Stephan Hermes

Deposition of microcrystalline [Cu3(btc)2] and [Zn2(bdc)2(dabco)] at alumina and silica surfaces modified with patterned self assembled organic monolayers: evidence of surface selective and oriented growth

The deposition of microcrystalline, phase pure [Cu3(btc)2] (1) and [Zn2(bdc)2(dabco)] (2) under solvothermal conditions on alumina and on silica surfaces modified with self assembled organic monolayers has been studied. The growth of 1 is remarkably surface selective and does not take place on silica but does on alumina. In contrast the growth of 2 is not surface selective at all and densely packed coatings were obtained on silica and on alumina surfaces. Most interestingly, [Cu3(btc)2] shows an oriented growth mode on both c-plane sapphire and COOH-terminated SAMs at SiO2/Si(100) wafers. The single crystals of 1 are attached to the organic surface via the (111) face, while on c-plane sapphire the crystals interact via the (100) lattice plane leading to different shapes of the crystals: pyramids on sapphire and fully developed octahedra on the COOH-SAM. The gas adsorption properties of the obtained coatings were demonstrated by reversible loading with water and with pyridine in the case of 1 and loading with [(η5-C5H5)Pd(η3-C3H5)] as a typical example of a MOCVD precursor for both 1 and 2 which allows the fabrication of Pd nanoparticle loaded MOF thin films.

Loading of porous metal–organic open frameworks with organometallic CVD precursors: inclusion compounds of the type [LnM]a@MOF-5

The highly porous coordination polymer [Zn4O(bdc)3] (bdc = benzene-1,4-dicarboxylate; MOF-5 or IRMOF-1) was loaded with typical MOCVD precursor molecules 1–10 for metals such as Fe, Pt, Pd, Au, Cu, Zn, Sn. Exposure of [Zn4O(bdc)3] to the vapour of the volatile organometallic compounds, e.g. ferrocene (3), resulted in the formation of inclusion compounds of the type [LnM]a@MOF-5, where [LnM] indicates the MOCVD precursor and a denotes the effective number of molecules per cavity of the MOF-5 lattice. The obtained inclusion compounds were characterised by C/H combustion analysis, determination of the metal content by atomic absorption spectroscopy, FT-IR and solid state NMR spectroscopy and by powder X-ray diffraction. The data prove that the host lattice and the guest molecules interact only by weak van der Waals forces without any change of the framework or the chemical nature of the included molecules. Rapid desorption is observed for small and comparably volatile compounds such as pentacarbonyliron or diethyl zinc. Less labile inclusion compounds were obtained for cyclopentadienyl complexes as guest molecules, e.g. a rather high loading of six molecules of ferrocene per cavity was observed. Careful hydrolysis/calcination of [Zn(C2H5)2]2@MOF-5 resulted in the composite (ZnO)2@MOF-5 pointing to the possibility to develop a subsequent chemistry of the embedded precursor molecules to yield novel nanocomposite materials based on MOFs as host matrices and MOCVD precursors in general.

Synthesis of periodic mesoporous organosilicas with chemically active bridging groups and high loadings of thiol groups

Chemically active isocyanurate-bridged periodic mesoporous organosilica materials with high loadings of pendant thiol groups have been synthesized via co-condensation under acidic conditions, using the triblock copolymer EO20PO70EO20 (P123) as template and a mixture of mercaptopropyl-containing silane and isocyanurate-containing silsesquioxane to form the framework. The obtained SH–ICS–PMOs were characterized by XRD, transmission electron microscopy (TEM), solid state 13C and 29Si MAS NMR spectroscopy, and N2 physical sorption. The data show that well-ordered SH–ICS–PMOs were obtained with 40% of the framework Si atoms bearing the thiol pendant groups. Interestingly, the introduction of the thiol groups improved the mesostructural ordering and favored the cross-linking of the pore walls. The determination of Hg2+ uptake from aqueous solution as a test case showed that both the bridging ICS groups and the pendant thiol groups in the SH–ICS–PMOs are active in adsorbing Hg2+. Our study demonstrated that well-ordered periodic mesoporous organosilicas are capable of supporting both chemically active bridging groups and active pendant groups with high loadings.

Non aqueous loading of the mesoporous siliceous MCM-48 matrix with ZnO: a comparison of solution, liquid and gas-phase infiltration using diethyl zinc as organometallic precursor

Zinc oxide species hosted in the siliceous matrix MCM-48 were prepared by an organometallic route using ZnEt2 as the ZnO precursor. Gas phase as well as liquid phase infiltration of the precursor was studied in detail by ICP-AES, FT-RAIRS, 1H- and 13C-MAS-NMR, PXRD, TEM/EDX and UV–VIS. Highly loaded ZnO@MCM-48 materials with a Zn-content of up to 29.6 wt% were synthesized. A comparison of the different preparation techniques was carried out in order to find a convenient way of preparing ZnO@MCM-48 species for catalytic applications.