Synthesis and characterisation of tungsten(vi) oxo-salicylate complexes for use in the chemical vapour deposition of self-cleaning films

Abstract

Tungsten(VI) oxo-salicylate complexes were prepared in moderate yield (47 to 63%) by the reactions of WOCl₄ and two equivalents of either 3-methylsalicylic acid (^MesaliH₂) or 3,5-di-isopropylsalicylic acid (^di-i-PrsaliH₂). Performing the reaction in refluxing toluene afforded the two analogous ditungsten complexes 1, [{WO(^Mesali)(^MesaliH)}₂(μ-O)], and 2, [{WO(^di-i-Prsali)(^di-i-PrsaliH)}₂(μ-O)], however in refluxing hexane the mononuclear tungsten complex 3, [WO(^di-i-Prsali)(^di-i-PrsaliH)Cl], was isolated. The single crystal X-ray study of 1–3 revealed a pseudo-octahedral geometry around the tungsten centres. Aerosol assisted chemical vapour deposition of 2 or 3 afforded brown tungsten trioxide thin films. These films were converted to yellow fully oxidised WO₃ on annealing in air at 550 °C for 30 minutes. The yellow WO₃ films demonstrate preferred orientation on the substrate and show interesting functional properties—photo induced hydrophilicity and photocatalytic activity.