DOE OSTI2020
Tm(AlC)3 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Tm3+ is bonded to six equivalent C4- atoms to form TmC6 octahedra that share corners with six equivalent AlC4 tetrahedra, edges with six equivalent TmC6 octahedra, and edges with six equivalent AlC4 tetrahedra. All Tm–C bond lengths are 2.52 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to four C4- atoms to form AlC4 tetrahedra that share corners with three equivalent TmC6 octahedra, corners with seven equivalent AlC4 tetrahedra, and edges with three equivalent TmC6 octahedra. The corner-sharing octahedral tilt angles are 19°. There are one shorter (2.02 Å) and three longer (2.10 Å) Al–C bond lengths. In the second Al3+ site, Al3+ is bonded in a trigonal planar geometry to three equivalent C4- atoms. All Al–C bond lengths are 1.97 Å. There are two inequivalent C4- sites. In the first C4- site, C4- is bonded to three equivalent Tm3+ and three equivalent Al3+ atoms to form distorted CTm3Al3 octahedra that share corners with three equivalent CTm3Al3 octahedra, corners with three equivalent CAl5 trigonal bipyramids, and edges with nine equivalent CTm3Al3 octahedra. The corner-sharing octahedral tilt angles are 0°. In the second C4- site, C4- is bonded to five Al3+ atoms to form CAl5 trigonal bipyramids that share corners with six equivalent CTm3Al3 octahedra and corners with six equivalent CAl5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 70°.