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An operationally unsaturated iridium-pincer complex that C–H activates methane and ethane in the crystalline solid-state
Get PDFFunding: The EPSRC (EP/W015552/1; EP/W015498/2, DTP to J.C.G.). The Leverhulme Trust (RPG-2020-184). The University of St. Andrews (PhD Scholarship to D.J.S). The Australian Nuclear Science and Technology Organization (ANSTO) is thanked for the generous allocation of beam-time to proposal P16248.The known complex [Ir(tBu-PONOP)MeH][BArF4], 1[BArF4] [tBu-PONOP = κ3-2,6-(tBu2PO)2C5H3N); ArF = 3,5-(CF3)2(C6H3); J. Am. Chem. Soc. 2009 , 131, 8603], is a robust precursor for in crystallo single-crystal to single-crystal (SC-SC) C–H activation of methane and ethane at 80 °C. This contrasts with the reported solution (CD2Cl2) behavior, where 1[BArF4] decomposes by methane loss. Crystalline 1[BArF4] is accessed as a single polymorph on a gram scale. A single-crystal neutron diffraction study locates the hydride. 13C{1H} SSNMR experiments on 1[BArF4] , and its isotopologue [Ir(tBu-PONOP)(CD3)D][BArF4], d4-1[BArF4] , suggest a rapid and reversible endergonic reductive bond formation is occurring in crystallo to access an Ir(I) σ-methane complex. Heating 1[BArF4] to 80 °C under high vacuum results in loss of methane and intramolecular C–H activation to form cyclometalated [Ir(cyclo-tBu-PONOP′)H][BArF4], 2[BArF4] , in a SC-SC reaction. This is reversible, and the addition of CH4 or CD4 to 2[BArF4] at 80 °C results in an equilibrium with 1[BArF4] or d4-1[BArF4] , respectively. Complex 2[BArF4] is thus an operationally unsaturated source of 14-electron [Ir(tBu-PONOP)][BArF4], III , that undergoes C–H activation with methane. Periodic DFT studies, alongside isotope labeling experiments, link 1[BArF4] and 2[BArF4] /CH4 via a reductive elimination/oxidative addition pathway. Heating 2[BArF4] to 80 °C under N2 forms [Ir(tBu-PONOP)(κ1-N2)][BArF4], in a SC-SC transformation. Reaction with CO forms [Ir(tBu-PONOP)(CO)][BArF4] at room temperature. Calculations suggest reaction with N2 occurs via an associative process or competitively through III , while with CO only an associative process operates. Heating 2[BArF4] to 80 °C under an ethane atmosphere results in alkane dehydrogenation, via a SC–SC reaction, forming a ∼1:1 mixture of [Ir(tBu-PONOP)(η2-H2C═CH2)][BArF4], and [Ir(tBu-PONOP)H2][BArF4].Peer reviewe
ZnH2 as a precursor to catalytically active Ru–ZnH heterometallic complexes
Get PDFFunding: The authors thank both the EPSRC (EP/T019743/1) and Heriot-Watt University (James Watt Scholarship to AC) for financial support.Reaction of [Ru(IPr)2(CO)H][BArF4] ( 1 ; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene; BArF4 = B{3,5(CF3)2C6H3}4) with an excess of ZnH2 in THF gives the structurally characterized neutral Ru(ZnH) complex [Ru(IPr)2(CO)(ZnH)H3] ( 6 ) and Ru(ZnH)2 salt [Ru(IPr)2(CO)(ZnH)2H3][BArF4] ( 5 ). Crystallographic and computational analyses show the presence of both bridging Ru–H–Zn hydrides and terminal Ru-hydrides in the two products. Calculations also identify a low-energy H/ZnH exchange pathway that rationalizes the experimentally observed (EXSY) fluxionality of the hydrides in 5 . At room temperature, this compound undergoes stoichiometric exchange with ZnMe2 to give [Ru(IPr)2(CO)(ZnMe)2H3][BArF4] ( 7 ), and also proves to be catalytically active for the hydrogenation of 1-hexene and 5-hexene-2-one.Peer reviewe
St Bartholomew’s Priory, West Smithfield : the tomb of Rahere and the book of the foundation
Get PDFA case exists for revising the dates normally assigned to two late medieval objects which commemorate the origins of St Bartholomew’s priory in West Smithfield (founded 1123). It is possible to show that the effigy of Rahere in the priory church is an addition, rather than original, to the founder’s tomb on the north side of the choir, and also that the manuscript containing the so-called Book of the Foundation was made considerably later than is usually thought. Doing so entails accounting for the assumptions on which the received dates rest (this is done first). It also involves looking more closely and critically at the objects in question than anyone seems to have done in the recent past.Peer reviewe
Bi-functional oxygen electrocatalysts for reversible solid oxide cells : the influence of A-site non-stoichiometry on the system (La or Ba)0.6–xSr0.4Co0.8Fe0.2O3−δ
Get PDFFunding: The funding for the presented research has been supported by the Council of Scientific and Industrial Research (CSIR), Govt. of India, under “CSIR Hydrogen Technology (H2T)-Mission Program” [CGCRI/BDPD/Project-OM-23 −24/32] and Centre for High Technology, Oil Industries Development Board MoP & NG [CGCRI/BDPD/Project-OM-22-23/04]. G.C.M. acknowledges the project PID2021-123308OB-I00, funded by MCIN/AEI/10.13039/501100011033 in Spain and “ERDF A way of making Europe” by the European Union.Selective tailoring of stoichiometry in perovskite oxide generates excellent electrocatalytic activity toward redox reaction of oxygen [oxygen evolution reaction (OER) and oxygen reduction reaction (ORR)]. The redox reaction of oxygen is kinetically sluggish (spin relaxed reaction) and is the rate-limiting step for solid oxide cells (SOCs). We have reported that introducing non-stoichiometry at the A-site in A0.6–xSr0.4Co0.8Fe0.2O3−δ imparts a bifunctional electrocatalyst for OER and ORR with excellent performance in fuel cell (FC) and electrolyzer cell (EC) mode. Two compositions, Ba0.6Sr0.4Co0.8Fe0.2O3−δ (BSCF-6482) and La0.6Sr0.4Co0.8Fe0.2O3−δ (LSCF-6482), are designed by varying the non-stoichiometry from 0.6 to 0.52 for Ba and La, respectively. X-ray photoelectron spectroscopy (XP spectroscopy), iodometric estimation, and O2-temperature-programmed desorption (O2-TPD) reveal that Ba0.54Sr0.4Co0.8Fe0.2O3−δ (BS-54) promotes oxygen surface exchange (higher β-oxygen population) and La0.54Sr0.4Co0.8Fe0.2O3−δ (LS-54) accelerates α-oxygen desorption (charge-transfer reaction). A study of the distribution of relaxation time (DRT) using EIS (electrochemical impedance spectroscopy) on cell configuration LS-54 (or BS-54)/GDC-LS-54 (or BS-54)//GDC//Pt@800 °C reveals that LS-54 has minimum electrode polarization (comprising dual processes of charge transfer and oxygen surface exchange) at both +0.8 V (OER) and −0.8 V (ORR), which resonates at 103–104 Hz. It is corroborated that α-oxygen is associated with the charge-transfer process and controls the ORR, whereas the OER is assisted by oxygen surface exchange, primarily linked with β-oxygen. Inclusion of non-stoichiometry at the A-site promotes oxygen-vacancy formation and stabilizes a lower valence state for the B-site cations. The rate-controlling steps for the OER and ORR thereby alter in LS-54 and BS-54 compared to LSCF/BSCF-6482. Electrochemical measurements show superior reversible solid oxide cell (SOC) performance of LS-54 having a current density (CD) of 1.27 A cm–2 @1.5 V and 0.66 A cm–2 @0.5 V for a cell with dimensions as large as 5 cm × 5 cm. A similar cell operated with a CD of 1.0 A cm2 under standalone mode of operation in FC. This work proposes a novel strategy to demonstrate A-site non-stoichiometric La0.54Sr0.4Co0.8Fe0.2O3−δ to be a superior bifunctional electrocatalyst for both OER and ORR for SOCs.Peer reviewe
Synthesis and growth mechanisms of (3,1)-graphene nanoribbons on Cu(111) : insights from STM and DFT analysis
Get PDFFunding: YYS acknowledges support from the Funds for Women Graduates (GA-00558). RS acknowledges financial support from the Scottish Funding Council through SRD-Grant HR07003.We present a comprehensive study on the bottom-up synthesis of chiral (3,1)-graphene nanoribbons (GNRs) on Cu(111) using two analogous precursors, 10,10'-dibromo-9,9'-bianthryl (DBBA) and bianthracene (BA). Through a temperature-programmed growth strategy supported by scanning tunnelling microscopy, we investigate the role of precursor diffusion, polymerization, and cyclodehydrogenation in GNR formation. Our results show that DBBA predominantly forms bisanthene due to restricted surface diffusion and premature cyclodehydrogenation, rendering it unsuitable for extended ribbon growth. In contrast, BA exhibits significantly higher surface mobility, leading to the formation of polyanthracene chains, which subsequently transform into long (3,1)-GNRs upon controlled annealing. We identify cyclodehydrogenation at chain termini as a key factor limiting ribbon length. Our findings provide new insights into optimizing growth conditions for extended GNRs on Cu(111), paving the way for their integration into future electronic and spintronic applications.Peer reviewe
An ethics of duty in the absence of hope : bereaved family activism in the aftermath of the Sewol ferry disaster
Get PDFFunding: This work was supported by the Cambridge Trust’s International Scholarship, King’s College, Cambridge, and the Cambridge University Fieldwork Fund.Families bereaved by the Sewol Ferry Disaster, who have been campaigning for truth, accountability, and memorialisation in South Korea since 2014, are not driven by hope. While they widely acknowledge their activism to be effectively thwarted by conditions that exceed them, the bereaved of Sewol continue to populate the everyday with a ceaseless flow of actions, however minute they may seem in the grand scheme of things. I suggest that the concept of duty refines and supplements our understanding of activism that continues in spite of hopeless circumstances. In conversation with the anthropology of hope, I propose an understanding of activist projects not defined exclusively by teleology but also by infinitude.Peer reviewe
PyTICS : an iterative method for photometric light-curve intercalibration using comparison stars
Get PDFFunding: RV acknowledges support from STFC studentship ST/Y509589/1. JVHS acknowledges support from Science and Technology Facilities Council (STFC) grant ST/V000861/1.Intensive reverberation mapping monitoring programs combine ground-based photometric observations from different telescopes, requiring intercalibration of light-curves to reduce systematic instrumental differences. We present a new iterative algorithm to calibrate photometric time-series data of active galactic nuclei (AGNs) using 100s of comparison stars on the same images, building upon the established method of ensemble photometry. The algorithm determines telescope-specific and epoch-specific correction parameters, and simultaneously computes a multicomponent noise model to account for underestimated uncertainties based on the scatter in the comparison star data, effectively identifying problematic epochs, telescopes, and stars. No assumptions need to be made about the AGN variability shape, and the algorithm can, in principle, be applied to any astronomical object. We demonstrate our method on light-curves taken with ten 1-m telescopes from the Las Cumbres Observatory (LCO) robotic telescope network. Comparing our results to other intercalibration tools, we find that the algorithm can more accurately quantify the uncertainties in the data. We describe additional corrections that can be made for particularly bluer AGNs like Fairall 9, arising due to systematic effects dependent on star colour.Peer reviewe
Terrestrial carbon isotope stratigraphy of the Eocene–Oligocene transition, Petrockstowe and Bovey basins, Devon, UK
Get PDFFunding: MC was funded by the Tertiary Education Trust Fund (TETFund) Abuja, via the intervention of academic staff training and development programme to the Federal University of Petroleum Resources, Effurun, Nigeria.The terrestrial sediments of the Petrockstowe and Bovey basins in Devon, UK were examined. Their age is considered to be Eocene and Oligocene. The sediments (kaolinitic clays, silts, sands, gravels, and lignites) from both basins were analysed for carbon isotopes of organic material, in conjunction with total organic carbon and palynological analyses used to unravel the type of and provenance of organic matter present. Within the Petrockstowe Basin, the lowermost interval examined shows a palynological distribution dominated by phytoclasts, whilst the upper part of the core is dominated by higher concentrations of palynomorphs (up to 90 %) and an increase in amorphous organic matter consistent (up to 37 %) with a change from sand-filled fluvial channels followed by an ephemeral lake or lake margin setting. Our palynological data from the South John Acres Lane Quarry section, Bovey Basin, show that within the lignites palynomorphs are high again (up to 95 %) consistent with them representing more ephemeral lakes or lake margins periodically exposed with mires. Our palynological data set further allows us to determine that isotope trends are not overly determined by the source of carbon in the basins. Our study suggests that the observed patterns were primarily produced by variations of the isotope ratios of terrestrial atmospheric carbon reservoirs. Even with our less than well constrained biostratigraphical control, the data indicate that the carbon isotope excursions seen in the Eocene and Oligocene could be associated with several transient carbon isotopic shifts (associated with the Paleocene–Eocene Thermal Maximum). Our findings therefore appear to lend support to the surface ocean and atmosphere behaving as coupled reservoirs at this time.Peer reviewe
Common mechanism of dual emission in linearly-linked donor-acceptor-type thermally activated delayed fluorescence molecules
Get PDFFunding: This work was partially supported by JSPS KAKENHI Grant Numbers JP23H01977, JP23H04631, JP23K20039, and JP24KJ1791. The work at the University of St Andrews was supported by the Engineering and Physical Sciences Research Council of the UK through grant ER/R035164/1.Linearly-linked donor–acceptor-type (D–A) thermally activated delayed fluorescence molecules have been expected to be used as efficient emitters in organic light emitting diodes. Despite their simple molecular structures, some of these molecules exhibit a complex dual emission mechanism due to their two conformers: quasi-coplanar (q-copl.) and perpendicular (perp.) conformers. We have investigated three molecules of this type: phenothiazine–triphenyltriazine, 9,9-dimethyl-9,10-dihydroacridine–triphenyltriazine, and phenoxazine–triphenyltriazine using picosecond time-resolved photoluminescence and femtosecond transient absorption spectroscopy measurements. We have revealed the dual emission mechanism common to the three molecules: after photoexcitation, in the q-copl. conformer, the second singlet excited state with local excitation character emits strong fluorescence, which decays in 3–7 ps as it relaxes to the lowest singlet excited state with charge transfer (CT) character. The CT state exhibits relatively weak fluorescence with a lifetime of tens to hundreds of picoseconds. In the perp. conformer, the excited state shows a pronounced CT character with a weaker oscillator strength reduced by two orders of magnitude, structural relaxation in about 4 ps and a slow decay in >1 ns. The dual emission intensity ratio is determined by the population ratio between the q-copl. and perp. conformers in the ground state. The difference in this intensity ratio between the three molecules is ascribed to the difference in relative energetic stability between the two conformers in the ground state. The emission mechanism common to the linearly-linked D–A molecules deepens the understanding of their photophysical properties and opens new pathways for the development of advanced photofunctional materials.Peer reviewe
Enhancing trap stiffness and Raman scattering in optical traps
Get PDFOptical tweezers have found applications in basic physics, medicine, biology, and nanotechnology. For a small particle in a Gaussian laser beam, the trapping force arises as a competition between gradient forces pulling the particle to the beam focus and scattering forces pushing the particle along the optical axis. Balancing these competing forces means that the optimal behaviour on a trapped particle occurs when the radius of the particle is approximately the beam waist of the trapping light.
In this work, I explore the application of a short wavelength laser into an optical trap to reduce the beam waist and obtain a substantial improvement in the stiffness per unit of power for subwavelength silica particles. I then harness the high optical scattering cross section of the particles at short wavelengths to realise a Raman optical tweezers setup for improved micro-plastic detection.
For very small particles, one cannot continue to move to shorter wavelength lasers. To generate sufficient trapping forces, one needs to overcome the diffraction limit and confine light even more tightly. Here, my collaborators and I exploit a Fano resonance effect in an all-dielectric quadrupole nanostructure to realize tight light confinement, enabling a high effective trap stiffness of 1.19fN/nm for a 100nm diameter polystyrene nanoparticle with 4mW/μm2 illumination. We furthermore show the capability of our nanostructure to trap two particles at different locations within the array."The work presented in this thesis was funded by St Leonard Research Scholarship and the UK Engineering and Physical Sciences Research Council (EP/P030017/1)."--Fundin
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