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The electronic structures of "Ti9-nFe2+nRu18B8" (n= 0, 0.5, 1, 2, 3); in connection to the recently synthesized Ti9-nFe2+n-RU18B8(n = 1, 2), have been investigated and analyzed using LSDA tight-binding calculations to elucidate the distribution of Fe and Ti, to determine the maximum Fe content, and to explore possible magnetic structures to interpret experimental magnetization results. Tbrough a combination of calculations on specific models and using tbe rigid band approximation, which is validated by the DOS curves for "T9-nFe2+nRu18B8" (n = 0, 0.5, 1, 2,3), mixing of Fe and Ti is anticipated at both tbe 2b- and 4h-chain sites. The model "Ti8.5Fe2.5Ru18B8" (n = 0.5) revealed that both Brewer-type Ti-Ru interactions as well as ligand field splitting ofthe Fe 3d orbitals regulated the observed valence electron counts between 220 and 228 electrons/formula unit. Finally, models of magnetic structures were created using "Ti6Fe5Ru18B8" (n = 3). A rigid band analysis of tbe LSDA DOS curves concluded preferred ferromagnetic ordering at low Fe content (n ⩽ 0.75) and ferrimagnetic ordering at higher Fe content (n > 0.75). Ferrimagnetism arises from antiferromagnetic exchange coupling in the scaffold of Fel-ladder and 4h-chain sites. [ABSTRACT FROM AUTHOR]

Transition-metal borides show not only promising physical properties but also a rich variety of crystal structures. In this context, quantum-chemical tools can shed light on important facets of the chemistry within such intermetallic borides. Using density-functional theory (DFT), we analyze in detail two phases of significant structural-chemical importance: the recently synthesized Ti1+xOs2-xRuB2 and the isotypical Ti1+xOs3-xB2. Starting from the observation of different Ti/Os occupations in X-ray crystal structure analysis, we assess suitable computational models and rationalize how the interplay of Ti-Ti, Ti-Os, and Os-Os bonds drives the site preferences. Then, we move on to a systematic investigation of the metal-boron bonds which embed the characteristic, trigonal-planar B4 units within their metallic surroundings. Remarkably, the different Ti-B bonds in Ti1+xOs2-xRuB2 (and also in its ternary derivative) are of vastly different strength, and the strength of these bonds does not correlate with their length. The tools presented in this work are based on simple and insightful chemical arguments together with DFT, and may subsequently be transferred to other intermetallic phases-transition-metal borides and beyond. [ABSTRACT FROM AUTHOR]