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Title: Chemical Composition of an Aqueous Oxalato-/Citrato-VO2+ Solution as Determinant for Vanadium Oxide Phase Formation
Authors: Peys, Nick
Maurelli, Sara
Reekmans, Gunter
Adriaensens, Peter J.
De Gendt, Stefan
Hardy, An
Van Doorslaer, Sabine
Van Bael, Marlies K.
Issue Date: 2015
Citation: INORGANIC CHEMISTRY, 54 (1), p. 69-78
Abstract: Aqueous solutions of oxalato- and citrato-VO2+ complexes are prepared, and their ligand exchange reaction is investigated as a function of the amount of citrate present in the aqueous solution via continuous-wave electron paramagnetic resonance (CW EPR) and hyperfine sublevel correlation (HYSCORE) spectroscopy. With a low amount of citrate, monomeric cis-oxalato-VO2+ complexes occur with a distorted square-pyramidal geometry. As the amount of citrate increases, oxalate is gradually exchanged for citrate. This leads to (i) an intermediate situation of monomeric VO2+ complexes with a mix of oxalate/citrate ligands and (ii) a final situation of both monomeric and dimeric complexes with exclusively citrato ligands. The monomeric citrato-VO2+ complexes dominate (abundance > 80%) and are characterized by a 6-fold chelation of the vanadium(IV) ion by 4 RCO2- ligands at the equatorial positions and a H2O/R-OH ligand at the axial position. The different redox stabilities of these complexes, relative to that of dissolved O-2 in the aqueous solution, is analyzed via V-51 NMR. It is shown that the oxidation rate is the highest for the oxalato-VO2+ complexes. In addition, the stability of the VO2+ complexes can be drastically improved by evacuation of the dissolved O-2 from the solution and subsequent storage in a N-2 ambient atmosphere. The vanadium oxide phase formation process, starting with the chemical solution deposition of the aqueous solutions and continuing with subsequent processing in an ambient 0.1% O-2 atmosphere, differs for the two complexes. The oxalato-VO2+ complexes turn into the oxygen-deficient crystalline VO2 B at 400 degrees C, which then turns into crystalline V6O13 at 500 degrees C. In contrast, the citrato-VO2+ complexes form an amorphous film at 400 degrees C that crystallizes into VO2 M-1 and V6O(13) at 500 degrees C.
Notes: [Peys, Nick; Hardy, An; Van Bael, Marlies K.] Hasselt Univ, Inst Mat Res Inorgan & Phys Chem, Diepenbeek, Belgium. [Reekmans, Gunter; Adriaensens, Peter] Hasselt Univ, Inst Mat Res, Diepenbeek, Belgium. [Peys, Nick; De Gendt, Stefan] IMEC VZW, Heverlee, Belgium. [Maurelli, Sara; Van Doorslaer, Sabine] Univ Antwerp, Dept Phys, BIMEF Lab, B-2020 Antwerp, Belgium. [De Gendt, Stefan] Katholieke Univ Leuven, Lab Phys & Analyt Chem, Heverlee, Belgium. [Hardy, An; Van Bael, Marlies K.] IMEC VZW, Div IMOMEC, Diepenbeek, Belgium.
URI: http://hdl.handle.net/1942/18660
DOI: 10.1021/ic5015779
ISI #: 000347506500014
ISSN: 0020-1669
Category: A1
Type: Journal Contribution
Validation: ecoom, 2016
Appears in Collections: Research publications

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