Call number: LD2668 .T4 1961 H64

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This dissertation describes a study of the electronic structure of some selected cyclopentadienyl metal olefin, (mu)-alkylidene, and carbonyl complexes. While most studies of this type are largely theoretical in nature, this work relies on the experimental observations which result from the application of photoelectron spectroscopy to the measurements of the important molecular energies of these compounds. The first part of the discussion is a study of metal-olefin bonding in the CpM(CO)₂L (L = C₂H₄, C₃H₆) compounds. Of particular interest are the observed changes in ionization energies of the olefin (pi) orbital upon coordination. These results also allow a comparison of the coordination of CO and C₂H₄. The valence ionizations of μ-CH₂-[(C₅H₄CH₃)Mn(CO)₂]₂ are also presented. This example of the increasingly important μ-alkylidene complexes provides evidence of a 3C-6e configuration with a net Mn-Mn single bond. The final chapter describes a study of the valence electronic structure of the CpM(CO)₂ (M = Co, Rh; Cp = η⁵-C₅H₅⁻) and η⁵-C₅(CH₃)₅⁻ ) system. This group of four closely related molecules demonstrates how photoelectron spectroscopy can be used to monitor the electronic effects of specific chemical modifications. The intent throughout is to not only present a detailed analysis of the specific compounds chosen for this study, but to also further demonstrate the applicability of photoelectron spectroscopy to a broad spectrum of problems concerning the structural and electronic make-up of organometallic molecules.

Cobalt-substituted carboxypeptidase and carbonic anhydrase were chosen as candidates for resonance Raman spectroscopy because they possess visible absorption due to the Co(II)-protein complex. However, no evidence for resonance-enhanced peaks due to the cobalt-containing chromophore was found with laser excitation near the visible absorption bands (514.5 nm) or closer to the ultraviolet absorption bands (457.9nm). Arsanilazocarboxypeptidase and model azotyrosine compounds were selected for a Raman spectroscopic investigation because they have intense absorption bands in the visible region. All of these substances yielded similar resonance Raman spectra. Although there was no evidence for specific zinc-ligand vibrations, shifts in vibrational frequencies of the azotyrosine chromophore could be used as proof of zinc complexation. The protonated azotyrosine model compound was found to have the phenoxy group hydrogen bonded to the azo group, forming a six-membered ring. Replacement of the proton by zinc resulted in the zinc atom being bound only to the phenoxy group. In arsanilazocarboxypeptidase the azotyrosine at position 248 in the polypeptide chain was found to have a structure similar to the protonated model compound, a six-membered ring with zinc bridging the phenoxy group and the azo group. This gave further proof that Tyr 248 is close to the zinc atom in the native enzyme, even in the absence of substrate.

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This Thesis describes the synthesis and structural characterisation of a range of heterometallic cluster compounds of platinum. Chapter 1 reviews the current knowledge in this area and gives examples of the kinds of cluster compounds which have been characterised, with some emphasis on their mode of synthesis and their structural and spectroscopic characterisation. The structures of the cluster compounds are rationalised in terms of the triangular Pt₃ unit which dominates the cluster chemistry of platinum. The bonding in the simplest triplatinum cluster compounds is analysed and is used as a basis for understanding the interconversion of platinum cluster compounds and the formation of heterometallic platinum-gold cluster compounds. Chapter 2 describes the synthesis and characterisation of the homometallic platinum cluster compounds which are convenient precursors for the formation of heterometallic cluster compounds. A general synthetic route to the platinum carbonyl phosphine clusters has been developed and the exchange of bridging CO and S0₂ ligands in this type of cluster was investigated. The synthesis of a new type of anionic 44 electron triplatinum cluster, [Pt₃(μ-S0₂)₂(μ-X)(PR₃)₃]¯ described. The syntheses of heterometallic clusters from the trianguloplatinum cluster compounds are reported in Chapter 3. The use of [AuPR₃] as a capping fragment generates clusters with a tetrahedral Pt₃Au framework. The synthesis and characterisation of two novel "sandwich" compounds are reported in which a gold or copper atom is coordinated between two parallel triplatinum units. A full single crystal X-ray crystallographic study has been carried out on each of these compounds and their geometric parameters contrasted. Chapter 4 describes the reactions of the platinum-sulphide complex [Pt₂(μ-S)(CO)(PPh₃)₃]. This compound is found to be chemically robust. The pt-Pt bond has so far proved resistant to insertion reactions and only the ligands trans to the sulphur atom are readily exchanged. The bridging sulphido- group appears to have an extensive coordination chemistry which has lead to the synthesis of some heterometallic complexes. This property does not, as yet, provide a route into cluster formation but instead produces complexes which are aggregates of metal atoms. The application of ³¹P and ¹⁹⁵Pt NMR studies to the characterisation of platinum cluster compounds is discussed in Chapter 5. The solution NMR spectra of compounds synthesised in the course of this research are described and analysed in detail. A large amount of NMR data for homometallic triplatinum clusters has been gathered and it has been possible to characterise a number of such compounds having relatively low symmetry. The heterometallic complexes described in Chapters 3 and 4 have also been characterised using NMR spectroscopy by considering the extra MPR₃ fragments as perturbations on the spectra of the compounds from which they were derived. Analysis of the complex spectra obtained for such compounds was greatly assisted by the use of computer simulation techniques.