Nanometallurgy of Colloidal Aluminides: Soft Chemical Synthesis of CuAl2 and α/β-CuAl Colloids by Co-Hydrogenolysis of (AlCp*)4 with [CpCu(PMe3)]

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 H 2 . 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(PMe 3 )] ( 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-CuAl 2 phase (Cu 0.33 Al 0.67 ), as revealed by elemental analysis, powder X-ray diffraction, transmission electron microscopy (TEM), and energy-dispersive X-ray analysis. The obtained Cu 0.33 Al 0.67 material was also characterized by the 27 Al Knight Shift resonance. Alloy particles Cu 1 - 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 27 Al NMR Knight Shift resonance moves to high field starting form the value of 1639 ppm for pure nano-aluminum particles to 1486 ppm of Cu 0.33 Al 0.67, reaching 1446 ppm for Cu 0.50 Al 0.50, 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 Al 2 O 3 @Cu 1 - y Al y (0.10 ≤ y ≤ 0.50) particles, was studied by UV−vis spectroscopy, 27 Al magic-angle spinning NMR, and X-ray photoelectron spectroscopy. The Al content can be freely adjusted and lowered down to about 15 atom % (Cu 0.85 Al 0.15 ) without oxidizing the Cu(0) core.