A review of the transition-metal pentafluoride structures and the theories put forward to explain them is held in Chapter 1, along with a brief discussion of the transition-metal oxide fluorides which have structures related to them. Chapters 2-5 detail the preparation and characterisation of NbF5:TaF5 [x:y] (Chapter 2), RuF5:TaF5 [x:y] (Chapter 3), VF5:TaF5 [x:y] (Chapter 4) and RuF5:VF5 [x:y] and RuF5:NbF5 [x:y] are grouped together in Chapter 5. Characterisation of these compounds has involved XRF analysis, infrared and Raman spectroscopy, mass spectrometry and X-ray diffraction techniques. In order to investigate the metal site occupancy of some of the mixed-metal pentafluorides the EXAFS spectra of suitable metal edges have been recorded and analysed. The results are reported in Chapter 6 along with a brief theoretical description of the technique and the method of data analysis used. The possibility of using MICVD (Metal Inorganic Chemical Vapour Deposition) as a method of forming thin layers of pure metals or alloys by the reduction of metal fluorides or mixed-metal pentafluorides respectively has been investigated both theoretically and experimentally. This is discussed in Chapter 8. Chapter 9 reports details of the experimental techniques used in the work in this thesis.