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(OC 6H4CHO)3]

Abstract

Reactions of aluminum isopropoxide with salicylaldehyde in 1:1, 1:2 and 1:3 molar ratios in anhydrous benzene yield complexes of the type [(OPr i)3-nAl(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 1H, 13C and 27Al 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 η2-(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 °C yielded α-Al2O 3 (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 α-Al2O3. The IR spectral studies of all the oxides indicate the formation of pure α-alumina, a versatile ceramic oxide known for exhibiting a wide variety of applications in engineering and biomedical areas. © the Partner Organisations 2014.