DOE OSTI2020
Ca2Ni7P4 crystallizes in the orthorhombic Pmn2_1 space group. The structure is three-dimensional. there are two inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded to six P3- atoms to form distorted CaP6 pentagonal pyramids that share corners with eight NiP4 tetrahedra, corners with two equivalent CaP5 trigonal bipyramids, edges with nine NiP4 tetrahedra, an edgeedge with one CaP5 trigonal bipyramid, and faces with two equivalent CaP6 pentagonal pyramids. There are two shorter (2.83 Å) and four longer (2.89 Å) Ca–P bond lengths. In the second Ca2+ site, Ca2+ is bonded to five P3- atoms to form distorted CaP5 trigonal bipyramids that share corners with two equivalent CaP6 pentagonal pyramids, corners with seven NiP4 tetrahedra, corners with four equivalent CaP5 trigonal bipyramids, an edgeedge with one CaP6 pentagonal pyramid, edges with six NiP4 tetrahedra, and edges with two equivalent CaP5 trigonal bipyramids. There are a spread of Ca–P bond distances ranging from 2.93–3.03 Å. There are seven inequivalent Ni+1.14+ sites. In the first Ni+1.14+ site, Ni+1.14+ is bonded to four P3- atoms to form NiP4 tetrahedra that share corners with two equivalent CaP6 pentagonal pyramids, corners with nine NiP4 tetrahedra, corners with two equivalent CaP5 trigonal bipyramids, edges with three equivalent CaP6 pentagonal pyramids, and edges with two equivalent NiP4 tetrahedra. There are two shorter (2.27 Å) and two longer (2.38 Å) Ni–P bond lengths. In the second Ni+1.14+ site, Ni+1.14+ is bonded to four P3- atoms to form NiP4 tetrahedra that share corners with four equivalent CaP6 pentagonal pyramids, corners with eight NiP4 tetrahedra, a cornercorner with one CaP5 trigonal bipyramid, an edgeedge with one CaP6 pentagonal pyramid, edges with two equivalent NiP4 tetrahedra, and edges with two equivalent CaP5 trigonal bipyramids. There are a spread of Ni–P bond distances ranging from 2.24–2.36 Å. In the third Ni+1.14+ site, Ni+1.14+ is bonded to four P3- atoms to form NiP4 tetrahedra that share corners with two equivalent CaP6 pentagonal pyramids, corners with six NiP4 tetrahedra, corners with two equivalent CaP5 trigonal bipyramids, edges with three equivalent CaP6 pentagonal pyramids, edges with four NiP4 tetrahedra, and an edgeedge with one CaP5 trigonal bipyramid. There are a spread of Ni–P bond distances ranging from 2.25–2.36 Å. In the fourth Ni+1.14+ site, Ni+1.14+ is bonded in a trigonal non-coplanar geometry to three P3- atoms. There are one shorter (2.15 Å) and two longer (2.31 Å) Ni–P bond lengths. In the fifth Ni+1.14+ site, Ni+1.14+ is bonded in a trigonal non-coplanar geometry to three P3- atoms. There are one shorter (2.17 Å) and two longer (2.30 Å) Ni–P bond lengths. In the sixth Ni+1.14+ site, Ni+1.14+ is bonded to four P3- atoms to form NiP4 tetrahedra that share corners with eleven NiP4 tetrahedra, corners with two equivalent CaP5 trigonal bipyramids, edges with two equivalent CaP6 pentagonal pyramids, and edges with three equivalent CaP5 trigonal bipyramids. There are a spread of Ni–P bond distances ranging from 2.29–2.42 Å. In the seventh Ni+1.14+ site, Ni+1.14+ is bonded in a trigonal non-coplanar geometry to three P3- atoms. There are one shorter (2.17 Å) and two longer (2.27 Å) Ni–P bond lengths. There are four inequivalent P3- sites. In the first P3- site, P3- is bonded in a 9-coordinate geometry to two equivalent Ca2+ and seven Ni+1.14+ atoms. In the second P3- site, P3- is bonded in a 9-coordinate geometry to two equivalent Ca2+ and seven Ni+1.14+ atoms. In the third P3- site, P3- is bonded in a 9-coordinate geometry to four Ca2+ and five Ni+1.14+ atoms. In the fourth P3- site, P3- is bonded in a 9-coordinate geometry to three equivalent Ca2+ and six Ni+1.14+ atoms.