No abstract

By using GdO, propanedioic acid (Hpda) and oxalic acid (Hox), a new Gd-based metal-organic framework (MOF) [Gd(pda)(ox)(HO)] (1) has been successfully constructed and structurally characterized. Interestingly, temperature- and vapor-induced reversible single-crystal-to-single-crystal transformations occurred and two new MOFs, namely [Gd(pda)(ox)(HO)] (1a) and [Gd(pda)(ox)] (1b), have been obtained. Complex 1 displays a two-dimensional (2D) layer structure composed of zigzag [Gd(pda)] chains and it could also be made up of numerous Gd macrocycles. Thermal dehydration leads to more complicated three-dimensional (3D) 'pillar-layer' structures (1a and 1b) with the same coordination mode of pda anions. Magnetic studies suggest the presence of ferromagnetic couplings between the intrachain or intralayer Gd ions and large magnetocaloric effects (MCEs) with -ΔS = 45.0 J kg K (1), 46.1 J kg K (1a) and 46.8 J kg K (1b) under a 7 T applied field. Therefore, the interest of 'robust magnetocaloric MOFs' is now extended to compounds showing weak ferromagnetic couplings and hence having better magnetocaloric performances for small field changes.

(3 of 32)www.advmatinterfaces.de compositions are exposed (theoretically and/or experimentally) and many more MXenes can be discovered by varying rations of M or X elements and their discoveries are ongoing, especially with 413 MAX type [54] (Figure 1a,b).

Both theory and experiment show that sp 2 carbon nanomaterials doped with N have great potential as high-efficiency catalysts for oxygen reduction reactions (ORR). At present, there are theoretical studies that believe that C-sites with positive charge or high-spin density values have higher adsorption capacity, but there are always some counter examples, such as the N-doped graphene nanoribbons with edge defects (ND-GNR) of this paper. In this study, the ORR mechanism of ND-GNR was studied by density functional theory (DFT) calculation, and then the carbon ring resonance energy was analyzed from the perspective of chemical graph theory to elucidate the cause and distribution of active sites in ND-GNR. Finally, it was found that the overpotential of the model can be adjusted by changing the width of the model or dopant atoms while still ensuring proper adsorption energy (between 0.5 and 2.0 eV). The minimum overpotential for these models is approximately 0.36 V. These findings could serve as guidelines for the construction of efficient ORR carbon nanomaterial catalysts.

A theoretical explanation of a time-to-failure relation is presented, with this relationship then used to describe the failure of materials. This provides the potential to predict timing (tf − t) immediately before failure by extrapolating the trajectory as it asymptotes to zero with no need to fit unknown exponents as previously proposed in critical power law behaviors. This generalized relation is verified by comparison with approaches to criticality for volcanic eruptions and creep failure. A new relation based on changes with stress is proposed as an alternative expression of Voight’s relation, which is widely used to describe the accelerating precursory signals before material failure and broadly applied to volcanic eruptions, landslides and other phenomena. The new generalized relation reduces to Voight’s relation if stress is limited to increase at a constant rate with time. This implies that the time-derivatives in Voight’s analysis may be a subset of a more general expression connecting stress derivatives, and thus provides a potential method for forecasting these events.

Understanding the intermolecular interactions in the context of crystal packing is of fundamental significance in molecular materials science. Infrared (IR) spectroscopy can provide complementary structural information; however, it still remains a great challenge to accurately predict the molecular IR vibrations in the crystalline phase. Here we report a cluster-model approach to simulate the IR spectra of triazine-based molecular crystals via density functional theory (DFT) calculations. In the properly designed cluster models, the molecular IR vibrations are expressed by a representative unit, while the nearest-neighbouring molecules are treated as a "frozen shell" to mimic the surrounding crystallographic environments. Much smaller clusters can be built by considering the crystallographic equivalence in the unit cell, which are able to perform DFT calculations on more complicated crystal structures with endurable computational costs. The simulated spectra show excellent consistencies with the experimental ones, particularly providing an in-depth understanding of the vibrational modes closely related to hydrogen bonding. Most importantly, the selectively built clusters based on the crystallographically independent molecules in the unit cell allow us to perform specific IR-spectral simulations, by which their distinct hydrogen-bonding environments have been clearly revealed for the first time.

Development of efficient bifunctional electrocatalysts for reversible oxygen reduction (ORR) and oxygen evolution reactions (OER) are of prime importance in rechargeable metal-air batteries. In this work, a relatively unexplored and...

No abstract