DOE OSTI2020
Na2UF6 crystallizes in the trigonal P3 space group. The structure is three-dimensional. there are four inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a distorted hexagonal planar geometry to six F1- atoms. There are three shorter (2.31 Å) and three longer (2.38 Å) Na–F bond lengths. In the second Na1+ site, Na1+ is bonded in a 9-coordinate geometry to nine F1- atoms. There are a spread of Na–F bond distances ranging from 2.46–2.58 Å. In the third Na1+ site, Na1+ is bonded in an octahedral geometry to six F1- atoms. There are three shorter (2.38 Å) and three longer (2.41 Å) Na–F bond lengths. In the fourth Na1+ site, Na1+ is bonded in a 9-coordinate geometry to nine F1- atoms. There are a spread of Na–F bond distances ranging from 2.51–2.53 Å. There are two inequivalent U4+ sites. In the first U4+ site, U4+ is bonded in a 9-coordinate geometry to nine F1- atoms. There are a spread of U–F bond distances ranging from 2.24–2.43 Å. In the second U4+ site, U4+ is bonded in a 9-coordinate geometry to nine F1- atoms. There are a spread of U–F bond distances ranging from 2.24–2.44 Å. There are four inequivalent F1- sites. In the first F1- site, F1- is bonded to three Na1+ and one U4+ atom to form distorted FNa3U trigonal pyramids that share corners with thirteen FNa2U2 tetrahedra, corners with four equivalent FNa3U trigonal pyramids, edges with four FNa2U2 tetrahedra, and edges with two equivalent FNa3U trigonal pyramids. In the second F1- site, F1- is bonded to three Na1+ and one U4+ atom to form distorted FNa3U tetrahedra that share corners with fourteen FNa2U2 tetrahedra, corners with three equivalent FNa3U trigonal pyramids, edges with three FNa2U2 tetrahedra, and edges with three equivalent FNa3U trigonal pyramids. In the third F1- site, F1- is bonded to two Na1+ and two U4+ atoms to form distorted FNa2U2 tetrahedra that share corners with thirteen FNa2U2 tetrahedra, corners with four equivalent FNa3U trigonal pyramids, edges with five FNa2U2 tetrahedra, and an edgeedge with one FNa3U trigonal pyramid. In the fourth F1- site, F1- is bonded to two Na1+ and two U4+ atoms to form distorted FNa2U2 tetrahedra that share corners with eleven FNa2U2 tetrahedra, corners with six equivalent FNa3U trigonal pyramids, and edges with six FNa2U2 tetrahedra.