Analysis of Uranium Azide and Nitride Complexes by Atmospheric Pressure Chemical Ionization Mass Spectrometry

Atmospheric pressure chemical ionization mass spectrometry (APCI-MS) has been used to characterize the air-sensitive paramagnetic organouranium azide and nitride complexes [(C₅Me₅)₂UN₃(μ-N₃)]₃ and [(C₅Me₅)U(μ-I)₂]₃N, respectively. The trimetallic complex [(C₅Me₅)U(μ-I)₂]₃E had been identified by X-ray crystallography, but the data did not definitively identify E as N^3- versus O^2- or (OH)^-, a common problem in heavy-element nitride complexes involving metals with variable oxidation states. A comparison of the 250 °C APCI-MS spectra of products made from NaN₃ and Na¹⁵NNN showed mixed [M]⁺ and [M + H]⁺ envelopes at expected ion intensities for the ¹⁴N and ¹⁵N isotopomers. A compilation of U−C(C₅Me₅) and U−I bond distance data for U³⁺ and U⁴⁺ is also reported that shows that the ranges for the two oxidation states have significant overlap.