Polycrystalline samples of two complex intermetallic borides Zr 2 Fe 1 À d Ru 5 + d B 2 and Zr 2 Fe 1 À d (Ru 1 À x Rh x ) 5 + d B 2 (d¼ ca. 0.10; x ¼ 0.20) were synthesized by high-temperature methods and characterized by single-crystal X-ray diffraction, energy dispersive spectroscopy, and magnetization measurements. Both structures are variants of Sc 2 Fe(Ru 1 À x Rh x ) 5 B 2 and crystallize in the space group P4/mbm (no. 127) with the Ti 3 Co 5 B 2 -type structure. These structures contain single-atom, Fe-rich Fe/Ru or Fe/Ru/Rh chains along the c-axis with an interatomic metal-metal distance of 3.078(1) Å, a feature which makes them viable for possible low-dimensional temperature-dependent magnetic behavior. Magnetization measurements indicated weak ferrimagnetic ordering with ordering temperatures ca. 230 K for both specimens. Tight-binding electronic structure calculations on a model ''Zr 2 FeRu 5 B 2 '' using LDA yielded a narrow peak at the Fermi level assigned to Fe-Fe antibonding interactions along the c-axis, a result that indicates an electronic instability toward ferromagnetic coupling along these chains. Spin-polarized calculations of various magnetic models were examined to identify possible magnetic ordering within and between the single-atom, Fe-rich chains.