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 degrees 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(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 theta-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 Al-27 Knight Shift resonance. Alloy particles Cul-,Al, (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 Al-27 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-yAly (0.10 <= y <= 0.50) particles, was studied by UV-vis spectroscopy, Al-27 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.