Standing out from the vast majority of metal organic coordination polymers is the class of highly porous basic zinc carboxylates developed by Yaghi and co-workers.[1] Its prototype is MOF-5 (MOF = metal organic framework), in which {Zn 4 O} building blocks are linked together by terephthalate bridges to form a zeolite-like, cubic framework.[2] The extremely high specific surface area [2] of up to 4500 m 2 g À1 and a pore volume of 0.69 cm 3 cm À3 (for MOF-177), which has not been surpassed by any other crystalline substance, and thermal stability (up to 350 8C) opens up fascinating perspectives for the supramolecular host-guest chemistry.[3] Applications for these materials in miniaturized fuel cells and convenient gas-storage devices (for H 2 , CH 4 ), as gas sensors and for gas separation, as catalyst materials, and also for molecular electronics are emerging. [4] A report on the quantitative inclusion of C 60 and large polycyclic dye molecules (e.g. Astrazon Orange R) into the cavities of MOF-177 single crystals attracted our attention. [5] Could these MOF host lattices also be suitable to efficiently and selectively absorb typical metal organic chemical vapor deposition (CVD) precursors, provided these were volatile (gas absorption) or very soluble in nonpolar hydrocarbons and had matching size and shape to fit into the cavity? The release of the metal atoms of the precursors imbedded in the
The kinetically controlled disproportionation of the metastable subvalent heavier Group 13 and 14 halides produces a library of species on the way to the elemental form. [1] A rich variety of these intermediates were isolated in the form of ligand-stabilized metalloid clusters of the type [E a R b ] (a > b, R = 2,6-Mes 2 C 6 H 3 , N(SiMe 3 ) 2 [4,5] The steric and the electronic nature of the ligand R plays a crucial role in the size and structural type of the formed clusters. [2,3] However, the yield of these heterogeneous reductions is usually very low owing to the potentially destructive radical reactions on the strongly reductive metal surfaces.In the course of our investigations into the chemistry of sterically encumbered low-valent Group 13 compounds RE (E = Al, Ga, In; R = anionic group), [10] we studied the b-diketiminate Ga(ddp) (ddp = HC(CMeNC 6 H 3--2,6-iPr 2 ) 2 ) as a ligand for late transition metals. Interestingly, (ddp)Ga inserts into transition metal halide bonds [L n MÀX], forming stable intermediates of the type [L n MÀGaX(ddp)] before the thermodynamically favorable gallium(III) species (ddp)GaX 2 is released.[10b] Therefore, we decided to expand the coordination chemistry of Ga(ddp) to main-group metals.[10a] We selected the combination of SnCl 2 with Ga(ddp) as a test case, and obtained the novel metalloid tin clusters [{(ddp)ClGa} 2 Sn 7 ] (1) and [{(ddp)ClGa} 4 Sn 17 ] (2). The reaction of Ga(ddp) with SnCl 2 in a 2:1 molar ratio in THF solution at À30 8C gives 1 in 24 % and 2 in 27 % yields of isolated product (Scheme 1).The initial yellow suspension in THF at low temperature changes to a clear yellow solution after one hour. When the solution is subsequently warmed to room temperature, it turns dark red. By removing half of the solvent in vacuo and layering with hexane, the products precipitate as orange (1) and dark red (2) crystals. The ratio of the products changes in favor of 2 with increasing reaction time at room temperature, ranging from almost pure crystalline samples of 1 (1 h at room temperature prior to crystallization at À30 8C) to pure crystalline samples of 2 (crystallization at room temperature for 1-2 days). It should be noted that using less than two equivalents of Ga(ddp) results in black solutions without formation of any crystalline material. Higher ratios of Ga(ddp) also strongly influence the crystallization rate, ranging from several hours to several weeks. As pure samples of isolated clusters 1 and 2 are completely insoluble in organic solvents, it is assumed that the simultaneous presence of different intermediates in solution prevents the oversaturated solutions from crystallizing at this early stage of the reaction.To favor the growth of even larger tin clusters, the same reaction was performed in pure THF and the reaction mixture was left at room temperature for three days, leading to a brown-black homogeneous solution. The transmission electron microscopic analyses of this solution unveil nearly spherical shapes, and primary particles having a relatively nar...
Aus der Fülle metall-organischer Koordinationspolymere ragt die von Yaghi und Mitarbeitern entwickelte Stoffklasse hoch poröser basischer Zinkcarboxylate heraus.[1] Ihr Prototyp ist MOF-5 (MOF = Metal Organic Framework), in dem {Zn 4 O}-Baueinheiten über Terephthalat-Brücken zu einem Zeolith-ähnlichen, kubischen Raumnetz verknüpft sind. [2] Die von keiner anderen kristallinen Substanz übertroffenen, extrem hohen spezifischen Oberflächen [2] bis zu 4500 m 2 g À1und Porenvolumina von 0.69 cm 3 cm À3 (für MOF-177) sowie die thermische Stabilität (bis zu 350 8C) eröffnen faszinierende Perspektiven für die supramolekulare Wirt-GastChemie.[3] Anwendungen für miniaturisierte Brennstoffzellen und Gasspeicher (für H 2 , CH 4 ), als Gassensoren sowie als Trennmedien und Katalysatormaterialien, aber auch Mög-lichkeiten für die molekulare Elektronik zeichnen sich ab. [4] Ein Bericht über die quantitative Einlagerung von C 60 und großen polycyclischen Farbstoffmolekülen (z. B. Astrazon Orange R) in die Hohlräume von MOF-177-Einkristallen erregte unsere Aufmerksamkeit.[5] Sollten diese MOF-Wirtsgitter nicht ebenso effizient und selektiv auch typische metallorganische CVD-Vorstufen aufnehmen können, solange diese nur flüchtig (Gasabsorption) oder sehr gut löslich in Kohlenwasserstoffen wären und eine zum Hohlraum passen- [8] und [Au(CH 3 )(PMe 3 )] (3).[9]Die Größen-bzw. Formselektivität ist erwartungsgemäß sehr hoch. Für 2, das nur wenig mehr Raum beansprucht als 1 oder 3, findet man nur zwei statt vier eingelagerte Moleküle
In this work, we present a novel soft chemical synthesis to aluminum nanoparticles based on the hydrogenolysis of the metastable organoaluminum (I) compound (AlCp*)4 (1) in mesitylene at 150 °C and 3 bar H2. Aiming at the development of a general wet-chemical, nonaqueous route to M/E intermetallic nanophases (E = Al, Ga, In), we studied the co-hydrogenolysis of 1 with [CpCu(PMe3)] (2) as the model case aiming at Cu/Al alloyed nanoparticles. One equivalent of 1 combined with 2 equiv of 2 yields the nanocrystalline intermetallic θ-CuAl2 phase (Cu0.33Al0.67), as revealed by elemental analysis, powder X-ray diffraction, transmission electron microscopy (TEM), and energy-dispersive X-ray analysis. The obtained Cu0.33Al0.67 material was also characterized by the 27Al Knight Shift resonance. Alloy particles Cu1 - x Al x (0.10 ≤ x ≤ 0.50), typically 15 ± 5 nm (TEM) in size, are accessible as colloidal solutions by variation of the molar ratio of 1 and 2 and by the addition of poly(2,6-dimethyl-1,4-phenylene oxide) during hydrogenolysis. The 27Al NMR Knight Shift resonance moves to high field starting form the value of 1639 ppm for pure nano-aluminum particles to 1486 ppm of Cu0.33Al0.67, reaching 1446 ppm for Cu0.50Al0.50, and was not detectable for Al contents below 50%. Upon oxidation (controlled exposure to the ambient), a selective oxidation of the Al component, presumably forming core−shell structured Al2O3@Cu1 - y Al y (0.10 ≤ y ≤ 0.50) particles, was studied by UV−vis spectroscopy, 27Al magic-angle spinning NMR, and X-ray photoelectron spectroscopy. The Al content can be freely adjusted and lowered down to about 15 atom % (Cu0.85Al0.15) without oxidizing the Cu(0) core.
Die kinetisch kontrollierte Disproportionierung von metastabilen subvalenten Halogeniden der schweren Elemente der Gruppen 13 und 14 liefert eine Reihe von Verbindungen zwischen Molekülen und Metallen.[
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