF2−8, ReF8
Point groupD4d
Coordination number8
μ (Polarity)0

In chemistry, the square antiprismatic molecular geometry describes the shape of compounds where eight atoms, groups of atoms, or ligands are arranged around a central atom, defining the vertices of a square antiprism.[1] This shape has D4d symmetry and is one of the three common shapes for octacoordinate transition metal complexes, along with the dodecahedron and the bicapped trigonal prism.[2][3]

Like with other high coordination numbers, eight-coordinate compounds are often distorted from idealized geometries, as illustrated by the structure of Na3TaF8. In this case, with the small Na+ ions, lattice forces are strong. With the diatomic cation NO+, the lattice forces are weaker, such as in (NO)2XeF8, which crystallizes with a more idealized square antiprismatic geometry.



  1. D. L. Kepert (1978). "Aspects of the Stereochemistry of Eight-Coordination". Progress in Inorganic Chemistry 24: 179–249. doi:10.1002/9780470166253.ch4. ISBN 9780470166253. 
  2. Jeremy K. Burdett; Roald Hoffmann; Robert C. Fay (1978). "Eight-Coordination". Inorganic Chemistry 17 (9): 2553–2568. doi:10.1021/ic50187a041. 
  3. Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications ISBN:0-19-855370-6
  4. Langer, V.; Smrčok, L.; Boča, M. (2010). "Redetermination of Na3TaF8". Acta Crystallographica Section C 66 (9): pi85–pi86. doi:10.1107/S0108270110030556. PMID 20814090. 
  5. Peterson, W.; Holloway, H.; Coyle, A.; Williams, M. (Sep 1971). "Antiprismatic Coordination about Xenon: the Structure of Nitrosonium Octafluoroxenate(VI)". Science 173 (4003): 1238–1239. doi:10.1126/science.173.4003.1238. ISSN 0036-8075. PMID 17775218. Bibcode1971Sci...173.1238P.