Controllable surfactant-directed zeolitic-imidazolate-8 growth on swollen 2D zeolites

The authors would like to thank the European Research Council for funding opportunities under Advanced Grant No. 787073. The EPSRC Light Element Analysis Facility under Grant No. EP/T019298/1 and the EPSRC Strategic Equipment Resource under Grant No. EP/R023751/1 are gratefully acknowledged.To meet society’s need for more and more specialized materials, this work focuses on the preparation of porous metal–organic framework (MOF)–zeolite hybrid materials based on two 2D zeolites, namely, IPC-1P (Institute of Physical Chemistry - 1 Precursor) and the metal–organic framework ZIF-8 (Zeolitic Imidazolate Framework-8). Using the previously well-established assembly–disassembly–organization–reassembly method, the zeolite was (i) synthesized, (ii) hydrolyzed to a layered zeolite, (iii) the interlayer distance was increased using the swelling agent cetyltrimethylammonium chloride, and (iv) nanocrystals of ZIF-8 were grown stepwise on the zeolite surface but predominantly at the edges of the crystallites where the openings to the interlayer region are located. This selective MOF growth and attachment was facilitated by a combination of intercalation of the metal ions and the swelling agent between the zeolite layers. The influence of the solvent and the number of additional steps on the ZIF-8 growth on the zeolite was systematically investigated, and the synthesis protocol was successfully adapted to a further two-dimensional silicate RUB-18 (Ruhr-Universität Bochum - 18). This paves the way toward the controlled preparation of more MOF–zeolite hybrid materials, which might provide interesting properties for future applications.Publisher PDFPeer reviewe

Silicate-analogous borosulfates featuring promising luminescence and frequency-doubling (SHG) properties based on a rich crystal chemistry

Our contribution adresses important features of the emerging compound class of silicate-analogous borosulfates, i.e. their rich crystal chemistry, their exciting optical properties and of course their syntheses – the chemistry behind. Silicate-analogous materials comprise tetrahedral anionic basic building units lacking an inversion centre enhancing the chance of non-centrosymmetric surroundings of metal ions promoting excellent optical properties. Since the very first characterization of crystalline borosulfates in 2012 over sixty members have been found. Therein, the reaction of boric and sulfuric acid yields supertetrahedral BX4 (X=SO4) moieties giving rise to a rich crystal chemistry from non-condensed [B(SO4)4]5– anions via band (see Fig.) and layer structures to anionic frameworks [B(SO4)2]– – which can be understood by principles well known from silicates (see Fig.). The selective synthesis of borosulfates can be challenging but we meanwhile found some basic principles helping to selectively synthesize new compounds as phase-pure samples. Great impact is ascribed to the nature of the boron source, the metal (salt) employed and the amount of oleum added. On one hand, borosulfates feature a low coordination strength which is beneficial for the luminescence and UV-Vis properties of compounds containing lanthanide and transition metal ions, such as Ce3+ (see Fig.), Eu3+, Tb3+ or Co2+ and Ni2+. On the other hand, borosulfates frequently adopt non-centrosysmmetric structures yielding optical properties like SHG (second harmonic generation) which – in combination with large band-gaps – makes them highly promising materials for frequency doubling in the high energy regime. Also ionic conductivity was observed recently

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

In situ single-crystal X-ray diffraction studies of physisorption and chemisorption of SO2 within a metal-organic framework and its competitive adsorption with water

Funding: The authors are also grateful for financial assistancefrom the ERC under advanced grant 787073, the EPSRC for a studentship (EP/N509759/1) and support via the Collaborative Computational Projecton NMR Crystallography CCP-NC (EP/T02662/1), and the CRITICAT Centre for Doctoral Training (EP/L016419/1).Living on an increasingly polluted planet, the removal of toxic pollutants such as sulfur dioxide (SO2) from the troposphere and power station flue gas is becoming more and more important. The CPO-27/MOF-74 family of metal–organic frameworks (MOFs) with their high densities of open metal sites is well suited for the selective adsorption of gases that, like SO2, bind well to metals and have been extensively researched both practically and through computer simulations. However, until now, focus has centered upon the binding of SO2 to the open metal sites in this MOF (called chemisorption, where the adsorbent–adsorbate interaction is through a chemical bond). The possibility of physisorption (where the adsorbent–adsorbate interaction is only through weak intermolecular forces) has not been identified experimentally. This work presents an in situ single-crystal X-ray diffraction (scXRD) study that identifies discrete adsorption sites within Ni-MOF-74/Ni-CPO-27, where SO2 is both chemisorbed and physisorbed while also probing competitive adsorption of SO2 of these sites when water is present. Further features of this site have been confirmed by variable SO2 pressure scXRD studies, DFT calculations, and IR studies.Publisher PDFPeer reviewe

Beyond the energy gap law : the influence of selection rules and host compound effects on nonradiative transition rates in boltzmann thermometers

P.N. and M.H. contributed equally to this work. H.A.H., P.N., M.H., and E.T. thank the Deutsche Forschungsgemeinschaft (DFG) for generous support (Project HO 4503/5-1). Open access funding enabled and organized by Projekt DEAL.Apart from the energy gap law, control parameters over nonradiative transitions are so far only scarcely regarded. In this work, the impact of both covalence of the lanthanoid–ligand bond and varying bond distance on the magnitude of the intrinsic nonradiative decay rate between the excited 6P5/2 and 6P7/2 spin–orbit levels of Gd3+ is investigated in the chemically related compounds Y2[B2(SO4)6] and LaBO3. Analysis of the temperature-dependent luminescence spectra reveals that the intrinsic nonradiative transition rates between the excited 6PJ (  J = 5/2, 7/2) levels are of the order of only 10 ms−1 (Y2[B2(SO4)6]:Gd3+: 8.9 ms−1; LaBO3:Gd3+: 10.5 ms−1) and differ due to the different degree of covalence of the Gd—O bonds in the two compounds. Comparison to the established luminescent Boltzmann thermometer Er3+ reveals, however, that the nonradiative transition rates between the excited levels of Gd3+ are over three orders of magnitude slower despite a similar energy gap and the presence of a single resonant phonon mode. This hints to a fundamental magnetic dipolar character of the nonradiative coupling in Gd3+. These findings can pave a way to control nonradiative transition rates and how to tune the dynamic range of luminescent Boltzmann thermometers.Publisher PDFPeer reviewe

Beyond the Energy Gap Law: The Influence of Selection Rules and Host Compound Effects on Nonradiative Transition Rates in Boltzmann Thermometers

Apart from the energy gap law, control parameters over nonradiative transitions are so far only scarcely regarded. In this work, the impact of both covalence of the lanthanoid–ligand bond and varying bond distance on the magnitude of the intrinsic nonradiative decay rate between the excited 6P5/2 and 6P7/2 spin–orbit levels of Gd3+ is investigated in the chemically related compounds Y2[B2(SO4)6] and LaBO3. Analysis of the temperature-dependent luminescence spectra reveals that the intrinsic nonradiative transition rates between the excited 6PJ (J = 5/2, 7/2) levels are of the order of only 10 ms−1 (Y2[B2(SO4)6]:Gd3+: 8.9 ms−1; LaBO3:Gd3+: 10.5 ms−1) and differ due to the different degree of covalence of the Gd-O bonds in the two compounds. Comparison to the established luminescent Boltzmann thermometer Er3+ reveals, however, that the nonradiative transition rates between the excited levels of Gd3+ are over three orders of magnitude slower despite a similar energy gap and the presence of a single resonant phonon mode. This hints to a fundamental magnetic dipolar character of the nonradiative coupling in Gd3+. These findings can pave a way to control nonradiative transition rates and how to tune the dynamic range of luminescent Boltzmann thermometers

On Silicate-Analogous Materials: Synthesis and Characterisation of Novel Borosulfates

Borosulfates represent a relatively new class of silicate–analogous materials, whose potential goes beyond a simple analogy to silicates. In order to explore their capabilities, this work deals with the systematic expansion of borosulfates. Herein, twenty cations, such as the alkaline earth metals Mg and Sr, the transition metals Mn, Co, Ni, and Zn and the rare earth metals Y, La–Nd, Sm, Eu, Tb–Lu could be incorporated in borosulfates for the very first time. Accompanied by the elemental diversity, the structural diversity could be enriched by four new anion topologies, such as the B–O–B bridges containing anion [B2O(SO4)6]8– in α-Mg4[B2O(SO4)6], the solely B–O–S bridges containing anion [B2(SO4)4]2– in α-Mg[B2(SO4)4], the S–O–S bridges containing anion [B2(SO4)3(S2O7)]2– in Sr[B2(SO4)3(S2O7)] and the Lewis acid–base adduct [H2O→B(SO4)3]3– in Mg3[H2O→B(SO4)3]2. The latter one represents a novel connection pattern, featuring a boron atom solely coordinated by three tetrahedra, and thus, provides a Lewis acidic site that forms an adduct with a water molecule. In addition, due to this tremendous progress, the first-ever UV-vis spectra could be recorded on the borosulfates of the open-shell transition metals Co2+ and Ni2+, and the first-ever fluorescence spectra could be measured on the borosulfates of Ce3+, Eu3+ and Tb3+, providing highly interesting insights into the coordination behaviour for borosulfates. Besides, the decisive progress that was achieved concerning the synthesis of borosulfates made it possible for the first time to selectively address a desired connection pattern of the anion with regard to S–O–S, B–O–S and B–O–B bridges in the quaternary systems M–B–O–S (M = Sr, Ba). The consequent thermal transformation of the anion from S–O–S to B–O–S to B–O–B bridges deepened the understanding of the stabilities of the respective connection pattern. Finally, computational investigations on Mg3[H2O→B(SO4)3]2 revealed high Lewis and Brønsted acidity. The knowledge gained in this work unravels the synthesis and stability of borosulfates, significantly advances the elemental and structural diversity of borosulfates, showed first insights into the properties and thus opens new horizons for borosulfate chemistry