DOE OSTI2020
Na5Co2As(CO4)4 crystallizes in the orthorhombic F222 space group. The structure is three-dimensional. there are five inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to six O2- atoms to form distorted NaO6 octahedra that share corners with eight NaO6 octahedra, edges with two equivalent CoO6 octahedra, and an edgeedge with one AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 59–88°. There are a spread of Na–O bond distances ranging from 2.45–2.54 Å. In the second Na1+ site, Na1+ is bonded to six O2- atoms to form distorted NaO6 octahedra that share corners with six NaO6 octahedra, edges with two equivalent CoO6 octahedra, and an edgeedge with one AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 59–88°. There are four shorter (2.47 Å) and two longer (2.57 Å) Na–O bond lengths. In the third Na1+ site, Na1+ is bonded to six O2- atoms to form distorted NaO6 octahedra that share corners with six NaO6 octahedra, edges with two equivalent CoO6 octahedra, and an edgeedge with one AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 60–88°. There are a spread of Na–O bond distances ranging from 2.47–2.55 Å. In the fourth Na1+ site, Na1+ is bonded to six O2- atoms to form distorted NaO6 octahedra that share corners with six NaO6 octahedra, edges with two equivalent CoO6 octahedra, and an edgeedge with one AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 55–88°. There are a spread of Na–O bond distances ranging from 2.42–2.55 Å. In the fifth Na1+ site, Na1+ is bonded to six O2- atoms to form distorted NaO6 octahedra that share corners with six NaO6 octahedra, edges with two equivalent CoO6 octahedra, and an edgeedge with one AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 55–88°. There are a spread of Na–O bond distances ranging from 2.42–2.54 Å. Co3+ is bonded to six O2- atoms to form CoO6 octahedra that share edges with five NaO6 octahedra. There are a spread of Co–O bond distances ranging from 2.02–2.10 Å. There are two inequivalent C4+ sites. In the first C4+ site, C4+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.29 Å) and two longer (1.30 Å) C–O bond length. In the second C4+ site, C4+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of C–O bond distances ranging from 1.28–1.31 Å. There are two inequivalent As5+ sites. In the first As5+ site, As5+ is bonded to four equivalent O2- atoms to form AsO4 tetrahedra that share edges with four NaO6 octahedra. All As–O bond lengths are 1.72 Å. In the second As5+ site, As5+ is bonded to four equivalent O2- atoms to form AsO4 tetrahedra that share edges with six NaO6 octahedra. All As–O bond lengths are 1.72 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Na1+, one Co3+, and one C4+ atom. In the second O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Na1+, one Co3+, and one C4+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to one Na1+, one Co3+, and one C4+ atom. In the fourth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Na1+, one Co3+, and one C4+ atom. In the fifth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Na1+, one Co3+, and one C4+ atom. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to two Na1+ and one As5+ atom. In the seventh O2- site, O2- is bonded in a 3-coordinate geometry to one Na1+, one Co3+, and one C4+ atom. In the eighth O2- site, O2- is bonded to three Na1+ and one As5+ atom to form distorted edge-sharing ONa3As trigonal pyramids.