Browsing by Author "Hall, Philip Simon"

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    A spectroscopic study of square planar platinum (2) complexes
    (1983) Hall, Philip Simon; Thornton, David A; Foulds, Gary André
    A number of spectroscopic techniques consisting of ultraviolet, ¹H-NMR and mass spectrometry have been used in the structural analysis of square planar Pt(II) complexes. The complexes trans-[PtBr₂(Y) (R-an)] (Y = C₂H₄,CO; R-an = substituted aniline) were prepared and investigated by the spectrosopic techniques. Infrared assignments were aided by isotopic labelling studies. The discussion of the two series of complexes are based on their relation to one another. The complexes trans-[PtX₂ (CO) (L)] (X = Cl, Br; L = aniline, pyridine N-oxide, pyridine, ammonia, imidazole and pyrazole) were prepared from their corresponding ethylene analogues. Infrared assignments, with labelling studies, are given for the complexes. The bonding effects in these complexes were studied using ¹H-NMR and ultraviolet spectroscopy. The ¹H-NMR spectra reveal that there is a fluxional behaviour of the ligands in some of the complexes. Hence, cold temperature studies were required to "freeze out" this fluxional behaviour and observe the expected signals due to the ¹⁹⁵pt-H coupling. The electronic effects are different when the ligand, L, was capable of forming σ-bonds with Pt²+, compared to when L was capable of forming both a- and π-bonds with Pt²+. The mass spectra show the M+ peak and subsequent fragmentation in the complexes. The fluxional behaviour of imidazole in trans-[PtX₂(C₂H₄) (Him)] was monitored by cold temperature studies. Using band shape analysis (with the aid of a computer) the activation paramaters for the exchange processes were determined. The dependence of the imidazole proton signals on temperature, solvent and excess ligand, all indicate that an intermolecular exchange process is occurring. Studies on the complex trans-[PtX₂(C₂H₄) (pyz)] and the effect of solvent on the complexes are being pursued, and it is hoped that an understanding of the role of the solvent in the exchange process will become apparent.
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    A spectroscopic study of square planar rhodium(I) complexes
    (1989) Hall, Philip Simon; Jackson, Graham Ellis; Moss, John R; Thornton, David A
    Ninety square planar Rh(I) complexes of the type cis-[Rh(CO)₂(X)(L)], [Rh(COD)(X)(L)], [Rh(CO)₂(L)₂]ClO₄ and [Rh(COD)(L)₂]ClO₄ (X is Cl or Br; COD is 1,5-cyclooctadiene; L is aniline, pyridine, pyridine N-oxide, imidazole and ammonia), as well as their isotopically labelled derivatives (¹³CO, ²H and ¹⁵N) were prepared, characterized by microanalysis and melting point, and investigated by the following spectroscopic techniques: infrared, Raman, ultraviolet, mass spectrometry, and 1H, ¹³C and ¹⁵N nmr spectroscopy. The comprehensive isotopic labelling studies allowed unambiguous assignment of the infrared modes in the 4000-50 cm⁻¹ region. The infrared assignments are discussed with reference to their vᴰ/Vᴴ ratios, the various ligands and halogens used, the charges on the complexes, and are compared to similar compounds. The 1H, ¹³C and ¹⁵N nmr runs were performed at room and low temperatures. Fluxionality of the ligands (L) was observed and the exchange process was monitored by variable temperature nmr. The enthalpy and entropy values for the intermolecular exchange of L in the complexes cis-[Rh(CO)₂(X)(L)] were obtained by a complete computer simulated band shape analysis of the carbonyl region of the ¹³C nmr spectra. The non-equivalence, and specific assignment of the carbonyl groups in the cis- [ Rh(CO)₂(X)(L)] complexes were determined by recording the variable temperature ¹³C nmr spectra of the doubly enriched species cis[Rh(¹³CO)₂(X)(¹⁵N-ligand)]. ²J(¹³C-Rh-¹⁵N) values are reported for the first time. The ¹J(¹⁵N-¹⁰³Rh) coupling constants are rationalized in terms of the metal-nitrogen bonding, and correlate with the s-character of the bonding electron on nitrogen. While the solution electronic spectra reveal that the complexes are discrete monomeric entities in solution, there are indications of metal-metal interactions in the solid-state. The normal coordinate analysis study of the complexes cis-[Rh(CO)₂(X)(L)] involved the calculation of a general valence force field by applying the eigenvector method of Becher and Mattes. The results show that point-mass-modelling and simplified force field, as assumed in our treatment, describes, to a good approximation, the vibrational properties of the complexes. The potential energy distribution provided further support for the proposed infrared assignments of the complexes.