AbstractThe one-dimensional compounds Sr₃MgPtO₆, Sr₃MgIrO₆, Sr₃MgRhO₆, Sr₃GdRhO₆, have been synthesized and structurally characterized by Rietveld refinement of powder X-ray diffraction data. All four compounds are isostructural with the rhombohedral K₄CdCl₆-type structure. The structure consists of infinite one-dimensional chains of alternating face-shared MO₆ octahedra (M = Pt, Ir, Rh) and M′O₆ (M′ = Gd, Mg) trigonal prisms. The strontium cations are located in a distorted square antiprismatic environment. Magnetic susceptibility data show that both Sr₃MgIrO₆ and Sr₃MgRhO₆ obey the Curie-Weiss law with θ = −6(1) K, and θ= −15(3)K, respectively. Sr₃GdRhO₆ obeys the Curie law with μ_eff = 7.80 B.M, consistent with an oxidation state of +3 for both rhodium and gadolinium.