Synthesis and crystal structure of Ba₂₆B₁₂Si₅N₂₇ containing [Si₂] dumbbells

Black, metallic luster, platelet single crystals of Ba₂₆B₁₂Si₅N₂₇ were grown on a BN crucible wall by slowly cooling from 900 °C to 27 °C. X-ray diffraction analysis revealed that Ba₂₆B₁₂Si₅N₂₇ crystallizes in an orthorhombic cell (a=17.6942(4) Å, b=34.1437(6) Å, c=10.0410(2) Å; space group Fdd2). Isolated nitridoborate anionic groups [BN₂]^3–, dumbbell-type Zintl polyanions [Si₂]^2.8–, and nitride anions N^3– are included in the structure. The structural formula is represented as (Ba²⁺)₂₆([BN₂]^3–)₁₂[([Si₂]^2.8–)_1.25(N^3–)_2×0.75]₂. The [Si₂]^2.8– dumbbell with a Si–Si length of 2.177(5) Å has a bond order of 2.6, which is close to the triple bond of Si. - Graphical abstract: Single crystals of Ba₂₆B₁₂Si₅N₂₇ grown by slow cooling from 900 °C have an orthorhombic crystal structure with space group Fdd2, containing nitridoborate anionic groups [BN₂]^3–, dumbbell-type Zintl polyanions [Si₂]^2.8–, and nitride anions N^3–. - Highlights: • A novel compound, Ba₂₆B₁₂Si₅N₂₇, was synthesized by slow cooling from 900 °C. • Single crystal X-ray diffraction clarified a new crystal structure. • Anionic groups [BN₂]^3– and dumbbell-type Zintl polyanions [Si₂]^2.8– are contained. • The [Si₂]^2.8– dumbbell has a bond order of 2.6, which is close to the triple bond