Synthesis and Crystal Structure of the Europium Hydride Oxide Iodide Eu[sub.5]H[sub.2]O[sub.2]I[sub.4] Showing Blue-Green Luminescence

As the first europium(II) hydride oxide iodide, dark red single crystals of Eu[sub.5]H[sub.2]O[sub.2]I[sub.4] could be synthesized from oxygen-contaminated mixtures of EuH[sub.2] and EuI[sub.2]. 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 [HEu[sub.4]][sup.7+] and [OEu[sub.4]][sup.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 (Eu[sup.2+])[sub.4] tetrahedra as repetition unit, two H[sup.−]-centred ones in the inner part, and two O[sup.2−]-centred ones representing the outer sides. They are positively charged, according to ∞1{[Eu[sub.5]H[sub.2]O[sub.2]][sup.4+]}, to become interconnected and charge-balanced by iodide anions. Upon excitation with UV light, the compound shows blue–green luminescence with the shortest Eu[sup.2+] emission wavelength ever observed for a hydride derivative, peaking at 463 nm. The magnetic susceptibility of Eu[sub.5]H[sub.2]O[sub.2]I[sub.4] follows the Curie-Weiss law down to 100 K, and exhibits a ferromagnetic ordering transition at about 10 K.