Showing papers in "Dalton Transactions in 2015"

Polyvinylpyrrolidone (PVP) in nanoparticle synthesis

Abstract: Colloidal synthesis offers a route to nanoparticles (NPs) with controlled composition and structural features. This Perspective describes the use of polyvinylpyrrolidone (PVP) to obtain such nanostructures. PVP can serve as a surface stabilizer, growth modifier, nanoparticle dispersant, and reducing agent. As shown with examples, its role depends on the synthetic conditions. This dependence arises from the amphiphilic nature of PVP along with the molecular weight of the selected PVP. These characteristics can affect nanoparticle growth and morphology by providing solubility in diverse solvents, selective surface stabilization, and even access to kinetically controlled growth conditions. This Perspective includes discussions of the properties of PVP-capped NPs for surface enhanced Raman spectroscopy (SERS), assembly, catalysis, and more. The contribution of PVP to these properties as well as its removal is considered. Ultimately, the NPs accessed through the use of PVP in colloidal syntheses are opening new applications, and the concluding guidelines provided herein should enable new nanostructures to be accessed facilely.

Large-scale delamination of multi-layers transition metal carbides and carbonitrides “MXenes”

Abstract: Herein we report on a general approach to delaminate multi-layered MXenes using an organic base to induce swelling that in turn weakens the bonds between the MX layers. Simple agitation or mild sonication of the swollen MXene in water resulted in the large-scale delamination of the MXene layers. The delamination method is demonstrated for vanadium carbide and titanium carbonitride MXenes.

Porphyrins as excellent dyes for dye-sensitized solar cells: recent developments and insights

Abstract: Dye-sensitized solar cells (DSSCs) have attracted much attention as an alternative to silicon-based solar cells because of their low-cost production and high power conversion efficiency. Among various sensitizers, numerous research activities have been focused on porphyrins due to their strong absorption bands in the visible region, versatile modifications of their core, and facile tuning of the electronic structures. In 2005–2007, Officer and Gratzel et al. had achieved a rapid increase in the power conversion efficiency of porphyrin DSSCs from a few percent to as much as 7%. Encouraged by these pioneering works, further high-performance porphyrin dyes have been developed in the last decade. These studies have provided us profound hints for the rational design of sensitizers toward highly efficient DSSCs. Push–pull structures and/or π-extensions have made porphyrins panchromatic in visible and even near-infrared regions. Consequently, porphyrin sensitizers have exhibited power conversion efficiencies that are comparable to or even higher than those of well-established highly efficient DSSCs based on ruthenium complexes. So far the power conversion efficiency has increased up to ca. 13% by using a push–pull porphyrin with a cobalt-based redox shuttle. In this perspective, we review the recent developments in the synthetic design of porphyrins for highly efficient DSSCs.

Mediator-free direct Z-scheme photocatalytic system: BiVO4/g-C3N4 organic–inorganic hybrid photocatalyst with highly efficient visible-light-induced photocatalytic activity

Abstract: We disclose the fabrication of a mediator-free direct Z-scheme photocatalyst system BiVO4/g-C3N4 using a mixed-calcination method based on the more reliable interfacial interaction. The facet coupling occurred between the g-C3N4 (002) and BiVO4 (121), and it was revealed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM). The crystal structure and optical properties of the as-prepared samples have also been characterized by Fourier-transform infrared (FTIR), scanning electron microscopy (SEM) and UV-vis diffuse reflectance spectra (DRS) in details. The photocatalytic experiments indicated that the BiVO4/g-C3N4 composite photocatalysts display a significantly enhanced photocatalytic activity pertaining to RhB degradation and photocurrent generation (PC) compared to the pristine BiVO4 and g-C3N4. This remarkably improved photocatalytic performance should be attributed to the fabrication of a direct Z-scheme system of BiVO4/g-C3N4, which can result in a more efficient separation of photoinduced charge carriers than band–band transfer, thus endowing it with the much more powerful oxidation and reduction capability, as confirmed by the photoluminescence (PL) spectra and electrochemical impedance spectra (EIS). The Z-scheme mechanism of BiVO4/g-C3N4 heterostructure was verified by a series of combined techniques, including the active species trapping experiments, NBT transformation and terephthalic acid photoluminescence probing technique (TA-PL) over BiVO4/g-C3N4 composites and the pristine samples. The present work not only furthered the understanding of mediator-free Z-scheme photocatalysis, but also shed new light on the design of heterostructural photocatalysts with high-performance.

Heterojunction engineering of graphitic carbon nitride (g-C3N4) via Pt loading with improved daylight-induced photocatalytic reduction of carbon dioxide to methane

Abstract: In this paper, noble-metal Pt nanoparticles of around 2.5 nm were deposited on graphitic carbon nitride (g-C3N4) synthesized by a chemical reduction process in ethylene glycol. Compared with pure g-C3N4, the resulting Pt-loaded g-C3N4 (Pt/CN) exhibited a considerable improvement in the photoreduction of CO2 to CH4 in the presence of water vapor at ambient temperature and atmospheric pressure under visible light irradiation. 2 wt% Pt-loaded g-C3N4 (2Pt/CN) nanocomposites produced the highest CH4 yield of 13.02 μmol gcatalyst−1 after 10 h of light irradiation, which was a 5.1-fold enhancement in comparison with pure g-C3N4 (2.55 μmol gcatalyst−1). The remarkable photocatalytic activity of Pt/CN nanostructures in the CH4 production was ascribed to the enhanced visible light absorption and efficient interfacial transfer of photogenerated electrons from g-C3N4 to Pt due to the lower Fermi level of Pt in the Pt/CN hybrid heterojunctions as evidenced by the UV-Vis and photoluminescence studies. The enriched electron density on Pt favored the reduction of CO2 to CH4via a multi-electron transfer process. This resulted in the inhibition of electron–hole pair recombination for effective spatial charge separation, thus enhancing the photocatalytic reactions. Based on the experimental results obtained, a plausible mechanism for improved photocatalytic performance associated with Pt/CN was proposed.

Beyond iron: non-classical biological functions of bacterial siderophores

Abstract: Bacteria secrete small molecules known as siderophores to acquire iron from their surroundings. For over 60 years, investigations into the bioinorganic chemistry of these molecules, including fundamental coordination chemistry studies, have provided insight into the crucial role that siderophores play in bacterial iron homeostasis. The importance of understanding the fundamental chemistry underlying bacterial life has been highlighted evermore in recent years because of the emergence of antibiotic-resistant bacteria and the need to prevent the global rise of these superbugs. Increasing reports of siderophores functioning in capacities other than iron transport have appeared recently, but reports of “non-classical” siderophore functions have long paralleled those of iron transport. One particular non-classical function of these iron chelators, namely antibiotic activity, was documented before the role of siderophores in iron transport was established. In this Perspective, we present an exposition of past and current work into non-classical functions of siderophores and highlight the directions in which we anticipate that this research is headed. Examples include the ability of siderophores to function as zincophores, chalkophores, and metallophores for a variety of other metals, sequester heavy metal toxins, transport boron, act as signalling molecules, regulate oxidative stress, and provide antibacterial activity.

Metal complex interactions with DNA

Abstract: Increasing numbers of DNA structures are being revealed using biophysical, spectroscopic and genomic methods. The diversity of transition metal complexes is also growing, as the unique contributions that transition metals bring to the overall structure of metal complexes depend on the various coordination numbers, geometries, physiologically relevant redox potentials, as well as kinetic and thermodynamic characteristics. The vast range of ligands that can be utilised must also be considered. Given this diversity, a variety of biological interactions is not unexpected. Specifically, interactions with negatively-charged DNA can arise due to covalent/coordinate or subtle non-coordinate interactions such as electrostatic attraction, groove binding and intercalation as well as combinations of all of these modes. The potential of metal complexes as therapeutic agents is but one aspect of their utility. Complexes, both new and old, are currently being utilised in conjunction with spectroscopic and biological techniques to probe the interactions of DNA and its many structural forms. Here we present a review of metal complex-DNA interactions in which several binding modes and DNA structural forms are explored.

Band gap-tunable potassium doped graphitic carbon nitride with enhanced mineralization ability.

Abstract: Band gap-tunable potassium doped graphitic carbon nitride with enhanced mineralization ability was prepared using dicyandiamide monomer and potassium hydrate as precursors. X-ray diffraction (XRD), N2 adsorption, UV-Vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS) were used to characterize the prepared catalysts. The CB and VB potentials of graphitic carbon nitride could be tuned from −1.09 and +1.56 eV to −0.31 and +2.21 eV by controlling the K concentration. Besides, the addition of potassium inhibited the crystal growth of graphitic carbon nitride, enhanced the surface area and increased the separation rate for photogenerated electrons and holes. The visible-light-driven Rhodamine B (RhB) photodegradation and mineralization performances were significantly improved after potassium doping. A possible influence mechanism of the potassium concentration on the photocatalytic performance was proposed.

Lanthanide single molecule magnets: progress and perspective

Abstract: The last few years have seen a huge renaissance in the study of single molecule magnets (SMMs) thanks to the extensive applications of lanthanide ions with large inherent anisotropy in molecular magnetism. Particularly, the recent theoretical developments and the experimental expansion into the organometallic avenue have led to an eye-catching boost in this field. Here we highlight the recent progress in this fascinating and challenging field, with emphasis on several combined experimental and theoretical studies.

Heterometallic 3d–4f single-molecule magnets

Abstract: The promising potential applications, such as information processing and storage or molecular spintronics, of single-molecule magnets (SMMs) have spurred on the research of new, better SMMs. In this context, lanthanide ions have been seen as ideal candidates for new heterometallic transition metal–lanthanide SMMs. This perspective reviews 3d–4f SMMs up to 2014 and highlights the most significant advances and challenges of the field.

A novel greenish yellow-orange red Ba3Y4O9:Bi3+,Eu3+ phosphor with efficient energy transfer for UV-LEDs

Abstract: A series of novel color-tunable Ba3Y4O9:Bi3+,Eu3+ phosphors were prepared for the first time via the high-temperature solid-state reaction route. The effect of Bi3+ concentration on the emission intensity of Ba3Y4O9:Bi3+ was investigated. The emission spectra of the Ba3Y4O9:Bi3+,Eu3+ phosphors present both a greenish yellow band of Bi3+ emission centered at 523 nm, and many characteristic emission lines of Eu3+, derived from the allowed 3P1–1S0 transition of the Bi3+ ion and the 5D0–7FJ transition of the Eu3+ ion, respectively. The energy transfer phenomenon from Bi3+ to Eu3+ ions is observed under UV excitation in Bi3+, Eu3+ co-doped Ba3Y4O9 phosphors, and their transfer mechanism is demonstrated to be a resonant type via dipole–quadrupole interaction. The critical distance between Bi3+ and Eu3+ for the energy transfer effect was calculated via the concentration quenching and spectral overlap methods. Results show that color tuning from greenish yellow to orange red can be realized by adjusting the mole ratio of Bi3+ and Eu3+ concentrations based on the principle of energy transfer. Moreover, temperature-dependent PL properties, CIE chromaticity coordinates and quantum yields of Ba3Y4O9:Bi3+,Eu3+ phosphors were also supplied. It is illustrated that the as-prepared Ba3Y4O9:Bi3+,Eu3+ phosphors can be potential candidates for color-tunable phosphors applied in UV-pumped LEDs.

Response surface methodology approach for optimization of simultaneous dye and metal ion ultrasound-assisted adsorption onto Mn doped Fe3O4-NPs loaded on AC: kinetic and isothermal studies

Abstract: In the present work, the usefulness of ultrasonic power as a dispersion and mixing tool to accelerate the adsorption of Safranin O (SO), methylene blue (MB), Pb2+ ions and Cr3+ ions onto the novel composite Fe3O4-NPs-AC adsorbent was investigated. This new material was extensively characterized and analyzed by different techniques such as XRD, FESEM, Raman spectroscopy and FT-IR. Central composite design (CCD) based on designed runs revealed that adsorbent mass, sonication time, MB concentration, SO concentration, Pb2+ ion and Cr3+ ion concentration and some of their interactions have significant contributions to the target compounds removal percentages. A combination of response surface methodology and Design-Expert software was used to qualify and estimate the influence and magnitude of each terms contribution to the response. An optimization study using the following investigated increments of the effective variables, adsorbent mass (0.01–0.03 g), sonication time (2–6 min), initial dye concentration (5–25 mg L−1), and initial metal ion concentration (20–60 mg L−1), revealed that fixing the experimental variables at 0.025 g of Mn–Fe3O4-NPs-AC, with a 3 min sonication time, and 20 mg L−1 of MB, 10 mg L−1 of SO, 38 mg L−1 of Pb2+ ions and 42 mg L−1 of Cr3+ ions at room temperature lead to the achievement of the best characteristics and performance. Conduction of 32 experiments according to the limitations of CCD and a subsequent analysis of variance (ANOVA) gave useful information about the significant and also approximate contributions of each term (main and interaction of variables) in an empirical equation for the expected response. The results indicate that the R2 values are more than 0.988 and the adjusted R2 values are in reasonable agreement with R2. Under the optimal conditions, the MB, SO, Pb2+ ion and Cr3+ ion removal efficiencies reached 99.54%, 98.87%, 80.25% and 99.54% after 3 min, while their equilibrium data with high performance can be represented by Langmuir isotherms and a pseudo second-order kinetic model. The maximum adsorption capacities for the single component system, 229.4 mg g−1 for MB, 159.7 mg g−1 for SO, 139.5 mg g−1 for Pb2+ ions and 267.4 mg g−1 for Cr3+ ions, support the high efficiency of Mn–Fe3O4-NPs-AC as a new adsorbent.

Few-layered MoSe2 nanosheets as an advanced electrode material for supercapacitors

Abstract: We report the synthesis of few-layered MoSe2 nanosheets using a facile hydrothermal method and their electrochemical charge storage behavior. A systematic study of the structure and morphology of the as-synthesized MoSe2 nanosheets was performed. The downward peak shift in the Raman spectrum and the high-resolution transmission electron microscopy images confirmed the formation of few-layered nanosheets. The electrochemical energy-storage behavior of MoSe2 nanosheets was also investigated for supercapacitor applications in a symmetric cell configuration. The MoSe2 nanosheet electrode exhibited a maximum specific capacitance of 198.9 F g(-1) and the symmetric device showed 49.7 F g(-1) at a scan rate of 2 mV s(-1). A capacitance retention of approximately 75% was observed even after 10 000 cycles at a high charge-discharge current density of 5 A g(-1). The two-dimensional MoSe2 nanosheets exhibited a high specific capacitance and good cyclic stability, which makes it a promising electrode material for supercapacitor applications.

The concept of mixed organic ligands in metal–organic frameworks: design, tuning and functions

Abstract: The research on metal–organic frameworks (MOFs) has been developing at an extraordinary pace in its two decades of existence, as judged by the exponential growth of novel structures and the constant expansion of its applicability and research scope. A major part of the research and its success are due to the vital role of the concept of mixed organic ligands in the design, tuning and functions. This perspective, therefore, reviews the recent advances in MOFs based on this concept, which is generally based on employing a small polydentate ligand (here labelled as “nodal ligand”) to form either clusters, rods or layers, which are then connected by a second ditopic linker ligand to form the framework. The structures of the materials can be grouped into the following three categories: layer-spacer (usually known as pillared-layer), rod-spacer, and cluster-spacer based MOFs. Depending on the size and geometry of the spacer ligands, interpenetrations of frameworks are occasionally found. These MOFs show a wide range of properties such as (a) crystal-to-crystal transformations upon solvent modifications, post-synthetic metal exchange or ligand reactions, (b) gas sorption, solvent selectivity and purification, (c) specific catalysis, (d) optical properties including colour change, luminescence, non-linear optic, (e) short- and long range magnetic ordering, metamagnetism and reversible ground-state modifications and (f) drug and iodine carriers with controlled release. In the following, we will highlight the importance of the above concept in the design, tuning, and functions of a selection of existing MOFs having mixed organic ligands and their associated structures and properties. The results obtained so far using this concept look very promising for fine-tuning the pore size and shape for selective adsorption and specificity in catalytic reactions, which appears to be one way to propel the advances in the application and commercialization of MOFs.

Understanding ferroelectricity in layered perovskites: new ideas and insights from theory and experiments

Abstract: ABO3 perovskites have fascinated solid-state chemists and physicists for decades because they display a seemingly inexhaustible variety of chemical and physical properties. However, despite the diversity of properties found among perovskites, very few of these materials are ferroelectric, or even polar, in bulk. In this Perspective, we highlight recent theoretical and experimental studies that have shown how a combination of non-polar structural distortions, commonly tilts or rotations of the BO6 octahedra, can give rise to polar structures or ferroelectricity in several families of layered perovskites. We discuss the crystal chemical origin of the polarization in each of these families – which emerges through a so-called ‘trilinear coupling’ or ‘hybrid improper’ mechanism – and emphasize areas in which further theoretical and experimental investigation is needed. We also consider how this mechanism may provide a generic route for designing not only new ferroelectrics, but also materials with various other multifunctionalities, such as magnetoelectrics and electric field-controllable metal-insulator transitions.

Advances in cobalt complexes as anticancer agents

Abstract: The evolution of resistance to traditional platinum-based anticancer drugs has compelled researchers to investigate the cytostatic properties of alternative transition metal-based compounds. The anticancer potential of cobalt complexes has been extensively studied over the last three decades, and much time has been devoted to understanding their mechanisms of action. This perspective catalogues the development of antiproliferative cobalt complexes, and provides an in depth analysis of their mode of action. Early studies on simple cobalt coordination complexes, Schiff base complexes, and cobalt–carbonyl clusters will be documented. The physiologically relevant redox properties of cobalt will be highlighted and the role this plays in the preparation of hypoxia selective prodrugs and imaging agents will be discussed. The use of cobalt-containing cobalamin as a cancer specific delivery agent for cytotoxins will also be described. The work summarised in this perspective shows that the biochemical and biophysical properties of cobalt-containing compounds can be fine-tuned to produce new generations of anticancer agents with clinically relevant efficacies.

Lead-free antiferroelectric: xCaZrO3-(1 − x)NaNbO3 system (0 ≤ x ≤ 0.10)

Abstract: This study demonstrates that antiferroelectricity can be stabilized in NaNbO3 (NN) based ceramics by lowering the tolerance factor. Through consideration of the crystal chemistry via the Goldschmidt tolerance factor and polarizability, we show that simultaneous substitution of Zr4+ and Ca2+ ions in the Nb and Na sites, respectively, lowers the polarizability and tolerance factor of the (Na1−xCax)(Nb1−xZrx)O3 (CZNN100x) solid solution, while maintaining charge neutrality. Structural investigations using both X-ray diffraction and transmission electron microscopy (TEM) indicated an enhancement of antiferroelectric (AFE) superlattice peaks with CaZrO3 substitution. The TEM domain analysis revealed that only AFE domains existed in the CZNN4 and CZNN5 ceramics; in contrast, normal NN ceramics displayed coexistence of AFE and ferroelectric (FE) domains at room temperature. The CZNN100x (0.02 ≤ x ≤ 0.05) ceramics showed double polarization hysteresis loops, characteristic of reversible AFE↔FE phase transition switching. The field-induced polarization decreased drastically with increasing substitution, an effect of the decreases in tolerance factor. In addition, the AFE switching field was increased by the chemical substitution. First principles calculations are performed to obtain insights into the relative stability and coexistence of the AFE and FE phases in single domains. The large decrease of polarization in the CZNN system is explained by a modification of the relative stability of the relevant structures, which favours nonpolar-to-polar AFE transitions over polar-to-polar FE domain switching.

Three new solvent-directed Cd(II)-based MOFs with unique luminescent properties and highly selective sensors for Cu2+ cations and nitrobenzene

Abstract: Three new solvent-induced metal–organic frameworks (MOFs)—[Cd(H2L)(H2O)3]·NMP (1), [Cd3(L)(H2O)4(OH)2] (2) and [Cd(L)0.5(H2O)]·H2O (3)—were designed and successfully prepared via solvothermal reaction by multidentate phenyltetracarboxylic acid [1,1′:4′,1′′-terphenyl]-2′,3,3′′,5′-tetracarboxylic acid (H4L) and Cd(II) salts in various solvent systems. Structural analyses indicated that the H2L/L ligands took three different coordination fashions in 1–3, and thus resulted in diversity of the targeted MOFs. Solid-state luminescent properties of the three MOFs were studied under ultraviolet light irradiation at ambient temperature; 3 in particular showed high selectivity and sensitivity for Cu2+ ions and nitrobenzene because of the quenching effect, which thus could make it a potential crystalline material for detecting these substances. The mechanisms of the quenching effect and sensing properties of 3 are discussed in detail.

Non-symmetric pincer ligands: complexes and applications in catalysis

Abstract: Pincer ligands have become ubiquitous in organometallic chemistry and homogeneous catalysis. Recently, new varieties of pincer ligands with non-symmetrical backbones and/or ligating groups have been reported and their application in transition metal complexes has been exploited in a variety of catalytic transformations. This non-symmetric approach vastly increases the structural and electronic diversity of this class of ligand. This approach has proven beneficial in a variety of ways, such as the use of a single weakly coordinating moiety, which can dissociate and thereby create a vacant coordination site to increase the catalyst activity. Additionally, this provides further access to chiral ligands and complexes for asymmetric induction. This perspective highlights recent, important examples of non-symmetric pincer ligands, which feature aryl or pyridine backbones, and the synthesis and use of subsequent complexes in catalytic transformations, and discusses the future potential of this type of ligand system.

Amorphous Co3O4 modified CdS nanorods with enhanced visible-light photocatalytic H2-production activity

Abstract: In this work, amorphous Co3O4 modified CdS nanorods were synthesized by a two-step solvothermal/hydrothermal method, and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy, UV-visible spectroscopy, nitrogen absorption and X-ray photoelectron spectroscopy. The photocatalytic performance of the as-synthesized Co3O4–CdS nanorods was evaluated through H2 generation from an aqueous solution containing sulfide and sulfite under visible light (λ ≥ 420 nm). The results showed that the photocatalytic activity of CdS nanorods for H2 evolution could be significantly enhanced by loading the amorphous Co3O4. The optimal Co3O4 loading was found to be approximately 3.0 mol%. The as-prepared CdS nanorods with 3 mol% Co3O4 exhibited the highest photocatalytic activity for H2 evolution under visible light irradiation, 236 μmol g−1 h−1, which is 33-fold higher than that of the pristine CdS nanorods. Furthermore, the co-loading of 1 wt% Pt can lead to another three times enhancement in the photocatalytic H2-production activity. The mechanism for the enhanced H2-production performance of Co3O4–CdS nanorods was discussed. The excellent performance of Co3O4–CdS nanorods is mainly ascribed to the loading of amorphous Co3O4 onto the surface of CdS nanorods, which could promote the separation of electron–hole pairs and enhance the stability of CdS nanorods due to the formation of p–n heterojunctions between the Co3O4 and CdS nanorods, thus leading to an enhanced activity for H2 generation. This work demonstrated that the loading of amorphous Co3O4 is a facile strategy to enhance the photocatalytic activity of CdS nanorods, which may provide some potential opportunities for designing other composite photocatalysts for water splitting.

Polyoxometalate – conductive polymer composites for energy conversion, energy storage and nanostructured sensors

Abstract: The exchange of electric charges between a chemical reaction centre and an external electrical circuit is critical for many real-life technologies. This perspective explores the “wiring” of highly redox-active molecular metal oxide anions, so-called polyoxometalates (POMs) to conductive organic polymers (CPs). The major synthetic approaches to these organic–inorganic hybrid materials are reviewed. Typical applications are highlighted, emphasizing the current bottlenecks in materials development. Utilization of the composites in the fields of energy conversion, electrochemical energy storage, sensors and nanoparticle “wiring” into conductive materials are discussed. The outlook section presents the authors’ views on emerging fields of research where the combination of POMs and CPs can be expected to provide novel materials for groundbreaking new technologies. These include light-weight energy storage, high-sensitivity toxin sensors, artificial muscles, photoelectrochemical devices and components for fuel cells.

Carboranes in the chemist's toolbox

Abstract: Once seldom encountered outside of a few laboratories, carboranes are now everywhere, playing a role in the development of a broad range of technologies encompassing organic synthesis, radionuclide handling, drug design, heat-resistant polymers, cancer therapy, nanomaterials, catalysis, metal–organic frameworks, molecular machines, batteries, electronic devices, and more. This perspective highlights selected examples in which the special attributes of carboranes and metallacarboranes are being exploited for targeted purposes in the laboratory and in the wider world.

Main group catalysed reduction of unsaturated bonds.

Abstract: This Perspective highlights the recent developments in the reduction of unsaturated substrates catalysed by main group element compounds. Various activation modes are discussed and comparison with relevant examples from transition metal systems is made when possible. Main group element catalysis offers significant advantages through its lower cost and more benign environmental impact and has now reached the point where it can successfully compete with the more common catalysis based on precious transition metals.

The exceptionally rich coordination chemistry generated by Schiff-base ligands derived from o-vanillin.

Abstract: Ortho-vanillin became very popular in coordination chemistry because of its Schiff bases, which generate a rich variety of complexes, ranging from oligonuclear species to coordination polymers. Some of these organic molecules are particularly useful in metallosupramolecular chemistry for assembling homo- and heterometallic helicates. The Schiff bases obtained using aminoalcohols open the door to the synthesis of homo- and heterometallic clusters with various nuclearities and surprising topologies of the metal centers. Several relevant structural types are reviewed. The heterobinuclear 3d-3d' and 3d-4f complexes are valuable building-blocks for the synthesis of heterotrimetallic systems. Beyond the richness of this chemistry, the complexes obtained from o-vanillin-based Schiff ligands show interesting properties: magnetism, luminescence, chirality, catalysis, cytotoxicity, and ferroelectricity. This paper reviews recent data that illustrate a very fertile and dynamic research field in coordination chemistry and materials science.

FIrpic: archetypal blue phosphorescent emitter for electroluminescence

Abstract: FIrpic is the most investigated bis-cyclometallated iridium complex in particular in the context of organic light emitting diodes (OLEDs) because of its attractive sky-blue emission, high emission efficiency, and suitable energy levels. In this Perspective we review the synthesis, structural characterisations, and key properties of this emitter. We also survey the theoretical studies and summarise a series of selected monochromatic electroluminescent devices using FIrpic as the emitting dopant. Finally we highlight important shortcomings of FIrpic as an emitter for OLEDs. Despite the large body of work dedicated to this material, it is manifest that the understanding of photophysical and electrochemical processes are only broadly understood mainly because of the different environment in which these properties are measured, i.e., isolated molecules in solvent vs. device.

A Zn(II) coordination polymer and its photocycloaddition product: syntheses, structures, selective luminescence sensing of iron(III) ions and selective absorption of dyes

Abstract: One coordination polymer [Zn2(L)2(bpe)2(H2O)2] (1) (L = 4,4′-((1,2-phenylenebis(methylene))bis(oxy))dibenzoic acid; bpe = (E)-1,2-di(pyridin-4-yl)ethene) was prepared and structurally determined. Compound 1 has a chain structure in which its pair of bpe ligands is arranged in a head-to-tail manner with their CC bonds being close enough for a [2 + 2] cycloaddition reaction. Upon exposure to UV light, compound 1 undergoes a single-crystal-to-single-crystal (SCSC) [2 + 2] photodimerization to generate one 2D coordination polymer [Zn(L)(rctt-tpcb)0.5(H2O)] (1a) (rctt (regio cis, trans, trans)-tpcb = tetrakis(4-pyridyl)cyclobutane). The tpcb ligands in the crystals of 1a show an intriguing in situ thermal isomerisation. The nanospheres of 1 can be obtained by recrystallization in DMSO/alcohol. The nanospheres of 1a can also be readily produced from the corresponding nanospheres of 1 by the photocyclodimerization method. Compared with those of 1a, the nanospheres of 1 display highly selective sensing of Fe3+ ions over mixed metal ions through fluorescence quenching. Moreover, the nanospheres of 1a can rapidly adsorb CR (congo red), MB (methylene blue) or RhB (rhodamine B) over MO (methyl orange) from aqueous solutions. This work offers a new photoinduced post-synthetic method for the synthesis of multifunctional MOFs, which show luminescence sensing of Fe3+ ions and dye adsorption properties.

Four super water-stable lanthanide-organic frameworks with active uncoordinated carboxylic and pyridyl groups for selective luminescence sensing of Fe(3.).

Abstract: Four super water-stable isostructural lanthanide–organic frameworks, [Ln(HL)(H2O)2]n·2H2O (1-Ln) (Ln = Eu, Tb, Nd and Sm), have been successfully synthesized under hydrothermal conditions with 3,5-di(2,4-dicarboxylphenyl)pyridine (H4L) and Ln(NO3)3·6H2O. 1-Ln shows a novel 2D layered structure with uncoordinated carboxylic and pyridyl groups pointing to the interior of interlayer channels. The luminescent properties of 1-Eu in the solid state and one steeped in aqueous solution have been measured, which show excellent luminescence and good luminescent stability in water. Next 1-Eu was chosen as a probe for sensing different metal ions. Consequently, 1-Eu exhibits a highly selective response to Fe3+ through the luminescence quenching effect in aqueous solutions. The probable mechanisms of the quenching effects have been investigated in detail.

Biogenic synthesis of metallic nanoparticles and prospects toward green chemistry

Abstract: The immense importance of nanoparticles and their applications is a strong motivation for exploring new synthetic techniques. However, due to strict regulations that manage the potential environmental impacts greener alternatives for conventional synthesis are the focus of intense research. In the scope of this perspective, a concise discussion about the use of green reducing and stabilizing agents toward the preparation of metal nanoparticles is presented. Reports on the synthesis of noble metal nanoparticles using plant extracts, ascorbic acid and sodium citrate as green reagents are summarized and discussed, pointing toward an urgent need of understanding the mechanistic aspects of the involved reactions.

Conduction mechanism, impedance spectroscopic investigation and dielectric behavior of La0.5Ca0.5-xAgxMnO3 manganites with compositions below the concentration limit of silver solubility in perovskites (0 ≤ x ≤ 0.2).

Abstract: This study presents the electrical properties, complex impedance analysis and dielectrical behavior of La05Ca05−xAgxMnO3 manganites with compositions below the concentration limit of silver solubility in perovskites (0 ≤ x ≤ 02) Transport measurements indicate that all the samples have a semiconductor-like behavior The metal-semiconductor transition is not observed across the whole temperature range explored [80 K–700 K] At a specific temperature, a saturation region was marked in the σ (T) curves We obtained a maximum σdc value at ambient temperature with the introduction of 20% Ag content Two hopping models were applied to study the conduction mechanism We found that activation energy (Ea) related to ac-conductivity is lower than the Ea implicated in dc-conductivity Complex impedance analysis confirms the contribution of grain boundary to conductivity and permits the attribution of grain boundary capacitance evolution to the temperature dependence of the barrier layer width From the temperature dependence of the average normalized change (ANC), we deduce the temperature at which the available density of trapped charge states vanishes Such a temperature is close to the temperature at which the saturation region appears in σ(T) curves Moreover, complex impedance analysis (CIA) indicates the presence of electrical relaxation in materials It is noteworthy that relaxation species such as defects may be responsible for electrical conduction The dielectric behavior of La05Ca05−xAgxMnO3 manganites has a Debye-like relaxation with a sharp decrease in the real part of permittivity at a frequency where the imaginary part of permittivity (e′′) and tg δ plots versus frequency demonstrate a relaxation peak The Debye-like relaxation is explained by Maxwell–Wagner (MW) polarization Experimental results are found to be in good agreement with the Smit and Wijn theory

Comparative investigations of the crystal structure and photoluminescence property of eulytite-type Ba3Eu(PO4)3 and Sr3Eu(PO4)3.

Abstract: In this study, the Ba3Eu(PO4)3 and Sr3Eu(PO4)3 compounds were synthesized and the crystal structures were determined for the first time by Rietveld refinement using powder X-ray diffraction (XRD) patterns. Ba3Eu(PO4)3 crystallizes in cubic space group I3d, with cell parameters of a = 10.47996(9) A, V = 1151.01(3) A3 and Z = 4; Ba2+ and Eu3+ occupy the same site with partial occupancies of 3/4 and 1/4, respectively. Besides, in this structure, there exists two distorted kinds of the PO4 polyhedra orientation. Sr3Eu(PO4)3 is isostructural to Ba3Eu(PO4)3 and has much smaller cell parameters of a = 10.1203(2) A, V = 1036.52(5) A3. The bandgaps of Ba3Eu(PO4)3 and Sr3Eu(PO4)3 are determined to be 4.091 eV and 3.987 eV, respectively, based on the UV–Vis diffuse reflectance spectra. The photoluminescence measurements reveal that, upon 396 nm n-UV light excitation, Ba3Eu(PO4)3 and Sr3Eu(PO4)3 exhibit orange-red emission with two main peaks at 596 nm and prevailing 613 nm, corresponding to the 5D0 → 7F1 and 5D0 → 7F2 transitions of Eu3+, respectively. The dynamic disordering in the crystal structures contributes to the broadening of the luminescence spectra. The electronic structure of the phosphates was calculated by the first-principles method. The analysis elucidats that the band structures are mainly governed by the orbits of phosphorus, oxygen and europium, and the sharp peaks of the europium f-orbit occur at the top of the valence bands.