Changing hafnium speciation in aqueous sulfate solutions

A high-energy X-ray scattering study

Ali Kalaji, S. Skanthakumar, Mercouri G Kanatzidis, John F. Mitchell, L. Soderholm

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

The relationship of solution speciation and the structures of corresponding precipitates is examined for an aqueous Hf4+ sulfate series. High-energy X-ray scattering (HEXS) and Raman spectroscopy data are used to probe atomic correlations in solutions. Hf4+ in acidic perchlorate solution shows no evidence of a mononuclear metal species but instead has a peak in the pair-distribution function (PDF), generated from the HEXS data, at 3.55 Å, indicating Hf4+-Hf4+ solution correlations. The peak intensity is consistent with clusters that are, on average, larger than the tetramic unit [M4(OH)8(H2O)16] 8+ usually attributed to Zr4+ and Hf4+ solution speciation under these conditions. Addition of sulfate results in a breakup of hydroxo-bridged oligomers into sulfate-capped dimers and, for higher concentrations, Hf-sulfate monomers. The bidentate coordination mode of sulfate dominates the dissolved precursors, although it is not found in the structure of the final crystallized product, which instead is comprised of bridging-bidentate sulfate ligation. Neither the PDF patterns nor the Raman spectra show any evidence of the larger oligomers, such as the octadecameric metal clusters, found in similar Zr4+ solutions. The oligomeric units found in solution provide insights into possible assembly routes for crystallization. In addition to expanding our understanding of synthesis science this study also reveals differences in the aqueous chemistries between Hf and Zr, two elements with ostensibly very similar chemical behavior.

Original languageEnglish
Pages (from-to)6321-6328
Number of pages8
JournalInorganic Chemistry
Volume53
Issue number12
DOIs
Publication statusPublished - Jun 16 2014

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Hafnium
hafnium
X ray scattering
Sulfates
sulfates
scattering
x rays
energy
oligomers
Oligomers
Distribution functions
Metals
distribution functions
metal clusters
perchlorates
Crystallization
Chemical elements
Dimers
Raman spectroscopy
Raman scattering

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Physical and Theoretical Chemistry

Cite this

Changing hafnium speciation in aqueous sulfate solutions : A high-energy X-ray scattering study. / Kalaji, Ali; Skanthakumar, S.; Kanatzidis, Mercouri G; Mitchell, John F.; Soderholm, L.

In: Inorganic Chemistry, Vol. 53, No. 12, 16.06.2014, p. 6321-6328.

Research output: Contribution to journalArticle

Kalaji, Ali ; Skanthakumar, S. ; Kanatzidis, Mercouri G ; Mitchell, John F. ; Soderholm, L. / Changing hafnium speciation in aqueous sulfate solutions : A high-energy X-ray scattering study. In: Inorganic Chemistry. 2014 ; Vol. 53, No. 12. pp. 6321-6328.
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