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 O2--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.

Strontium Nitridoborate Hydride Sr2BN2H Verified by Single-Crystal X-ray and Neutron Powder Diffraction.

Combining different anions in one material allows tuning of its structural, magnetic, and electronic properties. We hereby present the mixed anion compound Sr2BN2H, expanding the less-known class of nitridoborate hydrides. Solid-state reaction of Sr2N, BN, and SrH2 at 850 °C in a tube furnace yielded a gray, air- and moisture-sensitive powder of Sr2BN2H. It crystallizes as colorless platelets in the orthorhombic space group Pnma (no. 62) with a = 9.9164(2), b = 3.9079(1), and c = 10.1723(2) Å and Z = 4. An initial structural model was obtained from single-crystal X-ray diffraction data and corroborated by neutron powder diffraction data of the corresponding deuteride. Further validation by 1H and 11B MAS NMR, FTIR, and Raman spectroscopy complements the structural proof of anionic hydrogen present in the compound. Quantum chemical calculations support the experimental findings and reveal the electronic structure of Sr2BN2H.

Na3 SO4 H-The First Representative of the Material Class of Sulfate Hydrides.

The first representative of a novel class of mixed-anionic compounds, the sulfate hydride Na3 SO4 H, and the corresponding deuteride Na3 SO4 D were obtained from the solid-state reaction of NaH or NaD with dry Na2 SO4 . Precise reaction control is required, because too harsh conditions lead to the reduction of sulfate to sulfide. A combined X-ray and neutron diffraction study revealed that the compound crystallizes in the tetragonal space group P4/nmm with the lattice parameters a=7.0034(2) Šand c=4.8569(2) Å. The sole presence of hydride and absence of hydroxide ions is proven by vibrational spectroscopy and comparison with spectra predicted from quantum chemical calculations. 1 H and 23 Na MAS NMR spectra are consistent with the structure of Na3 SO4 H: a single 1 H peak at 2.9 ppm is observed, while two peaks at 15.0 and 6.2 ppm for the inequivalent 23 Na sites are observed. Elemental analysis and quantum chemical calculations further support these results.

Borate Hydrides as a New Material Class: Structure, Computational Studies, and Spectroscopic Investigations on Sr5 (BO3 )3 H and Sr5 (11 BO3 )3 D.

The unprecedented borate hydride Sr5 (BO3 )3 H and deuteride Sr5 (11 BO3 )3 D crystallizing in an apatite-related structure are reported. Despite the presence of hydride anions, the compound decomposes only slowly in air. Doped with Eu2+ , it shows broad-band orange-red emission under violet excitation owing to the 4f6 5d-4f7 transition of Eu2+ . The observed 1 H NMR chemical shift is in good agreement with previously reported 1 H chemical shifts of ionic metal hydrides as well as with quantum chemical calculations and very different from 1 H chemical shifts usually found for hydroxide ions in similar materials. FTIR and Raman spectroscopy of different samples containing 1 H, 2 H, nat B, and 11 B combined with calculations unambiguously prove the absence of hydroxide ions and the sole incorporation of hydride ions into the borate. The orange-red emission obtained by doping with Eu2+ shows that the new compound class might be a promising host material for optical applications.

Homogeneity of doping with paramagnetic ions by NMR.

In NMR, paramagnetic dopants change the relaxation behavior and the chemical shift of the nuclei in their immediate environment. Based on the concept that the "immediate environment" in a diamagnetic host material can be described as a sphere with radius r0, we developed a function for the fraction of unperturbed nuclei (the fraction of nuclei outside the sphere) which gives a link between the effective radius and the doping concentration. In the case of a homogeneous doping scenario a characteristic dependence is observed in both theory and experiment. We validated the model on a sample series where paramagnetic Eu(II) ions are doped into crystalline SrH2. The fraction of unperturbed nuclei was determined from the (1)H NMR signal and follows the predicted curve for a homogeneous doping scenario where the radius r0 is 17 Å.

Variation of the Eu(II) emission wavelength by substitution of fluoride by hydride in fluorite-type compounds EuH(x)F(2-x) (0.20 ≤ x ≤ 0.67).

Mixed-hydride fluorides EuHxF2-x were prepared by the solid-state reaction of EuF2 and EuH2 under hydrogen gas pressure in an autoclave. Eu(II) luminescence is observed for 0.20 ≤ x ≤ 0.67, while pure EuF2 does not show any emission. The energy of the emission depends strongly on the degree of substitution x. For low hydride contents, yellow emission is observed, whereas higher hydride contents lead to red emission. The red shift is attributed to the nephelauxetic effect of the hydride anion. Remarkably, limited concentration quenching is observed in EuHxF2-x (0.20 ≤ x ≤ 0.67). This observation is explained by suppression of long-range energy migration due to disorder in the local environment of Eu(2+) in the mixed H/F crystals. The strong x dependence of the luminescence maxima proves hydride-fluoride substitution to be a valuable tool to tune the emission wavelength of Eu(II)-containing phosphors.

Electronic structure of ternary rhodium hydrides with lithium and magnesium.

Chemical bonding in and electronic structure of lithium and magnesium rhodium hydrides are studied theoretically using DFT methods. For Li3RhH4 with planar complex RhH4 structural units, Crystal Orbital Hamilton Populations reveal significant Rh−Rh interactions within infinite one-dimensional ∞ 1 [RhH4] stacks in addition to strong rhodium−hydrogen bonding. These metal−metal interactions are considerably weaker in the hypothetical, heavier homologue Na3RhH4. Both compounds are small-band gap semiconductors. The electronic structures of Li3RhH6 and Na3RhH6 with rhodium surrounded octahedrally by hydrogen, on the other hand, are compatible with a classical complex hydride model according to the limiting ionic formula (M+)3[RhH6]3− without any metal−metal interaction between the 18-electron hydridorhodate complexes. In MgRhH, building blocks of the composition (RhH2)4 are formed with strong rhodium−hydrogen and significant rhodium−rhodium bonding (bond lengths of 298 pm within Rh4 squares). These units are linked together to infinite two-dimensional layers ∞ 2 [(RhH2/2)4] via common hydrogen atoms. Li3RhH4 and MgRhH are accordingly examples for border cases of chemical bonding where the classical picture of hydridometalate complexes in complex hydrides is not sufficient to properly describe the chemical bonding situation.

Bright yellow and green Eu(II) luminescence and vibronic fine structures in LiSrH3, LiBaH3 and their corresponding deuterides.

The luminescence of Eu(2+) in hydride and deuteride perovskite hosts LiMH3 and LiMD3 (M = Sr, Ba) is reported. Bright yellow (M = Sr) and green (M = Ba) emission is observed and assigned to 4f(6)5d-4f(7) emission from Eu(2+) in the highly symmetric 12-coordinated M(2+) site (m3[combining macron]m). The long wavelength of the emission is explained by the strong covalence and crystal field splitting in europium's coordination by hydride anions. A well-resolved vibrational structure in the emission and excitation spectra of Eu(2+) in the Sr-compounds allows for an accurate determination of the energy of the lowest 4f(6)5d state and vibrational frequencies, for both the hydride and deuteride. The isotope effect on the energy of the fd states is small (∼70 cm(-1)), as expected. Surprisingly, also the vibrational energies observed in the vibronic progression are similar for the d-f emission spectra in LiSrH3 and LiSrD3. This is explained by strong coupling of the d-f emission with low energy acoustic phonons which, contrary to optical phonons, are not strongly affected by replacing H by D. The present results provide insight into the long wavelength Eu(2+) emission in hydride coordination and the influence of isotope replacement on the luminescence.

Expanding the hydride chemistry: antiperovskites A3MO4H (A = Rb, Cs; M = Mo, W) introducing the transition oxometalate hydrides.

The four compounds A3MO4H (A = Rb, Cs; M = Mo, W) are introduced as the first members of the new material class of the transition oxometalate hydrides. The compounds are accessible via a thermal synthesis route with carefully controlled conditions. Their crystal structures were solved by neutron diffraction of the deuterated analogues. Rb3MoO4D, Cs3MoO4D and Cs3WO4D crystallize in the antiperovskite-like K3SO4F-structure type, while Rb3WO4D adopts a different orthorhombic structure. 2H MAS NMR, Raman spectroscopy and elemental analysis prove the abundance of hydride ions next to oxometalate ions and experimental findings are supported by quantum chemical calculations. The tetragonal phases are direct and wide band gap semiconductors arising from hydride states, whereas Rb3WO4H shows a unique, peculiar valence band structure dominated by hydride states.

Alkaline-earth metal hydrides as novel host lattices for Eu(II) luminescence.

Luminescence of divalent europium has been investigated for the first time in metal hydrides. A complete solid-solution series was found for the pseudobinary system Eu(x)Sr(1-x)H(2) [a = 637.6(1) pm -12.1(3)x pm, b = 387.0(1)-6.5(2)x pm, c = 732.2(2)-10.1(4)x pm]. Europium-doped alkaline-earth hydrides Eu(x)M(1-x)H(2) (M = Ca, Sr, Ba) with a small europium concentration (x = 0.005) exhibit luminescence with maximum emission wavelengths of 764 nm (M = Ca), 728 nm (M = Sr), and 750 nm (M = Ba); i.e., the emission energy of divalent europium shows an extremely large red shift compared to the emission energies of fluorides or oxides. Theoretical calculations (LDA+U) confirm decreasing band gaps with increasing europium content of the solid solutions.