Synthesis of tungsten oxo fluoroalkoxide complexes WO(OR)3L as precursors for growth of WOx nanomaterials by aerosol-assisted chemical vapor deposition

Abstract

Partially fluorinated oxo-alkoxide tungsten complexes bearing β-diketonate or ketoesterate ligands have been synthesized and their thermal and physical properties have been evaluated for Aerosol Assisted Chemical Vapor Deposition (AACVD) of WO x. Volatility and thermal stability of the complexes have been shown to depend on the bidentate ligand and the degree of fluorination of the alkoxides. Growth of tungsten oxide from the precursor WO(OC(CH 3) 2 CF 3) 3 (tbac) (tbac = tert-butyl acetoacetate) has been demonstrated. Deposits grown at temperatures from 150 to 300 °C are amorphous thin films of substoichiometric WO x. Deposition at temperatures from 350 to 500 °C produced either polycrystalline films or crystalline nanorods of W 18 O 49 .

Growth of WOx from Tungsten(VI) Oxo-Fluoroalkoxide Complexes with Partially Fluorinated β-Diketonate/β-Ketoesterate Ligands: Comparison of Chemical Vapor Deposition to Aerosol-Assisted CVD

“…This ion corresponds to pathways that involve W–O bond cleavage on the chelate through proton transfer from the alkyl group on a neighboring alkoxide ligand (Scheme a). This fragment was also previously observed for 1 . This common fragment observed for complexes that bear trifluorinated- tert -butoxide ligands ( 1 , 2 , and 3 ) suggests that they share similar decomposition pathways.…”

“…Complexes with fluorinated β-diketonates ( 2 , 5 , and 8 ) undergo initial mass loss at much lower temperatures in contrast to their nonfluorinated analogues 1 , 4 , and 7 . Similarly, 3 and 6 exhibit evaporation temperatures 20–30 °C lower than their counterparts WO­(OC­(CH 3 ) 2 CF 3 ) 3 (etac) and WO­(OC­(CF 3 ) 2 CH 3 ) 3 (etac), respectively, which are not fluorinated on the chelating ligand . This augmented volatility is attributed to the repulsive nature of the fluorine lone pairs, which lessens intermolecular interactions .…”

“…Incorporation of fluoroalkyl substituents on the ligands has also been shown to increase volatility by the introduction of repulsive interactions between nonbonding p electrons on the fluorines . We previously reported the series of complexes WO­(OR) 3 L [R = C­(CH 3 ) 2 CF 3 and C­(CF 3 ) 2 CH 3 , L = acetylacetonate (acac), dipivaloylmethanate (dpm), ethyl acetoacetate (etac), and tert -butyl pivaloyl acetate (tbac)], where fluorination was present only on the alkoxides . Our interest in testing the effects of fluorination of the chelating ligands suggested complexes 1–9 as target precursors.…”

“…Preparation of WO x material through AACVD has been successfully demonstrated by using precursors that contain both alkoxide and chelating ligands. , Fluorination of the ligands can improve the volatility of these complexes because of the repulsive nature of the fluorine atoms . By employing this strategy in precursor design, we previously reported the preparation of a series of oxo alkoxide complexes WO­(OR) 3 L, where L is a chelating β-diketonate or β-ketoesterate ligand and the alkoxide ligands −OR are partially fluorinated . In this work, we explore the properties of WO­(OR) 3 L complexes where both the alkoxide ligands and the chelating ligand are partially fluorinated.…”

“…29 By employing this strategy in precursor design, we previously reported the preparation of a series of oxo alkoxide complexes WO(OR) 3 L, where L is a chelating βdiketonate or β-ketoesterate ligand and the alkoxide ligands −OR are partially fluorinated. 30 In this work, we explore the properties of WO(OR) 3 L complexes where both the alkoxide ligands and the chelating ligand are partially fluorinated.…”