Negative Thermal Expansion in the Polymorphic Modification of Double Sulfate ß-AEu(SO4)2 (A-Rb+, Cs+).

New polymorphic modifications of double sulfates ß-AEu(SO4)2 (A-Rb+, Cs+) were obtained by the hydrothermal method, the structure of which differs significantly from the monoclinic modifications obtained earlier by solid-state methods. According to single-crystal diffraction data, it was found that the compounds crystallize in the orthorhombic system, space group Pnna, with parameters ß-RbEu(SO4)2: a = 9.4667(4) Å, b = 13.0786(5) Å, c = 5.3760(2) Å, V = 665.61(5) Å3; ß-CsEu(SO4)2: a = 9.5278(5) Å, b = 13.8385(7) Å, c = 5.3783(3) Å, V = 709.13(7) Å3. The asymmetric part of the unit cell contains one-half Rb+/Cs+ ion, one-half Eu3+ ion, both in special sites, and one SO42- ion. Both compounds exhibit nonlinear negative thermal expansion. According to the X-ray structural analysis and theoretical calculations, the polarizing effect of the alkali metal ion has a decisive influence on the demonstration of this phenomenon. Experimental indirect band gaps of ß-Rb and ß-Cs are 4.05 and 4.11 eV, respectively, while the direct band gaps are 4.48 and 4.54 eV, respectively. The best agreement with theoretical calculations is obtained using the ABINIT package employing PAW pseudopotentials with hybrid PBE0 functional, while norm-conserving pseudopotentials used in the frame of CASTEP code and LCAO approach in the Crystal package gave worse agreement. The properties of alkali ions also significantly affect the luminescent properties of the compounds, which leads to a strong temperature dependence of the intensity of the 5D0 → 7F4 transition in ß-CsEu(SO4)2 in contrast to much weaker dependence of this kind in ß-RbEu(SO4)2.

Tuning Magnetic and Photophysical Properties of Luminomagnetic Metal-Organic Framework Composites in an Inverse Core-Satellite Structure.

Luminomagnetic composites have been synthesized that allow for an individual tuning of luminescence intensity, chromaticity and magnetization by combination of superparamagnetic, citrate-stabilized iron oxide nanoparticles with the luminescent MOFs 3 ∞ [Ln2 (BDC)3 (H2 O)4 ] (Ln=Eu, Tb; BDC2- =terephthalate). The components are arranged to a concept of inverse structuring compared to previous luminomagnetic composites with MOF@magnetic particle (shell@core) composition so that the luminescent MOF now acts as core and is covered by magnetic nanoparticles forming the satellite shell. Thereby, the magnetic and photophysical properties are individually tuneable between high emission intensity (1.2 ⋅ 106  cps mg-1 ) plus low saturation magnetization (6 emu g-1 ) and the direct opposite (0.09 ⋅ 106  cps mg-1 ; 42 emu g-1 ) by adjusting the particle coverage of the MOF. This is not achievable with a core-shell structure having a magnetic core and a dense MOF shell. The composition of the composites and the influence of different synthesis conditions on their properties were investigated by SEM/EDX, PXRD, magnetization measurements and photoluminescence spectroscopy.

Iodine Chemisorption, Interpenetration and Polycatenation: Cationic MOFs and CPs from Group 13 Metal Halides and Dipyridyl Linkers.

Invited for the cover of this issue are Klaus Müller-Buschbaum and co-workers at Giessen University. The image depicts an aluminium-based MOF as a novel material for the capture of iodine radioisotopes from a potential gas atmosphere exposure. Read the full text of the article at 10.1002/chem.202104171.

Iodine-Chemisorption, Interpenetration and Polycatenation: Cationic MOFs and CPs from Group 13 Metal Halides and Di-Pyridyl-Linkers.

Eight cationic, two-dimensional metal-organic frameworks (MOFs) were synthesized in reactions of the group 13 metal halides AlBr3 , AlI3 , GaBr3 , InBr3 and InI3 with the dipyridyl ligands 1,2-di(4-pyridyl)ethylene (bpe), 1,2-di(4-pyridyl)ethane (bpa) and 4,4'-bipyridine (bipy). Seven of them follow the general formula 2 ∞ [MX2 (L)2 ]A, M=Al, In, X=Br, I, A- =[MX4 ]- , I- , I3 - , L=bipy, bpa, bpe. Thereby, the porosity of the cationic frameworks can be utilized to take up the heavy molecule iodine in gas-phase chemisorption vital for the capture of iodine radioisotopes. This is achieved by switching between I- and the polyiodide I3 - in the cavities at room temperature, including single-crystal-to-single-crystal transformation. The MOFs are 2D networks that exhibit (4,4)-topology in general or (6,3)-topology for 2 ∞ [(GaBr2 )2 (bpa)5 ][GaBr4 ]2 ⋅bpa. The two-dimensional networks can either be arranged to an inclined interpenetration of the cationic two-dimensional networks, or to stacked networks without interpenetration. Interpenetration is accompanied by polycatenation. Due to the cationic character, the MOFs require the counter ions [MX4 ]- , I- or I3 - counter ions in their pores. Whereas the [MX4 ]- , ions are immobile, iodide allows for chemisorption. Furthermore, eight additional coordination polymers and complexes were identified and isolated that elaborate the reaction space of the herein reported syntheses.

Characterization of copper complexes with derivatives of the ligand (2-aminoethyl)bis(2-pyridylmethyl)amine (uns-penp) and their reactivity towards oxygen.

A series of copper(I) complexes with ligands derived from the tripodal ligand (2-aminoethyl)bis(2-pyridylmethyl)amine (uns-penp) have been structurally characterized and their redox chemistry analyzed by cyclic voltammetry. While the redox potentials of most of the complexes were similar their reactivity towards dioxygen was quite different. While the complex with a ferrocene derived ligand of uns-penp reacted in solution at low temperatures in a two-step reaction from the preliminary formed mononuclear end-on superoxido complex to a quite stable dinuclear peroxido complex it did not react with dioxygen in the solid state. Other complexes also did not react with dioxygen in the solid state while some showed a reversible formation to a green compound, indicating formation of an end-on superoxido complex that unfortunately so far could not be characterized. In contrast, copper complexes with the Me2uns-penp and Et-iProp-uns-penp formed dinuclear peroxido complexes in a solid-state reaction. While the reaction of dioxygen with the [Cu(Me2uns-penp]BPh4 was quite slow an instant reaction took place for [Cu(Et-iProp-uns-penp]BPh. Very unusual, it turned out that crystals of the copper(I) complex that could be structurally characterized still were crystalline when reacted with dioxygen. Therefore, it was possible to solve the structure of the corresponding dinuclear peroxido complex directly from the same batch of crystals. The crystalline structures of the copper(I) and copper(II) complex revealed that the reason for this is the fact, that the copper(I) complex is kind of preorganized for the uptake of dioxygen and does not really change in its overall structure when being oxidized.