Relative energies of alpha and beta isomers of Keggin dodecatungstogallates

INOR 326

Karthik Sundaram1, Wade A. Neiwert, w-neiwert@bethel.edu2, Ira A. Weinstock, iaw@sci.ccny.cuny.edu3, and C. L. Hill, chill@emory.edu1. (1) Department of Chemistry, Emory University, 1515 Pierce Drive, Atlanta, GA 30322, (2) Department of Chemistry, Bethel University, 3900 Bethel Drive, St. Paul, MN 55112, (3) Department of Chemistry, City College of The City University of New York, 138th St and Convent Avenue, New York, NY 10031
The relative energies of β Keggin heteropolytungstates, Xn+W12O40(8–n)–, decrease as Xn+ is varied within period 3, from P5+ to Si4+ to Al3+. With heating of α-H5Ga3+W12O40 at 200 °C in water, an equilibrated mixture of α (Td; one 183W NMR signal) and β (C3v; three signals; 1:2:1 ratio) isomers is obtained. From ΔGexp = –RT ln Kβ→α, in which (from 71Ga NMR spectra) Kβ→α (= [α]/[β]) = 5.0, β-GaW12O405– is 0.65 kcal mol–1 higher in energy than α-GaW12O405–. This finding is evaluated by analysis of the X-ray crystal structure β-K2Na3[GaW12O40]•9.3H2O [trigonal, space group P3221, a = 18.9201(13) Å, b = 18.9201(13) Å, c = 12.5108(12) Å, Z = 3, T = 100(2)K], comparison of the Shannon and Prewitt radii and Pauling electronegativities of Al3+ and Ga3+, and insight from density functional theory calculations, which predicted Eβ – Eα ) 0.32 kcal mol–1.

 

Inorganic Chemistry in Water
7:00 PM-10:00 PM, Sunday, March 25, 2007 Hyatt Regency Chicago -- Riverside Center, Poster

Sci-Mix
8:00 PM-10:00 PM, Monday, March 26, 2007 Hyatt Regency Chicago -- Riverside Center, Sci-Mix

Division of Inorganic Chemistry

The 233rd ACS National Meeting, Chicago, IL, March 25-29, 2007