Polyoxotechnetates form only in strongly acidic conditions, such as in pertechnetic acid| or trifluoromethanesulfonic acid solutions. The first empirically isolated polyoxotechnetate was the red . It contains both Tc(V) and Tc(VII) in ratio 4: 16 and is obtained as the hydronium salt  by concentrating an  solution. Corresponding ammonium polyoxotechnetate salt was recently isolated from trifluoromethanesulfonic acid and it has very similar structure.
The only polyoxorhenate formed in acidic conditions in presence of pyrazolium cation. The first empirically isolated polyoxorhenate was the white . It contains Re(VII) in both octahedral and tetrahedral coordination.