New Examples for the Unexpected Stability of the 10π-Electron Hückel Arene [Si6]10–

✍ Scribed by Raul Cardoso Gil; Wilder Carrillo-Cabrera; Martin Schultheiss; Karl Peters; Hans Georg von Schnering; Yuri Grin

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: German
• Weight: 524 KB
• Volume: 625
• Category: Article
• ISSN: 0372-7874
• DOI: 10.1002/(sici)1521-3749(199902)625:2<285::aid-zaac285>3.0.co;2-v

✦ Synopsis

The compounds Ba 4 Ag 2 Si 6 , Eu 4 Ag 2 Si 6 , and Ca 4 Ag 2 Si 6 , prepared from the elements at 1273 K (the components in inner corundum crucibles are enclosed in sealed quartz ampoules), are brittle semiconductors with silvery luster. They react slowly with acids liberating hydrogen. Ba 4 Ag 2 [Si 6 ] and Eu 4 Ag 2 [Si 6 ] crystallize like Ba 4 Li 2 [Si 6 ] (space group Fddd

(No. 70); a = 8.613 A Ê , b = 14.927 A Ê , c = 19.639 A Ê , and a = 8.420 A Ê , b = 14.585 A Ê , c = 17.864 A Ê , respectively), whereas Ca 4 Ag 2 [Si 6 ] represents a new structure type (space group Fmmm (No. 69); a = 8.315 A Ê , b = 14.391 A Ê , c = 8.646 A Ê ). The three compounds are Zintl phases with the formal charges M 2+ , Ag + and [Si 6 ] 10± . The mean bond lengths d(Si±Si) = 2.335±2.381 A Ê in the 10p-Hu È ckel arene [Si 6 ] 10± as well as d(Ag±Si) = 2.464±2.595 A Ê vary with the size of the M 2+ cations. The chemical bonding was analyzed in terms of the Electron Localization Function (ELF) and compared with the bonding in related systems (Ce 4 Co 2 Si 6 ).