Synthesis and Crystal Structure of the Europium(II) Hydride Oxide Iodide Eu₅H₂O₂I₄ Showing Blue-Green Luminescence

As the first europium(II) hydride oxide iodide, dark red single crystals of Eu₅H₂O₂I₄ could be synthesized from oxygen-contaminated mixtures of EuH₂ and EuI₂. Its orthorhombic crystal structure (a = 1636.97(9) pm, b = 1369.54(8) pm, c = 604.36(4) pm, Z = 4) was determined via single-crystal X-ray diffraction in the space group Cmcm. Anion-centred tetrahedra [HEu₄]⁷⁺ and [OEu₄]⁶⁺ serve as central building blocks interconnected via common edges to infinite ribbons parallel to the c axis. These ribbons consist of four trans-edge connected (Eu²⁺)₄ tetrahedra as repetition unit, two H^--centred ones in the inner part, and two O^2--centred ones representing the outer sides. They are positively charged, according to ∞1{[Eu₅H₂O₂]⁴⁺}, to become interconnected and charge-balanced by iodide anions. Upon excitation with UV light, the compound shows blue-green luminescence with the shortest Eu²⁺ emission wavelength ever observed for a hydride derivative, peaking at 463 nm. The magnetic susceptibility of Eu₅H₂O₂I₄ follows the Curie-Weiss law down to 100 K, and exhibits a ferromagnetic ordering transition at about 10 K.