PNNL

Abstract

The Np(VII) compound with [Co(NH3)6]3+ cations was synthesized and structurally examined using powder X-ray diffraction. We confirmed the presence of multiple phases, consisting of octahedral [Co(NH3)6]3+ cations, discrete tetragonal bipyramidal [NpO4(OH)2]3– anions, and waters of hydration. We investigated the electric field gradient tensors at Co-sites by solid-state nuclear magnetic resonance (NMR) spectroscopy at 7.04 and 11.74 T and compared them with theoretical calculations. The contributions of the chemical shift tensor and electric field tensors are interpreted by a field dependent NMR study. 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 field-dependent NMR to expand the knowledge of the stability and electronic structure of neptunium compounds.