Research presented in this thesis falls into four areas. 1) Vibrational spectra of pentafluorides. 2) Preparation and spectra of NbF5 and TaF5 complexed with Lewis bases. 3) Preparation and some properties of some Nb, and Ta (V) fluoride-halides and pseudohalides. 4) 93Nb n.q.r. spectra of some compounds derived from 93Nb n.q.r. spectra of NbF5 and vibrational soectra of NbF5 and TaF5 are interpreted in terms of a very small deviation from C4v symmetry in the tetrameric molecules of the solid state. I.R. spectra suggest that NbF5, and TaF5 are polymeric in the liquid state up to at least 15
