Synthesis and Crystal Structure of the Europium(II) Hydride Oxide Iodide Eu 5 H 2 O 2 I 4 Showing Blue-Green Luminescence.

As the first europium(II) hydride oxide iodide, dark red single crystals of Eu 5 H 2 O 2 I 4 could be synthesized from oxygen-contaminated mixtures of EuH 2 and EuI 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 4 ] 7+ and [OEu 4 ] 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 2+ ) 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{[Eu 5 H 2 O 2 ] 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 2+ emission wavelength ever observed for a hydride derivative, peaking at 463 nm. The magnetic susceptibility of Eu 5 H 2 O 2 I 4 follows the Curie-Weiss law down to 100 K, and exhibits a ferromagnetic ordering transition at about 10 K.