The binary zirconium and hafnium polyazides [PPh4 ]2 [M(N3 )6 ] (M=Zr, Hf) were obtained in near quantitative yields from the corresponding metal fluorides MF4 by fluoride-azide exchange reactions with Me3 SiN3 in the presence of two equivalents of [PPh4 ][N3 ]. The novel polyazido compounds were characterized by their vibrational spectra and their X-ray crystal structures. Both anion structures provide experimental evidence for near-linear M-N-N coordination of metal azides. The species [M(N3 )4 ], [M(N3 )5 ]- and [M(N3 )6 ]2- (M=Ti, Zr, Hf) were studied by quantum chemical calculations at the electronic structure density functional theory and MP2 levels.