The molecular composition of non-modified and acac-modified propoxide and butoxide precursors of zirconium and hafnium dioxides
2009 (English)In: Journal of Sol-Gel Science and Technology, ISSN 0928-0707, E-ISSN 1573-4846, Vol. 51, no 1, 10-22 p.Article in journal (Refereed) Published
Long-term storage at 0 A degrees C of a paraffin-sealed flask with commercial 70 wt% solution of zirconium n-propoxide in n-propanol resulted in crystallization of an individual oxoalkoxide complex Zr(4)O(O(n)Pr)(14)((n)PrOH)(2) in over 20% yield. The structure of this molecule can be described as a triangular Zr(3)(mu(3)-O)(OR)(10)(ROH) core of 3 edge-sharing octahedrons with an additional Zr(OR)(4)(ROH) unit attached through a pair of (mu-OR) bridges. Mass spectrometric and (1)H NMR investigation of the commercial samples of the most broadly applied zirconium and hafnium n-propoxides and n-butoxides indicate the presence of analogous species in the commercial alkoxide precursors. The content of oxo-alkoxide species in the commercial precursors has been estimated to be similar to 20% for n-propoxide and similar to 35% for zirconium n-butoxide. A new route has been presented for synthesis of the individual crystalline mixed ligand precursor [Zr(O(n)Pr)(O(i)Pr)(3)((i)PrOH)](2), from zirconium n-propoxide. A high yield has been observed (similar to 90%), indicative of an almost complete precursor transformation. Mass spectrometry has shown that the synthesized mixed ligand precursor is dimeric, which makes it an attractive alternative to zirconium n-propoxide. Addition of 1 eq of Acetylacetone to zirconium or hafnium alkoxide precursors results in formation of dimeric [M(OR)(3)(acac)](2) in high yields. These species have limited stability (much higher for Hf than for Zr) and transform in solution into hydrolysis-insensitive M(acac)(4) through very unstable M(acac)(3)(OR) intermediates containing 7-coordinated metal centers. This transformation can be followed kinetically in hydrocarbon solvents by (1)H NMR and is noticeably accelerated by addition of parent alcohols. The obtained results clearly reveal limited applicability of EXAFS and XANES techniques for the study of such systems, especially in the context of structure prediction.
Place, publisher, year, edition, pages
2009. Vol. 51, no 1, 10-22 p.
Precursor chemistry, Zirconium propoxide, Zirconium butoxide, Mass spectrometry, Sol-gel of ZrO(2) and HfO(2), NMR, EXAFS, XANES, MTSAL concept
IdentifiersURN: urn:nbn:se:kth:diva-101646DOI: 10.1007/s10971-009-1988-0ISI: 000266482900003ScopusID: 2-s2.0-67349213630OAI: oai:DiVA.org:kth-101646DiVA: diva2:549264
QC 201209042012-09-042012-08-302012-09-04Bibliographically approved