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 Ni10.6Ga0.4B6 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. Ni10.6Ga0.4B6 (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).

Pentameric B5-units are longest fragments of a B–B zig-zag chain ever characterized in a boride. They are found in the structures of Ni12AlB8 and Ni12GaB8. The compounds are formed on annealing boron-rich τ-borides like Ni20AlB14.Figure optionsDownload as PowerPoint slide