Degree Type

Dissertation

Date of Award

1985

Degree Name

Doctor of Philosophy

Department

Chemistry

Abstract

N(C(,4)H(,9))(,4) (,2)Re(,2)Br(,8) crystallizes in the monoclinic space group P2(,1)/n. It has a disordered form, such that 62.1% of the Re-Re bonds are aligned in one direction while 37.9% are aligned in a direction perpendicular to this. For both the octabromo and octachloro salts, highly resolved vibrational structures for the first observed electronic band at about 14000 cm('-1) were recorded by the spectrophotometer. It was possible to resolve the Franck-Condon progressions for both the major and minor site components of each compound with intenstities consistent with the (delta) (--->) (delta)* (('1)A(,1g) (--->) ('1)A(,2u)) assignment. However, additional absorption features were observed that have been attributed to further disorder components that have not been revealed by the X-ray diffraction structures;Polarized electronic spectra in the 15000-35000 cm('-1) region are reported for Re(,2) O(,2)CC(CH(,3))(,3) (,4)Cl(,2). A peak at 20200 cm('-1) is assigned as the electric-dipole-allowed ('1)A(,1g) (--->) ('1)A(,2u) ((delta) (--->) (delta)*) transition with z-polarization. Weak transitions are observed at 21600, 24700, 29000, and 32000 cm('-1). The first three weak transitions appear to be electric-dipole-forbidden vibronically allowed transitions with x, y-polarization;The (beta)- and (gamma)-Mo(,2) O(,2)CC(CH(,3))(,3) (,4) form one-dimensional chains along the c-axis of the unit cell. Polarized spectra are reported for these two polymorphs at 300 and 6 K. The evidence available from earlier studies in this research group with Mo(,2)(O(,2)CCH(,3))(,4) and Mo(,2)(O(,2)CCF(,3))(,4) provides a justification for assigning the lowest energy bands as weak electric-dipole-allowed transitions with molecular z-polarization under the local D(,4h) symmetry. The polarization of the transitions is that expected for ('1)A(,1g) (--->) ('1)A(,2u) ((delta) (--->) (delta)*) transitions. The intensities are sufficiently low that Franck-Condon progressions based on vibronic origins have intensities comparable to the 0-0 progression. However, additional absorption bands were observed that have been attributed to different site components which have not been indicated by X-ray diffraction structures.

DOI

https://doi.org/10.31274/rtd-180813-8691

Publisher

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

Copyright Owner

Hai-Wei Huang

Language

en

Proquest ID

AAI8604474

File Format

application/pdf

File Size

167 pages

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