DOE OSTI2020
K2HfF6 crystallizes in the monoclinic Pm space group. The structure is three-dimensional. there are twelve inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 3-coordinate geometry to three F1- atoms. There are two shorter (2.51 Å) and one longer (2.81 Å) K–F bond lengths. In the second K1+ site, K1+ is bonded in a 7-coordinate geometry to seven F1- atoms. There are a spread of K–F bond distances ranging from 2.74–3.09 Å. In the third K1+ site, K1+ is bonded in a 2-coordinate geometry to two F1- atoms. There are one shorter (2.45 Å) and one longer (2.53 Å) K–F bond lengths. In the fourth K1+ site, K1+ is bonded in a 3-coordinate geometry to three F1- atoms. There are one shorter (2.39 Å) and two longer (2.54 Å) K–F bond lengths. In the fifth K1+ site, K1+ is bonded in a 9-coordinate geometry to nine F1- atoms. There are a spread of K–F bond distances ranging from 2.65–3.27 Å. In the sixth K1+ site, K1+ is bonded in a 5-coordinate geometry to five F1- atoms. There are a spread of K–F bond distances ranging from 2.46–2.88 Å. In the seventh K1+ site, K1+ is bonded to twelve F1- atoms to form KF12 cuboctahedra that share corners with two equivalent KF12 cuboctahedra, corners with two equivalent KF5 square pyramids, and faces with four HfF6 octahedra. There are a spread of K–F bond distances ranging from 2.97–3.31 Å. In the eighth K1+ site, K1+ is bonded in a 10-coordinate geometry to ten F1- atoms. There are a spread of K–F bond distances ranging from 2.77–3.36 Å. In the ninth K1+ site, K1+ is bonded in a 2-coordinate geometry to five F1- atoms. There are a spread of K–F bond distances ranging from 2.44–3.11 Å. In the tenth K1+ site, K1+ is bonded in a 9-coordinate geometry to nine F1- atoms. There are a spread of K–F bond distances ranging from 2.67–3.25 Å. In the eleventh K1+ site, K1+ is bonded to five F1- atoms to form distorted KF5 square pyramids that share corners with two equivalent KF12 cuboctahedra and corners with four HfF6 octahedra. The corner-sharing octahedra tilt angles range from 56–59°. There are a spread of K–F bond distances ranging from 2.37–2.82 Å. In the twelfth K1+ site, K1+ is bonded in a 12-coordinate geometry to twelve F1- atoms. There are a spread of K–F bond distances ranging from 2.84–3.33 Å. There are six inequivalent Hf4+ sites. In the first Hf4+ site, Hf4+ is bonded to six F1- atoms to form HfF6 octahedra that share corners with three HfF6 octahedra and corners with two equivalent KF5 square pyramids. The corner-sharing octahedra tilt angles range from 4–11°. There are a spread of Hf–F bond distances ranging from 1.94–2.08 Å. In the second Hf4+ site, Hf4+ is bonded to six F1- atoms to form distorted corner-sharing HfF6 octahedra. The corner-sharing octahedral tilt angles are 11°. There are a spread of Hf–F bond distances ranging from 1.93–2.26 Å. In the third Hf4+ site, Hf4+ is bonded to six F1- atoms to form HfF6 octahedra that share a cornercorner with one HfF6 octahedra and a faceface with one KF12 cuboctahedra. The corner-sharing octahedral tilt angles are 1°. There are a spread of Hf–F bond distances ranging from 1.95–2.24 Å. In the fourth Hf4+ site, Hf4+ is bonded to six F1- atoms to form corner-sharing HfF6 octahedra. The corner-sharing octahedral tilt angles are 1°. There are a spread of Hf–F bond distances ranging from 1.96–2.20 Å. In the fifth Hf4+ site, Hf4+ is bonded to six F1- atoms to form HfF6 octahedra that share faces with two equivalent KF12 cuboctahedra. There are a spread of Hf–F bond distances ranging from 1.99–2.02 Å. In the sixth Hf4+ site, Hf4+ is bonded to six F1- atoms to form HfF6 octahedra that share a cornercorner with one HfF6 octahedra, corners with two equivalent KF5 square pyramids, and a faceface with one KF12 cuboctahedra. The corner-sharing octahedral tilt angles are 4°. There are a spread of Hf–F bond distances ranging from 1.94–2.23 Å. There are twenty-four inequivalent F1- sites. In the first F1- site, F1- is bonded in a distorted single-bond geometry to one K1+ and one Hf4+ atom. In the second F1- site, F1- is bonded in a distorted linear geometry to two Hf4+ atoms. In the third F1- site, F1- is bonded in a distorted single-bond geometry to two K1+ and one Hf4+ atom. In the fourth F1- site, F1- is bonded in a rectangular see-saw-like geometry to four K1+ atoms. In the fifth F1- site, F1- is bonded in a distorted single-bond geometry to two K1+ and one Hf4+ atom. In the sixth F1- site, F1- is bonded in a distorted single-bond geometry to one K1+ and one Hf4+ atom. In the seventh F1- site, F1- is bonded in a distorted linear geometry to two K1+ atoms. In the eighth F1- site, F1- is bonded in a single-bond geometry to one Hf4+ atom. In the ninth F1- site, F1- is bonded in a distorted single-bond geometry to four K1+ and one Hf4+ atom. In the tenth F1- site, F1- is bonded in a 1-coordinate geometry to three K1+ and one Hf4+ atom. In the eleventh F1- site, F1- is bonded in a distorted single-bond geometry to one K1+ and one Hf4+ atom. In the twelfth F1- site, F1- is bonded in a distorted single-bond geometry to three K1+ and one Hf4+ atom. In the thirteenth F1- site, F1- is bonded in a distorted linear geometry to one K1+ and two Hf4+ atoms. In the fourteenth F1- site, F1- is bonded in a distorted single-bond geometry to four K1+ and one Hf4+ atom. In the fifteenth F1- site, F1- is bonded in a distorted single-bond geometry to two K1+ and one Hf4+ atom. In the sixteenth F1- site, F1- is bonded in a 1-coordinate geometry to three K1+ and one Hf4+ atom. In the seventeenth F1- site, F1- is bonded in a distorted single-bond geometry to three K1+ and one Hf4+ atom. In the eighteenth F1- site, F1- is bonded in a 2-coordinate geometry to three K1+ and one Hf4+ atom. In the nineteenth F1- site, F1- is bonded in a 2-coordinate geometry to three K1+ and one Hf4+ atom. In the twentieth F1- site, F1- is bonded in a distorted linear geometry to four K1+ atoms. In the twenty-first F1- site, F1- is bonded in a 2-coordinate geometry to three K1+ and one Hf4+ atom. In the twenty-second F1- site, F1- is bonded in a linear geometry to one K1+ and two Hf4+ atoms. In the twenty-third F1- site, F1- is bonded in a distorted single-bond geometry to two K1+ and one Hf4+ atom. In the twenty-fourth F1- site, F1- is bonded in a distorted single-bond geometry to two K1+ and one Hf4+ atom.