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Superconductors with exotic physical properties are critical to current and future technology. In this review, we highlight several important superconducting families and focus on their crystal structure, chemical bonding, and superconductivity correlations. We connect superconducting materials with chemical bonding interactions based on their structure–property relationships, elucidating our empirically chemical approaches and other methods used in the discovery of new superconductors. Furthermore, we provide some technical strategies to synthesize superconductors and basic but important characterization for chemists needed when reporting new superconductors. In the end, we share our thoughts on how to make new superconductors and where chemists can work on in the superconductivity field. This review is written using chemical terms, with a focus on providing some chemically intuitive thoughts on superconducting materials design. [ABSTRACT FROM AUTHOR]

We have successfully constructed a tetrahedral Ti4L6 cage with calixarene-like coordination-active vertices. It further features high solubility and stability in H2O and DMF/ H2O solution, affording an interesting stepwise assembly function with other metal ions. Through trapping of different amounts of Co or Ln ions, the Ti4L6 tetrahedra can be organized into various dimensional architectures, including a Ti4L6-Co3 cage, a Ti4L6-Ln2 cage, a Ti4L6-Ln2 chain, and a three-dimensional Ti4L6-Ln framework. An unusual mixed-valence phenomenon was observed in the Ti4L6 cage, whose Ti3+/4+ compositions were adequately identified by electron spin resonance and X-ray photoelectron spectroscopy analyses. More remarkably, the calixarene-like oxygen vertices of the Ti4L6 cage can also be used for the recognition of C3-symmetric dye molecules through N-H⋯O hydrogen bonding. Accordingly, driven by visible light, selective and efficient homogeneous photodecomposition of acid blue 93 and alkali blue 4B were successfully achieved. Therefore, this work not only represents a milestone in constructing symmetric Ti-based cages with interesting coordination assembly function but also provides a new method for preparing technologically important soluble photoactive cages. [ABSTRACT FROM AUTHOR]

On the basis of the same reaction starting materials, microporous to mesoporous Mn(II)-tris((4-carboxyl)phenylduryl)amine frameworks (FIR-34 to FIR-36, FIR denotes Fujian Institute of Research) with different interpenetration structures have been obtained by applying different solvents and reaction temperatures. FIR-34 is an 8-fold interpenetrating dia framework constructed from small dinuclear [Mn2(COO)4] secondary building units (SBUs), while FIR-35 based on large Mn5 SBUs is a non-interpenetrating framework with (3,8)-connected tfz-d network. Both of them have low porosity. However, the other non-interpenetrating framework (FIR-36) with large mesopores is built by rod-shaped Mn(II)-carboxylate SBUs. Gas sorption measurements for FIR-36 give a Langmuir surface area of 825.3 m2·g-1 and a H2 uptake of 134.5 cm3·g-1 at 77 K and 1 bar. Three microporous and mesoporous Mn(II)-tris((4-carboxyl)phenylduryl)amine frameworks (FIR-34 to FIR-36) have been obtained through effective interpenetration control. Different solvent systems and reaction temperatures determine the interpenetration of a MOF structure. FIR-36 with non-interpenetrating structure has Langmuir surface area of 825.3 m2·g-1 and a H2 uptake of 134.5 cm3·g-1 at 77 K and 1 bar. [ABSTRACT FROM AUTHOR]

Developing artificial enzymes with excellent catalytic activities and uncovering the structural and chemical determinants remain a grand challenge. Discrete titanium-oxo clusters with well-defined coordination environments at the atomic level can mimic the pivotal catalytic center of natural enzymes and optimize the charge-transfer kinetics. Herein, we report the precise structural tailoring of a self-assembled tetrahedral Ti 4 Mn 3 -cluster for photocatalytic CO 2 reduction and realize the selective evolution of CO over specific sites. Experiments and theoretical simulation demonstrate that the high catalytic performance of the Ti 4 Mn 3 -cluster should be related to the synergy between active Mn sites and the surrounding functional microenvironment. The reduced energy barrier of the CO 2 photoreduction reaction and moderate adsorption strength of CO* are beneficial for the high selective evolution of CO. This work provides a molecular scale accurate structural model to give insight into artificial enzyme for CO 2 photoreduction.

In this work, we report multiple-intercalation stages and universal T c enhancement of superconductivity in 1T-SnSe 2 through Li and organic molecule co-intercalation. We observe significantly increased lattice parameters of up to 40 Å and a dramatically enlarged interlayer distance of up to ∼11 Å in Li and N , N -dimethylformamide (DMF) co-intercalated SnSe 2 . Well-separated co-intercalation stages with different stacking patterns have been discovered by carefully controlled reaction times and concentrations of solutions. These co-intercalation stages are superconductors showing different superconducting signals. In addition, Li and various organic species such as acetone, dimethyl sulfoxide (DMSO), and tetrahydrofuran (THF) have been co-intercalated into SnSe 2 crystals; all of which show an enhanced superconducting T c compared to solely Li-intercalated SnSe 2 . Our findings may provide more insight into effectively tuning the electronic structure of the lamellar structure through organic molecule co-regulation and open a new strategy to engineer the physical properties of these layered materials by controlling their different intercalation stages.

Bi 4 I 4 belongs to a novel family of quasi-one-dimensional (1D) topological insulators (TIs). While its β phase was demonstrated to be a prototypical weak TI, the α phase, long thought to be a trivial insulator, was recently predicted to be a rare higher order TI. Here, we report the first gate tunable transport together with evidence for unconventional band topology in exfoliated α-Bi 4 I 4 field effect transistors. We observe a Dirac-like longitudinal resistance peak and a sign change in the Hall resistance; their temperature dependences suggest competing transport mechanisms: a hole-doped insulating bulk and one or more gate-tunable ambipolar boundary channels. Our combined transport, photoemission, and theoretical results indicate that the gate-tunable channels likely arise from novel gapped side surface states, two-dimensional (2D) TI in the bottommost layer, and/or helical hinge states of the upper layers. Markedly, a gate-tunable supercurrent is observed in an α-Bi 4 I 4 Josephson junction, underscoring the potential of these boundary channels to mediate topological superconductivity.

Materials with interfaces often exhibit extraordinary phenomena exemplified by rich physics, such as high-temperature superconductivity and enhanced electronic correlations. However, demonstrations of confined interfaces to date have involved intensive effort and fortuity, and no simple path is consistently available. Here, we report the achievement of interfacial superconductivity in the nonsuperconducting parent compounds AEFe 2 As 2 , where AE = Ca, Sr, or Ba, by simple subsequent annealing of the as-grown samples in an atmosphere of As, P, or Sb. Our results indicate that the superconductivity originates from electron transfer at the interface of the hybrid van der Waals heterostructures, consistent with the two-dimensional superconducting transition observed. The observations suggest a common origin of interfaces for the nonbulk superconductivity previously reported in the AEFe 2 As 2 compound family and provide insight for the further exploration of interfacial superconductivity.

A new ternary nonstoichiometric Zr 6.5 Pt 6 Se 19 has been discovered as a part of effort to dope Zr into the layered transitional metal chalcogenide PtSe 2 . With a new structure type ( oC 68), it is the first Pt-based ternary chalcogenide with group 4 elements (Ti, Zr, and Hf). The crystal structure adopts the orthorhombic space group Cmmm with lattice parameters of a = 15.637(6) Å, b = 26.541(10) Å, c = 3.6581(12) Å, and V = 1518.2(9) Å 3 . This unusual structure consists of several building units: chains of edge-sharing selenium trigonal prisms and octahedra centered by zirconium atoms, chains of corner-shared square pyramid, and square planar centered by Pt atoms. The condensation of these building blocks forms a unique structure with bilayered Zr 5.54 Pt 6 Se 19 slabs stacking along the b direction and large channels parallel to the c direction within the bilayered slabs. Band structure calculations suggest that partial occupancy of Zr atoms creates a pseudo gap at the Fermi level and is likely the main cause for the stability of this new phase.

Herein we report an efficient strategy to construct cage-based metal-organic frameworks (MOFs) via the assembly of Ti 4 L 6 (L = embonate) cages and N-contained ligands with Mn 2+ and Zn 2+ ions, respectively, and two Ti 4 L 6 -cage-based MOFs ( PTC-219 and PTC-220 ) with high stability and gas sorption properties have been generated through two-step reactions, respectively.

A nonstoichiometric ternary antimonide, Zr 3.55 Pt 4 Sb 4 , with a new structure type ( hP 24), has been synthesized via arc-melting. Its crystal structure was determined by single-crystal X-ray diffraction with hexagonal space group P 6 3 / mmc and lattice parameters a = 4.391(3) Å, c = 30.53(2) Å, and V = 509.7(8) Å 3 . It features the unique Pt 4 Sb 4 slab with Pt-Pt bonds and is reminiscent to hexagonal diamond substructures. Three different Zr atoms, occupying three different sites, aid in the close-packing of the Pt and Sb atoms. Electronic structure calculations show the half occupancy of one Zr site creates a pseudogap at the Fermi level and optimizes the Pt-Sb bonding interactions. This enhances the electronic stability and accounts for the very narrow phase width observed for this nonstoichiometric compound. Furthermore, strong Zr-Pt and Zr-Sb interactions play a crucial role in the chemical bonding of the title compound. Electrical transport measurements show metallic behavior of this compound down to 2 K, consistent with the band structure calculations.

Single crystals of Ln 2 Fe 4- x Co x Sb 5- y Bi y (Ln = La, Ce; 0 ≤ x < 0.5; 0 ≤ y ≤ 0.2) were grown using Bi flux and self-flux methods. The compounds adopt the La 2 Fe 4 Sb 5 structure type with tetragonal space group I4/ mmm. The La 2 Fe 4 Sb 5 structure type is comprised of rare earth atoms capping square Sb nets in a square antiprismatic fashion and two transition-metal networks forming a PbO-type layer with Sb and transition-metal isosceles triangles. Substituting Co into the transition-metal sublattice results in a decrease in the transition temperature and reduced frustration, indicative of a transition from localized to itinerant behavior. In this manuscript, we demonstrated that Bi can be used as an alternate flux to grow single crystals of antimonides. Even with the incorporation of Bi into the Sb square net, the magnetic properties are not significantly affected. In addition, we have shown that the incorporation of Co into the Fe triangular sublattice leads to an itinerant magnetic system.

Extensive residues of neonicotinoids (neonics) have been demonstrated in food and the environment by routine monitoring measurement, but little is known about the residue levels in "ready to eat" dietary samples. To obtain a more accurate picture of dietary exposure to total neonics, an ultrasensitive and effective cleanup analytical method for the quantification of neonics in dietary samples was established on the basis of cold-induced phase separation and pre-column dilution injection liquid chromatography-high-resolution mass spectrometry. A total of 10 neonics were quantified in ultratrace amounts (ng/kg) using stable isotope dilution, with calibration curves spanning 4 orders of magnitude. Satisfactory accuracy (73.5-109.2% for the recoveries) and precision (0.6-13.2% for the relative standard deviation ranges) were obtained in method validation. Moreover, tolerable absolute matrix effects (0.89-1.09) were also obtained in 12 kinds of dietary matrices with weak relative matrix effects (2.8-12.6%). The validated method was applied to the dietary samples collected from the Chinese Total Diet Study, and the results showed that 75% of the samples were contaminated with at least one neonicotinoid.

Presented here are binuclear Nb 2 , tetranuclear Ti 2 Nb 2 , and dodecanuclear Nb 12 complexes decorated by embonic acid ligands. These structures feature a unique Ti-O-Nb or Nb-O-Nb subunit. Besides, the unprecedented dodecanuclear Nb 12 cluster further displays a porous three-dimensional packing framework and stability in water, affording an interesting selective uptake for methylene blue molecules over rhodamine B.

We have successfully constructed a tetrahedral Ti 4 L 6 cage with calixarene-like coordination-active vertices. It further features high solubility and stability in H 2 O and DMF/H 2 O solution, affording an interesting stepwise assembly function with other metal ions. Through trapping of different amounts of Co or Ln ions, the Ti 4 L 6 tetrahedra can be organized into various dimensional architectures, including a Ti 4 L 6 -Co 3 cage, a Ti 4 L 6 -Ln 2 cage, a Ti 4 L 6 -Ln 2 chain, and a three-dimensional Ti 4 L 6 -Ln framework. An unusual mixed-valence phenomenon was observed in the Ti 4 L 6 cage, whose Ti 3+/4+ compositions were adequately identified by electron spin resonance and X-ray photoelectron spectroscopy analyses. More remarkably, the calixarene-like oxygen vertices of the Ti 4 L 6 cage can also be used for the recognition of C 3 -symmetric dye molecules through N-H···O hydrogen bonding. Accordingly, driven by visible light, selective and efficient homogeneous photodecomposition of acid blue 93 and alkali blue 4B were successfully achieved. Therefore, this work not only represents a milestone in constructing symmetric Ti-based cages with interesting coordination assembly function but also provides a new method for preparing technologically important soluble photoactive cages.

A metal-rich ternary phosphide, SrPt(6)P(2), with a unique structure type was synthesized at high temperatures. Its crystal structure was determined by single-crystal X-ray diffraction [cubic space group Pa3̅; Z = 4; a = 8.474(2) Å, and V = 608.51(2) Å(3)]. The structure features a unique three-dimensional anionic (Pt(6)P(2))(2-) network of vertex-shared Pt(6)P trigonal prisms. The Sr atoms occupy a 12-coordinate (Pt) cage site and form a cubic close-packed (face-centered-cubic) arrangement, and the P atoms formally occupy tetrahedral interstices. The metallic compound becomes superconducting at 0.6 K, as evidenced by magnetic and resistivity measurements.

Cadmium (Cd) is a non-essential heavy metal with high toxicity to plants. MicroRNAs (miRNAs) are a class of small non-coding RNAs that play important roles in plant abiotic stress responses. To investigate whether miRNAs function in Cd stress response, miRNA expression profiles in rice ( Oryza sativa ) under Cd stress were monitored using microarray assays. A total of 12 Cd-responsive novel miRNAs predicted previously were identified, of which 4 were further validated experimentally. A total of 44 target genes were predicted for the Cd-responsive miRNAs, many of which appeared to regulate gene networks mediating environmental stresses. Several target genes were validated to show a reciprocal regulation by miRNAs. A transgenic approach was also used to determine the role of miRNAs in rice response to Cd stress. Overexpression of miR192 retarded seed germination and seedling growth under Cd stress. These results implied the role of novel miRNAs in the involvement of Cd tolerance of rice.