An Investigation of the Photochemical and Excited State Properties of Selected Second and Third Row Transition Metal Complexes

Citation

Geoffroy, Gregory Lynn (1974) An Investigation of the Photochemical and Excited State Properties of Selected Second and Third Row Transition Metal Complexes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/5KPA-2F87. https://resolver.caltech.edu/CaltechETD:etd-10132005-154007

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The photochemical properties of several different types of 2nd and 3rd row transition metal complexes are discussed. Complexes of the type [...] have been prepared and characterized by electronic and infrared absorption spectral measurements. The complexes are readily prepared by thermal anation reactions of [[...]], the aquo complexes being formed by uv irradiation of acidic solutions of [...]. The lowest energy electronic absorption band in the [...] complexes is assigned to the ligand field transition [...], whereas in [...] both [...] and [...] absorptions are observed. The position of the [...] transition establishes the order of decreasing ligand field strength of X as [...] for both Rh(III) and Ir(III) complexes. Halide-to-metal charge transfer bands are observed for [...] complexes with X = [...] and [...]. Ultraviolet irradiation of H2 and O2 adducts of [...], [...], [...], and [...] has been found to induce reductive-elimination of molecular hydrogen and oxygen and regeneration of the square-planar complexes. The reactions occur in argon purged solutions and in frozen EPA solutions of the adducts at 77[degrees]K. Absorption and emission spectra for the square planar complexes [...] and [...] have been measured in the solid state and in frozen EPA [ethyl ether-isopentane-ethyl alcohol (5:5:2)] solution at 77[degrees]K. Of the four complexes, only [...] fails to luminesce in the solid state at room temperature. At 77[degrees]K in EPA the emission maxima fall in the range 16.8-18.4[...], and the emission lifetimes are between 8.2 and 20.8 [...]; [...] exhibits an unusually sharp, strongly overlapping emission/absorption system, with an emission quantum yield of 0.93 ± 0.07 It is suggested that in the Ir(I) cases emission occurs from a square planar [...] charge transfer state of [...] symmetry. The fact that the emission maxima of the two Rh(I) complexes are both red-shifted by about 4000 [...] from the lowest absorption peak is discussed in terms of an admixture of ligand field character in the primarily [...] emitting state, which could give rise to a distortion of the RhP4 core towards tetrahedral geometry. The absorption and emission spectra of several other Rh(I) complexes are also briefly discussed. Irradiation of [...] in CH3CN results in cleavage of the Re2 quadruple bond and formation of monomeric Re(III) products. The primary photoproduct is [...], and this species can be further photolyzed in CH3CN to give [...]. The quantum yield of disappearance of [...] upon irradiation at 313 nm was found to be 0.017 ± 0.005. [...] is also the primary photoproduct under 254 nm irradiation. Irradiation of [...] in CH3CN with a He-Ne laser (632.8 nm) does not lead to reaction, indicating that the excited state derived from the [...] transition is not photoactive. Cleavage of the Re2 unit is observed, however, when solutions are irradiated at 366 nm.

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