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Single crystals of A 1−x K x Fe 2 As 2 (A = Ba, Sr) with high quality have been grown successfully by an FeAs self-flux method. The samples have sizes up to 4 mm with flat and shiny surfaces. The x-ray diffraction patterns suggest that they have high crystalline quality and c-axis orientation. The non-superconducting crystals show a spin-density-wave (SDW) instability at about 173 and 135 K for the Sr-based and Ba-based compound, respectively. After doping K as the hole dopant into the BaFe 2 As 2 system, the SDW transition is smeared, and superconducting samples of the compound Ba 1−x K x Fe 2 As 2 (0 < x 0.4) are obtained. The superconductors, characterized by AC susceptibility and resistivity measurements, exhibit very sharp superconducting transitions at about 36, 32, 27 and 23 K for x = 0.40, 0.28, 0.25 and 0.23, respectively.

In this paper we report the fabrication and superconducting properties of GdO 1−x F x FeAs. It is found that when x is equal to 0.17, GdO 0.83 F 0.17 FeAs is a superconductor with the onset transition temperature T on c ≈ 36.6K. Resistivity anomaly near 130K was observed for all samples up to x = 0.17, such a phenomenon is similar to that of LaO 1−x F x FeAs. Hall coefficient indicates that GdO 0.83 F 0.17 FeAs is conducted by electron-like charge carriers.

Interest in porous metal-coordination polymers that are constructed by self-assembly processes has mushroomed recently, [1] because of their use in, for example, redox catalysis, cathodic electrolysis, ion exchange, adsorption, separation, sensors, and molecular recognition. [2][3][4][5] However, much of the work has so far focused on coordination polymers containing transition metals, [2,6] while rare-earth metal compounds have received much less attention. [7] To date, no systematic investigation of zeolite-type structures containing metal atoms from the lanthanide series along with transitionmetal atoms has been documented. Furthermore, the pores or channels reported were mainly formed through either hydrogen bonding, [2b] or p-p packing, [1b] and only in a few cases were they formed through metal-ligand bonding alone.On the other hand, the construction of mesoporous metal--organic polymers suffers from difficulties in the control of the polymer dimensionality. Although ligands can be designed to create a large hole, the resulting coordination polymers are often plagued by lattice interpenetration, [8] or framework breakdown on removal of a guest molecule. [9] In addition, the variable and versatile coordination behavior of 4f-metal ions limits their selective introduction into highly ordered structures.Herein we report the syntheses and structures of three coordination polymers formed through hydrothermal synthesis: [{[Ln(dipic) 3 Mn 1.5 (H 2 O) 3 ]·n H 2 O} ¥ ], H 2 dipic = pyridine-2,6-dicarboxylic acid; Ln = Pr, n = 2 (1); Ln = Gd, n = 3.5 (2); Ln = Er, n = 3 (3). These compounds have the relatively large nanometer-sized tubes associated with selfassembly processes directed by metal-ligand coordination only, and the framework remains intact on removing water molecules trapped in the nanotube.The three compounds are stable in air and are insoluble in common solvents. Single-crystal X-ray diffraction analyses were performed on selected crystal of these compounds. The crystal structures of the polymers are isomorphous, comprising a 3D framework containing nine-coordinate lanthanidemetal centers and six-coordinate transition-metal centers, which results in a nanotubelike structure (Figure 1). All three polymers crystallized in the hexagonal crystal system, space group P6/mcc. The crystal structure is built up of two distinct types of building blocks, Ln(dipic) 3 and MnO 4 (H 2 O) 2 (Figure 2). The Ln atom is located at the intersection of a threefold and a twofold axis and is coordinated by three tridentate (ONO) dipic anions; for which each carboxy group coordinates through one oxygen atom. Three N atoms and six O atoms complete the coordination sphere of the Ln 3+ center, which conforms most closely to a tricapped trigonal prism. The coordination geometry around Mn 2+ center is a slightly distorted octahedron, the equatorial plane of which comprises four O atoms from the carboxy groups of the dipic molecules that are chelated to four neighboring Ln 3+ centers; two water molecules occupy the remaining apic...

Developing photocatalysts capable of visible-lightdriven water splitting to produce clean hydrogen (H 2 ) is one of the premier challenges for solar energy conversion into clean and sustainable fuels. Inspired from the structure feature of photosystem I in nature, we have designed and synthesized a series of robust covalent organic frameworks (NKCOFs = Nankai University COFs) based on electric donor−acceptor moieties, in which the electron-donor group of pyrene can be used for harvesting light. Meanwhile, benzothiadiazole with different functional groups was introduced as an electron acceptor to tune the light-adsorption ability of COFs. Notably, the activity of NKCOF-108 for photochemical H 2 evolution under visible light was among the highest in COFs without hybridization with other materials. We attribute the high hydrogen evolution rate of NKCOF-108 to its distinct structural features and wide visible-lightresponse range. The highly ordered layered structure ensures that sufficient active sites are accessible for H 2 production, and the donor−acceptor design can promote the separation of photogenerated carriers. Our findings have provided an effective strategy to design photocatalysts for light-driven H 2 evolution.

Soft porous crystals (SPCs) that exhibit stimuli-responsive dynamic sorption behavior are attracting interest for gas storage/separation applications. However, the design and synthesis of SPCs is challenging. Herein, we report a new type of SPC based on a [2 + 3] imide-based organic cage (NKPOC-1) and find that it exhibits guest-induced breathing behavior. Various gases were found to induce activated NKPOC-1 crystals to reversibly switch from a "closed" nonporous phase (α) to two porous "open" phases (β and γ). The net effect is gate-opening behavior induced by CO 2 and C3 hydrocarbons. Interestingly, NKPOC-1-α selectively adsorbs propyne over propylene and propane under ambient conditions. Thus, NKPOC-1-α has the potential to separate binary and ternary C3 hydrocarbon mixtures, and the performance was subsequently verified by fixed bed column breakthrough experiments. In addition, molecular dynamics calculations and in situ X-ray diffraction experiments indicate that the gate-opening effect is accompanied by reversible structural transformations. The adsorption energies from molecular dynamics simulations aid are consistent with the experimentally observed selective adsorption phenomena. The understanding gained from this study of NKPOC-1 supports the further development of SPCs for applications in gas separation/storage because SPCs do not inherently suffer from the recyclability problems often encountered with rigid materials.

Traditional covalent organic frameworks (COFs) are prepared via polymerization based on small molecular monomers. However, the employment of polymers as building blocks to construct COFs has not been reported yet. Herein, we create a new concept of polymer covalent organic frameworks (polyCOFs) formed by linear polymers as structural building blocks, which inherit the merits from both COFs and linear polymers. PolyCOFs represent a new category of porous COF materials that demonstrate good crystallinity and high stability. More importantly, benefiting from the flexibility and processability of a linear polymer, polyCOFs can spontaneously form defect-free, flexible, and freestanding membranes that exhibit excellent mechanical properties and undergo reversible mechanical transformation upon exposure to various organic vapors. For the first time, we demonstrated that polyCOF membranes can be used as artificial muscles to perform various complicated motions (e.g., lifting objects, doing “sit-ups”) triggered by vapors. This study bridges the gap between one-dimensional amorphous linear polymers and crystalline polymer frameworks and paves a new avenue to prepare stimuli-responsive actuators using porous COF materials.

Two-dimensional heterostructures are excellent platforms to realize twistangle independent ultra-low friction due to their weak interlayer van der Waals interactions and natural lattice mismatch. However, for finite-size interfaces, the effect of domain edges on the friction process remains unclear. Here, we report on the superlubricity phenomenon and the edge pinning effect at MoS 2 /graphite and MoS 2 /h-BN van der Waals heterostructure interfaces. We find that friction coefficients of these heterostructures are below 10 -6 . Molecular dynamics simulations corroborate experiments highlighting the contribution of edges and interface steps to friction forces. Our experiments and simulations provide more information on the sliding mechanism of finite low-dimensional structures, which is vital to understand the friction process of laminar solid lubricants.