Materials Data on Na2U2Si(O4F)2 by Materials Project

Na2U2Si(O4F)2 crystallizes in the tetragonal I4_1/amd space group. The structure is three-dimensional. Na1+ is bonded to four equivalent O2- and two equivalent F1- atoms to form distorted NaO4F2 octahedra that share corners with six equivalent UO6F pentagonal bipyramids and faces with two equivalent NaO4F2 octahedra. All Na–O bond lengths are 2.58 Å. Both Na–F bond lengths are 2.33 Å. U6+ is bonded to six O2- and one F1- atom to form distorted UO6F pentagonal bipyramids that share corners with six equivalent NaO4F2 octahedra, corners with two equivalent SiO4 tetrahedra, edges with two equivalent UO6F pentagonal bipyramids, and an edgeedge with one SiO4 tetrahedra. The corner-sharing octahedral tilt angles are 49°. There are a spread of U–O bond distances ranging from 1.84–2.49 Å. The U–F bond length is 2.21 Å. Si4+ is bonded to four equivalent O2- atoms to form SiO4 tetrahedra that share corners with four equivalent UO6F pentagonal bipyramids and edges with two equivalent UO6F pentagonal bipyramids. All Si–O bond lengths are 1.64 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent U6+ and one Si4+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Na1+ and one U6+ atom. F1- is bonded in a distorted trigonal planar geometry to two equivalent Na1+ and one U6+ atom.