Solid state59Co NMR study of a Np(VII) compound

Np(VII) compounds with [Co(NH₃)₆]3+ cations were synthesized and structurally examined using powder X-ray diffraction. Multiple phases were observed, consisting of octahedral [Co(NH₃)₆]3+ cations, discrete tetragonal bipyramidal [NpO₄(OH)₂]3− anions, and waters of hydration. Electric field gradient tensors at Co sites were measured by solid state 59Co nuclear magnetic resonance (NMR) spectroscopy and compared with theoretical calculations. The relative contributions of the chemical shift and electric field tensors to the NMR lineshape were determined by recording spectra at field strengths of 7.04 and 11.74 Tesla. Further, the evolution of structure and morphology as a function of sample age and the effects on NMR spectral parameters has also been investigated. These results demonstrate the use of NMR at multiple fields to expand understanding of the stability and electronic structure of high valent neptunium compounds.