Configuration of the Uranyl Ion

Abstract

X-RAY crystallographic data^1,2 indicate that in solid uranyl salts and metallic uranates the UO₂⁺⁺ ion is linear, and if this configuration is retained, only one frequency corresponding to the symmetric ν₁ vibration should appear in the Raman spectra of uranyl salt solutions. Actual observations^3–5, however, have shown at least two fundamental frequencies, at about 860 cm.⁻¹ and 200 cm.⁻¹, which have been assigned to the symmetric ν₁ and bending ν₂ vibrations respectively. Satyanarayana⁴ found also a weak line at 909 cm.⁻¹, corresponding to the asymmetric ν₃ vibration. These results suggest that the UO₂⁺⁺ ion in solution is bent, a conclusion supported by the infra-red spectral measurements, in which the ν₁ frequency, forbidden for a linear model, has always been observed. Both Crandall⁵ and Satyanarayana have suggested that the ion might be linear in solution, local forces being responsible for the appearance of forbidden frequencies in the spectra. Hitherto, no experimental evidence has been put forward in support of this contention.