Method of preparing inorganic pentafluorides

A method of preparing an inorganic pentafluoride corresponding to the formula MF5, where M represents P or As, said method comprising:

• reacting a trihalide corresponding to the formula MX3, where M has the meaning given above and X is chlorine or bromine, with chlorine, bromine or iodine and with an excess of HF at elevated pressure and a temperature between −25° C. and 100° C. in a pressure vessel, whereby a mixture of MF5 and HX is formed;
• and
• releasing and discharging the mixture from the pressure vessel as a gaseous mixture and isolating the MF5 formed.