Nonaromatic Planar Si12 Ring System of Approximate D6h Symmetry in Ca7Mg7.5±δSi14

✍ Scribed by Reinhard Nesper; Antonio Currao; Steffen Wengert

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 310 KB
• Volume: 4
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/(sici)1521-3765(19981102)4:11<2251::aid-chem2251>3.0.co;2-#

✦ Synopsis

Ca 7 Mg 7.5AEd Si 14 is the correct stoichiometry of the so called Ca 7 Mg 6 Si 14 of Gladishevskii et al. [1] Ca 7 Mg 7.5AEd Si 14 is an approximate or unusual Zintl phase with metallic conductivity that is expected to be highly anisotropic. The crystal structure (P6/mmm (no. 191), a 12.696(2), c 4.4025(5) , Z 1) contains planar hexasilylhexasilacyclohexene anions (Si 12 ) of D 6h symmetry, with a formal charge of À (21 AE 2d), besides isolated Si 4À 4 anions. Quantum mechanical calculations based on the Extended Hückel and LMTO-ASA methods establish metallic properties due to a p* ± p* interaction of the ecliptically stacked Si 12 units. The planar ring system does not show aromaticity, but contains approximately 1.75 double bonds that are equally delocalized.