Spectroscopy and Photochemistry of Metal-Oxo Complexes

Citation

Winkler, Jay Richmond (1984) Spectroscopy and Photochemistry of Metal-Oxo Complexes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/DE5E-2Y69. https://resolver.caltech.edu/CaltechETD:etd-02272006-082939

Abstract

Electronic spectroscopic, photophysical, and photochemical investigations of two types of metal-oxo complexes are described. The electronic absorption spectra of various molybdenyl ions (MoO³⁺ were measured in crystals and solutions. These spectra clearly support ²B₁(x²-y²) ← ²B₂(xy) and ²E(xz, yz) ← ²B₂(xy) assignments for the two weak bands near 25,000 and 14,000 cm^-1, respectively, in these molecules. A Franck-Condon analysis of the ²B₁ ← ²B₂ band in the 5 K single crystal absorption spectrum of (Ph₄As)MoOCl₄ indicated a 0.07(1) Å elongation of the metal-chloride bond in the excited state. Crystalline (Ph₄As)MoOCl₄ luminesces from the lower energy component of a split ²E(xz, yz) state with a lifetime of 160 ns at 300 K, increasing to 1.4 µs at 5 K. No luminescence was detected from any molybdenyl ion in solution.

The electronic absorption and emission spectra of trans-ReO₂L₄^z (L = CN^-, z = 3-; L = 1/2(ethylenediamine), z = +; L = pyridine, z = +; L = 4-picoline, z = +; L = 4-t-butylpyridine, z = +) were also measured in crystals and solutions. The lowest energy absorption bands are assigned to components of a split ³E_g[(e_g)¹(b_2g)¹] state (ground state ¹Ag_1g[(b_2g)²]). Emission from at least two of these components was identified in the cyanide and pyridine complexes and only the ethylenediamine complex failed to luminesce. Franck-Condon analyses of the emission spectra indicated ca. 0.1 Å elongations of each Re-O bond in the ³E_g excited states. The lifetime of the ³E_g state varies from 10 to 300 µs in crystals and is ca. 10 µs for trans-ReO₂L₄^z species in aprotic solvents. Protons efficiently quench the luminescence of these molecules. Experiments directed toward photoinduced oxygen atom transfer chemistry are also described.

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