Metal-organic frameworks (MOFs) as well as porous coordination polymers (PCPs) are porous, organic-inorganic hybrid solids with zeolite-like structures and properties. Due to their extraordinarily high surface area and well defined pore structure MOFs can be used for the stabilization of metal nanoparticles with adjustable size. The embedded metal nanoparticles are still accessible for other reagents due to the high porosity of the MOF systems. This fact makes "metal@ MOF" systems especially interesting for heterogeneous catalysis, gas storage and chemical sensing. This review compiles the cases of metal nanoparticles supported by or embedded into MOFs reported so far and the main aspects and

The gas-phase loading of [Zn4O(bdc)3] (MOF-5; bdc = 1,4-benzenedicarboxylate) with the volatile compound [Ru(cod)(cot)] (cod = 1,5-cyclooctadiene, cot = 1,3,5-cyclooctatriene) was followed by solid-state (13)C magic angle spinning (MAS) NMR spectroscopy. Subsequent hydrogenolysis of the adsorbed complex inside the porous structure of MOF-5 at 3 bar and 150 degrees C was performed, yielding ruthenium nanoparticles in a typical size range of 1.5-1.7 nm, embedded in the intact MOF-5 matrix, as confirmed by transmission electron microscopy (TEM), selected area electron diffraction (SAED), powder X-ray diffraction (PXRD), and X-ray absorption spectroscopy (XAS). The adsorption of CO molecules on the obtained Ru@MOF-5 nanocomposite was followed by IR spectroscopy. Solid-state (2)H NMR measurements indicated that MOF-5 was a stabilizing support with only weak interactions with the embedded particles, as deduced from the surprisingly high mobility of the surface Ru-D species in comparison to surfactant-stabilized colloidal Ru nanoparticles of similar sizes. Surprisingly, hydrogenolysis of the [Ru(cod)(cot)]3.5@MOF-5 inclusion compound at the milder condition of 25 degrees C does not lead to the quantitative formation of Ru nanoparticles. Instead, formation of a ruthenium-cyclooctadiene complex with the arene moiety of the bdc linkers of the framework takes place, as revealed by (13)C MAS NMR, PXRD, and TEM.

The selective formation and stabilization of very small, naked metal particles inside the cavities of metal-organic frameworks (MOFs) and the simultaneous realization of an even distribution of the particles throughout the crystalline MOF host matrix over a wide range of metal loading are challenging goals. MOFs reveal high specific surface areas, tunable pore sizes, and organic linkers, which are able to interact with guests. The chemically very robust zeolite imidazolate frameworks (ZIFs) are a subclass of MOFs. We chose the microporous sodalite-like ZIF-8 (Zn(MeIM) 2 ; IM = imidazolate) and ZIF-90 (Zn(ICA) 2 ; ICA = imidazolate-2-carboxyaldehyde) as host matrices to influence the dispersion of imbedded gold nanoparticles (Au NPs). The metal loading was achieved via gas phase infiltration of [Au(CO)Cl] followed by a thermal hydrogenation step to form the Au NPs. Low-dose high-resolution transmission electron microscopy ((HR)TEM) and electron tomography reveal a homogeneous distribution of Au NPs throughout the ZIF matrix. The functional groups of ZIF-90 direct the anchoring of intermediate Au species and stabilize drastically smaller and quite monodisperse Au NPs in contrast to the parent not functionalized ZIF-8. The particles can be very small, match the cavity size and approach defined molecular clusters of magic numbers, i.e., Au 55 , independently from the level of loading. Post-synthetic oxidation of the aldehyde groups to yield alkyl esters by the adjacent, catalytically active metal NPs is presented as a new concept of encapsulating nanoparticles inside MOFs and allows multiple steps of metal loadings without decomposition of the MOF.

We illustrate the potential of advanced transmission electron microscopy for the characterization of a new class of soft porous materials: metal@Zn4O(bdc)3 (metal@MOF-5; bdc = 1,4-benzenedicarboxylate). By combining several electron microscopy techniques (transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and electron tomography) and by carefully reducing the electron dose to avoid beam damage, it is possible to simultaneously characterize the MOF-5 framework material and the loaded metal nanoparticles. We also demonstrate that electron tomography can be used to accurately determine the position and distribution of the particles within the MOF-5 framework. To demonstrate the implementation of these microscopy techniques and what kind of results can be expected, measurements on gas-phase-loaded metal−organic framework materials Ru@MOF-5 and Pd@MOF-5 are presented.