Host-guest Framework Research Articles

Wells-Dawson Arsenotungstate Porous Derivatives for Electrochemical Supercapacitor Electrodes and Electrocatalytically Active Materials.

Two Wells-Dawson arsenotungstate coordination polymers, [{CuII(bim)2}3(As2W18O62)] (1) and [(CuI10pz10Cl4)(As2W18O62)] (bim = 2,2'-biimidazole; pz = pyrazine), have been assembled via a hydrothermal method and fully characterized. Compound 1 exhibits a 2,6-connected two-dimensional hybrid layer based on asymmetrically modified {As2W18} anions and {Cu(bim)2} linkers, which is extended to a three-dimensional network with a special interlayer structure and a one-dimensional tunnel. Compound 2 is a host-guest framework that consists of a Cu-pz-Cl network with 20-member square rings, 16-member irregular rings, and embedded eight-node {As2W18} guest molecules. Compounds 1 and 2 show uncommon specific capacitance (834.8 and 960.1 F g-1, respectively, at a current density of 2.4 A g-1), enduring cycling stability (capacitance retention rates of 89.3% and 91.9%, respectively, after 5000 cycles), and good electrical conductivity, which are superior to those of the unmodified zero-dimensional Dawson arsenotungstate compound and most reported electrode materials in terms of their stable structure, special layer spacing, and orderly channels. Moreover, the title compounds exhibit excellent electrocatalytic activity for oxidizing ascorbic acid and reducing nitrite.

Ethyl Cellulose-Assisted Host-Guest Framework for Depositing Solution-Processed Yttria Films on the Inner Surface of a Narrow Quartz Tube.

Straightforward deposition protocols to coat flat surfaces are widely available. However, there are multiple constraints in coating a concave or convex surface, especially on the inner surface of narrow tubes. Coated surface helps in corrosion protection, internal cleanliness, strength, and alloy casting, and it also enhances product aesthetics. In the present work, a solution-based deposition protocol was developed to coat oxide films (Y2O3, Al2O3 among others) of tunable thickness (400 nm to 4 μm) on the inner surface of quartz tubes (inner diameter (ID) ∼ 2, 3, 5, 6, and 10 mm; length (L) ∼ 20, 110, and 500 mm) with the help of a venturimeter-based apparatus. In the course of this study, it was revealed that coating on the curved surface needed substantial optimization of the deposition parameters to minimize mainly the tearing and thinning of the film. Choice of organic solvents, acetic acid, precursor concentrations, and solution containing a binder element, such as ethyl cellulose (EC), was optimized to achieve homogeneous coating. An optimal upward air flow (speed 44 m/min) was maintained during drying the coating to prevent solvent condensation prior to annealing the film at 500-1000 °C in air for 30 min. The coating was studied with X-ray diffractometry (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDAX), and Raman spectroscopy. These coated tubes were used as a mold during injection casting of Ni rod at 1450 °C. Surface of the cast Ni was studied for Si as well as yttrium contaminations with EDAX. Raman spectra from a demolded quartz tube (retrieved from casting chamber) revealed characteristic Ag and Fg vibrational modes of cubic Y2O3 phase, indicating good thermal stability and adhesive features of the present coating.

Isotopic Consequences of Host-Guest Interactions; Noncovalent Chlorine Isotope Effects.

Although weak intermolecular interactions are the essence of most processes of key importance in medicine, industry, environment, and life cycles, their characterization is still not sufficient. Enzymatic dehalogenations that involve chloride anion interaction within a host–guest framework is one of the many examples. Recently published experimental results on host–guest systems provided us with models suitable to assess isotopic consequences of these noncovalent interactions. Herein, we report the influence of environmental and structural variations on chlorine isotope effects. We show that these effects, although small, may obscure mechanistic interpretations, as well as analytical protocols of dehalogenation processes.

Pressure-Induced Spin Crossover at Room Temperature in a Nanoporous Host-Guest Framework Structure.

The two-dimensional (2D) metal-organic framework compound Fe2 (azpy)4 (NCS)4 (azpy=trans-4,4'-azopyridine, NCS=thiocyanate) has been pressurized in isopropanol and ethanol that act as guest molecules and pressure-transmitting media. Room temperature conversion of metal-ion sites from high-spin to low-spin states under high-pressure-driven uptake of guest molecules was investigated. Upon isopropanol guest inclusion, spin conversion of ∼66 % low-spin abundance is attained by ∼3 GPa. Spin-crossover progression stimulated by ethanol guest inclusion is more sluggish and ∼56 % low-spin abundance is attained by ∼5.5 GPa. This pressure-facilitated guest-specific triggering of spin crossover is suggestive of guest-molecule interactions with the local coordination network of the Fe(II) core, which increases the ligand field. Appreciable low-spin abundances attained at room temperature upon pressurization, are comparable to maximal ∼50 % spin conversions only attainable below ∼150 K at ambient pressure.

A ternary ZnO/ZnS/MoS2 composite as a reusable SERS substrate derived from the polyoxomolybdate/ZIF-8 host–guest framework

A ternary nanocomposite of ZnMoNCs containing ZnO, ZnS and MoS2 has been synthesized by a facile strategy derived from polyoxometalate and ZIF-8, which shows high SERS activity by increased adsorption sites and synergistically improved charge transfer.

Online friendships in a hospitality exchange network: a sharing economy perspective

Purpose The present study aims to clarify how online friendships between local residents and tourists are made in a hospitality exchange network, one of the not-for-profit sharing economy platforms. Specifically, the study empirically examines three topics: the properties of dyadic relationships in the platform; the effect of face-to-face interactions on online friendships in the platform; and the role of locals in building host-guest relationships in the hospitality exchange network. Design/methodology/approach Social networks data in CouchSurfing.org were collected and analyzed using a social network analysis (SNA) program. Along with the descriptive analysis of the actors in the online hospitality network, several SNA indicators, including the degree of centrality, density and centralization, were measured to explore the nature of the network and identify the gatekeepers. Findings Findings suggest that latent ties between tourists and hosts are likely to be manifested through face-to-face events. In particular, local people play central roles in establishing host-guest relationships. Research limitations/implications This study contributes to the body of knowledge on the sharing economy in hospitality by synthesizing two areas in the literature, the host-guest framework and the online hospitality networks. Originality/value The social psychological aspects of the sharing economy have yet to receive attention from hospitality scholars. In addition, studies have largely focused on profit-driven models in the sharing economy (e.g. Airbnb). This study fills this gap by examining the host and guest behavior empirically in one of the not-for-profit hospitality sharing economy platforms.

Evans-Showell-Type Polyoxometalates Constructing High-Dimensional Inorganic-Organic Hybrid Compounds with Copper-Organic Coordination Complexes: Synthesis and Oxidation Catalysis.

Four new hybrid architectures containing a [Co2Mo10H4O38]6- polyoxoanion, (en)[Cu3(ptz)4(H2O)4][Co2Mo10H4O38]·24H2O (1), (Hbim)2[{Cu(bim)2(H2O)2}2{Co2Mo10H4O38}]·5H2O (2), H2[Cu(dpdo)3(H2O)4][{Cu2(dpdo)3(H2O)4(CH3CN)}2{Co2Mo10H4O38}2]·9H2O (3), and (H2bpp)4[{Cu(H2O)2}{NaCo2Mo10H4O38}2]·10H2O (4), where ptz = 5-(4-pyridyl)-1H-tetrazole, en = ethylenediamine, bim = benzimidazole, dpdo = 4,4'-bipyridine-N,N'-dioxide, and bpp = 1,3-bis(4-pyridyl)propane, have been prepared and characterized through elemental analysis, thermogravimetric analysis, IR spectroscopy, and powder and single-crystal X-ray diffraction. Compound 1 shows a 3D host-guest framework composed of 3D Cu-ptz as the host and Evans-Showell-type polyoxoanion [Co2Mo10H4O38]6- as the guest. Compound 2 is constructed from [Co2Mo10H4O38]6- polyoxoanions and Cu-bim coordination complexes to form a 2D covalent layer. Compound 3 also exhibits a 2D hybrid network based on [Co2Mo10H4O38]6- polyoxoanions linked by Cu-dpdo coordination groups. Compound 4 is a 1D double-chain structure composed of [Co2Mo10H4O38]6- polyoxoanions joined together by Na+ and Cu2+ cations. As far as we know, compound 1 is the first host-guest compound with an Evans-Showell-type polyoxometalate as the guest, and compounds 2 and 3 are the first 2D inorganic-organic hybrid architectures constructed from Evans-Showell-type polyoxometalates. Compounds 1-4 are redox catalysts that heterogeneously prompt sulfide and alcohol oxidation with excellent efficiency.

Recent Rituals of Indigenous Recognition in Australia: Welcome to Country

ABSTRACTIn this article, I examine the recent emergence in Australia of two small, and now regularly enacted, rituals: “Acknowledgments” and “Welcomes to Country.” These are expressions of recognition, or response to perceived neglect and injustice. Recognition has become a global theme, part of a broader politics of reparation focused on indigenous and other colonized and subordinated peoples, and includes practices of apology and reconciliation. In Australia, recognition implies expansion the of relationship between categories of people who have been on unequal, distant, and (at some levels) negligible terms as settlers and natives, colonizers and colonized. Practices of recognition are therefore ambiguous: What is to be recognized, and how is recognition to proceed? Here I consider these rituals and their putative origins, structure, content, variations, and affect of participants and audiences. Both rituals cast recognition in ways that continue recent decades of national emphasis on indigenous emplacement, judgments concerning originariness, and authenticity; “Welcomes” also recast relations in terms of a host–guest framework. The emergence of these rituals fosters new kinds of indigenous public expression and receptions of recognition as well as some standardization of both. It is an indication of change, as well as of its limits in indigenous–nonindigenous relationships.

Dependence of adsorption-induced structural transition on framework structure of porous coordination polymers.

Porous coordination polymers (PCPs) with soft frameworks show a gate phenomenon consisting of an abrupt structural transition induced by adsorption of guest molecules. To understand the dependence of the gating behavior on the host framework structure, we conduct grand canonical Monte Carlo simulations and a free-energy analysis of a simplified model of a stacked-layer PCP. The interlayer width of the rigid layers composing the simplified model can be changed by guest adsorption and by varying the initial interlayer width h0, which is controlled by the length of pillars between the layers. We introduce three types of gating behavior, one-step gating, filling and gating, and double gating, which depend on three parameters: the initial interlayer width h0; the interaction parameter ɛss, which determines the host-guest framework interaction as well as the inter-framework interaction; and the elastic modulus of the framework, which depends on the stiffness of the pillars. We show that the one-step gating and the filling and gating behaviors depend strongly on h0 rather than on ɛss, and thus a transformation from filling and gating to double gating can be achieved by reducing the stiffness of the host framework. This study should be a guideline for controlling the gating pressure of PCPs by modifying their chemical components.

Assembly of new organic–inorganic hybrids based on copper-bis(triazole) complexes and Keggin-type polyoxometalates with different negative charges

Three new organic–inorganic hybrid compounds based on copper-bis(triazole) complexes and Keggin-type polyoxometalates (POMs) with different negative charges, [Cu(I)BBTZ]3[PMo12O40] (1), [Cu(I)BBTZ][Cu(I)(HBBTZ)2][SiMo12O40]·2.5H2O (2) and [Cu(I)BBTZ]6[SiWV2WVI10O40]·2H2O (3) (BBTZ = 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene), have been hydrothermally prepared and characterized by elemental analyses, IR spectra, TG analyses, XPS spectra, powder X-ray diffraction and single-crystal X-ray diffraction analyses. Compounds 1 and 2 exhibit the POM-templated 3D host–guest supramolecular frameworks. Compound 3 displays a POM-supported 3D open framework. In these three hybrid compounds, the structural transformation from host–guest framework to open framework were modulated by the introduction of Keggin-type polyoxoanions with different negative charges. Moreover, the electrochemical properties of compounds 1–3 were investigated and all these compounds show the electrocatalytic activities towards the reduction of nitrite.

New Family of Silver(I) Complexes Based on Hydroxyl and Carboxyl Groups Decorated Arenesulfonic Acid: Syntheses, Structures, and Luminescent Properties

Self-assembly of silver(I) salts and three ortho-hydroxyl and carboxyl groups decorated arenesulfonic acids affords the formation of nine silver(I)-sulfonates, (NH(4))·[Ag(HL1)(NH(3))(H(2)O)] (1), {(NH(4))·[Ag(3)(HL1)(2)(NH(3))(H(2)O)]}(n) (2), [Ag(2)(HL1)(H(2)O)(2)](n) (3), [Ag(2)(HL2)(NH(3))(2)]·H(2)O (4), [Ag(H(2)L2)(H(2)O)](n) (5), [Ag(2)(HL2)](n) (6), [Ag(3)(L3)(NH(3))(3)](n) (7), [Ag(2)(HL3)](n) (8), and [Ag(6)(L3)(2)(H(2)O)(3)](n) (9) (H(3)L1 = 2-hydroxyl-3-carboxyl-5-bromobenzenesulfonic acid, H(3)L2 = 2-hydroxyl-4-carboxylbenzenesulfonic acid, H(3)L3 = 2-hydroxyl-5-carboxylbenzenesulfonic acid), which are characterized by elemental analysis, IR, TGA, PL, and single-crystal X-ray diffraction. Complex 1 is 3-D supramolecular network extended by [Ag(HL1)(NH(3))(H(2)O)](-) anions and NH(4)(+) cations. Complex 2 exhibits 3-D host-guest framework which encapsulates ammonium cations as guests. Complex 3 presents 2-D layer structure constructed from 1-D tape of sulfonate-bridged Ag1 dimers linked by [(Ag2)(2)(COO)(2)] binuclear units. Complex 4 exhibits 3-D hydrogen-bonding host-guest network which encapsulates water molecules as guests. Complex 5 shows 3-D hybrid framework constructed from organic linker bridged 1-D Ag-O-S chains while complex 6 is 3-D pillared layered framework with the inorganic substructure constructing from the Ag2 polyhedral chains interlinked by Ag1 dimers and sulfonate tetrahedra. The hybrid 3-D framework of complex 7 is formed by L3(-) trianions bridging short trisilver(I) sticks and silver(I) chains. Complex 8 also presents 3-D pillared layered framework, and the inorganic layer substructure is formed by the sulfonate tetrahedrons bridging [(Ag1O(4))(2)(Ag2O(5))(2)](∞) motifs. Complex 9 represents the first silver-based metal-polyhedral framework containing four kinds of coordination spheres with low coordination numbers. The structural diversities and evolutions can be attributed to the synthetic methods, different ligands and coordination modes of the three functional groups, that is, sulfonate, hydroxyl and carboxyl groups. The luminescent properties of the nine complexes have also been investigated at room temperature, especially, complex 1 presents excellent blue luminescence and can sensitize Tb(III) ion to exhibit characteristic green emission.

Towards docking-based prediction of host-guest framework systems

Towards docking-based prediction of host-guest framework systems

The “host” as uninvited “guest”: Hospitality, Violence and Tourism

The article explores the outsider status of handicraft traders in a tourism center in India. It demonstrates that they are seen as hosts by international tourists, and may even enact this role. But they are subjected to various forms of violence and exploitation by local landlords who, like many local residents, see them as uninvited outsiders rather than as guests. It is argued that the host-guest framework is inadequate for developing a more nuanced understanding of such interactions on the front line of international tourism. For the sense of welcome and hospitality that underwrites these interactions serves to depoliticize what are often highly exploitative relations.

Solvent provides a trap for the guest-induced formation of 1D host frameworks based upon supramolecular, deep-cavity resorcin[4]arenes

Co-crystallization of C-methylcalix[4]resorcinarene 1 with 4,4'-bipyridine 2 from ethanol in the presence of either an aromatic or a polycyclic guest yields a wave-like host-guest framework 3.guest {where 3 = 1.2(2), guest = p-chlorotoluene, adamantanone, [2.2]paracyclophane} in which 3 forms by way of guest template effects

Formation of isolated guest dimers vs. host-guest coordination. X-Ray crystal structures of four carboxylic acid inclusion compounds formed by roof-shaped and scissor-like host molecules

The crystal structures of the inclusion compounds oftrans-9,10-dihydro-9,10-ethano-anthracene-11,12-dicarboxylic acid host (1) with formic acid (1a), acetic acid (1b), and propionic acid (1c) as guests, and of the coordinatoclathrate of the 1,1′-binaphthyl-2,2′-dicarboxylic acid host (2) with acetic acid as guest (2b) have been studied by single crystal X-ray diffraction. These studies show that inclusion of small carboxylic acids by carboxylic acid hosts like1 and2 results in formation of isolated, hydrogen-bonded guest dimers. Additional H-bond contacts between host and guest carboxylic groups are only formed in cases1a and2b. The dimeric acidic guest units are sitting in the cavities of the host or host-guest framework and have no other interactions than those of a weak Van der Waals' type with the neighbouring molecules. Crystal data:1·formic acid (1:2): triclinic (PĪ),a = 11.6769(6),b = 9.4067(4),c = 9.0020(4) A,a = 81.522(4), β = 100.310(6), γ = 104.208(6)°,Z = 2,R = 0.048 for 2392 reflections;1·acetic acid (1:1): monoclinic (P21/n),a = 9.717(2),b = 14.462(2),c = 13.038(3)A, β = 104.27(1)°,Z=4,R=0.046 for 3042 observations;1·propionic acid (1:1): monoclinic (P21/n),a = 9.897(4),b = 14.671(7),c = 13.284(7) A, β = 105.92(6)°,Z = 4,R = 0.056 for 2302 reflections;2·acetic acid (2:3): triclinic (PĪ),a = 12.746(1),b = 17.781(2),c = 11.010(1) A, α = 105.606(4), β = 112.992(8), γ = 81.175(6)°,Z = 2,R = 0.067 for 4375 observations.