Defects engineering simultaneously enhances activity and recyclability of MOFs in selective hydrogenation of biomass.

The development of synthetic methodologies towards enhanced performance in biomass conversion is desirable due to the growing energy demand. Here we design two types of Ru impregnated MIL-100-Cr defect engineered metal-organic frameworks (Ru@DEMOFs) by incorporating defective ligands (DLs), aiming at highly efficient catalysts for biomass hydrogenation. Our results show that Ru@DEMOFs simultaneously exhibit boosted recyclability, selectivity and activity with the turnover frequency being about 10 times higher than the reported values of polymer supported Ru towards D-glucose hydrogenation. This work provides in-depth insights into (i) the evolution of various defects in the cationic framework upon DLs incorporation and Ru impregnation, (ii) the special effect of each type of defects on the electron density of Ru nanoparticles and activation of reactants, and (iii) the respective role of defects, confined Ru particles and metal single active sites in the catalytic performance of Ru@DEMOFs for D-glucose selective hydrogenation as well as their synergistic catalytic mechanism.

Single-Metallic Thermoresponsive Coordination Network as a Dual-Parametric Luminescent Thermometer.

The single-metallic coordination networks (CNs), simultaneously exhibiting temperature-dependent lifetime (TDLT) and emission band shift (TDEBS), are desirable for application in luminescent thermometers with high accuracy and reliability in a large temperature range. Nonetheless, up to date, there are no reports on such kinds of materials due to the lack of in-depth understanding of the origin of TDLT and TDEBS at a molecule level, being critical for exploiting a universal approach to design a dual-parametric CN phosphorescent thermometer (CN-PT). Herein, we have constructed a thermoresponsive CN [Cu2(L1)Br2]∞ (IAM21-1, L1 = N1,N6-di(pyridin-3-yl)adipamide) via a flexible-ligand-implanted strategy. The TDLT and TDEBS properties of IAM21-1 enable it to be applied as a single-metallic dual-parametric CN-PT in 50-500 K, which is the widest temperature range reported so far. The combination of structure analysis and DFT calculations demonstrates that the redshift of the emission band upon the decreasing temperature originates from the reversible skeleton-shrinkage-triggered narrower band gap. This work has unveiled the origin of TDLT and TDEBS properties and proposed an efficient strategy for designing dual-parametric CN-PTs.

The effect of surface-capping oleic acid on the optical properties of lanthanide-doped nanocrystals.

The rapid development of nanotechnology has placed a higher demand on the synthesis of nanomaterials. Benefiting from its capability to keep nanoparticles away from aggregation, oleic acid (OA) has been routinely utilized as a capping agent in the synthesis of monodisperse nanocrystals. To satisfy downstream biological applications, hydrophobic OA capping on the surface should be removed or coated, but scarce attention has been paid to its influence on the optical properties of nanocrystals. In this work, the effect of surface-capping OA has been systematically explored on the optical properties of lanthanide-doped upconversion and downshifting nanocrystals, respectively. The emission intensity and lifetime of emissive lanthanides have been compared between OA-capped and ligand-free nanocrystals either in solid state or in colloidal solution. In solid state, surface-capping OA can significantly influence both emission intensity and radiative transition possibility of emissive lanthanides. However, in colloidal solution, a distinct variation between OA-capped and ligand-free nanocrystals is observed. Besides, the effect of OA on the luminescence dynamics of lanthanides with different energy gaps (emitting level to the next-lower-energy level) has been investigated in colloidal solution. The possible mechanism for the effect of OA on the optical properties of lanthanide-doped nanocrystals has been further proposed.

Single-Irradiation Simultaneous Dual-Modal Bioimaging Using Nanostructure Scintillators as Single Contrast Agent.

The rising demand for clinical diagnosis tools has led to extensive research on multimodal bioimaging systems. Unlike single-modal detection, multimodal imaging not only can provide both function and structure information but also can address the issue of sensitivity, depth, and cost. Despite enormous efforts, conventional step-by-step procedures for obtaining multimodal imaging pose a significant constraint on their practical applications. In this work, X-rays as highly penetrating radiation is proposed as a single-irradiation resource, while lanthanide-based nanostructure scintillators are employed as the single contrast agent to attenuate and convert X-rays, achieving computer tomography (CT) and optical dual-modal imaging at the same time. In other words, CT and optical dual-modal imaging are simultaneously produced via single radiation combined with single contrast agent. The function and structure information of targeted tumors in a mouse model can be clearly provided with large penetration and high sensitivity, indicating that this strategy is a simple but promising route for multimodal imaging of molecular disease and preclinical applications.

Intentional anion incorporation to rationally modulate the size, shape and optical properties of lanthanide oxide nanocrystals.

Incorporating impure foreign atoms or ions has been extensively utilized in materials science for generating hybrid materials with desirable properties and functions. Despite most materials consisting of cations and anions, conventional routes only focus on incorporating cations. In this work, we proposed an intentional impure anion incorporation strategy as a facile and straightforward route to adjust the properties of yielded nanocrystals. Via incorporating diverse anions, the size, morphology, uniformity and optical properties of lanthanide oxide nanocrystals could be rationally tuned. Furthermore, the obtained nanocrystals could further serve as a bioprobe for imaging deep tissue.

Thinning shell thickness of CuInS2@ZnS quantum dots to boost detection sensitivity.

Quantum dots (QDs), drawing large attention during the past three decades, have been extensively applied in lighting, display, and biodetection. However, the mechanism for their ability in biodetection, especially in recognizing toxic metal ions, has scarcely been explored. In this work, three sets of CuInS2@ZnS QDs systems with inert shell thickness varying from 1.1 to 4.1 nm have been performed. As the shrinkage of inert shell, QDs not only show red-shift emission but also demonstrate more sensitive and higher response to the added Cd2+. The thin-shell CuInS2@ZnS QDs could detect 0.91 nM Cd2+, and could further detect 4.36 nM Cd2+ when integrated with paper-based platform. Importantly, thin-shell CuInS2@ZnS QDs combined with paper-based platform can detect 105.86 nM Cd2+ even just applying mobile phone as detector and hand-held UV lamp as excitation resource. The mechanism is further proposed based on the energy transfer routes. The thin inert shell can not completely protect the emissive core away from the surface defects, but it can neither exclude the energy transfer from the surface to the emissive core. The added Cd2+ would facilitate the formation of CdS on the surface of QDs, which not only can alleviate the surface defects but also can transfer energy to emissive CuInS2, thus thinning the thickness of inert shell greatly boost the detection sensitivity.

A Series of Lanthanide-Based Metal-Organic Frameworks: Synthesis, Structures, and Multicolor Tuning of Single Component.

The single component (SC) white-light emitting (WLE) metal-organic frameworks based on europium (Eu-MOFs), which could be applied in lighting and display, have drawn great attention but have rarely been exploited. In this work, we dedicated to design and synthesize SC-WLE Eu-MOFs via a dichromatic strategy on the balance of simultaneous ligand-based and Eu-based emissions. The Eu-MOF {[Eu4(obb)6(H2O)9]·(H2O)}∞ (IAM16-3) generated via the self-assembly of the flexible ligand 4,4'-oxybisbenzoic acid (H2obb) and europium ions displays fascinating excitation-wavelength-dependent photoluminescence (EWDP) property. Upon different excitation wavelengths, tunable WLE through manipulating the intensity ratio of characteristic emissions of Eu3+ ions and ligand-based emissions was performed. To the best of our knowledge, this is the first example for Eu-MOFs to yield SC-WLE stemming from EWDP property. Three isomorphic lanthanide-based MOFs (LnMOFs), that is, {[Ln4(obb)6(H2O)9]·(H2O)}∞ (Eu3+: IAM16-3; Tb3+: IAM16-4; Dy3+: IAM16-5) based on the flexible bridging linker, that is, 4,4'-oxybisbenzoic acid (H2obb), were obtained. The Eu-MOF, showing with EWDP property, is the first example of SC WLE Eu-MOFs via a dichromatic strategy on the balance of the simultaneous ligand-based and Eu(III)-based emissions at different excitation wavelengths.

Two Silver Coordination Network Compounds with Colorful Photoluminescence.

The excitation-wavelength-dependent photoluminescence (EWDP) property of flexible organic ligand 1,4-bis(2-methyl-imidazol-1-yl)butane (Bmib) was observed. Herein, Bmib was chosen as a bridge linker to react with AgX (X = Br and I) to synthesize novel coordination network compounds (CNCs) with interesting EWDP properties. As anticipated, under the same hydrothermal synthesis conditions, two new isomorphic CNCs, i.e. [Ag2(Bmib)Br2]∞ (IAM16-1) and [Ag2(Bmib)I2]∞ (IAM16-2), as the first examples of CNCs showing EWDP properties, have been obtained. The EWDP properties may be attributed to the stretch and rotation of the long -(CH2)4- chains of Bmib and the spatial orientation adjustment of the methyl group of each imidazole ring at different excitation wavelengths. It is a great challenge to point out the emission mechanisms of CNCs merely from the experimental results due to their multiple charge transfer routes. To address this issue, we adopt DFT calculations to pursue in-depth investigation of the emission mechanisms for IAM16-1 and IAM16-2, respectively.

Defect-Engineered Metal-Organic Frameworks.

Defect engineering in metal-organic frameworks (MOFs) is an exciting concept for tailoring material properties, which opens up novel opportunities not only in sorption and catalysis, but also in controlling more challenging physical characteristics such as band gap as well as magnetic and electrical/conductive properties. It is challenging to structurally characterize the inherent or intentionally created defects of various types, and there have so far been few efforts to comprehensively discuss these issues. Based on selected reports spanning the last decades, this Review closes that gap by providing both a concise overview of defects in MOFs, or more broadly coordination network compounds (CNCs), including their classification and characterization, together with the (potential) applications of defective CNCs/MOFs. Moreover, we will highlight important aspects of "defect-engineering" concepts applied for CNCs, also in comparison with relevant solid materials such as zeolites or COFs. Finally, we discuss the future potential of defect-engineered CNCs.

Structural complexity in metal-organic frameworks: simultaneous modification of open metal sites and hierarchical porosity by systematic doping with defective linkers.

A series of defect-engineered metal-organic frameworks (DEMOFs) derived from parent microporous MOFs was obtained by systematic doping with defective linkers during synthesis, leading to the simultaneous and controllable modification of coordinatively unsaturated metal sites (CUS) and introduction of functionalized mesopores. These materials were investigated via temperature-dependent adsorption/desorption of CO monitored by FTIR spectroscopy under ultra-high-vacuum conditions. Accurate structural models for the generated point defects at CUS were deduced by matching experimental data with theoretical simulation. The results reveal multivariate diversity of electronic and steric properties at CUS, demonstrating the MOF defect structure modulation at two length scales in a single step to overcome restricted active site specificity and confined coordination space at CUS. Moreover, the DEMOFs exhibit promising modified physical properties, including band gap, magnetism, and porosity, with hierarchical micro/mesopore structures correlated with the nature and the degree of defective linker incorporation into the framework.

PH-controlled construction of Cu(I) coordination polymers: in situ transformation of ligand, network topologies, and luminescence and UV-vis-NIR absorption properties.

Two new complexes [Cu(I)(3)(L1)I(3)](n) (1, L1 = 2,5-bis(4-pyridyl)-1,3,4-oxadiazole) and [Cu(I)(3)(L2)I(2)](n) (2, L2 = 2,5-bis(4-pyridyl)-1,2,4-triazolate) are controllably formed by using aqueous ammonia to regulate the pH value of the reaction involving CuI and L1. Interestingly, L2 of 2 is in situ generated from the ring transform of L1 when increase the pH value of the reaction. 1 exhibits 2-D layer, while 2 shows 3-D MOFs with a novel 3-nodal 4,4,5-connected net topology of an unprecedented Point (Schlafli) symbol: (4·5(2)·6(2)·7)(5(4)·8(2))(4(3)·5·6(6)). Although both 1 and 2 are built of CuI and similar ligands, different arrangements of CuI chains and ligands endow them with different physical properties. 1 displays a strong pure red luminescence emission, while 2 is nonluminescent and shows a broad absorption band covering the whole UV-vis-NIR spectrum range. The emissive excited states of 1 and the charge transitions of the optical absorption for 2 are solved by DFT calculations.

Structural, luminescent, and magnetic properties of three novel three-dimensional metal-organic frameworks based on hexadentate N,N'-bis(4-picolinoyl)hydrazine.

Three novel microporous three-dimensional (3-D) metal-organic framework materials [ML](n) [M = Ni, Co, Cd; L = N,N'-bis(4-picolinoyl)hydrazine] were obtained from hydrothermal reactions. The organic ligand L was formed through the in situ ring-opening hydrolysis reaction of 2,5-bis(4-pyridyl)-1,3,4-oxadiazole with the assistance of metal ions. Single-crystal X-ray diffraction studies reveal that complexes 1-3 adopt 6-connected 3-D networks of distorted alpha-Po topology, which are built from non-interpenetrated (4,4) grids cross-linked by zigzag chains. These isomorphic complexes are all of high thermal stability, but some other physical properties are quite different because of their different metal centers. Antiferromagnetic exchange was observed between Ni(II) centers of complex 1, while ferromagnetic for Co(II) centers of complex 2. Complex 3 exhibits strong fluorescence emission.