Sol-gel synthesis of highly pure α-Al2O3 nano-rods from a new class of precursors of salicylaldehyde-modified aluminum(III) isopropoxide. Crystal and molecular structure of [Al(OC6H4CHO)3]

Reactions of aluminum isopropoxide with salicylaldehyde in 1 : 1, 1 : 2 and 1 : 3 molar ratios in anhydrous benzene yield complexes of the type [(OPri)(3-n)Al(OC6H4CHO)(n)] {where n = 1(1); n = 2 (2); n = 3 (3)}. All the products are yellow solids and are soluble in common organic solvents. They were characterized by elemental analysis, ESI-mass spectrometry, FT-IR and H-1, C-13 and Al-27 NMR studies. The ESI-mass spectral studies indicate dimeric nature for (1) and (2) and monomeric nature for compound (3). Crystal and molecular structures of [Al(OC6H4CHO)(3)] (3) suggest that salicylaldehyde ligands bind to the metal in a side-on dihapto eta(2)-(O,O) manner, leading to the formation of a hexa-coordinated environment around the aluminum atom. Powder XRD, SEM image, and EDX analysis appear to indicate formation of nano-sized rods for precursor (3). Sol-gel hydrolysis of all the precursors Al(OPri)(3), (1), (2) and (3) followed by sintering at 1100 degrees C yielded alpha-Al2O3 (a), (b), (c) and (d), respectively. The powder X-ray diffraction patterns and the SEM images of all the oxides exhibit nano-sized microcrystalline morphology for (a) and mixed platelike nano-rod morphology for (b), (c) and (d). The EDX and TEM studies of (d) also corroborate the formation of alpha-Al2O3. The IR spectral studies of all the oxides indicate the formation of pure alpha-alumina, a versatile ceramic oxide known for exhibiting a wide variety of applications in engineering and biomedical areas.