Ladders of a magnetically active element in the structure of the novel complex boride Ti₉Fe₂Ru₁₈B₈: Synthesis, structure, bonding, and magnetism

Polycrystalline samples and single crystals of the complex boride Ti ₉Fe₂Ru₁₈B₈ were synthesized by arc-melting the elements and characterized by single-crystal X-ray diffraction and energy-dispersive X-ray analysis. Ti₉Fe₂Ru ₁₈B₈ is a new substitutional variant of the Zn ₁₁Rh₁₈B₈ structure type, space group P4/mbm (No. 127), whose remarkable feature is that it contains one-dimensional chains of dumbbells of magnetically active Fe atoms, which form "ladders" along the c axis. The Fe-Fe distance within a dumbbell is 2.489(2) Å, and the Fe₂-Fe₂ distance between two dumbbells is 2.968(1) Å; in contrast, the chains are well-separated from each other by distances of at least 11.217(2) Å. According to the results of tight-binding electronic structure calculations, Ru-B and Ti-Ru contacts are responsible for the structural robustness, while Fe-Fe interactions influence the magnetic behavior. According to magnetization measurements, Ti₉Fe ₂Ru₁₈B₈ orders ferromagnetically between 10 and 200 K. A model for ferromagnetism in this ladder-based structure identifies ferromagnetic coupling among neighboring spin-triplet Fe₂ dimers along the c axis as the origin of the magnetic behavior.