Structural Stability, Bonding, and Magnetism in the TiMOs ₂ B ₂ Series (M = Cr–Ni): Insights into Frustration, High- T C Ferromagnetism, and Off-Stoichiometry

In this study, we investigate the structural stability and magnetic properties of the TiMOs2B2 series (M = Cr–Ni). These Os-rich compounds adopt a single Ti1+xOs2–xRuB2-type structure (space group P6̅2m, no. 189), unlike the Ir-rich analogues that show structural transitions. Among the experimentally realized members, only the Cr-based phase shows the closest agreement with the idealized DFT structural model. The computed lattice parameters agree well with experiment for M = Cr but are smaller for M = Mn, Fe, and Ni because of excess Os. Indeed, only the M = Cr member approaches ideal stoichiometry, with the composition TiCr0.96(2)Os2.04(2)B2, whereas the other members show stronger deviations that may reflect kinetic or metastable effects under the present synthesis conditions. The strength of this layered framework is due to strong Os–B, M–B, Os–M, B–B, and M–M interactions revealed by pCOHP analysis. Electronic structure and magnetic calculations confirm strong ordering for M = Mn and Fe, pronounced frustration for M = Cr, and nonmagnetic behavior for M = Co and Ni. TiCrOs2B2 is a highly frustrated, nonordering magnetic system. The high TC of TiFeOs2B2 arises from the placement of the Fermi level (EF) at key antibonding interactions.