Framework Building Blocks Research Articles

Tunable Interlayer Interactions in Exfoliated 2D van der Waals Framework Fe(SCN)2(Pyrazine)2.

2D materials can be isolated as monolayer sheets when interlayer interactions involve weak van der Waals forces. These atomically thin structures enable novel topological physics and open chemical questions of how to tune the structure and properties of the sheets while maintaining them as isolated monolayers. Here, this work investigates 2D electroactive sheets that exfoliate in solution into colloidal nanosheets, but aggregate upon oxidation, giving rise to tunable interlayer charge transfer absorption and photoluminescence. This optical behavior resembles interlayer excitons, now intensely studied due to their long-lived emission, but which remain difficult to tune through synthetic chemistry. Instead, the interlayer excitons of these framework sheets can be modulated through control of solvent, electrolyte, oxidation state, and the composition of the framework building blocks. Compared to other 2D materials, these framework sheets display the largest known interlayer binding strengths, attributable to specific orbital interactions between the sheets, and among the longest interlayer exciton lifetimes. Taken together, this study provides a microscopic basis for manipulating long-range opto-electronic behavior in van der Waals materials through molecular synthetic chemistry.

Integration of STING activation and COX-2 inhibition via steric-hindrance effect tuned nanoreactors for cancer chemoimmunotherapy

Integrating immunotherapy with nanomaterials-based chemotherapy presents a promising avenue for amplifying antitumor outcomes. Nevertheless, the suppressive tumor immune microenvironment (TIME) and the upregulation of cyclooxygenase-2 (COX-2) induced by chemotherapy can hinder the efficacy of the chemoimmunotherapy. This study presents a TIME-reshaping strategy by developing a steric-hindrance effect tuned zinc-based metal-organic framework (MOF), designated as CZFNPs. This nanoreactor is engineered by in situ loading of the COX-2 inhibitor, C-phycocyanin (CPC), into the framework building blocks, while simultaneously weakening the stability of the MOF. Consequently, CZFNPs achieve rapid pH-responsive release of zinc ions (Zn2+) and CPC upon specific transport to tumor cells overexpressing folate receptors. Accordingly, Zn2+ can induce reactive oxygen species (ROS)-mediated cytotoxicity therapy while synchronize with mitochondrial DNA (mtDNA) release, which stimulates mtDNA/cGAS-STING pathway-mediated innate immunity. The CPC suppresses the chemotherapy-induced overexpression of COX-2, thus cooperatively reprogramming the suppressive TIME and boosting the antitumor immune response. In xenograft tumor models, the CZFNPs system effectively modulates STING and COX-2 expression, converting “cold” tumors into “hot” tumors, thereby resulting in ≈ 4-fold tumor regression relative to ZIF-8 treatment alone. This approach offers a potent strategy for enhancing the efficacy of combined nanomaterial-based chemotherapy and immunotherapy.

Photoinduced Electron Transfer in Multicomponent Truxene-Quinoxaline Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) can respond to light in a number of interesting ways. Photochromism is observed when a structural change to the framework is induced by the absorption of light, which results in a color change. In this work, we show that introducing quinoxaline ligands to MUF-7 and MUF-77 (MUF = Massey University Framework) produces photochromic MOFs that change color from yellow to red upon the absorption of 405 nm light. This photochromism is observed only when the quinoxaline units are incorporated into the framework and not for the standalone ligands in the solid state. Electron paramagnetic resonance (EPR) spectroscopy shows that organic radicals form upon irradiation of the MOFs. The EPR signal intensities and longevity depend on the precise structural details of the ligand and framework. The photogenerated radicals are stable for long periods in the dark but can be switched back to the diamagnetic state by exposure to visible light. Single-crystal X-ray diffraction analysis reveals bond length changes upon irradiation that are consistent with electron transfer. The multicomponent nature of these frameworks allows the photochromism to emerge by allowing through-space electron transfer, precisely positioning the framework building blocks, and tolerating functional group modifications to the ligands.

Recent Advances in Crystalline Oxidopolyborate Complexes of d-Block or p-Block Metals: Structural Aspects, Syntheses, and Physical Properties.

Crystalline materials containing hybrid inorganic–organic metal borates (complexes with oxidoborate ligands) display a variety of novel framework building blocks. The structural aspects of these hybrid metallaoxidoborates containing Cd(II), Co(II), Cu(II), Ga(III), In(III), Mn(II), Ni(II) or Zn(II) metal centers are discussed in this review. The review describes synthetic approaches to these hybrid materials, their physical properties, their spectroscopic properties and their potential applications.

Pore Tuning of Metal‐Organic Framework Membrane Anchored on Graphene‐Oxide Nanoribbon

AbstractAlthough the pore structures and gas transport properties of metal‐organic frameworks (MOFs) have been tuned mainly by modifying the framework building blocks, a pore‐tuned zeolitic imidazolate framework (ZIF)‐8 layer is directly grown on graphene oxide nanoribbons (GONR)‐treated polymer substrate. Oxygen‐containing functional groups and GONR dangling‐carbon bonds facilitated the spontaneous growth of ZIF‐8 oriented to the (100) grain on the GONR surface and also enhanced the rigidity by strongly anchoring the ZIF‐8 layer by metal‐carbon chemisorption. Gas permeation and molecular simulation results confirmed that the effective aperture size of ZIF‐8 is adjusted to 3.6 Å. As a result, ultrafast H2 permeance of 7.6 × 10−7 mol m−2 Pa s is achieved while blocking large hydrocarbon molecules. In particular, the membrane showed exceptionally enhanced hydrogen selectivity for the mixture separation than ideal selectivity, owing to the competitive transport between H2 and large hydrocarbon molecules, and the separation performance surpassed those of ZIF membranes previously fabricated on polymeric supports.

Photoresponsive Organic-Inorganic Hybrid Ferroelectric Designed at the Molecular Level.

Molecular ferroelectrics are becoming an important area of research due to their ability to form a variety of structures exhibiting the desired properties. However, the precise control over the assembly of molecular building blocks for the design and synthesis of photoresponsive molecular ferroelectrics remains a considerable challenge. Here, we report a new hybrid high-temperature ferroelectric, (Me2NH2)[NaFe(CN)5(NO)], by judiciously assembling inorganic photochromic nitroprusside anion, as the framework building block, and polar organic cation Me2NH2+, as the dipole-moment carrier, into the crystal lattice. Ferroelectricity arises through the synergetic ordering of Me2NH2+ below 408 K. Piezoresponse force microscopy witnessed the presence of 180° ferroelectric domains and evidenced polarization switching by repeatedly applying an external electric field. Irradiation of the N-bound nitrosyl ligand (ground state) leads to two different conformations: isonitrosyl O-bound (metastable state I) and side-on nitrosyl conformation (metastable state II). Such photoisomerization realized in solid-state molecular ferroelectrics allows for the photoswitching between the ferroelectric ground state and the metastable state. These results pave the way for new design approaches toward developing next-generation photostimulated ferroelectric materials at the molecular level.

Synthesis and characterization of lanthanide metal-organic framework with perylene 3,4,9,10-tetracarboxylate ligand

Metal-organic framework (MOF) as a semiconductor material has unique properties and potency to be utilized as a photocatalyst. The superiority of MOF compared to other semiconductor materials is due to the more possibility of adjusting its structure and properties by varying the metal type and organic ligand as the linker to create various framework building blocks, for a number of different applications. In this study, MOFs composed of lanthanide metals (samarium and dysprosium) and PTC ligand (perylene-3,4,9,10-tetracarboxylate), were synthesized and their structural and photochemical properties were characterized. MOFs synthesis were carried out using solvothermal method at 170 ºC, with the variation of metal to ligand mole ratio of 1:1, 2:1 and 1:2 for each metal. FT-IR characterization indicates that in all samples of MOF, PTC ligands coordinate with metals in bidentate ligand mode, which is supported by the existence of peak at around 1770 cm−1 that resembles stretching vibration peak of conjugated C=O anhydride. XRD characterization reveals a quite good crystalline phase in at least two samples, which are Sm-PTC MOF (1:1) and Dy-PTC MOF (1:1), although their crystal types are not known yet. Characterization with UV-Vis DRS shows band gap energy for all samples of MOF ranges from 2.175 eV to 2.328 eV. The obtained band gap energy values indicate that these MOFs will have an excellent respond toward the visible or solar light and, therefore, can be considered as materials suitable for photocatalysis.

Na7[Ga2B13O24(OH)4]: A Luminescent Sodium Gallium Borate Containing Two Different Types of Oxoboron Framework Building Blocks

A new crystalline luminescent sodium gallium borate, namely, Na7Ga2B13O24(OH)4 (1), has been successfully synthesized through a surfactant-thermal method, and characterized by single-crystal X-ray structural analysis, infrared spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and UV–Vis spectroscopy. Crystal data for 1: monoclinic, C2/c, a = 9.9918(8) A, b = 8.4550(8) A, c = 26.596(3) A, β = 94.279(6)o, V = 2240.6(3), Z = 4. Compound 1 displays a 3D framework and contains two different oxoboron framework building blocks, namely B3O6(OH) and B7O14(OH)2 units, linked by oxo bridges or by tetrahedral Ga3+ centres. To date, the use of surfactant media in the synthesis of metal borates is relatively unexplored. Compounds 1 emits blue luminescence. UV–Vis spectral investigation indicates that 1 is a wide-band-gap semiconductor. Our results offer a new opportunity to grow diverse crystalline metal borates using surfactant-thermal strategy.

Construction of Thermophilic Lipase-Embedded Metal-Organic Frameworks via Biomimetic Mineralization: A Biocatalyst for Ester Hydrolysis and Kinetic Resolution.

Enhancing the activity and stability of enzymes and improving their reusability are critical challenges in the field of enzyme immobilization. Here we report a facile and efficient biomimetic mineralization to embed thermophilic lipase QLM in zeolite imidazolate framework-8 (ZIF-8). Systematic characterization indicated that the entrapment of lipase molecules was successfully achieved during the crystal growth of ZIF-8 with an enzyme loading of ∼72.2 ± 1.88 mg/g lipase@ZIF-8, and the enzymes could facilitate the construction of framework building blocks. Then the composite lipase@ZIF-8 was observed to possess favorable catalytic activity and stability in the ester hydrolysis, using the hydrolysis of p-nitrophenyl caprylate as a model. Finally, the composite was successfully applied in the kinetic resolution of (R,S)-2-octanol, with favorable catalytic activity and enantioselectivity during 10 cycle reactions. Thus, the biomimetic mineralization process can be potentially used as an effective technique for realizing the entrapment of biomacromolecules and constructing efficient catalysts for industrial biocatalysis.

Post-Assembly Transformations of Porphyrin-Containing Metal-Organic Framework (MOF) Films Fabricated Via Automated Layer-By-Layer Coordination

Metal–organic frameworks (MOFs) are hybrid materials composed of inorganic vertices connected to organic linkers. Due to the plethora of available linkers and vertices, MOFs can be easily tuned towards specific applications such as electrochromics1 and catalysis2. For some of these applications, it is desirable that MOFs be deposited as thin films. Among the most versatile and useful approaches to MOF film synthesis is layer-by-layer (LbL) coordination also called liquid-phase epitaxy.3 This approach successively and repetitively introduces solutions of each framework building block into contact with functionalized substrate and subsequently the growing MOF film. The advantage of LbL over other techniques is that MOF layer thicknesses can be controlled with molecular-scale precision. Thus, complex, multifunctional crystalline MOF structures are obtainable. The presentation will demonstrate the robustness of LbL-assembled pillared-paddlewheel-type MOF films by utilizing solvent-assisted linker exchange (SALE) or post-assembly linker metalation towards the conversion of one LbL film (L2-MOF) to another LbL film (SALEF-1 and Mg-L2-MOF).4 Notably, Mg-L2-MOF cannot be formed through other de novo strategies. While beyond the scope of our initial investigation, we believe that the ability of the known metal lability of magnesiated porphyrins should facilitate incorporation of other metal ions, including weakly bound ions, displaying interesting redox and photophysical behaviors. The findings effectively diversify the arsenal of techniques that can be deployed to obtain desired MOF films for energy conversion applications. References Hod, I.; Bury, W.; Karlin, D. M.; Deria, P.; Kung, C. W.; Katz, M. J.; So, M. C.; Klahr, B.; Jin, D.; Chung, Y. W.; Odom, T. W.; Farha, O. K.; Hupp, J. T. Adv. Mater., 2014, 26, 6295.Nguyen, H. G. T.; Schweitzer, N. M.; Chang, C., Drake, T. L.; So, M. C.; Stair, P. C.; Farha, Omar K.; Hupp, J. T., Nguyen, S. T., ACS Catal., 2014, 4, 2496. So, M. C.; Jin, S.; Son, H.-J.; Farha, O. K.; Wiederrecht, G. P.; Hupp, J. T., J. Am. Chem. Soc., 2013, 135, 15698. So, M. C.; Beyzavi, M. H.; Sawhney, R.; Shekah, O.; Eddaoudi, M.; Al-Juaid, S. S.; Hupp, J. T.; Farha, O. K., Chem. Commun., 2014, DOI: 10.1002/adma.201401940. Figure 1

Controllable synthesis of metal–organic framework hollow nanospheres by a versatile step-by-step assembly strategy

Highly monodisperse metal–organic framework (MOF) hollow nanospheres have been rationally synthesized using monodisperse polystyrene (PS) nanoparticles as templates through a versatile step-by-step self-assembly strategy. The structure and composition of the hollow MOF-based nanostructures could be facilely tuned by choosing different framework building blocks (i.e. metal ions and polyfunctional organic ligands) and the hollow MOF shell thickness could also be easily controlled by tuning the number of growth cycles of the PS@MOF core–shell structures.

Induction of trimeric [Mg3(OH)(CO2)6] in a porous framework by a desymmetrized tritopic ligand

The use of a desymmetrized tritopic ligand with both carboxyl and pyridyl functionalities leads to the first occurrence of the [Mg(3)(μ(3)-OH)(CO(2))(6)] trimer as the 3-D framework building block in a porous crystal that shows relatively high H(2) uptake (1.37% at 77 K and 1 atm).

Multiple functions of ionic liquids in the synthesis of three-dimensional low-connectivity homochiral and achiral frameworks.

Multiple functions of ionic liquids in the synthesis of three-dimensional low-connectivity homochiral and achiral frameworks.

The role of modifier’s cation valence in structural properties of TeO2-based glasses

The compositional invariance of the Raman spectra of (1−x)TeO2–xMnOm glasses (M=Ti, Nb) is analyzed and interpreted as evidence for the conservatism of a framework-type constitution inherent to such glasses. This is assigned to the chemical similarity of cations in the X–O–Y bridges (X, Y=Te4+, Ti4+, Nb5+) considered as the framework building blocks. It is concluded that the atoms of metals having valence IV and V can be placed into the category of such cations, to which certain of the atoms with valence III can be added.

Electron Microscopy Reveals the Nucleation Mechanism of Zeolite Y from Precursor Colloids

The growth of nanoscale crystals of zeolite Y from colloidal aluminosilicate gel particles has been investigated with high-resolution electron microscopy. Each amorphous gel particle nucleates only a single zeolite crystal, with nucleation beginning at the gel-solution interface (see scheme). Further growth of these nanocrystals is possible through the solution-mediated transport of framework building blocks.

A Model for Random Si/Al Distribution in a Zeolite Framework Restricted by Loewenstein's Rule

Analytical expressions are derived for a description of random Loewenstein Si/Al ordering in the faujasite zeolite framework. These formulas served as a random distribution reference in the analysis by Melchior et al. of 29Si NMR spectra of faujasites for the determination of Si/Al ordering in framework building blocks. The equations are based on a model where correlations between the Al occupancies of T-sites belonging to different four-rings are ignored. This simple approach gives reliable results for 29Si peak intensities when the Si/Al ratio is larger than 1.5.