Materials Data on K2Ca4U(SiO4)4 by Materials Project
K2Ca4U(SiO4)4 is Esseneite-derived structured and crystallizes in the triclinic P-1 space group. The structure is three-dimensional. K1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of K–O bond distances ranging from 2.80–3.15 Å. There are two inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ca–O bond distances ranging from 2.41–2.60 Å. In the second Ca2+ site, Ca2+ is bonded to six O2- atoms to form distorted CaO6 pentagonal pyramids that share corners with four SiO4 tetrahedra, edges with two equivalent CaO6 pentagonal pyramids, and an edgeedge with one SiO4 tetrahedra. There are a spread of Ca–O bond distances ranging from 2.32–2.47 Å. U6+ is bonded to six O2- atoms to form UO6 octahedra that share corners with four SiO4 tetrahedra. There are a spread of U–O bond distances ranging from 1.89–2.22 Å. There are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share a cornercorner with one UO6 octahedra, corners with two equivalent CaO6 pentagonal pyramids, and a cornercorner with one SiO4 tetrahedra. The corner-sharing octahedral tilt angles are 38°. There are a spread of Si–O bond distances ranging from 1.63–1.66 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share a cornercorner with one UO6 octahedra, corners with two equivalent CaO6 pentagonal pyramids, a cornercorner with one SiO4 tetrahedra, and an edgeedge with one CaO6 pentagonal pyramid. The corner-sharing octahedral tilt angles are 44°. There are a spread of Si–O bond distances ranging from 1.63–1.66 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to three Ca2+ and one Si4+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to three Ca2+ and one Si4+ atom. In the third O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent K1+, one U6+, and one Si4+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one K1+ and two Si4+ atoms. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to three Ca2+ and one Si4+ atom. In the sixth O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent K1+, one U6+, and one Si4+ atom. In the seventh O2- site, O2- is bonded to three Ca2+ and one Si4+ atom to form distorted edge-sharing OCa3Si trigonal pyramids. In the eighth O2- site, O2- is bonded in a 1-coordinate geometry to one K1+, one Ca2+, and one U6+ atom.