Jennifer J. Cowan

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Trends in the stability of alpha- and beta-Keggin heteropolytungstates of the second-row main-group heteroatoms Al(III), Si(IV), and P(V) are elaborated by data that establish the roles of kinetic and thermodynamic control in the formation and isomerization of Keggin tungstoaluminates. Slow, room-temperature co-condensation of Al(III) and W(VI) (2:11 molar(More)
Although many enzymes can readily and selectively use oxygen in water-the most familiar and attractive of all oxidants and solvents, respectively-the design of synthetic catalysts for selective water-based oxidation processes utilizing molecular oxygen remains a daunting task. Particularly problematic is the fact that oxidation of substrates by O2 involves(More)
beta-[SiW(12)O(40)](4)(-) (C(3)(v) symmetry) is sufficiently higher in energy than its alpha-isomer analogue that effectively complete conversion to alpha-[SiW(12)O(40)](4)(-) (T(d)) is observed. By contrast, beta- and alpha-[AlW(12)O(40)](5)(-) (beta- and alpha-1; C(3)(v) and T(d), respectively) are sufficiently close in energy that both isomers are(More)
The reversible, stepwise formation of individual Nb-mu-O-Nb linkages during acid condensation of 2 equiv of A-alpha-[SiNb(3)W(9)O(40)](7-) (1) to the tri-mu-oxo-bridged structure A-alpha-[Si(2)Nb(6)W(18)O(77)](8-) (4) is demonstrated by a combination of X-ray crystallography and variable-pD solution (183)W and (29)Si NMR spectroscopy. Addition of DCl to a(More)
Nanoscale characterization of acid and redox properties of Keggin-type heteropolyacids (HPAs) with different heteroatoms, H(n)MW(12)O(40) (M = P, Si, B, Co), was carried out by scanning tunneling microscopy (STM) and tunneling spectroscopy (TS) in this study. HPA samples were deposited on highly oriented pyrolytic graphite surfaces to obtain images and(More)
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