Degree Type

Dissertation

Date of Award

1993

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Robert E. McCarley

Abstract

Novel ternary reduced molybdenum oxides containing infinite chains of trans edge-shared molybdenum octahedra have been well explored. In the past decade, synthetic efforts have examined "cutting" these infinite chains of Mo octahedra into smaller segments, termed oligomers. The oligomers can be formulated from the general formula, M[subscript]n-xMo[subscript]4n+2O[subscript]6n+4, where n equals the number of trans edge-shared Mo octahedra. The major emphasis of this research was to synthesize and characterize tetrameric oligomers, where n = 4. New oligomeric materials with n = 2,3,4, & 5 were discovered. These members are: K[subscript]0.06M[subscript]1.94MO[subscript]10O[subscript]16 (M = Ca,Sr), K[subscript]0.33Gd[subscript]1.67Mo[subscript]10O[subscript]16, SrBaMo[subscript]10O[subscript]16, K[subscript]1.29Sn[subscript]1.71Mo[subscript]140[subscript]22, K[subscript]1.66Pb[subscript]1.34Mo[subscript]14O[subscript]22, K[subscript]2.6Sr[subscript]0.4MO[subscript]14O[subscript]22, Ba[subscript]3Mo[subscript]18O[subscript]28, and K[subscript]0.19Ba[subscript]3.81Mo[subscript]22O[subscript]34.;The structural features and properties of the oligomers were compared and contrasted in terms of electron counting methods. The dimeric oligomers have a consistent, strong apical Mo-Mo bond and a very strong intercluster metal-metal bond that varies in length based on electron count. For the trimeric oligomers, the apical-apical bonds are arranged in a short-long fashion for the members with less than 44e[superscript]- and the apical-apical bonds become nearly equivalent for materials with greater than 44e[superscript]-. The intercluster metal-metal bonds for the n = 3 members are long if less than 43e[superscript]- are available, short if between 43 and 44e[superscript]-, and long if greater than 44e[superscript]-. The n = 4 oligomer, Ba[subscript]3Mo[subscript]18O[subscript]28, has four short and two long apical-apical bonds and a long intercluster bond. K[subscript]0.19Ba[subscript]3.81Mo[subscript]22O[subscript]34, the n = 5 member, has four short and four long apical-apical bonds and a long intercluster metal-metal distance;Two ternary reduced molybdenum oxide phases containing infinite chains of trans edge-shared Mo octahedra, connected in different manners, were prepared and characterized. The two materials are Ti[subscript]0.31Fe[subscript]1.69Mo[subscript]4O[subscript]7 and RE[subscript]4Mo[subscript]4O[subscript]11, where RE = Y, Nd, and Sm-Lu;Many of the known ternary and quaternary reduced molybdenum oxides have superstructural ordering, due in part, to mixed metal and/or partial occupation of cation sites. Transmission electron microscopy was used to explore the superstructures present in Fe[subscript]1.89Mo[subscript]4.11O[subscript]7, Sn[subscript]0.9Mo[subscript]4O[subscript]6, InMo[subscript]4O[subscript]6, and Mn[subscript]1.5Mo[subscript]8O[subscript]11. Proposed structural models consistent with the observed electron diffraction were presented.

DOI

https://doi.org/10.31274/rtd-180813-11547

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

George Louis Schimek

Language

en

Proquest ID

AAI9335015

File Format

application/pdf

File Size

341 pages

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