We demonstrate how a single-crystal to single-crystal transformation resulting from bridging-linker replacement is possible in extended 2D and 3D metal–organic frameworks (MOFs) by introducing ...pillared paddlewheel MOF structures into a solution containing dipyridyl linkers. No lateral movement of the layers was observed during this transformation, creating a templating effect from the “parent” structure to the “daughter” structure. A previously unattainable structure was obtained by a two-step synthetic method utilizing the bridging-linker replacement transformation method. Additionally, a bridging-linker insertion was observed when excess linker was used with the 2D MOF structure, inducing an overall 2D to 3D transformation.
The expanded compositional freedom afforded by high-entropy alloys (HEAs) represents a unique opportunity for the design of alloys for advanced nuclear applications, in particular for applications ...where current engineering alloys fall short. This review assesses the work done to date in the field of HEAs for nuclear applications, provides critical insight into the conclusions drawn, and highlights possibilities and challenges for future study. It is found that our understanding of the irradiation responses of HEAs remains in its infancy, and much work is needed in order for our knowledge of any single HEA system to match our understanding of conventional alloys such as austenitic steels. A number of studies have suggested that HEAs possess `special' irradiation damage resistance, although some of the proposed mechanisms, such as those based on sluggish diffusion and lattice distortion, remain somewhat unconvincing (certainly in terms of being universally applicable to all HEAs). Nevertheless, there may be some mechanisms and effects that are uniquely different in HEAs when compared to more conventional alloys, such as the effect that their poor thermal conductivities have on the displacement cascade. Furthermore, the opportunity to tune the compositions of HEAs over a large range to optimise particular irradiation responses could be very powerful, even if the design process remains challenging.
Purpose - The aim of this paper is to explore one of the biggest issues and challenges now faced by hospitality education and the hospitality industry: that of how to attract and retain a critical ...group of talented people.Design methodology approach - A review of the literature highlights the key studies that have investigated the nature of hospitality employment amongst new recruits in the hospitality industry and reports on thoughts of soon to graduate hospitality students. The paper reviews the current state of employment issues in the hospitality industry. It discusses contemporary attitudes toward the generation undertaking hospitality education and making career decisions. This paper also considers the current generation's specific attitudes toward education and careers and the potential consequences this will have for the hospitality industry in the future.Findings - The paper argues that educators require to be more fully aware of the consequences of reducing the practical and vocational nature of programmes and that adjustments to the management and administration of programmes are essential to allow students to complete programmes.Originality value - The paper creates the basis for a discussion on how best to handle these issues so that organizations within the hospitality industry can successfully recruit, select, train, retain and motivate future talent.
Focussing on a particular Swiss Hotel School, this research evaluates the student acceptance and overall effectiveness of the flipped classroom approach. The paper aims to evaluate the preference of ...adopting such an approach as the main teaching method for a range of undergraduate and postgraduate hospitality focused programmes and develop an understanding of students’ awareness of the flipped method. Adopting a quantitative approach, 167 students took part in this study and specifically provided their perspectives of the flipped classroom approach, compared it with a more traditional teaching method and identified the benefits and drawbacks of flipped learning. The findings of the study suggest that students appreciate the reversed classroom as it appears that learners felt safe, engage, and motivated in a student-oriented environment under the guidance of a teacher. However, respondents also highlighted the importance of appropriate guidance and facilitation of the flipped classroom as well as recognising the additional engagement in material prior to attending class.
We report three new porphyrin-based, pillared paddle-wheel homologous series: porphyrin paddle-wheel frameworks PPF-3, -4, and -5. These compounds are assembled from free base or palladium ...tetrakis(4-carboxyphenyl)porphine, M(NO3)2 (M = Co and Zn), and 4,4′-bipyridine via solvothermal reactions. The resulting solids exhibit 3D metal−organic frameworks, where 2D layers are pillared by bipyridine with three different packing arrangements.
A thermoresponsive, 3D hinged metal–organic framework (HMOF-1) assembled from meso-tetra(4-pyridyl)porphine and CdI2 exhibits a 3D “lattice fence” topology with extraordinary thermal expansion and ...shrinkage. A simple structural model is established to elucidate such a drastic thermal response. The hinged structure model presented here can also be applied to other “lattice fence” topologies with little or no modification, depending on the symmetry of the molecular building blocks.
A new series of porphyrin paddlewheel frameworks (PPFs) has been assembled from 5,10,15,20-tetrakis(4-carboxyl)-21H,23H-porphine (TCPP), Zn(NO3)2·6H2O, and organic pillars such as ...N,N′-di-(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide (DPNI) and 3,6-di-4-pyridyl-1,2,4,5-tetrazine (DPT). Here we report the synthesis and structural characterization of five new PPFs based on 2D porphyrin paddlewheel grid. In this homologous series, the stacking patterns of such 2D porphyrin sheets are varied and exhibit two new structures, namely, bilayer and interpenetrated AA stacking pattern, in addition to the ABBA pattern previously observed.
Seven new heterometallic frameworks have been synthesized with specific control over the metallic composition of each structure. Using Mn, Fe, Ni, V, and Pt metallated tetra-(4-carboxyphenyl)porphine ...(MTCPP) metalloligands and Zn and Co paddle-wheel building units, two series of heterometallic frameworks are assembled that maintain topology with changing metal composition.
We demonstrate how a bioinspired synthetic approach can help organic linkers distinguish between different types of metal centers in metal−organic frameworks (MOFs). Modification of an organic ...building unit with methyl groups enables the unit to selectively coordinate to one of the two metal sites present in the MOFs. We report four new porphyrin-based, pillared-paddlewheel frameworks: PPF-11-Zn/Zn, -Co/Co, -Mn/Zn, and -Fe/Zn, where the first and second metals indicate the metal center for the porphyrin core and paddlewheel cluster, respectively. These compounds exhibit 3D MOFs in which 2D layers are pillared by a sterically controlled bipyridine, leaving the metal centers inside the porphyrin structurally unconnected.
The UV−vis spectra, emission spectra and lifetimes, transient absorption characteristics, and optical limiting performances of three binuclear cyclometalated platinum(II) 4,6-diphenyl-2,2‘-bipyridine ...complexes with bis(diphenylphosphino)methane (dppm), bis(diphenylphosphino)ethane (dppe), and bis(diphenylphosphino)propane (dppp) bridging ligands have been investigated. All three complexes exhibit concentration-dependent photoluminescence in CH3CN at room temperature and 77 K, and the emission energy is affected by the length of the bridging ligand. Pt2L2(μ-dppm)(ClO4)2 (1) (L = 4,6-diphenyl-2,2‘-bipyridine) shows a broad, structureless emission band at about 667 nm when the complex concentration is higher than 6.0 × 10-5 mol/L, which can be attributed to a 3dσ*,π* state due to metal−metal interactions. Pt2L2(μ-dppe)(ClO4)2 (2) and Pt2L2(μ-dppp)(ClO4)2 (3) essentially exhibit no metal−metal interactions between the two platinum centers, and their emission can be ascribed to a 3MLCT (metal-to-ligand charge transfer) excited state. The emission lifetime is approximately 200 ns for 1 at 1.2 × 10-4 mol/L, ∼1.5 μs for 2 at 1.4 × 10-4 mol/L, and ∼2.0 μs (68%) and ∼0.4 μs (32%) for 3 at 1.3 × 10-4 mol/L. All complexes show moderately intense, broad positive transient difference absorption bands from near-UV and extending to near-IR spectral regions. The nonlinear transmission experiment at 532 nm using 4.1 ns laser pulses demonstrates that 2 and 3 exhibit stronger optical limiting for nanosecond laser pulses than SiNc, which is likely associated with their very low ground-state absorption cross sections and relatively long triplet excited-state lifetimes (approximately microseconds).
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