DOE OSTI2020
U2Ni12As7 crystallizes in the monoclinic Pm space group. The structure is three-dimensional. there are two inequivalent U3+ sites. In the first U3+ site, U3+ is bonded to six As3- atoms to form distorted UAs6 pentagonal pyramids that share corners with six NiAs5 square pyramids, corners with twelve NiAs4 tetrahedra, edges with three NiAs5 square pyramids, edges with nine NiAs4 tetrahedra, and faces with two equivalent UAs6 pentagonal pyramids. All U–As bond lengths are 2.96 Å. In the second U3+ site, U3+ is bonded to six As3- atoms to form distorted UAs6 pentagonal pyramids that share corners with six NiAs5 square pyramids, corners with twelve NiAs4 tetrahedra, edges with twelve NiAs4 tetrahedra, and faces with two equivalent UAs6 pentagonal pyramids. All U–As bond lengths are 2.96 Å. There are twelve inequivalent Ni+1.25+ sites. In the first Ni+1.25+ site, Ni+1.25+ is bonded to four As3- atoms to form NiAs4 tetrahedra that share corners with two equivalent UAs6 pentagonal pyramids, corners with four NiAs5 square pyramids, corners with ten NiAs4 tetrahedra, edges with three UAs6 pentagonal pyramids, an edgeedge with one NiAs5 square pyramid, and edges with four NiAs4 tetrahedra. There are a spread of Ni–As bond distances ranging from 2.36–2.45 Å. In the second Ni+1.25+ site, Ni+1.25+ is bonded to four As3- atoms to form NiAs4 tetrahedra that share corners with two equivalent UAs6 pentagonal pyramids, corners with four NiAs5 square pyramids, corners with ten NiAs4 tetrahedra, edges with three UAs6 pentagonal pyramids, an edgeedge with one NiAs5 square pyramid, and edges with four NiAs4 tetrahedra. There are a spread of Ni–As bond distances ranging from 2.36–2.46 Å. In the third Ni+1.25+ site, Ni+1.25+ is bonded to four As3- atoms to form NiAs4 tetrahedra that share corners with two equivalent UAs6 pentagonal pyramids, corners with four NiAs5 square pyramids, corners with ten NiAs4 tetrahedra, edges with three UAs6 pentagonal pyramids, an edgeedge with one NiAs5 square pyramid, and edges with four NiAs4 tetrahedra. There are a spread of Ni–As bond distances ranging from 2.36–2.46 Å. In the fourth Ni+1.25+ site, Ni+1.25+ is bonded to four As3- atoms to form NiAs4 tetrahedra that share corners with two equivalent UAs6 pentagonal pyramids, corners with two equivalent NiAs5 square pyramids, corners with twelve NiAs4 tetrahedra, edges with three UAs6 pentagonal pyramids, edges with two equivalent NiAs5 square pyramids, and edges with three NiAs4 tetrahedra. There are two shorter (2.35 Å) and two longer (2.41 Å) Ni–As bond lengths. In the fifth Ni+1.25+ site, Ni+1.25+ is bonded to four As3- atoms to form NiAs4 tetrahedra that share corners with two equivalent UAs6 pentagonal pyramids, corners with two equivalent NiAs5 square pyramids, corners with twelve NiAs4 tetrahedra, edges with three UAs6 pentagonal pyramids, edges with two equivalent NiAs5 square pyramids, and edges with three NiAs4 tetrahedra. There are two shorter (2.35 Å) and two longer (2.41 Å) Ni–As bond lengths. In the sixth Ni+1.25+ site, Ni+1.25+ is bonded to four As3- atoms to form NiAs4 tetrahedra that share corners with two equivalent UAs6 pentagonal pyramids, corners with two equivalent NiAs5 square pyramids, corners with twelve NiAs4 tetrahedra, edges with three UAs6 pentagonal pyramids, edges with two equivalent NiAs5 square pyramids, and edges with three NiAs4 tetrahedra. There are two shorter (2.35 Å) and two longer (2.41 Å) Ni–As bond lengths. In the seventh Ni+1.25+ site, Ni+1.25+ is bonded to five As3- atoms to form NiAs5 square pyramids that share corners with four UAs6 pentagonal pyramids, corners with four NiAs5 square pyramids, corners with eight NiAs4 tetrahedra, an edgeedge with one UAs6 pentagonal pyramid, edges with four NiAs5 square pyramids, and edges with seven NiAs4 tetrahedra. There are a spread of Ni–As bond distances ranging from 2.46–2.59 Å. In the eighth Ni+1.25+ site, Ni+1.25+ is bonded to five As3- atoms to form NiAs5 square pyramids that share corners with four UAs6 pentagonal pyramids, corners with four NiAs5 square pyramids, corners with eight NiAs4 tetrahedra, an edgeedge with one UAs6 pentagonal pyramid, edges with four NiAs5 square pyramids, and edges with seven NiAs4 tetrahedra. There are a spread of Ni–As bond distances ranging from 2.45–2.59 Å. In the ninth Ni+1.25+ site, Ni+1.25+ is bonded to five As3- atoms to form NiAs5 square pyramids that share corners with four UAs6 pentagonal pyramids, corners with four NiAs5 square pyramids, corners with eight NiAs4 tetrahedra, an edgeedge with one UAs6 pentagonal pyramid, edges with four NiAs5 square pyramids, and edges with seven NiAs4 tetrahedra. There are a spread of Ni–As bond distances ranging from 2.46–2.59 Å. In the tenth Ni+1.25+ site, Ni+1.25+ is bonded to four As3- atoms to form NiAs4 tetrahedra that share corners with four UAs6 pentagonal pyramids, corners with two equivalent NiAs5 square pyramids, corners with ten NiAs4 tetrahedra, an edgeedge with one UAs6 pentagonal pyramid, edges with four NiAs5 square pyramids, and edges with three NiAs4 tetrahedra. There are a spread of Ni–As bond distances ranging from 2.29–2.37 Å. In the eleventh Ni+1.25+ site, Ni+1.25+ is bonded to four As3- atoms to form NiAs4 tetrahedra that share corners with four UAs6 pentagonal pyramids, corners with two equivalent NiAs5 square pyramids, corners with ten NiAs4 tetrahedra, an edgeedge with one UAs6 pentagonal pyramid, edges with four NiAs5 square pyramids, and edges with three NiAs4 tetrahedra. There are a spread of Ni–As bond distances ranging from 2.29–2.37 Å. In the twelfth Ni+1.25+ site, Ni+1.25+ is bonded to four As3- atoms to form NiAs4 tetrahedra that share corners with four UAs6 pentagonal pyramids, corners with two equivalent NiAs5 square pyramids, corners with ten NiAs4 tetrahedra, an edgeedge with one UAs6 pentagonal pyramid, edges with four NiAs5 square pyramids, and edges with three NiAs4 tetrahedra. There are a spread of Ni–As bond distances ranging from 2.29–2.37 Å. There are seven inequivalent As3- sites. In the first As3- site, As3- is bonded in a 9-coordinate geometry to nine Ni+1.25+ atoms. In the second As3- site, As3- is bonded in a 9-coordinate geometry to two equivalent U3+ and seven Ni+1.25+ atoms. In the third As3- site, As3- is bonded in a 9-coordinate geometry to two equivalent U3+ and seven Ni+1.25+ atoms. In the fourth As3- site, As3- is bonded in a 9-coordinate geometry to two equivalent U3+ and seven Ni+1.25+ atoms. In the fifth As3- site, As3- is bonded in a 9-coordinate geometry to two equivalent U3+ and seven Ni+1.25+ atoms. In the sixth As3- site, As3- is bonded in a 9-coordinate geometry to two equivalent U3+ and seven Ni+1.25+ atoms. In the seventh As3- site, As3- is bonded in a 9-coordinate geometry to two equivalent U3+ and seven Ni+1.25+ atoms.