Metal-organic Clusters Research Articles

Rhodium Nanoparticles from Cluster Seeds: Control of Size and Shape by Precursor Addition Rate

The size-tunable synthesis of poly(vinylpyrrolidone)-stabilized cuboctahedral rhodium nanoparticles with mean diameters ranging between 3-7 nm and multipod structures was accomplished using seeded growth methods. Isotropic PVP-capped 2.9 nm seeds were prepared by ligand exchange on rhodium-triphenylphosphine metal-organic clusters. Quantitative investigation of reaction parameters in ethylene glycol revealed that size and shape could be controlled at a single reaction temperature of 120 degrees C. The rate of rhodium monomer addition was found to be critical for monodispersity and shape control, regardless of thermodynamic factors. Solvent viscosity, varied by changing the polyol solvents, indicated that autocatalytic addition kinetics are responsible for isotropic versus anisotropic growth.

Electronic structure and properties of isoreticular metal-organic frameworks: The case of M-IRMOF1 (M=Zn, Cd, Be, Mg, and Ca)

We investigate the possibility of tailoring the electronic properties of isoreticular metal-organic materials by replacing the metal atom in the metal-organic cluster and by doping. The electronic structure of M-IRMOF1, where IRMOF1 stands for isoreticular metal-organic framework 1 and M = Be, Mg, Ca, Zn, and Cd, was examined using density-functional theory. The results show that these materials have similar band gaps (ca. 3.5 eV) and a conduction band that is split into two bands, the lower of which has a width that varies with metal substitution. This variation prompted us to investigate whether doping with Al or Li could be used to tailor the electronic properties of the Zn-IRMOF1 and Be-IRMOF1 materials. It is shown that replacing one metal atom with Al can effectively be used to create IRMOFs with different metallic properties. On the other hand, adding Li produces structural changes that render this approach less suitable.

Metal Ions Play Different Roles in the Third‐Order Nonlinear Optical Properties of d10 Metal–Organic Clusters

Metal Ions Play Different Roles in the Third‐Order Nonlinear Optical Properties of d¹⁰ Metal–Organic Clusters

A homochiral metal-organic porous material for enantioselective separation and catalysis

Inorganic zeolites are used for many practical applications that exploit the microporosity intrinsic to their crystal structures. Organic analogues, which are assembled from modular organic building blocks linked through non-covalent interactions, are of interest for similar applications. These range from catalysis, separation and sensor technology to optoelectronics, with enantioselective separation and catalysis being especially important for the chemical and pharmaceutical industries. The modular construction of these analogues allows flexible and rational design, as both the architecture and chemical functionality of the micropores can, in principle, be precisely controlled. Porous organic solids with large voids and high framework stability have been produced, and investigations into the range of accessible pore functionalities have been initiated. For example, catalytically active organic zeolite analogues are known, as are chiral metal-organic open-framework materials. However, the latter are only available as racemic mixtures, or lack the degree of framework stability or void space that is required for practical applications. Here we report the synthesis of a homochiral metal-organic porous material that allows the enantioselective inclusion of metal complexes in its pores and catalyses a transesterification reaction in an enantioselective manner. Our synthesis strategy, which uses enantiopure metal-organic clusters as secondary building blocks, should be readily applicable to chemically modified cluster components and thus provide access to a wide range of porous organic materials suitable for enantioselective separation and catalysis.

Generation of O 2 and metalorganic cluster ion beams and its application to low-temperature thin oxide film formation

High-current O 2 and N 2 cluster ion beams were formed through a Laval nozzle by the combination of He mixing and gas cooling. The cluster current of 320 nA was obtained from O 2 cluster ions whose mean cluster size was 7000. Consequently, the equivalent ion current was as high as 2.2 mA. The optimum He flow ratio to obtain the most intense cluster beams was lower than those reported. The high-current O 2 cluster ion beams were successfully applied to the low-temperature formation of high-quality SiO 2 and PbO films. Generation of Ti(i-OC 3H 7) 4 cluster ion beams (1.7 nA) was also demonstrated with the He bubbling method for the first time.

STM and PES investigations on metal-organic gold clusters

STM and PES investigations on metal-organic gold clusters

Direct writing of iridium lines with a focused ion beam

Direct writing of metal features narrower than 100 nm is accomplished by scanning a focused ion beam over a substrate covered with a thin solid metalorganic film. A metalorganic cluster coordination compound [Ir4(CO)11Br][N(C2H5)4] is spun on an oxidized silicon wafer from acetone solution and the resulting layer is irradiated with a focused 20 keV Ga-ion beam. The partially decomposed irradiated film regions show a marked decrease of solubility in acetone. Developing by dissolving the nonirradiated parts of the surface hence leaves narrow lines of partially reacted metalorganic precursor. High temperature treatment of these lines, either in vacuum or in a reactive gas stream, completes the decomposition to quite pure iridium, as is confirmed by micro-Auger analysis. In these preliminary experiments we obtained lines with room temperature electrical resistivities as low as 400 μΩ cm, at direct writing speeds of 40 μm s−1 to 0.8 mm s−1, which correspond to ion doses of 3.1×1016 ions/cm2 to 1.6×1015 ions/cm2, respectively. The width of the metal lines decreases with decreasing ion dose in this range from 180 down to 90 nm. The adhesion to the substrate increases with increasing ion dose. The thickness of the resulting iridium lines depends mainly on the thickness of the metalorganic precursor layer. The maximum possible thickness of the [Ir4(CO)11Br][N(C2H5)4] layer that can be used depends on the effective penetration depth of the ions in this layer.