Synthesis and characterization of some binuclear alkylene dithiophosphate complexes of bis(acetylacetonato)aluminium(III)-di-(μ-isopropoxo)di-isopropoxoaluminium(III) and sol-gel synthesis of nanosized θ-alumina

Abstract

Reactions of bis(acetylacetonato)aluminum(III)-di-(μ–isopropoxo)-di-isopropoxoaluminum(III) (A) with a variety of alkylenedithiophosphoric acids in different molar ratio yield products of the type  [(CH₃COCHCOCH₃)₂Al(μ-OPrⁱ)₂Al{S(S)P(O-G-O)_n(OPrⁱ)_2-n] (1-9) {where G = C(CH₃)₂C(CH₃)₂, n=1[1], n=2[2]; -CH₂CH(C₂H₅), n=1[3], n=2[4]; CH₂CH(CH₃), n=1[5], n=2[6];C(CH₃)₂CH₂CH(CH₃), n=1[7]; CH(CH₃)CH(CH₃) n=1[8], n=2[9]}. Progress of the reactions was monitored by estimating liberated 2-propanol in benzene-2-propanol azeotrope by oxidimetric method. All pale coloured viscous products were soluble in common organic solvents and were characterized by elemental analyses, FT-IR and NMR (¹H and ¹³C{¹H} NMR) spectral studies. Molecular weight measurements in refluxing anhydrous benzene indicated binuclear nature of the complexes. ²⁷Al NMR spectra of two of the derivatives, (1) and (2), suggested the presence of aluminium(III) atoms in different coordination states. ³¹P NMR spectra of the representative derivatives (1) and (2) exhibited only a single peak at 95.71 and 90.59 ppm, respectively suggesting tetra-coordination around phosphorus atom and a bidentate mode of chelation of the dithio ligand. Sol-gel transformation of  Al(OPrⁱ)₃ and  [(CH₃COCHCOCH₃)₂Al(μ-OPrⁱ)₂Al(OPrⁱ)₂] (A) followed by sintering at ~850°C yield alumina (a) and (b), respectively. The powder X-ray diffraction patterns, SEM images and FT-IR spectral studies of (a) and (b) indicated formation of nano-crystallites of θ -Al₂O₃ [PDF # 110517] in both the cases. The energy band gaps of 4.78 eV and 5.01 eV for (a) and (b), respectively were obtained from the absorption spectra.