Synthesis and crystal structures of the new metal-rich ternary borides Ni12AlB8, Ni12GaB8 and Ni10.6Ga0.4B6—examples for the first B5 zig-zag chain fragment

Single crystals of the new borides Ni₁₂AlB₈, and Ni_10.6Ga_0.4B₆ were synthesized from the elements and characterized by XRD and EDXS measurements. The crystal structures were refined on the basis of single crystal data. Ni₁₂AlB₈ (oC252, Cmce, a=10.527(2), b=14.527(2), c=14.554(2) Å, Z=12, 1350 reflections, 127 parameters, R₁(F)=0.0284, wR₂(F²)=0.0590) represents a new structure type with isolated B atoms and B₅ fragments of a B-B zig-zag chain. Because the pseudotetragonal metric crystals are usually twinned. Ni_10.6Ga_0.4B₆ (oP68, Pnma, a=12.305(2), b=2.9488(6), c=16.914(3) Å, Z=4, 1386 reflections, 86 parameters, R₁(F)=0.0394, wR₂(F²)=0.104) is closely related to binary Ni borides. The structure contains B-B zig-zag chains and isolated B atoms. Ni₁₂GaB₈ is isotypical to the Al-compound (a=10.569(4), b=14.527(4) and c=14.557(5) Å).