RbFeF4, TlFeF4 and NH4FeF4 have been prepared from solution and shown to be isomorphous to tetragonal TlAlF4. Decomposition occurs prior to melting making crystal growth difficult. A more stable isomorph RbVF4 has been obtained from a melt of RbF and VF3. X-ray powder data are presented for each compound. © 1968.