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Dissertation Information for Jennifer J. Cowan

NAME:
- Jennifer J. Cowan

DEGREE:
- Ph.D.

DISCIPLINE:
- Chemistry

SCHOOL:
- Emory University (USA) (2001)

ADVISORS:
- Craig L. Hill

COMMITTEE MEMBERS:
- Karl S. Hagen
- Luigi G. Marzilli

MPACT Status: Fully Complete

Title: Aluminum-based heteropolytungstates of the Keggin structure: Synthesis, isomerism, and application

Abstract: A new method of preparation of the aluminum-centered tungstate of the Keggin structure, [AlW 12 O 40 ] 5- , was accomplished. Condensation of Al(III) and tungstate in boiling pH 7.7 solution leads to the formation of a mixture of á, â 2 , and â 3 -[Al(AlOH 2 )W 11 O 39 ] 6- . Further condensation of this isomeric mixture leads to the formation of á- and â-[AlW 12 O 40 ] 5- , in an overall crude yield of 95% for the two steps. Equilibrium between á- and â-[AlW 12 O 40 ] 5- was observed by 27 Al NMR spectra of 0.1 M aqueous solutions of either pure á-H 5 [AlW 12 O 40 ] or â-H 5 [AlW 12 O 40 ] heated at 473K. From K eq and Ä G = - RT ln K eq , á-[AlW 12 O 40 ] 5- is more stable than â-[AlW 12 O 40 ] 5- by 2.1 ± 0.5 kcal/mol at the given conditions. The monolacunary derivative of [AlW 12 O 40 ] 5- , [AlW 11 O 39 ] 9- , was prepared by selective base hydrolysis of either the á- or â-isomer of [AlW 12 O 40 ] 5- . Equilibrium between á-[AlW 11 O 39 ] 9- and â 3 -[AlW 11 O 39 ] 9- was observed; K eq (also determined from 27 Al NMR spectroscopy experiments) gives a difference in energy between these two isomers of 0.3 kcal/mol (333 K, 0.13 M). Isomeric equilibration studies of [Al(AlOH 2 )W 11 O 39 ] 6- showed that the á-isomer is sufficiently more stable than any of the â-isomers that solutions of mixtures of [Al(AlOH 2 )W 11 O 39 ] 6- isomers may be converted quantitatively to the á-isomer. The á-isomer of [AlW 11 O 39 ] 9- may be prepared selectively under certain conditions, from either á- or â-[AlW 12 O 40 ] 5- , as the potassium salt, á-K 9 [AlW 11 O 39 ]. While itself possessing marginal solubility, slurries of á-K 9 [AlW 11 O 39 ] react with aqueous metal cations to form more soluble transition-metal substituted POMs (TMSPs). These reactions result in the formation of anions of the formula [AlM n+ W 11 O 39 ] (9-n)- , where M n+ = Al(III), Co(II), Co(III), Mn(II), Mn(III), Mn(IV), [V IV O] 2+ , and [V V O] 3+ . These anions were characterized by 27 Al, 183 W, and 51 V NMR (as appropriate), infrared spectroscopy, UV-Visible spectroscopy, cyclic voltammetry, pH titration (to determine the pK a of water ligand on the transition metal, as appropriate), and elemental analysis. á-[AlVW 11 O 40 ] 6- was used as an oxidant for a phenolic lignin model compound, 1-(3,5-dimethoxy-4-hydroxyphenyl)-2-(phenoxy)propane-1,3-diol.

MPACT Scores for Jennifer J. Cowan

A = 0
C = 0
A+C = 0
T = 0
G = 0
W = 0
TD = 0
TA = 0
calculated 2008-04-07 07:43:52

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