Non-aqueous synthesis of nano-sized aluminium(III) isopropoxide derivatives with 8-hydroxyquinoline and their sol–gel transformation to nano-sized δ-alumina

Non-aqueous reactions of aluminum isopropoxide with 8-hydroxyquinoline (Hq = HONH6C9) in 1:1, 1:2 and 1:3 molar ratios in anhydrous benzene yield complexes of the type [qnAl(OPri)3−n] {where n = 1 (1), n = 2 (2), n = 3 (3)}. Progress of the reactions were monitored by estimating liberated 2-propanol in benzene-2-propanol azeotrope by oxidimetric method. All the products were fluorescent green powders, sparingly soluble in CHCl3. They were characterized by elemental analysis, 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 the compound (3). The XRD spectra of (1–3) showed crystalline nature with the average particle size of 45, 32 and 27 nm respectively, as evaluated from Debye–Scherrer equation. The XRD spectrum of (3) also suggests the formation of β-crystalline polymorphs of Alq3. The SEM images appear to indicate granular morphology for (1) and formation of cylindrical shaped rods for (2) and (3). Sol–gel hydrolysis of (1), (2) or (3) in presence of a strong acid as well as of the precursor, Al(OPri)3,without acid or base catalyst, followed by sintering at 950 °C yielded tetragonal primitive phase of nano-sized δ-alumina in all the cases, as reflected by their powder X-ray diffraction pattern. The IR, SEM and EDX studies also support the formation of transition alumina.