38 research outputs found
Easy-plane to easy-axis anisotropy switching in a Co(ii) single-ion magnet triggered by the diamagnetic lattice
Single ion magnets SIMs with large magnetic anisotropy are promising candidates for realization of single molecule based magnetic memory and qubits. Creation of materials with magnetically uncoupled spatially separated SIMs requires dilution in a diamagnetic matrix. Herein, we report that progressive dilution of paramagnetic Co II by diamagnetic Zn II in the SIM [CoxZn 1 amp; 8722;x piv 2 2 NH2 Py 2], x 1 0 beyond a threshold of 50 reveals an abrupt structural change, where the distorted tetrahedral Zn coordination structure is superimposed on the remaining Co ions, which were initially in a distorted octahedral environment. Dilution induced structure modification switches the magnetic anisotropy from easy plane D 36.7 cm amp; 8722;1 to easy axis type D amp; 8722;23.9 cm amp; 8722;1 , accompanied by a fivefold increase of the magnetic relaxation time at 2 K. Changes of the static and dynamic magnetic properties are monitored by electron paramagnetic resonance spectroscopy and AC susceptibility measurements. Complementary quantum chemical ab initio calculations quantify the influence of structural changes on the electronic structure and the magnetic anisotropy. Thus, magnetic dilution hits two goals at once, the creation of isolated magnetic centres and an improvement of their SIM propertie
Construction of C-C bonds via photoreductive coupling of ketones and aldehydes in the metal-organic-framework MFM-300(Cr).
From Europe PMC via Jisc Publications RouterHistory: ppub 2021-06-01, epub 2021-06-11Publication status: PublishedFunder: RCUK | Engineering and Physical Sciences Research Council (EPSRC); Grant(s): EP/I011870Funder: European Research Council; Grant(s): 742401Construction of C-C bonds via reductive coupling of aldehydes and ketones is hindered by the highly negative reduction potential of these carbonyl substrates, particularly ketones, and this renders the formation of ketyl radicals extremely endergonic. Here, we report the efficient activation of carbonyl compounds by the formation of specific host-guest interactions in a hydroxyl-decorated porous photocatalyst. MFM-300(Cr) exhibits a band gap of 1.75âeV and shows excellent catalytic activity and stability towards the photoreductive coupling of 30 different aldehydes and ketones to the corresponding 1,2-diols at room temperature. Synchrotron X-ray diffraction and electron paramagnetic resonance spectroscopy confirm the generation of ketyl radicals via confinement within MFM-300(Cr). This protocol removes simultaneously the need for a precious metal-based photocatalyst or for amine-based sacrificial agents for the photochemical synthesis
Magnetization dynamics and coherent spin manipulation of a propeller Gd(III) complex with the smallest helicene ligand
A homoleptic gadolinium(III) complex with the smallest helicene-type ligand, 1,10-phenanthroline-N,N'-dioxide (phendo) [Gd(phendo)(4)](NO3)(3)center dot xMeOH (phendo = 1,10-phenanthroline-N,N'-dioxide, MeOH = methanol), shows slow relaxation of the magnetization characteristic for Single Ion Magnets (SIM), despite negligible magnetic anisotropy, confirmed by ab initio calculations. Solid state dilution magnetic and EPR studies reveal that the magnetization dynamics of the [Gd(phendo)(4)](3+) cation is controlled mainly by a Raman process. Pulsed EPR experiments demonstrate long phase memory times (up to 2.7 mu s at 5 K), enabling the detection of Rabi oscillations at 20 K, which confirms coherent control of its spin state.</p
Understanding hysteresis in carbon dioxide sorption in porous metal-organic frameworks
Two
new isostructural microporous coordination frameworks [Mn3(Hpdc)2Â(pdc)2] (1) and [Mg3(Hpdc)2Â(pdc)2] (2) (pdc2â = pyridine-2,4-dicarboxylate) showing
primitive cubic (pcu) topology have been prepared and
characterized. The pore aperture of the channels is too narrow for
the efficient adsorption of N2; however, both compounds
demonstrate substantially higher uptake of CO2 (119.9 mL·gâ1 for 1 and 102.5 mL·gâ1 for 2 at 195 K, 1 bar). Despite of their structural
similarities, 2 shows a typical reversible type I isotherm
for adsorption/desorption of CO2, while 1 features
a two-step adsorption process with a very broad hysteresis between
the adsorption and desorption curves. This behavior can be explained
by a combination of density functional theory calculations, sorption,
and X-ray diffraction analysis and gives insights into the further
development of new sorbents showing adsorption/desorption hysteresis
Control of zeolite microenvironment for propene synthesis from methanol
Optimising the balance between propene selectivity, propene/ethene ratio and catalytic stability and unravelling the explicit mechanism on formation of the first carbonâcarbon bond are challenging goals of great importance in state-of-the-art methanol-to-olefin (MTO) research. We report a strategy to finely control the nature of active sites within the pores of commercial MFI-zeolites by incorporating tantalum(V) and aluminium(III) centres into the framework. The resultant TaAlS-1 zeolite exhibits simultaneously remarkable propene selectivity (51%), propene/ethene ratio (8.3) and catalytic stability (>50 h) at full methanol conversion. In situ synchrotron X-ray powder diffraction, X-ray absorption spectroscopy and inelastic neutron scattering coupled with DFT calculations reveal that the first carbonâcarbon bond is formed between an activated methanol molecule and a trimethyloxonium intermediate. The unprecedented cooperativity between tantalum(V) and BrĂžnsted acid sites creates an optimal microenvironment for efficient conversion of methanol and thus greatly promotes the application of zeolites in the sustainable manufacturing of light olefins.We thank EPSRC (EP/P011632/1), the Royal Society, National Natural Science Foundation of China (21733011, 21890761, 21673076), and the University of Manchester for funding. We thank EPSRC for funding and the EPSRC National Service for EPR Spectroscopy at Manchester. A.M.S. is supported by a Royal Society Newton International Fellowship. We are grateful to the STFC/ISIS Facility, Oak Ridge National Laboratory (ORNL) and Diamond Light Source (DLS) for access to the beamlines TOSCA/MAPS, VISION and I11/I20, respectively. We acknowledge Dr. L. Keenan for help at I20 beamline (SP23594-1). UK Catalysis Hub is kindly thanked for resources and support provided via our membership of the UK Catalysis Hub Consortium and funded by EPSRC grant: EP/R026939/1, EP/R026815/1, EP/R026645/1, EP/R027129/1 or EP/M013219/1 (biocatalysis). We acknowledge the support of The University of Manchesterâs Dalton Cumbrian Facility (DCF), a partner in the National Nuclear User Facility, the EPSRC UK National Ion Beam Centre and the Henry Royce Institute. We recognise Dr. R. Edge and Dr. K. Warren for their assistance during the 60Co Îł-irradiation processes. We thank Prof. A. Jentys from the Technical University of Munich for the measurement of the INS spectrum of iso-butene. We thank C. Webb, E. Enston and G. Smith for help with GCâMS; Dr. L. Hughes for help with SEM and EDX; M. Kibble for help at TOSCA/MAPS beamlines. Computing resources (time on the SCARF compute cluster for some of the CASTEP calculations) was provided by STFCâs e-Science facility. A portion of this research used resources at the Spallation
Neutron Source, a DOE Office of Science User Facility operated by ORNL. The computing
resources at ORNL were made available through the VirtuES and the ICE-MAN projects,
funded by Laboratory Directed Research and Development programme and Compute and
Data Environment for Science (CADES
The Origin of Catalytic Benzylic CâH Oxidation over a RedoxâActive MetalâOrganic Framework
From Wiley via Jisc Publications RouterHistory: received 2021-02-15, rev-recd 2021-03-27, pub-electronic 2021-06-04Article version: VoRPublication status: PublishedFunder: Engineering and Physical Sciences Research Council; Id: http://dx.doi.org/10.13039/501100000266; Grant(s): EP/I011870Funder: H2020 European Research Council; Id: http://dx.doi.org/10.13039/100010663; Grant(s): 742401Abstract: Selective oxidation of benzylic CâH compounds to ketones is important for the production of a wide range of fine chemicals, and is often achieved using toxic or precious metal catalysts. Herein, we report the efficient oxidation of benzylic CâH groups in a broad range of substrates under mild conditions over a robust metalâorganic framework material, MFMâ170, incorporating redoxâactive [Cu2II(O2CR)4] paddlewheel nodes. A comprehensive investigation employing electron paramagnetic resonance (EPR) spectroscopy and synchrotron Xâray diffraction has identified the critical role of the paddlewheel moiety in activating the oxidant tBuOOH (tertâbutyl hydroperoxide) via partial reduction to [CuIICuI(O2CR)4] species
Revisiting the Incorporation of Ti(IV) in UiO-type MetalâOrganic Frameworks: Metal Exchange versus Grafting and Their Implications on Photocatalysis
Revisiting the Incorporation of Ti(IV) in UiO-type
MetalâOrganic Frameworks: Metal Exchange versus Grafting and
Their Implications on Photocatalysi
Reversible adsorption and confinement of nitrogen dioxide within a robust porous metal-organic framework
Nitrogen dioxide (NO2) is a major air pollutant causing significant environmental and health problems. We report reversible adsorption of NO2 in a robust metalâorganic framework. Under ambient conditions, MFM-300(Al) exhibits a reversible NO2 isotherm uptake of 14.1âmmolâgâ1, and, more importantly, exceptional selective removal of low-concentration NO2 (5,000 to <1âppm) from gas mixtures. Complementary experiments reveal five types of supramolecular interaction that cooperatively bind both NO2 and N2O4 molecules within MFM-300(Al). We find that the in situ equilibrium 2NO2âââN2O4 within the pores is pressure-independent, whereas ex situ this equilibrium is an exemplary pressure-dependent first-order process. The coexistence of helical monomerâdimer chains of NO2 in MFM-300(Al) could provide a foundation for the fundamental understanding of the chemical properties of guest molecules within porous hosts. This work may pave the way for the development of future capture and conversion technologies
Modulation of uptake and reactivity of nitrogen dioxide in metalâorganic framework materials
We report the modulation of reactivity of nitrogen dioxide (NO2) in a charged metalâorganic framework (MOF) material, MFMâ305âCH3 in which unbound Nâcentres are methylated and the cationic charge counterâbalanced by Clâ ions in the pores. Uptake of NO2 into MFMâ305âCH3 leads to reaction between NO2 and Clâ to give nitrosyl chloride (NOCl) and NO3â anions. A high dynamic uptake of 6.58 mmol gâ1 at 298 K is observed for MFMâ305âCH3 as measured using a flow of 500 ppm NO2 in He. In contrast, the analogous neutral material, MFMâ305, shows a much lower uptake of 2.38 mmol gâ1. The binding domains and reactivity of adsorbed NO2 molecules within MFMâ305âCH3 and MFMâ305 have been probed using in situ synchrotron Xâray diffraction, inelastic neutron scattering and by electron paramagnetic resonance, highâfield solidâstate nuclear magnetic resonance and UV/Vis spectroscopies. The design of charged porous sorbents provides a new platform to control the reactivity of corrosive air pollutants