Materials Data on U20Si16C3 by Materials Project
U20Si16C3 crystallizes in the hexagonal P6/mmm space group. The structure is three-dimensional. there are five inequivalent U3+ sites. In the first U3+ site, U3+ is bonded to twelve equivalent Si3- atoms to form face-sharing USi12 cuboctahedra. All U–Si bond lengths are 3.05 Å. In the second U3+ site, U3+ is bonded to twelve equivalent Si3- atoms to form face-sharing USi12 cuboctahedra. All U–Si bond lengths are 3.06 Å. In the third U3+ site, U3+ is bonded in a distorted single-bond geometry to four Si3- and one C4- atom. There are two shorter (2.85 Å) and two longer (3.01 Å) U–Si bond lengths. The U–C bond length is 2.35 Å. In the fourth U3+ site, U3+ is bonded in a 8-coordinate geometry to six Si3- and two equivalent C4- atoms. There are two shorter (2.89 Å) and four longer (2.94 Å) U–Si bond lengths. Both U–C bond lengths are 2.65 Å. In the fifth U3+ site, U3+ is bonded in a distorted hexagonal planar geometry to six Si3- atoms. There are two shorter (2.89 Å) and four longer (2.90 Å) U–Si bond lengths. There are two inequivalent Si3- sites. In the first Si3- site, Si3- is bonded in a 9-coordinate geometry to nine U3+ atoms. In the second Si3- site, Si3- is bonded in a 9-coordinate geometry to seven U3+ and two equivalent Si3- atoms. Both Si–Si bond lengths are 2.34 Å. C4- is bonded to six U3+ atoms to form corner-sharing CU6 octahedra. The corner-sharing octahedral tilt angles are 26°.