No abstract

Ammonium hexafluorof errate(III), (NH4)3FeFe, and ammonium hexafluoroaluminate, (NH4)3A1F6, decompose 011 heating with an initial loss of 2 moles of ammonium fluoride, forming ammonium tetrafluoroferrate(III), iXHaFeFa (at ca. 140°), and ammonium tetrafluoroaluminate, NHaAlF4 (at ca. 170'). Further heating results in the gradual loss of ammonium fluoride, the final products being iron(II1) fluoride mixed with oxide (at ca. 285") and ?-aluminum fluoride, a new crystalline form (at ca. 300').The intermediate, ammonium tetrafluoroferrate(III), was found to be tetragonal, a = 3.78, c = 6.36 A. It can also be prepared by direct reaction of iron(II1) fluoride and ammonium fluoride a t 180".The structural relationships of the compounds are discussed.

The magnetic properties of Hf13 reported previously3 are at variance with those given here, apparently because of gross contamination of the earlier samples. The earlier results indicated 106xg values of about 15.5 (green) to 11.2 (black) a t 300°K and 5.2 kG, in contrast with only 0.27 found here for HfI3.3: a t 5.05 kG. The prior values of x also showed a broad maximum near 120'K and substantially larger field and temperature dependencies. However, the samples employed were the residues from the incomplete reduction of HfI4 with aluminum followed by sublimation of HfI4 and A113, and aluminum was evident in the powder patterns (together with seven unidentified lines.) In fact, the Hf13 yield was only 510% for the green product and 12% for the black,'* and the triiodide a t best comprised 59-847, of the residue after sublimation. The hafnium analysis of the water-(18) A. R . Janus, Ph.D. Thesis, Syracuse University, 1964. soluble portion was also quite low. Therefore it would appear that the high susceptibilities originated from more than Hf13 and aluminum, perhaps hafniumaluminum intermetallic phases. The present data for the triiodide phase are rather comparable with those obtained by Lewis, et nZ.,19 for the zirconium(II1) halides at only room temperature, Tvhich correspond to effective moments of about 0.4 p. The temperatureindependent character of the small paramagnetism for the hafnium iodide phase is rather typical.Acknowledgments.--hppreciation is expressed to a number of persons who provided significant assistance in this work : D. A. Lokken with the spectral and magnetic measurements, F. A. Schmidt and L. K. Reed with the preparation of metal foil, and E. L. DeKalb and K. L. Malaby with the zirconium analyses. (19) Approximate composition limits and lattice parameters of the rhombohedral and tetragonal phases observed in the system LnOl-,F1+2, (Ln = Nd, Gd, Er) are reported. Variation of tile c / a ratio of the tetragonal phase with atomic number is noted and discussed. The rhombohedral to cubic transition temperatures of LnOl-,F1+2, (Ln = La, F d , Sm, E u , Gd, T b , Dy, Y , Ho, and Er) determined from differential thermal analysis are reported and the transition is discussed. Thermal expansion data are reported for NdOF and its mode of thermal decomposition is indicated.