Henning A. Höppe

Recent Developments in the Field of Inorganic Phosphors

Because fossil fuels are becoming scarce and because of the expected climate change, our standard of living can only be maintained by a significant increase in energy efficiency. Large amounts of energy are consumed for lighting and during operation of displays. Thus, the targets are the development of economical light sources like white-light-emitting diodes and display panels with enhanced efficiency. Solar energy is converted into electricity by solar cells, and their efficiency must be improved considerably. A possible contribution might be delivered by phosphors which allow the conversion of thermal radiation into electrical energy. Although the target of energy efficiency is very important, we must not overlook that medical imaging diagnostic methods require efficient and sensitive detectors. For the solution of these central questions, inorganic solid-state materials doped with rare-earth ions are very promising and are therefore in the focus of current research activities.

Luminescence in Eu2+-doped Ba2Si5N8: fluorescence, thermoluminescence, and upconversion

Abstract Fluorescence emission was investigated in a series of Ba2−xEuxSi5N8 compounds. Two maxima corresponding to the two crystallographic Eu2+ sites are observed. Excitation with intense laser light at 1.047xa0μm reveals strong fluorescence emission at ∼600xa0nm due to two-photon-excitation. In Ba1.89Eu0.11Si5N8 the long lasting luminescence was studied. The emission peaking at about 590xa0nm has been observed in the dark with the naked eye even 15xa0min after removal of the activating lamp. This effect is due to the recombination of holes and traps consisting of nitrogen vacancies formed by reducing synthesis conditions. The maximum emission was observed at −7°C.

Crystal structure solid-state cross polarization magic angle spinning 13C NMR correlation in luminescent d10 metal-organic frameworks constructed with the 1,2-Bis(1,2,4-triazol-4-yl)ethane ligand.

Hydrothermal reactions of 1,2-bis(1,2,4-triazol-4-yl)ethane (btre) with copper(II), zinc(II), and cadmium(II) salts have yielded the dinuclear complexes [Zn2Cl4(mu2-btre)2] (1) and [Zn2Br4(mu2-btre)2] (2), the one-dimensional coordination polymer infinity1[Zn(NCS)2(2-btre)] (3), the two-dimensional networks infinity2[Cu2(mu2-Cl)2(mu4-btre)] (4), infinity2[Cu2(mu2-Br)2(mu4-btre)] (5), and infinity2{[Cd6(mu3-OH)2(mu3-SO4)4(mu4-btre)3(H2O)6](SO4).6H2O} (6), and the three-dimensional frameworks infinity3{[Cu(mu4-btre)]ClO4.0.25H2O} (7), 3{[Zn(mu4-btre)(mu2-btre)](ClO4)2} (8), infinity3{[Cd(mu4-btre)(mu2-btre)](ClO4)2} (9), and infinity3[Cu2(mu2-CN)2(mu4-btre)] (10, 2-fold 3D interpenetrated framework). The copper-containing products 4, 5, 7, and 10 contain the metal in the +1 oxidation state, from a simultaneous redox and self-assembly reaction of the Cu(II) starting materials. The cyanide-containing framework 10 has captured the CN- ions from the oxidative btre decomposition. The perchlorate frameworks 7, 8, or 9 react in an aqueous NH4+PF6- solution with formation of the related PF6--containing frameworks. The differences in the metal-btre bridging mode (mu2-kappaN1:N1, mu2-kappaN1:N2 or mu4-kappaN1:N2:N1:N2) and the btre ligand symmetry can be correlated with different signal patterns in the 13C cross polarization magic angle spinning (CPMAS) NMR spectra. Compounds 2, 4, 5 and 7 to 10 exhibit fluorescence at 403-481 nm upon excitation at 270-373 nm which is not seen in the free btre ligand.

Crystal structures and solid-state CPMAS 13C NMR correlations in luminescent zinc(II) and cadmium(II) mixed-ligand coordination polymers constructed from 1,2-bis(1,2,4-triazol-4-yl)ethane and benzenedicarboxylate

The hydrothermal reaction of M(NO(3))(2).4H(2)O (M = Zn and Cd) with benzene-1,4-dicarboxylic acid (H(2)bdc) or benzene-1,3-dicarboxylic acid (H(2)ip) and 1,2-bis(1,2,4-triazol-4-yl)ethane (btre) produced the mixed-ligand coordination polymers (MOFs) {[Zn(2)(micro(2)-bdc)(2)(micro(4)-btre)]} (), {[Cd(2)(micro(4)-bdc)(micro(4)-btre)(2)](NO(3))(2).H(2)O} and {[Zn(2)(micro(3)-ip)(2)(micro(2)-btre)(H(2)O)(2)].2H(2)O} (). The compounds, characterized by single-crystal X-ray diffraction, X-ray powder diffraction, solid-state cross-polarization (CP) magic-angle-spinning (MAS) (13)C NMR and thermoanalysis, feature 3D metal-organic frameworks for and and 2D double layers which are connected through hydrogen bonds from the aqua ligands for 3. The CPMAS (13)C NMR spectra picture the symmetry-independent (unique) C atoms and the bdc/ip-to-btre ligand ratio in agreement with the crystal structures. The zinc and cadmium coordination polymers show a strong bluish fluorescence upon excitation with UV light (the free btre ligand is non-luminescent).

Spontaneous resolution upon crystallization of chiral La(III) and Gd(III) MOFs from achiral dihydroxymalonate

The achiral chelating and bridging dihydroxymalonato (mesoxalato) ligand is a new enantiopurity enforcer in extended structures by yielding the Λ/Δ-metal configured homochiral MOFs 2D-[Ln(2)(μ-mesoxalato)(3)(H(2)O)(6)] (Ln = La(III), Gd(III)) through self-resolution during crystal growth.

Homochiral lanthanoid(III) mesoxalate metal–organic frameworks: synthesis, crystal growth, chirality, magnetic and luminescent properties

The achiral chelating and bridging mesoxalato ligand (H2mesox2−), the conjugate base of mesoxalic or dihydroxymalonic acid (H4mesox), is a new enantiopurity enforcer in extended structures by yielding the Λ/Δ-metal configured homochiral MOFs 2D-[Ln2(μ-H2mesox)3(H2O)6], [with Ln(III) = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Er (10) and Yb (11)]; through self-resolution during crystallization. Single crystals of the compounds have been grown in agarose gel. All the compounds obtained are isostructural as deduced by means of single crystal and powder X-ray diffraction analysis and exhibit the Ln(III) ions covalently connected by the mesoxalato ligands into a corrugated grey arsenic-type (6,3)-net (or layer) with chair-shaped six-membered rings. Luminescence measurements reveal that the Eu(III) compound (6) exhibits several strong characteristic emission bands for isolated europium(III) ions in the visible region when excited between 350 and 420 nm; similarly the terbium(III) compound (8) displays the characteristic emission bands for isolated terbium(III) ions. Magnetic susceptibility measurements show deviations from the Curie law mainly owing to the split of the ground term due to the ligand field and spin–orbit coupling in the case of Sm(III) (4) and Eu(III) (6) compounds.

Single-walled carbon nanotubes filled with M OH (M = K, Cs) and then washed and refilled with clusters and molecules

Heating single-walled carbon nanotubes (SWNTs) with molten hydroxides MOH (M = K, Cs) gave MOH@SWNT in good yield; high resolution transmission electron microscopy (HRTEM) indicated that CsOH in CsOH@SWNT often adopts twisted 1D crystal structures inside SWNTs; treating MOH@SWNT with water at room temperature removes the soluble hydroxide filling and the resulting SWNTs may then be filled using aqueous solutions of uranyl acetate or uranyl nitrate at rt giving SWNTs filled with UO(2) clusters and uranyl acetate molecules.

Synthesis, crystal structure, vibrational spectroscopy, and thermal behaviour of lead dicyanamide Pb[N(CN)2]2

Abstract Lead dicyanamide, Pb[N(CN)2]2, was synthesized through ion exchange in water starting from Na[N(CN)2]. The crystal structure was determined by single-crystal X-ray diffraction (Pnma, Z=4, a=1350.45(10), b=399.89(4), c=1199.39(11) pm, R1=0.0275, wR2=0.0557, 68 parameters, 1073 independent reflections). In the solid Pb[N(CN)2]2 consists of Pb2+ ions and bent planar [N(CN)2]− ions. The dicyanamide anions exhibit Cue5f8N bond lengths of 114.0(13)–116.0(10) pm to the terminal and 128.8(11)–131.9(12) pm to the bridging N atoms. The bond angles within the [N(CN)2]− ions are 173.1(8)–174.5(10)° (Nue5f8Cue5fcN) and 122.0(8)° (Cue5f8Nue5f8C). The crystal structure of Pb[N(CN)2]2 is isotypic with that of Ba[N(CN)2]2. It can be derived from the cotunnite structure type (PbCl2). Above 230xa0°C Pb[N(CN)2]2 transforms into amorphous products. Detailed IR spectroscopic data of Pb[N(CN)2]2 are reported. The observed frequencies agree well with those observed for isotypic Ba[N(CN)2]2.

Homoallyl-substituted vinylcyclopropanes from alpha,beta-unsaturated ketones and allylindium derivatives

Simply reversing the order of addition of aqueous acid and Et2 O to the Barbier intermediate 1 of the known indium-mediated allylation leads to unprecedented deoxygenative rearrangements [Eq. (a)].

The First Borosulfate K5[B(SO4)4]

Sulfate anions SO4 2 do not show a strong tendency to form condensed oligoanions owing to the high formal charge of sulfur. A recent very interesting example for an oligosulfate is ReO2Cl(S2O7). [1] Disulfate tetrahedra share common corners with an adjacent ReO6 octahedron forming a cyclic moiety. Regarding oligosulfates, only chainlike anions, typically S3O10 2 or even S5O16 2 , were described. In K5[B(SO4)4], sulfate tetrahedra avoid direct condensation but form the unprecedented anion [B(SO4)4] 5 shown in Figure 1. In