Synthesis and crystal structures of the new metal-rich ternary borides Ni_(12)AlB_8, Ni_(12)GaB_8 and Ni _(10.6)Ga_(0.4)B_6-examples for the first B _5 zig-zag chain fragment

摘要

Single crystals of the new borides Ni_(12)AlB_8, and Ni_(10.6)Ga_(0.4)B_6 were synthesized from the elements and characterized by XRD and EDXS measurements. The crystal structures were refined on the basis of single crystal data. Ni_(12)AlB_8 (oC252, Cmce, a=10.527(2), b=14.527(2), c=14.554(2), Z=12, 1350 reflections, 127 parameters, R_1(F)=0.0284, wR_2(F~2)=0.0590) represents a new structure type with isolated B atoms and B_5 fragments of a BB zig-zag chain. Because the pseudotetragonal metric crystals are usually twinned. Ni_(10.6)Ga_(0.4)B_6 (oP68, Pnma, a=12.305(2), b=2.9488(6), c=16.914(3), Z=4, 1386 reflections, 86 parameters, R_1(F)=0.0394, wR_2(F~2)=0.104) is closely related to binary Ni borides. The structure contains BB zig-zag chains and isolated B atoms. Ni_(12)GaB_8 is isotypical to the Al-compound (a=10.569(4), b=14.527(4) and c=14.557(5)).