A Spectroscopic Study of Some Phosphorus Chalcogenides

Abstract

This thesis consists of a systematic study of some members of the series P4Sex" and P4Sx ( x = 3-10 ). A comparative study of the physical, electronic and structural properties of the selenide and the related sulphide reveals the importance of Se...Se intermolecular bonding. A new normal crystalline phase of tetraphosphorus triselenide, α'-P4Se3, has been identified. Interactions between molecules appear to be weaker in the α'- than in the α- phase as indicated by x-ray crystallography, Raman spectroscopy and x-ray photoelectron spectroscopy. The transitions between the normal crystalline phases and the orientationally disordered phases, β- and γ-P4Se3, have been studied by differential scanning calorimetry and by variable temperature Raman spectroscopy. [CHAPTER 4] An investigation of the temperature and pressure dependences of the internal and external first-order Raman-active phonons of, crystalline α-P4S3, shows that intra- intermolecular coupling is present in α-P4S3, but that it is weaker than that in the selenide, α-P4Se3. [CHAPTER 5] The Raman spectrum of a film of polycrystalline P4Se4 suggests that, more than one isomer and / or phase is present. A strong band at 187 cm-1 is characteristic of P4Se4. [CHAPTER 6] P4Se5 is the only member of the selenide series, apart from the parent molecule P4Se3 whose structure has been confirmed by x-ray structure determination. Significantly short se...Se interactions exist between molecules. Intermolecular contacts in the sulphide α-P4S5 are not shorter than expected. The temperature dependences of the Raman-active phonons of α-P4S5 do not indicate significant intra- intermolecular coupling. P4Se5 was not prepared in sufficient quantities to allow a similar analysis. [CHAPTER 7] The presence of interactions between molecules in P4S10 has been confirmed by an investigation of the temperature and pressure dependences of the Raman-active phonons. The Raman spectrum of P4Se10, which is isostructural to P4S10 at a molecular level, is reported. [CHAPTER 8] The Raman spectra of crystalline α'-P4Se3I2, β-P4Se3I2, α-P4S3I2 and β-P4S3I2 have been measured as a function of temperature and the Raman spectra of the selenodiiodides have also been measured as a function of pressure. These studies support the general conclusion that coupling between intra- and intermolecular bonds is present in these phosphorus chalcogenide derivatives as has previously been observed for the parent molecules, α-P4Se3 and α-P4S3. Coupling is stronger in the selenodiiodides than in the thiodiiodides and would appear to be stronger in the β- than in the α- or ?'- isomers. [CHAPTER 9] α-P4S3, reacts with the copper halides to form compounds, P4S3.CuX (X = C1, Br, I). The differences between the Raman spectra of these derivatives and that of α-P4S3 suggest the formation of stronger interactions between cage molecules in the P4S3.CuX structures. [CHAPTER 9] The assignment of the α-P4S3 normal modes of vibration based on the cumulative data from polarisation measurements, temperature and pressure dependent Raman data and infrared data has been used in a normal coordinate analysis of α-P4S3, and yields a reasonably well defined forcefield. The choice of internal coordinates makes explicit the intramolecular S...S bond. This forcefield for the A1 and E species of α-P4S3, provides reasonable estimates for the A' and A" wavenumbers of the mixed species P4SSe2, and P4S2Se. [CHAPTER 10]