A complex fluoride A2MF6 wherein M is a tetravalent element Si, Ti, Zr, Hf, Ge or Sn, A is an alkali metal Li, Na, K, Rb or Cs is prepared by providing a first solution containing a fluoride of M, providing a second solution containing a compound of A and/or the compound of A in solid form, mixing the first solution with the second solution and/or the solid for reacting the fluoride of M with the compound of A, and recovering the resulting solid product via solid-liquid separation.