This study has been concerned with the fluoro-complexes of the elements of Groups IVA and IVB. The infrared, Raman and 19F n.m.r. spectra of the hexafluoro-anions show that for all the elements except lead (IV) the predominant species in aqueous solutions of the ammonium salts are the octahedral MF6 2- ions; when M = Pb no conclusion was reached. Fluorine exchange in these solutions is slow on an n.m.r. time scale when hi = Si, Ge, Sn or Ti, but much faster when H = Zr, Hf or Fe. The fluorine resonances of the Group IVA hexa-fluoro-metallates are at much lower applied fields than those of the Group IVB complexes.