“…The molar refractivities of 7NH4F.6UF4 and of fl-NH4F.UF4 are, respectively, 22.4 and 21-2 cm 3. The difference is 1.2 cm a which is accounted for nicely by the 1 mole of NH4F difference in stoichiometry [the empirical molar refractivity of NH+F is 6.79 cm a in such complexes (Penneman, 1969)]. However, the refractivity values of both structures are somewhat below the values expected for close-packed structures.…”