DOE OSTI2020
Na2W2O5 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a 2-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.40–3.00 Å. In the second Na1+ site, Na1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Na–O bond distances ranging from 2.34–2.90 Å. In the third Na1+ site, Na1+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of Na–O bond distances ranging from 2.35–3.10 Å. In the fourth Na1+ site, Na1+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of Na–O bond distances ranging from 2.43–3.06 Å. There are four inequivalent W4+ sites. In the first W4+ site, W4+ is bonded to six O2- atoms to form WO6 octahedra that share corners with four equivalent WO6 octahedra and a cornercorner with one WO4 trigonal pyramid. The corner-sharing octahedra tilt angles range from 7–20°. There are a spread of W–O bond distances ranging from 1.94–2.10 Å. In the second W4+ site, W4+ is bonded to six O2- atoms to form WO6 octahedra that share corners with four equivalent WO6 octahedra and a cornercorner with one WO4 trigonal pyramid. The corner-sharing octahedra tilt angles range from 7–20°. There are a spread of W–O bond distances ranging from 2.03–2.12 Å. In the third W4+ site, W4+ is bonded to four O2- atoms to form corner-sharing WO4 trigonal pyramids. The corner-sharing octahedra tilt angles range from 12–14°. There are a spread of W–O bond distances ranging from 1.97–2.08 Å. In the fourth W4+ site, W4+ is bonded in a rectangular see-saw-like geometry to four O2- atoms. There are a spread of W–O bond distances ranging from 1.92–2.17 Å. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded to four Na1+ and two W4+ atoms to form distorted ONa4W2 octahedra that share corners with two equivalent ONa4W2 octahedra, corners with four ONa2W2 trigonal pyramids, and edges with two equivalent ONa4W2 octahedra. The corner-sharing octahedra tilt angles range from 1–2°. In the second O2- site, O2- is bonded in a 4-coordinate geometry to four Na1+ and two W4+ atoms. In the third O2- site, O2- is bonded in a 4-coordinate geometry to four Na1+ and two W4+ atoms. In the fourth O2- site, O2- is bonded to four Na1+ and two W4+ atoms to form distorted ONa4W2 octahedra that share corners with two equivalent ONa4W2 octahedra, corners with four ONa2W2 trigonal pyramids, and edges with two equivalent ONa4W2 octahedra. The corner-sharing octahedra tilt angles range from 1–2°. In the fifth O2- site, O2- is bonded in a 5-coordinate geometry to three Na1+ and two W4+ atoms. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to three Na1+ and two W4+ atoms. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to four Na1+ and two W4+ atoms. In the eighth O2- site, O2- is bonded in a 2-coordinate geometry to four Na1+ and two W4+ atoms. In the ninth O2- site, O2- is bonded to two Na1+ and two W4+ atoms to form distorted ONa2W2 trigonal pyramids that share corners with four ONa4W2 octahedra and corners with two equivalent ONa2W2 trigonal pyramids. The corner-sharing octahedra tilt angles range from 18–81°. In the tenth O2- site, O2- is bonded to two Na1+ and two W4+ atoms to form ONa2W2 trigonal pyramids that share corners with four ONa4W2 octahedra and corners with two equivalent ONa2W2 trigonal pyramids. The corner-sharing octahedra tilt angles range from 45–59°.