Na₂Ir^IVCl₆: Spin-Orbital-Induced Semiconductor Showing Hydration-Dependent Structural and Magnetic Variations

Iridium(IV) oxides have gained increased attention in recent years owing to the presence of competing spin-orbit coupling and Coulomb interactions, which facilitate the emergence of novel quantum phenomena. In contrast, the electronic structure and magnetic properties of Ir^IV-based molecular materials remain largely unexplored. In this paper, we take a fresh look at an old but puzzling compound, Na₂IrCl₆, which can be hydrated to form two stable phases with formulas Na₂IrCl₆·2H₂O and Na₂IrCl₆·6H₂O. Their crystal structures are well illustrated based on X-ray powder diffraction data. Magnetic studies reveal that Na₂IrCl₆ and Na₂IrCl₆·2H₂O are canted antiferromagnets with ordering temperatures of 7.4 and 2.7 K, respectively, whereas Na₂IrCl₆·6H₂O is paramagnetic down to 1.8 K. First-principle calculations on Na₂IrCl₆ reveal a J_eff = 1/2 ground state, and the band structures show that Na₂IrCl₆ is a spin-orbital-induced semiconductor with an indirect gap of about 0.18 eV.