Aluminum distribution in the boron framework of γ-AlB12

摘要: The crystal structure of γ-AlB12 (P212121; a = 16.573(4), b 17.510(3), c 10.144(1)A) was reinvestigated by single-crystal X-ray diffractometry and the nature metal distribution in boron framework examined. Starting from data published Hughes et al. (Journal American Chemical Society 83, 2337 (1977)), 458 independent parameters, including occupancies 11 Al sites, were finally refined to conventional R value 2.9%. A total 5282 observed unique reflections (MoKα radiation; 2θ < 64°) used. Although distributed an apparently complicated manner, aluminum atoms occur according simple rule as crystals α-AlB12 type. numbers valence electrons Al, allotted six subunits, B12(i–iv), B20-(C2, Cs), proportionately contact frequencies with units, are 2.2, 1.9, 5.3, 5.2, respectively. charge assignment is compatible ionic formula 203Al+3 · 4B12−2 2B20−6, proposed preliminary molecular orbital calculations. negative balance among units at about 1:1:1:1:3:3 seems be essential for making up stable γ-AlB12.