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Ba(Hf2As3)6 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are two inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded in a 7-coordinate geometry to seven As+2.78- atoms. There are a spread of Ba–As bond distances ranging from 3.38–3.78 Å. In the second Ba2+ site, Ba2+ is bonded in a 8-coordinate geometry to eight As+2.78- atoms. There are a spread of Ba–As bond distances ranging from 3.20–3.90 Å. There are twenty-four inequivalent Hf4+ sites. In the first Hf4+ site, Hf4+ is bonded in a 6-coordinate geometry to six As+2.78- atoms. There are a spread of Hf–As bond distances ranging from 2.59–2.97 Å. In the second Hf4+ site, Hf4+ is bonded in a 6-coordinate geometry to six As+2.78- atoms. There are a spread of Hf–As bond distances ranging from 2.53–3.14 Å. In the third Hf4+ site, Hf4+ is bonded to seven As+2.78- atoms to form distorted HfAs7 pentagonal bipyramids that share a cornercorner with one HfAs6 octahedra, a cornercorner with one HfAs6 pentagonal pyramid, and an edgeedge with one HfAs7 pentagonal bipyramid. The corner-sharing octahedral tilt angles are 24°. There are a spread of Hf–As bond distances ranging from 2.62–3.02 Å. In the fourth Hf4+ site, Hf4+ is bonded in a 6-coordinate geometry to six As+2.78- atoms. There are a spread of Hf–As bond distances ranging from 2.56–3.05 Å. In the fifth Hf4+ site, Hf4+ is bonded to five As+2.78- atoms to form HfAs5 square pyramids that share a cornercorner with one HfAs6 octahedra, a cornercorner with one HfAs7 pentagonal bipyramid, a cornercorner with one HfAs6 pentagonal pyramid, and edges with two HfAs5 square pyramids. The corner-sharing octahedral tilt angles are 46°. There are a spread of Hf–As bond distances ranging from 2.57–2.91 Å. In the sixth Hf4+ site, Hf4+ is bonded in a 6-coordinate geometry to seven As+2.78- atoms. There are a spread of Hf–As bond distances ranging from 2.60–3.41 Å. In the seventh Hf4+ site, Hf4+ is bonded in a 5-coordinate geometry to six As+2.78- atoms. There are a spread of Hf–As bond distances ranging from 2.64–3.26 Å. In the eighth Hf4+ site, Hf4+ is bonded to five As+2.78- atoms to form distorted HfAs5 square pyramids that share a cornercorner with one HfAs7 pentagonal bipyramid, a cornercorner with one HfAs5 square pyramid, an edgeedge with one HfAs5 square pyramid, and a faceface with one HfAs6 pentagonal pyramid. There are a spread of Hf–As bond distances ranging from 2.52–2.86 Å. In the ninth Hf4+ site, Hf4+ is bonded to seven As+2.78- atoms to form distorted HfAs7 pentagonal bipyramids that share a cornercorner with one HfAs7 pentagonal bipyramid, edges with two HfAs6 octahedra, an edgeedge with one HfAs7 pentagonal bipyramid, and a faceface with one HfAs6 pentagonal pyramid. There are a spread of Hf–As bond distances ranging from 2.70–2.96 Å. In the tenth Hf4+ site, Hf4+ is bonded in a 6-coordinate geometry to six As+2.78- atoms. There are a spread of Hf–As bond distances ranging from 2.65–3.28 Å. In the eleventh Hf4+ site, Hf4+ is bonded to six As+2.78- atoms to form distorted HfAs6 octahedra that share corners with two HfAs7 pentagonal bipyramids, an edgeedge with one HfAs6 octahedra, and an edgeedge with one HfAs7 pentagonal bipyramid. There are a spread of Hf–As bond distances ranging from 2.67–3.00 Å. In the twelfth Hf4+ site, Hf4+ is bonded to five As+2.78- atoms to form HfAs5 square pyramids that share a cornercorner with one HfAs6 octahedra, a cornercorner with one HfAs5 square pyramid, an edgeedge with one HfAs6 pentagonal pyramid, and an edgeedge with one HfAs5 square pyramid. The corner-sharing octahedral tilt angles are 33°. There are a spread of Hf–As bond distances ranging from 2.59–2.82 Å. In the thirteenth Hf4+ site, Hf4+ is bonded to six As+2.78- atoms to form distorted HfAs6 pentagonal pyramids that share an edgeedge with one HfAs6 octahedra and faces with two HfAs7 pentagonal bipyramids. There are a spread of Hf–As bond distances ranging from 2.69–2.92 Å. In the fourteenth Hf4+ site, Hf4+ is bonded in a 5-coordinate geometry to five As+2.78- atoms. There are a spread of Hf–As bond distances ranging from 2.68–2.74 Å. In the fifteenth Hf4+ site, Hf4+ is bonded to seven As+2.78- atoms to form distorted HfAs7 pentagonal bipyramids that share a cornercorner with one HfAs6 octahedra, a cornercorner with one HfAs7 pentagonal bipyramid, corners with two HfAs5 square pyramids, a faceface with one HfAs6 octahedra, and a faceface with one HfAs6 pentagonal pyramid. The corner-sharing octahedral tilt angles are 35°. There are a spread of Hf–As bond distances ranging from 2.67–2.86 Å. In the sixteenth Hf4+ site, Hf4+ is bonded in a distorted pentagonal planar geometry to five As+2.78- atoms. There are a spread of Hf–As bond distances ranging from 2.68–2.81 Å. In the seventeenth Hf4+ site, Hf4+ is bonded to six As+2.78- atoms to form HfAs6 octahedra that share corners with two HfAs5 square pyramids, an edgeedge with one HfAs6 octahedra, an edgeedge with one HfAs7 pentagonal bipyramid, an edgeedge with one HfAs6 pentagonal pyramid, and a faceface with one HfAs7 pentagonal bipyramid. There are a spread of Hf–As bond distances ranging from 2.71–2.80 Å. In the eighteenth Hf4+ site, Hf4+ is bonded in a 7-coordinate geometry to eight As+2.78- atoms. There are a spread of Hf–As bond distances ranging from 2.60–3.36 Å. In the nineteenth Hf4+ site, Hf4+ is bonded in a 6-coordinate geometry to six As+2.78- atoms. There are a spread of Hf–As bond distances ranging from 2.58–2.95 Å. In the twentieth Hf4+ site, Hf4+ is bonded in a 5-coordinate geometry to five As+2.78- atoms. There are a spread of Hf–As bond distances ranging from 2.54–3.16 Å. In the twenty-first Hf4+ site, Hf4+ is bonded in a 6-coordinate geometry to six As+2.78- atoms. There are a spread of Hf–As bond distances ranging from 2.64–3.05 Å. In the twenty-second Hf4+ site, Hf4+ is bonded in a 5-coordinate geometry to six As+2.78- atoms. There are a spread of Hf–As bond distances ranging from 2.53–3.55 Å. In the twenty-third Hf4+ site, Hf4+ is bonded in a 6-coordinate geometry to six As+2.78- atoms. There are a spread of Hf–As bond distances ranging from 2.56–3.16 Å. In the twenty-fourth Hf4+ site, Hf4+ is bonded to six As+2.78- atoms to form distorted HfAs6 pentagonal pyramids that share a cornercorner with one HfAs7 pentagonal bipyramid, a cornercorner with one HfAs5 square pyramid, an edgeedge with one HfAs5 square pyramid, and a faceface with one HfAs5 square pyramid. There are a spread of Hf–As bond distances ranging from 2.58–2.87 Å. There are thirty-six inequivalent As+2.78- sites. In the first As+2.78- site, As+2.78- is bonded in a distorted pentagonal planar geometry to one Ba2+ and four Hf4+ atoms. In the second As+2.78- site, As+2.78- is bonded in a 4-coordinate geometry to one Ba2+ and three Hf4+ atoms. In the third As+2.78- site, As+2.78- is bonded in a 6-coordinate geometry to four Hf4+ and two As+2.78- atoms. There are one shorter (2.54 Å) and one longer (2.57 Å) As–As bond lengths. In the fourth As+2.78- site, As+2.78- is bonded in a 2-coordinate geometry to one Ba2+, two Hf4+, and one As+2.78- atom. The As–As bond length is 2.49 Å. In the fifth As+2.78- site, As+2.78- is bonded in a 4-coordinate geometry to one Ba2+ and three Hf4+ atoms. In the sixth As+2.78- site, As+2.78- is bonded in a 3-coordinate geometry to three Hf4+ atoms. In the seventh As+2.78- site, As+2.78- is bonded in a 5-coordinate geometry to five Hf4+ atoms. In the eighth As+2.78- site, As+2.78- is bonded in a 3-coordinate geometry to four Hf4+ and one As+2.78- atom. The As–As bond length is 2.61 Å. In the ninth As+2.78- site, As+2.78- is bonded in a 4-coordinate geometry to one Ba2+ and three Hf4+ atoms. In the tenth As+2.78- site, As+2.78- is bonded in a 6-coordinate geometry to one Ba2+, four Hf4+, and one As+2.78- atom. In the eleventh As+2.78- site, As+2.78- is bonded in a 4-coordinate geometry to one Ba2+ and four Hf4+ atoms. In the twelfth As+2.78- site, As+2.78- is bonded to five Hf4+ atoms to form distorted corner-sharing AsHf5 trigonal bipyramids. In the thirteenth As+2.78- site, As+2.78- is bonded in a 3-coordinate geometry to four Hf4+ atoms. In the fourteenth As+2.78- site, As+2.78- is bonded in a distorted pentagonal planar geometry to five Hf4+ atoms. In the fifteenth As+2.78- site, As+2.78- is bonded to five Hf4+ atoms to form distorted AsHf5 trigonal bipyramids that share a cornercorner with one AsHf5 trigonal bipyramid and an edgeedge with one AsBaHf4 square pyramid. In the sixteenth As+2.78- site, As+2.78- is bonded to one Ba2+ and four Hf4+ atoms to form a mixture of distorted edge and corner-sharing AsBaHf4 square pyramids. In the seventeenth As+2.78- site, As+2.78- is bonded in a 6-coordinate geometry to one Ba2+ and six Hf4+ atoms. In the eighteenth As+2.78- site, As+2.78- is bonded in a 5-coordinate geometry to one Ba2+, three Hf4+, and one As+2.78- atom. The As–As bond length is 2.60 Å. In the nineteenth As+2.78- site, As+2.78- is bonded in a 4-coordinate geometry to four Hf4+ atoms. In the twentieth As+2.78- site, As+2.78- is bonded in a 5-coordinate geometry to one Ba2+ and four Hf4+ atoms. In the twenty-first As+2.78- site, As+2.78- is bonded in a 5-coordinate geometry to five Hf4+ atoms. In the twenty-second As+2.78- site, As+2.78- is bonded in a 1-coordinate geometry to two Hf4+ and one As+2.78- atom. The As–As bond length is 2.66 Å. In the twenty-third As+2.78- site, As+2.78- is bonded to five Hf4+ atoms to form distorted corner-sharing AsHf5 square pyramids. In the twenty-fourth As+2.78- site, As+2.78- is bonded in a 6-coordinate geometry to one Ba2+, four Hf4+, and one As+2.78- atom. In the twenty-fifth As+2.78- site, As+2.78- is bonded in a 4-coordinate geometry to three Hf4+ and one As+2.78- atom. In the twenty-sixth As+2.78- site, As+2.78- is bonded in a 4-coordinate geometry to four Hf4+ atoms. In the twenty-seventh As+2.78- site, As+2.78- is bonded to one Ba2+ and four Hf4+ atoms to form distorted corner-sharing AsBaHf4 square pyramids. In the twenty-eighth As+2.78- site, As+2.78- is bonded in a 2-coordinate geometry to one Ba2+, five Hf4+, and two As+2.78- atoms. The As–As bond length is 2.97 Å. In the twenty-ninth As+2.78- site, As+2.78- is bonded in a 5-coordinate geometry to six Hf4+ atoms. In the thirtieth As+2.78- site, As+2.78- is bonded in a 2-coordinate geometry to three Hf4+ atoms. In the thirty-first As+2.78- site, As+2.78- is bonded in a rectangular see-saw-like geometry to four Hf4+ atoms. In the thirty-second As+2.78- site, As+2.78- is bonded in a distorted rectangular see-saw-like geometry to four Hf4+ atoms. In the thirty-third As+2.78- site, As+2.78- is bonded in a 3-coordinate geometry to three Hf4+ and one As+2.78- atom. In the thirty-fourth As+2.78- site, As+2.78- is bonded in a 6-coordinate geometry to four Hf4+ and two As+2.78- atoms. In the thirty-fifth As+2.78- site, As+2.78- is bonded in a 4-coordinate geometry to four Hf4+ atoms. In the thirty-sixth As+2.78- site, As+2.78- is bonded in a 6-coordinate geometry to one Ba2+ and five Hf4+ atoms.

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