DOE OSTI2020
Ni21Zn2B20 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional and consists of one Ni21B20 framework and four zinc molecules. In the Ni21B20 framework, there are six inequivalent Ni+1.81+ sites. In the first Ni+1.81+ site, Ni+1.81+ is bonded in a 6-coordinate geometry to six B+2.10- atoms. There are a spread of Ni–B bond distances ranging from 2.12–2.18 Å. In the second Ni+1.81+ site, Ni+1.81+ is bonded in a 8-coordinate geometry to eight B+2.10- atoms. There are six shorter (2.15 Å) and two longer (2.21 Å) Ni–B bond lengths. In the third Ni+1.81+ site, Ni+1.81+ is bonded to six B+2.10- atoms to form distorted NiB6 octahedra that share corners with four equivalent NiB6 octahedra and edges with two equivalent NiB4 tetrahedra. The corner-sharing octahedral tilt angles are 76°. There are two shorter (2.11 Å) and four longer (2.29 Å) Ni–B bond lengths. In the fourth Ni+1.81+ site, Ni+1.81+ is bonded to four equivalent B+2.10- atoms to form distorted edge-sharing NiB4 tetrahedra. All Ni–B bond lengths are 1.99 Å. In the fifth Ni+1.81+ site, Ni+1.81+ is bonded in a square co-planar geometry to four equivalent B+2.10- atoms. All Ni–B bond lengths are 2.06 Å. In the sixth Ni+1.81+ site, Ni+1.81+ is bonded in a 8-coordinate geometry to eight B+2.10- atoms. There are four shorter (2.14 Å) and four longer (2.16 Å) Ni–B bond lengths. There are three inequivalent B+2.10- sites. In the first B+2.10- site, B+2.10- is bonded in a 9-coordinate geometry to seven Ni+1.81+ and two equivalent B+2.10- atoms. Both B–B bond lengths are 1.76 Å. In the second B+2.10- site, B+2.10- is bonded in a 9-coordinate geometry to six Ni+1.81+ and three B+2.10- atoms. The B–B bond length is 1.77 Å. In the third B+2.10- site, B+2.10- is bonded in a 9-coordinate geometry to seven Ni+1.81+ and two equivalent B+2.10- atoms.