Intriguing Topologies Research Articles

Electronic Lieb lattice signatures embedded in two-dimensional polymers with a square lattice.

Exotic band features, such as Dirac cones and flat bands, arise directly from the lattice symmetry of materials. The Lieb lattice is one of the most intriguing topologies, because it possesses both Dirac cones and flat bands which intersect at the Fermi level. However, the synthesis of Lieb lattice materials remains a challenging task. Here, we explore two-dimensional polymers (2DPs) derived from zinc-phthalocyanine (ZnPc) building blocks with a square lattice (sql) as potential electronic Lieb lattice materials. By systematically varying the linker length (ZnPc-xP), we found that some ZnPc-xP exhibit a characteristic Lieb lattice band structure. Interestingly though, fes bands are also observed in ZnPc-xP. The coexistence of fes and Lieb in sql 2DPs challenges the conventional perception of the structure-electronic structure relationship. In addition, we show that manipulation of the Fermi level, achieved by electron removal or atom substitution, effectively preserves the unique characteristics of Lieb bands. The Lieb Dirac bands of ZnPc-4P shows a non-zero Chern number. Our discoveries provide a fresh perspective on 2DPs and redefine the search for Lieb lattice materials into a well-defined chemical synthesis task.

Pressure-Tuning Superconductivity in Noncentrosymmetric Topological Materials ZrRuAs.

Recently, the hexagonal phase of ternary transition metal pnictides TT'X (T = Zr, Hf; T' = Ru; X = P, As), which are well-known noncentrosymmetric superconductors, were predicted to host nontrivial bulk topology. In this work, we systematically investigate the electronic responses of ZrRuAs to external pressure. At ambient pressure, ZrRuAs show superconductivity with Tc ~ 7.74 K, while a large upper critical field ~ 13.03 T is obtained for ZrRuAs, which is comparable to the weak-coupling Pauli limit. The resistivity of ZrRuAs exhibits a non-monotonic evolution with increasing pressure. The superconducting transition temperature Tc increases with applied pressure and reaches a maximum value of 7.93 K at 2.1 GPa, followed by a decrease. The nontrivial topology is robust and persists up to the high-pressure regime. Considering both robust superconductivity and intriguing topology in this material, our results could contribute to studies of the interplay between topological electronic states and superconductivity.

Synthesis, Structures and Magnetic Properties of CuII and CoII Compounds Based on Asymmetric 5‐(1H‐Imidazole‐1‐yl)‐3‐pyridine Carboxylic Acid

Five coordination compounds [Cu2(impc)2(µ2‐OH)Cl]n (1), [Cu2(impc)2(µ2‐OH)Br]n (2), [Co(impc)2(H2O)2]n (3), [Co4(impc)4(SO4)2(H2O)]n (4) and {[Co(impc)(H2O)2]·H2O} (5) based on asymmetric 5‐(1H‐imidazole‐1‐yl)‐3‐pyridinecarboxylic acid (Himpc) have been hydrothermally synthesized and structurally characterized. 1 and 2 are isostructural and consist of binuclear CuII units and display two‐dimensional (2D) framework, where 1 and 2 present a new {(4.62)(42.65.82.10)(4)} topology. 3 features a 1D chain structure. Polymer 4, which also displays a new Schläfli symbol {(413.620.88.104)(43)2(4)}, contains tetranuclear CoII cluster and is a 2D structure. The planar‐type tetranuclear CoII cluster with SO42– bridge in 4 has not been reported. Compound 5 possesses a mononuclear structure. Magnetic susceptibility studies for 1 and 2 with Cu2 units reveal the antiferromagnetic coupling with J = –3.42 cm–1 for 1 and J = –3.83 cm–1 for 2. Contrary to the only example of class F2 ferromagnetic VII, 1 and 2 (class F2) exhibit different antiferromagnetic behavior. Compounds 3 and 5 exhibit ferromagnetic behavior, and their M(H) curve is consistent with the ferromagnetic nature. No peaks are observed in the out‐of‐phase (χ'') plots of 3, suggesting no long‐range order and no spin canting. For 4 with the Co4 units, it also exhibits ferromagnetic behavior, and the M(H) curve is consistent with the ferromagnetic nature.

Plasmon-polaritonic quadrupole topological insulators

Quadrupole topological insulator is a symmetry-protected higher-order topological phase with intriguing topology of Wannier bands, which, however, has not yet been realized in plasmonic metamaterials. Here, we propose a lattice of plasmon-polaritonic nanocavities which can realize quadrupole topological insulators by exploiting the geometry-dependent sign-reversal of the couplings between the daisy-like nanocavities. The designed system exhibits various topological and trivial phases as characterized by the nested Wannier bands and the topological quadrupole moment which can be controlled by the distances between the nanocavities. Our study opens a pathway toward plasmonic topological metamaterials with quadrupole topology.

Synthesis, structure and photocatalytic degradation of organic dyes of a copper(II) metal-organic framework (Cu-MOF) with a 4-coordinated three-dimensional CdSO4 topology.

Metal-organic frameworks (MOFs) have attracted much interest in the fields of gas separation and storage, catalysis synthesis, nonlinear optics, sensors, luminescence, magnetism, photocatalysis gradation and crystal engineering because of their diverse properties and intriguing topologies. A Cu-MOF, namely poly[[(μ2-succinato-κ2O:O'){μ2-tris[4-(1,2,4-triazol-1-yl)phenyl]amine-κ2N:N'}copper(II)] dihydrate], {[Cu(C4H4O4)(C24H18N10)]·2H2O}n or {[Cu(suc)(ttpa)]·2H2O}n, (I), was synthesized by the hydrothermal method using tris[4-(1,2,4-triazol-1-yl)phenyl]amine (ttpa) and succinate (suc2-), and characterized by IR, powder X-ray diffraction (PXRD), luminescence, optical band gap and valence band X-ray photoelectron spectroscopy (VB XPS). Cu-MOF (I) shows a twofold interpenetrating 4-coordinated three-dimensional CdSO4 topology with point symbol {65·8}. It presents good photocatalytic degradation of methylene blue (MB) and rhodamine B (RhB) under visible-light irradiation. A photocatalytic mechanism was proposed and confirmed.

Novel nonlinear wave equation: Regulated rogue waves and accelerated soliton solutions

A new exactly solvable (1+1)-dimensional complex nonlinear wave equation exhibiting rich analytic properties has been introduced. A rogue wave (RW), localized in space–time like Peregrine RW solution, though richer due to the presence of free parameters is discovered. This freedom allows to regulate amplitude and width of the RW as needed. The proposed equation allows also an intriguing topology changing accelerated dark soliton solution in spite of constant coefficients in the equation.

Construction of a three-dimensional supramolecular framework based on an anionic cadmium(II) coordination network and protonated dipyridine organic cations.

As a class of multifunctional materials, crystalline supramolecular complexes have attracted much attention because of their unique architectures, intriguing topologies and potential applications. In this article, a new supramolecular compound, namely catena-poly[4,4'-(buta-1,3-diene-1,4-diyl)dipyridin-1-ium [(μ4-benzene-1,2,4,5-tetracarboxylato-κ6O1,O1':O2:O4,O4':O5)cadmium(II)]], {(C14H14N2)[Cd(C10H2O8)]}n or {(1,4-H2bpbd)[Cd(1,2,4,5-btc)]}n, has been prepared by the self-assembly of Cd(NO3)2·4H2O, benzene-1,2,4,5-tetracarboxylic acid (1,2,4,5-H4btc) and 1,4-bis(pyridin-4-yl)buta-1,3-diene (1,4-bpbd) under hydrothermal conditions. The title compound has been structurally characterized by IR spectroscopy, elemental analysis, powder X-ray diffraction and single-crystal X-ray diffraction analysis. Each CdII centre is coordinated by six O atoms from four different (1,2,4,5-btc)4- tetraanions. Each CdII cation, located on a site of twofold symmetry, binds to four carboxylate groups belonging to four separate (1,2,4,5-btc)4- ligands. Each (1,2,4,5-btc)4- anion, situated on a position of -1 symmetry, binds to four crystallographically equivalent CdII centres. Neighbouring CdII cations interconnect bridging (1,2,4,5-btc)4- anions to form a three-dimensional {[Cd(1,2,4,5-btc)]2-}n anionic coordination network with infinite tubular channels. The channels are visible in both the [1-10] and the [001] direction. Such a coordination network can be simplified as a (4,4)-connected framework with the point symbol (4284)(4284). To balance the negative charge of the metal-carboxylate coordination network, the cavities of the network are occupied by protonated (1,4-H2bpbd)2+ cations that are located on sites of twofold symmetry. In the crystal, there are strong hydrogen-bonding interactions between the anionic coordination network and the (1,4-H2bpbd)2+ cations. Considering the hydrogen-bonding interactions, the structure can be further regarded as a three-dimensional (4,6)-connected supramolecular architecture with the point symbol (4264)(42687·84). The thermal stability and photoluminescence properties of the title compound have been investigated.

A rod-spacer mixed ligands MOF [Mn3(HCOO)2(D-cam)2(DMF)2]n as coating material for gas chromatography capillary column

The interest in metal-organic frameworks (MOFs) is rapidly expanding because of their fascinating architectures and intriguing topologies which allowed for potential applications in gas storage, separation, heterogeneous catalysis, and several other areas. As suitable chromatographic separation media, several MOFs have been employed as stationary phase for gas chromatography and high-performance liquid chromatography. In this work we report the use of a mixed ligands rod-spacer MOF [Mn3(HCOO)2(D-cam)2(DMF)2]n as coating material for capillary column of gas chromatographic separation of a series of biochemical important compounds having linear alkyl hydrocarbon (aldehyde, alcohol and ester), aromatic hydrocarbon with two phenyls (ether, ester and ester with alcohol) and aromatic hydrocarbon (ester, ester with amino and two esters). The mixture of functional ligands, good thermal and chemical stabilities and host-guest interaction sites of the MOF are attributes to the good efficiency in gas chromatographic separation.

Double-Bridged 1-D Chain Polymers of Zinc and Cadmium Constructed by a Flexible Dipyridyl-Type Linking Ligand: {[ML1.5(NO3)2].(CH3OH)}∞ {M = Zn or Cd; L = (3-py)-CH2-NH-(CH3)C6H3-C6H3(CH3)-NH-CH2-(3-py)}

36 Ligand L3 is a reduced form of L2, and coordination polymers based on ligand L3 have novel intriguing topologies, consistent with our expectation that free rotations about the Ar-NH, NH-CH2, and CH2-(4-py) bonds may be possible. In other words, our previous work demonstrated that reduced species of diimine ligands possess a greatly enhanced structural flexibility, which may create novel polymers that cannot be obtained from the original rigid diimine ligands. As an extension of that work, we decided to reduce ligand L1 and to prepare coordination polymers by employing the resulting reduced ligand. It is worth noting that ligand L1 is a structural isomer of ligand L2 due to the different nitrogen positions in the terminal pyridyl rings. We report herein the preparation of ligand L, (3-py)-CH2-NH-(CH3)C6H3-C6H3(CH3)NH-CH2-(3-py), and structures of its zinc and cadmium coordination polymers.

Design and evaluation of polypseudorotaxanes of pegylated insulin with cyclodextrins as sustained release system

Supramolecular assemblies have attracted a great attention, due to their intriguing topologies and their application in various fields such as nanodevices, sensors, molecular switches, and drug delivery systems. In this study, we prepared the monosubstituted insulin with poly(ethylene glycol) (PEG, MW about 2200) and its cyclodextrin (CyD) polypseudorotaxanes. The pegylated insulin formed polypseudorotaxanes with α- and γ-CyDs, by inserting one PEG chain in the α-CyD cavity and two PEG chains in the γ-CyD cavity. The pegylated insulin/α- and γ-CyD polypseudorotaxanes were less soluble in water and the release rate of the drug decreased in the order of drug alone > the γ-CyD polypseudorotaxane > the α-CyD polypseudorotaxane. The plasma levels of the pegylated insulin after subcutaneous administration of the γ-CyD polypseudorotaxane to rats were significantly prolonged, accompanying an increase in the area under plasma concentration-time curve, which was clearly reflected in the prolonged hypoglycemic effect. The results indicated that the pegylated insulin/CyD polypseudorotaxanes can work as a sustained drug release system, and the polypseudorotaxane formation with CyDs may be useful as a sustained drug delivery technique for other pegylated proteins and peptides.

Directing Role of Hydrophobic−Hydrophobic and Hydrophilic−Hydrophilic Interactions in the Self-Assembly of Calixarenes/Cucurbiturils-Based Architectures

Two supramolecular architectures were assembled from the supermolecular building blocks of calixarenes and cucurbiturils through noncovalent binding. They not only exhibit an intriguing topology but also show clearly the role of hydrophobic−hydrophobic and hydrophilic−hydrophilic interactions in directing the supramolecular assembly.

Engineering Macrocyclic Figure‐Eight Motif

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Engineering macrocyclic figure-eight motif

The design and synthesis of figure-eight macrocycles are very scarce owing to the intricacies and lack of predictability from first principles. This review emphasizes on discrete macrocyclic systems both synthetic and natural with a defined figure eight knotted topology. In almost all the helical macrocycles, the helical arrangement is held by intramolecular hydrogen bonding or as a backbone requirement, but in all cases, a planar graph can be drawn and so these compounds are trivial from the topological stand point. Nature presents great deal of complexity in terms of structures in macromolecules like DNA and proteins and also displays intriguing topology in simple natural products. Patellamide, tawicyclamides, nosiheptide and thiostrepton are natural products with figure eight topology which shows interesting biological activity. Expanded porphyrins, Cu(II) complexes of thiomacrocycles, cyclic peptides and oligoesters are synthetic macrocycles showing intriguing topology. Analysis of structure and folding behaviour will enable chemists to design molecules with intriguing topology.

Synthesis of carbon nanotubes and nano-necklaces by thermal plasma process

High-yield syntheses of peculiar carbon nanotubes and carbon `necklace'-like morphologies have been obtained using a sophisticated thermal plasma technology. This method is based on a thermal plasma, which vapourizes the carbonaceous precursor in the presence of metal catalyst. Electron microscopy analyses provide evidences for a `stacked-cup' structure for the carbon nanotubes. Carbon nano-`necklaces' are constituted by the repetition of multi-wall carbon spheres, connected along one direction in a `bell'-like structure, and containing frequently an encapsulated metal particle. Microscopic growth mechanisms are also proposed to interpret both syntheses. Due to their intriguing topology, these new carbon nanotubes and necklaces may find important applications in nano-technology.