Unraveling the Intertwining Factors Underlying the Assembly of High-Nuclearity Heterometallic Clusters.

Two closely related yet distinctly different cationic clusters, [Dy52Ni44(HEIDA)36(OH)138(OAc)24(H2O)30]10+ (1) and [Dy112Ni76(HEIDA)44(EIDA)24(IDA)4(OH)268(OAc)48(H2O)44]4+ (2) (HEIDA = N-(2-hydroxyethyl)iminodiacetate), each featuring a multi-shell core of Platonic and Archimedean polyhedra, were obtained. Depending on the specific conditions used for the co-hydrolysis of Dy3+ and Ni2+, the product can be crystallized out as one particular type of cluster or as a mixture of 1 and 2. How the reaction process was affected by the amount of hydrolysis-facilitating base and/or by the reaction temperature and duration was investigated. It has been found that a reaction at a high temperature and/or for an extended period favors the formation of the compact and thermodynamically more stable 1, while a brief reaction with a large amount of the base is good to the kinetic product 2. By tuning these intertwining conditions, the reaction can be regulated toward a particular product.

A Cubic Tinkertoy-like Heterometallic Cluster with a Record Magnetocaloric Effect.

Clusters showing a giant magnetocaloric effect (MCE) are of interest as molecular coolants for magnetic refrigeration. Herein, we report two heterometallic clusters, denoted as Gd152Ni14@Cl24 and Sm152Ni8, just to highlight their inorganic core motifs, obtained by ligand-controlled co-hydrolysis of Ni2+ and Ln3+ (Ln = Gd, Sm) in the presence of N-(2-hydroxyethyl)iminodiacetic acid (H2HEIDA). Both clusters display fascinating cubic Tinkertoy-like structures, with the core motifs being built of multiple metallic shells of Platonic and Archimedean polyhedra. The isothermal magnetic entropy change─a direct measurement of MCE─was determined to be 52.65 J·kg-1·K-1 at 2.5 K and 7.0 T for the Gd-containing cluster; this value is the highest known for any molecular clusters so far reported.

Lanthanide complexes with an azo-dye chromophore ligand: syntheses, crystal structures, and near-infrared luminescence by long-wavelength excitation.

Near-infrared (NIR) emissive probes are becoming increasingly popular in biological sensing and imaging due to the advantages of non-invasiveness and deep tissue-penetrating ability. Herein, a series of complexes of trivalent lanthanide ions (Ln = Yb, Er, and Gd) with the commercially available azo dye chromophore 2R (Na2H2C2R) as ligand and featuring respectively H2O and dimethylsulfoxide (DMSO) as ancillary ligands have been prepared. Formulated as [Ln2(HC2R)2(H2O)10]·8H2O (1-3, Ln = Yb, Er, Gd) and [Ln2(HC2R)2(DMSO)10]·2DMSO (4-6, Ln = Yb, Er, Gd), their structures have been determined by single-crystal X-ray diffraction studies. Photophysical property studies revealed NIR emissions of the DMSO complexes characteristic of Yb(III) and Er(III), effectively sensitized by the dye ligand arising mainly from the π-π* transition of the chromophore. The long-wavelength excitation of the complexes, covering the whole visible-light range and extending into the NIR region, portends the potential applications of such complexes for flexible bioimaging and sensing.

Modulating the Catalytic Properties of Polyoxovanadates with Transition-Metal-Complex Units for Selective Oxidation of Sulfides.

Selective oxidation of sulfides to sulfoxides is of great significance in the synthesis of pharmaceuticals, desulfurization of fuels, and detoxification of sulfur mustard chemical warfare agents. Designing selective catalysts to achieve the efficient transformation of sulfides to sulfoxides is thus highly desired. Herein, we report three transition metal-complex-functionalized polyoxovanadates, [Zn2(BPB)2][V4O12]·0.5BPB·H2O (1), [Ni(BPB)(H2O)][V2O6]·2H2O (2), and [Co(HBPB)2][V4O12] (3) (BPB = 1,4-bis(pyrid-4-yl)benzene)), and explore their applications for selective oxidation of sulfides using H2O2 as an oxidant. All three compounds were catalytically effective for the oxidation of methyl phenyl sulfide to methyl phenyl sulfoxide, with 1 being best-performing with complete conversion and a selectivity of 96.7%. In the selective oxidation of a series of aromatic and aliphatic sulfides to corresponding sulfoxides, 1 also showed satisfactory performance; in particular, the chemical warfare agent stimulant 2-chloroethyl ethyl sulfide can be completely and selectively oxidized to the nontoxic 2-chloroethyl ethyl sulfoxide within 20 min at room temperature. Catalyst 1 can be recycled and reused at least six times with uncompromised performance. The perfect performance of 1 is attributed to the synergistic effect of coordinatively unsaturated V and Zn sites in bimetallic oxide, as revealed by comparative structural and catalytic studies.

A tetravalent praseodymium complex with field-induced slow magnetic relaxation.

Herein the synthesis, structural characterization, and magnetic properties of a Pr(IV) complex [Pr(OSiPh3)4(L)] (1, L = 4,4'-dimethoxy-2,2'-bipyridine) are reported. The stability of the Pr(IV) complex significantly enhanced with the use of the bidentate ligand L. Slow magnetic relaxation was observed at low temperatures, indicating that the complex may be the first single-ion magnet with a tetravalent lanthanide ion being the magnetic center.

Solvent- and Additive-Free Dehydrogenation of N-Heterocycles with Oxygen Catalyzed by Polyoxovanadate-Based Metal-Organic Frameworks.

N-heteroarenes are a family of organics with significant chemical and pharmaceutical applications. They are generally prepared by the catalytic oxidative dehydrogenation (ODH) of partially saturated N-heterocycles. In this work, we prepare and demonstrate the catalytic ODH applications of two polyoxovanadate-based metal-organic frameworks of the general formula {[MII(bibp)1.5][VV2O6]}·H2O (M = Ni 1, Co 2; bibp = 4,4'-bis(imidazol-1-ylmethyl)biphenyl). They are based on nonprecious metals, need no additives or organic solvents typically required for catalytic ODH, and utilize molecular O2 as the oxidant, thus possessing all the traits desirable for practical catalysis. Catalyst 1 shows tolerance for a range of substrates with different electronic and steric features, including 2,3-dihydro-1H-indole and tetrahydroquinolines substituted with various functional groups. Mechanistic studies supported primarily by evidence from electron paramagnetic resonance and X-ray photoelectron spectra suggest that the VV sites in 1 are catalytically responsible, first enabling the formation of the substrate-based radical species by a single electron transfer event while being converted into its mixed-valence form, followed by the production of the superoxide radical anion (O2•-) upon contact with O2. The reaction mixture containing O2•- and the initially formed substrate-based radical then undergoes a series of steps, including the hydrogen abstraction and formation of the hydroperoxyl radical, the production and tautomerization of the partially dehydrogenated intermediate, and finally a repeating cycle of the aforementioned steps, to achieve the high-yield conversion of substrates to the corresponding N-heteroarenes.

Substituent Positioning Effects on the Magnetic Properties of Sandwich-Type Erbium(III) Complexes with Bis(trimethylsilyl)-Substituted Cyclooctatetraenyl Ligands.

Lanthanide complexes with judiciously designed ligands have been extensively studied for their potential applications as single-molecule magnets. With the influence of ligands on their magnetic properties generally established, recent research has unearthed certain effects inherent to site differentiation due to the different types and varying numbers of substituents on the same ligand platform. Using two new sandwich-type Er(III) complexes with cyclooctatetraenyl (COT) ligands featuring two differently positioned trimethylsilyl (TMS) substituents, namely, [Li(DME)Er(COT1,5-TMS2)2]n (Er1) and [Na(DME)3][Er(COT1,3-TMS2)2] (Er2) [COT1,3-TMS2 and COT1,5-TMS2 donate 1,3- and 1,5-bis(trimethylsilyl)-substituted cyclooctatetraenyl ligands, respectively; DME = 1,2-dimethoxyethane], and with reference to previously reported [Li(DME)3][Er(COT1,4-TMS2)2] (A) and [K(DME)2][Er(COT1,4-TMS2)2] (B), any possible substituent position effects have been explored for the first time. The rearrangement of the TMS substituents from the starting COT1,4-TMS2 to COT1,3-TMS2 and COT1,5-TMS2, by way of formal migration of the TMS group, was thermally induced in the case of Er1, while for the formation of Er2, the use of Na+ in the placement of its Li+ and K+ congeners is essential. Both Er1 and Er2 display single-molecule magnetic behaviors with energy barriers of 170(3) and 172(6) K, respectively. Magnetic hysteresis loops, butterfly-shaped for Er1 and wide open for Er2, were observed up to 12 K for Er1 and 13 K for Er2. Studies of magnetic dynamics reveal the different pathways for relaxation of magnetization below 10 K, mainly by the Raman process for Er1 and by quantum tunneling of magnetization for Er2, leading to the order of magnitude difference in magnetic relaxation times and sharply different magnetic hysteresis loops.

Rheological engineering of perovskite suspension toward high-resolution X-ray flat-panel detector.

Solution-processed polycrystalline perovskite film is promising for the next generation X-ray imaging. However, the spatial resolution of current perovskite X-ray panel detectors is far lower than the theoretical limit. Herein we find that the pixel level non-uniformity, also known as fixed pattern noise, is the chief culprit affecting the signal-to-noise ratio and reducing the resolution of perovskite detectors. We report a synergistic strategy of rheological engineering the perovskite suspensions to achieve X-ray flat panel detectors with pixel-level high uniformity and near-to-limit spatial resolution. Our approach includes the addition of methylammonium iodide and polyacrylonitrile to the perovskite suspension, to synergistically enhance the flowability and particle stability of the oversaturated solution. The obtained suspension perfectly suits for the blade-coating process, avoiding the uneven distribution of solutes and particles within perovskite films. The assembled perovskite panel detector exhibits greatly improved fixed pattern noise value (1.39%), high sensitivity (2.24 × 104 µC Gyair-1 cm-2), low detection limit (28.57 nGyair·s-1) as well as good working stability, close to the performance of single crystal detectors. Moreover, the detector achieves a near-to-limit resolution of 0.51 lp/pix.

Spatiotemporally and Chemically Resolved Imaging of Electrocatalytic Oxygen Evolution on Single Nanoplates of Cobalt-Layered Hydroxide.

Transition metal-layered hydroxides have been extensively studied in order to address the key challenge of slow kinetics of the oxygen evolution reaction (OER). However, how the catalytically active sites are evolved and the corresponding heterogeneous structure-property relationship remain unclear. Herein, using cobalt-layered hydroxide as a representative catalyst, we report a strategy for the comprehensive in situ investigation of the electrocatalytic OER process at the single electrocatalyst level using combined electrochemiluminescence (ECL) and vis-absorption microscopy. The stepwise heterogeneous electrocatalytic responses of single-cobalt hydroxide nanoplates are unveiled with ECL imaging, and the corresponding valence state changes are revealed by vis-absorption imaging. The correlated in situ and ex situ multimode analyses indicate that, during the oxidation process, the Co2+ cations in the tetrahedral sites (CoTd2+) turned into CoTd3+ and even the highly unstable CoTd4+, assisted by the interlayer water in a metastable CoOOH·xH2O phase. Crucially, the CoTd4+ sites are mainly distributed in the inner part of the nanoplates and show superior electrocatalytic properties. The correlative single-particle imaging approach for electrocatalytic process analysis with high spatiotemporal and chemical resolution enables in-depth mechanistic insights to be generated and, in turn, will benefit the rational design of electrocatalysts with enhanced performance.

Additive-free selective oxidation of aromatic alcohols with molecular oxygen catalyzed by a mixed-valence polyoxovanadate-based metal-organic framework.

Selective oxidation of alcohols to aldehydes is an industrially significant chemical transformation. Herein, we report a mixed-valence polyoxovanadate-based metal-organic framework (MOF), (H2bix)5{[Cd(bix)2][VIV8VV7O36Cl]2}·3H2O (V-Cd-MOF), for catalyzing the additive-free oxidation of a series of aromatic alcohols with high selectivity and in nearly quantitative yield to the corresponding aldehydes with O2 as the oxidant. Experimental results, corroborated with density functional theory calculations, indicate that it is the synergistic operation of the dual active sites of the VIV-O-VV building units in the polyoxovanadate cluster that is responsible for the excellent catalytic performance observed: on the one hand, the exposed and readily accessible reduced VIV site is believed to activate O2, resulting in a reactive oxygen species for the subsequent activation and breaking of the substrate's Cα-H bond. On the other hand, the VV site coordinates with the alcoholic O atom to facilitate the cleavage of the O-H bond. The catalyst can be recycled by centrifugation and re-used at least five times with uncompromised performance. To our knowledge, V-Cd-MOF represents the first example of a polyoxometalate-based MOF catalyst for additive-free selective oxidation of alcohol to aldehyde with O2 as an oxidant.

Self-wavelength shifting in two-dimensional perovskite for sensitive and fast gamma-ray detection.

Lead halide perovskites have recently emerged as promising X/γ-ray scintillators. However, the small Stokes shift of exciton luminescence in perovskite scintillators creates problems for the light extraction efficiency and severely impedes their applications in hard X/γ-ray detection. Dopants have been used to shift the emission wavelength, but the radioluminescence lifetime has also been unwantedly extended. Herein, we demonstrate the intrinsic strain in 2D perovskite crystals as a general phenomenon, which could be utilized as self-wavelength shifting to reduce the self-absorption effect without sacrificing the radiation response speed. Furthermore, we successfully demonstrated the first imaging reconstruction by perovskites for application of positron emission tomography. The coincidence time resolution for the optimized perovskite single crystals (4 × 4 × 0.8 mm3) reached 119 ± 3 ps. This work provides a new paradigm for suppressing the self-absorption effect in scintillators and may facilitate the application of perovskite scintillators in practical hard X/γ-ray detections.

Mechanochemical Synthesis of High-Entropy Perovskite toward Highly Sensitive and Stable X-ray Flat-Panel Detectors.

Perovskites are attracting attention for optoelectronic devices. Despite their promise, the large-scale synthesis of perovskite materials with exact stoichiometry, especially high-entropy perovskites, has been a major challenge. Moreover, the difficulty in stoichiometry control also hinders the development of perovskite X-ray flat-panel detectors. Previous reports all employed simple MAPbI3 as the active layer, while the performance still falls short of optimized single-crystal-based single-pixel detectors. Herein, a scalable and universal strategy of a mechanochemical method is adopted to synthesize stoichiometric high-entropy perovskite powders with high quality and high quantity (>1 kg per batch). By utilizing these stoichiometric perovskites, the first FA0.9 MA0.05 Cs0.05 Pb(I0.9 Br0.1 )3 -based X-ray flat-panel detector with low trap density and large mobility-lifetime product (7.5 × 10-3 cm2 V-1 ) is reported. The assembled panel detector exhibits close-to-single-crystal performance (high sensitivity of 2.1 × 104 µC Gyair -1 cm-2 and ultralow detection limit of 1.25 nGyair s-1 ), high spatial resolution of 0.46 lp/pixel, as well as excellent thermal robustness under industrial standards. The high performance in the high-entropy perovskite-based X-ray FPDs has the potential to facilitate the development of new-generation X-ray-detection systems.

High Chemical Potential Driven Amorphization of Pd-based Nanoalloys.

Amorphous metals and alloys are promising candidates for superior catalysts in many catalytic and electrocatalytic reactions. It is of great urgency to develop a general method to construct amorphous alloys and further clarify the growth mechanism in a wet-chemical system. Herein, inspired by the conservation of energy during the crystallization process, amorphous PdCu nanoalloys have been successfully synthesized by promoting the chemical potential of the building blocks in solution. Benefiting from the abundant active sites and enhanced corrosion resistance, the synthesized amorphous PdCu nanostructures exhibit superior catalytic activity and durability over the face-centered cubic one in formic acid decomposition reaction. More importantly, the successful fabrications of amorphous PdFe, PdCo, and PdNi further demonstrate the universality of the above strategy. This proposed strategy is promising to diversify the amorphous family.

Polysaccharides from apple pomace exhibit anti-fatigue activity through increasing glycogen content.

The polysaccharides were isolated from apple pomace by hot-water extraction, and their anti-fatigue activity was evaluated in C2C12 muscle myoblasts and male Kunming mice. The purified polysaccharides from apple pomace (PAP) have a molecular weight of 1.74 × 105 Da and were composed of mannose, rhamnose, glucose, galactose and arabinose. In C2C12 myoblasts, PAP showed no cytotoxicity in the concentrations of 0-300 µg/ml. PAP treatment increased the glycogen content, while the ATP content was not affected in C2C12 myoblasts. Further investigation found that the activity and gene expression of glycogen synthase, rather than glycogen phosphorylase, were upregulated by PAP treatment. The studies in vivo showed that PAP treatment did not affect the food intake and weight again in mice. Importantly, PAP prolonged the exhaustive swimming time, increased hepatic and skeletal muscle glycogen levels, and effectively inhibited the accumulation of blood lactic and blood urea nitrogen in mice. Taken together, the results suggested that PAP exhibit anti-fatigue activity in vitro and in vivo through increasing glycogen content.

Regulating Morphological Features of Nickel Single-Atom Catalysts for Selective and Enhanced Electroreduction of CO2.

Single-atom catalysts (SACs) are of interest for chemical transformations of significant energy and environmental relevance because of the envisioned efficient use of active sites and the flexibility in tuning their coordination environment. Future advancement in this vein hinges upon the ability to further increase the number and accessibility of active sites in addition to fine-tuning their chemical environment. In this work, a Ni SAC is reported with a unique hierarchical hollow structure (Ni/HH) that allows increased accessibility of the active sites. The successful obtainment of such a uniquely structured catalyst was enabled by the judiciously chosen solvent mixtures for the preparation of the precursor whose hierarchical feature is maintained during the subsequent pyrolysis and etching of the pyrolysis product. Comparative catalytic and mechanistic studies with reference to three closely related but more compact Ni SACs established the superior performance of Ni/HH for selective electroreduction of CO2 to CO. Experimental analyses by in situ attenuated total reflection surface-enhanced infrared spectroscopy reveal that it is the facilitated formation of the *COOH intermediate in the rate-determining step that leads to the enhanced reaction kinetics and the overall catalytic performance.

Linking Enhanced Kinetics of Electrocatalytic Oxygen Reduction Reaction with Increased Utilization of Active Sites in a Hierarchical Single-Atom Catalyst.

Single-atom catalysts (SACs) are of tremendous current research due to maximized use of metal atoms and enhanced activity and selectivity for a great variety of chemical reactions. Hierarchically structured SACs have been explored to further increase the number and accessibility of active sites to realize the full potentials of SACs. However, though plausible-sounding, these supposed advantages of hierarchically structured SACs are largely untested. The assumed enhancing effects on the formation of intermediates on and the overall reaction kinetics remain largely unknown. Herein is reported a Fe-SAC with a hierarchical hollow structure (Fe/HH) that showed excellent activity in oxygen reduction reaction and proton exchange membrane fuel cell. Comparative experimental and computational studies with respect to Fe/SS-the counterpart of Fe/HH with a compact primary structure-reveal a significantly increased number of active sites and their utilization in Fe/HH as reflected by the facilitated formation of the rate-determining-step intermediate Fe-OOH*. This work thus establishes unambiguously the connection between the increased utilization of active sites and the enhanced kinetics of the electrocatalytic reduction of oxygen.

Thiacalix[4]arene-Sandwiched Sandglass-like Ln9 Clusters (Ln = Tb and Eu): Insights into the Selective Luminescence Quenching Properties by p-Nitrobenzene Derivatives.

Nonanuclear lanthanide clusters Ln9 (Ln = Tb and Eu) based on p-tert-butylthiacalix[4]arene (H4TC4A) have been synthesized by the solvothermal reaction and were structurally determined by single-crystal X-ray diffraction. The framework of Ln9 can be termed as a sandglass-like structure whose two Ln4-TC4A polynuclear secondary building units are bridged by one octa-coordinate {Ln(µ3-O)8} unit. Efficient TC4A-to-Ln energy transfer was observed for Tb9 but not for Eu9. The luminescence quantum yield (QY) of Tb9 in the solid state at room temperature was determined to be 17.6%, while its highest QY in a methanolic solution (2 × 10-5 mol/L) is 59.2% upon excitation at 318 nm. The luminescence of Tb9 was quenched selectively by derivatives of p-nitrobenzene, as demonstrated by the results of photoluminescence and UV-vis titration experiments and supported by density functional theory calculations. We believe that the interactions between the analyte molecules and the pocket of Tb9 are primarily responsible for the observed quenching. As such, this work represents one of the few examples of utilizing structurally interesting lanthanide cluster complexes as a sensory platform for the recognition of meaningful analytes and portends the further development of lanthanide-calixarene-complex-based functional materials.

Heterostructured FeNi hydroxide for effective electrocatalytic oxygen evolution.

Hydrogen production technology by water splitting has been heralded as an effective means to alleviate the envisioned energy crisis. However, the overall efficiency of water splitting is limited by the effectiveness of the anodic oxygen evolution reaction (OER) due to the high energy barrier of the 4e- process. The key to addressing this challenge is the development of high-performing catalysts. Transition-metal hydroxides with high intrinsic activity and stability have been widely studied for this purpose. Herein, we report a gelatin-induced structure-directing strategy for the preparation of a butterfly-like FeNi/Ni heterostructure (FeNi/Ni HS) with excellent catalytic performance. The electronic interactions between Ni2+ and Fe3+ are evident both in the mixed-metal "torso" region and at the "torso/wing" interface with increasing Ni3+ as a result of electron transfer from Ni2+ to Fe3+ mediated by the oxo bridge. The amount of Ni3+ also increases in the "wings", which is believed to be a consequence of charge balancing between Ni and O ions due to the presence of Ni vacancies upon formation of the heterostructure. The high-valence Ni3+ with enhanced Lewis acidity helps strengthen the binding with OH- to afford oxygen-containing intermediates, thus accelerating the OER process. Direct evidence of FeNi/Ni HS facilitating the formation of the Ni-OOH intermediate was provided by in situ Raman studies; the intermediate was produced at lower oxidation potentials than when Ni2(CO3)(OH)2 was used as the reference. The Co congener (FeCo/Co HS), prepared in a similar fashion, also showed excellent catalytic performance.

Direct Visualization of the Evolution of a Single-Atomic Cobalt Catalyst from Melting Nanoparticles with Carbon Dissolution.

Transition metal single-atom catalysts (SACs) are of immense interest, but how exactly they are evolved upon pyrolysis of the corresponding precursors remains unclear as transition metal ions in the complex precursor undergo a series of morphological changes accompanied with changes in oxidation state as a result of the interactions with the carbon support. Herein, the authors record the complete evolution process of Co SAC during the pyrolysis a Co/Zn-containing zeolitic imidazolate framework. Aberration-corrected environmental TEM coupled with in-situ EELS is used for direct visualization of the evolution process at 200-1000 °C. Dissolution of carbon into the nanoparticles of Co is found to be key to modulating the wetting behavior of nanoparticles on the carbon support; melting of Co nanoparticles and their motion within the zeolitic architecture leads to the etching of the framework structure, yielding porous C/N support onto which Co-single atoms reside. This uniquely structured Co SAC is found to be effective for the oxidation of a series of aromatic alkanes to produce selective ketones among other possible products. The carbon dissolution and melting/sublimation-driven structural dynamics of transition metal revealed here will expand the methodology in synthesizing SACs and other high-temperature processes.

Anion-Guided Stepwise Assembly of High-Nuclearity Lanthanide Hydroxide Clusters.

The ability to construct complex molecular architectures with precise control is critical for realizing molecule-based materials and functions. Using the assembly of a 60-metal complex of ErIII with histidine as an example, we demonstrate the rational assembly of otherwise synthetically elusive polynuclear lanthanide hydroxide clusters directed by the combined set of I- and CO3 2- as templates. We succeeded in the stepwise transformation starting from Er12 to Er60 by way of two key intermediates Er34 and Er48 . The Er12 , Er34 , and Er48 core motifs represent respectively 1/6, 1/2, and 3/4 of the complete sodalite cage of Er60 . This work, representing a rare example of rationally constructing high-nuclearity lanthanide clusters guided by judiciously chosen templates, is expected to stimulate more future efforts for the controllable synthesis of complex molecular or supramolecular architectures with unprecedented structural sophistication and possibly useful properties.