Synthesis and crystal structure of Ba26B12Si5N27 containing [Si2] dumbbells

Abstract Black, metallic luster, platelet single crystals of Ba 26 B 12 Si 5 N 27 were grown on a BN crucible wall by slowly cooling from 900 °C to 27 °C. X-ray diffraction analysis revealed that Ba 26 B 12 Si 5 N 27 crystallizes in an orthorhombic cell ( a =17.6942(4) A, b =34.1437(6) A, c =10.0410(2) A; space group Fdd 2). Isolated nitridoborate anionic groups [BN 2 ] 3– , dumbbell-type Zintl polyanions [Si 2 ] 2.8– , and nitride anions N 3– are included in the structure. The structural formula is represented as (Ba 2+ ) 26 {[BN 2 ] 3– } 12 [{[Si 2 ] 2.8– } 1.25 (N 3– ) 2×0.75 ] 2 . The [Si 2 ] 2.8– dumbbell with a Si–Si length of 2.177(5) A has a bond order of 2.6, which is close to the triple bond of Si.