DOE OSTI2020
Ba2Ni7F18 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. Ba2+ is bonded to twelve F1- atoms to form BaF12 cuboctahedra that share corners with seven NiF6 octahedra, edges with two equivalent BaF12 cuboctahedra, edges with five NiF6 octahedra, a faceface with one BaF12 cuboctahedra, and faces with three NiF6 octahedra. The corner-sharing octahedra tilt angles range from 28–53°. There are a spread of Ba–F bond distances ranging from 2.75–2.99 Å. There are four inequivalent Ni2+ sites. In the first Ni2+ site, Ni2+ is bonded to six F1- atoms to form NiF6 octahedra that share corners with two equivalent BaF12 cuboctahedra, corners with four NiF6 octahedra, edges with two equivalent BaF12 cuboctahedra, and edges with three NiF6 octahedra. The corner-sharing octahedra tilt angles range from 48–53°. There are a spread of Ni–F bond distances ranging from 1.97–2.10 Å. In the second Ni2+ site, Ni2+ is bonded to six F1- atoms to form NiF6 octahedra that share a cornercorner with one BaF12 cuboctahedra, corners with four NiF6 octahedra, an edgeedge with one BaF12 cuboctahedra, edges with two equivalent NiF6 octahedra, and faces with two equivalent BaF12 cuboctahedra. The corner-sharing octahedra tilt angles range from 51–54°. There are a spread of Ni–F bond distances ranging from 1.97–2.07 Å. In the third Ni2+ site, Ni2+ is bonded to six F1- atoms to form NiF6 octahedra that share corners with two equivalent BaF12 cuboctahedra, corners with six NiF6 octahedra, an edgeedge with one BaF12 cuboctahedra, an edgeedge with one NiF6 octahedra, and a faceface with one BaF12 cuboctahedra. The corner-sharing octahedra tilt angles range from 48–54°. There are a spread of Ni–F bond distances ranging from 1.97–2.08 Å. In the fourth Ni2+ site, Ni2+ is bonded to six F1- atoms to form NiF6 octahedra that share corners with four equivalent BaF12 cuboctahedra, corners with four NiF6 octahedra, edges with two equivalent BaF12 cuboctahedra, and edges with two equivalent NiF6 octahedra. The corner-sharing octahedra tilt angles range from 50–52°. There are four shorter (2.02 Å) and two longer (2.04 Å) Ni–F bond lengths. There are nine inequivalent F1- sites. In the first F1- site, F1- is bonded in a 3-coordinate geometry to one Ba2+ and three Ni2+ atoms. In the second F1- site, F1- is bonded in a 2-coordinate geometry to one Ba2+ and two Ni2+ atoms. In the third F1- site, F1- is bonded in a distorted bent 120 degrees geometry to two equivalent Ba2+ and two Ni2+ atoms. In the fourth F1- site, F1- is bonded in a 3-coordinate geometry to one Ba2+ and three Ni2+ atoms. In the fifth F1- site, F1- is bonded in a distorted trigonal planar geometry to three Ni2+ atoms. In the sixth F1- site, F1- is bonded in a 2-coordinate geometry to two equivalent Ba2+ and two Ni2+ atoms. In the seventh F1- site, F1- is bonded in a distorted bent 120 degrees geometry to one Ba2+ and two Ni2+ atoms. In the eighth F1- site, F1- is bonded in a 2-coordinate geometry to two equivalent Ba2+ and two Ni2+ atoms. In the ninth F1- site, F1- is bonded in a distorted bent 120 degrees geometry to two equivalent Ba2+ and two Ni2+ atoms.