Citation: Smith, Anna L.; Hen, Amir; Raison, Philippe E.; Colineau, Eric; Griveau, Jean-Christophe; Magnani, Nicola; Sanchez, Jean-Pierre; Konings, Rudy J. M.; Caciuffo, Roberto; Cheetham, Anthony K. (2015). X-ray Diffraction, M\"ossbauer Spectroscopy, Magnetic Susceptibility, and Specific Heat Investigations of Na4NpO5 and Na5NpO6.. Inorganic chemistry, 54, pp. 4556-4564.