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The ability of Co3Mo3N to act as catalyst for the hydrogen evolution reaction at low overpotential is demonstrated. The identity of catalytic sites is established using DFT simulations.

Molecular metal chalcogenides have attracted great attention as electrocatalysts for the hydrogen evolution reaction (HER). However, efficient utilisation of the active sites and catalytic performance modulation has been challenging. Here we explore the design of immobilized molecular molybdenum polyselenides [Mo2O2S2(Se2)(Sex)]2– that exhibit efficient hydrogen evolution at low overpotential and stability over 1000 cycles. Density functional calculations provide evidence of a unimolecular mechanism in the HER process via the exploration of viable reaction pathways. The discussed findings are of a broad interest in the development of efficient molecular electrocatalytic materials.

Aqueous solutions of polyoxometalates (POMs) have been shown to have potential as high-capacity energy storage materials due to their potential for multi-electron redox processes, yet the mechanism of reduction and practical limits are currently unknown. Herein, we explore the mechanism of multi-electron redox processes that allow the highly reduced POM clusters of the form {MO3}y to absorb y electrons in aqueous solution, focusing mechanistically on the Wells–Dawson structure X6[P2W18O62], which comprises 18 metal centers and can uptake up to 18 electrons reversibly (y = 18) per cluster in aqueous solution when the countercations are lithium. This unconventional redox activity is rationalized by density functional theory, molecular dynamics simulations, UV–vis, electron paramagnetic resonance spectroscopy, and small-angle X-ray scattering spectra. These data point to a new phenomenon showing that cluster protonation and aggregation allow the formation of highly electron-rich meta-stable systems in aqueous solution, which produce H2 when the solution is diluted. Finally, we show that this understanding is transferrable to other salts of [P5W30O110]15– and [P8W48O184]40– anions, which can be charged to 23 and 27 electrons per cluster, respectively.

Two-dimensional (2D) transition-metal dichalcogenides have become promising candidates for surface-enhanced Raman spectroscopy (SERS), but currently very few examples of detection of relevant molecules are available. Herein, we show the detection of the lipophilic disease marker beta-sitosterol on few-layered MoTe2 films. The chemical vapor deposition (CVD)-grown films are capable of nanomolar detection, exceeding the performance of alternative noble-metal surfaces. We confirm that the enhancement occurs through the chemical enhancement (CE) mechanism via formation of a surface-analyte complex, which leads to an enhancement factor of approximate to 10(4), as confirmed by Fourier transform infrared (FTIR), UV-vis, and cyclic voltammetry (CV) analyses and density functional theory (DFT) calculations. Low values of signal deviation over a seven-layered MoTe2 film confirms the homogeneity and reproducibility of the results in comparison to noble-metal substrate analogues. Furthermore, beta-sitosterol detection within cell culture media, a minimal loss of signal over 50 days, and the opportunity for sensor regeneration suggest that MoTe2 can become a promising new SERS platform for biosensing.

MoTe2 has been shown to undergo an electrochemical activation in operando, which is evidenced by a dramatic reduction of the overpotential. This work identifies the optimum reaction conditions in which MoTe2 can be activated. The activation can be achieved by sweeping the potential between the optimal range of +0.2 V and -0.5 V (vs. NHE) for 100 cycles.

Food demand due to the growing global population has been stretching the agriculture sector to the limit. This demands the cultivation of plants in shrinking land areas which makes the search for highly effective systems for plant nutrition and pest control important. In this context, the application of nanoparticles (NPs) in agriculture can have a transformative effect on food production techniques as it can enable the delivery of bioactive agents (including growth factors, pesticides, and fungicides) directly to plants. Herein, we report the application of unfunctionalized as well as amine-functionalized and polycaprolactone-coated Fe

Antimicrobial resistance (AMR) has become a global concern as many bacterial species have developed resistance to commonly prescribed antibiotics, making them ineffective to treatments. One type of antibiotics, gallium(III) compounds, stands out as possible candidates due to their unique "Trojan horse" mechanism to tackle bacterial growth, by substituting iron(III) in the metabolic cycles of bacteria. In this study, we tested three polysaccharides (carboxymethyl cellulose (CMC), alginate, and pectin) as the binding and delivery agent for gallium on three bacteria (

The production of hydrogen through water splitting using earth-abundant metal catalysts is a promising pathway for converting solar energy into chemical fuels. However, existing approaches for fine stoichiometric control, structural and catalytic modification of materials by appropriate choice of earth abundant elements are either limited or challenging. Here we explore the tuning of redox active immobilised molecular metal-chalcoxide electrocatalysts by controlling the chalcogen or metal stoichiometry and explore critical aspects of the hydrogen evolution reaction (HER). Linear sweep voltammetry (LSV) shows that stoichiometric and structural control leads to the evolution of hydrogen at low overpotential with no catalyst degradation over 1000 cycles. Density functional calculations reveal the effect of the electronic and structural features and confer plausibility to the existence of a unimolecular mechanism in the HER process based on the tested hypotheses. We anticipate these findings to be a starting point for further exploration of molecular catalytic systems., While hydrogen offers a potential carbon neutral fuel, its production from water using earth-abundant, heterogeneous materials has proven challenging to understand. Here, authors present a series of molecular electrocatalysts based on molybdenum, sulphur, and oxygen for aqueous hydrogen evolution.

Metal alloys have become a ubiquitous choice as catalysts for electrochemical hydrogen evolution in alkaline media. However, scarce and expensive Pt remains the key electrocatalyst in acidic electrolytes, making the search for earth-abundant and cheaper alternatives important. Herein, we present a facile and efficient synthetic route towards polycrystalline Co3Mo and Co7Mo6 alloys. The single-phased nature of the alloys is confirmed by X-ray diffraction and electron microscopy. When electrochemically tested, they achieve competitively low overpotentials of 115 mV (Co3Mo) and 160 mV (Co7Mo6) at 10 mA cm&minus, 2 in 0.5 M H2SO4, and 120 mV (Co3Mo) and 160 mV (Co7Mo6) at 10 mA cm&minus, 2 in 1 M KOH. Both alloys outperform Co and Mo metals, which showed significantly higher overpotentials and lower current densities when tested under identical conditions, confirming the synergistic effect of the alloying. However, the low overpotential in Co3Mo comes at the price of stability. It rapidly becomes inactive when tested under applied potential bias. On the other hand, Co7Mo6 retains the current density over time without evidence of current decay. The findings demonstrate that even in free-standing form and without nanostructuring, polycrystalline bimetallic electrocatalysts could challenge the dominance of Pt in acidic media if ways for improving their stability were found.

Minor structural changes in transition metal dichalcogenides can have dramatic effects on their electronic properties. This makes the quest for key parameters that enable a selective choice between the competing metallic and semiconducting phases in the 2D MoTe2 system compelling. Herein, we report the optimal conditions at which the choice of the initial seed layer dictates the type of crystal structure of atomically-thin MoTe2 films grown by chemical vapour deposition (CVD). When Mo metal is used as a seed layer, semiconducting 2H-MoTe2 is the only product. Conversely, MoO3 leads to the preferential growth of metallic 1T′-MoTe2. The control over phase growth allows for simultaneous deposition of both 2H-MoTe2 and 1T′-MoTe2 phases on a single substrate during one CVD reaction. Furthermore, Rhodamine 6G dye can be detected using few-layered 1T′-MoTe2 films down to 5 nM concentration, demonstrating surface enhanced Raman spectroscopy (SERS) with sensitivity several orders of magnitude higher than for bulk 1T′-MoTe2. The polymorphism of MoTe2 can be used to realize planar metallic/semiconducting homojunctions in 2D devices, greatly reducing the contact resistance. Here, the simultaneous growth of both phases is achieved on the same substrate by single-step chemical vapor deposition and seeding layer engineering.

Made available in DSpace on 2020-12-12T02:47:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-07-20 Food demand due to the growing global population has been stretching the agriculture sector to the limit. This demands the cultivation of plants in shrinking land areas which makes the search for highly effective systems for plant nutrition and pest control important. In this context, the application of nanoparticles (NPs) in agriculture can have a transformative effect on food production techniques as it can enable the delivery of bioactive agents (including growth factors, pesticides, and fungicides) directly to plants. Herein, we report the application of unfunctionalized as well as amine-functionalized and polycaprolactone-coated Fe3O4 NPs to seed treatment in tomato (Solanum lycopersicum). The study reveals that the treatment has no side effects on plant germination and development. Furthermore, the translocation of NPs in seeds and seedlings posttreatment depends on the surface functionalization of the NPs. X-ray fluorescence spectroscopy analysis of seedlings suggested that around 66% of unfunctionalized Fe3O4 NPs were translocated in the cotyledons, while only 50% of functionalized NPs (both amine and polycaprolactone) were translocated. Our results demonstrate that all particles were taken up by the seeds, thus suggesting that the functionalized NPs can act as a versatile platform for delivering of active compounds, such as fungicides and growth factor agents. Chemical Engineering School of Engineering and Physical Sciences Heriot-Watt University Institute of Science and Technology São Paulo State University (UNESP), Avenida Três de Março 511 Center for Nuclear Energy in Agriculture University of São Paulo School of Chemistry University of Glasgow Joseph Black Building, University Avenue Institute of Science and Technology São Paulo State University (UNESP), Avenida Três de Março 511

There has been substantial interest in research aimed at conductive carbon-based supports since the discovery that the electrical stimulus can have dramatic effect on cell behavior. Among these carbon-aerogels decorated with biocompatible polymers were suggested as future materials for tissue engineering. However, high reaction temperatures required for the synthesis of the aerogels tend to impair the stability of the polymeric networks. Herein, we report a synthetic route towards carbon-aerogel scaffolds decorated with biocompatible ceramic nanoparticles of tricalcium phosphate. The composites can be prepared at temperature as high as 1100 °C without significant effect on the morphology of the composite which is comparable with the original aerogel framework. Although the conductivity of the composites tends to decrease with the increasing ceramic content the measured conductivity values are similar to those previously reported on polymer-functionalized carbon-aerogels. The cell culture study revealed that the developed constructs support cell proliferation and provide good cell attachment suggesting them as potentially good candidates for tissue-engineering applications.

Minor structural changes in transition metal dichalcogenides can have dramatic effects on their electronic properties. This makes the quest for key parameters that can enable a selective choice between the competing metallic and semiconducting phases in the 2D MoTe2 system compelling. Herein, we report the optimal conditions at which the choice of the initial seed layer dictates the type of crystal structure of atomically-thin MoTe2 films grown by chemical vapour deposition (CVD). When Mo metal is used as a seed layer, phase-pure semiconducting 2H-MoTe2 is the only product. Conversely, MoO3 leads to the preferential growth of phase-pure metallic 1Tꞌ-MoTe2. The control over phase growth allows for simultaneous deposition of both 2H-MoTe2 and 1Tꞌ-MoTe2 phases on a single substrate during one CVD reaction. Furthermore, Rhodamine 6G dye can be detected using few-layered 1Tꞌ-MoTe2 films down to 5 nM concentration which is several orders of magnitude higher than the value observed for bulk 1Tꞌ-MoTe2.

© 2019 Elsevier Ltd The development of an efficient process to simultaneously extract oxygen and metals from lunar regolith by way of in-situ resource utilisation (ISRU) has the potential to enable sustainable activities beyond Earth. The Metalysis-FFC (Fray, Farthing, Chen) process has recently been proven for the industrial-scale production of metals and alloys, leading to the present investigation into the potential application of this process to regolith-like materials. This paper provides a proof-of-concept for the electro-deoxidation of powdered solid-state lunar regolith simulant using an oxygen-evolving SnO2 anode, and constitutes the first in-depth study of regolith reduction by this process that fully characterises and quantifies both the anodic and cathodic products. Analysis of the resulting metallic powder shows that 96% of the total oxygen was successfully extracted to give a mixed metal alloy product. Approximately a third of the total oxygen in the sample was detected in the off-gas, with the remaining oxygen being lost to corrosion of the reactor vessel. We anticipate, with appropriate adjustments to the experimental set-up and operating parameters, to be able to isolate essentially all of the oxygen from lunar regolith simulants using this process, leading to the exciting possibility of concomitant oxygen generation and metal alloy production on the lunar surface.

Antimicrobial resistance (AMR) has become a global concern as many bacterial species have developed resistance to commonly prescribed antibiotics, making them ineffective to treatments. One type of antibiotics, gallium(III) compounds, stands out as possible candidates due to their unique “Trojan horse” mechanism to tackle bacterial growth, by substituting iron(III) in the metabolic cycles of bacteria. In this study, we tested three polysaccharides (carboxymethyl cellulose (CMC), alginate, and pectin) as the binding and delivery agent for gallium on three bacteria (Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus) with a potential bioresponsive delivery mode. Two types of analysis on bacterial growth (minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC)) were carried out while iron(III)-loaded polysaccharide samples were also tested for comparison. The results suggested that gallium showed an improved inhibitory activity on bacterial growth, in particular gallium(III)-loaded carboxymethyl cellulose (Ga-CMC) sample showing an inhibiting effect on growth for all three tested bacteria. At the MIC for all three bacteria, Ga-CMC showed no cytotoxicity effect on human dermal neonatal fibroblasts (HDNF). Therefore, these bioresponsive gallium(III) polysaccharide compounds show significant potential to be developed as the next-generation antibacterial agents with controlled release capability.

The electrochemical generation of hydrogen is a key enabling technology for the production of sustainable fuels. Transition metal chalcogenides show considerable promise as catalysts for this reaction, but to date there are very few reports of tellurides in this context, and none of these transition metal telluride catalysts are especially active. Here, we show that the catalytic performance of metallic 1T'-MoTe

The electrocatalytic hydrogen evolution reaction (HER) is of central importance for the production of H₂ from sustainable sources. Currently, platinum is the best electrocatalyst for this transformation, but other materials based on less precious elements are now attracting increasing attention. Of these alternatives, the molybdenum chalcogenides show particular promise. MoS₂ has been explored extensively in this regard, which has highlighted the important role of polymorphism for catalytic activity. However, the conversion process into an active polymorph is complex and the stability of the catalyst under electrochemical conditions is poor. In contrast, MoTe₂ has barely been studied as an electrocatalyst for the HER. Herein, we isolate the semiconducting and metallic polymorphs of MoTe₂ using an easy solid state route and show that interconversion between the two polymorphs of MoTe₂ can be achieved without change in morphology by a simple temperature annealing protocol. Whilst the semiconducting form is a rather poor electrocatalyst for the HER, the metallic 1T'-MoTe₂ polymorph is an efficient and stable electrocatalyst for the hydrogen evolution reaction in 1 M H₂SO₄. Even in the bulk form, it achieved low overpotential with a Tafel slope of 78 ± 4 mV / dec and full Faradaic efficiency. These findings highlight the importance of polymorphic control in the development of HER catalysts, and suggest an efficient route for the discovery of new and improved electrocatalysts.

Metal chalcogenides, and doped molybdenum sulfides in particular, have considerable potential as earth-abundant electrocatalysts for the hydrogen evolution reaction. This is especially true in the case of solar-to-hydrogen devices, where an ability to deposit these materials on transparent substrates is therefore desirable. Hydrothermal methods are perhaps the most common route by which metal chalcogenide materials suitable for the hydrogen evolution reaction are produced. Such methods are simple and scalable, but the direct hydrothermal deposition of metal chalcogenides on transparent oxide electrodes has hitherto never been reported. Such an advance would greatly facilitate the expansion of the field by removing the requirement for separate hydrothermal-synthesis and catalyst-deposition steps. In this paper, we show that the ternary chalcogenide Co2Mo9S26 can be synthesised on a fluorine-doped tin oxide substrate by hydrothermal methods directly from solutions of the simple metal salts. These films display good activity for the hydrogen evolution reaction from acid solution, achieving current densities of 10 mA cm−2 at 260 mV overpotential with a Tafel slope of 64 mV per decade. Moreover, the resulting films can be made to be translucent, a very useful property which would allow light to be transmitted through the catalyst to an underlying light-harvesting array in any solar-to-hydrogen device employing this material at the cathode.

The electrochemical generation of hydrogen is a key enabling technology for the production of sustainable fuels. Transition metal chalcogenides show considerable promise as catalysts for this reaction, but to date there are very few reports of tellurides in this context, and none of these transition metal telluride catalysts are especially active. Here, we show that the catalytic performance of metallic 1T′-MoTe2 is improved dramatically when the electrode is held at cathodic bias. As a result, the overpotential required to maintain a current density of 10 mA cm−2 decreases from 320 mV to just 178 mV. We show that this rapid and reversible activation process has its origins in adsorption of H onto Te sites on the surface of 1T′-MoTe2. This activation process highlights the importance of subtle changes in the electronic structure of an electrode material and how these can influence the subsequent electrocatalytic activity that is displayed., The performance of electrocatalysts for the renewable production of hydrogen is currently limited due to the difficulty of materials design. We show that tailoring the electronic structure under applied reductive bias is key to optimal electrocatalytic performance of a 2D chalcogenide material.

A novel method to obtain Al2O3–ZrO2 nanocomposites is presented. It consists of the co-precipitation step of boehmite (AlO(OH)) and ZrO2, followed by microwave hydrothermal treatment at 270 °C and 60 MPa, and by calcination at 600 °C. Using this method, we obtained two nanocomposites: Al2O3–20 wt % ZrO2 and Al2O3–40 wt % ZrO2. Nanocomposites were characterized by Fourier transformed infrared spectroscopy, Raman spectroscopy, X-ray diffraction, and transmission electron microscopy. Sintering behavior and thermal expansion coefficients were investigated during dilatometric tests. The sintering temperatures of the nanocomposites were 1209 °C and 1231 °C, respectively—approximately 100 °C lower than reported for such composites. We attribute the decrease of the sintering temperature to the specific nanostructure obtained using microwave hydrothermal treatment instead of conventional calcination. Microwave hydrothermal treatment resulted in a fine distribution of intermixed highly crystalline nanoparticles of boehmite and zirconia. Such intermixing prevented particle growth, which is a factor reducing sintering temperature. Further, due to reduced grain growth, stability of the θ-Al2O3 phase was extended up to 1200 °C, which enhances the sintering process as well. For the Al2O3–20 wt % ZrO2 composition, we observed stability of the zirconia tetragonal phase up to 1400 °C. We associate this stability with the mutual separation of zirconia nanoparticles in the alumina matrix.

In this article, we report a new sustainable synthesis procedure for manufacturing chitosan/silica CO2 adsorbents. Chitosan is a naturally abundant material and contains amine functionality, which is essential for selective CO2 adsorptions. It is, therefore, ideally suited for manufacturing CO2 adsorbents on a large scale. By coating chitosan onto high-surface-area mesoporous silica supports, including commercial fumed silica (an economical and accessible reagent) and synthetic SBA-15 and MCF silicas, we have prepared a new family of CO2 adsorbents, which have been fully characterised with nitrogen adsorption isotherms, thermogravimetric analysis/differential scanning calorimetry, TEM, FTIR spectroscopy and Raman spectroscopy. These adsorbents have achieved a significant CO2 adsorption capacity of up to 0.98 mmol g−1 at ambient conditions (P=1 atm and T=25 °C). The materials can also be fully regenerated/recycled on demand at temperatures as low as 75 °C with a >85 % retention of the adsorption capacity after 4 cycles, which makes them promising candidates for advanced CO2 capture, storage and utilisation technology.

The most expanded fcc-structured alkali fulleride, Cs3C60, is a Mott insulator at ambient pressure because of the weak overlap between the frontier t1u molecular orbitals of the C603− anions. It has a severely disordered antiferromagnetic ground state that becomes a superconductor with a high critical temperature, Tc of 35 K upon compression. The effect of the localised t1u3 electronic configuration on the properties of the material is not well-understood. Here we study the relationship between the intrinsic crystallographic C603− orientational disorder and the molecular Jahn–Teller (JT) effect dynamics in the Mott insulating state. The high-resolution 13C magic-angle-spinning (MAS) NMR spectrum at room temperature comprises three peaks in the intensity ratio 1:2:2 consistent with the presence of three crystallographically-inequivalent carbon sites in the fcc unit cell and revealing that the JT-effect dynamics are fast on the NMR time-scale of 10−5 s despite the presence of the frozen-in C603− merohedral disorder disclosed by the 133Cs MAS NMR fine splitting of the tetrahedral and octahedral 133Cs resonances. Cooling to sub-liquid-nitrogen temperatures leads to severe broadening of both the 13C and 133Cs MAS NMR multiplets, which provides the signature of an increased number of inequivalent 13C and 133Cs sites. This is attributed to the freezing out of the C603− JT dynamics and the development of a t1u electronic orbital glass state guided by the merohedral disorder of the fcc structure. The observation of the dynamic and static JT effect in the Mott insulating state of the metrically cubic but merohedrally disordered Cs3C60 fulleride in different temperature ranges reveals the intimate relation between charge localization, magnetic ground state, lifting of electronic degeneracy, and orientational disorder in these strongly-correlated systems.

The identification and contribution of the different phonons present in the G-line Raman response in Stage-1 and Stage-2 graphite intercalation compounds (GIC) is crucial for a correct stage determination. Different factors like laser induced de-intercalation play an important role in the precise stage assignment of these phases, and their intrinsic Raman response. In this contribution, an in situ micro-Raman analysis was conducted under high-vacuum conditions. Local heating of the samples was induced by using a high laser power (8.5 mW) in order to study the de-intercalation process from Stage-1 to Stage-2 GICs. A detailed Raman line-shape analysis was performed from the recorded spectra to determine the changes from the G-line response of KC8, CaC6, and LiC6. We confirmed the assignment of the broad E2g Fano mode at ∼1510 cm−1 to the intrinsic Stage-1 Raman response in GICs. Additionally, the most evident change from Stage-1 to Stage-2 was observed in an asymmetric Fano mode in the range of 1565–1610 cm−1. This mode is linked to the first-order stretching Raman mode of Graphite, which tends to increase in frequency and decrease in width as function of de-intercalation. Finally, the response of the Stage-2 phase after de-intercalation was confirmed to be a useful benchmark for the identification of the intercalation stage in highly doped GICs.

Alkali metal intercalation into polyaromatic hydrocarbons (PAHs) has been studied intensely after reports of superconductivity in a number of potassium- and rubidium-intercalated materials. There are, however, no reported crystal structures to inform our understanding of the chemistry and physics because of the complex reactivity of PAHs with strong reducing agents at high temperature. Here we present the synthesis of crystalline K2Pentacene and K2Picene by a solid–solid insertion protocol that uses potassium hydride as a redox-controlled reducing agent to access the PAH dianions, and so enables the determination of their crystal structures. In both cases, the inserted cations expand the parent herringbone packings by reorienting the molecular anions to create multiple potassium sites within initially dense molecular layers, and thus interact with the PAH anion π systems. The synthetic and crystal chemistry of alkali metal intercalation into PAHs differs from that into fullerenes and graphite, in which the cation sites are pre-defined by the host structure.

Ordering of the tetrahedral site vacancies in two crystals of refined compositions K0.93(1)Fe1.52(1)Se2 and K0.862(3)Fe1.563(4)Se2 produces a fivefold expansion of the parent ThCr2Si2 unit cell in the ab plane which can accommodate 20% vacancies on a single site within the square FeSe layer. The iron charge state is maintained close to +2 by coupling of the level of alkali metal and iron vacancies, producing a potential doping mechanism which can operate at both average and local structure levels., Comment: 5 pages 3 figures accepted for publication in Chemical Science Chem. Sci., DOI:10.1039/C1SC00070E

The crystal structure of a solid controls the interactions between the electronically active units and thus its electronic properties. In the high-temperature superconducting copper oxides, only one spatial arrangement of the electronically active Cu(2+) units-a two-dimensional square lattice-is available to study the competition between the cooperative electronic states of magnetic order and superconductivity. Crystals of the spherical molecular C(60)(3-) anion support both superconductivity and magnetism but can consist of fundamentally distinct three-dimensional arrangements of the anions. Superconductivity in the A(3)C(60) (A = alkali metal) fullerides has been exclusively associated with face-centred cubic (f.c.c.) packing of C(60)(3-) (refs 2, 3), but recently the most expanded (and thus having the highest superconducting transition temperature, T(c); ref. 4) composition Cs(3)C(60) has been isolated as a body-centred cubic (b.c.c.) packing, which supports both superconductivity and magnetic order. Here we isolate the f.c.c. polymorph of Cs(3)C(60) to show how the spatial arrangement of the electronically active units controls the competing superconducting and magnetic electronic ground states. Unlike all the other f.c.c. A(3)C(60) fullerides, f.c.c. Cs(3)C(60) is not a superconductor but a magnetic insulator at ambient pressure, and becomes superconducting under pressure. The magnetic ordering occurs at an order of magnitude lower temperature in the geometrically frustrated f.c.c. polymorph (Néel temperature T(N) = 2.2 K) than in the b.c.c.-based packing (T(N) = 46 K). The different lattice packings of C(60)(3-) change T(c) from 38 K in b.c.c. Cs(3)C(60) to 35 K in f.c.c. Cs(3)C(60) (the highest found in the f.c.c. A(3)C(60) family). The existence of two superconducting packings of the same electronically active unit reveals that T(c) scales universally in a structure-independent dome-like relationship with proximity to the Mott metal-insulator transition, which is governed by the role of electron correlations characteristic of high-temperature superconducting materials other than fullerides.

The ternary iron chalcogenide, Fe(1.03)Se(0.57)Te(0.43) is a member of the recently discovered family of Fe-based superconductors with an ambient pressure T(c) of 13.9 K and a simple structure comprising layers of edge-sharing distorted Fe(Se/Te)(4) tetrahedra separated by a van der Waals gap. Here we study the relationship between its structural and electronic responses to the application of pressure. T(c) depends sensitively on applied pressure attaining a broad maximum of 23.3 K at approximately 3 GPa. Further compression to 12 GPa leads to a metallic but nonsuperconducting ground state. High-resolution synchrotron X-ray diffraction shows that the superconducting phase is metrically orthorhombic at ambient pressure but pressurization to approximately 3 GPa leads to a structural transformation to a more distorted structure with monoclinic symmetry. The exact coincidence of the crystal symmetry crossover pressure with that at which T(c) is maximum reveals an intimate link between crystal and electronic structures of the iron chalcogenide superconductors.

The hyperexpanded (CH3NH2)K3C60 fulleride and its perdeuterated analogue were investigated by 1H and 2H NMR spectroscopy between room temperature and 4 K. Two phase transitions at TS = 220 K and TN = 11 K clearly were detected in the temperature dependence of the NMR line shapes, the spectral first (M1) and second (M2) moments, and the spin lattice relaxation times, T1. From 2H NMR line shape analysis, we found that the structural phase transition at TS was driven by the freezing out of the discrete Markovian-type jump motion of the entire K+-ND2CD3 unit that is characterized by an activation energy, Ea = 236(51) meV. Below TS, a sudden change in the temperature dependence of M1 suggests the appearance of a small but nonzero spin density on the K+-NH2CH3 unit. This could influence the electronic properties of the fulleride phase by modulating the strength of the exchange interactions between C603− anions and controlling the width, W, of the t1u-derived band. The 1H NMR spectra below TN show significant li...

Substitution of the pillaring ligand in the homochiral open-framework [Ni(2)(L-asp)(2)(bipy)] by extended bipy-type ligands leads to a family of layer-structured, homochiral metal-organic frameworks. The 1D channel topology can be modified by the nature of the organic linker, with shape, cross-section and the chemical functionality tuneable. In addition, the volume of these channels can be increased by up to 36 % compared to the parent [Ni(2)(L-asp)(2)(bipy)]. The linker 1,4-dipyridylbenzene (3rbp) gives access to a new layered homochiral framework [Ni(2)(L-asp)(2)(3rbp)] with channels of a different shape. In specific cases, non-porous analogues with the linker also present as a guest can be activated to give porous materials after sublimation. Their CO(2) uptake shows an increase of up to 30 % with respect to the parent [Ni(2)(L-asp)(2)(bipy)] framework.

C(60)-based solids are archetypal molecular superconductors with transition temperatures (Tc) as high as 33 K (refs 2-4). Tc of face-centred-cubic (f.c.c.) A(3)C(60) (A=alkali metal) increases monotonically with inter C(60) separation, which is controlled by the A(+) cation size. As Cs(+) is the largest such ion, Cs(3)C(60) is a key material in this family. Previous studies revealing trace superconductivity in Cs(x)C(60) materials have not identified the structure or composition of the superconducting phase owing to extremely small shielding fractions and low crystallinity. Here, we show that superconducting Cs(3)C(60) can be reproducibly isolated by solvent-controlled synthesis and has the highest Tc of any molecular material at 38 K. In contrast to other A(3)C(60) materials, two distinct cubic Cs(3)C(60) structures are accessible. Although f.c.c. Cs(3)C(60) can be synthesized, the superconducting phase has the A15 structure based uniquely among fullerides on body-centred-cubic packing. Application of hydrostatic pressure controllably tunes A15 Cs(3)C(60) from insulating at ambient pressure to superconducting without crystal structure change and reveals a broad maximum in Tc at approximately 7 kbar. We attribute the observed Tc maximum as a function of inter C(60)separation--unprecedented in fullerides but reminiscent of the atom-based cuprate superconductors--to the role of strong electronic correlations near the metal-insulator transition onset.

The electron paramagnetic resonance (EPR) technique is used to study the temperature evolution of the electronic and magnetic properties of the hyperexpanded fulleride (CH 3 NH 2 )K 3 C 60 in the temperature range 4-294 K. Unambiguous signatures for the development of large internal magnetic fields and a transition to an antiferromagnetic ground state below T N = 11 K are provided by the temperature dependence of the spin susceptibility, the EPR line width, and the position of the EPR line. The EPR results in the paramagnetic regime are indicative of an insulating electronic state, with localized S = 1/2 moments on the C 60 3- ions. The accompanying complex evolution of the spin susceptibility, EPR line width, and g-factor anisotropy furthermore reveals that effects of electronic origin (t 1u orbital order-disorder transition, crossover from static to dynamic Jahn-Teller distortions) in the vicinity of the structural transformation are important for the understanding of the exchange interactions between the fulleride ions.

A superconductivity dome is created by the electronic structure of the molecular building block of an unconventional superconductor., Understanding the relationship between the superconducting, the neighboring insulating, and the normal metallic state above Tc is a major challenge for all unconventional superconductors. The molecular A3C60 fulleride superconductors have a parent antiferromagnetic insulator in common with the atom-based cuprates, but here, the C603– electronic structure controls the geometry and spin state of the structural building unit via the on-molecule Jahn-Teller effect. We identify the Jahn-Teller metal as a fluctuating microscopically heterogeneous coexistence of both localized Jahn-Teller–active and itinerant electrons that connects the insulating and superconducting states of fullerides. The balance between these molecular and extended lattice features of the electrons at the Fermi level gives a dome-shaped variation of Tc with interfulleride separation, demonstrating molecular electronic structure control of superconductivity.

Four hexagonal molybdenum nitrides—three modifications of δ-MoN and Mo5N6—were prepared by the plasma-enhanced chemical vapour deposition (PECVD) method and ammonolysis of MoCl5 and MoS2. The nitrides were structurally characterised by X-ray diffraction, high-resolution transmission electron microscopy, and selected area electron diffraction. δ1-MoN is best described by the WC-type structure with stacking faults due to nitrogen atom disorder. Ordering of nitrogen atoms results in δ2-MoN with the NiAs-type structure. Formation of trigonal molybdenum clusters in δ3-MoN is responsible for the doubling of the unit cell in a and b directions compared to δ2-MoN. Mo5N6 can be viewed as an intergrowth structure of the WC- and NiAs-type building blocks, accompanied by vacancies on Mo sites. Influence of reaction conditions on the formation of the four nitrides is discussed; their magnetic properties are presented.

A solution chemistry synthetic route yields Cs3C60 with a face-centred cubic structure. The described method uses well-established Schlenk techniques and THF as a solvent. The controlled addition of an organo-metallic salt reducing agent prevents the formation of C604− salts. The final product can be precipitated from the solution using hexane as an anti-solvent.

We have investigated the low-temperature magnetic state of face-centered-cubic (fcc) ${\mathrm{Cs}}_{3}{\mathrm{C}}_{60}$, a Mott insulator and the first molecular analog of a geometrically frustrated Heisenberg fcc antiferromagnet with $S=1/2$ spins. Specific heat studies reveal the presence of both long-range antiferromagnetic ordering and a magnetically disordered state below ${T}_{N}=2.2$ K, which is in agreement with local probe experiments. These results together with the strongly suppressed ${T}_{N}$ are unexpected for conventional atom-based fcc antiferromagnets, implying that the fulleride molecular degrees of freedom give rise to the unique magnetic ground state.

The alkali fullerides, A(3)C(60) (A = alkali metal) are molecular superconductors that undergo a transition to a magnetic Mott-insulating state at large lattice parameters. However, although the size and the symmetry of the superconducting gap, Δ, are both crucial for the understanding of the pairing mechanism, they are currently unknown for superconducting fullerides close to the correlation-driven magnetic insulator. Here we report a comprehensive nuclear magnetic resonance (NMR) study of face-centred-cubic (f.c.c.) Cs(3)C(60) polymorph, which can be tuned continuously through the bandwidth-controlled Mott insulator-metal/superconductor transition by pressure. When superconductivity emerges from the insulating state at large interfullerene separations upon compression, we observe an isotropic (s-wave) Δ with a large gap-to-superconducting transition temperature ratio, 2Δ0/k(B)T(c) = 5.3(2) [Δ0 = Δ(0 K)]. 2Δ0/k(B)T(c) decreases continuously upon pressurization until it approaches a value of ~3.5, characteristic of weak-coupling BCS theory of superconductivity despite the dome-shaped dependence of Tc on interfullerene separation. The results indicate the importance of the electronic correlations for the pairing interaction as the metal/superconductor-insulator boundary is approached.

Cs3C60 is a correlated superconductor under pressure, but an insulator under ambient conditions. The mechanism causing this insulating behavior is the combination of Mott localization and the dynamic Jahn-Teller effect. We show evidence from infrared spectroscopy for the dynamic Jahn-Teller distortion. The continuous change with temperature of the splitting of infrared lines is typical Jahn-Teller behavior, reflecting the change in population of solid-state conformers. We conclude that the electronic and magnetic solid-state properties of the insulating state are controlled by molecular phenomena. We estimate the time scale of the dynamic Jahn-Teller effect to be above 10^(-11) s and the energy difference between the conformers less than 20 cm-1., 6 pages, 4 figures, 1 supplementary movie; XXI International Symposium on the Jahn-Teller Effect, Tsukuba, Japan, August 26-31, 2012

Expanded alkali fullerides are molecular superconductors with a Mott parent insulating state. Klupp et al. use infrared spectroscopy to detect the molecular Jahn–Teller distortion of fulleride ions and establish its relevance to strongly correlated superconductivity.

We report on an investigation of the lattice dynamical properties in a range of Fe1+yTe1−xSex compounds, with special emphasis on the c-axis polarized vibration of Fe with B1g symmetry, a Raman active mode common to all families of Fe-based superconductors. We have carried out a systematic study of the temperature dependence of this phonon mode as a function of Se x and excess Fe y concentrations. In parent compound Fe1+yTe, we observe an unconventional broadening of the phonon between room temperature and magnetic ordering temperature TN. The situation smoothly evolves toward a regular anharmonic behavior as Te is substituted for Se and long-range magnetic order is replaced by superconductivity. Irrespective to Se contents, excess Fe is shown to provide an additional damping channel for the B1g phonon at low temperatures. We performed density functional theory ab initio calculations within the local density approximation to calculate the phonon frequencies, including magnetic polarization and Fe nonstoichiometry in the virtual crystal approximation. We obtained a good agreement with the measured phonon frequencies in the Fe-deficient samples, while the effects of Fe excess are poorly reproduced. This may be due to excess Fe-induced local magnetism and low-energy magnetic fluctuations that cannot be treated accurately within these approaches. As recently revealed by neutron scattering and muon spin rotation studies, these phenomena occur in the temperature range where anomalous decay of the B1g phonon is observed and suggests a peculiar coupling of this mode with local moments and spin fluctuations in Fe1+yTe1−xSex.