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

Author: Geoffroy, Gregory Lynn

Year: 1974

Degree: Dissertation (Ph.D.)

Advisors: Hammond, George Simms; Gray, Harry B.

Committee Member: Unknown, Unknown

Option: Chemistry

DOI: 10.7907/5KPA-2F87

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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