Surface Oxygen Chemistry on Some Isopoly and Heteropolyoxoanions (Polyoxoanion)

Schwartz, Curtis

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Description

Title

Surface Oxygen Chemistry on Some Isopoly and Heteropolyoxoanions (Polyoxoanion)

Author(s)

Schwartz, Curtis

Issue Date

1986

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Chemistry, Inorganic

Abstract

• The dynamic behavior of the (alpha)-Mo(,8)O(,26)('4-), C(,6)H(,5)AsMo(,7)O(,25)('4-), and (C(,6)H(,5)As)(,2) Mo(,6)O(,24)('4-) ions as (n-C(,4)H(,9))(,4)N('+) salts in CH(,3)CN have been studied by variable temperature ('17)O NMR lineshape analysis, ('17)O spin saturation transfer techniques, and ('17)O label crossover experiments. The C(,6)H(,5)AsMo(,7)O(,25)('4-) ion shows two distinct types of fluxional behavior that can be related to the anion's structure. The low temperature process involves Mo(,6)O(,18) ring inversion accompanied by twisting of the C(,6)H(,5)AsO(,3)('2-) subunit and twisting or flipping of the MoO(,4)('2-) subunit. Only weak (>2.2(ANGSTROM)) molybdenum-oxygen bonds are broken and reformed. The higher temperature process, although mechanistically undefined, involves cleavage of stronger (1.7-2.0(ANGSTROM)) molybdenum-oxygen bonds. Evidence is presented for related processes in the (alpha)-Mo(,8)O(,26)('4-) and (C(,6)H(,5)As)(,2)Mo(,6)O(,24)('4-) ions.
• Compounds of the composition Nb(,2)W(,4)O(,19)R (n-C(,4)H(,9))(,4)N (,3) R = CH(,3), C(,2)H(,5), CH(CH(,3))(,2), C(CH(,3))(,3), Si(CH(,3))(,3), C(CH(,3))(,3) (CH(,3))(,2)Si, and Si(C(,6)H(,5))(,3) have been synthesized and isolated in crystalline form. For R = CH(,3) and C(,2)H(,5), the alkyl group is bound exclusively at the ONb(,2) bridging oxygen site on the polyoxoanion cage. For the bulkier R groups, binding to a terminal ONb oxygen site is observed. Reaction of Nb(,2)W(,4)O(,19)('4-) with RX R = CH(,3), C(,2)H(,5); X = OSO(,2)R results in the formation of Nb(,2)W(,4)O(,19)('4-) as a mixture of five diastereomers where the R group binds to the five symmetry inequivalent bridging oxygens on the polyoxoanion surface. Reaction of Nb(,2)W(,4)O(,19)('4-) with RX R = CH(CH(,3))(,2), (CH(,3))(,3)C (CH(,3))(,2)Si, X = O(,3)SCF(,3); R = (CH(,3))(,3)Si, X = Cl, NH(CH(,3))(,3)Si gives Nb(,2)W(,4)O(,19)R('3-) where R is bound to a terminal ONb oxygen. The Nb(,2)W(,4)O(,19)H('3-) ion has been prepared and the ONb(,2) oxygen site determined to be the predominant protonation site on the polyoxoanion cage. The product distributions described above are discussed in terms of relative metal-oxygen bond lability effects of the polyoxoanion, steric effects between the organic group and polyoxoanion surface oxygens, and electronic charge distribution on the polyoxoanion surface which govern the relative nucleophilicities and basicities of the different polyoxanion oxygens.
• The polyoxothioanions MW(,5)O(,18)S (n-C(,4)H(,9))(,4)N (,3) M = Ta, Nb have been synthesized and isolated in crystalline form by reaction of MW(,5)O(,19) (n-C(,4)H(,9))(,4)N (,3) with (CH(,3))(,3)Si (,2)S. Oxygen-17 NMR and IR spectroscopy indicates that one terminal ONb or OTa oxo ligand has been replaced by a thio ligand in the polyoxothioanion product. (Abstract shortened with permission of author.)

Graduation Semester

1986

Type of Resource

text

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