Ladders of a Magnetically Active Element in the Structure of the Novel Complex Boride Ti9Fe2Ru18B8: Synthesis, Structure, Bonding, and Magnetism

Abstract

<p>Polycrystalline samples and single crystals of the complex boride Ti₉Fe₂Ru₁₈B₈ were synthesized by arc-melting the elements and characterized by single-crystal X-ray diffraction and energy-dispersive X-ray analysis. Ti₉Fe₂Ru₁₈B₈ is a new substitutional variant of the Zn₁₁Rh₁₈B₈ structure type, space group <em>P</em>4/<em>mbm</em> (No. 127), whose remarkable feature is that it contains one-dimensional chains of dumbbells of magnetically active Fe atoms, which form “ladders” along the <em>c</em> 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, Ti₉Fe₂Ru₁₈B₈ 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 <em>c</em> axis as the origin of the magnetic behavior.</p>